User’s Guide
for the
LS1-131
LS2-215
LS3-231
Constant Q Graphic Equalizers
Crate Pro Audio’s Live Sound Graphic Equalizers feature constant Q circuits which, unlike inferior broad band EQs, let
you boost or cut only the frequencies you choose. Combined with a switchable equalization range, these EQs allow greater
system control and accuracy whether using them for house coloration, feedback control, or speaker correction.
In order to achieve the highest level of performance from your equalizer, please read this owners guide prior to its use.
“Thank You” from
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
Congratulations on the purchase of your new Crate Pro Audio Live Sound Graphic Equalizer. These outstanding
devices have been designed with the audio professional in mind, providing the degree of accuracy and level of quality you demand. Their ease of use and straight-forward design lend them to use by novices as well. This owner’s
guide is designed to acquaint you with the workings of these equalizers and how they may be used in your sound
system and should be read through before using them.
Table of Contents:
An Introduction to Equalizers........................................................3
The LS1-131/LS3-231 Front and Rear Panels ................................6
The LS2-215 Front and Rear Panels ..............................................7
Using an Equalizer........................................................................8
Applications:
Some Methods of Connection ...........................................9
Room Equalization ..........................................................10
Fletcher-Munson Equal Loudness Contours .....................10
Feedback Control ............................................................11
Creative or Enhancement Equalization ............................11
Technical Specifications .....................................back cover
CAUTION
ATTENTION
VORSICHT
RISK OF ELECTRIC SHOCK
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RISQUE D'ELECTROCUTION
NE PAS OUVRIR
ELEKTRISCHE SCHLAGGEFAHR
NICHT OFFENEN
CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK,
DO NOT REMOVE COVER.
NO USER-SERVICEABLE PARTS INSIDE.
REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.
ATTENTION: POUR REDUIRE D'ELECTROCUTION NE PAS
ENLEVER LE COUVERCLE. AUCUNE PIECE INTERNE N'EST REPRABLE
PAR L'UTILISATEUR. POUR TOUTE REPARATION, S'ADRESSER A UN
TECHNICIEN QUALIFIE.
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DEN DECKEL ABENHMEN. INTERNE TEILE KONNEN NICHT VOM
BENUTZER GEWARTET WERDEN. DIE WARTUNG IS QUALIFIZIERTEM
WARTUNGSPERSONAL ZU UBERLASSEN.
THIS EQUIPMENT HAS BEEN DESIGNED AND ENGINEERED TO PROVIDE SAFE AND RELIABLE OPERATION. IN ORDER TO PROLONG THE
LIFE OF THE UNIT AND PREVENT ACCIDENTAL DAMAGES OR INJURY, PLEASE FOLLOW THESE PRECAUTIONARY GUIDELINES:
CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT OPEN CHASSIS; DO NOT DEFEAT OR REMOVE THE GROUND PIN OF THE
POWER CORD; CONNECT ONLY TO A PROPERLY GROUNDED AC POWER OUTLET.
WARNING: TO REDUCE THE RISK OF FIRE OR ELECTRIC SHOCK, DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE.
CAUTION: NO USER-SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.
EXPLANATION OF
GRAPHICAL SYMBOLS:
2
"DANGEROUS VOLTAGE"
= "DANGER HAUTE TENSION"
"GEFAHLICHE SPANNUNG"
"IT IS NECESSARY FOR THE USER TO REFER TO THE INSTRUCTION MANUAL"
= "REFERREZ-VOUS AU MANUAL D'UTILISATION"
"UNBEDINGT IN DER BEDIENUNGSANLEITUNG NACHSCHLAGEN"
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
An Introduction to Equalizers:
The Crate Pro Audio Live Sound Graphic Equalizers are available in two mounting configurations: a 1-3/4”
single rack space (LS1-131/LS2-215) and a 3-1/2” double rack space (LS3-231). These equalizers are a perfect
addition to any professional sound system, particularly the Crate Pro Audio systems.
The Crate Pro Audio LS1-131/LS2-215/LS3-231 equalizers offer precision control of the audio spectrum.
