Preprint
DesigncontrolI.

of a high powerroom
monitorMartikainen,

Genelec
lisalmi,A.

Varla,

2755 (J-2)

activeT.

Partanen

Oy
FinlandPresented at
the 86th Convention
1989 March 7-10
Hamburg

Au DIOThis preprint has been reproduced from the author's advance
manuscript, without editing, corrections or consideration by
they Review Board. The AES takes no responsibility for thecontents.
Additional preprints may be obtained by sending request
and remittance to the Audio Engineering Society, 60 East
42nd Street, New York, New York 10165, USA.
All rights reserved. Reproduction of this preprint, or any
portion thereof, is not permitted without direct permission
from the Journal of the Audio Engineering Society.

AN AUDIO ENGINEERING

SOCIETY PREPRINTDESIGN OF A HIGH POWER ACTIVE CONTROL ROOM MONITOR

I. Martikainen,
A, Varla,T.Partanen
GenelecOy
Tehtaantie
1774100lisalmi
FINLAND

Abstract

This report describes the design of an active control room monitor for SPLs
in excess of 130 dB(lin). To ensure good sound quality a new direct radiating
midrange system was developed with an acoustic loading technique whichallows 103 dB/W sensitivity and 1 kW peak power handling. Power amplifiersand driver unit protection logic are also presented.

1. INTRODUCTION

Traditionally large control room monitors have been designed around twolarge woofers and a horn-loaded mid/treble unit. The main problems in hornloaded systems are distortion due to air nonlinearity in the throat,
problematic
reproductionof lower midrange and rapid changes of directivity.
Direct radiating drivers are today preferred due to sound quality reasons.
Several designs known as "soft dome monitors" have recently emerged
towards more accurate reproduction. However, they suffer from output
power limitations or reliability problems at levels commonly used in rockstudios. Aisc they are omnidirectional
at Iow midrange and thus prone toresponse aberrations due to control room.
It would be useful to find a solution which could combine the direct-radiating
driver sound quality and mild but constant directivity. This would yield in flat
frequency response, flat power response and thus better immunity to listening environment
inconsistencies.
High amplifier powers are, however, needed
and thus certain protective features are necessary in system electronics toensure safe operation.
-1-2. PRACTICAL DESIGN REQUIREMENTS
2.1. Monitoring environment
Thevolume of a typical large control room is around 200 m3. Reverberation
time dependson designerbut in most cases0.2 s is a typical value in themidband and 0.4 s around 80 Hz.At lowestoctaves separate standingwave
modes dominateand it is better to look how the modes decay.Typical decay
times are 0.4to 0.6 s. Reverberationradiusis 1...2 m which means that thelistening position is always in reverberant field. This fact has led thedesignersto look more closelythe sound field build-up in time domain to
keep early reflectionsaway from the listener'sears.
The monitoring speakers should be (and they usually are) flush mounted into
an acousticallyhard wall. The radiation space is thus always 27r or smaller,
depending of frequency.At lowestfrequenciesthe speaker is radiatingto 7r
or even _r/2space which has beneficialeffect on sound power output due toincreased radiationresistance,but tends to spoil the frequencyresponse if
not corrected.
Ballagh [1] has described the boundary effects in speaker
power output; well known is also Allison'swork on the subject [2]. Whencorrectly appliedthis can be used to relaxthe woofer displacement
requirementsat extremelyIow frequencies.
Table 2-1 below showsthe requiredvolume displacementin litres forconstant 130 dB SPL at 2 m reverberation radius and the speaker radiating
in _r space.

f/Hz

Vdpeak/I for 130 dB

V d,P_eak/I, from 4 x 385 mm

30

9,3

16,1

40

5,2

4,9

50

3,3

3,6

60

2,3

3,3

100

0,84

2,8

at 2 m reverberation
radius into 7rspace

Table 2-1 Volume Displacement-2-drivers in 4 x 200 I
fb=28 HZcabinet, _+9 mm
excursion

2.2 Sound pressure level
In most industrialized countries the noise levels in work have been limited toaround 85 dB(A) for an 8 hour noise exposure time to reduce risks ofhearing damages. Some broadcasting companies have tried to recommend
the same in control rooms [3]. However, the levels found around themusicians in an orchestra can exceed 120 dB(A) for symphonic music. In
rock music the levels are still higher and at 2 meters from a drum set levelsof 115 dB(fast), 118 dB(imp) and 129 dB(peak) have been recorded. At thedrummer's position the corresponding levels are 123 dB(fast), 128 dB(imp)and 139 dB(peak). High listening levels are thus occasionally necessaryduring track laying and specially when the musicians want to listen theirrecorded performance. Thus the short term SPL design target for themonitoring system shall be 130 dB(lin) at lm in 2_r space. Peak values withwideband program material will then be around 136 dB.

