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## Re: 3032 capsules on PIP

 Subject: Re: 3032 capsules on PIP madl74 Fri Jun 13, 2014 4:15 pm ((PDT))
 ```> 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