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post #1 of 41 Old 01-18-2012, 03:04 PM - Thread Starter
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I've had a really good thread going about my sonosub build but I had a more esoteric question that I thought merited a new thread topic.

After my conversation with LTD02 and ScottSimonian I've settled (I hope) on four 5 cu ft sonotubes each running a 15 inch Dayton RSS390HF-4 setup sealed with an iNuke NU3000DSP powering them.

The question I have relates to how to best take advantage of the four subs to quell room modes and nulls.

I have read some about the "Geddes's approach" and I'd like to know what everyone's opinion is on that and specifically in my case-should I build one or two of the four with an upward facing driver? I'm thinking pretty strongly that I should do at least one of them facing up but since I've already got 4, am I just giving up extra spl from not corner loading them all?

Thanks
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post #2 of 41 Old 01-18-2012, 04:10 PM
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what ever sounds best at your seating position. Try out some places and see what you like best.

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post #3 of 41 Old 01-18-2012, 04:51 PM
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One option would be to build two very tall units, each with a bottom and top firing driver, presenting equal radiation to the two largest planes in the room, the floor and ceiling. Also saves some floor space and if placed in the two front corners of the room and covered in batts of OC703 , they could act as very efficient bass traps, stomping out some modal responses. Kills quite a few birds........
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post #4 of 41 Old 01-18-2012, 05:31 PM - Thread Starter
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Quote:
Originally Posted by mayhem13 View Post

One option would be to build two very tall units, each with a bottom and top firing driver, presenting equal radiation to the two largest planes in the room, the floor and ceiling. Also saves some floor space and if placed in the two front corners of the room and covered in batts of OC703 , they could act as very efficient bass traps, stomping out some modal responses. Kills quite a few birds........

Hmm...I already have bass traps so I know of the benefits of corner trapping. This idea is intriguing to me but do you have any examples of such a design?

I was planning to go sealed, would tall units with dual drivers change that? Also wondering if I would run dual drivers in phase or out of phase...
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post #5 of 41 Old 01-18-2012, 06:17 PM
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No example, just thinking outside the box with the info at hand. Two independent chambers in each tube, with the drivers wired in phase. Although you already have the traps, I think you can see the advantage of replacing them with the 'Sonos-traps?'......meaning still more floor space saved.
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post #6 of 41 Old 01-18-2012, 07:42 PM
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Quote:
Originally Posted by evac311 View Post

IThe question I have relates to how to best take advantage of the four subs to quell room modes and nulls.

There's no answer to that except - measure, measure, measure.

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Originally Posted by evac311 View Post

I have read some about the "Geddes's approach" and I'd like to know what everyone's opinion is on that

I've only heard subs configured in three ways that provide natural-sounding bass in a small room:

(1) Geddes
(2) double bass array (DBA)
(3) OB down to ~40Hz, single closed box below that

Given that OB's are unsightly (because they have to be wide and stuck way out into the room) and most people can't meet the room and/or placement criteria for a DBA, that pretty much leaves Geddes' approach as the only practical way to clean, natural-sounding bass in a domestic living room.

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and specifically in my case-should I build one or two of the four with an upward facing driver?

Yes. Between one and three of them should face up. Determine that experimentally.

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Originally Posted by evac311 View Post

I just giving up extra spl from not corner loading them all?

If the goal is BOOM BOOM BOOM, then yes. You'll be better off clustering them in a corner, cranking the gains to 11, and letting 'em rip.

If the goal is natural-sounding bass, no.

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post #7 of 41 Old 01-18-2012, 08:50 PM
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Quote:
Originally Posted by DS-21 View Post


There's no answer to that except - measure, measure, measure

+1. Geddes and the Harman papers are a good place to start, but nothing can replace measuring gear for optimal results. There is also the issue of gain vs. level matching, optimal crossover settings and phase adjustments that can all have a huge impact on SQ. There's no effective way to tackle these issues aside from RTA that I'm aware of.

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post #8 of 41 Old 01-18-2012, 09:20 PM
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Quote:
Originally Posted by DS-21 View Post

There's no answer to that except - measure, measure, measure.

