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Old 28th September 2005, 11:45 PM   #1
morbo is offline morbo  Canada
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Default Subwoofer EQ/integration question

I will soon be running a system which crosses satellites to stereo subwoofers which will act as stands. I would like to integrate a Behringer 1124 feedback destroyer into the system to use as a stereo low frequency EQ, as described here:

http://www.snapbug.ws/bfd.htm

I am using an outboard active stereo crossover after my receiver's preamp outputs, with the receiver set to LARGE for the L/R front speakers, subwoofer set to OFF. The BFD would be connected to the this outboard crossover's low pass outputs, and its output would in turn be fed to the subwoofers.

My question is this: in the guide referenced above, it says to increase the 'subwoofer distance' (read: delay setting) setting in your surround processor by 1 foot to compensate for the DSP-induced delay. My outboard crossover makes no allowance for a distance setting or delay. How can I then add this delay to the signal the subwoofer receives?
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Old 29th September 2005, 02:11 PM   #2
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Morbo, I don't think it's really worth doing anything about. I have ultracurve and can set delay to the subs, and I have played around with it, but I don't find the difference is audible until it is far more out than you are dealing with.

If you are counteracting a "DSP induced delay" then you want to decrease the delay, not increase it! Don't you have a setting for subwoofer distance on your receiver? You could tweak that if it bothers you. You would decrease the distance entered by 1ft on that case, as you are not adding delay, but subtracting it.
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Old 29th September 2005, 08:02 PM   #3
morbo is offline morbo  Canada
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Sorry if I wasn't clear in my original post, you are right that the distance setting on my processor would be the obvious place to do this, however I'm doing my bass management using an external active crossover which does not have distance or delay settings. I suppose I could just leave it, but having seen how big a difference adjustments in the variable phase on my crossvoer make, I think this is something that needs to be addressed.

Are you using the ultracurve on your whole system, or just on the subs? If the former, then there would be no need for delay adjustment, as both satellites and subs would be 'delayed' the same amount. Also, to be clear, the delay referenced in the snapbug guide is the inherent delay of processing the signal - because it takes some small but significant time to do the processing then output the signal, if only the subwoofer signal is being processed, it will lag behind the satellites' signal. The snapbug guide author suggests that this delay is equivalent to ~ a 1 foot physical distance.

Actually, now it occurs to me that maybe this can be compensated for using the variable phase dial, the same way subwoofer placement across the room is 'dialed in' by adjusting the phase.
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Old 30th September 2005, 07:10 AM   #4
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Do you have to bypass ALL of the bass management controls?

1ft is not something I'd worry about! ...

Yes, I use ultracurve for the whole system. It's a cheat way to make sure it all sums flat in my listening position. Sub integration is impossible to get right without some kind of measuring.
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Old 30th September 2005, 07:44 AM   #5
morbo is offline morbo  Canada
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Luckily I do have measurement gear and software, so I have already been experimenting with nearfield and farfield measurements of this integration. I have a big hum at 100hz and another at 50hz that the BFD will hopefully help me control, but I have yet to build my second subwoofer and I'm sure it will measure slightly differently.

I do have to disable all bass management in my reciever, since to get a full range signal from the pre outs, I have to set subwoofer to "off" and r/l speakers to large. This automatically disables all subwoofer settings in the menu system. I guess I will just use the variable phase on my active XO to tune this, measuring all the way. I just figured there must be someone else doing their filtering like I am and applying EQ, so they may have this experience already.

BTW I wouldnt call the ultracurve a 'cheat', its an excellent idea, if anything its a maybe the most frugal way to achieve a very desirable result. But the concept is totally sound IMHO, I know some are against EQ of any sort, I'm all for it in some situations (especially LF!).
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Old 30th September 2005, 08:19 AM   #6
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I say "cheat" because I'm a bit naughty in how I use it - to fix up my integration being otherwise not quite right. I haven't got measurement setup happening fully yet, although I can use the RTA and noise in UC to do quasi measurements. It's probably more technically correct to rely on it a little less than I do - correctly integrating crossover slopes and so on.

I plan to get Ultradrive at Christmas time, by then I'll have a better integration, and it has a nice auto phase correct feature, as well as time delays on all outputs.

Can you set sub as ON but set mains to large? I haven't really messed with HT receivers yet as I have a lot of things to do with 2 channel and a projector first.
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