# Help, Placement of four subs regarding room modes



## mikesp1 (Oct 30, 2012)

I am wondering if someone can give me some advice regarding placement of four subs regarding room modes.

room is 11.7 foot wide
20.8 foot long
7.6 foot high

Two subs in middle of front and back wall, four subs in all corners, four subs at 1/4 of all corners, subs 1/4 elevated from floor?

Thanks a lot!

Read more: http://www.hometheatershack.com/for...er-klipsch-palladium-p17-9.html#ixzz2a88ACcaN


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## hjones4841 (Jan 21, 2009)

I have my 4 Hsu ULS-15s spread across the 12' front wall of my HT. With that spacing, each one is 1/4 wavelength or less from the one next to it. According to what I read, that will allow reinforcement by co-location down to the 1/4 wavelength. Of course, that is more about output than room mode "control" but it does provide a smooth response. I am using a receiver with Audyssey XT32, so that helps.

Bass traps will help room modes to a degree, but also will control ringing in the room to "tighten up" the bass response in the room.


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## sdurani (Oct 28, 2010)

Your room's width modes are: 48Hz, 97Hz, 145Hz, 193Hz, 241Hz, etc. 

Your room's length modes are: 27Hz, 54Hz, 163Hz, 217Hz, 272Hz, etc. 

My ideal placement with 4 subs would be to place them at the quarter points of room width and length (2.9 feet in from the left/right walls, 5.2 feet in from the front/back walls). This will cancel the room's first 3 length and width modes. 

Alternate placements will depend on seating: do you have one row of seats or two rows? Are you willing to move your seating to get smoother bass response?


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## mikesp1 (Oct 30, 2012)

Sdurani, 

Thanks, very usefull information!

I have one row of seats approx 6.5' from backwall. Cant move seat much.

Would installing the two back subs in the rear wall at 1/4 from left and right side wall make a hugh difference? The rest of the subs ad per your recommandation.

Hjones,

The method of four subs on frontwall did not work verry well in my room, but any way thanks for the recomdation!


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## sdurani (Oct 28, 2010)

Placing the listeners' ears 1/3 of room length from the back wall will put you where there is the least variation in frequency response. Your current seating location is inches away from that spot, so it is up to you whether to move your seating to the 1/3 room length location. 

With that in mind, I would place the subs on the side walls, 1/4 of room length from the front and back walls. This will cancel your first width mode at 48Hz (higher modes at 97Hz and 145Hz are likely above the subwoofers' crossover point). Because the subs are at quarter points of room length, they will cancel the first 3 modes at 27Hz, 54Hz and 81Hz (the first 2, if not all 3, are likely within the range your subwoofers will be reproducing). 

You can read the science behind it in the following paper: 

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/LoudspeakersandRoomsPt3.pdf

You only need to read the first paragraph on page 14 and look the diagram above it.


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## mikesp1 (Oct 30, 2012)

Verry interesting again,

So if i understand correctly as per your last recommandation the subs will face with the drivers from side walls to middle of room, first recommandaion the drivers were facing fron front an bacwall to middle of room?

Last recommandation is less doable because of room doorways etc.

I could stack them and build in two subs in right side wall at 1/4 from back and stack the two other in right sidewall at 1/4 from frontwall? Ofcourse This will not give the same performance as decribed in the harman papers.


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## sdurani (Oct 28, 2010)

They're subwoofers, so the drivers can point in any direction, even down.


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## mikesp1 (Oct 30, 2012)

sdurani said:


> They're subwoofers, so the drivers can point in any direction, even down.


The relative phase will change if the drivers are facing other directions...and as i understand from the Harman papers the drivers must be all in phase to overcome roommodes?

So i think it does make a difference how the drivers are facing regarding wich modes they handle.


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## sdurani (Oct 28, 2010)

mikesp1 said:


> The relative phase will change if the drivers are facing other directions.


I never heard that, but I'm no subwoofer expert.


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## fusseli (May 1, 2007)

You should give the latest beta version of REW a try, which includes simulation for rectangular rooms with up to four subs.


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## mikesp1 (Oct 30, 2012)

fusseli said:


> You should give the latest beta version of REW a try, which includes simulation for rectangular rooms with up to four subs.


Thanks, i will try!


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## mikesp1 (Oct 30, 2012)

Well, nice simulation program!

It would be nice if i could simulate some subwoofers build in to the back walls also, right now the minimum distance to the wall is 30.

I think the best location for my subs is two on front an back wall.
One in the four corners is even better, gives less peaks, but not possible in my room because of permanent installed basstraps in all corners.
I can filter the minor peaks out with a mini dsp and have same results as with subs in all corners. (Spl is the same, just a few peaks within 5 db)

All the other mentioned positios, for example 1/4 on side wall etc was worse with the simulation.
So, verry handy program and it seems to stroke with my conservations by ear.


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