Some features of these equalizers include:
• Balanced and unbalanced inputs and outputs
• Constant “Q” bandpass filter sets for precision control
• Two control ranges for greater accuracy
• Hardwire switchable bypass from input jacks to output jacks for total elimination of the
equalizer from the system
• Peak LEDs to obtain optimal signal levels
• High signal-to-noise ratio (greater than 94dB) and a wide frequency response (20Hz to
20kHz)
• Flat phase response for accurate reproduction and stereo imaging
• Very low THD (less than 0.01%)
• Maximum input level of +22dBm
• Variable low cut and high cut controls (LS1-131/LS3-231 only)
• Built in power supply
The LS1-131 and LS3-231 provide 31 bands of equalization at standard ISO center frequencies, 1/3
octave apart. They cover the entire audio spectrum from 20Hz to 20kHz. This allows precision control and
fine tuning of your audio system. (The LS3-231 offers two channels of 31 band equalizers.) The LS2-215
provides two channels of 15 band equalization at standard ISO center frequencies, 2/3 octave apart from
25Hz to 16kHz.
All of the new Crate Pro Audio Live Sound Equalizers incorporate constant “Q” multiple-feedback
bandpass filter sets for high resolution with minimal interaction between bands (see Figure 1 below).
Figure 1: Constant Q Response:
Constant "Q" filters: width
of filter does not change
with amplitude.
500
1k
2k
5k
0
200
200
Amplitude (dB)
Amplitude (dB)
200
Inferior broad band filters:
width of filter changes with
amplitude.
Frequency (Hz)
500
1k
2k
ƒ
L
ƒ
C
ƒH
ƒ
= lower frequency
ƒ
= center frequency
L
C
ƒH =
higher frequency
5k
500
1k
2k
1k
2k
5k
0
200
500
Frequency (Hz) ƒ
L
ƒL ƒH
ƒ
C
5k
ƒH
ƒ
= lower frequency
ƒ
= center frequency
L
C
ƒH =
higher frequency
3
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
These filters have a relatively low “Q” thus preventing “ringing”. Ringing occurs when a filter instantaneously receives an input signal and hangs on to the signal for a period of time after it has stopped (see Figure 2
below).
Figure 2: Q vs. Ringing:
1kHz TONE BURST
1kHz TONE BURST
INPUT SIGNAL
START
INPUT SIGNAL
START
INPUT SIGNAL
STOP
INPUT SIGNAL
STOP
All three equalizers have a flat phase response (see Figure 3 below) for accurate sound reproduction
with no coloration to your speaker system. This maintains pure stereo imaging without the “comb filter”
effect. As your ear passes across the stereo plane of your system, the comb filter effect sounds like “peaks”
and “nulls” in the response which can change the imaging dramatically.
Figure 3: Phase Response:
180
150
120
90
PHASE (Degrees)
60
30
Smooth, flat phase
response of the
Crate Pro Audio
equalizers
0
-30
-60
-90
-120
Example of an extremely
bad phase response,
typical of some "other"
equalizers
-150
-180
10
4
20
50
100
200
500
1k
FREQUENCY (Hz)
2k
5k
10k
20k
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
The LS1-131/LS3-231 both feature variable Low Cut and High Cut controls. The low cut control is not
only useful for subsonic filtering, but provides a wider range of control for low frequency “ringing” in some
sub-woofer systems and controls “wind” noises in microphones. This filter is extremely useful in using amplifier power more efficiently. This is accomplished by eliminating inaudible subsonic frequencies below 30Hz
from reaching the system thus conserving power. Most full range P.A. enclosures do not produce frequencies
below 30Hz due to speaker limitations. This is typical for all enclosures of this type. Some of these enclosures
begin to roll-off at approximately 50Hz with a usable low frequency limit of about 35 to 40Hz (-10dB down).
These frequencies may be recovered by using an equalizer to boost the low frequencies to compensate for the
speaker’s roll-off. But frequencies below 30Hz may cause displacement-limited distortion, which is distortion
due to excessive movement of the speaker cone. Dial the Low Cut control to 30Hz and add a 12dB/octave
roll-off at that frequency. This will result in a noticeably cleaner sound. Figure 4a shows the rolloff curves for
this control at the frequencies shown on the front panel.
Figure 4a: The Low Cut Control:
1dB
0dB
-1dB
-2dB
-3dB
10
15
40
150
250
-4dB
-5dB
-6dB
10Hz
100Hz
1k
The High Cut control can be used to reduce high frequency noise in your source material (instruments,
recorded music, etc.) and can help achieve a more natural sound when reproducing some acoustic instruments. Figure 4b shows the rolloff curves for this control at the frequencies shown on the front panel.
