Home Theater Calibration Guide.indd

Home Theater Calibration Guide.indd
Home Theater
©2003 AudioControl. All rights reserved.
Section I
In the real world, any space in which you want to install loudspeakers can be a bad space in some way. The only perfect
rooms, acoustically speaking, are anechoic test chambers;
and unless your customer is very, very weird, it is unlikely
you will be installing a theater in such a space.
Room Acoustics
Let’s first review the basic physics that determine how sound
works and the affects of a room on sound waves, to understand the kind of problems you are likely to face.
The human ear perceives sound because it is responding to both the physical vibration of the
molecules that make up air, and the pressure
changes (waves) produced by sound waves
moving through the ear’s various passages and
All mammalian ears respond in a similar fashion
(although their range of frequency sensitivity varies substantially) to the vibration and detect it as frequency. They also
respond to the pressure and detect it as level or intensity.
Figure 1 – Sound waves eminate
from a central point like a stone
being tossed in a pond.
All sound producing devices produce a series of ‘waves’ in
the air, water, steel or anything but a vacuum. Remember
there is no sound in outer space.
Figure 2 – Energy produced
by loudspeakers or any other
source will reflect from all
surfaces of a room.
Room Acoustics
Section I
A Room’s Effect On Sound Waves
As shown in figures 2 and 3, sound waves react with every
surface, barrier or boundary they encounter. There are only
two possible reactions - reflection or absorption.
If the energy contained in the waves is absorbed it will be
transformed (according to the laws of physics) into another
form of energy - usually heat. Surfaces that are absorptive,
such as fiberglass, draperies or curtains, reduce the amount
of energy in the system
Figure 3 – When reflections occur,
they may cause cancellation of the
original energy wave producing
“nulls”, especially noticeable
at low frequencies in various
positions within the room.
Surfaces that reflect, or refract the energy waves (most solid,
hard surfaces) will produce a series of ‘counter-waves’ of energy. There are always multiple reflections, at differing angles
in every reflective situation.
For our purposes we are concerned with only those reflective
waves that can produce energy peaks or dips in the perceived frequency response of the sound system in the room.
Remember that despite what you may read or have been
told elsewhere - all rooms are bad in some way. Every space
has its own unique set of problems, and therefore all rooms
force some set of audio performance compromises to be
Room Acoustics
Section I
Room Modes and Wavelengths
Room resonances (also called standing waves or room
modes) are one of the most significant problems affecting
perceived sound quality and loudspeaker spectral presentation. These resonances are caused by reflected energy
bouncing around the room from the various surfaces, (walls,
ceilings, floor, etc.)
Remember that the perceived sound quality of the system
is what the customer is judging and how your work will be
viewed. Regardless of what type or brand of equipment you
install, its price or reputation; the overall system’s performance in the customer’s space is what makes you a hero or
gets you the call from their attorney!
Given that all rooms have some acoustical problems, the two
key questions we need to answer are:
1. How bad, and where, will the problems produced by the
resonances and reflections be?
2. What other acoustic problems are present within the
In order to obtain a preliminary answer to question number
one, and frame the overall problem we have to do some
simple math.
No groaning please, its all just straightforward long division!
So. . . f =
speed of sound in ft/s = ( then 2x, 3x, 4x)
2 x length in feet
f is the frequency of the standing wave mode.
1130 is the speed of sound in air at normal temperature (70°
F [21° C])
Note: the formula works the same way for metric dimensions
Room Acoustics
Section I
Every room will have length, width, and height modes, plus
each mode will then have “orders”.
What are orders? Orders are the relative number of a particular resonance.
This is usually expressed using a three coordinate (x, y, z)
structure and three numbers (i.e. 1,0,0 represents the first
order mode along the x axis of the room and so forth.)
For the most part, the modes we are concerned with will
be first, second and third order axial (length, width, height)
The likelihood of a fourth order mode being at a frequency
and of a level to be an issue is relatively small. You can calculate a mode of any order using the following formula.
For example if the room is 15 feet long the math would be:
f = 1130/30 which produces a first order mode of: 37.66
Thus, we should expect standing waves around 40 Hz or the
lower limit of many subwoofers to show up.
Wavelength - The Key to Finding Modes:
Remember all sound waves have a WAVELENGTH.
To get the wavelength of a particular frequency you can look
it up - the tables are in dozens of reference books or... simply divide the speed of sound by the frequency.
Using the frequency derived from the formula on the previous page you would divide 1130 by 38 Hz. You should get
29.7 or roughly 30 feet. This means that the wavelength is
almost twice our example 15 foot room length. This is a bad
Knowing the wavelength will help you quickly predict potential standing wave or mode problems in any space whose
dimensions you have.
For example, if your room dimensions are some even fraction of any low frequency (under 200 Hz) wavelength (½, ¼,
etc.) you are looking at a standing wave problem.
The only question is how much, where and how audible.
Room Acoustics
Section I
If you are looking at plans of a new house, or plans for the
renovation of an older structure look VERY CAREFULLY at the
dimensional rations for the space(s) you may have to deal
It will pay you to remember that all mode phenomena will
produce a first minimum (null) at precisely 1⁄4 the wavelength
from the reflecting surface or in the case noted above around
3.75 feet - one fourth of the way down the room and another
at 1⁄2 and 3⁄4 of the distance
In our example, this means it is VERY likely that the seating
area will be in a pressure maximum or peak at this frequency,
as well as all of it’s relatives, i.e. 76Hz, 114Hz, 152 Hz and
so forth.
In plain English, this means you are going to have a LOT OF
BASS around the probable seating position.
You can do this type of calculation and determination for any
room - even rooms that exist only on paper.
Getting this information in advance of any construction can
help you and your client avoid potentially incurable problems
before the first nail is driven.
Knowing this information and the equivalent distances (feet
or meters) will allow you to quickly determine how bad the
room is likely to be.
(Note: You need to know how much trouble you are facing
going into any project- since it is unlikely you will be dealing
with a good to excellent room to start with.)
Confirming the Math
Once you have done the math and gotten a rough idea of
what you might expect in a room, you must actually measure the space as built.
This is because the predictive math will only give you an
approximation of what will happen in a precisely rectangular
space with perfectly flat walls, and uncontaminated reflections. If you ever find a room that matches the drawings, put
the construction contractor on a lifetime retainer.
Room Acoustics
Section I
Multi-channel Audio Compromises
We have been looking at this issue so far as if there is only
one sound source in the room. In a residential entertainment
space, this is, to say the least, unlikely.
Therefore you must also recognize that the acoustic problems will always be worse for multi-channel - 5.1, 6.1, 5.2,
6,2, 7.1 type installations - than for any mono or stereo
setup, because you have more sources; and therefore, more
energy being introduced into the space.
These additional sources automatically produce higher overall
levels, and in particular more low frequency energy, the specific spectral area where most of the worst problems occur.
Room Acoustics
Section II
Residential Entertainment Space
Room Design and Setup Guidelines
Room Design
Realistically, every room you encounter will need some form
of correction to be fully functional as a high performance audio or theater environment.
You can, to a certain extent, maximize any room’s potential
and minimize your probable difficulties by following some basic design and setup guidelines at the outset of any project.
Please remember these are only GUIDELINES, not rules!
Every room and every system is different, with their own
unique problems.
Room Design Basics
The first thing to recognize is that all room dimensions are
ratios. There are good and bad ratios as well as good and
bad shapes for rooms. Square rooms and rooms with equal
length walls are generally VERY BAD ideas.
Ratios that are multiples of each other - i.e. a length that is
exactly twice the width or height are BAD because they will
create families of room resonances/modes.
