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Old 09-01-2014, 08:31 PM
 
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Quote:
Originally Posted by LastButNotLeast View Post
Earl Geddes came up with this answer many years ago:
https://mehlau.net/audio/multisub_geddes/
and the oft-quoted Harman white paper:
http://www.harman.com/EN-US/OurCompa...s/multsubs.pdf
LOL - no he didn't... the math was first outlined in a practical manner by Tesla. Thomas back in and around 1993-4 was the first to apply it, as you just viewed. It is common practice now, when application calls for it. - truly a funny statement!

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Old 09-02-2014, 12:12 PM - Thread Starter
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Would 4 subwoofers be too many in this room? I needed speaker stands for my main speakers (thinking about Seaton Sound Catalyst 8C all around for the 5 channels) so I thought I might as well get 4 subwoofers and place the Catalyst 8C speakers on them (the center Catalyst 8C will be on a stand). The subwoofers would be 2 SubMersive HPi+ with 2 slaves.

Would getting 2 SubMersives placed up front under the front left/right Catalyst 8C speakers with stands for the surrounds be better?

Here is a quick/very rough drawing of my room.

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Old 09-02-2014, 03:28 PM
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Originally Posted by Kain View Post
Would 4 subwoofers be too many in this room?
Impossible to say. I'd get two to start, place one in the front of the room, one in the back, take the required measurements, apply the necessary EQ. If they do the job you have enough subs. If they don't get one or two more.

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Old 09-02-2014, 04:56 PM
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Your room has almost the same dimensions, leading to doubling of room modes. You might find placing the subs asymmetrically, or in pairs at odd points along the wall (e.g. front and 1/3 or 2/3 points) may provide better room response. Best is to try and see, preferably using measurements.

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Old 09-02-2014, 04:58 PM
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The room is almost the same dimension L x W, potentially leading to doubling of room modes. Placing the subs at the front wall and 1/3 or 2/3 points may lead to better response. You could do it in pairs, but that's a fairly small room for four subs. I would personally try two first.

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Old 09-03-2014, 09:53 AM
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Quote:
Originally Posted by Kain View Post
Would 4 subwoofers be too many in this room? I needed speaker stands for my main speakers (thinking about Seaton Sound Catalyst 8C all around for the 5 channels) so I thought I might as well get 4 subwoofers and place the Catalyst 8C speakers on them (the center Catalyst 8C will be on a stand). The subwoofers would be 2 SubMersive HPi+ with 2 slaves.

Would getting 2 SubMersives placed up front under the front left/right Catalyst 8C speakers with stands for the surrounds be better?

Here is a quick/very rough drawing of my room.

Given you have rather limited placement options for subs in the room, I do expect the 4 locations you noted can be made to work well together. This also happens to be exactly one of the uses I had in mind for the HP+ & Slave option with pairs front and rear.

My preference based on lots of measurements in setting up various rooms is to blend the subwoofers with an external device and then let any room correction system handle the subwoofers as a system. I would recommend getting REW working (or OmniMic) and DSP with 2 channel output for the subwoofers. The MiniDSP and MiniDSP's Open-DRC-AN can both work. You might be able to get away with 2 separate subwoofer outputs with distance settings on an Audyssey XT32 or similar receiver, but you will want to take measurements rather than relying on what Audyssey comes up with.

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Old 09-03-2014, 10:20 AM
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Quote:
Originally Posted by Mark Seaton View Post
Given you have rather limited placement options for subs in the room, I do expect the 4 locations you noted can be made to work well together. This also happens to be exactly one of the uses I had in mind for the HP+ & Slave option with pairs front and rear.

My preference based on lots of measurements in setting up various rooms is to blend the subwoofers with an external device and then let any room correction system handle the subwoofers as a system. I would recommend getting REW working (or OmniMic) and DSP with 2 channel output for the subwoofers. The MiniDSP and MiniDSP's Open-DRC-AN can both work. You might be able to get away with 2 separate subwoofer outputs with distance settings on an Audyssey XT32 or similar receiver, but you will want to take measurements rather than relying on what Audyssey comes up with.
Mark can you elaborate more on blending the subwoofers. For example, 2 master - slave pairs would be four sub. Do you treat each pair as one in the setup? I
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Old 09-03-2014, 03:13 PM
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Originally Posted by derrickdj1 View Post
Mark can you elaborate more on blending the subwoofers. For example, 2 master - slave pairs would be four sub. Do you treat each pair as one in the setup? I
Yes. The master & slave combo is effectively one large subwoofer sold in 2 pieces where you can add the 2nd half at any time and place (locate ) separately. They are powered from one amplifier, so always get the identical signal. As I've written about many times, with 2 subwoofers at similar front-to-back depth in the room, it is exceedingly rare that you will find any benefit in sending them separate signals. For front/back or front/side wall where they are at different depths in the room, there can certainly be benefits. In most cases, you get a WORSE result by trying to send different signals to 2 subwoofers placed at the front wall of the room.