Figure 4b: The High Cut Control:
1dB
0dB
-1dB
-2dB
-3dB
3k
5k
10k
30k 40k
-4dB
-5dB
-6dB
1kHz
10kHz
50k
All units provide a Bypass switch which connects the input jacks directly to the output jacks. This is
extremely useful when troubleshooting or comparing your equalizer setting to the original signal. These
units also feature a “Range” switch. By pressing this switch, the “boost” and “cut” or control range changes
from ±12dB to ±6dB. This allows for greater accuracy. When using these equalizers with a Real Time or
Spectrum Analyzer, improved accuracy is important for fine tuning.
5
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
The LS1-131/LS3-231 Front and Rear Panels:
NOTE: The LS1-131 is shown; the LS3-231 is identical, except it has two channels, one over the other, in a 2 rack-space enclosure.
1
2
9
10
3
11
4 5
6
7
8
12 13 14
1 - POWER: Use this switch to turn the unit on and off.
2 - EQ SLIDERS: Use these slide controls to make adjustments at the standard ISO 1/3-octave frequencies indicated above
each slider. Each slider adjusts the signal ±6dB or ±12dB depending on the setting of the RANGE switch (#3). Moving a
slider up boosts the signal; moving it down cuts the signal. The center detent is the “flat” position (no boost or cut).
3 - RANGE: Use this switch to select one of two adjustment ranges for the EQ sliders (#2). With the switch out, the adjustment range is ±12dB. When this switch is depressed, the adjustment range is ±6dB. Care should be taken not to accidentally change the range from 6dB to 12dB during operation if extreme boosts are used, since the boosts will dramatically
increase if this occurs.
4 - BYPASS: When depressed, this switch routes the input signal directly from the BALANCED INPUT jacks (#9) to the
BALANCED OUTPUT jacks (#10), bypassing the equalizer controls completely. This is useful when comparing the equalized signal to the original. The adjacent LED (linked graphically to the switch with a solid line) glows red when in the
bypass mode.
5 - PEAK LED: This indicator glows red when the input or output signal is within 5dB of clipping. Adjust the LEVEL control (#8) so this LED only flashes during strong, peak-level signals.
6 - LOW CUT: Use this control to set the rolloff frequency for the high pass filter. The filter is continuously variable from
10Hz to 250Hz with a rolloff of 12dB/octave.
7 - HIGH CUT: Use this control to set the rolloff frequency for the low pass filter. The filter is continuously variable from
3kHz to 40kHz with a rolloff of 12dB/octave.
8 - LEVEL: Use this control to adjust the input signal level. For the best signal to noise ratio set this control so the PEAK
LED (#5) flashes on strong, peak-level signals. The overall output signal level of the equalizer is determined by the setting
of this control and the EQ sliders (#2).
9 - BALANCED INPUTS: The mixing board, amplifier or instrument (“source”) may be connected to the equalizer using
either of these jacks. However, only one jack may be used at a time. Different methods of connection are described and
illustrated on pages 9 and 10.
10 - BALANCED & UNBALANCED OUTPUTS: The equalizer may be connected to the mixing board or amplifier using
either of these jacks. The 1/4” phone jack and the XLR jack are balanced. The RCA jacks are unbalanced. Different methods of connection are described and illustrated on pages 9 and 10.
11 - GROUND LIFT: Use this switch to electronically disconnect the signal ground from the mains and chassis earth
ground. This may be helpful in eliminating ground loops which cause hum.
12 - VOLTAGE SELECTOR: The equalizer is designed to be used with either 95-130VAC or 190-250VAC power sources.
Check the AC line voltage of the outlet and set this switch accordingly before plugging in the unit.
13 - FUSE HOLDER: This contains the fuse for the AC mains. If the fuse blows, replace it with only the same size and
type. If the fuse blows repeatedly, check the AC line voltage and the equalizer’s voltage selector switch. If the problem
persists contact your Crate Pro Audio dealer.
14 - POWER CORD: Connect the power cord to a suitable source of AC line voltage. Be sure to match the voltage selector
switch (#12) to the line voltage before making this connection! In order to reduce the risk of shock, DO NOT defeat the ground pin
of the power cord!
