Double filtering bass

Ron-P

Currently I am running the Plate Amp for my Sonosub off the Pre/Pro with the X-over dial on the amp being used.

With the recent addition of the Outlaw ICBM would I lose any impact quality if I ran the sub off the pre/pro, through the ICBM and then into the amp. The amp itself has no by-bass for the x-over.

I would gain better bass control if I ran it though the ICBM but not too sure how double filtering it would affect the quality of bass.


Peace Out~:D

Dr. Spec

In the Klipsch unit, set all speakers to large and the sub to yes/on. That will send a full range signal for each channel, and the LFE channel, to the ICBM.

At the ICBM, select whatever xo for each channel you feel is appropriate.

Tell the ICBM to combine the low passed surround bass with the LFE (.1) channel.

Since you are using vented surrounds which have a natural 4th order roll-off below the tune point, you can play with the high pass xo points and filter slopes to achieve better parity with the low pass filter rate for the subwoofer.

In any event, you will be probably be using an 80 Hz (or thereabouts) xo for the subwoofer low pass, so just set the filter on the plate amp to its highest setting (what - maybe 120 Hz?) to avoid cascading the ICBM low pass and the plate amp low pass filters.

Ron-P

Excellent, as always, thanks for the help Doc.


Peace Out~:D

Dr. Spec

No prob, Ron. A few more thoughts on your particular rig:

Below the tune point, the vented speaker will roll-off at 24 dB/octave by design.

Imposing any additional filtering (like say a 2nd order high pass) on a vented speaker will result in an even steeper roll-off below the tune point - in this example the combined effect will be a 36 dB/octave roll-off.

Since you are using fairly large surround speakers with pretty low F3 ratings, you can assume they will stay flat in response down to that point.

If you select a high pass xo point well above the F3 of the speaker, you will want to match the high pass and low pass filter slopes to achieve slope parity and minimum sat/sub overlap.

For example, if all your surround speakers have an F3 of say 50-55 Hz and you select an xo point of say 90 Hz, you can use a 4th order high pass and a 4th order low pass filter rate and not only achieve slope parity, but also really ramp down the response of the surrounds quickly, further minimizing cone excursion and further decreasing intermodulation distortion, resulting in an even more clear/distinct upper midrange.

Doc

HBombToo

Originally posted by Dr. Spec


Below the tune point, the vented speaker will roll-off at 24 dB/octave by design.

Imposing any additional filtering (like say a 2nd order high pass) on a vented speaker will result in an even steeper roll-off below the tune point - in this example the combined effect will be a 36 dB/octave roll-off.

Doc just to make sure I'm following you I need to clarify something.

In a double filter situation the slopes are additive and thats how you arrived at 36 dB/octave by adding 12 + 24? 12 is from second order crossover?

Its been a long time since school but intuitivly I agree... just can't remember all the detail at this time.

HBomb

Dr. Spec

Hi Henry:

Filter slopes are only additive if they are both applied equally over the entire bandwidth.

In the case of "double filtering" with a subwoofer, you are typically sending the subwoofer a signal that has been passed through a 4th order (24 dB/octave) low pass filter in the AVR bass management circuit.

If you also engage the low pass filter in the subwoofer, it will apply its own low pass filter to the already filtered signal.

The typical low pass filter slope in a subwoofer plate amp is 2nd order (12 dB/octave).

So the combined low pass filter rate becomes 36 dB/octave (24 + 12 ) or 6th order.

At the filter frequency (say 80 Hz), the amplitude of the signal is already depressed by a certain amount. Depending on the slope of the filter, it can vary but is typically 3-6 dB.

Normally, if the high pass and low pass filter slopes are the same - in a perfect world the high pass depression in the surround speakers and the low pass depression in the subwoofer will combine at the xo point and sum to create no depression at all - in other words a flat/seamless transition from sub to sat.

But if you double filter the sub signal and effectively create a 6th order low pass filter, the depression on the low pass side becomes larger at the xo point than it normally would be, and the depression on the the high pass side is no longer large enough to compensate and they will not sum to 0 and there will be a "hole" centered at around 80 Hz, probably amounting to about 3-4 dB.

Doc

HBombToo

I see said the blind squirrel looking for a NUT:D

No really though... Thanks Doc.

HBomb

Ron-P

Ok, this audio rookie needs some esplain'n...Luuuuccccccc.

What are all these "orders" to x-overs? 4th, 5th order? Shed some light here boys.

Also, whats the F3 stand for?

Help a blind man see will ya.


Peace Out~:D

On a side note, I just had lunch at hOOters. Talk about big, exposed subwoofers.

gatemplin

Ron,

The F3 is the point (Hz) where the response is down 3 dB IIRC.
I cant help you with the orders of crossovers though. I would like to know that info myself. I will search for it and tell you if I find out.

BTW, can you tell me about your Tempest. How big? Tuning frequency etc. I recently built a EBS Tempest and threw a BFD on it.

Ron-P

It's 177L, based on a mid-Q design. It's 36" x 24" tube. Lined with polyfill. It's ported with 2-17" flared kits to roughly 17Hz. It's powered with a 250w Plate Amp.


Peace Out~:D

Dr. Spec

http://www.eaw.com/support/processors/faq.shtml

This might help, Ron.

All crossovers have filters. A filter has a slope - the rate at which it ramps down the signal.

1st order is short hand for a slope of 6 dB/octave.

2nd order is a 12 dB/octave slope, 3rd order is 18 dB/octave, and so on.

I just checked the ICBM and the highest slope you can apply is 2nd order for either high pass or low pass. That is a fairly shallow slope for a low pass on a sub.

In that event, I recommend an xo of 80 Hz since the sub will be allowed to play quite a bit higher before it trails off completely.

Doc

HBombToo

I can't recall the filter type in the subsonic filter I bought with the dual CS+. Do you recall the slope of the filter? I sent you my voltage curves didn't i?

I would think a Linkwitz-Riley would be best for cutoff in the sub region?

1/4Twin

HBombToo

Originally posted by HBombToo
I can't recall the filter type in the subsonic filter I bought with the dual CS+. Do you recall the slope of the filter? I sent you my voltage curves didn't i?

I would think a Linkwitz-Riley would be best for cutoff in the sub region?

1/4Twin

BTW Doc. the reason my feet began sweating is I hated convalution intergrals:(

Dr. Spec

Subsonic filter is a 4th order slope on the SVS01 Marchand Bass Box.

My armpits began to sweat when I saw my credit card bill this month. Sweat is sweat, I guess.............

Ron-P

Thanks Doc. I'll read up.

Peace Out~:D