Yup. +1

Then read this (or read it first): http://mehlau.net/audio/multisub_geddes/


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post #9 of 41 Old 01-18-2012, 10:37 PM
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Quote:
Originally Posted by Gooddoc View Post

There is also the issue of gain vs. level matching

That's not an issue.

Both "gain matching" and "level matching" approaches lead to suboptimal results.

Doing it right means folding the subs into the mains. The mains are the most important part of the system, after all. Everything should sound like it's coming from the soundstage they generate.

So, run sweeps in the mains and then add the subs in one at a time. Take sub one - the one closest to the mains - and play with the level and phase/delay until the bass is smooth but a bit under the mains level. (Each sub should at least have level controls and either a variable phase, or if one is using something like a miniDSP, delay.) Then add sub 2, doing the same but also if possible experimenting with different lowpass filters. Ditto for three, and four.

I don't like to touch a band of parametric EQ until everything is as smooth as it can be using just levels, phase/delay, and possibly staggered crossover slopes. I used to first get the main sub to play down to my desired LF cutoff with EQ first, but now I save all EQ'ing to the end. That's more a personal preference thing than anything else, though.

It's kind of tedious - and frankly often best done listening to music or something like NPR at background levels through IEM's with good isolation! - but I've never heard another method get equal, let alone better, results.

As for "matching," the relative levels will fall where they will fall. Who cares, really? The goal is to optimize the system, not maximize the contribution of each part.

Yes, chances are with four identical subs, one or two of the will be loafing along and one or two of them will seem to be barely contributing at all. One can bring them up in level, but that usually costs smoothness of response. That's why I don't use identical subs, but try to fit the subs to their role. Smaller subs are easier to hide.

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post #10 of 41 Old 01-19-2012, 07:01 AM
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I agree with DS-21.

To add to what he said, you need to think of each cluster of subs as a single "bass source". Multi-sub in the Geddes or Welti context does not refer to the number of drivers but the number of locations for bass sources. If you put all four RS15s in one spot you would not have a multi-sub setup.

I would shoot for 3-4 discrete bass sources. You should have individual level and phase control over each of these discrete sources. I would suggest placing the sources 1 and 2 up front near your mains. One in a corner and one away from a corner is best, but you can put both in corners. These sources should be your most capable and should provide the bulk of your output. I would use the RSS390HFs in pairs with all four up front. You can build them however you please (sonosub, dual opposed, separate boxes). Does that make sense?

For the rear you should be fine with a single small subwoofer although you might get better results with two rear subs (I would start with a single). These subs need to be low distortion but they don't need to have tons of displacement because they won't need to produce nearly as much SPL and they won't need to produce the lowest bass (<25hz). Something like a single RSS265HF-4 ($135) in about 1 cu ft with about 200w would work well. There are other options but just keep in mind that this bass source can be much smaller and less capable. I would suggest putting a high pass filter on it as it will limit excursion. Most plate amps will have this such as the Dayton SA250.
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post #11 of 41 Old 01-19-2012, 07:24 AM
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On the AudioKinesis page on the AudioCircle website Duke and users describe some of their set-up experiences with the AK's Swarm multiple sub system. The Swarm is based on Geddes' work so the application to the issue herein is appropriate. The link is:

http://www.audiocircle.com/index.php?board=135.0

You can read the Swarm postings and you'll have some insight.
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post #12 of 41 Old 01-19-2012, 09:42 AM
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Quote:
Originally Posted by coctostan View Post

I agree with DS-21.

To add to what he said, you need to think of each cluster of subs as a single "bass source". Multi-sub in the Geddes or Welti context does not refer to the number of drivers but the number of locations for bass sources. If you put all four RS15s in one spot you would not have a multi-sub setup.

I would shoot for 3-4 discrete bass sources. You should have individual level and phase control over each of these discrete sources. I would suggest placing the sources 1 and 2 up front near your mains. One in a corner and one away from a corner is best, but you can put both in corners. These sources should be your most capable and should provide the bulk of your output. I would use the RSS390HFs in pairs with all four up front. You can build them however you please (sonosub, dual opposed, separate boxes). Does that make sense?