2.3. Frequency

response

As mentioned earlier, systems of this category are flush mounted. More
important than free field frequency response is then the performance in theroom. For design purposes the frequency response requirements were set to
30 Hz...20 kHz +/- 2 dB in 2_rfield, in control room the f3 will then be around
25 Hz.

2.4. Distortionand coloration

Again some broadcasting companies have tried to specify the loudspeakerdistortion performance [4]. For music recording industry no suchspecification is known to the authors. In [5] the frequency response wasfound to be the most significant single factor affecting the perceived soundquality. However, the frequency response can be flat and still the systemsuffers from severe colorations, for example in a form of delayedresonances. The Hi-Fi industry has been active in minimizing different forms
colorations although exact definitions, audible limits and measuring methods
are missing. It should therefore be natural that monitoring speakers which
are used to control recordings, which will later be listened with very gooddomestic speakers, should, at comparable level, be better in any respect
than the end user's system.

-3-3. LOUDSPEAKERDESIGN
The acousticaldesign was made usinga three way system principle.The
cabinet was designedprimarilyfor flush mounting although a free standing
situationshall also be possible.

3.1 Low frequency reproduction
To reachthe target SPL figures both sensitivityand utilizationof the available
displacementcapacity shallbe maximized.In these terms the basic B6alignmentis very good. One advantageis the 2nd order term which isusually made electricallyand is thus easy to make variable.
In this case f3was set to 28 Hz. Withthe variable2nd order term the cutoff
can be raisedto 40 Hz to compensate LF boost which is often present incontrol rooms.
The VDrequirementsof table 2-1 can be met best with multipledrivers.Two
385 mm driverswere chosen with VDof 0.8 I each. Anothercriteria for thischoice is limitedenclosurefront panel area and necessaryperformanceat
crossover frequency.With larger cone diametersreproduction of 400 Hz may
be problematic.
The Iow frequencyenclosureconsists of two 200 1vented and mutually
isolated cabinets, Tuningfrequencyis 28 Hz and sensitivity98 dB/W.
3.2 Mid and high frequency

systemHigh frequency driver
Directradiatinghigh frequencydome drivers normally offer a sensitivity
90...95 dB/W at lm. Maximumlong term power input is, due to the small
motor system,limited to 10...20W. The maximumlong term acoustical
output is thus 100._108dB at 1 m distance. 1 kW amplifierpower would
result in short term RMSoutput of 120...125dB, providedthat no power
compressionoccurs. 130 dB short term output would thus require an
amplifierpower of at least3 kW.
Large ribbon-typedrivers are also availableand their sensitivityand power
handling are better than dome tweeters.However,due to their large
dimensionstheir radiation patternis very narrowat high frequencies.
Using a compressiondriverwith 25 mm throat and only moderate horn
loading a sensitivityof approximately105 dB/W is available(seefig. 3.1)
from 1,5 to 8,5 kHz above which the responsetilts smoothly down to 101
dB/W at 15 kHz. Using a 300 W amplifierand a long term power limitationto-4-12 W RMS short and long term outputs of 130 dB and 116 dB are obtained,
respectively. The higher sensitivity is, of course, the benefit of compression
drivers as well as good control of the radiation pattern. The penalty is higher
distortion and to minimize that penalty, crossover frequency should be high.
Mldrange driver
Midrange drivers currently found in large monitoring systems fall into thefollowing categories:
a compression driver in a two-way system with crossover
frequency at 450 Hz...1.5 kHz.
a 200 mm...315 mm cone driver in a 3- or 4-way system withcrossover frequencies at 150 Hz...300 Hz and 800 Hz...2 kHz.
Above this a compression driver or a direct radiator is used.
a 75 mm...100 mm soft dome unit covering the range from 250
Hz...500 Hz to 2.5 kHz...3.5 kHz.
two 100 mm direct radiating soft cone drivers covering thefrequency range from 200 Hz...400 Hz to 2.5 kHz...3 kHz.
Since a compression driver was selected for high frequencies, the upper
cutoff frequency was to be kept high enough to avoid 2nd order harmonic
distortion occurring at midband. The upper crossover frequency was
selected to 3.5 kHz and thus the midrange driver passband will be 400 Hz ...
3.5 kHz. Conventional 200 mm ... 315 mm midrange drivers (developed fromwoofers), although showing an acceptable sensitivity of 98...102 dB/W and acontinuous power handling of 75..150 W, cannot cope with the highcrossover frequency without considerable colouration and non-uniform
directivity because of their large cone diameter. Soft dome and small
diameter cone units offer better freedom from colouration but their sensitivity
is at maximum 90...94 dB/W and continuous power handling 50...120 W.
See the comparison in table 3-1.
Since the only driver type capable of producing the required SPL falls shortin bandwidth, and the driver with sufficient bandwidth cannot handle thepower, a new type of cone midrange had to be developed.
Small diaphgram is necessary to avoid breakups at passband and nonuniform directivity at higher frequencies. Because of high SPL, the moving
system must also be able to handle acceleration forces up to 200 N without
mechanical breakdown. High temperature voice coil materials are needed toallow sufficient power handling. Lightweight motor and diaphragm arenecessary for maximum sensitivity and for reduced need of mechanicaldamping for breakup modes.

