Dr. Floyde Toole and Sub Placement in a Room

[paul08]

Hi folks,

Dr. Floyde Tool has demonstrated through years of research that sub placement in a rectangular room (Mine is 25 X 15 X 10) is most efficient and smooth response when subs are placed at the mid point of each wall. After hours of measuring and moving subs all around my room I have found that five subs across the front of the room (25') has the smoothest measured response. I'm certainly no one who could hold a candle to Dr. Toole's long career and knowledge in audio acoustics. I've read all the FAQ's on the website here and all of the threads regarding sub placement. I was wondering if anybody has done extensive multiple sub placement in a room prior to installing IBS's? I have the luxury the way my house is built that I can install IBS's (Single or multiple) in any location in the floor.

Thanks for any help.

Paul

[ThomasW]

Nope no one has done anything like what Toole recommends since no one is custom designing and building a house around their subwoofers.

My guess is as it evolves this build will be as close to a Toole design as we get.
ibsubwoofers.proboards.com/index.cgi?board=projects&action=display&thread=1391

[paul08]

Hey guess what?!? I'm one of those idiots that actually did design my entire house around the Audio/Video room!!! The width of the room was supposed to be 24' but some how my tape measure measured 25'! Stupid tape meaure!!! The shape and size of the room was based on software by the late great Roy Allison (not Orbison, though he's cool too). Currently I am using five of Seigfried Linkwitz's "Thor" subwoofers. I'm curious why 5 sub woofers across the front of the room have a smoother response than 4 sub at the mid point of each wall. Does anyone have any idea why this appears to be better than what Dr. Toole has to say?

[ThomasW]

It's a little difficult to comment not being about to see the acoustical 'map' of room showing measurements of the subs in the various locations.

[matt]

After reading your post, I read Todd Welti's presentation on multiple subwoofer placement, based on work instigated by Floyd Toole.

Subwoofers: Optimum Number and Locations by Todd Welti
www.harman.com/EN-US/OurCompany/Technologyleadership/Documents/White Papers/multsubs.pdf

There's an academic paper available as well, but I haven't read that yet.

The conclusion seemed to be that the recommended number of subwoofers worked best to reduce the standard deviation between the different seats in the listening area, and thus gave the best result after equalisation, not that it gave the smoothest response before equalisation.

There was a simulation of 5 subs across the front wall. That gave one of the worst min-max and std.deviation variations between seats.

Are you saying that 5 subs gives you the best unequalised result for a single listening position, that it gives you the best equalised result over a range of positions, or something else?

Thanks for putting me onto Floyd Toole's work, it's fascinating.

[paul08]

Here are some measurements. I used a RS meter first, but then I went back and varified the numbers with my Audio Control SA-3055 SPL meter.

[paul08]

Correction: On the fourth graph down it should say "Center sub " not "Center speaker".

[chrisbee]

On the last graph the red line looks useful.

[ThomasW]

This is a bit confusing. Your thread focuses Toole's/Harman multi-sub placement concepts, then you post graphs of a single listening position.

It would be best to use more modern measurement techniques and equipment. Gated energy/time or swept sine are far superior to fixed frequency sine-waves or ungated pink noise.

When you talk about 'in-phase' do you actually have a device that adjusts phase or are you just reversing the polarity of the subs mentioned?

[paul08]

If you notice the first graph is the only one marked single listening position. All of the other graphs are multiple positioned, and then averaged.

The audio source is a 1/2 octave Warbler Oscillator, which is somewhat of an analog swept sine. The Audio Control was used for measurement, not source.

What I mean by reverse phase is electrical, yes 180 degrees.

[twisterz]

I would like to see someone do 4 IB manifolds at the 1/4 distance from each corner in the ceiling

[paul08]

Okay folks, after weeks of measuring and running sweeps using REW, I have some results. After measuring for five listening positions with 12 different sub placements (60 measurements), I sent all the measurements to Todd Welti at Harmon International for optimizing the best locations for the least amount of spatial variance per listening position. The point of this was not for the maximum SPL for the subs.

This first image is a rendering of the audio room (seating placements and room dimension).



And here is the data Todd sent back (I believe he used Matlab). Thanks, Todd for all your help with this exercise.

[dougsmith]

Interesting. Were the measurements made with only one sub? I would go for #1.

[jonfo]

Very cool, thanks for sharing. And I'm impressed Todd did the analysis.


Based on my reading of Floyd's work and Todd's research as well as Sean Olive's writing, I've decided to pursue a dual manifold setup in my dedicated HT.

I already have an IB centered on the front wall, and will be adding another IB centered on the opposite wall.

This is one of the 'ideal' configurations from their research.

I'll then let my Denon AVP-A1, which handles multiple subs (independently) plus Audyssey Pro handle getting it tuned just right.

The primary benefit will be smoother seat-to-seat response as well as mitigating a slight null at the main listening position (even though this was a custom room design designed to minimize that stuff).