omsi@reed.UUCP (OMSI) (05/25/87)
I have an application where it would be useful to boost the volume through a speaker based on the level of background noise in the area. The obvious problem is how to cancel the sound from the speaker so the noise level can be measured. Any ideas? Thanx, Bob Ankeney tektronix!reed!omsi
cslug2@dalcsug.UUCP (05/29/87)
In article <6412@reed.UUCP>, omsi@reed.UUCP (OMSI) writes: > > I have an application where it would be useful to boost the volume through > a speaker based on the level of background noise in the area. The obvious > problem is how to cancel the sound from the speaker so the noise level can > be measured. Any ideas? > Thanx, Bob Ankeney tektronix!reed!omsi ELECTOR magazine (UK publication) had a motorcycle intercom a while back using that idea. They placed a mike at the front of the helmet and another in the hollow space below the cheekbone. By feeding the two mike signals to an OpAmp as common mode signals, the side mike was algebraically subtracted from the front mike. The output could then be fed to another OpAmp or audio amp for boost and distribution. Don't forget to return an attenuated signal in real time to the user's earphone so they can judge voice volumn (like a phone instead of like a CB radio). See: front mike [----------|\ LM741 +| \ | \_____ 'clean' ouput | / -| / side mike [-----------|/ Both mikes to common ground. Some feedback will be required or clipping will result. Grab a textbook.
rbl@nitrex.UUCP (06/01/87)
In article <90@dalcsug.UUCP> cslug2@dalcsug.UUCP (me) writes: >In article <6412@reed.UUCP>, omsi@reed.UUCP (OMSI) writes: >> >> I have an application where it would be useful to boost the volume through >> a speaker based on the level of background noise in the area. > >> ... >ELECTOR magazine (UK publication) had a motorcycle intercom a while back >using that idea. > ... MANY years ago, Ford had a radio option (I believe for the Thunderbird) that adjusted the volume per the vehicle speed. As I recall, there was a pulse from the distributor or tachometer. This was probably in the late '60's. Rob Lake