Subjective Method-tf
test instrumentation is not available,
proper results can be obtained based on program material
as follows:
1. Adjust volume level for comfortable listening and set
approximate system balance using pink noise or the noise
heard between stations of an FM tuner.
2. Listen to a recording of a male voice long enough to
become accustomed to the performance of the loud-
speaker system.
3. Reverse polarity of the high frequency loudspeaker, which
will produce a change in voice character.
When the transducers are properly phased, a recorded
male voice should sound natural and exhibit presence (or an
"up front" quality], as contrasted to an undesirable "hollow"
sound that can be heard when transducers are out of phase.
Note: If the crossover frequency lies above
2 kHz,
reversing polarity of the high frequency component will
create very little, if any, perceptible difference in system
performance. The "correct" polarity will be that which
yields the most natural quality with a variety of program
material.
Once proper phase a m o n g the transducers of a loud-
speaker system has been determined, other loudspeaker
systems in the installation [assuming they are the same) may
be phased accordingly. If different loudspeaker systems are
used, establish c o m m o n phase a m o n g the low frequency
drivers and follow the above procedures for each system.
Level Control Adjustment
In most instances, manufacturers of multi-amplified loud-
speaker systems provide instructions for balancing levels of
the individual drivers of the system. In the absence of formal
instructions, or in the case of custom loudspeaker systems,
balance can be established by adjusting levels to achieve
flattest response on a real time analyzer, as described in the
transducer phasing instructions beginning on the previous page,
or on the basis of subjective evaluation of familiar program
material (or, more accurately, by using pink noise or the noise
between FM stations] as described in the following paragraphs.
Each program channel should be adjusted individually;
subjective evaluation should be made while seated in the
normal listening location. If subjective analysis is to be used,
and the power amplifiers are equipped with level controls,
initially adjust the controls to one-half of their full rotation and
then regulate as necessary.
Subjective Adjustment Of Bi-Amplified Systems-Jhe
fol-
lowing applies to a 5233 or to each channel of a 5234 used in
dual channel bi-amplification
1. With the High Frequency Level control at " 0 " adjust
program source level for comfortable listening.
2. Rotate the network control clockwise until a satisfactory
high frequency balance has been obtained in the program
material. If necessary, trim source or amplifier levels.
Subjective Adjustment Of Tri-Amplified Systems—
When
both channels of a 5234 are used for a tri-amplified loud-
speaker system, it is generally installed so that the Channel 1
level control regulates the output of the midrange driver and
the Channel 2 level control governs the high frequency driver,
control governs only the high frequency driver.
1. With both High Frequency Level controls at "0',' adjust the
source level for comfortable listening.
2. Rotate the Channel 1 level control clockwise until a satis-
factory midrange level has been obtained in the program
material. If necessary, adjust source or amplifier levels
as appropriate.
3. Increase the Channel 2 level until a satisfactory high
frequency balance has been obtained. It may be necessary
to readjust midrange, source or amplifier levels to achieve
the most desirable overall balance of the loudspeaker
system.
Once high frequency and amplifier output levels have been
established, readjustment is not generally needed. Some
method of marking or locking the power amplifier level
controls is recommended.
A p p e n d i x
Blank Crossover Card Assembly
In addition to the standard crossover cards, circuits for other
crossover frequencies may be assembled on a blank cross-
over card (JBL Model 52-5120) using standard components.
Filter slopes (12 dB per octave) are identical to those of the
standard crossover cards. The circuits are designed to use
five identical resistors and five identical capacitors. The cross-
over frequency can be written on the card bracket and will
appear through the front panel window of the network.
6
