# setting up dual subs... input please!



## Todd Anderson (Jul 24, 2009)

I'm geting ready to integrate dual subs into my HT. My AVR only has one SUB-out. So, I'm going to be splitting that feed. I've attached the 3 best possible placement solutions.

Based on the dual-sub Audioholics article, it looks like Configuation 6 and 5 would be my best first shots... followed up configuration 7. I currently run configuration 2 with an HSU Sub and an Energy Sub (Energy's gain is turned down quite a bit) as this produced the best REW results, so I guess I could always run it in this configuration also.

Ultimately, space-wise, Configuration 6 and 7 would be the best... here's my question though:

My Elite AVR is going to ask me to input a distance for the "sub" (or will try to measure it, itself). I'm assuming that the AVR will take this measurement and use it to time manage the LFE. If I use configuration 6 or 7, what do I realistically do? Obviously, this means that the front and back subs will be playing the same LF at the same exact time... 

I read somewhere - can't remember where - that I should measure from both subs and divide by 2. So if the front sub is 11 feet away and the rear sub is 2 feet away, I would input 6.5' into my AVR.

I know that if I roll with configuation 5, I won't have this problem... but the subs will be REALLY close to my primary seating position. Think this will create a problem??


A side from placement, my plan is to play my AVR's white noise... adjust each sub's gain using a Radio Shack SPL meter (and it's correction table) so that each sub is playing the test tone about 72-73 dBs (my mains are calibrated to 75 dBs). Then, I will play both subs at the same time and adjust the output through my AVR to be just a few dB's above 75 dB's). Does this sound right?

Thanks for all of your input! :T


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## Peter Loeser (Aug 11, 2012)

Why not start with what you already had since it worked for you, and go from there?


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## Todd Anderson (Jul 24, 2009)

Definitely could... I also know that when I integrated the other two subs, I didn't follow the steps I outlined. I may not have done it correctly.

Ultimately, I'd like to try (and measure w/ REW) different the different positions I've diagramed just to make sure I have the best placement for these new subs...

Mainly interested in understanding how to manage the sub distance issue if I split them apart to the front and back of the room?


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## sdurani (Oct 28, 2010)

Configurations 5 & 6 are more geared for getting better consistency across the seating area than getting smoother bass. If you are using a room correction program in your receiver that measures at multiple locations, then it helps to have consistency across the seating area. 

One of the biggest problems with equalization is that fixing a problem in one seat can create a problem elsewhere. If you measure all three seats on your couch, and the centre seat has a peak at 50Hz while the other two seats are fine at that frequency, then bringing down that peak at the centre seat will now create a dip at 50Hz in the other two seats. 

The solution is to make the response as close to the same as you can in all seats. Doesn't have to be better, just more consistent. This way, the room correction systems sees similar peaks & dips in all seats and can fix more of those problems (to the benefit of all the listeners, no matter where they're seated). 

According to the latest research paper on subwoofer placement by Todd Welti of Harman (who might have gotten a mention in the Audioholics article), configuration 5 will result in less variance from seat to seat than configuration 6. The side benefit, of course, is that both subs will be equidistant from your main listening position, making it easier for you to set the subwoofer distance on your receiver. 

Having the subs nearby shouldn't be a problem, since you will set distances and levels so that they sound the same distance away as your main speakers. In fact, having the subs in the nearfield might even yield some benefits, since you'll hear more of your subs and less of the room (which is what causes all the problems in the low frequencies).


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## Andre (Feb 15, 2010)

I would probably try the Energy front and center and adjust its output to woofer status to reinforce the front speakers and center. Once that is done and your happy add the HSU in and do the sub crawl to find its location.


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## Todd Anderson (Jul 24, 2009)

Andre said:


> I would probably try the Energy front and center and adjust its output to woofer status to reinforce the front speakers and center. Once that is done and your happy add the HSU in and do the sub crawl to find its location.


Ah... the Energy and the HSU are history. I have two new, matching, subs.


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## Todd Anderson (Jul 24, 2009)

sdurani said:


> Configurations 5 & 6 are more geared for getting better consistency across the seating area than getting smoother bass. If you are using a room correction program in your receiver that measures at multiple locations, then it helps to have consistency across the seating area.
> 
> One of the biggest problems with equalization is that fixing a problem in one seat can create a problem elsewhere. If you measure all three seats on your couch, and the centre seat has a peak at 50Hz while the other two seats are fine at that frequency, then bringing down that peak at the centre seat will now create a dip at 50Hz in the other two seats.
> 
> ...



Thanks for you input. Appreciate it. Config 5 does look optimal. Do you think that it would be a problem if I can't center them along those side walls? Technically the middle point on my side walls is 8.5 feet... I think, realistically, my room will allow the subs to be about 7 feet from the front wall. So the symmetry up and down the side walls is lost some... hmmmm.


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## Andre (Feb 15, 2010)

Sorry considering what is listed on your "my system" and first post also has the HSU and Energy I thought that is what you are using.

The sub crawl will work with dual subs just do it twice with the first sub running for the second placment.


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## sdurani (Oct 28, 2010)

27dnast said:


> Do you think that it would be a problem if I can't center them along those side walls?


Not as long as you understand that it will result in less seat-to-seat consistency than midpoint placement. The effect doesn't fall off like an on/off switch, so you have a bit of flexibility, though at the price of a little less effectiveness.


27dnast said:


> I think, realistically, my room will allow the subs to be about 7 feet from the front wall.


How come? The sub is only 18" wide, so that leaves 9'5" of space between them. If you place them at 8'6" from the front, will the foot rest on your seating bump into the subs? Is your seating more than 9'5" wide?


