Wavelength & accoustic "short circuit"?
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 25th May 2005, 07:18 AM #1 Jennice   diyAudio Member   Join Date: Jun 2003 Location: Planet Earth Wavelength & accoustic "short circuit"? Hi all, I need some help in brushing up on my theory. I was feeding a "random noise" (white noise) to a woofer, which is about 210mm diameter. It is placed with magnet to the floor, without enclosure. What the microphone picked up seemd to relate well to the audio source signal, exccept that it dropped off below about 780 Hz. I then recalled something about accoustic short circuit, where the air travels directly from the front to the back of the driver, without creating an audible sound pressure. With a frequency of about 780 Hz, the wavelength should be (in my math) = 334 / 780 = 0,428 m This would give a very nice fit with the driver diameter being 1/2 * wavelength. Too close to be coincidence, I think. Is that what I experienced? Is it the same math for baffle step on enclosures? I have read sources saying that baffle step happens at 1/2 * wavelength, and others say it's at 1/4 wavelength. Can anyone enlighten me, to put theory and practice together the correct way? Jennice __________________ I get paid to break stuff. My g/f gets paid to play with children. Life is good.
planet10
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Location: Victoria, BC, NA, Sol III
Re: Wavelength & accoustic "short circuit"?

Quote:
 Originally posted by Jennice Is that what I experienced?
yes

Quote:
 Is it the same math for baffle step on enclosures?
Baffle step isn't a cancelation it is a transition from 2 pi to 4 pi radiation... an empirical formula based on the work of Olson if f3 = 4560/w where w is the baffle width in inches... now this would be for a circular baffle and the real world is more complex... there is software called The Edge that does more accurate modelling.

For more BS info:

http://www.t-linespeakers.org/tech/b...intro-bds.html

dave
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p10-hifi forum here at diyA

 25th May 2005, 08:34 AM #3 Hans L   diyAudio Member     Join Date: Apr 2004 Location: Planet Earth You're right about the acoustic cancellation. See Linkwitz' site for all the theory behind dipole speakers. Bafflestep is centered (theoretical -3dB point) around 1/4 wavelength. __________________ In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move. --- Douglas Adams
 25th May 2005, 10:09 AM #4 Jennice   diyAudio Member   Join Date: Jun 2003 Location: Planet Earth Thanks guys! It's the first time I get to compare theory and reality by this kind of measurement, so it's great to have experienced guys around! Jennice __________________ I get paid to break stuff. My g/f gets paid to play with children. Life is good.

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