For example, a room that is 20 feet long, 10 feet wide and
10 feet high is VERY BAD.
Because any modes created by the 10 foot dimensions will
have an acoustical family member created by the 20 foot dimension and because you have two identical dimensions any
problems will be multiplied by a factor of two as well.
These family members will be VERY close in frequency to
the original modes. When you get clusters of modes nearby
to each other in frequency – i.e. within 10 Hz of each other,
things go from bad to really awful very quickly.
There are no “fixed in concrete” rules here, but generally,
ratios that come out looking like (L X W X H) 2.0 / 1.0 / 1.0
are bad.
Room dimension ratios that come out unevenly, for example
2.4 / 1.1 / 1.0 are much better, since the mode distribution
will not have as many grouped frequency clusters. [ Please
Room Acoustics
Section II
note that there will still be clusters but they will be spread out
more evenly across the frequency spectrum, and thus create
less of a problem.]
Room Design
Seating Locations
Your seating location options are going to be determined primarily by the video device’s screen size and location.
There are specific rules for distance from the screen (optimally 5 to 8 times picture height; with a minimum of 1.5 to
2 times picture height if resolution enhancement is used) ,
but your project’s particular conditions may make it difficult
to achieve these distances.
You must be extremely careful to insure that your chosen/
dictated seating location does not fall in a low frequency
Why is a NULL so much worse than a peak??
It’s really simple if you remember what we discussed earlier
in the section on modes and standing waves. You can correct for peaks using equalization to remove energy from the
system, but you CANNOT fix nulls.
If you are really lucky, you can get both optimal viewing
distance and seating right on the edge of a peak. If you do,
thank the home theater gods and have a cold beverage!!!!!.
Room Mode Placement
Speaker Placement
The key point to remember about speaker placement is
- equal distance. The closer you can get to having the LCR
speakers equidistant from the wallet seat the better you are.
The same applies to each pair of surrounds.
If you are setting up a 5.1 system, you are better off locating
the surrounds to the sides and slightly to the rear of the seating location than directly in the rear. This will provide more
envelopment from the surrounds. If you are using bi-polar
THX surrounds this is a critical element of a successful system.
In more complex systems, position is also critical to ensure
an even soundfield, and as smooth an overall coverage pattern as possible.
Room Acoustics
Section II
However, if you cannot position the speakers at the optimum
physical location – don’t panic! You have a clever trick up
your sleeve. The AudioControl DIVA gives you the option to
move speakers “electronically” to their optimal position.
Room Design
This can greatly help you in compensating for interior decorators and less than ideal positions. More on that later.
In summary try to position your speakers to “surround”
the seating area as evenly as possible. Also as noted below
- ALWAYS take attendance before enclosing or otherwise permanently mounting the speakers. This allows you to ensure
everyone is working correctly while you can still get at the
speakers easily.
What We Need to Know
To find out what has to be done and how to do it, you need
to ask and answer, as precisely as possible the following
1. What are the obvious physical issues that can affect audio
performance? - i.e. windows, construction type, spatial/dimensional ratios, and furniture - yes, furniture.
2. What measurable problems can be detected, and how bad
are they? This includes what may be obvious issues such
as :
A: Is everything connected properly and operating as
B: Are all devices in the correct polarity and connected to
the right outputs?
C: Are any speakers “wounded” - that is, are the output
characteristics of all similar devices actually similar?
3. Of the problems we have, how do we address each one?
Even more significantly, which ones CANNOT be
Room Acoustics
Section II
Room Design
Here is a reflected view room layout showing length
and width and height.
The dimensions are:
Width __________Feet
Length _________Feet
Height _________Feet
Practice using the basic math we just discussed:
Using the formula: f= speed of sound in ft. per second÷
2x the dimension in feet, calculate the first order room
modes for this space.
1st order length mode = f ________________ Hz
1st order width mode = f ________________ Hz
1st order height mode = f ________________ Hz
Now calculate the second order modes by multiplying your
answers to the 1st order calculation by two.
2nd order length mode= f ________________ Hz
2nd order width mode= f ________________ Hz
2nd order height mode= f ________________ Hz
Room Acoustics
Section II
Divide the speed of sound [1130ft/s] by the frequency or
1130÷f [in Hz] which will give you the wavelength in feet
Room Design
Calculate the wavelengths for each of the six modes you
1st order length mode wavelength = __________________ft.
1st order width mode wavelength = __________________ft.
1st order height mode wavelength = __________________ft.
2nd order length mode wavelength = _________________ft.
2nd order width mode wavelength = __________________ft.
2nd order height mode wavelength = _________________ft.
Room Acoustics
Room Acoustics
Section III
System Analysis Tools
System Analysis
Now its time to:
Measure Twice - Then we will need to EQ only once
To make the most of your correction capabilities you must first
accurately establish the room’s “ acoustic signature”.
This means you must both measure from multiple points and in
multiple ways, and compare your actual data to the predictions
you did. If there is a significant difference between them, then
you did something wrong.
Acoustic Spaces:
There are two ways to view any acoustical environment - from a
frequency perspective and from a time perspective. These two
views are the essence of the Fast Fourier Transform mathematics
that allows data from one domain to be convolved and converted into data for the other.
To examine the frequency perspective of an acoustic space you
will need to measure it with a Real Time Spectrum Analyzer.
How an RTA Works - The AudioControl SA-3052
The microphone that comes with the SA-3052 RTA measures pressure changes caused by the sound waves. The analyzer converts
these pressure changes to AC voltage and then displays them in 1⁄3
octave bandwidths on the screen.
When utilizing a test tone of known (or predictable)
amplitude (volume) in each band, the screen then
displays the relative amplitude of each 1⁄3 octave band
of the frequency spectrum.
‘Pink noise’ is the recommended test signal to
conduct this measurement because it is readily
available from the pink noise generator in the SA3052 and it provides the proper combination of spectral width
and amplitude- that’s the right bandwidth of frequencies at the
right level.
AudioControl SA-3052
All RTA’s display steady state( data that is not sensitive to anything in the time domain), broadband information, giving you
an overall picture of the spectral/frequency environment in the
space being measured.
Room Acoustics
Section III
System Analysis
To insure that you have an accurate picture you must take
RTA measurements from multiple points within the listening
This averaging method removes certain kinds of non-equalizable data from the spectral “portrait” which emerges when
you are done. But remember, that such averaged data can
also hide nearby problems. This is why you need to look at
both the individual measurements and the averaged data
over a length of time.
Features of the SA-3052 RTA
1. LED DISPLAY: The left portion of the display shows the
one-third octave energy content of the input signal from 25
Hz to 20 kHz.
2. POWER SWITCH: Depressing the power switch turns the
SA-3052 on or off.
3. ON/CHARGE LED: The dual-color ON/CHARGE indicator
illuminates green during normal operation of the SA-3052.
[While operating the SA-3052 on the rechargeable batteries,
a flashing green ON/CHARGE light indicates that the batteries
need recharging. When plugged in and turned off, the ON/
CHARGE light is red, and by flashing or staying on, indicates
the amount of charge the batteries have. A longer flash indicates more charge is needed.] When not using your
SA-3052, keep it plugged in.
4. SPL: Momentarily pressing the SPL push-button switch
turns the SPL bargraph display in the right side of the display
window on and off. Pressing and holding the SPL push-button
activates the full-screen digital SPL display.
5. DISPLAY SPEED: The display speed push-button switch is
located underneath the SPL switch and to the left of the FAST,
MED, and SLOW LEDs. The lighted LED to the right of the
switch indicates the decay time of the display.
