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[OTR-jkl]

If I add a 2nd sub, theoretically I will only have to use somewhere near about 1/2 the power on both than what I'm using for 1 now. IOW, I should be able to turn the level of 2 subs down to about 1/2 of where my 1 is operating at now. Yes? No? Kinda...?

I'm sure its a little more complicated than that but is that about the sum of it? or will I get into a whole lot more tuning issues by adding a 2nd...?

Thanks.

[seriousfun]

You will probably get between 3 and 6 dB extra gain by adding a second sub.

If you put the second sub on top or near the first, you will get the most gain from coupling.

If you position the second sub somewhere else in the room, from your listening position you may or may not get 3 dB of gain, depending on the room modes each subwoofer excites. In some cases, this positioning can use one subwoofer to excite different modes than does the first one, resulting in flatter frequency response, but in practicality this happens in very few rooms.

6 dB is actually a lot of headroom. Bass needs a lot of headroom. Enjoy!

[Andy Krehm]

OTR-jkl wrote on Fri, 02 June 2006 15:30

If I add a 2nd sub, theoretically I will only have to use somewhere near about 1/2 the power on both than what I'm using for 1 now. IOW, I should be able to turn the level of 2 subs down to about 1/2 of where my 1 is operating at now. Yes? No? Kinda...? I'm sure its a little more complicated than that but is that about the sum of it? or will I get into a whole lot more tuning issues by adding a 2nd...? Thanks.

I used a single sub for years. Recently, based on positive comments posted by others, I tried stereo subs.

I would never, ever go back! Mind you, my room is on the small side and the mains are Lipinski 505's which roll off fairly high. So, because of that, my Velodyne DD-10 subs are calibrated higher than most set-ups. I was amazed at the amount of subtle stereo information comes from the upper range of the subs. They provide a perfect foundation for the Lipinski's, much better than a single sub did. With full range mastering towers, the stereo image would already be there right down to 20 or 30 Hz and in that case, using a single or stereo sub would make little to the the stereo field.

When our new room was tuned by the designer, we spent a lot of time trying the subs in different positions. The most useful ones were directly below the satellites, off the floor, and secondly, just to the outsides. Of course we tried the inside as well, just to be thorough. The clear winner and permanent position is now just outside and below the mains.

The other benefit is that there are very few "hot spots" as the stereo subs smoothed them out. I can't remember about the power difference but I'm pretty sure running two subs means that each one is working less than a single.

Andy,

Silverbirch Productions.

[zetterstroem]

it's called stereo.... i think it's here to stay  

two subs rocks

[bblackwood]

After adding my second DD12 a couple of years ago, I was surprised at the diff. There are lots of potential explanations (and it's likely a combination of all of them), but one not mentioned so far in this thread is the difference between electrically summing the signals and doing so acoustically...

[Andy Krehm]

bblackwood wrote on Sat, 03 June 2006 09:38

After adding my second DD12 a couple of years ago, I was surprised at the diff. There are lots of potential explanations (and it's likely a combination of all of them), but one not mentioned so far in this thread is the difference between electrically summing the signals and doing so acoustically...

Huh? Please explain!

Andy,

Silverbirch Productions.

[OTR-jkl]

Thanks for the help. I figured it would be a benefit.

As for placement, in this room it will have to be stacked on top of the current sub. I'll turn the first one on its side and then put some rubber feet on the side of the 2nd and lay it on top. Hopefully it will work well that way since there are very few other options...

[bblackwood]

Andy Krehm wrote on Sat, 03 June 2006 09:04

bblackwood wrote on Sat, 03 June 2006 09:38 After adding my second DD12 a couple of years ago, I was surprised at the diff. There are lots of potential explanations (and it's likely a combination of all of them), but one not mentioned so far in this thread is the difference between electrically summing the signals and doing so acoustically... Huh? Please explain!

A signal common equally to both channels will give you a 6dB increase in gain when summed electrically. The same thing done acoustically will rarely give you the same 'ideal' gain you get from the electrically summed signal.

[Dave Davis]

In discussions with REL, it was recommended that we consider opposing front/back corners of the room.  While I had all sorts of reasons NOT to go with this in my mind, the more I thought about it, the more sense it made.  The underlying reasoning says that by putting them front/back you equalize pressure changes resulting from the sub's operation, while the opposing corners improve localization.  We're definitely going to try it out and measure/listen.

-d-

[barefoot]

bblackwood wrote on Mon, 05 June 2006 05:10

A signal common equally to both channels will give you a 6dB increase in gain when summed electrically. The same thing done acoustically will rarely give you the same 'ideal' gain you get from the electrically summed signal.

You're in the right ballpark Brad, but I think it can be expressed more specifically.   First of all, putting the signal through two subs rather than one yields lower distortion.   Bass mostly runs up the middle, so that's 1/2 the amplitude and 1/4 the power going into each sub.    Secondly, subs act as antinodes with respect to room modes.   Two subs placed in different locations make the modal structure in the room more complex than a single sub and can actually help break up stronger modes, especially if you place them near natural nodal points.  

Thomas

[matucha]

Like putting subs near the max position of the weaker modes and near the null of the dominant (over the top) mode?

[OTR-jkl]

So if I have any low-end problems (likely) and add a 2nd sub placing it on top of the existing one, will I then accentuate those problems making them worse?

Also, do subs like to be run hot or do they do better at a lower setting?

[barefoot]

OTR-jkl wrote on Fri, 09 June 2006 08:31

So if I have any low-end problems (likely) and add a 2nd sub placing it on top of the existing one, will I then accentuate those problems making them worse??

Yeah, it will probably make things worse

OTR-jkl wrote

Also, do subs like to be run hot or do they do better at a lower setting?

Pretty much every speaker works better at lower levels.  Lower level means lower distortion - one of the advantages of dual subs I mentioned above.  

[OTR-jkl]

Diggin' up old bones here.......

I've moved into a new room which is much larger than my previous little box and, so far, things are much easier to dial in. I'm trying to tighten up the bottome end a bit. I've put my 2 subs about 3-4' apart from each other close to the front wall and have (somewhat) decoupled them from the floor. I'm wanting to experiment with their placement and have a question or 2:

How far apart should the subs be from each other (the room is about 12' wide)? How close to the wall should they be? How far from the corners? Is there some formula for figuring a starting point for this? Do they need to be time-aligned with the mains (by physically aligning the drivers)?

I'm sure I'll have more questions as I play with this....
Thanks.

[Bob Olhsson]

I screwed around with subs for twenty years. What finally worked for me translation-wise was placing the subs right next to the speakers, treating it as a full range speaker and dealing with the low frequency room issues.