Implementing a Rumble Filter before the Amp?

[Bogie]

My January project is to complete the Big Boxes o' Whoopass (4 Dayton Quatro 15s in 7 cubic foot slot-ported boxes, tuned to 21hz). This is going to be driven by a pro amp (leaning toward the Behringer EP-2500). The boxes will be sized to fit _roughly_ under my projector screen.

I'd like to make the thing fairly idiot proof. The amp's going to be locked (in a rack), but WinISD shows bad nasties down in the low movie area... I've only bottomed out my two existing subs, the Big Cans o' Whoopass (Q15s in 5.5 cube sonotubes, tuned to 18.5hz), once - one of the scenes in Sin City caused major thwappage. So I definitely want to implement rumble filter(s) to avoid the low-end cone liftoff.

Looking at the calcs, 2nd order highpass filters at between 15-18hz for each sub are gonna be some major buckage. Do any of y'all know of a design for this sort of thing to feed the signal through _before_ it hits the amp? How do plate amps achieve this? I'm not an electrical engineer, but I have done okay after taking Remedial Soldering...

[mikee55]

You could either use a passive,a capacitor in series with the signal like you would connect a tweeter to a woofer to block bass appx 4.7 uf or go active and accurate and use a 12db linkwitz reily highpass filter set to say 13 hz.It might give you more sub but better protection from subsonics.Crossovers are all over the web. Google Linkwitz Lab and visit the site or Rod Elliott at ausound.com.Both always on my Favorites button for these moments in life.Have Fun.mikee55

[Bogie]

So a 4.7 mike cap before the amp will act the same as a mondo-huge one after the amp? I'd prefer to do a _really_ steep cut tho - how hard would it be to approx a 24-48db slope, down around 17hz or so? Ive found plenty of info on regular crossovers, but next to nothing on stuff before you amplify.

[Collo]

24dB Linkwitz is fairly easy to do. Here's one I built.
http://www.users.bigpond.com/bcolliso/active-filter.htm

WinISD makes it easy to find just the right design frequency.

As Mikee says, Rod Elliot has great designs. He has a 2 / 3 way Linkwitz design and can supply a circuit board - just populate the section you need....
http://sound.westhost.com/project09.htm

regards
Collo

[Bogie]

So these things use power to run, rather than just modifying the signal from the amp? Can you throw a few hundred watts at 'em? I was _hoping_ to just mod the signal before I split it for the amp.

[mikee55]

It goes after your pre and before your amp.Your amp can be as big as u like.Go to Rods site an read
cheers.mikee55

[Bogie]

Okay, I'm confused... The one from the "bigpond" web site says that it goes between the amp and the sub... it's the other one I want then... Looks like some major fun with excel and a soldering iron then...

[Collo]

Originally posted by Bogie
The one from .....says that it goes between the amp and the sub...

What I mean is that you take the signal from the "Subwoofer Out" connection on the AV amp, and feed it to the "Line In" connection on the subwoofer's Plate amplifier.

Active filters operate at "Line Level", not "Speaker Level"

Hope that clears up the confusion
Collo

[Bogie]

Uh, yeah, but I'm not going to be using a plate amp, since I'm going to want to be able to throw about 1200 watts at the things... I'll probably run 'em in two pairs, so I'm looking for something that'll run 600 watts/channel into an 8 ohm load, which means pro amps... Hence the need for the rumble filter (most plate amps seem to have 'em built in, it seems).

Note: This filter is inserted between the surround amplifier and the subwoofer. This is important because all OP amps have a limited gain * bandwidth product.

I'll guess here that the folks are confusing "amplifier" with "pre-amplifier."

My current setup:

Sony DVD/SACD into
Denon 2803 into
Hafler DH-225 (center)
Hafler P-230 (right)
Hafler P-230 (left)
Hafler DH-500 (side surrounds)
Hafler DH-500 (rear surrounds)

LFE split into
Behringer Feedback Destroyer into
R) split into two 240 watt Parts Express plate amps into the first two subs
L) 100 watt plate amp that's running the shakers under my front sofa

What I'm looking to do is add two more subs, which will either get really stupid re: splitting the signal to umpty plate amps, or will require a pro amp... Since I don't want the drivers overexcursing on ultra low bass, I want to cut them hard at about 15-17hz.

If you say the gizmo will do it, I'll go ahead and start ordering stuff...

[Collo]

The design will do the trick.

If you need any help choosing the design frequency, post your driver and project files, and I'll have a look at them for you

Collo