Adding a second sub - AVS Forum
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post #1 of 15 Old 10-18-2012, 05:08 PM - Thread Starter
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Considering adding a second sup to our 5.1 setup. Would it be perfectly fine if we purchased a second sub, same model as the first, then simply connect the two to the single AVR input using an RCA splitter?
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post #2 of 15 Old 10-18-2012, 05:13 PM
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Yes. No problem.


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post #3 of 15 Old 10-18-2012, 06:08 PM - Thread Starter
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Thank you. Forgot to ask if that would be the better of two options:

1. Y-connecter
2. Connecting each sub to a separate input

Our single sub is currently connected to the Audio Pre-Out section where there are 8 inputs' 4-L and 4-R, two each for FRONT/SURR/SUBW and SURR-B. Our single sub is connected to the lower SUBW input which is R. Question is that the input directly above that which is L, is labeled CENTER. The other three inputs; FRONT/SURR/SURR-B all have L & R inputs w/o any other designation. Only the SUBW input R has a differently labeled input CENTER just above it.

With that in mind, does it mean that top input labeled CENTER should only be used for a center channel and not for a second subwoofer?
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post #4 of 15 Old 10-18-2012, 06:14 PM
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What receiver do you have?


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post #5 of 15 Old 10-18-2012, 06:34 PM - Thread Starter
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NAD T-747
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post #6 of 15 Old 10-18-2012, 06:54 PM
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I'm looking at the rear diagram. It looks to me that there is only one subwoofer pre-out (directly above the center output). The L and R don't apply to the two outputs here. They are for the Fronts, Surrounds, and Surround-Backs.

Your best and only option is to split the signal from the sub pre-out to both of your subs. Some receivers with two sub pre-outs will allow for distinct level and delay adjustments for each, but others (probably the majority), are identical, which would net the same result as using a splitter, as you will do. Should work just fine. You will want to re-run your calibration after adding the second sub. If you are inclined and have the flexibility, you can also experiment with different placement arrangements for the two subs.


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post #7 of 15 Old 10-18-2012, 07:01 PM
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Yep only one sub preout on that panel. Like Baniels says. I have an Onkyo 7.2 avr but it just has an internal y cable...

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post #8 of 15 Old 10-18-2012, 08:36 PM - Thread Starter
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Thank you gentlemen. I shall proceed with the Y splitter/connector to the one input jack labeled SUBW, which is on the bottom, the R level for the other inputs. The jack labeled CENTER is above it on the L level of the other inputs.

I thought there might be the outside chance that the CENTER could be used for a second sub connection but now I think you have it right in connecting both using a Y splitter/connector to the SUBW input only.

Again, thank you very much for your help.
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post #9 of 15 Old 10-19-2012, 05:32 AM
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Quote:
Originally Posted by batuche View Post

Considering adding a second sup to our 5.1 setup. Would it be perfectly fine if we purchased a second sub, same model as the first, then simply connect the two to the single AVR input using an RCA splitter?

This Harman (JBL, Infinity, Revel) paper seems to give some insight to recommended ways for deploying 2 subwoofers for optimal results:

http://www.aes.org/e-lib/download.cfm?ID=13680&name=harman

To summarize they tested the following configuations:



The dots are the seating locations and the numbers represent subwoofer locations.

From those configurations they found the following results for uniformity of sound field over 16 seating positions for the best speaker configurations:



The x and y coordinates in the pictures below are room dimensions. The configurations with the least shading are the most desirable.

The subwoofers were in effect connected with Y cables. The side wall locations gave the best uniformity of bass distribution over likely seating locations.
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post #10 of 15 Old 10-21-2012, 07:37 PM - Thread Starter
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Holy sound waves, Batman! This certainly explains what one can do with an engineering degree or two. Now if we could only rearrange all our furniture. This is really, really in-depth stuff however our initial speaker layout will not match any of the placement pictures.