-5-Driver

200 mm cone
midrange driver

315 mm cone
midrange driver

3" soft dome

Pe

100 W

150 W

120 W

Sensitivity

97 dB/W

100 dB/W

92 dB/W

Maximum
continuous
SPL

117 dB

121 dB

113 dB

Voice coilvolume500 mm3

750 mm3

260 mm3

Voice coilthermal time
constant

5s

6s

5 s

Amplifierpower for130 dB
short term
output2.0 kW

1.0 kW

6.3 kW

Usablebandwidth

200...1 kHz

150...600 Hz

450...3,5 kHz

Table 3-1 Midrange Driver Comparison 1

A smaller diameter voice coil offers better high frequency behaviour and, due
to less thermal expansion, can work with tighter air gap tolerances thanlarger diameter coils with equivalent conductor volume. Thus the heat
conductivity can be kept high [6]. In fact, the short peak power input islimited by the coil mass, not the diameter. The extreme input limit is thefusing current of the wire.
The designed driver is a 130 mm cone transducer operating in a 0,40 I
sealed enclosure which forms the unit's chassis (see fig 3.2). The chassis
works also as an effective heat conductor for the voice coil power
dissipation. The laminated hard Kevlar cone is integrated with a self centeringand field replaceable assembly. The one-layer voice coil diameter is 40 mm
and it is wound from aluminium ribbon wire on a Kapton former andsupported by a lightweight and stiff spider. A center phase plug is used. The
other data is shown in table 3-2.
-6-

Nominal diameter
Effective piston diameter
Voice coil diameter
Airgapheight
Voice coil length
Voicecoil volume
Voice coil resistance
Voice coil thermal resistance
Maximum voice coil temperature
Maximum short term temperature
Thermal time constantPe
Program power handling
Fluxdensity
Resonance frequency
Qt
Sensitivity
Usable bandwidth
Nominal impedance

130 mm
105 mm
40 mm
6 mm
7 mm
280 mm3
5,7 ohm
3°K_W
250v0
350°C
5,5 s
70 W
1000 W
1,5T
370 Hz0.64
99 dB/W @ 1 m
370...4,5 kHz
8 ohm

Table 3-2 Midrange Driver Data

Two midrange drivers were connected in parallel in close vertical array toobtain the desired sensitivity and power handling and to increase the verticaldirectivity for less floor and mixing console reflections.

Directivity

Control Waveguide

Direct radiators have their directional characteristics mainl7 dependent on
their physical size, or when using parallel drivers, the distance of theradiators relative to wavelength. When two 385 mm drivers are crossed overto two 120 mm midrange drivers at 400 Hz, system's power response will
have a peak above the crossover point because of the lower directivity of thesmaller drivers. In order to increase the directivity of the midrange system
under 1 kHz a special large area curved plate (Directivity Control Waveguide)
was constructed to the front of the drivers. It has also a moderate loading
effect under 1 kHz increasing the sensitivity up to 3 dB at the range 350._800
Hz (see fig. 3.3). The midrange average sensitivity becomes thus 103 dB/W
and the total Pe is 140 W. The comparison to a 315 mm cone midrange
driver and a 75 mm soft dome is shown in table 3-3 in the next page.
The Directivity Control Waveguide was made from die-cast aluminium alloy. It
works also as a large heat sink for the midrange and tweeter drivers. The
short and rapid flare-rate tweeter horn was integrated into the plate allowing
the closest possible driver placement. The DCW plate dimensions are 645 x
645 mm, which allows it to be rotated in either horizontal or vertical position-7-

(see fig. 3.4). Ribs were included in the casting to prevent vibration andextra damping was laid on the inner edges to terminate higher orderresonances.

