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CEDIA presentation of 4 subwoofer configurations

bluestone, modified 12 Years ago.

CEDIA presentation of 4 subwoofer configurations

Youngling Posts: 2 Join Date: 6/15/09 Recent Posts
My collegue recently attended a CEDIA talk given by Dr Floyd Toole which advocated aiming for 4 subwoofers in home theatre designs.

The aim was to create an opposing subwoofer displacement that would counteract a few of the primary room cancellations thus providing predictatable seating corridores away from the main room modes and eliminate some of the big modes.

For a typical rectangle theatre, a suggested layout was for 2 x subs on the front wall each placed 25% in from the left and right corners. The same layout applied for 2 x subs on the back wall.

The paper also recomended putting all of the subwoofers in phase with each other and all running at the same volume.

Some issues I see or would need to be adressed would include;
* Achieveing a tight phase relationship to the main speakers
*Creating new and less predeictable cancellations in audience seating zones by the timing issues between 4 subs in different locations.
*The impact on the attack of the system - a smearing of the subs
*Is there a potential impact on the mid-high frequencies when the room is preasurised to this level?
* "Sub to Audience" proximity issues where many typical home theatres lack the extra space at the back as you have between the front wall and the front row.
*The assumption that all walls will provide the same and predictable or equal boundary barriers.

Given that CEDIA have featured this as a Keynote talk and that many of your designers and installers are probably CEDIA members, I thought this is worth exploring from a Genelec perspective and what Genelec have observed with multiple subwoofer placements such as this.
dupe, modified 12 Years ago.

Re: CEDIA presentation of 4 subwoofer configurations

Youngling Posts: 14 Join Date: 5/8/09 Recent Posts

Good question and one that I am also interested in, I did the THX training in the UK a couple of months ago and raised the same questions you have. From the tests that I have done so far with 2 subwoofers I can confirm that subjectively its difficult to set up due to phase/time issues, even using my test kit (time domain) its hard work and obviously you have to compromise. Gun shots etc are very clearly time smeared and the transient response is lost. Its very similar to using very heavy EQ on a system where you have phase differences at the points you filter heavily. I want to do more work, but I am not convinced, the THX training is VERY focussed on frequency response and I know that this is only part of the story. I won't be using these methods yet, one sub positioned well, along with correctly positioned seating is the way I will continue to design rooms for the moment anyway...

I would be interested to here the Genelec response too....

ilkka-rissanen, modified 12 Years ago.

Re: CEDIA presentation of 4 subwoofer configurations

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts

Thank you for your post and question. Unfortunately I can't give you much more information beyond Todd Welti's paper ( because we haven't really looked into the issue here at Genelec. The honest truth is that not many of our customers have the possibility to use this kind of 4 subwoofer configuration, so therefore we either haven't seen it as a very important issue to look into. I'm not saying it doesn't work (at least in theory and in "perfect" rooms) but there are some hurdles in normal rooms which aren't perfectly shaped and don't have identical or even similar walls/boundaries construction wise.

But if you are interested, I could set up four identical subwoofers to one of our listening rooms, take some measurements, and post them as well as my subjective notes on the issues you brought up? :?:
tolka, modified 7 Years ago.

Re: CEDIA presentation of 4 subwoofer configurations

Youngling Posts: 1 Join Date: 1/27/15 Recent Posts
I added a 7050b subwoofer to my 8030 stereo monitoring system. I don't have a measuring equipment available at the moment so I tried to make the adjustments by ear following the manuals instructions........!!!!!!!!!!!
digipete, modified 7 Years ago.

SAM system use of multi sub's

Padawan Posts: 99 Join Date: 6/18/11 Recent Posts

I think it would be extremely valuable to have an in depth study of the value of multiple sub's in a SAM system.
Few of us can afford to buy 2 - 4 SAM sub's just to play around and find what work and not.
And even before that the base questions:

1) What possible ways can you X-over / split the .1 and sub 80-120hz and still benefit from the room correction in SAM ?
2) Does GLM 2.0 add to these possibilities?
3) Is the "Steinway Lyngdorf" type use of two subs in front corners beneficial and best sub setup possible under GLM?
4) Will Genelec allocate some resources to investigate, implement & advise / whitepaper findings in multi-sub use in the future?


Peter Ring