For the rear you should be fine with a single small subwoofer although you might get better results with two rear subs (I would start with a single). These subs need to be low distortion but they don't need to have tons of displacement because they won't need to produce nearly as much SPL and they won't need to produce the lowest bass (<25hz). Something like a single RSS265HF-4 ($135) in about 1 cu ft with about 200w would work well. There are other options but just keep in mind that this bass source can be much smaller and less capable. I would suggest putting a high pass filter on it as it will limit excursion. Most plate amps will have this such as the Dayton SA250.

I'm with you on this method, Coctostan. I plan on doing the same thing in my room, even. Put the heavy hitters up front near the mains and use a couple more smaller subs in other positions around the room.


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post #13 of 41 Old 01-19-2012, 10:40 AM
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One other thing...I'd suggest trying a a subwoofer low pass crossover as high as your receiver will allow (usually around 150hz). That is a good starting point. With multiple low distortion subs that play cleanly well beyond the crossover point, it is my experience that you will not have localization issues. The 100-150hz range is also probably the most problematic area and most useful area for multisubs.

If you find that they are localizable after the full setup, you can lower the crossover and try again. It is partly room dependent and related to where your room, based on its size, is dominated by modes.

You will also have several options with your mains. I would let your receiver run a highpass on them at the very least around 40hz. Unless you have some very unique main speakers, it is unlikely they will produce frequencies that low very well. From that beginning point, you can tweak this crossover point to achieve the best frequency response. There can certainly be overlap with your sub channel.
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post #14 of 41 Old 01-19-2012, 10:51 AM - Thread Starter
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Quote:
Originally Posted by DS-21 View Post

That's not an issue.

Both "gain matching" and "level matching" approaches lead to suboptimal results.

Doing it right means folding the subs into the mains. The mains are the most important part of the system, after all. Everything should sound like it's coming from the soundstage they generate.

So, run sweeps in the mains and then add the subs in one at a time. Take sub one - the one closest to the mains - and play with the level and phase/delay until the bass is smooth but a bit under the mains level. (Each sub should at least have level controls and either a variable phase, or if one is using something like a miniDSP, delay.) Then add sub 2, doing the same but also if possible experimenting with different lowpass filters. Ditto for three, and four.

I don't like to touch a band of parametric EQ until everything is as smooth as it can be using just levels, phase/delay, and possibly staggered crossover slopes. I used to first get the main sub to play down to my desired LF cutoff with EQ first, but now I save all EQ'ing to the end. That's more a personal preference thing than anything else, though.

It's kind of tedious - and frankly often best done listening to music or something like NPR at background levels through IEM's with good isolation! - but I've never heard another method get equal, let alone better, results.

As for "matching," the relative levels will fall where they will fall. Who cares, really? The goal is to optimize the system, not maximize the contribution of each part.

Yes, chances are with four identical subs, one or two of the will be loafing along and one or two of them will seem to be barely contributing at all. One can bring them up in level, but that usually costs smoothness of response. That's why I don't use identical subs, but try to fit the subs to their role. Smaller subs are easier to hide.


So you suggest dialing in each sub's individual level as it contributes to the overall system level? So hypothetically if each sub "should" give my system about a 3 db rise then you'd say it's ok that the one in the corner only requires 25% level to achieve that versus one off the wall in the back of the room that takes 75% as long as they all contribute equally at the listening position? Assuming 4 identical subs, what effect does this method have on distortion?

I'd also like to expand on the issue of individually adjustable phase. I'd originally wanted to do 4 seperate amps so I could dial in phase to each sub but then two things occured to me that made me think that won't be necessary.

For one thing, a big reason for running multiple subs is that I want good sound not just at the main listening position but everywhere around the room. So if I've got the phase dialed in @LP what good does that do when you move 10 feet away with now some subs closer and others farther away?

Also with an average wavelenth in this range being maybe +/-25 feet most of the sound we're hearing is reflected anyway.

How does this all factor together when dialing in phase?

I've been thinking about this build for a long time and at the end of the day I just want the best sound possible, so I look forward to everyone's opinions. If I need to buy 4 seperate amps or an external mini dsp to get there, so be it.
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post #15 of 41 Old 01-19-2012, 11:28 AM
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This was accomplished with just one sub next to the listening position, added to my main sub system. With a PEQ filter centered at 40hz, that small peak could be dealt with.....Are you suggesting sweeps with mains and sub, or the whole system and subs...



