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```Advanced System Installation
We like to call this our “Lessons Learned” section, where we expose some critical lessons that we
have learned through thousands upon thousands of hours of trial and error:
Lesson One: Off-Axis Response
When a speaker system like the Legatia is placed in an automotive environment, we hear the direct
(shortest path) and reflected (longer path) sounds, such as resonances and reverberations. The two
sounds are processed by the brain as one sound, and this influences our perception of height, width,
and depth of soundstage, as well as rearward ambience. For this reason, the off-axis radiation pattern
of any speaker in a vehicular environment has a significant influence on how natural the music
sounds.
The lesson to learn here is that most mobile audio sound systems benefit greatly from having the
front stage speakers at least partially “off-axis.” Off-axis means that the speakers are not pointing at
you, but rather at some angle less than 90 degrees away from you.
Lesson Two: Equalization of Pathlength Differences
Quite possibly the most important functional consideration that a do-it-yourself enthusiast or
professional installer should give to the Legatia speaker placement is to optimize, as best as possible,
pathlength differences (PLD’s) in the vehicle. PLD’s are defined mathematically as follows (this
example assumes a right-hand drive vehicle---PLD’s are always a positive number):
X–Y=Z
Where:
X = distance of the center of the left speaker from your left ear.
Y = distance of the center of the right speaker from your right ear.
Z = pathlength difference.
Applying this formula, assume that the distance of the left speaker from your left ear is 140cm, and
the distance of the right speaker from your right ear is 100cm, the pathlength difference is 40cm.
Good stereo imaging is completely dependent on arrival times of the fundamental vocal frequencies.
Differences as little as 10 microseconds can be detected by the brain. A PLD of 30 centimeters
equates to the sound from the nearest channel arriving about 0.9 milliseconds earlier than the furthest
channel. It is Hybrid Audio’s opinion that the end-user should try to keep PLD’s to less than 30
centimeters in a vehicle which is intended to have good imaging and staging character from both
seated positions.
The best way to go about evaluating certain locations in your vehicle is, in general, to look for the
potential locations as far forward and away from you as possible, but still with a general “line of sight”
to the speakers (particularly the speaker on the far side of the vehicle). An easy way to test various
potential locations is to hold a tape measure or other measurement device from the potential speaker
mounting locations, and measure those locations with respect to your ears.
Reference the figure, below. In this scenario, three potential locations for the mounting of the Legatia
midbass driver are shown:
In scenario “a”, we show the installation of the Legatia midbass in the dashboard, high in a door
panel, or in the dashboard. As you can see from the diagram, the PLD’s between the left and right
speakers are large, due to the proximity of the listener to the near-side speaker. While the mounting
of primary drivers in the dashboard or a-pillars has become increasingly popular, this configuration
will undoubtedly require both time and intensity domain equalization in most vehicles to ensure a
good, focused center image, properly located in the center of the vehicle for one seated position.
There are, however, some rare exceptions, and you may actually find that the dashboard locations
provide the best equalized PLD of the available mounting locations; this is very rare though – in our
experience, less than one percent of vehicles on the market today have optimized dashboard speaker
locations for the midbass drivers.
In scenario “b”, a typical door installation location is shown, and in many vehicles represents a good
improvement in PLD’s from the dashboard, high in the door panel, and a-pillar location identified in
scenario “a.” The door speaker installation scenario is the one detailed in the basic installation section
at the beginning of this manual, and in most vehicles represents a satisfactory location to mount
speakers; not ideal but satisfactory. The door speaker installation scenario will likely also require
some amount of time and intensity equalization to ensure a centered image in most vehicles; this can
be as simple as adjusting the balance control on your source unit, to more advanced ways of digital
time and intensity manipulation.
