Subwoofer Equalization

[Tarheel TJ]

   I'd like to see what everyone is doing for subwoofer equalization.  I built a THT horn sub a couple years ago to fill in the bottom end that my LaScalas don't provide.  I power it with a ~350 watt Yamaha pro amp (P2200), and it is a BEAST!  It will actually shake pictures off the wall if you turn it up all the way (my wife loves it when I do this).  However, I used a very simple crossover (100hz Fmod low pass), and have not done any measuring or tuning.  I am certain that, like most subs in most rooms, I probably have some pretty serious peaks and dips in the response.  Now that I have done a little room treatment for the higher frequencies, I would like to address the bottom end.

   What is everyone using to EQ their subs?  I have looked at some of the different solutions out there like MiniDSP, Behringer FBQ, etc.  However, I like to listen to LPs a lot, and I don't really want to send my entire signal path through a ADC/DAC conversion if I don't have to.  Seeing as analog parametric EQs are pretty rare and hard to find, can I use a DSP based equalizer on the subwoofer signal only?  If I do this, will it throw off the time alignment between my sub and my mains?  In other words, does the ADC/DAC conversion cause signal delay?  Or is there another easy solution to this problem that I am not seeing?

  I would love to hear how you are tackling this issue.  Thanks.

[CECAA850]

There's already a time alignment issue between your mains and your sub as the length of the horn is shorter in the Lascala than it is in the THT.

 

When I built my HT years ago, the Behringer BFD was what was commonly used as a PEQ for subs.  I'll let one of the guys with newer stuff chime in with what's common today.  You'll need a method of measuring and an EQ.

[Paducah Home Theater]

You'll probably have a time alignment even without horns or a DSP, even plain sealed boxes sitting at the same location will usually be delayed more, you'll see this in Audyssey where the sub distance setting ends up being longer than the physical measured distance.  

 

Look at MiniDSP but only the HD models, like 2x4 HD.  It's too easy to clip them with the normal USB powered ones.  And yes only use it on the sub output.  

[jason str]

EQ options are endless, any method will work.

 

Time alignment is not needed in the subwoofer pass band (under 100 Hz) but using one will not hurt anything either.

[Paducah Home Theater]

6 minutes ago, jason str said:

Time alignment is not needed in the subwoofer pass band (under 100 Hz) but using one will not hurt anything either.

 

Maybe horns have something magical where they are immune to this, but with normal speakers and subs, It's easy to get a null if they're not time aligned.  I have a graph at home where I took about 10 measurements while changing the sub distance 0.1 foot at a time, frequency response near the crossover frequency was all over the charts, anywhere from pretty flat to a horrible null, and everywhere in between.  Of course simply by listening to music, you'd likely never know it's there.  Actually measuring is a different story.  

 

One well known installer makes this mistake, he uses a laser measuring tool to set the Audyssey distance for both the subs and mains.  Well, it produces a big fat null when you do this, just not accurate at all.  

[jason str]

22 minutes ago, MetropolisLakeOutfitters said:

 

Maybe horns have something magical where they are immune to this, but with normal speakers and subs, It's easy to get a null if they're not time aligned.  I have a graph at home where I took about 10 measurements while changing the sub distance 0.1 foot at a time, frequency response near the crossover frequency was all over the charts, anywhere from pretty flat to a horrible null, and everywhere in between.  Of course simply by listening to music, you'd likely never know it's there.  Actually measuring is a different story.  

 

One well known installer makes this mistake, he uses a laser measuring tool to set the Audyssey distance for both the subs and mains.  Well, it produces a big fat null when you do this, just not accurate at all.  

 

Sounds like a phase issue, not delay.

[Paducah Home Theater]

Flipping the phase switch isn't going to fix that.  

[Tarheel TJ]

Ok, so it sounds like the ADC/DAC delay is not an issue then. Good to know.  I think a measurement mic and a DSP equalizer are in my near future.  Now the question is, which one?  I am tempted by the Behringer unit because of the price.  Anybody have any experience with the FBQ units?

[derrickdj1]

First, you need to do some measurements.  Once this is done, correcting peaks and dips using only 2-3 filters may be needed.  Time aligning things will only help.  I posted a sub EQ method in the General Info under the Chicago GTG, page 5.  This should give you some ideal on how get going.  Correcting the FR will employ the concept of minimum phase and take care of most phase issues. 

 

Get an Omnimic, REW, or something similar.  After you have this, you will never want to be without it.

 

If the sub EQ flow sheet appears resonable, I may posted it in the subwoofer section.  There are other ways to go about but, I have used this with many subwoofer combination and it's worked for some difficult placement issues and setups.  Any feedback on the flow sheet is appreciated.

[wvu80]

2 hours ago, MetropolisLakeOutfitters said:

One well known installer makes this mistake, he uses a laser measuring tool to set the Audyssey distance for both the subs and mains.  Well, it produces a big fat null when you do this, just not accurate at all.  

 

Even a dummy like me knows that when Audyssey set sets distance especially for subs, it is not physical distance, it is time.  My sub is physically 14' away but Audyssey sets it at 25', a slight delay from the L/C/R which typically are set a physical distance.

[Paducah Home Theater]

1 hour ago, derrickdj1 said:

If the sub EQ flow sheet appears resonable, I may posted it in the subwoofer section.  There are other ways to go about but, I have used this with many subwoofer combination and it's worked for some difficult placement issues and setups.  Any feedback on the flow sheet is appreciated.

 

Mark Seaton made a very detailed step by step process that gets referred to a lot especially with multiple subs, you may want to cross reference that if you haven't already.  

[wvu80]

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[derrickdj1]

I've read most of the stuff on AVS forum and other sources.  Mine is fairly simple and can be used if you have MCACC, Auddysee or no advaced EQ program, just less steps.  We also have a guy in our area that works with Mark Seaton and has showed us the way they do it.

 

Our subwoofer forum should have a EQ technique flow sheet like some some other forums.  The sub/s are the hardest speaker to integrate in the system and yet, there is no guide on this forum.

[Paducah Home Theater]

First step is to buy a microphone.   Until you do this, you don't know what you've got.  If you look at Cross Spectrum's site, those are calibrated lower than the normal UMIK's.  $100 or so, and REW is free, and very popular, which is good for when questions come up.  I haven't seen anything that justifies spending another $200 on OmniMic.  Way more money and way less people familiar with it.