Calling those with multiple subwoofers - AVS Forum
View Poll Results: Why did you incorporate multiple subwoofers in your home theater?
To even-out the bass response in the room 26 32.91%
To increase overall SPL 2 2.53%
To even-out bass response and increase overall SPL 51 64.56%
Voters: 79. You may not vote on this poll

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post #1 of 77 Old 05-12-2014, 01:39 PM - Thread Starter
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Why did you incorporate multiple subwoofers in your home theater?
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post #2 of 77 Old 05-12-2014, 07:30 PM
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I have a large space and a relatively dead space and wanted an awesome subwoofer experience. I ended up with 4 subs that produce a lot of slam and a great tactile experience. With one or two subs the bass in the room was uneven and lacked a little in the spl department for me.

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post #3 of 77 Old 05-12-2014, 07:47 PM
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Another potential benefit is being able to achieve your output goals without having to push your gear too hard. I think a lot of subs die prematurely because people have unrealistic expectations as to how it should fill a room and flog it to death.

I have three subs in my system that can easily play a lot louder than I'll ever listen and I like it that way. Less distortion too.
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post #4 of 77 Old 05-13-2014, 01:21 AM
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Same as Derrick and DPC for me. I have the most disgustingly laid out living room for bass response. So, the main reason is to even out the response in my room, but the extra SPL is nice.

I need three subs just to get a fairly smooth response across all positions, and I have lots of headroom on the SPL, basically, the subs work a lot less hard to achieve the same thing.

Am building a fourth soon.
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post #5 of 77 Old 05-13-2014, 07:52 AM
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To even-out bass response and increase overall SPL. smile.gif
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post #6 of 77 Old 05-13-2014, 11:26 AM
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I voted "To even-out bass response and increase overall SPL" but what it should really say is "To even-out bass response and increase headroom." The SPL shouldn't change or increase if the calibration is done with all the subs running combined. The only thing that will change is the headroom available, (and the smoothness of the FR.)

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post #7 of 77 Old 05-14-2014, 10:55 AM - Thread Starter
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Some questions...

Does having more subwoofers produce bass that sounds "larger" or "bigger"? Just like how bigger speakers, generally, produce a larger sound, does having more subwoofers produce bass that sounds more "expansive"?

If I have 4 subwoofers placed in the 4 corners of the room (well not exactly the corners, more like 4/5th of the wall's length towards the corners), and calibrate each subwoofer individually to 75 dB and then run all 4 together, how hot would my bass end up being? Is this what most do or do they calibrate to 75 dB with all subwoofers operating together resulting in greater headroom as each subwoofer will be working less?
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post #8 of 77 Old 05-14-2014, 02:58 PM
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Calibrate each sub to 70 db at the MLP when using 4 subs. The difference between running one sub calibrated at 75 db will go up to around 10-12 db when the number goes up to 4 subs calibarted at 75 db. this mean the sound at the MLP with be above 85 db if they are all in phase.

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post #9 of 77 Old 05-14-2014, 03:08 PM
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 I voted for "To even out bass response" because that's what I was primarily after but I won't lie, the headroom was a bonus. 
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post #10 of 77 Old 05-14-2014, 03:14 PM
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My room is large, 25 x 18'... One sub was just not cutting it... I have a 12" an a 15" and it still seems weak... Oddly, I used to have two ported subs with dual 10" drivers and there was a lot of mid-bass but nothing below 35Hz. I now have bass below 35Hz but nothing above it...

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post #11 of 77 Old 05-14-2014, 04:02 PM
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I voted to increase overall SPL....although evening out response is the ultimate goal, my room is simply too large to concern myself with that if the SPL is too low. I run in a 6000 cubic foot room and am currently running 6 18" subs pushed by 14.4kW in amps all squarely colocated in the front of the room just so I can reach the SPL I want. Obviously I'm still not there but to me the sound is much better this way.
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post #12 of 77 Old 05-14-2014, 04:46 PM
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Quote:
Originally Posted by Kain View Post

Some questions...