The third and final potential mounting location as shown in this diagram (scenario “c”) represents a
kick panel installation, where the midbass are placed far forward in the A-frame cavity of the kick
panels, present in most vehicles. The kick panels are the small panel next to the throttle and brake
pedals, down by your feet. While it is not immediately obvious looking at a two-dimensional drawing,
in many cases the kick panel location affords the best equalization of pathlength differences for most
vehicles. And the reason why this is a good choice for most vehicles is defined in the second full
paragraph of Lesson Three, below.
The lesson to be learned here is that by taking a few moments to evaluate the potential mounting
locations in your vehicle, in a very short period of time, you will be able to find the best location for
your Legatia midbass by determining the location with the smallest PLD.
Lesson Three: The Effect of HRTF, ITD, and IID
Head-related transfer function (HRTF), interaural intensity differences (IID), and interaural time delay
(ITD) all play a key role in the optimum placement location for the Legatia component speakers. A
sound wave approaching the eardrum from your chosen speaker location is shaped by interactions
with the size and shape of your head, torso, and outer ear, resulting in the HRTF. More specifically,
the HRTF is the ratio between the sound pressures of the wave at the eardrum, as compared to the
sound pressure that would exist at the center of the head if the head were removed. In general, the
sound arriving at the ear further from the source is attenuated and delayed relative to the sound
arriving at the ear closer to the source. This generates an interaural intensity difference (IID) and an
interaural time delay (ITD). As a sound approaches the head, the ratio of distances from the speaker
location to the near and far ears increases, and the effects of head-shadowing are amplified, causing
the IID to increase. The spectral shaping caused by the head and the shape of the outer ear may also
change. The ITD, which results from the absolute difference in path length from the source to the
ears, remains approximately constant as distance decreases. From this we learn:
• ITD is the dominant factor for frequencies below about 500 Hz;
• A combination of ITD and IID are dominant for frequencies between approximately 500 Hz and
2,000 Hz; and
• IID, in concert with HRTF, are dominant above about 2,000 Hz.
These are generalizations, and are subject to the size and shape of one’s head and torso, and size
and shape of the outer ear (the folds and ridges of the ear), but in general, the above is a good
guideline for establishing ITD, IID and HRTF thresholds for the human auditory system.
Because the Legatia midbass’ ability to play into the sub-200 Hz range, an effect clearly dominated
by ITD, up to and including frequencies exceeding 6,000 Hz, an effect clearly dominated by IID and
HRTF, placement of this driver is extremely important. The driver should be placed as far forward as
possible in the vehicle to optimize ITD. Lateral (forward to back) placement is much more important
than horizontal placement (up and down). This is because of the brain’s ability to process sounds
such as spectral envelope cues, and use a phenomenon known as the “precedence effect”; the brain
can be easily “fooled” into thinking a sound stage is high with kick panel or floor-mounted speakers (a
word to the wise: the best place to put a set of speakers is not always “up high”, as most vehicles do
not offer an amicable location in the dashboard or a-pillars for good image placement for both seated
passengers, especially in the critical frequencies sub-500 Hz). In addition to the time equalized
placement of the drivers, the end-user must also consider that above approximately 2,000 Hz,
intensity plays a key role in good sound staging and imaging. Therefore, the Legatia midbass’ should
be placed in an area where intensity differences can be equalized, either mechanically or
electronically, to ensure good imaging and sound staging.
The lesson to be learned is that, like Lesson Two, the Legatia midbass should be placed as far
forward from your listening position as possible, and every effort should be made to optimize time and
intensity domain characteristics of the installation.
Lesson Four: Point-Sourcing
The term “point-sourcing” is often used to describe the technique of having a single pair of speakers
in an installation cover the majority of the critical middle band frequencies. In many installation
scenarios, the Legatia midbass could be considered a point-source speaker driver, because it has the
ability to reproduce six octaves of tones. Point-sourcing, if done correctly, can lend itself to a variety
of valuable attributes, including precise image definition and stable sound staging character. By
applying Lessons 1-3 above, the Legatia midbass can be used as a point-source driver to achieve
excellent staging and imaging results.