6
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
The LS2-215 Front and Rear Panels:
1
2
7
8
3
8
4 5 6
7
2
9
4
4 5 6
10 11
12
1 - POWER: Use this switch to turn the unit on and off.
2 - EQ SLIDERS: Use these slide controls to make adjustments at the standard ISO 2/3-octave frequencies indicated above
each slider. Each slider adjusts the signal ±6dB or ±12dB depending on the setting of the RANGE switch (#3). Moving a
slider up boosts the signal; moving it down cuts the signal. The center detent is the “flat” position (no boost or cut).
3 - RANGE: Use this switch to select one of two adjustment ranges for the EQ sliders (#2). With the switch out, the adjustment range is ±12dB. When this switch is depressed, the adjustment range is ±6dB. Care should be taken not to accidentally change the range from 6dB to 12dB during operation if extreme boosts are used, since the boosts will dramatically
increase if this occurs.
4 - BYPASS: When depressed, this switch routes the input signal directly from the BALANCED INPUT jacks (#7) to the
BALANCED OUTPUT jacks (#8), bypassing the equalizer controls completely. This is useful when comparing the equalized signal to the original. The adjacent LED (linked graphically to the switch with a solid line) glows red when in the
bypass mode.
5 - PEAK LED: This indicator glows red when the input or output signal is within 5dB of clipping. Adjust the LEVEL control (#6) so this LED only flashes during strong, peak-level signals.
6 - LEVEL: Use this control to adjust the input signal level. For the best signal to noise ratio set this control so the PEAK
LED (#5) flashes on strong, peak-level signals. The overall output signal level of the equalizer is determined by the setting
of this control and the EQ sliders (#2).
7 - BALANCED INPUTS: The mixing board, amplifier or instrument (“source”) may be connected to the equalizer using
either of these jacks. However, only one jack may be used at a time. Different methods of connection are described and
illustrated on pages 9 and 10.
8 - BALANCED & UNBALANCED OUTPUTS: The equalizer may be connected to the mixing board or amplifier using
either of these jacks. The 1/4” phone jack and the XLR jack are balanced. The RCA jacks are unbalanced. Different methods of connection are described and illustrated on pages 9 and 10.
9 - GROUND LIFT: Use this switch to electronically disconnect the signal ground from the mains and chassis earth
ground. This may be helpful in eliminating ground loops which cause hum.
10 - VOLTAGE SELECTOR: The equalizer is designed to be used with either 95-130VAC or 190-250VAC power sources.
Check the AC line voltage of the outlet and set this switch accordingly before plugging in the unit.
11 - FUSE HOLDER: This contains the fuse for the AC mains. If the fuse blows, replace it with only the same size and
type. If the fuse blows repeatedly, check the AC line voltage and the equalizer’s voltage selector switch. If the problem
persists contact your Crate Pro Audio dealer.
12 - POWER CORD: Connect the power cord to a suitable source of AC line voltage. Be sure to match the voltage selector
switch (#10) to the line voltage before making this connection! In order to reduce the risk of shock, DO NOT defeat the ground pin
of the power cord!
IMPORTANT! PLEASE NOTE: The equalizers are equipped with a voltage selector switch (12 on
page 6, #10 on page 7). BEFORE PLUGGING THE EQUALIZERS INTO AN AC OUTLET, MAKE SURE
THE VOLTAGE SELECTOR SWITCH IS SET TO THE CORRECT RANGE FOR THE AC SOURCE!
Improper switch setting may harm the equalizer!
7
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
Using an Equalizer:
Mixing and equalizing music requires an experienced ear and knowledge of the different tonal characteristics of
each instrument. The voice characteristics of some common instruments are compared to a conventional 88-note
piano keyboard in figure 5 below. As indicated on the chart, the piano has the widest frequency range among the
instruments shown. This makes the comparison easier to understand. For instructional purposes, we will separate
the equalizer bands into six distinct ranges and briefly explain the tonal characteristics of each section.