Even if his case was 4 identical powered units, I would still adjust them as 2 groups of front/rear. Note the front and rear do not need to be perfectly symmetrical. You can see thebland's system has 2:1 capability front:rear. I've done many systems with 2 subs at the front wall and one placed strategically to have strong response where ever the front pair have weak points. Just as in the case of thebland's system, over specific frequency ranges, the single unit in the correct location can be more efficient than 2 elsewhere. Here is a comparison of 2 SubMersives up front vs. 2 at the rear corner in thebland's room driven to identical levels:

You can see that while the rear corner is very inefficient at delivering anything below 15Hz, it is 6-10dB more efficient in the critical 20-32Hz range.
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Old 09-03-2014, 06:44 PM
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Thank Mark. I did read the other post and that helped clear up a couple of questions. I have 4 sub and calibrate them in a similar fashion, front 2 and rear 2 with delays. I have nowhere near as sophisticated calibration gear but, it get a decent result. I do see how there is room for improvement with better gear.
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Old 09-03-2014, 06:48 PM
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Old 09-04-2014, 12:59 PM - Thread Starter
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Quote:
Originally Posted by Mark Seaton View Post
Given you have rather limited placement options for subs in the room, I do expect the 4 locations you noted can be made to work well together. This also happens to be exactly one of the uses I had in mind for the HP+ & Slave option with pairs front and rear.

My preference based on lots of measurements in setting up various rooms is to blend the subwoofers with an external device and then let any room correction system handle the subwoofers as a system. I would recommend getting REW working (or OmniMic) and DSP with 2 channel output for the subwoofers. The MiniDSP and MiniDSP's Open-DRC-AN can both work. You might be able to get away with 2 separate subwoofer outputs with distance settings on an Audyssey XT32 or similar receiver, but you will want to take measurements rather than relying on what Audyssey comes up with.
Thanks!

Sorry for the noob question but what is the purpose of having a dedicated external subwoofer DSP or EQ? How is it different compared to simply connecting the subwoofer(s) to your A/V processor and having it apply the EQ?
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Old 09-04-2014, 02:10 PM
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Quote:
Originally Posted by Kain View Post
Sorry for the noob question but what is the purpose of having a dedicated external subwoofer DSP or EQ? How is it different compared to simply connecting the subwoofer(s) to your A/V processor and having it apply the EQ?
Not many AVRs can EQ the subwoofer frequencies.

And there are those who feel that "auto" isn't always better.

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Old 09-04-2014, 05:42 PM
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Originally Posted by Kain View Post
Thanks!

Sorry for the noob question but what is the purpose of having a dedicated external subwoofer DSP or EQ? How is it different compared to simply connecting the subwoofer(s) to your A/V processor and having it apply the EQ?
The auto EQ systems do a fairly good job at smoothing the response they are given. They can't tell you if you put the sub in a useful spot, and I have yet to see any have much intelligence toward creating an optimum blend between multiples. The external DSP allows you to blend 2 subwoofers using real measurements and delay or other adjustments as needed. See the thread I linked previously on thebland's sub setup. You can make dual subs on Audyssey work fairly well, but you need to measure the results or you have no idea what the combined result is.

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Old 09-05-2014, 02:12 AM - Thread Starter
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Quote:
Originally Posted by Mark Seaton View Post
The auto EQ systems do a fairly good job at smoothing the response they are given. They can't tell you if you put the sub in a useful spot, and I have yet to see any have much intelligence toward creating an optimum blend between multiples. The external DSP allows you to blend 2 subwoofers using real measurements and delay or other adjustments as needed. See the thread I linked previously on thebland's sub setup. You can make dual subs on Audyssey work fairly well, but you need to measure the results or you have no idea what the combined result is.
Would you still recommend an external subwoofer DSP even with something like the RS20i?
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Old 09-05-2014, 10:31 AM
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Quote:
Originally Posted by Kain View Post
Thanks!

Sorry for the noob question but what is the purpose of having a dedicated external subwoofer DSP or EQ? How is it different compared to simply connecting the subwoofer(s) to your A/V processor and having it apply the EQ?
Other posters have answered your question really well but I thought I'd relay my own experience. Maybe it will add some context...