Our HT/Music room measures 12.5’ x 22.5’ with the listening/viewing done across the center of the short dimension, so we’re relatively close to everything. The two 8” subs will end up about 8’ apart with stand mounted speakers about 5.5’ apart just inside the two subs with the TV centered. Either sub will be about 6’ in from the nearest corner location

Like most audio decisions for the home, we’re doing this THINKING that it will improve/balance the sound. We’ll only KNOW after trying it. Your pictures suggest great alternative locations for two subs, especially configuration #3, but that it would prove impractical the way our room is laid out. If our idea doesn’t work out we’ll just go back to a single sub which is pretty ok as it is.

Thank you, arnyk.
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post #11 of 15 Old 10-24-2012, 05:11 AM
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When using many subwoofers, the result of stacking them would also be of interest. There are also other interesting placements, namely those that yield an equally distanced line of subwoofers when taking the wall-mirrored locations into consideration.

Personally, I has two stacks of 4 subwoofers (sealed, 12" NHT 1259:s) in the front corners of my livingroom, but that's to a large degree a matter of not being too intrusive about placement. It made quite a difference, not as much from 6 to 8 unless we go into the infrasonic range where the added pump capacity comes into play.

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post #12 of 15 Old 10-24-2012, 05:23 AM
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Quote:
Originally Posted by Nightlord View Post

When using many subwoofers, the result of stacking them would also be of interest. There are also other interesting placements, namely those that yield an equally distanced line of subwoofers when taking the wall-mirrored locations into consideration.

Stacking wasn't tried in the tests shown in post #9 above because it was believed that spreading them around would be more to the point. I think that point was made because with every increase in the number of subs in the optimal but vastly different locations, greater bass uniformity was obtained.
Quote:
Personally, I has two stacks of 4 subwoofers (sealed, 12" NHT 1259:s) in the front corners of my living room, but that's to a large degree a matter of not being too intrusive about placement. It made quite a difference, not as much from 6 to 8 unless we go into the infrasonic range where the added pump capacity comes into play.

The evidence in post 9 seems to be a strong suggestion that:

(1) Putting 2 subs in the front corners is suboptimal when you have 8 subs to work with. My first cut on stacks of subs is that they are just a way to add undistorted SPL capability over single subs. If you are going to use 2 subs or 2 stacks of subs, put them along the side walls if you can.

(2) Your next option after the side walls is stacks of 2 in all 4 corners. This might be even better.
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post #13 of 15 Old 10-24-2012, 05:41 AM
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Quote:
Originally Posted by arnyk View Post

The evidence in post 9 seems to be a strong suggestion that:
(1) Putting 2 subs in the front corners is suboptimal when you have 8 subs to work with. My first cut on stacks of subs is that they are just a way to add undistorted SPL capability over single subs. If you are going to use 2 subs or 2 stacks of subs, put them along the side walls if you can.
(2) Your next option after the side walls is stacks of 2 in all 4 corners. This might be even better.

Besides nitpicking that front corners are along the side walls cool.gif I don't disagree that it couldn't be done better if all things would have been possible in the room. In my case it's not.
(There isn't really a back left corner for instance and the side walls are quite occupied with more needed things - cupboards for china etc)

On the other hand, the performance I have exceeds my needs... and the theoretical capacity exceeds what can be used without causing damage. biggrin.gif There are definitely other acoustical details that should be handled with higher priority than improving subwoofers further (such as wall-to-wall carpet and side-wall absorption (or/and diffusion)).

Stacking does flatten the resonanse behaviour of a room on some of the modes, so if the Harman-way isn't possible for some - like me - do try!

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post #14 of 15 Old 10-24-2012, 06:04 AM
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Quote:
Originally Posted by Nightlord View Post

Stacking does flatten the resonance behaviour of a room on some of the modes, so if the Harman-way isn't possible for some - like me - do try!

If we turn the Harman results on their side, it appears that instead of stacking subs on top of each other, the upper sub should be stacked with a spacer so that it touches the ceiling.
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post #15 of 15 Old 10-24-2012, 06:14 AM
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Quote:
Originally Posted by arnyk View Post

If we turn the Harman results on their side, it appears that instead of stacking subs on top of each other, the upper sub should be stacked with a spacer so that it touches the ceiling.

Yes. Mine are like that - I'm just using another two subs as spacers. cool.gif



Excuse the mess - we have kids. smile.gif

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