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Old 4th February 2003, 05:55 AM   #1
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Default Subsonic filter for a SubWoofer

Hi there,
I'm new to this list so I'll introduce myself first...
My name is Guy, I'm a computer programmer in Melbourne Australia.

I've recently got into subwoofer building and am about to start my first project. It's a home theater active sub, using a 12" peerless driver with 2 passive radiators. It will use a 240W RMS amp.

I've been using WinISD software to model the various properties of the sub and can see that the cone excursion of the driver gets too large when the frequency goes below 20Hz.

So I guess that I need a 24db per octave high pass filter at about 20Hz. My question is whether anyone on this list can suggest what I should do. Is there a good filter on the market I can buy, or is it easy enough to make one?

Any information would be greatly appreciated.
Regards,
Guy
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Old 4th February 2003, 07:07 AM   #2
f4ier is offline f4ier  Australia
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Guy,

Making a subsonic filter is very easy, especially if you go the kit route. Both DSE and Jaycar Electronics would have kits of Rob Evan's Subwoofer Processor (which only has a 6dB/oct subsonic filter if memory serves me well). Try Elliott Sound Products for more projects.

Cheers
Isaac

Quote:
I'm a computer programmer in Melbourne Australia.
I'd give anything to get work like yours. It's hard being a fresh graduate
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Old 6th February 2003, 05:17 AM   #3
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Thanks for the reply Isaac,

I sent an email to Elliott Sound Products (good web site btw) asking them if they had a high pass filter like the one I'm after.

Rod sent me a reply saying that he is going to design a 36dB/octave "phono rumble" high pass filter. This is exactly what I want, so I'll probably wait for this.
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Old 8th February 2003, 09:07 AM   #4
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Default rumble

>>>>It's a home theater active sub, using a 12" peerless driver >>>>with 2 passive radiators. It will use a 240W RMS amp.

have u seen www.geocities.com/adrian_mack/index.html

?

>>I've been using WinISD software to model the various >>properties of the sub and can see that the cone excursion of >>the driver gets too large when the frequency goes below >>20Hz.

are u planning on playing LPs or 20hz test tones i wouldnt worry too much (or pipe organ music)

still good to have a subsonic filter though

i thought of getting a peerless XLS but i dont want to buy Passive radiators when pvc pipe will do,, perhaps a cerwin cega 12,,
or 18sound (15inch)

:-D
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Old 9th February 2003, 11:04 PM   #5
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This article from our moderator, Planet 10's site, shows how to put passive filters in line to the amplifier that feeds the subwoofer.

Looks useful for what you want.

http://www.t-linespeakers.org/tech/f...ssiveHLxo.html
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Old 21st February 2003, 11:17 AM   #6
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Quote:
I sent an email to Elliott Sound Products (good web site btw) asking them if they had a high pass filter like the one I'm after.
guylemar,

Did Rod get back to you on that 36dB/oct filter? (likely availability etc...?)

I'd be interested as well.

Thanks,
David.
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Old 23rd February 2003, 06:48 AM   #7
SteveW is offline SteveW  United States
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Default Re: Subsonic filter for a SubWoofer

Quote:
Originally posted by guylemar
Hi there,
I'm new to this list so I'll introduce myself first...
My name is Guy, I'm a computer programmer in Melbourne Australia.

I've recently got into subwoofer building and am about to start my first project. It's a home theater active sub, using a 12" peerless driver with 2 passive radiators. It will use a 240W RMS amp.

I've been using WinISD software to model the various properties of the sub and can see that the cone excursion of the driver gets too large when the frequency goes below 20Hz.

So I guess that I need a 24db per octave high pass filter at about 20Hz. My question is whether anyone on this list can suggest what I should do. Is there a good filter on the market I can buy, or is it easy enough to make one?

Any information would be greatly appreciated.
Regards,
Guy
24db @ 20hz is about perfect for a subsonic filter for exactly the reason you stated. I generally like to use filters on in my builds. For HT they are a good idea as some movies have quite a lot of energy down low. For music a low cut filter will allow for maximum output from the sub without overload.

Whatever your source material, a low cut filter will optimize your subwoofers performance envelope.

You might want to try these as an interim solution while awaiting the real deal - they are good to have around anyway:

http://www.partsexpress.com/pe/showd...ID=16209&DID=7

cheers!!!!

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Old 23rd February 2003, 06:56 AM   #8
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Assuming that the sub is being powered by it's own amplifier, it's probably easiest to use an active 4th-order (Linkwitz-Riley) high pass filter @ 20Hz. When all is said and done, this is probably the simplest option available to you.
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Old 26th February 2003, 06:43 AM   #9
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AudioFreak,

I know very little about passive xovers, let alone active ones. Would I be best off with a kit?

I'm guessing passive at that frequency is not an option due to size of inductors required?

Can you recommend a good book on xovers? (apart from Dickason's cookbook)?

thanks,
David.
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Old 26th February 2003, 07:11 AM   #10
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Hmm... if it's a rumble filter you're going for, it's a high-pass filter, and those are usually done with capacitors...

though I too know very little about crossovers.

What I do know came from Radio Shack OP-AMP books (grin) and is pretty, um, rudimentary.

http://www.maxim-ic.com/appnotes.cfm...te_number/1795

That's a very good thing if you're going to do active crossing over... I haven't read the whole thing yet but it gets very in-depth. I suspect you could just pluck one of the designs out of there and modify values according to the equations given, and have an adequate filter for what you're going for.
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