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Old 17th July 2006, 07:35 PM   #11
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Quote:
Originally posted by 454Casull
So no BSC circuit is necessary for OB speakers?
Dipole output drops 6dB/octave with decreasing frequency plus there's a +6dB peak where the back and front waves combine in-phase.

Dipole roll-off can be corrected for by using (shelving) low-pass filters on the bass drivers (Linkwitz Orion, Phoenix, etc.) or very high-Q drivers where sensitivity decreases with increasing frequency (Bob Carver Amazing dipoles, probably Gillmore Audio).
Wide baffles can push the effect lower in frequency so you get away without equalization.

You can use notches to correct the peak or just cross-over lower to keep it out of the driver's pass band.

You really want to visit www.linkwitzlab.com

Baffle dimensions being significant compared to typical listening distances mean the cancellation isn't as complete as the math predicts, so you might get away with less correction.

John Kreskovsky and Siegfried Linkwitz both have measurements of this effect.
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Old 17th July 2006, 09:25 PM   #12
Rudolf is offline Rudolf  Germany
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Quote:
Originally posted by Drew Eckhardt
... plus there's a +6dB peak where the back and front waves combine in-phase.
...
You can use notches to correct the peak or just cross-over lower to keep it out of the driver's pass band.
This peak is only 6 dB for a driver in the center of a circular baffle. For "normal" baffles this peak can be sufficiently attenuated by positioning the driver off baffle center. Again EDGE is a nice tool to accomplish that.

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Old 19th May 2012, 12:15 PM   #13
PA0SU is offline PA0SU  Netherlands
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What about 'covering/wainscoting/paneling - which is the right word? - the baffle at the front, around the speaker with some mm of wool? Would this not suppress all defractions from the edges (and the step)?
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Old 19th May 2012, 12:28 PM   #14
Pano is offline Pano  United States
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Hey, nice old thread back from the dead. Maybe it was just asleep.

Wool can attenuate the diffraction at the edges (a good thing), but won't do much at all to eliminate the wrap around cancellation of an open baffle. The reason they put woofers in boxes it to prevent this cancellation.

In an open baffle crossover you need to take the rising response of the woofer into account. That often means a very low electrical crossover point, to get the correct acoustical crossover point.
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Old 19th May 2012, 02:30 PM   #15
PA0SU is offline PA0SU  Netherlands
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Quote:
Originally Posted by Pano View Post
Hey, nice old thread back from the dead. Maybe it was just asleep.

Wool can attenuate the diffraction at the edges (a good thing), but won't do much at all to eliminate the wrap around cancellation of an open baffle.
Thanks! However I am not talking about a woofer. I have built me an array of small wide band speakers in an open baffle. If interrested, look at foto 1 and foto 2 in the dutch article in:

http://www.by-rutgers.nl/PDFiles/LSPdipool.pdf
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Old 19th May 2012, 03:12 PM   #16
Pano is offline Pano  United States
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Thanks for the link!

It really doesn't matter whether it's woofer, mid or tweeter - it's baffle size vs the frequencies you want to produce that matters. Sure, midrange OBs can use a smaller baffle, but you're working with higher frequencies/shorter wavelengths.
Think wavelength vs baffle dimensions.
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