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Discussion Starter · #1 ·
I know i've asked this before but I dont think anyone had a clear answer.

I currently have one sub which I've eqed with a BFD. If I were to add another sub, how would I eq the two together?

Eq each sub one at a time or eq both subs running simutaneously?
 

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Since EQ is the last step in setting up a sub (or two), we'll assume that you've used some sort of tool to get the placements as good as possible, and you've applied whatever acoustic treatments you can manage?


If so, the EQ them both together, measuring at the primary listening position.
 

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Discussion Starter · #3 ·
OK DMF, eq them both together......however, I have other people telling me to eq seperately? Which is correct or do I need to just try both methods and see which works best?
 

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Here's the procedure that I recommend:


EQ them separately first, to get them "in the ballpark." Verify that their SPLs are about equal, and if not, adjust the gains to make them so. Then you must EQ them together, because their phases will interact. You may have to make some significant adjustments.


- Terry
 

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Terry,


I guess I don't see the point of spending the time EQ'ing them separately.


Depending on how they interact, might not the results not be worse than just doing them together to begin with?
 

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I find it faster to do them separately first. There are half the number of variables to deal with at once, and you can get lucky and just need minor tweaking for the combination. I don't adjust the two ruler-flat individually -- just approximate.
 

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How does that work, practically? You use one set of filters for one sub, a second set for the second sub. But then when you play them together, now adjust both sets of filters at once?


And that's easier than feeding both subs through one set of filters? I certainly believe you, it just feels like I'm missing the 'how' part of it.
 

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Quote:
Originally Posted by cme
How does that work, practically? You use one set of filters for one sub, a second set for the second sub. But then when you play them together, now adjust both sets of filters at once?


And that's easier than feeding both subs through one set of filters? I certainly believe you, it just feels like I'm missing the 'how' part of it.
Ah, you pointed out a critical assumption I was making! I assumed we were talking about the case of two subs being fed the same signal, but with separate equalizer channels. The BFD has two available channels.


If the subs are on a single EQ channel, and cannot be adjusted independently, then it does no good at all to adjust them separately.


Regards,

Terry
 

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Maybe a dumb question but should not the mains be in the picture too when eq'ing as they would interact significantly with the subs as well specially round about the xover frequencies.
 

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Discussion Starter · #10 ·
Interesting discussion guys. Keep it going.

Seems to me eqing two subs is more of a black art than a science.
 

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Terry, thanks for the clarification. Even with the BFD, it seems a little difficult to adjust both EQ channels at once.


So let's say I run the same signal through the two BFD channels and I use 4 filters per sub. Now I remeasure and find that I now have some monkey business in two places - one that was previously filtered and a second in an entirely new place. I would then:


1) Change the existing filters at the previously filtered frequency, trying to split the difference, then

2) Add a new filter to each sub for the new frequency, again trying to split the difference so that when you add both subs together you get a flat response


Did I understand that as you intended?


dollarman, you'd certainly want to EQ your subs with the mains - I'm still trying to understand where in the chronology this step takes place.
 

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Yes, cme. The procedure is a little easier using an EQ with analog controls. It is best done in real-time, using pink noise and a high resolution RTA. The phase relationships between the two subs at different frequencies are not at all obvious, or even readily measurable.


It is better to EQ the subs separately from the mains, and then use the subwoofer phase control to match them at the xover frequency. Otherwise, you may end up trying to boost a frequency which is simply a phase cancellation between mains and subs.


- Terry
 

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Quote:
I know i've asked this before but I dont think anyone had a clear answer.

I currently have one sub which I've eqed with a BFD. If I were to add another sub, how would I eq the two together?

Eq each sub one at a time or eq both subs running simutaneously?
It depends on what you mean by “add another sub.â€


The hand-down easiest way to add and EQ a second sub is to add an identical sub in the same location as the first. That way the second requires no specific EQing. You can split the equalizer’s output to the second sub, and you’re done.