The lesson to be learned here is that the Legatia midbass, given its wide-bandwidth design, can
faithfully reproduce as much as six octaves of tones, and would make a valuable addition to any
sound system as a point-source driver for the spectrum comprising vocal imaging cues.
Lesson Five: Reference
One of the most important things to do before completing your Legatia installation is to get a
reference for your future listening tests. To really know what a snare drum sounds like, you must go
and listen to one, in person, live and un-amplified. There is no substitute for the visceral impact and
emotion of live music. Nothing else in life can touch your soul the way music does. Whether it’s a
200-member orchestra, or a four-piece fusion band, nothing compares to the phenomenon of live
music.
Take this as Hybrid Audio’s official request: become a student of music and your mobile audio sound
system will be better for it. We want nothing more than to know there are great sounding audio
systems around the world using our products, and you’d make us all very proud if you became a
student of music and learned its beauty and passion.
Advanced Installation of the Legatia Component Systems
Mounting Baffle Considerations
Now that we have revealed five of our most important “Lessons Learned”, we can now apply these
lessons to the Legatia installation. The first important matter is the physical installation of your Legatia
midbass and/or midrange, and more specifically with respect to improving the Legatia midbass’ or
midrange’s mounting baffles. Most vehicles’ factory mounting locations for speakers are less than
ideal. In most cases, the OEM speaker mounting flanges are likely nothing more than flimsy extruded
plastic, and provide no sonic benefit to your Legatia installation. The Legatia drivers are long-throw
midbass, and high-performance midrange, and the plastic mounting baffles that come from the
factory in virtually every vehicle will lead to buzzes, rattles, vibrations, and resonances, all of which
negatively affect the Legatia installation. In other vehicles, you may have attached the Legatia
midbass’ or midrange’s directly to the door metal (hopefully with a layer or two of self-adhesive sound
damping in between), but this is still not entirely ideal. In whatever scenario you have installed your
Legatia midbass and/or midrange, there are certain “tricks” and techniques that may be applied to get
the most out of your Legatia component set, specifically the midbass and midrange installation, as
follows:
Mounting the baffle, sound damping, and “decoupling”: the mounting baffle or mounting location
should either be secured extremely well to the vehicle’s body, or completely isolated from the
vehicle’s chassis. The reasoning is that the speaker baffle panel will vibrate and will radiate sound.
Even small vibrations can result in the baffle itself radiating more sound than the actual speaker at
certain frequencies. The mounting baffle or mounting location should be damped with a layer of
typical sound damping to reduce the Q of the baffle and lower its vibration resonance frequency
below the range of the driver’s frequency response. In many cases, using thicker baffle panel in
concert with self-adhesive sound damping can also be advantageous, provided the rearward wave of
the speaker has no obstructions created by the baffle itself. Finally, if possible, the speaker should be
mechanically decoupled from the baffle. This can be something as simple as a layer of self-adhesive
foam tape, to more exotic examples of decoupling, including rubberized rings or multiple-layer septum
shielding.
Building solid mounting baffles: in many cases, it is advisable to mount your Legatia midbass’
and/or midrange’s in high-stiffness wood or high-density fiberglass (or wood treated with fiberglass
resin). Hybrid Audio Technologies recommends the use of a solid hardwood, such as birch or oak,
namely because these woods are stiff and help to dissipate resonance, and screws can be inserted
and removed multiple times without stripping. Avoid Medium Density Fiberboard (MDF), particularly in
wet environments like the door, as the MDF will act like a sponge with humidity and moisture, and not
only that, the MDF is a dense, but not stiff type of wood, and the results may not be particularly
noticeable if you use MDF. Once your baffle is built, it must be covered in one or two layers of a
good-quality, brand name self-adhesive damping product; a solid wood mounting baffle with sound
damping treatment will augment the Legatia installation by eliminating resonances.