6. MEMORY: The SA-3052 can store up to six different frequency response curves in its internal memory. Press the
MEMORY button to select which memory to store or recall.
The associated LED indicators show which memory is currently being displayed. Up to six previously stored curves
may be ‘averaged’ together. The result is stored in memory
register SIX.
Room Acoustics
Section III
7. STORE/FREEZE: The STORE/FREEZE switch freezes the
display and stores the contents of the display in the memory
indicated by the MEMORY LEDs. Pressing and holding the
STORE/FREEZE pushbutton activates the averaging function.
The calculated average is stored in memory register six.
System Analysis
8. RECALL RTA: The RECALL-RTA push-button switch alternately selects between the normal real-time analyzer mode
and the memory-recall mode.
The associated LEDs indicate the selected mode. Pressing
and holding the RECALL-RTA switch activates the peak-hold
function. The analyzer now displays the highest peaks of the
input signal on a real-time basis.
9. PINK NOISE: The internal pink noise generator is an accurate, digital laboratory-grade test source. The signal level at
this connector is controlled by the knob to its immediate left.
The pink noise generator has sufficient output to drive virtually any speaker or passive crossover directly.
10. dB PER STEP: This switch sets the resolution of the
spectrum analyzer portion of the display. The setting represents the value of each LED in the display.
and switch selects the reference level of the curve shown in
the display window. The control to the right of the input selector switch is a fine adjustment and alters the range selected
by the switch over a range of +/-10 dB.
12. INPUT 3: Accommodates a 1/4
inch tip-ring-sleeve phono
jack used for connecting to
balanced and unbalanced
13. INPUT 2: This accepts
a standard audio RCA connector that allows for connecting almost any audio
source to this input.
14. INPUT 1: This accommodates a +12 volt,
phantom powered, balanced microphone input.
SA-3052 Front Panel
Room Acoustics
Section III
System Analysis
On the back of the SA-3052 is the printer interface (which
connects to any IBM-compatible printer) and the print button.
Iasys HT - The Tool To Create Perfection
Iasys HT allows you to look into spectral issues with much
more detail due to its higher resolution. It provides time
based information and equalizable spectra data that can give
a you a major head start toward determining where your
problems are and what you can do about them.
Features of the Iasys HT
1. Inputs Input 1 is where the microphone supplied with the
Iasys (the CM-10) plugs in. We do not recommend any other
microphone. Input 2 is reserved for future, to be defined,
applications and expansions. The Speaker Level input is for
monitoring of the speaker level signal during the limiter test.
2. Output From here Iasys puts out a variety of test tones.
This connects to the HT-100 to route signals.
3. Automatic Tests The gray and two blue buttons to the
right of the inputs are for the automatic tests of Iasys. From
these tests, you get answers on how to set the tools noted
by the label of the buttons. That is, for setting delay times,
you select the delay button. Push any of these gray buttons
and Iasys will give you instructions on what to do next.
Iasys HT-100
White buttons for
Automatic test
HELP for info
ENTER for menu
Iasys HT Front Panel
Room Acoustics
Section III
4. Display Screen The display is the gas plasma type for
comfortable viewing in most light conditions and extremely
good visibility from side angles.
5. Octave Selects and Soft Keys Below the display screen
are dark gray buttons, each for an octave center point. These
are quite useful to go quickly to a frequency. They are used in
more tests than we can mention here, and are usually applied in conjunction with the wheel for fine tuning. The buttons right below the screen with the arrow above, are used
to select on-screen options.
6. Help After pressing the “Help” button, press any other button for a brief explanation of the function of that other button. To exit help, press “Quit”.
7. Manual Tests Pure sine wave, sweep sine wave and pink
noise with real time analyzer are the manual tests available
from the same labeled buttons on the lower right of Iasys HT.
The wheel is used after selecting either frequency or level
to fine tune those aspects. For the sweep, the octave select
buttons program the start and stop points of the sweep.
8. Function Keys “F1” through “F4” are special keys which
now and in the future take on different functions in different
tests. The adjacent red light is on when any of these buttons
is active.
9. Wheel With the wheel you can scroll through numbers,
memories, or other functions. When the wheel is active, a
small circle ( ) shows in the upper right hand corner of the
System Analysis
Frequency Response
20.00 kHz
> -15 dBu
--dB rel
85 db
One-Third Octave RTA
Delay Test Records
Bank 1 in MSEC
LR: 25.14RR: 24.65+
LS: 23.41RS: 22.47+
Precise Distance Measurement
Balance Levels:
Accurate Level Setting
EQ Spectra Records
Bank 2A
10. Enter and Quit The “Quit” button always functions and
you should use it any time you want to stop or back out of a
function. Enter is used with the special functions menu.
How Iasys HT Helps Create Magic
1. Accurate equalization
2. Shows what is correctable
3. Precise level setting
4. Exact signal alignment (delay)
5. Pinpoint resonances and rattles
⁄ Octave Equalizable Spectra
1 12
Sweep Output
40 Hz
10 sec/swp
85 dB
Sweep Tones for Finding Rattles
6. Fuzzy logic intelligent testing
7. No computer or software hassles
Room Acoustics
Room Acoustics
Section IV
Theater Calibration
Theater Calibration
Proper measurements, coupled with a tool such as DIVA (with
its extensive array of filters, delay and signal processing) can
provide all the ELECTRONIC tools you might require to correct
those problems.
We must remember that we are dealing with both physical
acoustics issues and those that can be dealt with using electronic correction.
RULE NUMBER 1: There is no type of electronic correction/EQ
that will fix all problems
Or to put it another way: You cannot fix bad loudspeakers,
impossible room acoustics, or non-equalizable spectral issues
with any type of electronic correction.
Often the only available solution is ... explosives!! Or more
realistically, sometimes you just have to walk away from a
This is why it is absolutely crucial that you verify from actual
measurements where your problems really are, and what
they are. This is the only way you can determine whether or
not the problem is addressable with electronic correction.
Now - Lets Measure!
(NOTE: Make printouts or record EVERYTHING on paper for reference. Keeping an acoustic signature file of every job allows
you to go back and re-create what you did, and also show
what you’ve done.)
You will need to collect and save the following from both an
RTA and Iasys:
1. Wallet Seat data
Seating Ring
Wallet Seat
2. Surrounding seating plane data
3. Seating ring data (at least three points)
By doubling up here you insure that:
A: You don’t miss anything important
B: You build in a cross-check of the data you get
Examine the data, both the individual responses and averaged responses, and look for significant peaks and or dips in
the overall response. Significant means at
least 3 dB.
Section IV
Theater Calibration
If these changes are wide from an octave standpoint ( 1.5
octaves or more), they may not be serious. If they are very
sharp ( let’s say 5-10Hz wide), they may not be fixable or
What you want to look for are the big hills or deep valleys.
Once we’ve completed the measurement/equalization process, which will enable you to tune the room’s acoustic
signature to be as accurate as feasible, then we can examine
the creative options you can employ to enhance and expand
the possibilities.
Later in this manual you will find an extended discussion of
setup procedures, a checklist and some additional guidelines. It is strongly recommended that you review these
EVERY time you do a job.
For now you need to recognize that there are five basic signal
processing areas you will have to examine, adjust and LISTEN
1. Sub-woofer to main system crossover splicing
2. Internal main/surround speaker crossovers (if being
done electronically)
3. Delay setting and time/distance relationships
4. General systems equalization (customer happy EQ)
5. System dynamics - limiting and compression
Note: This list assumes the gain levels are already properly
adjusted and matched. See Iasys section for level matiching
Room Acoustics
Section IV
Sound System Analysis with the RTA
Theater Calibration
The basic steps for analyzing any space with an RTA are:
1. Using a microphone stand, place the microphone from
the analyzer in the head position of the primary listener.
