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#413050 - 06/26/15 02:42 PM So how do you 'sub crawl' two units?
MatManhasgone Offline
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Registered: 05/06/14
Posts: 998
Loc: Lost in the great wide yonder
I have ordered, but they won't get shipped for a bit yet, two EP500 units.

Right now I have a pretty cheep Polk 10" sub that I think has a frequency range of 35hz-100hz, but considering my LFR1100 can cleanly get much lower than that sub, I didn't see the point.

Now I have seen many video's both here and you-boob-tube that covered the sub crawl where you put your sub where your listening spot is then crawl around to find the best sounding spot, then move your sub there.

Great for a single sub, but how does one go about setting up two subwoofers?? As each is sending out it's own wave, you are going to get potentially now more peeks (where the two waves cross on a peek or valley) or nulls (where a peak crosses a valley). How is best to find the right spot for two of them?
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#413052 - 06/26/15 03:40 PM Re: So how do you 'sub crawl' two units? [Re: MatManhasgone]
casey01 Offline
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Registered: 07/03/08
Posts: 852
Loc: Toronto
Frankly speaking, if you have purchased two EP500s, I wouldn't worry that much about location as long as they are not located directly opposite each other on opposing walls. As with many of us, the sub crawl has limitations in that what might sound the best to your ears at a particular location in the room might not necessarily be practical for placement. Two subs of the EP500s caliber will mitigate many of the issues you are concerned about. You just have to make sure phase and volume levels are set properly.

I have FOUR subs and because of those space limitations in my A/V room, I had to place one in each corner slightly behind each one of my Left/Right Main speakers. The other two are behind me on opposite walls. When all is said done the sound turned out great. I never did the sub crawl, there is just too much furniture in the room to worry about all that. As I stated, once you set your phase and volume levels correctly, everything should work out fine.

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#413055 - 06/26/15 04:17 PM Re: So how do you 'sub crawl' two units? [Re: MatManhasgone]
nickbuol Offline
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Registered: 09/16/04
Posts: 5325
Loc: Marion, IA
There are some articles on the interwebs that state that if you can't do "the crawl" as to where things should be placed for minimizing room modes (peaks and nulls).

I looked this up when I added my second sub.

The #1 suggestion was one sub dead center in front and one sub dead center of the back wall.

Obviously if you have a TV setup, that can be difficult. For me, I just didn't like the look of the sub on the back wall. It also was a bit odd for me because I have 2 rows of seats and my large 4cuft sub is downfiring, meaning that the woofer is "walled in" on 2 sides by, well, a wall and 12" of riser (plus the seats).

The 2nd best option was to put them both up front on the main wall, about 1/3 of the width of the wall in from the sides. This may force some to bump their front left and right speakers out to make room for the subs. That all assumes a reasonably sized room and not something with a 20+ foot wide front wall.

I went with option #2 because it also let me hide everything up front behind my false wall and screen.

I don't recall what a 3 sub configuration looked like. A 4 sub setup was 1 sub centered on each of the 4 walls. That is supposed to be "ideal" and no sub crawl required, but who has space for 4 subs. LOL (I joke because I know some people do.)
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#413056 - 06/26/15 04:29 PM Re: So how do you 'sub crawl' two units? [Re: MatManhasgone]
Serenity_then Offline
connoisseur

Registered: 03/28/14
Posts: 1565
Loc: PEI, Canada
Heres a link to a relink of a harman subwoofer presentation/study. I cant expound on anything Nick said. Spot on as usual. wink

http://www.wghwoodworking.com/audio/multsubs.pdf
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Trevor. Cold turkey. Thanks guys. Cheers.

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#413057 - 06/26/15 04:33 PM Re: So how do you 'sub crawl' two units? [Re: MatManhasgone]
Serenity_then Offline
connoisseur

Registered: 03/28/14
Posts: 1565
Loc: PEI, Canada
_________________________
Trevor. Cold turkey. Thanks guys. Cheers.

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#413059 - 06/26/15 04:54 PM Re: So how do you 'sub crawl' two units? [Re: MatManhasgone]
DrStrangeQuark Offline
old hand

Registered: 05/09/14
Posts: 87
Loc: Texas
Hey Matt -- Congrats on your subs! I've got the same coming, probably on a similar timetable. To go with m80s, not the LFRs though. They will be in my office for the next "little bit" until the theater room is done.