Mounting baffle dimensions: While building baffles is important, it is notable that mounting baffle
size is equally important. All mounting baffles should be kept as small as possible with respect to the
size of the speaker. The purpose of using a small baffle is to avoid the potential for low amplitude
diffracted sound waves becoming summed with the incidental waves. A narrower baffle also becomes
increasingly important as frequencies range into the Legatia midbass’ and/or midrange’s upper
bandwidth, where the power response is more uniform and incident and reflected waves are
indistinguishable. In practical terms, keep baffle dimensions small with respect to the size of the
Legatia midbass and/or midrange, chamfer or round sharp edges (including, in particular, the
mounting hole’s rear inner edge), flush-mount the speaker whenever possible, and use shallow,
surface-mounted hardware. Also, remove all unnecessary protrusions from the baffle surface.
Crossovers
One of the most fundamental and important considerations in the final tweaking of a car audio system
is the set-up of the speaker’s crossovers. The Legatia drivers use rigid paper cones that exhibits little
if any cone breakup in its upper frequency bandwidth. However, it is still important to utilize
crossovers, especially active crossover networks to suit the speaker system to the car’s acoustic
signature. It has been Hybrid Audio’s philosophy to tune the speaker system to the vehicle’s acoustic
signature using just active crossovers, and only a very minor amount of equalization. Our very best
world championship vehicles have always had one thing in common: creative use of active crossover
filters and very minimal equalization. Use your crossovers to tune your car, and the equalizer to suit
the vehicle’s speaker response to your own tastes.
The first thing to remember is that every speaker exhibits some sort of a natural roll-off. This rolloff
typically amounts to about 12 dB/octave, and needs to be taken into account, especially when
designing passive crossover systems (this roll-off has been accounted for in the Legatia L2x and L3x
designs). Simply adding a capacitor and inductor in series (6 dB/octave bandpass filter) to a Legatia
midrange driver does not necessarily mean that you’ll see a phase coherent 6 dB/octave bandpass
filter at its crosspoints. In fact, summing the effect of the driver’s natural bandpass roll-off, you might
actually be approaching a theoretical 18 dB/octave bandpass filter at certain frequencies. Not only
this, but the speaker could potentially begin to exhibit significant intermodulation distortion as the
cone becomes non-linear trying to reproduce the lowest octave of tones, not to mention irregular
polar radiation patterns between the Legatia midbass/midrange and the accompanying Legatia
tweeter.
Given the large uncertainty of low-order crossover systems, Hybrid Audio recommends the use of
higher-order electronic crossovers so that fine tuning can be done electronically. The active network
benefits from easy correction of different speaker sensitivities and equalizing not only the individual
drivers but the combined response as well. Not having to account for the speaker’s impedance
verses frequency, as well as the passive device impedance and phase shift makes the active filter
superior to most passive crossover networks, due to the fact that each and every aspect can be
tailored to better suit the individual installation’s requirements. However, we understand that in some
cases that passive filters are required, and thus the reason why we have manufactured the Legatia
L2x two-way and Legatia L3x three-way passive crossover systems. In our humble opinion, however,
the ideal crossover system for most users, is an active one that takes into account the Legatia driver
location and its characteristics, in concert with the polar radiation patterns of other speakers involved,
all the while balancing linear and non-linear distortion (non-linear harmonic distortion increases with
sound pressure level or cone displacement, and thus, crossover frequency is critical and can be
vehicle and user dependent).
As mentioned previously in “Lesson Three”, imaging cues of near-field (within 3m) sources come from
effectively two auditory methods: ITD and IID. ITD is the time it takes for sound to reach the far ear
after reaching the near ear. Typical adult male heads have an ITD maximum of approximately 400
microseconds. IID is the measure of intensity difference of the far ear as compared to the near ear.