Does having more subwoofers produce bass that sounds "larger" or "bigger"? Just like how bigger speakers, generally, produce a larger sound, does having more subwoofers produce bass that sounds more "expansive"?
I don't know if "expansive" is the right word. The bass is fuller, smoother and less boomy sounding. These can all be attributed to the flatter FR throughout the room.
Quote:
Originally Posted by Kain View Post

If I have 4 subwoofers placed in the 4 corners of the room (well not exactly the corners, more like 4/5th of the wall's length towards the corners), and calibrate each subwoofer individually to 75 dB and then run all 4 together, how hot would my bass end up being? Is this what most do or do they calibrate to 75 dB with all subwoofers operating together resulting in greater headroom as each subwoofer will be working less?
We need way more info before we can provide setup advice:
What subs are they? Ported? Sealed?
Are they all identical?
How big is the room?
Where is the seating placed in relation to the room and the subs?
What receiver or pre/pro do you have?
Do you have any EQ capability besides what's in your receiver or pre/pro?
Do you have any way to measure your response?

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post #13 of 77 Old 05-15-2014, 01:30 AM
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Four subs should be calibrated lower than one sub. Calibrate each sub no more than 70 db at the MLP. I run 4 subs and have to calibrate them to 65-66 db so the autocalibration will not tell me the subs are to loud. I an also in a large space, 53-5600 cu ft. Spreading the 4 subs out as far as I can helps smooth the room response with no loss in spl or tactile feel at the MLP. I have no need to run things hot since the spl in adequate.

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post #14 of 77 Old 05-15-2014, 06:14 AM
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Running 3 subs at the moment, not only to increase SPL but don't want to run them hot, as i most of the time listen at or near reference. Also of course to even-out bass response.

room is 22x16x10
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post #15 of 77 Old 05-15-2014, 07:06 AM
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Quote:
Originally Posted by derrickdj1 View Post

Four subs should be calibrated lower than one sub. Calibrate each sub no more than 70 db at the MLP. I run 4 subs and have to calibrate them to 65-66 db so the autocalibration will not tell me the subs are to loud. I an also in a large space, 53-5600 cu ft. Spreading the 4 subs out as far as I can helps smooth the room response with no loss in spl or tactile feel at the MLP. I have no need to run things hot since the spl in adequate.

I think the distinction here would be if one is level matching or gain matching wouldn't it? For gain matching I set my subs gain for 85 db and let the auto cal do it's thing. 

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post #16 of 77 Old 05-15-2014, 08:24 AM
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I have a combination of 2 vented sub and 2 sealed subs. I am an advocated of level matching the subs at the MLP. The subs all have to have enough spl and power so that one is not over driven. I think in general gain matching is done at 1 or 2 meters so the level at the MLP may be lower. Both techniques work. One of the hardest thing to get right is the impulse response of the system when two or three of the subs are not equal distance from the MLP. Three of my subs are corner loaded which greatly increases the headroom of the system. This results in a lot of slam and great LFE.
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post #17 of 77 Old 05-15-2014, 08:57 AM
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Quote:
Originally Posted by derrickdj1 View Post

I have a combination of 2 vented sub and 2 sealed subs. I am an advocated of level matching the subs at the MLP. The subs all have to have enough spl and power so that one is not over driven. I think in general gain matching is done at 1 or 2 meters so the level at the MLP may be lower. Both techniques work. One of the hardest thing to get right is the impulse response of the system when two or three of the subs are not equal distance from the MLP. Three of my subs are corner loaded which greatly increases the headroom of the system. This results in a lot of slam and great LFE.

Good points. Did you have much trouble dialing in your system running sealed and ported together or did they play nice with one another without much effort?

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post #18 of 77 Old 05-15-2014, 01:34 PM
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Quote:
Originally Posted by derrickdj1 View Post

I have a combination of 2 vented sub and 2 sealed subs. I am an advocated of level matching the subs at the MLP. The subs all have to have enough spl and power so that one is not over driven. I think in general gain matching is done at 1 or 2 meters so the level at the MLP may be lower. Both techniques work.
I was going to wait until the OP replied to my questions posted above, but I'll jump in here anyway.

