How Can I Suppress an Annoying PA System Annunciator Tone?

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Discussion Overview

The discussion revolves around finding a solution to suppress a loud audio annunciator tone from a public address system at work, while still allowing the message to be heard. Participants explore various technical approaches and potential modifications to the existing system.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests using a relay activated by rectifying the annunciator tone to block the signal temporarily, but notes difficulties in getting the relay to function properly.
  • Another participant proposes using a notch filter to attenuate the 950 Hz frequency, acknowledging that it may distort the voice but still allow for message recognition.
  • A different approach involves using a 567 tone decoder chip and a Picaxe chip to detect the tone and control a relay, with specific programming to manage timing and signal detection.
  • One participant raises a concern about the appropriateness of the beeper tone, suggesting it should only be used for emergencies and recommending communication with the audio paging system managers.
  • Several participants express a sense of familiarity with the topic, indicating it may have been discussed previously in the forum.

Areas of Agreement / Disagreement

There is no clear consensus among participants, as multiple competing views and approaches are presented. Some participants focus on technical solutions, while others emphasize the appropriateness of the annunciator's use.

Contextual Notes

Participants mention the need for careful detection of the tone to avoid interfering with actual speech, highlighting the complexity of the problem. There are also references to previous discussions on similar topics, suggesting ongoing interest and unresolved issues in this area.

Who May Find This Useful

Electricians, audio engineers, and individuals interested in public address systems or sound engineering may find the discussion relevant.

XYZ343631
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I am searching for an easy solution for an exasperating nuisance.

There is a public address system at work and before the start of the messaage a loud audio annunciator frequency has been added to warn people of the upcoming message and I want to locally supress it but still receive the message.

The speaker is located just above my shop and do not want to interfere with the global annunciator but only this one speaker.

I am an electrican who was trained in electronics decades ago and my idea is that when the annunciator tone is present, rectify it and pick up a relay that starts a delay on timer that blocks the signal until timing is completed.

The annunciator tone is app. 900HZ to 1000HZ and centered around 950HZ as measured with an o'scope. The annunciator tone lasts for one second and is very disturbing and want to cancel it during that time and then have the timer close the circuit again to hear the message. That is it in a nut shell.

I tried using a standard bridge rectifer powering a 5V relay but the relay would not pick up and if I can pick up the relay then the local problem will be solved.

Please give me advice on how to accomplish my goal which will make all of the electricans happy in the electrical shop. Thanks for any and all responses.
 
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Would it be easier to just put a notch filter inline that attenuated 950Hz, wouldn't have to be very narrow so not hard to design.
It would distort the voice a bit but should still be recognizable

The trouble with detecting the tone and turning it off is that unless you do some clever analysis of rise time etc, just detecting the frequency would mean you would also turn off the speaker when the person talking happened to hit that note.

- pf readers are all over the world in different time zones, but mostly in USA/Europe - so depending when you post you might have to wait 8-12 hours for anyone to see it.
 
XYZ343631 said:
I am searching for an easy solution for an exasperating nuisance.

There is a public address system at work and before the start of the messaage a loud audio annunciator frequency has been added to warn people of the upcoming message and I want to locally supress it but still receive the message.

The speaker is located just above my shop and do not want to interfere with the global annunciator but only this one speaker.

I am an electrican who was trained in electronics decades ago and my idea is that when the annunciator tone is present, rectify it and pick up a relay that starts a delay on timer that blocks the signal until timing is completed.

The annunciator tone is app. 900HZ to 1000HZ and centered around 950HZ as measured with an o'scope. The annunciator tone lasts for one second and is very disturbing and want to cancel it during that time and then have the timer close the circuit again to hear the message. That is it in a nut shell.

I tried using a standard bridge rectifer powering a 5V relay but the relay would not pick up and if I can pick up the relay then the local problem will be solved.

Please give me advice on how to accomplish my goal which will make all of the electricans happy in the electrical shop. Thanks for any and all responses.

The beeper tone should only be used in case of emergencies. Have you tried talking to the folks that manage the audio paging system? You should be able to make a case for only using the beeper for emergency messages. That's how many paging systems are run.
 
You could connect the speaker so that it only gets sound if a relay is pulled in.

Then you would need the following:
a source of regulated 5 volts.
a 567 chip
a Picaxe 8M chip
a transistor to pull the relay in.

Run the speaker input line to the 567 tone decoder chip.
This will make its output go low when the input tone matches the 950 Hz expected.

Take this to the Picaxe chip.
Program this to look for this low input on one of its pins.
Look again each 50 mS to see if it is still there.
When it isn't there any more, pull in the relay via the transistor.

Estimate the longest time anyone would talk on the PA and double it.
Leave the relay pulled in for that amount of time. (Easier than trying to detect speech on the line.)

Disconnect the relay.

If the 567 detects another message starting while the relay is still pulled in, the Picaxe can disconnect the relay while the tone is present. However, you may hear the beginning of the tone if this happened because the Picaxe would have to allow a period of 50 mS to be sure the tone was a sustained tone and not an accidental 950 Hz in someone's voice.
 
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