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inverting amplifier schematic

2005-10-18 14:05:36.860365+00 by Dan Lyke 5 comments

[ related topics: Hardware Hackery Music ]

comments in ascending chronological order (reverse):

#Comment Re: made: 2005-10-18 18:25:07.698933+00 by: Mark A. Hershberger

recalling the earlier post about decibels: do noise-canceling headphones have decibels? Or do they just kill the decibels?

I guess they just kill them: http://www.crmav.com/62/shure_...tter_than_noise_canceling_.shtml

Sorry for the stupid question. However, this quote from the above link is interesting:

The study results revealed that the E3c with foam sleeves was the best performer among the Shure units tested, as it reduced noise by 10 - 27 decibels more than even the best-performing noise-canceling model tested.

Seems to be a press release, but I'm wondering if that really is the case: that cup 'phones are better than noise-canceling ones.

#Comment Re: made: 2005-10-18 19:05:23.320092+00 by: Dan Lyke

Sound wavelengths are in that "noise canceling just can't work that well" range. The wavelenght of A above middle C is in the 31" range, and the distance between your microphone and your speakers is probably half an inch, and the speakers to the ear is probably an inch. Right there your margin is 4% or so, and as the frequency goes up the error grows, by the time you're getting to the upper end of audible frequencies you're a wavelength away from the ear, and half a wavelength between the microphone and the speaker.

So, yeah, my next headphone set is either going to be full ear cups, or the Etymotic plugs.

#Comment Re: made: 2005-10-18 19:18:22.526677+00 by: Mark A. Hershberger

That's what I thought: it can't work that well. If you're getting less than 30db of noise reduction, that's only going to get you down to about 60db in the subway (http://www.lhh.org/noise/decibel.htm).

So, $300+ for ear nubs? wow.

#Comment Re: made: 2005-10-18 19:26:52.965812+00 by: Dan Lyke

I was thinking the $139 ones...

#Comment Re: made: 2005-10-18 21:28:40.147941+00 by: Dan Lyke

Oh yeah, going back a few: They have decibels, because there error introduces white noise. In theory they should add no noise, but that'd be only if you can put the audio source, mic, speaker and ear inline, and make sure that the delay between the speaker and the mic exactly match the distance. And, of course, that theory goes away pretty quickly because you need the mic shadowed from the speaker to prevent feedback, but as soon as you have shadows you're going to have refraction and all that nice theory goes away.