Gain-matching is only appropriately used when the subs are identical. They need to use the same amps, with the same drivers in the same enclosure and alignment. If they don't, the gain-structures and sensitivities will not match and they won't be able to be gain-matched. In that situation, level-matching is one of the next-best-things. Actually, if I had multiple, non-identical subs, I would first try the Geddes method of subwoofer integration: http://mehlau.net/audio/multisub_geddes/ It requires the ability to measure your system, but it does work.

Having said that, IF THE SUBS ARE IDENTICAL, gain matching is the preferred method for integration. It ensures that all subs are driving equal energy into the room at all levels and frequencies. It also ensures that no single sub encounters compression, distortion or clipping before any of the other subs. It allows maximal use of system headroom.

With level-matching of identical subs, one of the subs could end up being set substantially different than the others. For example, this is 3 identical subs placed in 3 different placements within my room:

Left 1/5th wall:


Front between CC and R speaker:


Right 2/3 wall:


(Focus on the response below 80 Hz. I am using an 80 Hz crossover so the response above 80 Hz is primarily from the speakers and is virtually identical in all 3 graphs.)

That 3rd graph has a lot less "average" energy below 80 Hz than the other 2, and that sub would be set significantly higher, (10 to 12 dB higher!), if it were to be level-matched with the other 2. When it's set so much higher, it'll hit it's limits long before the other 2, and it would become the limiting factor in the *system.* By gain-matching it, it is driving the same energy into the room, irrespective of how it measures at any one location within the room, and it will never be the limiting factor in the system. It may not contribute equally as the other subs at this particular position where it was measured, but that is arbitrary and immaterial, (at least to me.)

To gain-match IDENTICAL subwoofers, you would set their gains to the identical positions, no matter how they measure at the LP. If you want to get really compulsive about it, you could move each sub, one at a time, to the middle of the room. (Moving to the middle of the room reduces any interactions of the sub with the room and enables you to measure the "native" response and output of each sub.) Measure each sub nearfield, with the measurement mic 2" from the driver. (Turn the volume down before you do this because the sub will measure much higher nearfield than it will in-room.) Place tape on the floor where the sub is positioned and don't move the measurement mic when you move each sub in and out of position. Set all their gains so they measure exactly the same on the nearfield measurement. Then move each sub back into its' in-room position, send each of them the exact same signal, and they will all be "gain-matched." I use about 83 dB as the nearfield SPL setting. When I move the subs back to their in-room placements, they usually measure 65 to 70 dB, and then when combined, they're in the vicinity of 75 dB, or at least close enough that I can use the subwoofer trim control to get them properly calibrated with the speakers.

The purpose of doing the above is to ensure that, if there are small variations in the amps or drivers, they are accounted for in the gain-match. If you're not concerned about those small variations, then, as I said, you can just set the gains on all of the sub amps to the same setting.

Craig
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post #19 of 77 Old 05-15-2014, 02:25 PM
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Craig, excellent points on gain matching and level matching. I always enjoy your comments.


Hopinater, it took a little work to get the subs to work below the vented subs tunning frequency but, not to difficult. As Craing said in one of his post correctly, the goal of multiple subs is to increase headroom and get a better room response.

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post #20 of 77 Old 05-15-2014, 04:24 PM
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Craig,
Are you having all three subs upfront or two in front and one in the back? Are those graphs before eq applied? If so, do you have the graphs of those individual sub and all three combined after eq? I also followed your technique from another thread to gain match my dual. Thanks.
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post #21 of 77 Old 05-15-2014, 06:00 PM
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Quote:
Originally Posted by tvuong View Post