Figure 5: Frequency Range Comparison Chart:
PICCOLO
FLUTE
OBOE
CLARINET (Bb)
BASSOON
TRUMPET
FRENCH HORN
TROMBONE
TUBA
TIMPANI
CYMBALS
VIOLIN
VIOLA
CELLO
BASS VIOLIN
SOPRANO
ALTO
TENOR
BASS
PIANO
27.50
30.87
32.70
36.71
41.20
43.65
49.00
55.00
61.71
65.41
73.42
82.41
87.31
98.00
110.00
123.47
130.81
146.83
164.81
174.61
196.00
220.00
246.94
261.63
293.66
329.63
349.23
392.00
440.00
493.88
523.25
587.33
659.26
698.46
783.99
880.00
987.77
1046.50
1174.66
1318.51
1396.91
1567.98
1760.00
1975.53
2093.00
2349.32
2637.02
2793.83
3135.96
3520.00
3951.07
4186.01
A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C
Bass Range: (20Hz-125Hz)
Unlike the other instruments shown, the piano contains some fundamental frequencies in the 20Hz-40Hz range . The 40Hz-120hz
range has a greater audible effect on “low bass”. The electric bass
guitar and the acoustic bass both have fundamentals in this region
(The “E” string on an electric bass is 41.2Hz). This region provides
much of the low end “punch” in bass instruments and drums.
Mid-Bass Range: (125Hz-250Hz)
The “fullness” of the mix will be determined in
this region, either adding a “thicker” or “fatter”
characteristic or making it “thin” or “weak”. The
guitar and bass both contain fundamentals in this
range along with the male or tenor voice. This
region also provides the apparent “loudness” of a
mix, especially around 160Hz.
Low-Mid Range: (125Hz-250Hz)
This range tends to add a harsh
“muddy” sound when boosted,
particularly around 300Hz.
This sliders in this region
should be adjusted to the
detent (flat) position or even
reduced slightly to produce a
more appealing tonal quality.
Mid-Range: (500Hz-4kHz)
This is the range at which the human ear is most sensitive. Very small
changes in this area can produce a dramatic effect. This region is most
commonly reduced in amplitude to produce a rich sound with more
emphasis on low bass and upper high end regions. When equalizing individual instruments in a mix, this range becomes very important to bring
them to the “front” of the mix, cutting through the rest of the instruments.
8
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
Upper-Mid Range: (4kHz-8kHz)
This region is the “presence” range which can determine
whether the mix or instrument is “harsh” and “piercing”
or “distant” and “muffled”. This range will also help
voices and other instruments cut through a mix when
boosted. When high frequency “feedback” occurs, this
region is one of the most critical in eliminating it.
High Range: (8kHz-20kHz)
High end, as it is usually perceived, is actually below 12kHz.
However, the 10kHz to 16kHz range is used to enhance vocals
and wind instruments by bringing out “breath” sounds that give
them distinction and clarity. Cymbals on drums can also be
made to appear more cutting and clear in this region. The range
of 16kHz to 20kHz can be used to compensate for off-axis high
frequency deficiencies of horns and tweeters.
APPLICATIONS:
SOME METHODS OF CONNECTION:
There are several different ways to connect an equalizer to a sound system. The equalizer may be connected
directly in-line with the signal source (see figure 6 below), to the “insert” jack of a mixer/amplifier’s channel section
(figure 7, below), or in-line between a mixer and an amplifier (figure 8, following page). Your dealer can assist you in
choosing the connection which is best suited for your particular needs.
Figure 6: In-Line with Signal Source:
SOURCE
MIXER (OR AMPLIFIER)
EQUALIZER
Source connects to
BALANCED INPUT
jack of equalizer
BALANCED OUTPUT
jack of equalizer
connects to INPUT
jack of mixer or
amplifier
Figure 7: Connect to an Insert Jack:
"Send" side of the signal cable
harness connects to the eq's
BALANCED INPUT jack
IN
"Insert" cable
harness,
connected to the
mixer/amplifier's
INSERT jack
(see detail to
the right)
EQUALIZER
OUT
"Return" side of the signal cable
harness connects to the eq's
BALANCED OUTPUT jack
TIP
"INSERT" CABLE DETAIL:
MIXER (OR AMPLIFIER)
TIP
TIP
TIP
RING
SLEEVE
SLEEVE
SLEEVE
RING
SLEEVE
Typical "Insert" cable harness
assembly. Stereo end of harness plugs
into INSERT jack. "Tip" of stereo end
carries signal to one of two mono plugs,
"ring" carries signal to other plug.
TIP
SLEEVE
SLEEVE
TIP
"Send" side of INSERT jack goes to eq's IN jack, "Return" side goes to eq's
OUT jack. This may vary from mixer to mixer; some experimentation may be
required to achieve the proper results.