If you’re adding a non-matching sub to the same location as the first, it should require essentially the same equalizing as the first, since the response curve for the most part is room-induced. However, if one sub is more capable than the other, the weaker one will probably have inferior extension, or less maximum output. Trying to EQ that one to “make†it perform up to snuff with the other one would require a second channel of EQ. It would be best not to mess with this, because you’re asking for all kinds of phase troubles, as Terry noted.


In the case of putting an identical second sub in a second location, be prepared for an equalizing nightmare. The idea is to get uniform volume for both across their entire operating range within a dB or so, and in most rooms this will be a challenge. RTAing each separately with broadband pink noise didn’t get it for me here. I found that when I double-checked with filtered pink noise or sine waves that the two were often 2 dB or more off at specific 1/3- or 1/6-octave frequencies. It was extremely tedious to get both subs EQ’d so that their output was uniform across their entire range.


The exception would be in a perfectly symmetrical shoe-box shaped room where you put the subs in say, front left and right corners. It’s much easier to EQ two subs in that situation than in most others.

Quote:
dollarman, you'd certainly want to EQ your subs with the mains - I'm still trying to understand where in the chronology this step takes place.
Equalize the sub first, then add the L/R mains only, and re-check response. (I don’t fool with using all the mains because of the potential for added phase problems. Stereo music is where your sub accuracy really matters anyway.) Additional EQ may be required to address phase-induced anomalies that may appear an octave or so above and below the crossover point when you add the two mains. My experience has been that they usually respond nicely to EQ. I would think you’d want to adjust a variable phase control before EQing, but since I’ve never used one I’ll defer to Terry’s judgement (assuming he has :) ).


Regards,

Wayne A. Pflughaupt
 

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Quote:
Originally Posted by Wayne A. Pflughaupt
I would think you’d want to adjust a variable phase control before EQing, but since I’ve never used one I’ll defer to Terry’s judgement (assuming he has :) ).
Hi Wayne,


I should elaborate on this. With variable phase controls on multiple subs, they must be adjusted the same after EQ. Otherwise, you just re-introduce inter-sub phase problems. If you have just polarity switches on the subs, then these should be flipped on all subs if necessary, not just on one.


- Terry
 

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Quote:
Originally Posted by Bulldogger
http://www.audioholics.com/news/pres...1DSPsystem.php Velodyne SMS-1 designed to work with any sub. What about this?
It can run multiple subs with one eq setup or you can daisy-chain multiple SMS-1s with different eq setups for each sub (or group of subs!) and have individual as well as linked gain/preset control.


Kal
 

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"Otherwise, you may end up trying to boost a frequency which is simply a phase cancellation between mains and subs. "


It would seem that EQ'ing two subs with one EQ channel could really help here if only one sub has the null when measured from the listening position.


"The idea is to get uniform volume for both across their entire operating range within a dB or so, and in most rooms this will be a challenge."


Do you mean uniform volume from each when measured alone or from both running?
 

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Quote:
Originally Posted by noah katz
"Otherwise, you may end up trying to boost a frequency which is simply a phase cancellation between mains and subs. "


It would seem that EQ'ing two subs with one EQ channel could really help here if only one sub has the null when measured from the listening position.
Yes, that's one of the main advantages to multiple subwoofer positions. And it's even better with separate EQ channels. Then, you can fill in a frequency null in one sub by boosting the other sub's equalizer by around 3 dB at this frequency.

Quote:
"The idea is to get uniform volume for both across their entire operating range within a dB or so, and in most rooms this will be a challenge."


Do you mean uniform volume from each when measured alone or from both running?
You want the combination of the subs to be uniform. You can pretty much rule out the idea of getting each perfectly flat, and expecting the combination to be flat as well.


Regards,

Terry
 

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Agreed. If you can get your mains and 2 subs to within +/-4-5db, you're doing good. The idea is not to get each one flat, but to get the combination as smooth as possible at the listnening position.
 
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