EST3-Microphone - Remote Microphone Feedback

[Leo]

EST3 - Remote Microphone Feedback
Introduction
Recently, we have received reports from a small number of sites that announcements made using 3-REMICA and 3-REMICP remote microphones are experiencing feedback generated through the fire alarm speakers. This technical bulletin is to inform you of the issue and how to resolve it.

Issue
Typically, this feedback issue is caused from improperly balanced amplifiers and low-level recorded messages. While most of the customers reporting the issue are using 70 V audio systems, 25 V audio systems may also experience this condition.

Solution
To prevent feedback in your audio system, we recommend the following:

1. Make sure your amplifiers are properly balanced. Use the attached WAV file to adjust each amplifier’s output to the correct level (25 VRMS or 75 VRMS depending on the amplifier). Measure the output levels using a true RMS voltmeter or an oscilloscope at the amplifier’s output terminals with the speaker circuit connected.

2. Once you have balanced your amplifiers do not adjust the gain to compensate for low-level recorded messages. Instead, use a third-party WAV editor to adjust the level of your recordings before you import them into the 3-ASU. Adjust your recorded messages to the same level as the 1 kHz signal above then import, compile, convert and download to all CPUs and the ASU.

3. If possible, do not install speakers near a paging microphone. If a speaker is
installed near a paging microphone, configure the speaker using the lowest output power setting. FNN 08043 • ISS 24NOV08 Page 2 of 2 Please note that you may follow the recommendations listed above and still experience feedback in the audio system. We have sent this issue to our engineering group for further investigation. If their investigation results in a change to our product we will let you know in a future technical bulletin.