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post #16 of 41 Old 01-19-2012, 11:42 AM
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Quote:
Originally Posted by evac311 View Post

So you suggest dialing in each sub's individual level as it contributes to the overall system level?

Yes, but not as you describe. See here for a more thorough explanation.

Quote:
Originally Posted by evac311 View Post

So hypothetically if each sub "should" give my system about a 3 db rise

No. See link, supra.

Quote:
Originally Posted by evac311 View Post

as long as they all contribute equally at the listening position?

The chances of the result for a given room, when optimizing for smoothness of modal-region response prior to EQ as I think is the correct approach, being each sub contributing equally is IMO vanishingly small.

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Assuming 4 identical subs, what effect does this method have on distortion?

You might have less headroom, you might not. Depends on the room. With 4 good 15's, I doubt it will be an issue.

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Originally Posted by evac311 View Post

I'd also like to expand on the issue of individually adjustable phase. I'd originally wanted to do 4 seperate amps so I could dial in phase to each sub but then two things occured to me that made me think that won't be necessary.

Because of the way sound waves move in the modal region of a small room, a sub system set up as described above will have low spatial variance. Yes, the bass will be more prominent along room boundaries.

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So if I've got the phase dialed in @LP what good does that do when you move 10 feet away with now some subs closer and others farther away?

Depends on which 10', I guess. If those 10' put you up against a wall, then chances are any approach will lead to over-prominent and lumpy bass.

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Originally Posted by evac311 View Post

If I need to buy 4 seperate amps or an external mini dsp to get there, so be it.

You need to buy 3-4 separate amps. (You may want to lump two tubes as one sub, depending on your room.)

If the amps don't have built-in DSP, a miniDSP or Berry DCX will be useful to get the nth degree of performance. If you have subs tuned similarly, though, you can get very good results without a separate, if you can individually adjust levels, phase/delay, and slopes on the subs, and your main processor has a good room correction program.

One word of caution if you're using a miniDSP is to get the balanced one if you're considering pro amps. You need the extra voltage. Also, noise may be a problem. I also had problems with noise from the interaction between a signal-sensing power outlet and a Peavey IPR-3000, one of the few pro amps with enough gain to be useful with the unbalanced miniDSP. I ended up running a Snell SPA-750 (a more conservatively-rated Dayton SA1000, really, currently available on eBay cheaper than the SA1000 due to Snell's liquidation), an older Dayton HPSA-1000R, and a little Gallo amp for my 3-sub system, and that's trouble free so far.

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post #17 of 41 Old 01-19-2012, 12:22 PM
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Although you are asking DS-21, we tend to agree on this stuff (except I like content below 20hz and DS doesn't much care for it) so I will respond.

The reason for the individual phase control is not for dialing in the system for a single position but to "alter" how each bass source interacts with the other bass sources. Delay or phase is not as simple as adjusting for a specific distance, especially at these frequencies. You are simply trying to excite a combination of modes that gives you the most even response across multiple positions. Small phase adjustments is just an additional tool.

Like I said before, you are best served using your "heavy lifters", the 4 RSS390HFs up front in two separate positions. These front bass sources can be set up to provide your full SPL and frequency tilt that you desire. I would put them in 5 cu ft each wired in series for an 8 ohm stereo load on the NU3000DSP. That is 315w RMS/channel which happens to be about how much power it will take to reach Xmax. Place one of the pairs in a front corner (Sub A) and place the other pair (Sub B) a few feet from the other corner along the front wall.

Start bringing up the level of Sub A (the corner sub) until its average level is about 2-3db below your final target (probably 75 or 85db). Once you have that set, adjust the phase/delay until you get the nicest response you can get (this should be done with your mains running the same test signal).

Next, while Sub A is still running, bring up the level of Sub B (front wall non-corner sub) until you have reached your desired level match. Adjust phase/delay to get the best response you can.

