Microphones in parallel to reduce noise
in [Design]
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From: George Herold on 16 Dec 2009 22:53 Phil Allison wrote: > <osr(a)uakron.edu> > > > > My boss laid a unit on my desk today. Its got ten electret mics fed > > into one low noise opamp. Any ideas how they did this without a ton > > of noise. All I can see from the board layout is it is NOT the classic > > op amp summer. > > > > Any suggestions for papers on low noise signal combining? > > > > ** Likely all the mics are simply wired in series and supplied with power > from a DC current source and the signal taken from the top most mic. The s/n > advantage comes from *correlation*. > > The 10 noise signals ( from the internal JFET pre-amps) are un-correlated > while the sound arriving at each co-sited mic will be heavily correlated. > So the output signal will be 10 times that of one mic, while the self noise > will be only 3.16 times - so a 10 dB improvement is possible. > > I suspect the mics are arranged to create a directional pick up pattern too. > > BTW > > Dynamic mics have much less self noise than typical electrets - cos there is > no internal pre-amp. Means it is easy to get a 10dB or more improvement, > just by using one instead. > > > ..... Phil Phil, you're great! How much does a good Dynamic mic cost and who makes it? Say in the $10 - $20 range. George H.
From: John Larkin on 16 Dec 2009 22:55 On Wed, 16 Dec 2009 17:01:55 -0800 (PST), osr(a)uakron.edu wrote: >BIENT ** �noise pickup, �not self noise !! >> >> In any case, �YOU �are �100% �WRONG in your assumption that there ought to >> be a noise problem when combining the mics signals. Wired either in series >> or parallel, correlation still works to improve the s/n ratio. >> >> .... �Phil > >Mixer front ends still add thermal noise, "pal", and yes, its a >conference mike. > >Steve Is there any mic switching or multiple acquisition paths? A good conference mic would be directional in a bunch of directions and select the dominant-signal mic, excluding the noise from other directions. John
From: John Larkin on 16 Dec 2009 23:01 On Wed, 16 Dec 2009 19:46:01 -0800 (PST), George Herold <ggherold(a)gmail.com> wrote: > > >o...(a)uakron.edu wrote: >> My boss laid a unit on my desk today. Its got ten electret mics fed >> into one low noise opamp. Any ideas how they did this without a ton >> of noise. All I can see from the board layout is it is NOT the classic >> op amp summer. >> >> Any suggestions for papers on low noise signal combining? >> >> Steve > >Crazy idea, Is there anyway to add them in series? > >George H. They could just be in parallel. That would work if they were raw electrets or if they were the more common electret+jfet. But it sounds more complicated. John
From: krw on 16 Dec 2009 23:09 On Thu, 17 Dec 2009 02:25:00 +0000, Eeyore <rabbitsfriendsandrelations(a)removethishotmail.com> wrote: >krw wrote: >> "Phil Allison" <phil_a(a)tpg.com.au> wrote: >>> "krw" >> >>>> Some "dynamics" are really electrets in drag. >>> >>> ** Totally stupid bullshit. >>> >> In fact, you are. You and DimBulb; a perfect pair. > >Provide a link to one of these 'electret dynamics' or SHUT UP ! Wow, a trio of DimBulbs. We've hit the mother load!
From: krw on 16 Dec 2009 23:10
On Wed, 16 Dec 2009 22:37:10 -0500, "Michael A. Terrell" <mike.terrell(a)earthlink.net> wrote: > >krw wrote: >> >> On Thu, 17 Dec 2009 11:29:21 +1100, "Phil Allison" <phil_a(a)tpg.com.au> >> wrote: >> >> > >> >"krw" >> >> >> >> Some "dynamics" are really electrets in drag. >> > >> > >> >** Totally stupid bullshit. >> > >> In fact, you are. You and DimBulb; a perfect pair. > > > Just don't try to seperate them. You know what happens when you try >to divide zero by zero. You get a DimBulb Donkey? <shudder> |