Its an interesting question. In my my case, and in keeping with Casey's comments, the placement will be largely dominated by the design of the room. Unless it just really doesn't work at all, the placement will be outside the screen, behind and to the outside of the mains, close to the front L/R corners. Corners are good for exciting all room modes & getting lots of output but potentially there are downsides as well. Potentially, the symmetry of this setup could work against this placement (mirrored excitation of modal points), but I will guess that some phase tweaking could help.

My impression of the newer Audyssey SubEQ HT module is that it first analyzes each sub's output separately (up to 2 IIRC) and then secondarily considers the question of how they interact . This could potentially be handy. In fact, here's an official quote I just found from their Q/A page .

Quote:
MultEQ XT32 is the flagship version of our technology to measure and correct room acoustical problems. Sub EQ HT is a method we came up with to deal with multiple subs. If you only have one sub then it's not in use. The idea is to first measure each sub separately, then apply delay and level settings so that the two subs are now time and level aligned. Then we ping them once more as "one" sub to derive the room correction filter.


Delay, phase adjustment, and relocation of the sub will have some overlapping consequences (with more or less similarity in the first two depending on the implementation (digital vs analog, say). Some interesting discussion on the difference between phase and delay here (posts 19,22,23 are insightful, among others) . I seem to recall a comment from Andrew that the phase is usually set correctly whenever the bass feels the "fullest". Again, I will guess that the phase dial might be comparably valuable to (and perhaps even more valuable than) physical relocation for tweaking the 2-sub interference pattern (possibly while retaining the benefits of corner excitations), although there could likewise be consequences to changing the phase relationship relative to your mains in the frequencies where they are playing together (crossover range).

My best guess to a starting point on the answer is this: place each sub where the sub crawl tells you to put it on its own. Then adjust the relative delay/phase to optimize the pair together (either by hand or with Audyssey, etc.). Disclaimer: this is a low experience opinion ... those with more experience might confirm or refute. In my case, the plan will be to place according to the room design (with the idea that corner positioning is generally good for output levels, at least), and then let Audyssey try its thing out.

Don't know if that helps, but interested in hearing your experience on i) the optimization of dual subs and ii) how the subs contribute the the experience with your LFRs. The residual benefits of a (near) full range speaker when you have a nice sub have been discussed elsewhere, and since your speakers are about as full-range as they come (and well powered to boot) the contribution will be interesting. As will Craig's upcoming "super speaker" M100 + EP800 experiment.

Cheers - DSQ

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#413060 - 06/26/15 07:01 PM Re: So how do you 'sub crawl' two units? [Re: Serenity_then]
DrStrangeQuark Offline
old hand

Registered: 05/09/14
Posts: 87
Loc: Texas
Originally Posted By Serenity_Now
Heres a link to a relink of a harman subwoofer presentation/study. I cant expound on anything Nick said. Spot on as usual. wink

http://www.wghwoodworking.com/audio/multsubs.pdf


Very interesting read, thanks Serenity. Nice takeaways here:

Quote:
Four subwoofers are enough to get
the best results of any configuration
tried. Two subwoofers is very nearly
as good and has very good low
frequency support as well.

One subwoofer at each wall midpoint is the best in terms of
Std, Max-ave and Max-min but does not support low
frequencies particularly well. Two subwoofers, at opposing
wall midpoints, performs very nearly as well as four at the
midpoints and gives a much better LF factor. One
subwoofer in each corner also has good low frequency
support, but does not perform quite as well as one
subwoofer at each wall midpoint, in terms of Std, Max-ave
and Max-min. If cost and aesthetics are considered,
subwoofers at 2 wall midpoints is preferred.


Indeed, it backs up Nick's comments.

Interesting note regarding front corner placement canceling odd harmonic modes (because opposing walls are both at pressure maxima, but out of phase). But, presumably this is at the cost of reinforcing even harmonics, and scoring only a very average point-to-point standard deviation score (configuration 4). Its a delicate balance ... modes help with output and coupling of the room/driver, but also introduce coloration to the response.

