Just an FYI...seems like a good read. Chime in with any thoughts...

Multiple Subwoofer Set-Up & Calibration Guide

Yup. If there is one thing Audioholics has done well over the years it is guides like this.

Excellent discussion by Gene both as to multiple subwoofer placement and Audyssey use. As he mentioned, this in large part results from Dr. Toole's research, as most recently updated in his book Sound Reproduction. I might add that one arrangement not mentioned in the article, two subs in diagonally opposite corners, can also be quite effective.

Thanks John, I was wondering about this. I may have to try this as I have both my subs in front corners. Which obviously is not in the guide.

My room won't allow me to place the subs on opposite mid walls, but I can do opposite corners. I'll have to try this over the weekend.

Dana

It's not in the guide, but is mentioned here:

http://www.audioholics.com/tweaks/get-go...s-part-1-page-6

Thanks, haven't seen that yet.

Dana

Well, so much for my plan to do the four subs in each mid-wall. It sounds like the four corners is the way to go, but there's no good way to do that in the layout my basement will have. One corner is going to be a problem.

Not so fast, Charles. First, the language "...it will cause uneven frequency response for every seat..." doesn't appear to be supported by Dr. Toole's research or any other to my knowledge. In fact, the arrangement with one sub at each of the four mid-wall locations is one of those recommended both in the original Harman paper and the Toole book. Now, this relates to bass evenness, not bass strength. A sub in a corner is louder than a sub at mid-wall, so the mid-wall location is "inefficient" from the standpoint of level, although it can reduce unevenness caused by room modes. If the level is still adequate, this shouldn't be grounds for rejecting the mid-wall configuration.

If you read the book at pp.226-227, you'll see that a different four sub arrangement is most highly recommended from the standpoint of both level and evenness. This is a two mid-wall placement, but with two subs co-located(can be either vertically or side-by-side)at each position with drivers within a quarter wave length of each other so that they support each other with a resulting 6dB level increase. Dr. Toole states that "...it is, by a narrow margin in both MSV and overall sound level, the prime choice for a four-subwoofer solution. Either side or end midwall locations can be used. If corner locations turn out to be more practical, use them".

I agree John, I don't recall Dr Toole making such statements, actually the opposite would be true according to his work. 4 subs at midpoint would be ideal and give you great response at all seating locations. Even Ian confirms this in his videos and graphs. This may not be possible for everyone. 2 subs at midpoints gets you almost to the same results and is easier for most to accomplish.

Thanks for the reassurance, guys. It did seem odd to me. It was the first I'd seen of anyone shooting down the 4 mid-wall configuration.

I thought this way of calibrating the subs was interesting, in that I hadn't seen it before. I'm certainly not as well-read as a lot of you. I always assumed measuring at the listening position was the way to go. What do you guys think?

John, do you have a photographic memory?

Fred, I've got the book; so even if I got one of them pornographic memories I didn't need it for this.

Its wierd seeing the two 'K's talking directly to each other like this. I've always envisioned you two as siamese twins connected at the shoulders. Each with your own computer and keyboard, your own identity and all that good stuff...

But I guess I always figured if you ever wanted to say something to one another, you would just turn your head and say, "dang, you got some kinda photographic memory bro? I didn't get one of them darn it".

I did turn, but he had a book in his face.

John, you have a lot of enthusiasm for this hobby then. I'm happy to point people in the direction of reference material, but I am not motivated enough to look up specific page references to make a point.

Guy's

I've been in constant contact with Dr. Toole, and the senior folks at Harman (Sean Olive, Tod Welti). I don't want to speak on anyones behalf but Floyd was pretty clear to me that he preferred 4 corner placement with SFM (sound field management) vs 4 midwall placement with SFM or proper EQing. 4 midwall is very inefficient and a waste of sub power in most cases. I've never heard a 4 midwall placement that I thought exceeded a 4 corner placement or 2 midwall placement. I have Harman running real world tests and Matlab sims of my recommendations in my article and will be posting a followup. I also have some updates coming to this article based on my convos with Harman. They also invited me out to their facility to do further testing.

I've been slammed the last few days doing our annual speaker shootout for $1k towers which happened to include Axiom M60v3s. Very interesting results to post.

