Processing and Control for Professional AV Installations
Legacy Hardware

372 SPL Computer


The main reason to synchronize the sense events between units is to eliminate acoustic bleed-over between adjacent zones, and/or to eliminate problematic speaker line crosstalk while the sample is being taken.

Because the 372 SPL Computer uses the speakers of a sound system as sensing microphones, the sound?system is briefly disabled (~250 milliseconds) every time a reading is taken.

The 372 SPL Computer can be set to 1, 2, 4, or 8 and average together the number of samples to make a gain changes. After a calibration the sample buffer is cleared and set to the same relative level taken during the calibration. In other words if the 372 is set to 4 samples and calibrated at -30dB relative and during the first sample it reads -20dB it would average -20dB, -30dB, -30dB and -30dB to determine the gain change.

There are two separate AC supplies coming out of the PS-3: 8.5 VAC @ 1A and 34.5 VAC CT @ 250mA. Pinout is as follows: 8.5 VAC on pins 6 and 1, 17 VAC on pins 7 and 3, center tap @ pins 4 and 5 are connected to earth ground. This is when viewed at the end of the PS-3 7-pin DIN plug.

View Image

After a lightning strike, flood, nuclear blast, or other catastrophic disturbance, the 372 may become inoperative if the data stored in its EPROM memory has been corrupted. The 372 can be returned to its factory default state by performing a master reset. To do this:

1. Unplug AC power

2. Press and hold in the EXIT and CAL buttons.

3. Reconnect AC power.

4. Let go of the EXIT and CAL buttons.

Now the LCD screen will display “EEPROM defaults restored” followed by the software version number. After doing this, all previous setup and calibration data will have been lost and must be re-entered as if it were a brand-new installation.

When the 372 SPL Computer does a sense event it fades the audio down from its current gain setting to -80dB at X amount of time per dB, then opens a relay and takes a series of samples via the installed speaker(s). If multiple 372s/zones are synched together, the master unit first fades down it’s audio then activates its relay, simultaneously sending a trigger event signal via the EXT.RELAY pin to the slaved unit’s TRIGGER pin inputs, because the master first fades its audio then sends the trigger signal, the master and slave(s) are slightly out of sync. Furthermore, if the slaves are at different gain settings, the fade times may be far enough apart that the slaved relays operate at slightly different times. In other words, a 372 with it’s gain at +5dB will take longer to fade down the audio and open it’s relay than a unit set at 0dB.

This was corrected in version 2.09 of the firmware. To update the firmware to version, contact Symetrix Technical Support.

See if the AGC is active, this is applied independently of the SPL functions and will not show as a gain change.

No, the only option would be to use a 12VDC to 117VAC inverter with the supplied PS-3 inline power supply.

When controlling amplifiers larger than 200 watts (8-ohms), you must use an external DPDT relay. The 372 SPL Computer’s internal relay cannot handle more than 8-amps of load current. The recommended maximum amplifier wattages are as follows: 300 watts at 70V, 200 watts at 8-ohms, and 100 watts at 4-ohms. The 24-volt version of the Potter & Brumfield PRD11DGO works well. Its DPDT contacts are rated at 30 amps.