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## phillihp23 (Mar 14, 2012)

What direction are the woofers facing in configuration 5 ?
I'm very interested in this conversation as I have dual subs in my HT room. I am trying to get optimum placement (sound) for them also. Currently mine are in the back left and right corners of the room.


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## Todd Anderson (Jul 24, 2009)

sdurani said:


> If you place them at 8'6" from the front, will the foot rest on your seating bump into the subs? Is your seating more than 9'5" wide?


Yes. Unfortunately this is the case...


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## Todd Anderson (Jul 24, 2009)

I could pull off the mid points of the front and back wall, tho.

I read the white paper by Todd Welti of Harman... Pretty intense, info-wise. I didn't see, however, where he stated that the mid-point of the side walls is better than the mid-point of the front and back walls.

His overall conclusion was:

_One subwoofer at each wall midpoint is the best in terms of Std, Max-ave and Max-min but does not support low frequencies particularly well. Two subwoofers, at opposing wall midpoints, performs very nearly as well as four at the midpoints and gives a much better LF factor. One subwoofer in each corner also has good low frequency support, but does not perform quite as well as one subwoofer at each wall midpoint, in terms of Std, Max-ave and Max-min. If cost and aesthetics are considered, subwoofers at 2 wall midpoints is preferred._


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## sdurani (Oct 28, 2010)

27dnast said:


> I read the white paper by Todd Welti of Harman... Pretty intense, info-wise. I didn't see, however, where he stated that the mid-point of the side walls is better than the mid-point of the front and back walls.


The paper you read is a good starting point even though it was released 10 years ago. Welti presented a new paper last month, which can be purchased from AES. However, you can download colour versions of his presentation slides (the paper only includes black & white versions) for free from the Harman site; it's the item at the top of *this page*. 

The slides have 49 mean spatial variance (MSV) graphs, with each combining 3 variables: room dimensions, seating location and number/configuration of subwoofers. One of the 7 seating variations has a Small seating area in the Rear half of the room (SR). If you look at the 7 subwoofer configurations for that seating area, taking into account the width & length of your room (X and Y axis, respectively), you'll see that the Left-Right Midpoint (LRM) configuration yields less variance than Front-Back Midpoints (FBM). The only way to do better is by using 4 subs.


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## ALMFamily (Oct 19, 2011)

Since I will soon be running 3 subs - subscribed! Very interested to see how you come out Todd.


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## Todd Anderson (Jul 24, 2009)

Here's a desktop picture of 6 REW graphs... each graph represents the subs positioned at a specific location (I took 3 measurements for each sub position... one at the center seating position, one at the seating position to the far right, and one at the seating position to the far left... hence the reason each graph has 3 lines). I'm hoping that each graph gives a pretty good idea what's happening across the seating, LFE response-wise, for each sub configuration.

To fit them on the screen, I clipped the dB scale on the left side of each graph... but you can see the Hz along the bottom. Each frequency sweep was from 1-100Hz, completed four times.

I've labeled each graph in it's upper right corner, 1-6.

You pick --- which one would you choose?

And what would you do, EQ-wise?


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## Peter Loeser (Aug 11, 2012)

Overall you seem to be getting nice uniform response from the three different seating locations. To me, #1 and #3 look best from 10-80Hz, with the exception of the one seat in #3 experiencing the dips around 40Hz and 70Hz.


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## Todd Anderson (Jul 24, 2009)

I'm thinking that graph #1 is looking the best... I agree with you about 3. Looks almost as good as 1 with the exception of that one seating position that drops off a cliff around 70Hz.

So, let's say I go with #1... it looks like I have a nice little curve... probably the best of all 6 configurations.


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## sdurani (Oct 28, 2010)

27dnast said:


> You pick --- which one would you choose?


Easily the first one, with the subs at the quarter points on the front wall. Variation seems to start around 60Hz, so that might be a good point to cross over to the main speakers.


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## vann_d (Apr 7, 2009)

#1 defo looks best to me both from a consistency perspective and a house curve perspective...gl


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## Todd Anderson (Jul 24, 2009)

sdurani said:


> Easily the first one, with the subs at the quarter points on the front wall. Variation seems to start around 60Hz, so that might be a good point to cross over to the main speakers.


I did give them their final resting spots at the 1/4 points on the front wall... at least for now.

Interesting comment you have about the variations beginning about 60 Hz. If I did xover there, wouldn't the same problem just be picked up by my front three speakers?


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## ALMFamily (Oct 19, 2011)

27dnast said:


> I did give them their final resting spots at the 1/4 points on the front wall... at least for now.
> 
> Interesting comment you have about the variations beginning about 60 Hz. If I did xover there, wouldn't the same problem just be picked up by my front three speakers?


If I understand correctly, no. The reason is that you are mostly likely seeing boundary interactions, and since the front three speakers are not in the same location as the subs, there are different boundary interactions.


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## Todd Anderson (Jul 24, 2009)

Ok. I'll fool around with it and see what happens..


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## sdurani (Oct 28, 2010)

27dnast said:


> Interesting comment you have about the variations beginning about 60 Hz. If I did xover there, wouldn't the same problem just be picked up by my front three speakers?


Above the crossover there's 3 transducers at different locations from the subs, so you'll have to measure and see whether you pick up the same problem. If so, you could try doing what you did with the subs: measure from all three seats, but this time send the same signal (maybe up to 200-300Hz) to all 3 speakers, moving the left and right speakers closer and wider apart until you get a compromise you can live with. 

The reason I said 'compromise' is because you have to weigh seat-to-seat consistency in the low(er) frequencies against soundstage width. For example: if you find that the three seats get the most consistent results when the 3 front speakers are a foot apart, then that's a non-starter. Besides, as you already know, crossovers aren't brick walls, so there is going to be a transition area between your speakers and subs that may not be as smooth as the speakers or subs alone. There's only so much you can do, so pick the best compromise.


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