I have a Yamaha AVR that does a good job of room correction above sub frequencies but nothing below 70 hz IIRC. I considered multiple subs, different placements, a new AVR etc. before finally settling on the following path:


1) starting with one SUB (PB1000) and experimenting with placement. I was going to go with a higher end sub but figured I'd eventually add a 2nd PB1000.


2) adding a DSP if necessary (my AVR is perfect absent the sub eq)


3) adding a second SUB if necessary


I found that my single sub located in the corner had plenty of output for my needs but something just did not sound right. I found some bass sweeps and realized that modes at 40 hz & 80hz were really pronounced. The AVR may have also been setting the sub too low due to the modes resulting in too little output below 30Hz while other frequencies still remained exaggerated. Moving the one sub around did not really help matters much so I returned it to the front left corner.


I added an 8033 cinema anti-mode and all my issues were solved. The 8033 fixed the peaks and the sub ended up being set a couple notches higher such that output below 30hz was more than I'd ever really need. My only complaint is that the secondary listening position (which is a couch on the right side of the room that is against the wall) has a bit too much bass. The MLP and just about anywhere else is great. A second sub would likely balance things out better but at the cost of aesthetics, and another $500.


I agree with everyone that says 2 or 3 or 4 properly integrated subs will sound better than fewer subs and that the law of diminishing returns is also a factor.


In my room, a modest sub "corner loaded", with an external EQ works great. I fully expected to have to purchase a second sub but I don't see a need to now.


If I'm you I'm starting with 2 better subs and equalization vs. 3 or 4 lessor subs (assuming budget is a concern)
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Old 09-05-2014, 12:15 PM
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This seems like a decent place to ask this question regarding mutual coupling. Since it's seemingly accepted that two subs are mutually coupled when they are less than a 1/4-wavelength apart, that implies that for a given separation distance, they are mutually coupled below some threshold frequency, and "distinct" (i'll use that as my term for not mutually coupled) above that same frequency. Being a geeky engineer, i plotted it (see attached graph).



My question is, should you strive to have that threshold outside the normal operating range of the sub? Or in other words, if that threshold falls right in the 20 - 60 hz range, does it create problems? If you want to have them mutually coupled all the way to 80 hz, you'd have to have them <3.5 ft apart, or if you want them to be distinct down to 18 hz, you'd have to have them at least 15.6 ft apart. Any reason to not have them at say 9 ft apart, where the coupling threshold frequency is ~30 hz?

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Old 09-05-2014, 01:16 PM
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Keep in mind the purpose of mutual coupling, which is to have two or more subs essentially act as one, with their outputs fully constructively summed. There are circumstances where that's useful, mainly in pro-sound applications, where response throughout most of the listening area is mainly determined by the speakers, not the room. In that case mutual coupling usually works best, by preventing power alley effects.
http://www.prosoundweb.com/article/i...e_power_alley/

In homes room modes and boundary interactions are just as responsible for response at the LP as the speakers themselves. Mutually coupling subs in that case won't improve response, as all of the subs in the stack will excite the same room modes, and suffer from the same boundary interactions. Splitting them has each exciting different room modes and different boundary effects, which will usually give a better result than mutual coupling.

As to your math, if the subs are, for instance, 3.5 feet apart, they'll couple at all frequencies below 80Hz. If you had them 9 feet apart they'd couple at all frequencies below 32Hz. That's not to say that they don't couple at all above the 1/4 wavelength frequency, they do, but with response dips based not only on their distance apart but also the listener's position relative to them.

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Old 09-05-2014, 01:33 PM
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Ok, thanks for that. So if you have room mode issues causing dips in the FR at the MLP at say 40 or 50 hz, then having dual subs placed <9 ft apart probably won't help (or at least not as much as if they were more widely spaced), since they're still acting as 1 big sub at those frequencies?

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Old 09-05-2014, 02:08 PM
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if you have room mode issues causing dips in the FR at the MLP at say 40 or 50 hz, then having dual subs placed <9 ft apart probably won't help (or at least not as much as if they were more widely spaced), since they're still acting as 1 big sub at those frequencies?
It's not how far apart in and of itself that matters, it's the combination of where they are, where the room boundaries are, and where you are. If they're close enough together to be mutually coupled at the dip frequency that could be part of the problem. At 40Hz that would be less than 7 feet. But just as likely a culprit is the distance from the LP to a boundary. That's why it's important to spread the subs wide, so if you're sitting in the null caused by the boundary reflection of the output of one sub the second (or third or fourth etc,) sub isn't creating a null at that same frequency.

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