Fitting a subsonic filter to a plate amp - diyAudio
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Old 12th September 2008, 08:55 AM   #1
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Default Fitting a subsonic filter to a plate amp

Id like to use a plate amp to drive an EBS subwoofer. Id need to fit a subsonic filter to avoid over excursing. Restricting the choice of plate amps to those with subsonic filters built-in, cuts out many good options (including one I already own, below)

How easy would it be fitting a filter? I was thinking of this amp

http://www.jaycar.com.au/productView...Max=&SUBCATID=

and this configurable subsonic filter
http://sound.westhost.com/project99.htm

Thanks
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Old 12th September 2008, 01:37 PM   #2
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The solution could be as easy as a passive line level filter. It might cost a couple bucks to make, or you can buy them premade. Partsexpress has some that just fit over the end of your rca inputs. You can acheive 6 or 12 db filter with this passive method, no higher.
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Old 12th September 2008, 11:27 PM   #3
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jag

Is this what you were referring to

http://www.partsexpress.com/pe/showd...number=266-242

That appreantly attenuates across all frequencies

A configurable subsonic filter can be set to filter out at say 24 dB/ ocatve, below a configurable (by change of components) frequency, ie below say 18 Hz.

the http://sound.westhost.com/project99.htm does that, but I dont know if/ how it could be used with a plate amp
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Old 13th September 2008, 02:56 AM   #4
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No that's just an attenuator, that makes EVERYTHING quieter, so it's useless in this discussion.

Here's one by the same manufacturer, this is a 12db/oct, 30 hz high pass filter, aka rumble filter. http://www.partsexpress.com/pe/showd...number=266-248

Or you can make your own. Also, don't discount the fact that the reason that most plate amps have no rumble filter is usually because they naturally drop off fast below 20 or 30 hz anyway, which is a type of rumble filter anyway. Try to find response graphs of the amps you are interested in. They probably won't be strong down low anyway.

Passive line level crossovers can be used up to 12 db/oct slope. If you need more, you need active, in which case the thing you linked to probably does everything you need. IMO, I would get a behringer xo if I needed to go active. The project rumble filter is probably cheaper though.
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Old 13th September 2008, 03:22 AM   #5
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jag

A high pass filter at 30 hz (the lowest of the filters at PE of that brand) would attenuate all the gains at 15 30 Hz ~ for HT ~ that Id get with an EBS.

The subsonic filter I posted is a pair of cascaded 18 dB/octave filters, giving an ultimate rolloff of 36 dB/octave: perfect for EBS. The -3 dB point is chosen by the capacitor values.

Theres no response graph posted for the plate amp Id like to use, but the vendor says its one of their best. Id assumed that a reasonable plate amp might only drop off say 1-3 dB between say 25 Hz and 12 Hz.

I dont have a problem making my own, the link Ive posted is a diy project.

My only uncertainty is how to connect it with a plate amp . . your links have suggested (doh!) it should best be connected between the HT sub out, and the plate amp.

cheers
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Old 13th September 2008, 03:38 AM   #6
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Default Re: Fitting a subsonic filter to a plate amp

Quote:
Originally posted by otto88
Id like to use a plate amp to drive an EBS subwoofer. Id need to fit a subsonic filter to avoid over excursing. Restricting the choice of plate amps to those with subsonic filters built-in, cuts out many good options (including one I already own, below)

How easy would it be fitting a filter? I was thinking of this amp

http://www.jaycar.com.au/productView...Max=&SUBCATID=

and this configurable subsonic filter
http://sound.westhost.com/project99.htm

Thanks

I don't know of any subwoofer plate amp that doesn't have a subsonic (aka "rumble") filter. The Jaycar amp almost certainly has one, since it has a boost at 35Hz. The boost is usually added by making the subsonic filter have a high Q. This results in a peak at the boost frequency followed by a 12-db rolloff for the low frequencies.

There is a small spreadsheet at the following link to calculate the resistor values for different amounts of boost and different cutoff frequencies. Look at the schematic on this page for some ideas on how to modify the filter to fit your needs: http://home.comcast.net/~neilrdavis/...30009_Mods.htm
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Old 13th September 2008, 04:04 AM   #7
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I just posted that as an example. These are very easy and cheap to make, much cheaper and easier than the active project you linked to, so I only thought I 'd mention it if you haven't heard about it. You can make them with a 6db or 12db slope at any frequency you like.

Sounds like you do not want a passive solution though, and that's fine. That project should work for you, but how much will it cost? There are a variety of options that don't cost much, but if you want to try that project, it should work for you. (Just to clarify, I only read the title of your link, and assume it's what you want.)

Both your link and my link are both line level solutions, so they have to be placed before the sub amp.
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Old 13th September 2008, 04:15 AM   #8
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Click the image to open in full size.

This is pretty typical of plate amp performance. IIRC it's from one of the current partsexpress plate amps. Plate amps are a notoriously bad choice for low frequency apps. Ymmv, but I think they all pretty much work like this. Plate amps are cheap and not really meant for serious subsonic duty.
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Old 13th September 2008, 11:07 AM   #9
HK26147 is offline HK26147  United States
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Along the same lines as Elliot's circuit is this filter circuit board:
Originally from Audio Amateur 4/75:

http://www.audioxpress.com/bksprods/products/pcbf-6.htm

This basic circuit has been updated over time ( w better op amps as they became available ).
I first built one as a (HP) rumble filter for my turntable in the 70's.
It can be modified to fit a variety of needs
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Old 13th September 2008, 02:03 PM   #10
Mikey p is offline Mikey p  Canada
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Quote:
I don't know of any subwoofer plate amp that doesn't have a subsonic (aka "rumble") filter.
Non of the Elemental Designs plate amps have a rumble filter when I inquired about them some time ago.
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