Does open baffle suffer from baffle step?

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If you mean a 6dB difference in SPL that occurs across a range of frequencies determined by the baffle width (typically a few hundred Hertz) before rolling off due to the box tuning, no it does not. The OB low frequency SPL rolls off below a value that is a function of the baffle size, this is where the front and rear waves start to cancel. Model a baffle in the EDGE program and switch back and forth between a box and an OB to see this effect.
 
Well, I wouldn't call it a baffle step since the result of the baffle is a slope below a certain frequency. Maybe one could call it a baffle slope?

Anyway, the cause for this slope is similar to that of the baffle step. Sound from the edges of the baffle interfere with the direct sound from the driver. For the closed box this "edge sound" is diffraction/reflection of the sound that has travelled from the driver to the edge. For the open baffle this sound is twice as large, since the same amount of sound comes from the back of the driver (and is also diffracted at the edge around the corner).

Green is the baffle step for a certain closed box, red is the "baffle slope" for an open baffle of the same size. The identical baffle dimensions give rise to similar behaviour, eg the peak at 1 kHz and the dip at 2.8 kHz. The difference is that the closed box settles at 0 dB for low frequencies, whereas the open baffle slopes towards negatve infinity (dB) at 0 Hz.

An externally hosted image should be here but it was not working when we last tested it.
 
Someone correct me if I'm wrong but I thought the Edge models baffle response in free infinite space. A normally placed OB will have a large delayed backwave from the rear wall and, the bottom of the baffle being normally flush to the floor, a greater effective baffle size than the software's model captures. Both factors would accentuate the actual bass response relative to predicted.
 
454Casull said:
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.
 
Drew Eckhardt said:
... 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.

Rudolf
 
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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.
 
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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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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