9
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
APPLICATIONS:
SOME METHODS OF CONNECTION (Continued):
Figure 8: In-Line Between a Mixer and Amplifier:
MIXER
(OR PREAMP)
POWER AMPLIFIER
EQUALIZER
Output signal from
mixer/preamp
connects to
BALANCED INPUT
jack of equalizer
BALANCED OUTPUT
jack of equalizer
connects to INPUT
jack of power amplifier
SPEAKER OUTPUT
jack of power amplifier
connects to INPUT
jack of speaker
APPLICATIONS:
ROOM EQUALIZATION:
Any sound system, whether it is a home stereo, a large sound reinforcement system, or recording studio monitors, will vary in its perceived reproduction depending on its environment; its room. When sound is produced, some
frequencies are reflected and some are absorbed. This results in an uneven sound field. If speakers are placed in
room corners or against walls, a large increase in the lower frequencies will occur. Some speakers are designed to
use this increase to flatten their response. Other speakers, such as near field monitors and P.A. speakers, are designed
to be flat in a free air environment (that is, having no external boundaries). These speakers, when placed in the
wrong environment, will produce an increased low frequency response. An equalizer may be used to compensate
for this condition.
By using a spectrum analyzer or Real Time Analyzer (RTA) and any of the Crate Pro Audio Live Sound equalizers, a flat response can be obtained with precision and accuracy. This also may be achieved by ear, though not with
the same accuracy, by using a favorite recording with which you are familiar.
Another means of achieving a flat response with your system is called “Feedback Tuning” or “Ringing the
Room”. This method requires an omni-directional microphone with a very flat response to be placed in the listening
area and connected to your system in an unequalized channel of your mixer. With your graphic EQ set flat, slowly
turn the gain of your microphone up until a frequency starts to ring (WARNING! Be careful not the let this ring
excessively or speaker damage may occur.) Pull down on the EQ slider that makes the ringing stop. Pull only a few
dB, not all the way. Increase the system gain again, and another frequency will begin to feed back. Pull down on
the corresponding slider again. Repeat this procedure three or four times only. After that, go to the sliders you have
not yet moved and bring up their level until that frequency begins to feedback, then pull the slider down until the
feedback just stops. Continue this procedure with each slider. This method takes a lot of practice and patience but it
will adjust the response of your system to electronically compensate for the room. Additional equalization may be
required at this point; the next section will explain.
FLETCHER-MUNSON EQUAL LOUDNESS CONTOURS:
The human ear does not hear all frequencies equally. For example, the ear is less sensitive to bass notes at
lower levels than at higher levels. To compensate for this, additional equalization may be necessary to create a pleasing overall sound, even after a room has been EQ’d. A “preferred curve” is actually a series of boosting and cutting
at various frequencies, depending on the overall performance level, so the ear perceives all frequencies at the same
level. These curves are known as the Fletcher-Munson Equal Loudness Contours (see figure 9 on the following page).
Notice that the amount of boosting changes with overall listening levels, since the ear hears lower frequencies better
as the volume level increases.
After achieving an electronically flat response from your speakers in the room, use the Fletcher-Munson chart to
adjust the contour according to the sound pressure level of the performance. These curves are intended to be used as
guidelines only. Experimentation is always necessary to find your own “preferred” sound.
10
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
Figure 9: Fletcher-Munson Equal Loudness Contours:
140
LOUDNESS LEVEL IN PHONS
120
120
200
100
100
20
90
80
80
2.0
70
60
60
0.2
50
40
40
PRESSURE DYNES PER CM2
SOUND PRESSURE LEVEL IN dB
110
0.02
30
20
20
0.002
10
0
0
20
100
1000
FREQUENCY IN Hz
0.000
10,000
FEEDBACK CONTROL:
Feedback can be a major problem in live sound reproduction. Feedback occurs when an outgoing signal finds
its way back into the system via a microphone or a guitar pickup and gets re-amplified. The outgoing signal is the
transmitter and the microphone or pickup is the receiver. The best and most effective way to eliminate feedback is to
separate the transmitter from the receiver.