Finally, add in the smaller 10-12" sealed sub with the plate amp. The ideal location for this is elevated above the halfway point of the wall, but that is not necessary. Now, while everything else is running, bring up the level of this subwoofer until you see some smoothing effect. You shouldn't see any significant increase in level. Then adjust phase until you get the smoothest response across multiple positions. This sub will put out very little relative to the fronts.

You should see smoothing from the 3rd sub and more smoothing as your tweak the phase. Peaks should come down and nulls should fill.

Finally, adjust eq to flatten the response at your primary position. It should be pretty flat already, but some tweaking might be needed. Test in other listening positions to make sure you aren't throwing things way off.

The only catch to this is that you will only have EQ on your front subs and not the third sub. This shouldn't be much of an issue IMO, but you do lose some flexibility. You could go with a MiniDSP instead. I'd probably suggest that route anyway so you can do a proper Linkwitz Transform on your subs.

Which brings up another point. You should setup your Linkwitz Transform prior to any of this. How you do this will be based on how your sub reacts to your room (aka room gain) and how much headroom you have down low. If you are using the NU3000DSP you will apply a shelf filter. With the MiniDSP you will apply a proper LT. I wouldn't apply any more than 4-5db of boost with your setup. (that would target an LT with a tuning around 25hz with your subs) How deep that will get you depends on your room.

Feel free to ask questions. I'm just writing this off the top of my head and is the process I use. Some of it may not make as much sense to other people as it does in my head.
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Coctostan,

Do you do an average of all seats, or look to decrease seat-to seat variance by looking at all traces on one REW screen? I am not a fan of averaging, it can hide large seat-seat variances, especially with modal behavior which can show a null at one seat, and a peak at the same freq in another seat, averaging to a false 'flat' FR.....

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post #19 of 41 Old 01-19-2012, 03:42 PM - Thread Starter
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Quote:
Originally Posted by coctostan View Post

One other thing...I'd suggest trying a a subwoofer low pass crossover as high as your receiver will allow (usually around 150hz). That is a good starting point. With multiple low distortion subs that play cleanly well beyond the crossover point, it is my experience that you will not have localization issues. The 100-150hz range is also probably the most problematic area and most useful area for multisubs.

If you find that they are localizable after the full setup, you can lower the crossover and try again. It is partly room dependent and related to where your room, based on its size, is dominated by modes.

You will also have several options with your mains. I would let your receiver run a highpass on them at the very least around 40hz. Unless you have some very unique main speakers, it is unlikely they will produce frequencies that low very well. From that beginning point, you can tweak this crossover point to achieve the best frequency response. There can certainly be overlap with your sub channel.

I've found that a 24db cross @80hz works pretty good but if I can have individual control over each sub that will give me some room to play around with different approaches. I use REW and a Radio Shack meter to do my testing.

I like the idea of crossing these higher to try and cancel some modes higher in the frequency band above 80hz but I feel like that may cause more problems with phase misalignment than it solves. Anyone care to chime in on whether or not it's a good idea to run multiple subwoofers at different low pass frequencies from one another? That way I could avoid localization by crossing the front stage subs higher. I know I can always try it out myself but the conversation could be interesting.

Also changing the plan for the build for the nth time LOL... Coctostan made a great argument in favor of all-channels phase adjustment..."The reason for the individual phase control is not for dialing in the system for a single position but to "alter" how each bass source interacts with the other bass sources. Delay or phase is not as simple as adjusting for a specific distance, especially at these frequencies. You are simply trying to excite a combination of modes that gives you the most even response across multiple positions. Small phase adjustments is just an additional tool."

So what this means is I'll be going with the Behringer DCX2496 crossover to take advantage of it's ability to phase adjust and create the type of filters I want. Asuming that with 6 output channels I'll have 2 left over to run with my main speakers so I can finally have my subs and main speakers in proper phase alignment for the first time! This is getting exciting. Anyone have a recommendation for a good pro amp? I'll need 4 discrete channels or two 2 channel amps.
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post #20 of 41 Old 01-19-2012, 04:53 PM
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JSS-

I just eyeball it with a live RTA and move the mic around using a mic stand. I then take sweeps that are more precise and also just analyse it visually. When I was referring to averaging early I just meant the average SPL when matching levels with the mains.