Driver2 x 120mm
development
units on the
DCW-plate

315mm cone
midrange driver

75 mmsoft
dome

Pe

140W

150W

120
W

Thermal time
constant

5,5s

6s

5s

Sensitivity

103 dB/W

100 dB/W

92 dB/W

Maximum
continuous
SPL

124dB

121dB

113dB

Maximum
displacement
volume_+17 cm3+ 100 cm3

+ 9 cm3

Amplifierpower for130 dB
short term
output

500W

1.0kW

6,3kW

Usablebandwidth

370...4,5 kHz

150...600 Hz

450...3,5 kHz

Table 3-3 Midrange Driver Comparison 2
Distortion
The following distortion figures were measured for the midrange system at
110 dB continuous SPL at 1 m distance:

f/Hz

d2/%

da/%

500
1k
2k
4k

0,2
0,25
0,3
0,4

< 0,1
< 0,1
< 0,1
< 0,1

Table 3-4 Distortion Figures-8-

3.3 Loudspeaker enclosure
The enclosurefront panel dimensionsare 1105x 820 mm. Wallsare made ofa two layer materiallaminatedwith a vibrationabsorbing compound. Internal
bracing is used and the front platerigidity is assisted by the internal
partitioningwall betweenthe two isolated bass enclosures.The DCW-plateis
acousticallyisolatedfrom the bass section. A display panel with overloadandfailure indicatorsis includedin the DCW-plate.
4.

ELECTRICAL DESIGN

4.1

Block Diagram

A simplified block diagramof the system designedis shown in Fig 4.1. The
circuitry is dividedto threefunctionallydifferentsections,which are: Audio
ProcessingUnit (APU),PowerAmplifiersand Speaker Enclosure.The APU isfurther split to CrossoverSection and Control Section.
The input signal is taken via activebalancedamplifier,attenuatorand a buffer
amplifier to the active crossoverfilter. The signalis divided in the filter into
the bass, midrangeand treble channels and finally amplified with separate
power amplifiers.
The loudspeakerdriver units are protectedagainst excessive power
levels by a special Driver Unit ProtectionProcessor (DPP)located in thecontrol section of the APU-unit.This protectioncimuit also takes care of theprotection of the loudspeakerdrivers against a power amplifierfailure.
4.2

Crossover Network

The crossover section of the APUconsists of a balancedinput amplifier andthree parallel band pass filters. The input sensitivityof the whole amplifiercan
be varied 20 dB with input attenuatorswitch and input sensitivitycontrol. The
acoustic response in the control room can to a certain extent bebalanced with five tone control switches:TREBLE-LEVEL,MIDDLE-LEVEL,BASS-LEVEL(1 dB/step), and BASS-TILTand
BASS-ROLL-OFF(2 dB/step). Fig. 4.2 shows the effect of the control
switchesto the speakerfree field response.

-9-Crossover filters are aligned for equal acoustical phase and delay over the
crossover region taking into account the drive elements' own transfer
functions including phase and group delay responses. This ensures theacoustical axis to remain constant regardless of frequency.

4.3

Protection Circuits

The Control Logic section of the APU-unit contains several protection andsafety functions for the amplifier and the driver units. The self
diagnostics/starting sequencer controls the operating status of the entire
system during the start-up as well as during normal operation. The systemstatus is displayed on APU front panel. For the operator, the summary of thereal time status display of the APU is monitored with the loudspeakerenclosure status display.
The Driver Unit Protection Processor (DPP) monitors continuously the safe
operation area of the tweeter and midrange drivers. As stated in section 3.
the design values for the long term and short term power limits of the treble
driver are 12 W and 300 W. The thermal time constant of the treble driver is
2 s. The corresponding values for the midrange are 100 W (long term) and
600 W (short term), and thermal time constant is 5.5 s. The system tracks
the voice coil temperature from the present signal and its previous history.
If safe limits are exceeded, the DPP gives a warning to the user. If theoverload continues, the gain of the whole channel is reduced to safe level
and a red warning light is flashed on the status panels of the APU-unit andthe speaker enclosure. The essential factor in overload is total energy andthe system should react correctly to signals having different duty cycles.
Figure 4.3 shows the maximum continuous power supplied to the midrange
and tweeter drivers while varying the burst ratio of the overloading signal
from 5 to 100 %.
The control logic of the APU also senses the temperature of the power
amplifier modules and the DC-voltage at their outputs. All driver units
including the speaker interconnection cable are tested when the system isswitched on and the user is alerted if any fault is detected. The muting
operation in the starting sequence eliminates all undesired tone bursts in the
speaker during power-on/power off conditions.