Craig,
Are you having all three subs upfront or two in front and one in the back?
They're currently configured pretty much the way I described above, with one on the left side at 1/5 wall, one on the front wall between the CC and the R speaker, and one on the right wall The one in front and the one on the right, rear are the same distance to the LP. They're both connected to Sub1 on my pre/pro. The one on the left wall is closer and it is connected to Sub2 on the pre/pro. The Distances are compensated for in the pre/pro, but the levels are held constant so all subs receive the same signal level. That is important if the entire signal chain is to be "gain-matched."
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Are those graphs before eq applied? If so, do you have the graphs of those individual sub and all three combined after eq?
Yes, they are the raw, un-ED'd responses of each of the subs individually. I don't have their individual responses after EQ. I don't EQ the individual responses. I EQ the combined responses because it is the combined responses that you end up hearing, not the individual EQ'd responses. You could EQ each individual sub separately and get each sub absolutely flat... but when you combine them, they would no longer be flat. Better to EQ them all together as one subwoofer signal, than individually.

Here is a graph of the combined response of all 3 subs with no EQ applied:


Note that these are subwoofer-only graphs, without the speakers. I am using 80 Hz crossovers so the graphs roll off above 80 Hz, as expected. There are no longer any nulls, only some peaks. Audyssey XT32 is then applied to that result and the following is what Audyssey does to flatten the FR:


Audyssey only needs to applies cuts to the FR, no boosts.
Quote:
Originally Posted by tvuong View Post

I also followed your technique from another thread to gain match my dual. Thanks.
I hope that's working well for you! smile.gif However, just to be clear, it's not really "my" technique. I learned it from Mark Seaton. Who he learned it from I have no idea. smile.gif

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post #22 of 77 Old 05-15-2014, 06:21 PM
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I've implemented four UXL-18's so seven seats have similar FR...........................

 

All four subs are integrated together rather than individually and are placed at 1/4 wall space.  I'm close to flat down to almost 8-10 hz at reference.............and might add, not driving the four anywhere near capabilities.  Headroom is key for implementing a dynamic system.  Definitely happy I've gone the extra mile to implement.....................no smoothing, MiniDSP Open-DRC-AN with XT32

 

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post #23 of 77 Old 05-15-2014, 06:56 PM
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Quote:
Originally Posted by doublewing11 View Post

I've implemented four UXL-18's so seven seats have similar FR...........................

All four subs are integrated together rather than individually and are placed at 1/4 wall space.  I'm close to flat down to almost 8-10 hz at reference.............and might add, not driving the four anywhere near capabilities.  Headroom is key for implementing a dynamic system.  Definitely happy I've gone the extra mile to implement.....................no smoothing, MiniDSP Open-DRC-AN with XT32


That looks *excellent*!!! However, I'm surprised you're using Audyssey XT32 after some of the disparaging comments you've made in the past. Nonetheless, I'm glad it's working our for you. smile.gif

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post #24 of 77 Old 05-15-2014, 07:08 PM
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Wow, all the graphs look great guys. Good work setting up your systems. 

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post #25 of 77 Old 05-15-2014, 08:08 PM
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Quote:
Originally Posted by craig john View Post

They're currently configured pretty much the way I described above, with one on the left side at 1/5 wall, one on the front wall between the CC and the R speaker, and one on the right wall The one in front and the one on the right, rear are the same distance to the LP. They're both connected to Sub1 on my pre/pro. The one on the left wall is closer and it is connected to Sub2 on the pre/pro. The Distances are compensated for in the pre/pro, but the levels are held constant so all subs receive the same signal level. That is important if the entire signal chain is to be "gain-matched."
Yes, they are the raw, un-ED'd responses of each of the subs individually. I don't have their individual responses after EQ. I don't EQ the individual responses. I EQ the combined responses because it is the combined responses that you end up hearing, not the individual EQ'd responses. You could EQ each individual sub separately and get each sub absolutely flat... but when you combine them, they would no longer be flat. Better to EQ them all together as one subwoofer signal, than individually.

