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Old 11th May 2009, 03:33 AM   #1
Buzzy is offline Buzzy  Singapore
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Default Over excursion protection for subwoofer

Hi ! I am looking for a circuit that can prevent a subwoofer from over excursion so that it doesn't bottom out. I don't know what is the right name for this kind of circuit.

I shall also elaborate what i am trying to do here. I upgraded the driver for my SVS subwoofer i bought some time ago. So i have the old driver which is in perfect working condition. I have built an enclosure for it. The original SVS subwoofer has variable subsonic filter switch with 25Hz, 20Hz, 16Hz and bypass settings. http://www.svsound.com/products-sub-box-plus2.cfm I would like a circuit that will do the same. But i think i will not need so many. Maybe just the 20 Hz filter.
Thank you.
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Old 11th May 2009, 02:27 PM   #2
Bakmeel is offline Bakmeel  Netherlands
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Why are you afraid that in the new design your woofer will bottom out? Do you expect the new application to be of such different loading or more power capabilities?

Anyway, I would say that you are looking for current limitation. For my knowledge, speakers are current-driven transducers, and their excursion is a function of current provided to them.

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Old 11th May 2009, 02:44 PM   #3
AndrewT is offline AndrewT  Scotland
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Default Re: Over excursion protection for subwoofer

Quote:
Originally posted by Buzzy
I am looking for a circuit that can prevent a subwoofer from over excursion so that it doesn't bottom out.
it's called ears, brain and fingers. They form a feedback system to tell the sensible, it's gone too loud.
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Old 11th May 2009, 02:50 PM   #4
Buzzy is offline Buzzy  Singapore
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Its not the loudness factor. It plays fine but when play movie with bass that extends down to 5Hz can hear funny noises in the woofer. Quite a few movies have this kind of crazy bass. Thats y i want to protect the woofer from breaking apart.
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Old 14th May 2009, 12:02 AM   #5
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Quote:
Originally posted by AndrewT
it's called ears, brain and fingers. They form a feedback system to tell the sensible, it's gone too loud.
T.F.F. AndrewT
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Old 14th May 2009, 09:09 AM   #6
dangus is offline dangus  Canada
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Maybe use a limiter circuit (as in compressor/limiter), and stick a circuit in the sidechain that models the excursion limitations of the driver? That would be something like what Bag End does for their subs to prevent the 12dB/octave boost from clipping amps or sending cones into outer space. (Although they may use a VCA to tune a high-pass filter to limit low bass without affecting mid or high bass.)

There used to be a single-chip compressor/limiter from Analog Devices, but I expect you could buy a complete used compressor/limiter or a new one from China pretty cheap.

Or maybe you just need a sharp high-pass filter. 24 dB/octave? Marchand Electronics should have a kit like that.
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Old 16th May 2009, 06:09 AM   #7
Buzzy is offline Buzzy  Singapore
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I have found a circuit which is a rumble filter from rod elliot website Project 99 Rev-B. http://sound.westhost.com/project99.htm

Is this the one i should be using ?

I want to achieve the frequancy graph shown at the end of the page in this website http://www.svsound.com/products-sub-box-plus2.cfm . For now i have subwoofer frequency response down to 5Hz. This causes some funny noises in the driver even when i don't turn up the volume too much. Pls help. I am now stuck and unable to complete my subwoofer project.
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Old 16th May 2009, 09:50 AM   #8
AndrewT is offline AndrewT  Scotland
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yes, that ESP circuit is a rumble filter.
6pole (-36dB/Octave) instead of the more usual 2pole or 4pole.
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Old 18th May 2009, 01:12 AM   #9
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-36db/octave? that's about as close to a "brick wall" filter as you can get
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Old 18th May 2009, 11:37 PM   #10
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Maybe a better woofer?
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