OPERATOR'S MANUAL
Four Channel Microphone Multiplexer
Model MX4
A multiplexer is a device that allows a single channel Real Time Analyzer to average information from up
to four microphone positions in a single test. When this information is processed by an analyzer that has
“time averaging”, the resulting curve is called “spatially averaged”. Spatial averaging is recommended by
all of the major film cinema/home theater organizations, including LucasFilm, and Dolby Laboratories.
The advantage of multiplexing is that the resulting curve on the real time analyzer reflects the overall
response of the room across the entire seating area, rather than only the acoustics of a single point in the
room. The multiplexer itself is essentially a small 4x1 mixing board combined with a switching network
that automatically samples information from each of the microphones for a specified amount of time.
The MX4 can be used with all Gold Line 1/3 octave Real Time Analyzers and with most other popular
models. If using an analyzer other than a Gold Line, make sure that your RTA has a balanced XLR
microphone input. We do not recommend using the MX4 with older analyzers that do not have Time
Averaging. Minimum time average for the test should be 20 seconds, and for greatest accuracy we
recommend 60 seconds. If used on an RTA that does not have time averaging, slow mode should be used.
The MX4 allows the user to enable single channels or any combination of channels, allowing for
comparison of individual microphone locations versus the spatially averaged data from multiple
microphone tests.
Each of the four channels has a gain control to allow the user to match the input level from different
locations. The MX4 can be provided with three or four model TEF04 reference microphones. If you have a
DSP30, use your RTA microphone as the fourth microphone. Additional microphones are available from
Gold Line.
Recommended Test Procedures:
Before beginning the test you must match the sound pressure level for each of the microphones. This is
required because SPL decreases with distance, and typically measurements should provide an even sample
from each microphone. Accordingly, the microphones closest to the speaker are cut in level by the MX4 to
match the level of microphones that are further from the speakers. All microphones being used for the test
should be identical, and must be appropriate for the RTA being used.
1. Plug the battery eliminator supplied with the MX4 into the unit.
2. Plug up to four microphones into the rear panel of the MX4 via standard microphone cables. Place the
channel 1 microphone in the left rear of the seating area (furthest from the speaker being tested), at ear
level, pointing towards the ceiling, preferably in a microphone stand. Place the channel 2 microphone in the
right of the seating area. Place the channel 3 microphone in the left front of the seating area, and the
channel 4 microphone in the right front of the seating area. In larger areas, more than 6 seats, you may
wish to move all microphones in approximately ¼ of the length of the seating area.
3. Plug the output XLR cable on the front of the MX4 into the microphone input on your real time
analyzer.
4. The white on/off button for channel 1 should be set to the in/on position, and the white on/off buttons
for channels 2,3,4 should be set to the out/off position.
5. Turn the gain control for channel 1 of the MX4 to the straight up middle position on the control. In this
position the MX4 should not provide significant boost or cut.
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