2. Play pink noise through the system at the normal
listening level (85dB is the recognized room
calibration setpoint).
3. With the dB Per Step switch in the ‘3’ position and the
display speed in the ‘Med’ mode, make certain that all
of the LEDs in the display fall within the ± 12dB range
of the display.
4. Switch the display speed to ‘Slow’, and start taking
your measurements across the seating plane - remember you will need three or more measurements for any
seating area. Store your measurements in the memories and note what memory represents what seating
Remember, when equalizing, the result you are after is not
necessarily a ‘flat’ curve across the center of the screen, but
a smooth curve in which there are no variations exceeding
±3dB between any two adjacent bands.
Remember, we recommend using both an RTA and the Iasys
HT system because they supply different types of information.
Sub-woofer to Main System Crossover Splicing
The fundamental issue with this parameter is to ensure a
smooth and seamless “splice” between the upper end of the
subwoofer’s output and the lower end of the main system’s
capability. If you’ve got this right you will not be able to tell
when the transition occurs or precisely where the subwoofer
is. If you can hear either of these parameters you need to go
back and make further adjustments.
Section IV
Theater Calibration
Internal Main/Surround Speaker Crossovers
(If Being Done Electronically)
If you are using DIVA or another device to create the crossovers for the main loudspeaker system, you need to insure
that the LCR speakers are exactly the same acoustically (
if the speakers are the same). You will want to match the
crossovers as precisely as feasible to avoid shifting speech
when it moves across the frontal presentation plane. This
is a VERY delicate adjustment and should be avoided unless
the speakers require an external crossover. Normally the factory supplied crossover is tuned to produce optimum results
from the particular drivers.
NOTE: Using Iasys HT, you can verify the energy centers (as
shown earlier) to confirm that the LCR speakers are operating
properly and are acoustically similar.
Delay Setting and Time/Distance Relationships
This is one of the “creative” areas, where your ears and your
brain will work together to help you find the best combination. In essence you want to make the room appear as large
as feasible, the sound field as even as possible, and produce
the most spatiality from the system as possible. This is an
ART, and you need to practice to get it right.
You must begin, however, by precisely positioning the speakers in space so that they are all equidistant from your selected TIME ZERO point which is normally the center channel.
Iasys HT is the ideal tool for this job, and it can provide all the
data you need to get this done quickly and accurately.
After getting all signals to arrive together, you can then move
them to where you want them to be.
General Systems Equalization
(Customer Happy EQ)
This is the LAST step in any setup process. It is where you
usually apply 1/3 octave type EQ (available on all channels in
DIVA) to produce you chosen “house curve” or a curve you
feel will make the customer happy.
Room Acoustics
Section IV
This step should NOT be used to correct for loudspeaker
anomalies or other problems. That should be addressed with
the PARAMETRIC EQ tools as discussed above and again
later on.
Theater Calibration
Be VERY VERY careful to apply identical EQ to any PAIRS of
loudspeakers - that is Front L/R; Side L/R; or Surround L/R. If
you do not you will cause image shifting and create a whole
lot of trouble for yourself.
Dynamics Processing - Limiting and Compression
DIVA offers you a unique opportunity to affect the audio
signal, because it provides both limiting and compression
options. You can, using these tools, efficiently manage the
dynamic range of the signals reaching the power amplifier
inputs and ultimately, loudspeakers.
Applying these tools is a complex process and should be
done with a gentle hand and careful listening. We strongly
recommend you experiment with this option a lot, before attempting to use it in the field.
A basic rule of thumb is to apply these options ONLY to the
subwoofer and center channel.
Later on in this manual is a complete discussion of these
signal processing options. It should be read carefully before
attempting to use any of the dynamics management tools
available in DIVA.
You should first try the factory presets, as these have been
optimized for most applications.
Room Acoustics
Section V
Equalization Terminology
Equalizers are the single most cost effective improvement to
any quality audio system.
Some Key terms:
Amplitude - A measure of the strength of a signal.
Bandpass - A combination of a lowpass and highpass filter.
The bandpass filter has rapidly decreasing output above or
below its -3dB frequencies. (see below) The bandpass filters
used in most equalizers for tonal correction have bell-shaped
curves. Another type of bandpass filter has rather straight
skirts, and a flat response characteristic in its passband (the
area between the lower and upper -3dB points).
Bandwidth - A measure of the amount of the audio spectrum
affected by the equalizer. Bandwidth is usually measured in
fractions of an octave across the -3dB points. (see Figure 4)
Center - The frequency at which the output signal from the
equalizer is at its maximum cut or boost.
Equalizer - An electronic filter network that effects the transmission of alternating current with respect to
Octave - A musical term representing a pitch
ratio of 2:1. Thus, A-440 (A above middle-C on
a piano, or 440 Hz) is one octave lower than A880.
Q - Similar to bandwidth, Q is the quality factor
of a filter. It is calculated as the center frequency
divided by the bandwidth.
Skirt - The skirts of a filter are those frequencies
that lie above and below the center frequency.
Figure 4 - The shape of a typical
bandpass filter (1/3 octave type)
Section V
Types of Equalizers
There are many equalization products on the market.
Although there will be alleged unique capabilities, and often
claims that appear to violate the known laws of physics and
possibilities using electronic components made in this universe, the reality is fairly simple. ALL equalization products on
the market today are based on one of two core types of filter
Graphic: Graphical layout of controls, fixed center frequencies and bandwidths, variable amplitude. e.g. DIVA and other
AudioControl EQs
Parametric: Variable Bandwidth, Amplitude, and Frequency.
e.g. DIVA.
A key point to remember when applying any type of equalization or correction:
If we optimize the on-axis response of the reproduction system, the off-axis response will be as good as it gets.
What to do and How to do it
Once you have both calculated and measured the space to
determine what the room’s acoustic characteristics are, here
is a step by step procedure that should produce the best
results available for any space:
1. Insure that you have properly measured the distances
from the center of the seating area or wallet seat to each
speaker precisely (that is to the inch/cm). If you are using
Iasys this data has been calculated precisely for you.
Never-the-less you should repeat and re-verify your data
to insure it is accurate to the final loudspeaker positions
in the room. Better yet, have someone else do it to cross
check your measurements.
2. Getting the basic loudspeaker array distances exactly correct is VITAL to making any other adjustment and to insuring that all your work will result in positive changes.
(Remember 12" = approx. 1 millisecond. . .1 microsecond = .012 millisecond)
Room Acoustics
Section V
3. Set all decoder delays as per manufacturer’s instructions.
If the system incorporates a DIVA unit, you can set the
channel delays to far more precision using microsecond
In this case, DO NOT set any delay in the decoder; or, use
it only for basic delay and add the precision needed using
Now - Check timing and delay setting using Iasys HT.
4. Correct until you have it as accurate as feasible.
Remember flight-time as processed with Iasys HT is far
more accurate than any tape measure to seat distances.
Using Diva to Create the Best Room/Sonic
Presentation and Impact Possible
First remove any major LF bumps or problems.
These will likely be masking other problems. THIS IS A CUT
ONLY PROCEDURE. You want to take energy OUT of the system to reduce or remove the excess.
DO this in small steps 1-2 dB maximum per pass to allow for
both listening tests and re-measurement to verify your affect.
Measure again. Repeat !
