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



## bairda (Apr 7, 2009)

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-


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## brucek (Apr 11, 2006)

> 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


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## bairda (Apr 7, 2009)

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-


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## brucek (Apr 11, 2006)

> 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


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## Wayne A. Pflughaupt (Apr 13, 2006)

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


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## bairda (Apr 7, 2009)

Wayne A. Pflughaupt said:


> 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.
> 
> ...


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-


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## brucek (Apr 11, 2006)

> 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


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## bairda (Apr 7, 2009)

brucek said:


> I think most people would love to have such smooth plots.
> 
> You have very little to worry about with those results.
> 
> ...


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!


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## Wayne A. Pflughaupt (Apr 13, 2006)

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


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## bairda (Apr 7, 2009)

Wayne A. Pflughaupt said:


> 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-


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## JRace (Aug 24, 2006)

Hmm...two schools of thought I guess, but there are some experts (Earl Geddes comes to mind) that actually recommend different sub woofers to achieve the smoothest in room response at multiple locations.

I myself have been experimenting with a dual 8" Aperion Audio combined with a 12" sonotube style sub.
I will be getting a real measurement rig this week and hope to take some measurements.


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## tonyvdb (Sep 5, 2007)

JRace said:


> Hmm...two schools of thought I guess, but there are some experts (Earl Geddes comes to mind) that actually recommend different sub woofers to achieve the smoothest in room response at multiple locations.


I agree, I was in the other camp before I tried adding a second sub from a different manufacturer and it made a huge difference in the low end response. I spent several days tweeking both subs and to my ears it "sounds" great or should I say "feels" great. I have not done any REW graphs of the room so that may say a different story.:hide: but is that not the ultimate goal, to have it sound good?


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## bairda (Apr 7, 2009)

JRace said:


> Hmm...two schools of thought I guess, but there are some experts (Earl Geddes comes to mind) that actually recommend different sub woofers to achieve the smoothest in room response at multiple locations.
> 
> I myself have been experimenting with a dual 8" Aperion Audio combined with a 12" sonotube style sub.
> I will be getting a real measurement rig this week and hope to take some measurements.


I saw that thread over @ avs. It seems to stir strong debate amongst the serious hobbyists. 

Lets say that I could add another, different sub from the PB13. I have a ported 12" Paradigm PW2200 and a sealed Supercube Reference. Which one would probably work better to smooth it out? 

Thanks,
-Alex-


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## Wayne A. Pflughaupt (Apr 13, 2006)

Something to keep in mind when you see those "debate threads": People who find the "magic bullet" for their room tend to dogmatically think it will be the "magic bullet" for every room, despite the fact that every room is different, and what works in one won't necesarily work in another. Likewise, what _doesn't_ work on one room won't necessarily not work in another either. As such, experimentation is never a bad thing. Fortunately, we have REW to verify if our perceptions of "improvement" are valid or not. I seldom see anyone show any graphs in those debate threads to back up their perceptions, however...

Regards,
Wayne


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## bairda (Apr 7, 2009)

Wayne A. Pflughaupt said:


> Something to keep in mind when you see those "debate threads": People who find the "magic bullet" for their room tend to dogmatically think it will be the "magic bullet" for every room, despite the fact that every room is different, and what works in one won't necesarily work in another. Likewise, what _doesn't_ work on one room won't necessarily not work in another either. As such, experimentation is never a bad thing. Fortunately, we have REW to verify if our perceptions of "improvement" are valid or not. I seldom see anyone show any graphs in those debate threads to back up their perceptions, however...
> 
> Regards,
> Wayne


I agree.

Just for fun I tried adding the Paradigm PW2200 back into the mix with the PB13 ultra. After much moving of the sub, adjustment of phase and gain, I got what I thought was a good compromise between the one problem seating area and the other good areas where I wasn't killing the good too much while improving the bad. Measuring with REW and rechecking all the results I was sure that I was going to have bass Nirvana.

So I put in "Flight of the Phoenix" Blu-Ray and cranked up the crash sequence for a little A/B comparison of the Ultra by itself and the Ultra with the PW2200. Long story short, boominess in the "good seats" and not much noticeable improvement in the one bad location compared to the Ultra by itself. So ultimately I just left the Ultra by it self, realizing that I need to stop pushing that edge for awhile and just enjoy the good sound I have.

I did learn a couple of important lessons, one of which you described above. There is no magic bullet for everyones bass issues. The second lesson, and the more important one I think, is that the ultimate criteria for good sound is not the measurements you get from any programs but how it sounds to your own two ears. REW and measurement will get you going in the right direction, but ultimately you will have to decide what sounds good to you. 

Thanks for the help!
-Alex-

Hey, wait...I didn't try my Supercube Reference in the mix. Maybe that will do the trick! Or maybe the Ultra, the Paradigm and the Supercube....Or maybe......:scratchhead:


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## Wayne A. Pflughaupt (Apr 13, 2006)

> The second lesson, and the more important one I think, is that the ultimate criteria for good sound is not the measurements you get from any programs but how it sounds to your own two ears. REW and measurement will get you going in the right direction, but ultimately you will have to decide what sounds good to you.


Yup. I've got plenty of equalized graphs for my subs on file that look great but didn't sound good. :rolleyesno:

Regards,
Wayne


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## sickboy013 (Feb 28, 2009)

I tried adding in the onkyo s5100 sub with my premier acoustics pa-120 this last weekend. The onkyo sub is not terrible, but is not great by any means (10" 290W peak). With the several locations I tried it sounded horrible. I had the gain all the way down on the onkyo sub and it still sounded like it was being overdriven. It really took away the nice clean bass I get from the pa-120.

So I know for me that it's not a good idea. I'm way happier with just the pa-120 running.


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