It is remarkable how much lower the point to point variation is in configuration 6 (center walls, opposite), while it does just as well in the net low frequency output. In this case I would suppose that it is tending to excite the even (symmetric spatial distribution & even number multiples of the lowest resonant frequency) axial modes associated with the side-to-side room dimension (which are the same to survive in the corner placement), while exciting all modes in the direction of the sub's separation, but again with cancellation of the odd harmonics. Not obvious why this is better. Hmm ...

Also remarkable is how steady these results are with regards to changes in the room dimension. I guess this makes sense ... the specific modal frequencies will scale (inversely) with room dimensions, but the nodal locations will keep their same relative spatial distribution. Not to say room dimension is irrelevant, but rather just that this metric doesn't capture it ... the even distribution of modes in frequency space may be much better/worse as certain dimensions become more independent or redundant, respectively.

Last thought ... one of the explicit assumptions of this test was that the transducers were in phase. I am curious if it might be possible to essentially invert the conclusions by tinkering with phase, giving better flexibility in placement.

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#413062 - 06/26/15 09:57 PM Re: So how do you 'sub crawl' two units? [Re: MatManhasgone]
MatManhasgone Offline
aficionado

Registered: 05/06/14
Posts: 998
Loc: Lost in the great wide yonder


My room has some difficulties in it's almost square 17' wide by 18' long. At one end there is a small room for the electrical box because they didn't leave enough room for the wires to lie flat against the wall. At the other end there is a large draining pipe that sticks into the room. The ceiling is multiple levels with the lowest part being 6'2" high, and another part is 7'6" but by the speakers it's 8'6".

Now with the electrical room, I loose a good 18" into the room. Ideally I would put the LFR's 3' from the wall, but doing that, the seating position would need to be pretty much against the back wall. Alternatively if I move the left speaker inwards and put it beside the electrical room, and say put the speakers 2' off the wall then I could get the seating position inline with the QS8 surrounds on the side walls.

My thought was to put the two subs on the left hand wall where the pre/amp's are going.


Edited by oakvillematt (06/26/15 10:09 PM)
_________________________
Anthem: AVM60
Axiom: ADA1000, LFR1100, VP180, QS8, EP500, M3, M3comp
AudioSource: Amp One/A

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#413063 - 06/27/15 06:54 AM Re: So how do you 'sub crawl' two units? [Re: MatManhasgone]
Serenity_then Offline
connoisseur

Registered: 03/28/14
Posts: 1565
Loc: PEI, Canada
Matt-

Where is your sofa front to back? In that room for performance/practicality sidewall midpoints would be where I'd start. Then they are out of the path of walkways. The front wall would work too, but you would have to test just where the best spots were due to the mech. bulkouts. Can you center it up better at all?

I suppose its too late to suggest using the right wall or left wall as the front orientation of your setup. Or is this your temp room?

I wouldnt put them both alongside the left wall. Your seating will fall in an area where the distance away from the subs varies too much and seat to seat performance will be all over the place.

Nick, DSQ, everyone-

Since we are talking about "ideal" subwoofer outcomes, here's a podcast where Paul Hales refutes the notion of all seat optimization in preference of reference performance for a smaller footprint in the room. The setup Nick employs is preferred by me as opposed to midpoints (have lived with both scenarios in same old room) because of the net wavefront effect subs have when placed in tandem on the front wall at 1/4 or 1/3 points. Midpoints net equal bass distribution, but equal bass is not always the best bass.

_________________________
Trevor. Cold turkey. Thanks guys. Cheers.

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#413071 - 06/27/15 04:25 PM Re: So how do you 'sub crawl' two units? [Re: MatManhasgone]
MatManhasgone Offline
aficionado

Registered: 05/06/14
Posts: 998
Loc: Lost in the great wide yonder
I never really thought of having the screen on the other wall. it's a bit late now to change as wires are already in the wall and drywall is going up.



and from the other side



The ceiling isn't quite as bad as I had said.. there are sections that are lower and i have tried to box it in the best as to give you head room. i don't like sitting under a very low ceiling personally.
_________________________
Anthem: AVM60
Axiom: ADA1000, LFR1100, VP180, QS8, EP500, M3, M3comp
AudioSource: Amp One/A

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