Does open baffle suffer from baffle step?

454Casull · 16th July 2006, 05:59 PM

Is there a right answer for this?

leadbelly · 16th July 2006, 06:09 PM

Yes and yes to both questions.

MJK · 16th July 2006, 08:25 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, 09:13 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.

454Casull · 16th July 2006, 09:29 PM

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

rdf · 16th July 2006, 09:32 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, 09:36 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, 09:43 PM

So no BSC circuit is necessary for OB speakers?

MJK · 16th July 2006, 10:08 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, 07:01 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.

16th July 2006, 05:59 PM	#1
454Casull diyAudio Member Join Date: Jan 2004 Location: Toronto, ON, Canada	Does open baffle suffer from baffle step? Is there a right answer for this?

16th July 2006, 06:09 PM	#2
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Yes and yes to both questions. __________________ Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it. Stephen Leacock

16th July 2006, 08:25 PM	#3
MJK diyAudio Member Join Date: Feb 2002 Location: Clifton Park, NY	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. __________________ Quarter Wavelength Loudspeaker Design www.quarter-wave.com

16th July 2006, 09:13 PM	#4
Svante diyAudio Member Join Date: Feb 2004 Location: Stockholm	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. __________________ Simulate loudspeakers: Basta! Simulate the baffle step: The Edge

16th July 2006, 10:08 PM	#9
MJK diyAudio Member Join Date: Feb 2002 Location: Clifton Park, NY	I am not using one, so I guess the answer is no. OB speakers are a different set of design challenges. __________________ Quarter Wavelength Loudspeaker Design www.quarter-wave.com


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16th July 2006, 09:29 PM	#5
454Casull diyAudio Member Join Date: Jan 2004 Location: Toronto, ON, Canada	Are there any rules of thumb for modifying BSC circuits (values for sealed boxes) for use on open baffles?

16th July 2006, 09:32 PM	#6
rdf diyAudio Member Join Date: Jun 2004 Location: the thermionic past	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.

16th July 2006, 09:43 PM	#8
454Casull diyAudio Member Join Date: Jan 2004 Location: Toronto, ON, Canada	So no BSC circuit is necessary for OB speakers?

17th July 2006, 07:01 AM	#10
mikelm diyAudio Member Join Date: May 2003 Location: currently living & working is USA	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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