-10-

4.4

Power Amplifiers

Use of separate amplifiersfor eachfrequency band will give benefitsfor
examplein terms of output current requirements[7],[8], equalization,
widebandoutput leveland driver unit damping [9]. Calculatingfrom theachievedsensitivityfigures the necessaryamplifier powers are 2000 W for
bass, 500 W for midrangeand 300 W for treble. The bass sectionis
naturallywise to divideinto two 1000W channels.
The power amplifiersystem hasthree identicalmodules,each consisting of
two separate amplifiers.Two modules are used in bridged modefor bass
channels and the output power is 2x1000W. One module is used for mid
and treble channels in single ended configuration.The modules areconnectedto the system back wiring board through 30 pin connectors at
the rear of each module.
The power amplifiermodule can be divided into three functionallydifferent
parts: Driverstage, Powerstage and Powersupply.The input and voltage
amplificationstagesof each power amplifierchannelare located on two
separate plug-in circuit boards. These boards are made using surfacemounttechnology (SMT)and they are fully discretedesign without operational
amplifiers.The completeboard can easily be changed if any serviceis
needed.
For high output current capacitythe power circuitfor each moduleconsistsof 12 pcs of 200W/17A 35 MHzfast powertransistors and of 8 drivertransistors.The power supply capacitorsize for each moduleis 60000 uF
and the DC-currentfrom the capacitors is suppliedto the power transistors
through 10X40mm2 aluminiumbarswhich also act as mounting site for thetransistors.The voltage amplificationstages are poweredfrom separate
regulatedpower supplies.All componentsare visible after withdrawingthe
power module from the rack frame.
The main power supply consistsof 3.5 kVA continuous duty shieldedtoroidaltransformerwith separatewindings for each power amplifiermodule. A
special delayingcircuit driven by APU control logic is used for suppressinga
huge starting current of the transformer.The power transformer has a built inthermal switch which is sensed by the APU control logic. A thermal-magnetic
circuit breakerwith its handleon the front panel functions as ON/OFF
switch and also acts as power mains protector,

-11 -

4.5

Mechanics

For the mechanics the key parameters for design were ease of maintenanceand general rigidity because of heavy mass of some components. For
example the 3.5 kVA power transformer only weights 30 kg. The amplifier isbuilt into a 19" welded iron rack frame. The power amplifier modules and the
APU module are plug-in units, and can be removed by only removing twoscrews and pulling the module out of the rack. The power amplifierelectronics is integrated together with a massive aluminium heat sink which
also acts as the module frame. Four Iow noise fans are used for cooling theamplifier.
5. PERFORMANCE
5.1 Frequency

response

Free field frequency response is shown in fig. 5.1. Active equalisation allows
the Iow frequency response to be set for flat free field or flat half space
responses with the aid of the bass tilt adjustment. Overall passband
tolerance of +/- 2 dB from 29 Hz to 17 kHz is achieved. Frequency
response in a control room is shown in figure 5.3. Measuring distance was
3.2 meters (engineer's chair) and 1/3 octave warble signal was used.
5.2 Directivity
Curves in figure 5.2 show the frequency response of the system in different
horizontal angles. The advantage of the DCW-plate can be seen at the rangeof 200...2 kHz where the directivity is very uniform and free from cabinetedge diffraction.
5.3 Maximum

soundpressurelevel

Peak level of 136 dB per pair was recorded in control room conditions at 2.2
m from the speakers. Material was Madonna: True blue, track 1. The
following SPL readings were obtained in free field conditions at 1 meter:

IEC weighted
pink noise

123 dB continuous RMS, 135 dB peak

IEC weighted
pink noise bursted

138 dB peaksine burst
f=500 Hz135 dB peak

Table 5-1 SPL readings- 12 -

5.4 Thermal compression
The following measurementswere madewith continuoussinusoidal signal.
The drive elementshad sufficienttime to reach stable voice coiltemperature. Measuringdistancewas 1 m in free field.