Measure again. Repeat !
Measure again. Repeat !
Once LF issues have been resolved to produce the best possible (THIS DOES NOT MEAN FLAT) spectra and level, look at
the Center channel for dialog intelligibility, and at LCR for even
In the center channel look for the smoothest possible response from 100 to 3kHz - 4kHz - the speech band.
Also, look for any real peaks below or above those frequencies and gently reduce them.
Look at LCR to SUB splice and surround to LCR spectral balance.
Apply graphic or parametric EQ to remove problems.
Section V
General Equalization Guidelines
The overall goal of equalizing any sound system is to have a
smooth transition from one frequency to the next with variations of no greater than 3 dB. Do not attempt to use any
equalizer to re-invent the laws of physics and try and make a
speaker do something it can’t.
Although the audio police will not hold you accountable, you
should follow some guidelines when it comes to making
equalization corrections:
1. Your equalization curve should always start by being
some position of the inverse of what your analyzer
2. If the analyzer shows a 3 dB bump a given frequency,
you should cut the frequency 2 dB for starters.
3. Cut the peaks
4. Use extreme care when boosting any dip – in fact
never boost at all unless you have a lot of experience
with the system and the hardware.
5. Try to keep your EQ applications to less than 3 dB.
6. After making initial equalization adjustments, reanalyze the system and adjust again if necessary.
7. If your left and right speakers are mounted symmetrically you can measure and equalize them together.
8. When in doubt, re-analyze and re-equalize a particular
speaker or group of speakers.
LCR Speakers
In this step, you will want to measure the frequency response of each speaker at each listening position; and, then
average them together to achieve a spatial average of the
listening room.
Set the SA-3052 in the 2 dB per step division with the speed
set at “averaging”(20 second averaging).
The volume level should be set at a reference position of
approximately 75dB (THX reference level to a maximum of
90dB to avoid loudspeaker damage.) Pink noise should be
used as test material.
Room Acoustics
Section V
Starting with the center channel, use the following procedures:
1. Take a measurement in each seating position and store
them in memories #1 through #5 of the analyzer.
2. Average the measurements of each seating location
into memory #6
3. Following the “Equalization Guidelines”, make the
appropriate equalization corrections to the frequency
4. After making equalization corrections, repeat the above
After you have completed the above steps, repeat them for
the left and right channels.
Disconnect the channels you are not equalizing by unplugging the connectors for the appropriate amplifiers.
Subwoofer Equalization
To measure and equalize the subwoofer you will want to follow the same procedures as you do for the LCR speakers.
However, because of the numerous fluctuations caused by
pink noise at lower frequencies it will not be necessary to
take subwoofer measurements at all of the various seating
Splicing the Subwoofer
Given the numerous possible speaker locations, there tends
to be an occurrence of peaks or dips at the point where the
subwoofer and the main LCR speakers energy output overlaps commonly called - THE CROSSOVER FREQUENCY. It is
important to smooth out this transition point.
Center Splice: Disable all channels, except for the subwoofer
and center channel. Play pink noise through them and use
the center channel equalization controls to smooth out the
splice between the subwoofer and the center channel.
L & R Splice: Disable all channels except for the left & right
mains and the subwoofer. Play pink noise through them and
use the left & right channel equalization controls to splice in
the subwoofer.
Section V
Chop Off the Peaks - Never Fill the Valleys
You can use more than minus 6dB if need, but use caution,
there may be an easier physical way to reduce some of your
Once you have worked through the subwoofers, Center
channel and L/R systems examine the spectral data from the
Look for BIG peaks and gently soften them if possible.
Delay and Psycho-Acoustics
How to use DIVA to change apparent room size, and, how
to apparently position a center channel speaker up or down;
front or back using the channel delay in DIVA .
First: There is no such thing as time delay in audio without
the use of a micro black hole to alter time.
What DIVA and all other delay units supply is signal delay.
The ear/brain processor equates delay with distance and the
impression of spaciousness or ambiance.
That’s why all studio engineers apply some pre-delay to the
sends for reverb units and often add additional delay to the
You can use delay to do something similar.
Now you will understand why it was so important to get the
actual position of the speakers calibrated so precisely.
Because ... we can move them electronically.
For example:
Apparent Room
If you have a 7.1 system which uses both side and rear
speakers, you can by increasing the delay to the side speakers move the apparent position of the side walls of the room
away from the listener, or by decreasing the relative ratios
the reverse.
By increasing the delay to the rear speakers, you can push
the rear wall back.
Room Acoustics
Section V
Here are some examples for a medium size room
Side add 10 ms = 10 feet
Rear add 12 ms = 12 feet
Finally . . . Conduct a Listening Test
The two commandments of equalization that cannot be ignored are:
1. Always, always, always conduct numerous listening
tests throughout the process to insure that what you
doing is actually having a beneficial effect.
2. Never, never, never do equalization without also
listening to the system with the EQ in and the EQ out to
Given the tools now have available, you can electronically
correct a significant portion of the equalizable problems. With
the proper application of the right kind of acoustical treatment
you can tackle many of the others.
Remember choosing and using the right tool for the job can
go a long way to improving the acoustic performance of any
room, and thus the performance of the sound system you
put in that room.
Room Acoustics
Section VI
The Art of Listening
The Art of Listening
The Emotional Power of Sound
Listening to and experiencing an audio environment is a
unique and intense multi-level encounter.
Stephen Handel, Professor of Psychology at the University of
Tennessee, put it as well as anyone has in the Preface to his
wonderful book called Listening (The MIT Press, 1993):
“ Listening puts me in the world. Listening gives me a
sense of emotion, a sense of movement, and a sense
of being there that is missing when I am (just) looking. I
am more frightened by thunder than by lightning, even
though I know that thunder is harmless and lightning is
deadly. I feel far more isolation living with ear plugs,
than living with blinders. Listening is centripetal, it pulls
you into the world. Looking is centrifugal, it separates
you from the world ”.
Let’s understand precisely what Handel is saying. If the audio
system’s re-creation capability is working correctly, it can and
should pull the listener into the presentation with the power
to make them believe that they are “There” , wherever there
may be.
To do this, the ‘there’ must be perceived to be real enough
to place the listener in the scene or story with enough
strength to make them forget that they care actually sitting
someplace else.
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The Art of Listening
The Almost Lost Data
Every time you hear an audio system (especially a multichannel one) you are, without formally recognizing the process, being provided with a huge amount of information on
that system’s specific attributes and capabilities.
Unfortunately, you will actually use and process only a small
portion of what you are hearing, primarily because you are
not ‘listening’ for the rest of the information.
The AudioControl Iasys HT
measurement system provides
the most comprehensive data set
available that shows an association
with how and what we hear,
because it uses fuzzy logic and
recognizes the time-based nature
of sound within a space as does
the human hearing system.
The industry has over the years used a variety of hardware
types and analysis approaches such as the AudioControl
3052 RTA or the AudioControl IasysHT System, to measure
and determine audio system performance. Because these
methods produce for the most part totally objective, accurate* and repeatable data that has no ‘subjective component’ , we have been trained to and accepted the concept of
relying almost totally on our test equipment to tell us what
we are hearing.
(* The accuracy of the data gathered by any measurement
system is very much dependant on the care and precision
taken during the measurement process. Good technology
can most certainly produce bad data.)
But, no matter how sophisticated that instrumentation may
be or how expert the operator none of those systems can
(as yet) measure, compile or quantify to the same degree
of precision the complex psychoacoustical aspects that are
inherent in the way the ear/brain system processes sound.
