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-   -   Does open baffle suffer from baffle step? (http://www.diyaudio.com/forums/multi-way/83255-does-open-baffle-suffer-baffle-step.html)

454Casull 16th July 2006 06:59 PM

Does open baffle suffer from baffle step?
 
Is there a right answer for this? :(

leadbelly 16th July 2006 07:09 PM

Yes and yes to both questions.

MJK 16th July 2006 09:25 PM

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.

Svante 16th July 2006 10:13 PM

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.

http://www.tolvan.com/OB_CB.gif

454Casull 16th July 2006 10:29 PM

Are there any rules of thumb for modifying BSC circuits (values for sealed boxes) for use on open baffles?

rdf 16th July 2006 10:32 PM

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.

MJK 16th July 2006 10:36 PM

Quote:

Are there any rules of thumb for modifying BSC circuits (values for sealed boxes) for use on open baffles?
Why would you want to add a filter? The BSC filter attenuates the SPL above the baffle step, I am not sure it is even applicable to an open baffle. I am not sure I understand what you would try and accomplish by adding a filter.

454Casull 16th July 2006 10:43 PM

So no BSC circuit is necessary for OB speakers?

MJK 16th July 2006 11:08 PM

I am not using one, so I guess the answer is no. OB speakers are a different set of design challenges.

mikelm 17th July 2006 08:01 AM

check out this sofware

http://www.tolvan.com/edge/

for best results try to stop that baffle shaking - concrete / marble etc

also experiment with speaker chassis position using programme above to get optimum distribution of cancelation and edge effect.


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