Adding a second sub: not the same as primary...

[bairda]

I have recently added a SVS PB13 Ultra to my HT. I love its ability to dig lower than my previous subs: a paradigm PW2200 and a Supercube Reference. For most of the positions in my theater the PB13 sounds good. However there are two seats that seem to have pretty nasty nulls at ~19hz and 60 hz. I have tried playing with the Phase and different sub locations and this would only make the other positions worse.

I am wondering if I could add one of my old subs back into the mix and smooth out the problems. I know that adding a additional sub that is NOT the same as the current is not recommended, but is it really going to kill the performance of the PB13? Am I better off not even trying it?

If I do try it, should I get a equalizer like the Anti-Mode 8033 to help balance the two subs and compensate for the delay?

I am not looking to increase the SPL, just balance the bad spots.

Thanks,
-Alex-

[brucek]

I am wondering if I could add one of my old subs back into the mix and smooth out the problems.

No.

is it really going to kill the performance of the PB13?

Yes.

I am not looking to increase the SPL, just balance the bad spots.

And that's the root of the problem when adding a good sub with one that is more challenged.
The good sub and bad sub are additive at all frequencies. So they both add at 60Hz because they can. What happens at 15Hz - there's only one sub at that frequency? You now have a peak at 60Hz, so you have to turn down the good one. The result is that the good sub dumbs down to the poor subs response.

I know it's tempting to think that more is better, but it isn't. If you want a second sub, then add an identical model or at least one with identical specs.

brucek

[bairda]

Thanks for the information! I was suspecting that this would be the case.

So I guess that the only way to get rid of the nulls is to get another PB13 or to apply room treatments?

-Alex-

[brucek]

So I guess that the only way to get rid of the nulls is to get another PB13 or to apply room treatments?

Yeah, positioning certainly will work, but not for all seating positions over a large area. There's usually a trade off.

Multiple subs is tricky. It can take a lot of work to get them to fight each other to produce a smooth response over the large area. Some people are lucky and others are not - they give up and co-locate the two. In those cases, that's quite an expense to get some extra headroom if you don't really need it.

Maybe check out our acoustics section and get advice on treatment.

brucek

[Wayne A. Pflughaupt]

Yeah, like brucek said, dual separately-located subs are usually tricky, but it can't hurt to try. Using REW's real-time feature could eliminate the guess work and minimize the time spent. I wouldn't waste my time on the 19 Hz null, since the second sub probably won't get that low anyway. Maybe you could find a location for the second sub that could "fill in" the 60 Hz null at those seats, and keep its volume low enough so that its effect on the main sub would be minimal. The goal would be to improve the null, not necessarily totally eliminate it, especially at the expense of the main sub's response.

Before even trying, take in consideration what the 60 Hz null is like. If it's broad, then this exercise might be worth the effort. However, if it's narrow and deep it won't be readily audible anyway, so no sense wasting your time with this.

Regards,
Wayne

[bairda]

Wayne A. Pflughaupt wrote:

Yeah, like brucek said, dual separately-located subs are usually tricky, but it can't hurt to try. Using REW's real-time feature could eliminate the guess work and minimize the time spent. I wouldn't waste my time on the 19 Hz null, since the second sub probably won't get that low anyway. Maybe you could find a location for the second sub that could "fill in" the 60 Hz null at those seats, and keep its volume low enough so that its effect on the main sub would be minimal. The goal would be to improve the null, not necessarily totally eliminate it, especially at the expense of the main sub's response.

Before even trying, take in consideration what the 60 Hz null is like. If it's broad, then this exercise might be worth the effort. However, if it's narrow and deep it won't be readily audible anyway, so no sense wasting your time with this.

Regards,
Wayne

To give you an idea of what the issues are here are some measurements. I have a central measurement in the middle of the listening area that looks pretty good:

Center of Listening Area


Center of Listening Area waterfall

Here is the couch to the right that looks pretty good to:

Right couch of Listening Area


Right couch of Listening Area waterfall

And here is the problem area to the left of the center of the listening area:

Left couch of Listening area


Left couch of Listening area waterfall


As you can see on the left couch measurement, quite a null at around 19hz and also a drop qound 50 hz that stays low through 85hz.

Could this be a phase problem? I am willing to spend some $$ on treatments or an equalizer like the BFD, Anti-Mode or the new EQ1 from SVS.

What do you think?
Thanks,
-Alex-

[brucek]

What do you think?

I think most people would love to have such smooth plots.

You have very little to worry about with those results.

The dip in the yellow graph at 19hz is a sharp dip that wouldn't probably be perceivable. It is a typical cancellation caused by a reflection.
The dips around the crossover could likely be ameliorated with the phase or distance controls. Either way, they aren't bad enough to consider a second sub to remove them.

BTW, switch the waterfall graphs to LOG from LIN mode to get the full graph.

brucek

[bairda]

brucek wrote:

I think most people would love to have such smooth plots.

You have very little to worry about with those results.

The dip in the yellow graph at 19hz is a sharp dip that wouldn't probably be perceivable. It is a typical cancellation caused by a reflection.
The dips around the crossover could likely be ameliorated with the phase or distance controls. Either way, they aren't bad enough to consider a second sub to remove them.

BTW, switch the waterfall graphs to LOG from LIN mode to get the full graph.

brucek

Thanks! Looks like I have it better than I know!

Guess I will do the hardest thing there is...enjoy my current setup!

-Alex-

PS - I have corrected the waterfalls. Thanks for pointing that out!

[Wayne A. Pflughaupt]

Yeah, probably not bad enough to worry about. Most movie bass is nothing but "boom" anyway. If you change your phase or distance controls, be sure and make a note of their current settings, as changing them may whack response at the two places where it's good now.

Regards,
Wayne

[bairda]

Wayne A. Pflughaupt wrote:

Yeah, probably not bad enough to worry about. Most movie bass is nothing but "boom" anyway. If you change your phase or distance controls, be sure and make a note of their current settings, as changing them may whack response at the two places where it's good now.

Regards,
Wayne

I will see if I can tweak it. However, I think that Audyssey really is sensitive to the distance, so I have to be careful there.

Thanks for all the help!
-Alex-