It is critical to understanding the listening process to recognize that unless your ear/brain system is impaired in some
way, 100% of the time you are awake and aware, your ears
are delivering a flood of information to your brain about what
kind of space you are in by constantly painting a complex
sonic landscape in full 3D and covering a full 360 degrees.
In created physical spaces such as residential entertainment
rooms or motion picture theaters, you are receiving input
from the complex speaker/room combination about what
kind of perceivable acoustical reality that ‘system’ is creating in that particular space.
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Section VI
But, if you just look at just the numbers from your measurement systems, you may not recognize how much information you are either ignoring or discarding.
The Art of Listening
You can look at this disparity by recognizing that if you just
use the pure data alone, you are taking your High Definition,
full color, 3D, 360 degree virtual reality and limiting it in every
parameter to a less detailed lower resolution image of the
same scene. Its the difference between the Star Trek HoloDeck and today’s simulation rides.
You are not using a good deal of the available information because you have never been trained to listen for it and exploit
the information that is sitting there in plain ‘view’ if you will
pardon the pun.
Do not misunderstand this point. I am not in any way suggesting that you give up instrumentation and use only the
cognitive, psychoacoustical and to a degree subjective information (although I constantly read articles and reviews that
seem to indicate that the author has done precisely that).
While that approach will allow you to use very inventive
descriptive verbiage, without the scientific information you
cannot really use the other data as effectively and you have
no objective foundation upon which to position the other
It is crucial to recognize that the approach described below is
NOT a case of either - or.
It is a methodology that combines the recognized and respected instrumentation produced information and the stuff
you were not using, to give you a much more powerful analytical tool to use in determining the quality and performance
of audio systems.
Why do we need to do this? Because it is the ears (and the
listening experience they produce) of your customer that will
make the final judgment on your work.
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Section VI
The Art of Listening
Judging the Reality Creation Quotient
In combining the information from both the objective data
and the listening experience, what we are trying to judge is
the effectiveness of the efforts of a speaker/room combination in re-creating the audio reality envisioned by those who
conceived/created the particular soundtrack, recording or
How Can You Do this Efficiently and Accurately?
Well, at least for the moment there is no quick, easy onehour class/course you can take to teach you how to do this.
However, I can provide you with some guidelines and methods to help you get started. I must emphasize that the only
way you will become truly proficient at this is to practice,
practice, practice.
Only over time can you train your ears and your brain to
‘listen’ through the system to hear the cues that will tell you
what you want to know.
To give you a start, we will explore what you can do to add to
your capabilities and offer some basic tips on how to do this.
The first and most critical step in building up your ability
to use your listening skills is learning how to breakdown a
soundtrack or other source into it’s component pieces and
understand how they must fit back together to deliver the
audio experience with its maximum power and believability.
While you can use almost any recorded sound source to do
this, motion picture soundtracks provide, in our experience,
the best sources.
Why Should You use Soundtracks and What You
Should Be Listening For
Why do soundtracks offer the best source options? Because
those soundtracks are created from a set of component
pieces, with the deliberate goal of producing a specific reality, a ‘willing suspension of audio disbelief ‘ . The complex
interweaving of literally hundreds of sounds in the process of
combining dialog, music and effects into a seamless audio
environment produces the “space” that the
The Art
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Section VI
picture and story occupy. That space is what allows the
soundtrack to put/pull the listeners ‘into’ the movie.
The Art of Listening
When listening critically to a sound track to judge system
performance, you must of course observe the accuracy of
the music reproduction, and the naturalness of the dialog.
These elements are crucial to the overall experience. The
measured data you produce about loudspeaker spectral accuracy using such tools as the AudioControl 3052 RTA and
Iasys measurement systems, plus a good careful listen to
a variety of program material, will give you significant information about how well any system is going to handle these
How even is the response? How un-colored is the delivered
soundfield at the listening positions?
Any real problems in those areas will show up almost immediately in a lack of musicality to the score or an unnaturalness
of the dialog, and of course should also be evident in your
measured data.
• SPACE — The concept of ‘space’ refers to the ability of
the reproduction system to produce a convincing sense of
the ambiance of the physical place(s) represented by the
on screen image or the acoustical ambiance of the space
where a recording was produced in the case of performing
arts sources without picture.
• ACCURACY — While this can be a highly subjective parameter, the measurements collected on system performance using appropriate tools are the basis for determining if a system is producing a smooth even soundfield
within the space. Subjectively it is essential to verify that
the speaker system is not producing any output that is not
within the original signal (see colored/uncolored below).
• DIALOG — Dialog is the core element for any motion picture presentation. The Center channel speaker is producing almost all of this information. Insuring that the speech
sounds natural and is accurate to the actor/actresses’
actual presentation is essential. They must
Art ofAcoustics
Section VI
The Art of Listening
sound ‘real’ and not constrained or thin. Dynamic range
and clarity are also key parameters to check.
• COLORED/UNCOLORED — Coloration is caused by the addition of unwanted harmonics or resonances to the original
signal. These may be produced by the loudspeaker itself,
or the speaker room combination. You must ‘know’ what
something is supposed to sound like to determine coloration. Listening to your selected test material on a good
system is the best way to establish these benchmarks.
• NATURALNESS – This is a largely subjective parameter.
However if voices or ambiance do not seem ‘real’ and
unforced then they are probably not ‘natural ’ either.
Its All in the Details
The best way to use this listening technique is to pick one or
two film segments (see below) and listen to them on several systems that you know to be best in class. You need to
pick just a few chapters (we recommend no more than two
or three 5-6 minute segments) from each film and listen to
them repeatedly to establish a benchmark of what they are
supposed to “sound” (and by the way look) like.
Once you have this benchmark embedded in your brain you
should be able to play those same segments on any system
you are testing or calibrating and get immediate data on that
systems performance status.
This method has been used for decades by live sound engineers who play a few of their favorite cuts from their “test”
CD’s every time they set up a system.
This gives them both a feel for how the system is performing within the specific space, and also a good indication as
to whether or not the basic system parameters are within
spec.; as well as a quick and easy check to insure that the
hardware is all working properly.
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Section VI
Field of Dreams
The Art of Listening
The first is Field of Dreams - Collectors edition. I use Chapters 2 and 7. Chapter 2 takes place in the cornfield, where
Kevin Costner is walking through the corn and hears the “if
you build it” voice for the first time. The detail I look for is
the rustling of the corn as he walks, the sound of the shovel
hitting the dirt, the distant squeak of the porch swing where
the wife and child are slowly rocking back and forth, the ice
in their drinks, their footsteps on the porch as they walk into
the house.
All these sounds are positioned across the LCR sound stage,
with the voice coming from both the LCR’s and the surrounds. The amount of detail in this seen is immense, including insect sounds, and wind, all designed to create that
summer afternoon cornfield/farmhouse “place”.
If the system is properly set up all of this information will
be there. If not, much of it will be buried and lost. Positional
information like the fact that the wife/child/swing are all center left to match the camera shot, will also be smeared and
indistinct. This scene lets me determine if the system is
properly equalized, delayed and level balanced, because if it’s
not, all of this stuff collapses and the ambiance is not created.
Chapter seven starts in the farmhouse living room with Costner and Amy Madigan discussing if they can keep the farm.
The daughter enters the room and tells Costner that “Daddy,
there’s a man on your lawn”- announcing the first appearance of Shoeless Joe Jackson.
Costner gets up walks across the floor, out on to the porch,
across the porch to turn on the three light poles, down the
steps across the yard, onto the gravel and then on to the
grass of the baseball diamond. Again there is a huge amount
of subtle detail like the various sounds Costner’s shoes make
as they change surfaces, and motion he makes as he walks
across the front sound stage, the sharp clicks of the light
switches, the squeaky swing of the screen door, and so forth.