Evac-

The different crossovers I was referring to can be done in your receiver most likely. Most mid-level and up receivers allow you to choose a highpass crossover frequency for your mains. What is best really depends on the capability of your mains. What do you have currently?

As far as "proper phase alignment" it really doesn't exist at these frequencies, at least not in the sense that there is a specific delay value that aligns everything. The whole idea behind the multiple subwoofer approach is to act as multiple sources in both time and space. Through a pseudo-random excitation of room modes you are getting a combination of degrees of in and out of phase signal at each position that ultimately leads to a smoothed frequency response.

Ultimately all that matters is frequency response and everything else will fall in line.

As far as the tools you use, I see two prudent routes:

NU3000DSP, stereo 8 ohm each channel powering a pair of parallel'd RSS390HF
+
Dayton SA250 plate amp powering a single RSS265HF or RSS315HF

The iNuke allows for delay control over the front primary subs and the plate amp allows for delay using a knob for the third sub. You can also boost the lower frequencies of the RSS390's to extend your output a little with the DSP or to tailor a house curve response.

OR

EP4000, stereo 8 ohm each channel powering a pair of parallel'd RSS390HF
+
Dayton SA250 plate amp powering a single RSS265HF or RSS315HF
+
MiniDSP 2x4 Balanced with 4-way advanced plugin

You will send your LFE output to the MiniDSP and it will split the signal to the 3 bass sources. You will be able to control phase, eq and level for all bass sources directly from MiniDSP. You can also implement a proper Linkwitz transform which is handy IMO.

The iNuke DSP approach is probably a few bucks cheaper, but I'd go with the MiniDSP for greater flexibility. Both approaches can get you where you want to be.

Do you have the budget for the 3rd sub (estimated $300-400 total including box)? IMO, it is much smarter than basically wasting the capability of 1-2 of the RSS390HF's. You will make better use of the displacement by running them as your "workhorse" subs up front. Plus, you can go with a tiny box in the back instead of the 5 cu footers.
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Quote:
Originally Posted by coctostan View Post


The different crossovers I was referring to can be done in your receiver most likely. Most mid-level and up receivers allow you to choose a highpass crossover frequency for your mains. What is best really depends on the capability of your mains. What do you have currently?

Right now I have a Berhringer SuperX Pro, it's a 4th order crossover. I use that instead of the cross on my Denon 4308ci because I prefer the sound of a 4th order high pass vs 2nd order. My main speakers are a pair of B&W CDM1 2-way 6.5in bookshelfs on stands.

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As far as "proper phase alignment" it really doesn't exist at these frequencies, at least not in the sense that there is a specific delay value that aligns everything. The whole idea behind the multiple subwoofer approach is to act as multiple sources in both time and space. Through a pseudo-random excitation of room modes you are getting a combination of degrees of in and out of phase signal at each position that ultimately leads to a smoothed frequency response.

From your experience, how relatively important is phase adjustment to good frequency response?


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Originally Posted by coctostan View Post

As far as the tools you use, I see two prudent routes:

NU3000DSP, stereo 8 ohm each channel powering a pair of parallel'd RSS390HF
+
Dayton SA250 plate amp powering a single RSS265HF or RSS315HF

The iNuke allows for delay control over the front primary subs and the plate amp allows for delay using a knob for the third sub. You can also boost the lower frequencies of the RSS390's to extend your output a little with the DSP or to tailor a house curve response.

OR

EP4000, stereo 8 ohm each channel powering a pair of parallel'd RSS390HF
+
Dayton SA250 plate amp powering a single RSS265HF or RSS315HF
+
MiniDSP 2x4 Balanced with 4-way advanced plugin

You will send your LFE output to the MiniDSP and it will split the signal to the 3 bass sources. You will be able to control phase, eq and level for all bass sources directly from MiniDSP. You can also implement a proper Linkwitz transform which is handy IMO.

Does the iNuke DSP not produce a "proper Linkwitz" I assume you're refering to Linkwiz-Riley 4th order crossover? Please correct me if I'm wrong.

Would the MiniDSP allow me enough channels to run my mains through it since I use external eq?

