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## Re: 3032 capsules on PIP

 Subject: Re: 3032 capsules on PIP "Eric Benjamin" ericbenjamin2 Sat Jun 14, 2014 1:03 am ((PDT))
 ```> Greg O. wrote > I need to have a firm grasp on the concept of the thermal noise of air an= d how it affects microphones. I now have about a 12" stack of acoustic texts on my desk. =C2=A0Beranek's = "Acoustics" was most helpful. =C2=A0Morse and Ingaard's "Theoretical Acoust= ics" gave me a 3-aspirin headache. Beranek gives calculated values for the real part of the impedance seen by = a disc on the end of a cylinder. =C2=A0That sounds like a microphone to me.= =C2=A0The real part of the impedance is the resistance, and that's what we= need to calculate the noise. =C2=A0For a 1-inch microphone diaphragm, I ca= lculate that the noise amounts to about -20 dB SPL. That is, the noise of t= he air is 28 dB quieter than an Audio Technica 4032 (but the 3032 diaphragm= is smaller than 1 inch) and about 15 dB quieter than a Bruel and Kjaer 417= Message: 9. Subject: =C2=A0But that doesn't do much to point us towards making a microphone t= hat can measure the thermal noise of the air. =C2=A0It's the noise from the= air that is trapped _behind_ the diaphragm in a conventional microphone th= at limits how quiet it can be. =C2=A0Along with all of the other noise sour= ces. I hope that helps. =C2=A0I can show the details of the calculation if anyon= e would like to see it. =C2=A0This venue doesn't seem like the place! On Friday, June 13, 2014 11:10 PM, "Gregory O'Drobinak m("sbcgloba","gmodrobinak");= l.net [naturerecordists]" wrote: =C2=A0 David: What a lovely memory to have, being there in the mountains of India! i wish we could not only hear the recording of that soundscape as you perce= ived it, but also to see a good picture of what the space was like. Perhaps in the future, we can look forward to such things [Mike Rooke, you = have much work to do. ++]. Please take a look at the Gras microphone that i posted and its data sheet. It claims that the lowest measurable SPL level is limited by the thermal no= ise of the microphone, which is spec'd at -2 dB SPL. This implies that one can break the 0 dB SPL barrier as Miike has proposed. But it will certainly take quite a lot of creative thinking and work to mak= e this happen. Gras claims to have it already, but we need an affordable solution that is = compact and adaptable to a large variety of recording arrays. I'm not sure that I understand the idea of random thermal noise causing a 3= dB hit on the self noise of a mic. Eric B., can you please help us out here? Also, I need to have a firm grasp on the concept of the thermal noise of ai= r and how it affects microphones. Somehow there must be a way to convert thermal noise power into dB SPL at t= he microphone diaphragm. I suspect that this involves some integration of the noise power over some = distance as a function of the area and compliance of the microphone diaphra= gm. Can anyone with a solid background in acoustics help us out here? BTW, sorry to burden all of the nature recordists out there with all of thi= s crazy tech. But, ultimately this will benefit all of us, assuming that there will still= be some pristine natural habitats left to record. Thanks & BR, Greg O. From: "m("dsl.pipex.com","brini"); [naturerecordists]" To: m("yahoogroups.com","naturerecordists"); Sent: Friday, June 13, 2014 6:15 PM Subject: [Nature Recordists] Re: 3032 capsules on PIP =C2=A0 > Recall that 'dB' is a relative logarithmic measure that is useless withou= t some reference level to refer to. Again, dB is always relative! > So when you say 'dBA' or 'dB-anything it is always relative to some absol= ute reference value. Gregory, This is just laziness when what is meant is dB(SPL) which is usually taken= to mean as referred to 20 =C2=B5Pa (rms) as you said. > Oh, let's now address the thermal noise of the air. > I suspect that in absolute measurement terms, the thermal noise of the ai= r is very much lower than the absolute value of 20 uPA. Like, way lower. > > Can someone please help out and provide the equations to calculate the 't= hermal noise of the air' in absolute terms, i.e., in uPa? > Please give a good description as to what all of this means, too. The general thermal noise equation is: P =3D kB T Delta f P =3D power kB =3D Boltzmann's constant T =3D absolute temperature Delta f =3D frequency bandwidth My physics is 50 years old and I'm struggling to turn this into dB(SPL) but= note that any thermal noise is proportional to frequency at the rate of 3dB= per octave. This means that a weighting curve must be specified to turn thi= s into as audible noise threshold. Unfortunately no suitable curve is recognised at 0 dB(SPL). In particular the phon is defined with the 40dB(SPL) weighting curve which is nothing like the threshold curve. See: https://en.wikipedia.org/wiki/Equal-loudness_contours Note in particular, the threshold curve which goes down to -6dB(SPL) so kee= n ears should hear thermal noise. I claim to have heard the thermal noise in air in my youth when I could hea= r very high frequencies. At some frequency the rising thermal noise met my falling frequency response and I heard a hiss. It was in an exceedingly quitet grassland in the mountains of South India and I could hear my heart= thumping away noisily, the blood coursing through my ears, and faitly in th= e background, a high pitched hiss. David Brinicombe ```
 Current Thread 3032 capsules on PIP, Dan Dugan Re: 3032 capsules on PIP, yg Re: 3032 capsules on PIP, Dan Dugan Re: 3032 capsules on PIP, brini Re: 3032 capsules on PIP, yg Re: 3032 capsules on PIP, brini Re: 3032 capsules on PIP, Gregory O'Drobinak Re: 3032 capsules on PIP, brini Re: 3032 capsules on PIP, Gregory O'Drobinak Re: 3032 capsules on PIP, Eric Benjamin <= Re: 3032 capsules on PIP, Gianni Pavan Re: 3032 capsules on PIP, brini Re: 3032 capsules on PIP, Gregory O'Drobinak Re: 3032 capsules on PIP, Gianni Pavan Re: 3032 capsules on PIP, brini Re: 3032 capsules on PIP, Eric Benjamin