ITD is typically used by the brain to localize low frequency sources below 500 Hz. IID is typically used
by the brain to localize high frequency sources, above 2,000 Hz. HRTF is also used in conjunction
with IID. Above approximately 4,000 Hz, the higher frequencies are attenuated by the head for the
far side ear. A sound to your left will have a different spectral content for the left ear as compared to
the right ear. The HRTF is unique for each individual (based upon shape and size of the head and
torso) but typically occurs at around 4,000-5,000 Hz. HRTF will affect the IID at even higher
frequencies, more so than simple average SPL. Above 6,000 Hz or so, the HRTF portion of IID
becomes the dominant factor. The spoken word (human voice) comprises a fundamental frequency
range of approximately 150 Hz to 6,000 Hz.
Taking the above into account, your desired crossover frequency for the Legatia midrange and/or
midbass should be one that allows the midbass or midrange to play as much of the audible spectrum
of the spoken voice to ensure point-source delivery of the tones and pinpoint image definition. In
many cases, this would be around 200-250 Hz for high pass, and around 6,000 Hz, or higher, for low
pass. In all cases, the chosen crossover frequencies should be evaluated for sonic character, while
balancing distortion and power compression at high amplitude levels.
Time Correction
It is our humble opinion that time correction should only be used in three different circumstances:
1) When the installer recognizes that a vehicle cannot image properly from both seated positions
and it seems more plausible to make the vehicle stage and image well from only one seated
position.
2) To counter the effects of group delay.
3) Time alignment between pairs of drivers.
Scenario 1
The first scenario is rather elementary. If a vehicle is too small to achieve equalized PLD’s, it doesn’t
lend itself well to equalized PLD’s, or the vehicle’s owner doesn’t wish to embark on physical
reconstruction of the car to achieve optimized PLD’s, it is a good use of time correction to make the
vehicle image well from the single seated position. It should be noted that it is Hybrid Audio’s opinion
that it is always better to improve the car mechanically and attempt to fix mechanical problems with
mechanical solutions, than it is use to electronics to fix mechanical problems. However, we realize
that there is the occasion when there is little desire to try to mechanically optimize one’s listening
space, and electronic manipulation is desired. It is important to recognize that, given the
fundamentals of ITD and IID discussed previously, time alignment is rendered virtually useless for
frequencies above approximately 2,000 Hz.
Scenario 2
In the second scenario, the use of time correction is much more cognitive, and shows great promise
for countering the effects of group delay. Group delay is impulse response over time. Group delay
increases significantly at low frequencies, and is considerable in larger midbass and subwoofers. An
excellent use of time correction would be to delay the smaller Legatia midranges and tweeters with
respect to the larger midbass and subwoofers, so that the low frequency delay of these drivers is
synchronized in the time domain with the output of the midrange and treble frequencies.
Scenario 3
The final scenario is time alignment between pairs of drivers. When employing multiple drivers in
order to achieve a unified listening experience within a vehicle, it’s usually a requirement to install the
drivers at physically separated locations; for example, your midbass may be located in the doors, and
the midrange and tweeter may be located in the dashboard or a-pillar. In order to compensate for
this, you might choose to selectively delay certain speakers in the installation so that all of the tones
reach your ears at the same time (note that as previously alluded to, time alignment of your tweeters
would be rendered virtually useless).
Amplitude Equalization
An excellent use of today’s dual-mono equalizers and advanced digital signal processing is the ability
to equalize amplitude anomalies between speakers and sets of speakers installed in a vehicle. In a
vehicular installation, the frequency response of drivers can sometimes be manipulated for the
betterment of the system using independent left and right amplitude adjustment. Virtually any good
car audio system can be made better with judicious use of a minor amount of equalization. And while
equalization will not cure phasing anomalies in a car, usually the product of vehicular mechanics, they
can certainly be helpful in fine-tuning the system to your own personal taste or in the quest for
playback accuracy to the original musical composition.