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The Art of Listening
As in Chapter 2, the detail makes the scene real and brings it
to life. If you have calibrated and balanced the system properly the soundtrack should pull you right onto that porch, and
with Costner as he walks out to the diamond. It still sends
chills down my spine when it works right, and it should do
this for you too - if the system is accurate.
In investigating this soundtrack, and asking questions of
some of the people involved, I was told that there were over
100 sound elements used to make these scenes real, and
each has a specific place in space and sound to contribute.
If they all mesh correctly you will not want to stop the disc
- you will fall into the movie- which is of course exactly the
Another excellent, if totally different film is Crimson Tide
- Chapters 12-15 or 18 and 19. Here the goal is to put you
on this nuclear missile boat, under high stress, as the captain and crew deal with internal conflicts and their orders to
fire missiles. The detail used to create the ambiance inside
this sub, and the dozens of small sounds contributing to
this “space” such as beeping sonar, communications warning tones, clicks from internal speaker systems and microphones, breaking plastic sounds as the officers open their
code authenticator packs, combination locks on safes, keys
jangling, the dramatic shift in ambiance from inside to outside the sub as torpedoes are detected and fired, and so
forth all combine to produce a very intense, very high tension scene.
On a fair to good system the scenes will be interesting, but
on a great system properly set up these scenes are absolutely compelling, holding you riveted to the screen and making you believe totally that you are standing in that control
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The Art of Listening
Another excellent clip is Chapter 12 – “The Old Code” from
Dragonheart with the voice of Sean Connery as the dragon.
Make sure you get and use the anamorphic widescreen
(2.35:1)version. This also makes an excellent screen image
size/location tester. In this screen the dragon flies around the
room while speaking and beating it’s wings. Moving across
the LCR stage and around through the surrounds and back.
If the system is set up correctly the wing beats slide seamlessly and smoothly from speaker to speaker and the whole
ambiance rotates with the on screen image of the dragon.
There is also substantial low frequency content added into
the voice so it also tests your main system to subwoofer
splice and subwoofer accuracy and tone. The voice should be
solid and very ‘heavy’ with out boominess.
This film contains a number of segments that can be used.
Chapter 4, Chapter 6 ( the rain) Chapter 8, and the now
semi-famous Chapters 14/15 containing the depth charging sequences. The depth charge scenes not only provide
a good check of the system’s overall dynamic capability and
reality creation quotient, but also allow you to see how well
the system handles both soft (dialog passages) and loud
(explosions in rapid sequence) .
The rain in Chapter 6 is a fine test for surround ambiance
creation and a system’s overall ability to create a sense of
‘there’ as was discussed earlier.
Every time I use these scenes, in classes or on jobs, I know
if things are working properly because people stop what they
are doing and become glued to the movie.
The Art
of Listeningw
Section VI
The Art of Listening
Often there will be a physical ‘jerk’ or snap in their body
language when the stop button is pushed and all of a sudden
the place they are shifts instantly from the picture back to
the reality of the room we are in. This tells me that we have
successfully re-created the acoustical space intended, and
that detail is coming through to make everything seem ‘real’
What Are You Shooting For?
It may be difficult to understand what happens until it happens to you, but when it does, you will never look at your
systems the same way again.
We encourage you to experiment for yourself and find what
works for you, but remember if you don’t disappear into
the movie, if the listening experience is not centripetal and
doesn’t pull you in then, there are probably things wrong with
the acoustical envelope you are producing that are interfering
with your ability to fool the ear/brain into believing it is someplace else.
There is an element of art and magic to this process, and
once you get it to work for you, it will allow you to really
showcase your systems to their utmost ability. Enjoy the
( NOTE: Another version of this material appeared as an
article in the October 2001 issue of Residential Systems
Magazine and in training materials prepared for Audio Control
Industrial .)
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of Listening
Section VI
The Art of Listening
Listening for the Details — Before
For each film we demonstrate before we calibrate
the system:
1. Did what you hear positionally match what was on the
screen? yes or no
2. Write in each loudspeaker box what you heard coming
from that position in the room.
Film: ______________________________
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Art of Acoustics
Section VI
The Art of Listening
Listening for the Details — After
For each film we demonstrate after we calibrate
the system:
1. Did what you hear positionally match what was on the
screen — yes or no
2. Write in each loudspeaker box what you heard coming
from that position in the room.
Film: ______________________________
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Section VII
Creating Magic
Creating Magic
However - Misapplication will always make things worse !
The same methodology can be used on center channel
speakers to control apparent position.
The key point to remember here is APPARENT position.
The brain can be fooled into accepting locations that are not
precisely matched to the physical positions.
Careful and judicious use of delay can both correct for
physical abnormalities in the room and allow you to create a
unique acoustic space for each client, tailored to their own
mental map of what the space could sound like. You can,
within certain limits, actually re-do the room to make a new
“space” from the old.
Additionally, differing delay patterns and lengths can be
programmed in and saved into memory to be triggered by
different modes on the decoder such as stadium spaces
for sports, etc. Even the most sophistical processor’s algorithms can be enhanced by tailored delay processing.
Subwoofers and Rooms - Creating Impact
The first thing to understand about subwoofers is that they
are designed to work into some specific room volume.
If the subwoofer is THX certified, its recommended room volume is part of the spec. If not, most manufacturers specify
this information.
It is VITAL to know exactly how much room volume your
subwoofer(s) are facing.
That number is the sum of:
• The actual room volume of your theater space
• Any additional coupled spaces such as hallways, adjacent
rooms not completely sealed off by a
door, and so forth.
For example if your theater space has a cubic volume of
1500 feet (length x width x height), and the sub you choose
is designed to work into room volumes of 800 square feet
(common for small subs) you will need TWO subs to cover
the space.
Section VII
Creating Magic
However if the theater room is coupled to a hallway of 250
cubic feet, and a den through an archway of an additional
1000 cubic feet, your subwoofers are looking at a cumulative
volume of 2750 cubic feet so you will need FOUR subwoofers to provide enough output to produce bass in the actual
cubic volume you have.
Be CAREFUL here- customers expect BASS and you can easily destroy a small sub trying to fill a large space.
DIVA , unique amongst all room correction tools, provides
compressors and a limiter on its subwoofer outputs which
can be used to protect subs, as well as shape and control
the sound of subwoofers.
This is in addition to the equalization provided, which can be
used to both correct problems and “tune” the sub’s sound to
the room, client and program material. Remember you have
memories in DIVA, so your subs can have many “sounds”.
You can use the Compression, Limiting and EQ in DIVA as
tools to create a sub “sound” or manage Bass impact and
presentation in any space.
The best way to understand this is, to hear it; so let’s do a
little listening first and then we can discuss what is happening and why.
Compression changes the overall dynamic ratio of any signal
by making the loud parts softer and the soft parts louder.
The RATIO used reflects the relative change being made
- the higher the number [x] over the 1 (x /1 the more compression is being applied.
Thus, a compression ratio of 2:1 is much gentler than a ratio
of 10:1.
Limiting is sort of selective compressor in that it only affects
the top or high level portion of a signal. Limiters essentially
prevent a signal from getting any louder than a pre-set point.
They can do this all at once (a brick-wall) or gradually starting
at some pre-determined “threshold” point.
The subjective quality of either process is entirely dependant
on it’s time constants or the amount of time it takes for the
device to “attack” the signal, and “release” the signal from
electronic bondage.