SPLtheoretical/dB

SPL out/dB Compression/dB

f= 100 Hz

100,0
105,0
110,0
115,0
120,0
125,0

100,0
105,0
109,9
114,5
119,0
121,5

0,0
0,0
0,1
0,5
1,0
3,5

f=l kHz

100,0
105,0
110,0
115,0
120,0

100,0
105,0
109,6
114,0
116,8

0,0
0,0
0,4
1,0
3,2

f= 10 kHz

100,0
105,0
110,0

100,0
104,9
109,5

0,0
0,1
0,5

Table 5-2 ThermalCompression

6. CONCLUSION
A high power activecontrol room monitor was designed.The key fornecessarySPLsand Iow coloration was a new midrangedriver and its
loading. On amplifier sidethe most importantdevelopmentwas the driverunit protection logic, becausepowerful amplifierscan also easily destroythe
drivers, In additionto sound engineersthe systemhas satisfied in listening
tests also discerninghifi listeners.

-13-

References[1]

K.O.Ballagh, "Optimum Loudspeaker Placement Near Reflecting
Planes", J.Audio Eng.Soc., vol. 31, pp. 931-935 (1983 Dec)

[2]

R.F.Allison,"The Influence of Room Boundaries on Loudspeaker Power
Output," J.Audio Eng.Soc., vol. 22, pp. 314-320 (1974 June)[3]

N12-A, "Listening Conditions in Sound Control Rooms", Technical
Recommendation from Danmarks Radio, Norsk Rikskringkasting,Rikisutvarpid, Sveriges Radio, Yleisradio, 1986.

[4]

N12-B, "Studio Monitor Loudspeakers", Technical Recommendationfrom Danmarks Radio, Norsk Rikskringkasting, Rikisutvarpid, Sveriges
Radio, Yleisradio, 1986.

[5]

Toole, F. "Loudspeaker Measurements and Their Relationship to
Listener Preferences: Part 2", J.Audio Eng. Soc., Vol 34, No 5, pp. 323348 (1986 May)

[6]

Henricksen, C.A., "Heat Transfer Mechanisms in Loudspeakers:
Analysis, Measurement, and Design", J.Audio Eng.Soc.,Vol.35, No 10(1987 October)[7]

Martikainen I.,Varla A., "About Loudspeaker system Impedance withTransient Drive", AES Preprint 1886.

[8]

Otala M., Huttunen P.,"Peak Current Requirement of Commercial
Loudspeaker Systems", J.Audio Eng. Soc., Vol. 35, pp.455-462, (1987
June).

[9]

Martikainen I., "Monitoring Speakers: Active or Passive?", StudioSound, April 1983, p.82.

-14-

,_,,,,,_,",'' ' i i_fi_ 'i'ii i'iilT'ii' rrT_-- '........_

i0 Hz =0

_

_

,,

5o0

HII
1

kH

2

Figure 3,1 Sensltivl_of the HighFrequencyDriver

Figure 3.2 MldrangeDriverMountedon DCWPlate

-15-

5

I

I

!_

,_-f--H,-_-1___-__:_',,_'
10_0

40 O ^ B c L

10

Hz

20

60

I_

200

50O

1

kHz

2

6

10

-

Figure 3.3 Sensitivityof the MldrangeDriverIn the Wavegulde

Vertical Mounting® 0

Q
Horizontal Mounting

Figure3.4 HorizontalandVerticalMounting

-16-

®

40 D

A B C

Lin.

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Figure- 17 -

1

30

50

30

Effectof BASSRO LL-OFF SWITCH,
approx. 2 dB/step at 30 Hz

50

300

Effectof BASS-TILT SWITCH
approx. 2 dB/step at 50 Hz

7
I

500

-6

OdB

1

3k

,500

Effectof BASSand TREBLE
LEVELCONTROLS, 1dB/stepat 100 Hz and 10 kHz

3k

Effect of MIDRANGELEVELCONTROL, 1 dB/step at 1 kHz

Figure 4.2 Effect of the Tone Control Switches

U/RMS
2O

P/W(8 OHM)
5O

19
18
17

'_

45
4O
36
32
28

M-channel
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16
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14
13
12
11
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24
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9
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-_

18
15
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T-channel_,,,,...._

3

5

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B

7

I

7

9

11

13

15

Figure 4.3 Maximum Continuous Power vs. Signal Burst Ratio

-18-

17

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Zero

Figure5.2 FrequencyResponsein DifferentHorizontalAngles-19-

1 5{_Hz2

5

10 (1512/2112)
20

i-_-/:i_,_d__r_._-4_4__,_--_a_,,_- ,- ....

I'__-.-._,_-T_"-_--

Figure 5.3 FrequencyResponseIn ControlRoom- 20 -