One important consideration of amplitude equalization (also known in some circles as “amplitude
alignment”) is the ability to tune those frequencies above about 500 Hz that are not completely
affected by time correction. The very best vehicles have some sort of amplitude equalization
between the left and right speakers to account for IID and HRTF. After your Legatia system is
installed, you may wish to attempt some minor amplitude equalization between the left and right
channels to achieve a more stable image that is not frequency dependent, or perhaps to improve
image placement or stage coherency.
Acoustic Treatment
A considerable benefit can be made to any mobile audio system with the select placement of acoustic
treatments. The purpose of using acoustic treatments is to reduce the amount of reflected energy in
the hostile automotive environment, and hear more of the direct sound being emanated from the
speaker. It is akin to the signal to noise (S/N) ratio in a piece of electronics, where the signal could be
considered the direct energy coming from the speaker, and the noise could be considered the
reflected waves off of nearby surfaces, such as windows, hard center consoles and door panels,
windscreens, and etc. A word of warning though: there is a fine line between too little and too much
acoustic treatment; just as some vehicles can benefit from some selectively applied treatments, there
is a point where the vehicle can begin to approach “semi-anechoic” conditions, and lose its liveliness,
which is not ideal. Reflections are all around us, and are a part of our day-to-day lives. It is our
opinion that some lateral reflection is a good thing; it helps to establish stage boundaries, and gives
the recoded playback and more visceral and “believable” sound.
The first principle to understand is that below 200 Hz, acoustic treatments are rendered virtually
useless. It is Hybrid Audio’s assertion that only those frequencies above 200 Hz benefit from the use
of treatments, given that a 200 Hz waveform is about 1.7 m long; 1.7 meters is less than or equal to
most vehicle widths. This is also the frequency where we believe pure tones in the vehicle are going
to be difficult, if not impossible to localize. Finally, most vehicles exhibit a Schroeder Frequency (Fs)
between 50 at 125 Hz; the Fs (or cabin-gain frequency) is vehicle dependent, and is the frequency at
which resonances become so tightly packed in frequency and space that the acoustical properties of
the vehicle behave quite uniformly. (As an aside, one significant benefit of car audio sound systems
is that frequencies below the lowest room resonance increase at a theoretical 12 dB/octave…it’s no
wonder car audio systems have such great bass!)
Acoustic treatment can be very effective above 200 Hz, depending mostly on the polar radiation
pattern of the speaker. In the case of the Legatia midbass, the polar radiation pattern is quite large at
lower frequencies, with a narrowing of the radiation pattern (“beaming”) at frequencies into the treble
bandwidth.
Should the Legatia midbass and/or midrange be placed in the kick panel locations, one may find that
a notable improvement can be made by adding acoustical treatments, such as open-cell foam, into
the underside of the dashboard. Likewise, should the midbass, midrange, and/or tweeter be placed
up high on a-pillars, or in the dashboard, where comb filtering (reflective summation and cancellation
off of a hard surface, such as a windscreen) may become an issue, a dashboard “mat” or other soft
furnishing may be a noticeable improvement. It will require trial and error to get it right, but the
learning is in the experimentation!
Sadly, there are no rules in mobile audio, only several hypothesis and theorems that seem to work for
most vehicles. Your vehicle may be different, and defy everything we know, and everything written in
this manual. You may find that getting that rich, detailed sound that you crave may require some
experimentation and a lot of work to make it right. Or you might be fortunate to have a vehicle that
sounds excellent with minimal work. Have patience and work through the issues; the result will be a
rewarding musical experience in your vehicle! Just remember, it is critical to get a reference, as
detailed in Lesson 5. Go out and become a student of music and audio, learn, and improve your
audio system one step at a time. The journey is exciting and rewarding!
What we have included above is only a very brief primer to the world of high-end mobile audio
systems. We invite you to read more by going to our website.
Legatia User’s Manual ©Hybrid Audio Technologies
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