Room Acoustics
Section VII
DIVA provides factory presets (developed by Technology Visions for/with Audio Control) for these function which is where
you should ALWAYS start.
Creating Magic
Make any changes in very small amounts and listen carefully
before making any addition changes.
Selling Calibration and Equalization
They key to getting your customers to accept this option,
and for you to be able to sell and profit from the service is to
plant the seed VERY early on.
You should point out that EVERY system can benefit from this
process, because no room is perfect. Additionally you should
make sure they recognize that, and that every room in which
the programming they will enjoy is produced has had been
calibrated, equalized and measured intensively to insure its
They should take advantage of your ability to provide the
same scientific analysis and calibration to get the most out
of their space.
Remember equalization will enhance system performance,
provide flexibility for various programming sources (using the
recallable pre-sets in DIVA) and insure optimal enjoyment of
every programming source.
Your customers simply want the system to sound good - TO
THEM, and you have the tools to provide precisely that. Your
competitors probably do not!
You can give them whatever they want (within reason and the
known laws of physics) and for the money provide a much
better performing, more stabile, more consistent sonic stage
that anyone else.
SELL that idea!
The objection you are likely to encounter are easy to overcome if you can demonstrate the difference you can make.
You must not only tell them what you can do, you must let
them HEAR the difference.
To do that you need to build up a library of selected demonstration software.
This should NOT be explosions and screaming jet fighters,
Room Acoustics
Section VII
Creating Magic
although a bit of that is always fun. It should be selected 23 minute clips that you can run in a before and after mode
showcasing your skills and the capabilities of the hardware.
Here is a short list of the discs I like to use.
You should spend time to add to this your own favorites,
ones you can talk about and demo with.
You must insure enough variety to appeal to all customer
types, both male and female.
(All these are DVD’s)
Finally . . . Conduct a Listening Test
The two commandments of system calibration that cannot
be ignored are:
Always, always, always conduct numerous listening tests
throughout the process to insure that what you are doing is
actually having a beneficial effect.
Never, never, never do any equalization without also listening
to the system with the EQ in and the EQ out to compare.
Given the tools now have available, you can electronically
correct a significant portion of the equalizable problems. With
the proper application of the right kind of acoustical treatment
you can tackle many of the others.
Remember choosing and using the right tool for the job can
go a long way to improving the acoustic performance of any
room, and thus the performance of the sound system you
put in that room.
Room Acoustics
Section VIII
Using the SA-3052 Real Time Spectrum Analyzer
1. Take attendance using pink noise
2. Look at frequency response to check if they are similar.
3. Use tape measure to set delays.
4. Look at frequency response and set equalization.
5. Check subwoofer splice
6. Listen and enjoy.
Using the the Iasys HT and the Diva
1. Place microphone in the money position.
During the testing, make sure the microphone stays in this
2. Play Pink Noise, take attendance.
The purpose here is to make sure all speakers are working,
that the connections go to the correct speaker and to see if
there are any significant inconsistencies between speakers. If
everything is perfect the first time, you
are one of the lucky few.
3. Make sure there are no rattles.
Use the sine sweep at
high volume and listen
for distortion as it
sweeps. Tighten the
sweep frequencies
to home in on the
problem area. As you
get close, change
to the constant sine
output, then use the
wheel to move small
amounts. Most likely
there will be rattles in
screen covers, light
fixtures and the like.
Room Acoustics
Section VIII
At the end of each delay test,
push the COHERENCE button and
let Iasys HT do a full sweep before
pushing QUIT.
4. Run Delay test on each speaker
Pick an empty memory within Iasys HT or empty a memory
via the main menu. Press DELAY/POLARITY and follow the
The HT-100 will route the signal to the correct output. You will
need to run these automatic tests on each speaker. While
this will take some time, you need only start the test for
each speaker, then the Iasys HT will do the rest.
5. Check Energy Center for speaker consistency
After running all delay tests, press RECALL and Iasys HT will
display the energy centers for all speakers. “Like” speakers,
e.g. left and right front, surrounds, should have energy centers within one-sixth octave. This is a great test for finding
inconsistent or “wounded” speakers. Finding a problem now
will save much grief later. See octave chart on page 52.
6. Set all SPL levels equal
Press CROSSOVER button until the pink noise is cycling to
all the different speakers via the HT-100. Using the Diva, set
the gain levels so that the SPL in each channel is identical.
While simple, this is a very important step for a great sounding system.
7. Adjust delays for Left, Right, Center, Subwoofer, sides
and back.
Select DELAY/POLARITY. Look at the Delay information and be
sure that all the Polarities are correct. If not, this is the time
to fix them.
Then push the DELAY button another time. The new information is “relative delays” calculated from the farthest speaker.
With Diva, set the delays as noted on the Iasys HT. In Diva,
adding “overall delays” will not change the “relative delays”.
Now that we have done a fair bit of adjusting with Diva, this is
a good time to save into a memory just to be safe.
8. Adjust equalizer using Equalizable Spectra
Equalizable Spectra will be in the Iasys HT memory for each
channel from the Delay and Coherence tests. Set the equalizer based on these memories, paying special attention to
the missing data parts of the frequency spectrum.
Room Acoustics
Section VIII
Do the major adjustments then use the one-third octave analyzer via the PINK noise to check the results. If you want to see
the one-twelfth octave response, you will need to re-run the
delay test for that channel, then as that test concludes switch
to the sweeping more of the equalizable spectra.
Use PAUSE not QUIT if you want to stop the noise and then
continue as that will keep you from having to re-run the delay
test again.
9. Check Subwoofer splice
Check to make sure at the frequency of the subwoofer crossover, there is not a peak or dip in the response. You will need
to play the speakers physically closer to the subwoofer(s)
using the noise/RTA and manual selects of the HT-100, then
look at the frequency response. Since the delays are set
right, this might not be as much a problem as without the
10. Select Subwoofer mode on Diva
Hard is a good choice for most movies as it is tweaked for action and effects. Normal is better for just music as discussed
in the Diva manual.
11. Add extra Delay to side and back speakers for effect
See the recommendations early in this manual. Try it and you
will be amazed at the improvement.
12. Add Delay time per individual preference to Left and
Right which brings forward Center
This one is individual preference but in the author’s opinion
makes the images on the screen more 3D as the sound from
the Center speaker arrives just slightly ahead of the Left and
Right speakers.
13. Listen
14. Season to taste
More side or rear delay? With the Diva, this is easy to add
and listen as you go. Change the equalization to the owner’s
preference? Again, this is easily done. Remember to save
into permanent memory on the Diva more often than you
think is necessary.
15. Enjoy
At this point, the system should be Magic. Use the Bypass
feature of the Diva to hear the differences.
Room Acoustics
Octave Chart
Frequency distribution of
common musical instruments
Room Acoustics
1. “The Audio Dictionary”, second edition, G.D.White
2. “Home THX Room Equalization Manual”, revised 1.5 Lucasfilm, Ltd
3. “Home Theater Acoustical Problems and Equalization Solutions”, Fred Ampel/AudioControl
4. “Learning to Listen”, Residential Systems Magazine, October 2001
Special thanks to Fred Ampel of Technology Visions
for his efforts towards creating this guide.
Frederick Ampel
Technology Visions
9512 West 93rd Street
Overland Park, Kansas 66212-4801 USA
Phone: 913 492 3047
Fax: 913 492 6226
Email: fampel@mindspring.com
22410 70th Avenue West
Mountlake Terrace, WA 98046
425-775-8461 • Fax 425-778-3166
Room Acoustics
Room Acoustics
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