Rest assured there will be many followup articles to this sub article referenced here. Please also realize these are general recommendations to start with. Experimentation is key of course and not every configuration will be suited for any particular room. The main purpose of my article was to provide a methodical way to setup and calibrate multi subs to achieve the best results and minimize the guest work.

Hey, look what the cat dragged in.

I look forward to the sub articles and the speaker shootout. I'm curious to know how the M60 ranks against some of the more recent contenders in the $1k range.

Gene, good to have you stop by again and comment on this topic discussed in your excellent article. As I pointed out, Dr. Toole specifically endorsed the two mid-wall arrangement with two co-located subs at each position as being the best, by a narrow margin, of the options for four subs.

Guys;

I updated the article to remove the "uneven" comment of 4 midwall sub placement and also added a comment about the 4 corner placement as follows:

Used in conjunction with global equalization, this option provides nearly as good frequency response and seat to seat variation as the midwall placement with the huge advantage in efficiency.

There is much more coming trust me. This article is already over 8600 words so I didn't want to turn it into a novel. Its also been read by many of the key players in the industry and most of them have an interest in furthering this topic for industry education since its very confusing to people how to properly setup multi subs.

Regarding the Shootout
The Axioms did nicely in the shootout and more importantly we ate a lot of great food, consumed mass quantities of beer, and had fun doing it. But moving around the speakers on carpeted floors was quite a pain

Thanks for the clarifications, Gene. I look forward to further words on the subject. I know I'm going to need a lot of help when I finally get my system in its more permanent home.

Looks like I will have to get 2 more subs to fill in the last 2 corners of my room...

Dana

4 subs in my room is a pipe dream. The one I have now is the only one I will ever have in this room........if I want to stay married

Well...do you?

My room is octagonal, I need 8 subs.

What a wealth of knowledge here, gotta love it.

Isn't it more like:

My room is octagonal, I need 8 subs.

Technically, it's more like: My room is octagonal, standing waves are less of an issue.

True.

Wait, is this a typo or did the feline get released from the sack? Either Axiom is just trying to use up all the misprinted v3 labels or there is/will be a new desigination.

So... if someone wants to utilize the four corner placement of the subs but also wants to employ bass traps in the four corners, what effect does that have on the efficiency gains? Any penalties?

Corner traps are not effective much below 100Hz, so I would think you could do both without penalty.

This assumes you can fit both in the corner. I'm not sure how well that would work with 4 EP800s.

Very true. That could intrude into the room quite a bit. I imagine my room wouldn't allow that sort of configuration. I was asking mostly out of curiosity. I'm still looking at doing the four mid-walls. Even if it's not the most efficient, I don't think headroom will be a problem with four EP800s.

I think you are right with that, CV. Four of them shouldn't be straining at all. I still like the idea of mid-wall placement (or close to it) to minimize standing waves.

The corner placement is to maximize standing waves (or at least excite all the room modes with the least amount of energy). Then you can use what ever means to trim the worst peaks down, be it electronic or physical.

Sean, mid-wall placement uses the two techniques for lessening the effects of room modes(placement at points where the mode is at a minimum or placement where they're opposite in polarity and cancel)in combination. For example, mid side walls are at length mode minima and width mode maxima(but the opposite side wall is at the opposite width mode polarity). Corner placement is at all mode maximum points and uses the fact that the longitudinally and/or diagonally opposite sub is at a point where the mode is opposite in polarity to cancel the effects.

The two placements are similarly effective as to evenness of response, but the corner placement leads to a higher sound level per sub being realized. Note again the comments from pp. 226-227 of the book where Dr. Toole states that a two mid-wall placement with two subs co-located at each spot(and therefore strengthening the mid-wall output)was by a narrow margin the best of the options for a four sub placement.

*searches for the light bulb icon*

Thanks, that makes more sense now!

I wouldn't mind co-locating two EP800s on opposite mid-walls, but then it kind of defeats the justification for me getting two more EP800s. I was keeping the horizontals in anticipation of using them on the front and rear walls, where they would fit the best. The verticals, on the other hand, work better for me on the side-walls. If I was going to co-locate, then I would want all four as verticals to be placed on the side mid-walls. I suppose I'll try out both configurations and see how it plays out. If I end up wanting to keep them co-located, though, then the holes for the feet on the horizontals might bother me. I guess one way around that would be to have the horizontals laying down like they're supposed to and then have a stand of some sort elevating the verticals above them. Ha ha.