Another reason I want to run the mains through external DSP is so I can apply some delay to them. This is based on my belief that the mains and subs are never on the same sound cycle due to the fact that the sound from the mains always reaches your ears first because they're closer. You can't make your subs go foward in time, that's my thinking on that one, maybe I'm grasping at straws.

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Do you have the budget for the 3rd sub (estimated $300-400 total including box)? IMO, it is much smarter than basically wasting the capability of 1-2 of the RSS390HF's. You will make better use of the displacement by running them as your "workhorse" subs up front. Plus, you can go with a tiny box in the back instead of the 5 cu footers.

Not to beat a dead horse here, but can you breifly expand on that opinion?

My thinking:

More subs=less distortion

More subs=smoother response

More subs=higher spl

I see your point about the smaller size sub being more flexible for placement. Is it a waste to have the big 15inch sub at the midpoint of a rear wall, for example?
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I would suggest ditching the EQ on the mains and let the receiver handle the high pass.

In all honesty, you will be operating in a completely different world when you move to a multisub setup. Your preference for the 4th order crossover will be a thing of the past.

The capability of a well tuned multisub setup like we've detailed above will give you a frequency response like you've never experienced before.

The ability to adjust phase is an important tool in a multisub setup. I'm not sure how to explain it, but there isn't a "right" phase so much as you utilize the ability to delay a bass source to better conjugate with the other bass sources and with the multiple placements you can achieve a smooth bass response across multiple seats in a small room.

I'm referring to a Linkwitz Transform, not a LR crossover. It is a filter that alters the Q and rolloff frequency of a sealed speaker. It basically takes out a little of the upper bass hump and boosts the low end so your sealed sub conjugates to the room for a flat response. You can google it, but I'm not sure the explanations are great. The DCX and iNuke DSP can do something similar with a combination of PEQ and shelving. You are fine either way.

The catch in your logic at the bottom of your post is that you ideally get most of your output from the first two bass sources and the third source only contributes a very small amount of output, thus wasting the capacity of a RSS390HF. This multisub approach is not the most efficient approach, but I think it provides the best results.

Simply having multiple subs won't give you a smooth response. You must implement them properly.
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Should be putting steel to MDF soon, but this is my first AUX SUB....I ended up a little bigger 30" wide and 18" high..... These will be along the floor, assuming i get the same reaction as my BIC had.


This is some of the best info in a while....


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post #24 of 41 Old 01-20-2012, 07:52 AM
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wow...this is a great thread.

but i haven't seen two things mentioned yet.

1) where does the receiver calibration (e.g Audyssey, MACC, etc.) falls into this?
2) what if you have a single amp (EP4000) running all the subs (4, 6, 8)

would anyone care to elaborate? thanks
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KG-

I look forward to see your results.

Evac, I'm suggesting you follow KG's lead. The RSS265 and RSS315 are good choices depending on space and budget.

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Originally Posted by smokarz View Post

wow...this is a great thread.

but i haven't seen two things mentioned yet.

1) where does the receiver calibration (e.g Audyssey, MACC, etc.) falls into this?
2) what if you have a single amp (EP4000) running all the subs (4, 6, 8)

would anyone care to elaborate? thanks

You can run auto-setup first with your mains, surrounds and Sub A (preferrably the farthest away front sub that puts out most of SPL) so your receiver will have the distances and levels set for your LCRs and surrounds. Then do the multisub setup like I've described above.

I would do Audyssey after all of this. You will run all of your multisubs off of the LFE channel, so Audyssey will treat your multisub as just a single sub. I only have experience with Denon's Audyssey and it works for me, but I wouldn't be surprised if it got a little thrown off. I don't know how MCACC or the others work well enough to say.

Don't be afraid to override crossover points. Auto-setup will determine this based on criteria that is not really relevant IMO. Tweak this to suit (basically as high as you can go until you reach your threshold for localization...it will be higher than you'd guess).

Audyssey should smooth some stuff out. You might let it do any EQing at this point. There are really a number of ways to go about it and they depend on many variables unique to each person's situation.

How do you do this with a single mono amp running all subs? Well, you are really kind of cutting yourself off at the knees. I'd probably suggest trying to split your primary subs (Sub A and B from above) onto stereo channels of the amp.