Here is a graph of the combined response of all 3 subs with no EQ applied:


Note that these are subwoofer-only graphs, without the speakers. I am using 80 Hz crossovers so the graphs roll off above 80 Hz, as expected. There are no longer any nulls, only some peaks. Audyssey XT32 is then applied to that result and the following is what Audyssey does to flatten the FR:


Audyssey only needs to applies cuts to the FR, no boosts.
From your eq graph, doesn't it seem Audyssey boosts 5db from 42-63hz? Regardless, isn't it amazing what Audyssey alone can do? Are you using just a regular xt32 subeqHT or a pro version?
Quote:
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I hope that's working well for you! smile.gif However, just to be clear, it's not really "my" technique. I learned it from Mark Seaton. Who he learned it from I have no idea. smile.gif
Craig
You tell me if it works well for me. I am also using 80hz xovers. This graph is from just the LFE channel with it turned up to 200hz (I want to see my subs FR all the way up there).
You still get credit for passing the knowledge from your write up smile.gif
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post #26 of 77 Old 05-15-2014, 08:29 PM
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Quote:
Originally Posted by tvuong View Post

From your eq graph, doesn't it seem Audyssey boosts 5db from 42-63hz? Regardless, isn't it amazing what Audyssey alone can do? Are you using just a regular xt32 subeqHT or a pro version?
Yes, you're right. Upon further review, it does appear that there is some boost at those frequencies. redface.gif Nonetheless, I can live with that... smile.gif

My application of Audyssey is just XT32 in a consumer pre/pro, a Marantz 8801... no Pro version.
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You tell me if it works well for me. You still get credit for passing the knowledge from your write up smile.gif
WOW!!! That must sound spectacular! Congratulations. If I get *any* credit for that at all, I am very happy to have helped. However, the collective knowledge we share on this forum is really what should be given the credit!

Please enjoy that system! I'm sure it sounds incredible!

Craig

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post #27 of 77 Old 05-15-2014, 08:33 PM
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^^ Thanks Craig. It does indeed sound incredible. You and and a few others are great asset here as I have learnt quite a bit from you all smile.gif
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post #28 of 77 Old 05-16-2014, 05:28 AM - Thread Starter
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Quote:
Originally Posted by craig john View Post

I don't know if "expansive" is the right word. The bass is fuller, smoother and less boomy sounding. These can all be attributed to the flatter FR throughout the room.
We need way more info before we can provide setup advice:
What subs are they? Ported? Sealed?
Are they all identical?
How big is the room?
Where is the seating placed in relation to the room and the subs?
What receiver or pre/pro do you have?
Do you have any EQ capability besides what's in your receiver or pre/pro?
Do you have any way to measure your response?

Craig

Here is a quick diagram of my room:

ZtIfU4c.jpg

Basically, I have 4 subwoofers in each corner of the home theater with the left/right front speakers and the left/right surround speakers placed on top of the subwoofers. The surround speakers will be angled towards the seating position. Even though I have not illustrated it, the front left/right speakers will also be slightly toed-in.

The subwoofers will be the SubMersive HPi+ (all with amplifiers and none as slaves so that I can EQ each one separately).
Pre/pro could be the Datasat RS20i.
I don't have any experience measuring rooms so if I do it this time, it will be my first time.
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post #29 of 77 Old 05-16-2014, 05:49 AM
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I too wondered the reason for having multiple subwoofers. I'm sure a lot has to do with both personal preference and budget, but at what size room would you recommend/consider getting a second subwoofer? I've got a SVS PB-12NSD which I love to death, currently it's in a room 14' x 16' x 7' and next month I'm moving into a new place where the living room is less deep (about 11-12') but much wider (30-35') and the same height.

Secondly, when getting a second subwoofer does it need to be the same model or brand as your first sub?
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post #30 of 77 Old 05-16-2014, 05:59 AM
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Quote:
Originally Posted by whatupdet View Post

at what size room would you recommend/consider getting a second subwoofer?
The size of the room doesn't matter, the size of the listening position does. You can use EQ to get perfectly flat response from a single sub, but only within a fairly small area. Move as little as a couple of feet and you might see major response dips. The more subs you add the smoother the response will be over an ever increasingly larger area, although you reach the point of diminishing returns in most rooms with more than four.

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