Charles, of course that two mid-wall plus co-location option can use either the side walls or the front and back wall.

The co-located subs can either be stacked on top of each other(presumably better with the horizontals)or placed immediately beside each other(better with the verticals). Note that the strongest mutual support would be if they were turned so that the drivers faced each other and were maybe just 2" apart.

Could the drivers possibly hit each other that close?

Interesting. I didn't know that about co-location. Poor subwoofers, doomed to never quite kiss all to give ME pleasure.

That's what I was thinking, too.

Don't know what the maximum excursion on the EP800 drivers is, but if it might be a problem, make it 3-4" apart. The idea is to have the two sets of drivers pressuring each other.

I suppose if the grill cloths didn't touch each other, the driver cones obviously wouldn't either.

I'm picturing Rock 'Em Sock 'Em Robots. . .but with subwoofers instead.

See which grille gets knocked off first.

CV needs to paint them red and blue first!

Xmech (maximum mechanical excursion) on the highest excursion woofers I know of is around 60mm. That is 30mm from the resting position or 1".

John. I thought you had to worry about compression if your driver is too close to another large object like a wall. The rule of thumb seems to be that if you locate two subs within a quarter wave Lent of each other you get the maximum gain (~6db) from co-location. This would suggest that a few inches would not make an appreciable difference.

On the other hand, if you put two EP800s about a foot apart facing each other, there should be just enough room for your head and maximum pressurization at the ears.

This is a most interesting thread indeed. But I for one would love it if someone could draw up some diagrams showing in detail the different positions so that I can confirm if I'm getting this right in my head. I think I have a pretty good grasp of 'four corner placement', but I'm not quite sure if I have the correct picture of 'co-existing mid-wall' sub placement kicking around up there.

Also, John when you say, "two mid-wall placement with two subs co-located at each spot(and therefore strengthening the mid-wall output)was by a narrow margin the best of the options for a four sub placement", does it matter which two walls were being used? I have a fireplace in the midwall location to the right of my seating area, and french doors in the midwall position to the left of my seating position. So the only midwall location available to me is the back wall (since the TV is obviously taking up the front wall).

So then, would the best 4-subwoofer set-up in my room be two subs co-located midwall along the back wall, and two corner loaded subs in the front two corners? Just curious.

One more question, I understand when talking about EP800's there are only woofers to contend with. But say with two EP600's or EP500's, do the ports pose any problems in doing this?

I want to see Obsi turn his eD subs towards eachother, crank it up, and see if he can't shift the earth axis point a smidge.

Kind of makes you wonder about the effect on a passive rad subwoofer too.

I don't think a port would make a difference. what happens is the two drivers/ports fire together and you get a sum of the output from the two devices as one wave.

Micah, the walls used have to be opposite each other so that the output of the sub(or subs)at one wall reaches the other sub or subs at a point where they're of opposite polarity and cancel some of the modes. So, if neither both side mid-wall areas nor both front and back mid-walls were available to you, then Dr. Toole's suggested setup(again, note he said just by a "narrow margin")couldn't be implemented. The four corner arrangement would appear to be best available option. The two front corner and back mid-wall co-location plan you suggest certainly shouldn't be bad, but there's no info available as to how it would compare with the four corners setup.

Ah, I see. Yeah my fiancee has her desk in the back, right hand corner, so 4 corners wouldn't work in here either. Not to worry though, as I was only asking out of curiosity. I don't ever see me having 4 EP800's in here.

Still, a guy can dream.

Aren't you still going to try an infinite baffle sub sometime?

It's still on the back burner... but once Axiom sent me the new EP800 with the new sub amp in it, the back burner got turned down to LOW!!! The performance I get now is really so satisfying that my eagerness to experiment with a lot of those other sub idea's died down quite a bit.

It's sort of like a teenage virgin thinking about sex 24/7 because he doesn't have it, so sex consumes his every thought... Then 5 years later the same kid is working in porn, shooting 3 or 4 movies a day, constantly bombarded with sex, sex, sex all day long... I'm not saying he gets tired of sex, I'm just saying it's definately not going to be the ONLY thing on his mind anymore!