If this is not possible, then an equalizer with narrow bandwidth filters, such as the LS1-131 or LS3-231, is an
effective alternative. To find the frequency at which the feedback is occurring, simply select the frequency you feel is
the problem and move it to maximum “cut”. If the feedback doesn’t stop then return the control back to its original
position and adjust another frequency until the feedback stops. Once you have isolated the feedback frequency, then
move the control back towards its original position until the feedback occurs again then reduce the level down until
it just stops. This process allows you to eliminate feedback problems without sacrificing overall level or frequency
response.
CREATIVE OR ENHANCEMENT EQUALIZATION:
The graphic equalizer can also be a creative tool. The LS1-131, LS2-215 or LS3-231 may be used on individual
instruments, vocals, signal processors, and recording equipment to shape or mold them to the exact sound you
want. With vocals, the frequencies between 10kHz and 20kHz may be boosted to help separate syllables for greater
clarity and distinction. The vocal range is from about 150Hz up to 4kHz. When speech intelligibility is your main
concern, this frequency range is critical. Emphasis is typically greater around 4kHz, particularly in a highly reverberant environment.
Using your equalizer with a digital reverb gives you the ability to change the characteristics of the “room” or
“hall” you’ve selected, offering greater versatility.
Your equalizer can also be used to make a “de-esser”. A “de-esser” is what it sounds like, a clever way to control “S’s” in a speech or vocal performance. This will require a compressor with a trigger input. You must first split
your vocal source into two output signals. The first vocal signal is simply sent to the input of the compressor. The second vocal signal is sent to the input of your equalizer. The output of the equalizer is sent to the “trigger” input of your
compressor. The output of your compressor is sent back to a channel on your mixer. The de-esser is made by boosting the 6.3kHz control to the +12dB position and then adjusting the compressor threshold until the desired effect is
reached, that is, when an “S” is pronounced then the signal will be reduced. Some other adjustments can also be
made on your compressor with the “attack time”, “decay time” and the “compression ratio” to enhance the effect.
11
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
Technical Specifications
Filters
LS1-131: 1x31 Constant Q Multiple-feedback 1/3 octave ISO spacing from 20Hz to 20kHz
LS2-215: 2x15 Constant Q Multiple-feedback 1/3 octave ISO spacing from 20Hz to 20kHz
LS3-231: 2x31 Constant Q Multiple-feedback 1/3 octave ISO spacing from 25Hz to 16kHz
Center Frequencies, Hz (±3%)
LS1-131/LS2-231: 20, 25, 31.5, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500,
630, 800, 1k, 1.25k, 1.6k, 2k, 2.5k, 3.15k, 4k, 5k, 6.3k, 8k, 10k, 12.5k, 16k, 20k
LS2-215: 25, 40, 63, 100, 160, 250, 400, 630, 1k, 1.6k, 2.5k, 4k, 6.3k, 10k, 16k
Control Range
±6dB or ±12dB, switchable
Frequency Response
20Hz-20kHz ±0.5dB (flat settings)
Total Harmonic Distortion
Less than 0.01% (20Hz-40kHz +10dBu)
Signal to Noise Ratio
>94dB (20kHz noise bandwidth)
Gain (flat settings)
LS1-131/LS2-231: ±12dB
Maximum Input Level
+22dBm (Level control at center position)
LS3-231: -∞ to +12dB
Common Mode Rejection Ratio
50:1
Channel Separation
50dB (1kHz)
Low Cut Filter
10Hz-25Hz, 12dB/octave
High Cut Filter
3kHz-40kHz, 12dB/octave
Input Impedance
10k ohms
Output Impedance
2.2k ohms
Output Impedance
600 ohms
Bypass switch
“Hardwire” Input to Output
Power Requirements
95-130VAC, 50/60Hz
190-250VAC, 50Hz
Input AC Power
12W
Size (HxWxD)
LS1-131/LS2-215: 1.75” (4.5cm) x 19” (48.3cm) x 8.5” (21.6cm)
LS3-231: 3.50” (8.9 cm) x 19” (48.3cm) x 8.5” (21.6cm)
Weight
LS1-131/LS2-215: 4.5 lbs (2.5kg)
LS3-231: 9 lbs (4.1kg)
Due to ongoing product development and improvement, the specifications
contained herein are subject to change without notice.
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©1999 SLM Electronics, Inc. • A Division of St. Louis Music, Inc.
1400 Ferguson Avenue • St. Louis, MO 63133
47-056-01 • 05/99