The comb filter article is about microphone elements in parallel. Those are widely spaced, but the physics is the same.
Even a small array of microphone elements is a substantial fraction of a sound wave. Wavelengths for sound in air are very small. At 3KHz, a full wavelength is about 12cm (under 5 inches). You can get full cancellation at a 1/4 wavelength distance (3cm, ~1.2 inches). A microphone with multiple elements can sound great, then after you move your head an inch or more, sound different. wunder K6WRU CM87wj http://observer.wunderwood.org/ On Jan 25, 2015, at 1:40 PM, Harry Yingst <hlyin...@yahoo.com> wrote: > Anything Specific to just the actual elements being in parallel? > > I do now there is one commercial mic doing this and is supposed to have good > reviews. > > > > > From: Walter Underwood <wun...@wunderwood.org> > To: Harry Yingst <hlyin...@yahoo.com>; "elecraft@mailman.qth.net" > <elecraft@mailman.qth.net> > Sent: Sunday, January 25, 2015 3:57 PM > Subject: Re: [Elecraft] My KX3 desk microphone project > > You could start with these two, read “close miking” in the Wikipedia article. > The second article is about speech recording for oral historians, so that is > fairly applicable to voice communications. Neither article even mentions > using multiple microphones for one person. The Wikipedia article section on > stereo recording gives a hint of some of the strange things that can happen > with multiple mics. > > http://en.wikipedia.org/wiki/Microphone_practice > http://ohda.matrix.msu.edu/2012/06/understanding-microphones/ > > Multiple microphones act very similar to phased arrays of antennas. They have > directionality and nulls that change with frequency. With a source in one > position, they can have a frequency response with a number of peaks and > nulls. This is called “comb filtering”. > > This article goes over that, including the 3-to-1 rule: "There is a popular > microphone placement adage that is known as the 3 to 1 Rule. The 3 to 1 Rule > says that if multiple microphones can hear the same source, then no other > microphone should be less than 3 times the distance to the source for the > microphone nearest the source. In other words, if a person is talking into a > microphone that is one foot away from them, then no other microphone in the > room should be closer than 3 feet away from that person in order to minimize > comb filtering." > > http://support.biamp.com/Tesira/Miscellaneous/Comb_filters > > wunder > K6WRU > CM87wj > http://observer.wunderwood.org/ > > > > On Jan 25, 2015, at 12:31 PM, Harry Yingst via Elecraft > <elecraft@mailman.qth.net> wrote: > > > Can you please provide a reference for this? > > > > > > From: Jim Brown <j...@audiosystemsgroup.com> > > To: elecraft@mailman.qth.net > > Sent: Sunday, January 25, 2015 12:48 PM > > Subject: Re: [Elecraft] My KX3 desk microphone project > > > > On Sun,1/25/2015 5:20 AM, Gary - NC3Z wrote: > >> In my opinion much, much better words should of been choose than > >> "seriously misguided", they have connotations that one is an idiot. > >> Seriously misguided would be trying to run a 12V device off 120V. > > > > Why? If an idea is seriously misguided, saying so is entirely > > appropriate. I did not expand on the advice because this is an email > > reflector dedicated to Elecraft radios, not microphones. > > > > There are (at least) three reasons why an array of microphones is a > > really bad idea. First, really good sounding mics to work with our > > radios are widely available cheap. Second, a microphone is an > > electroacoustic device -- it collects sound at a point in space and > > converts it to voltage. A microphone at a different point in space > > collects different sound -- there is a difference in time between those > > sounds, which results in a difference in phase. The difference in phase > > results in peaks and dips in the frequency response, which in the audio > > world is called comb filtering. Third, one mic loads another > > electrically, degrading the performance of each. > > > > Third, those of us working in pro audio learned a long time ago that one > > mic feeding a single channel is always better than one for picking up a > > single sound source like the human voice. Putting more of them in > > parallel does not make them work better. > > > > When you see two mics on either side of a podium, it's an indication > > that whoever put them there didn't understand that. As the talker moves > > side to side, the sound of his/her voice changes due to the > > cancellation. Almost 40 years ago, I did a couple of big outdoor sound > > reinforcement gigs for the President, and the White House sound > > engineers DID understand that -- they studied at the same workshops that > > I did. They had Shure build a special mic for them with three capsules > > in it, each coming out on their own shielded twisted pair. Two went to > > me, the second was for redundancy -- in case wiring for the first one > > failed. Each went to a different input of my mix console. The third went > > to them for their recording. > > > > 73, Jim K9YC > > > > > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:Elecraft@mailman.qth.net > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to hlyin...@yahoo.com > > > > > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:Elecraft@mailman.qth.net > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to > wun...@wunderwood.org > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