I would suggest having the ability to alter level and phase for each independent "bass source" or cluster of subs.

Of course you can try just spreading the 4-8 subs out across the front to excite different modes and treat them as one along with "Sub C" in the back as the filler. YMMV. You might get results equally as good or slightly less. There are many ways to skin this cat and experimentation is key.
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1) where does the receiver calibration (e.g Audyssey, MACC, etc.) falls into this?

It doesn't.

None of the major auto-calibration systems handle modern multisub systems properly. Not even ARC. JBL's external BassQ unit is theoretically the closest, but it seems there are about six of them in the world.... (Its price makes it generally unpopular. Its performance limits - no manual overrides, just one band of PEQ per channel, 20Hz fixed HP, etc. - make it unpopular with many hard-core enthusiasts who would otherwise be willing to pay for it. Roger Dressler has written a few posts about his use of it, which are very useful reading.)

Honestly, with a multisub system and properly-placed high-quality mains, the major benefits of a "room correction" suite are really just master volume control calibration (setting "0dB" as cinema reference level) and other things like loudness compensation (Audyssey DynamicEQ, Dolby Volume with the compression part turned off).

Chances are, when you run the room correction, it's going to mess something up. IMO, the best approach is to set things up with a room correction system is as follows:

(1) Set things up properly, as discussed above. One could argue that using parametric EQ to flatten to the nth degree optional here, because the receiver calibration will run EQ to fit the bass to its target curve, and if it does badly it'll mess up your work with the PEQ anyway;
(2) run Audyssey/ARC/etc;
(3) manually change the xover settings to what you determined in the initial setup;
(4) run sweeps with the mains and subs running together again, to fix anything that the autocal system messed up, employing PEQ here to set the overall curve to your preference;
(5) Enjoy music.

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2) what if you have a single amp (EP4000) running all the subs (4, 6, 8)

Don't do that. One loses too many degrees of freedom that way. If one must do that, then one should expect to require some fairly drastic EQ'ing.

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The big problem with Audyssey is it will try to boost in the null, which will cause HD at the null causing the driver to max out at the frequency.

Here is a graph of just that... I did a short window to see what the driver was doing and uncovered this. You couldnt see it at the LP with a plain sweep frequency response graph.... It was like 5%HD


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post #28 of 41 Old 01-20-2012, 09:34 AM
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Are you suggesting sweeps with mains and sub, or the whole system and subs...[/IMG]

Sorry, missed that earlier.

Front three mains and subs, all at the same time. The way I usually do it is to use a 2-channel mono source (Velo SMS-1; for longer sweeps or if I want to verify that the results from the SMS-1 sweeps are valid, I use FuzzMeasure Pro on my Mac, with a Y-connector on the output channel) and play with DPL2's center width control until all front speakers are playing the sweeps at the same level when close-mic'ed.

If someone has a better way to get an equal mono sweep to all three front channels, I'm all ears. My way is a bit of a kludge. Seems to work, though.

Only caveat is that for my purposes it can't involve analog multichannel inputs, because my AVR doesn't have them.

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Sorry, missed that earlier.

Front three mains and subs. The way I usually do it is to use a 2-channel mono source (Velo SMS-1; for longer sweeps or if I want to verify that the results from the SMS-1 sweeps are valid, I use FuzzMeasure Pro on my Mac, with a Y-connector on the output channel) and play with DPL2's center width control until all front speakers are playing the sweeps at the same level when close-mic'ed.

If someone has a better way to get an equal mono sweep to all three front channels, I'm all ears. My way is a bit of a kludge. Seems to work, though.

Only caveat is that for my purposes it can't involve analog multichannel inputs, because my AVR doesn't have them.

why not use the AVR's test tone?
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why not use the AVR's test tone?

It cycles from channel to channel, right? If there's an AVR test tone that plays in all front channels and the sub simultaneously, that could work on some software packages. Even though it would generally be pink noise, not a timed sweep.

Also, the hardware/software I use (SMS-1, FuzzMeasure Pro) generates its own sweeps. I don't know if FuzzMeasure can even use external tones. So I'd want to use those.

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