Room design question re: dual sub placement - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 6 Old 07-06-19, 10:15 AM Thread Starter
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Question Room design question re: dual sub placement

I'm rebuilding my basement theater. It's irregularly shaped, as shown in the attached drawing. The screen wall (on the left of the drawing) is 14' 1" wide. The main part of the room is 15' 9"' deep, but halfway across it goes back another 6' 3" into a recessed area.

My wire-frame equipment stack with everything from my disk player to my projector will be in the mouth of the recess.

I've been planning to put my two subwoofers in the front left and right rear corners, 21' 1.5" apart (according to Pythagoras), but it has occurred to me that I could get longer wavelengths - and thus lower frequency bass - if I used the longer 26' 1" throw from the right front to the left rear.

However, that would put my disk player and other equipment almost directly in line with those standing waves.

What advice can I get on this?

PS To enlarge the drawing, click on it thee times. The theater is the area near the bottom of the drawing.
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Last edited by Philnick; 07-06-19 at 12:01 PM. Reason: Add diagram
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post #2 of 6 Old 07-06-19, 01:31 PM
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Re: Room design question re: dual sub placement

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I've been planning to put my two subwoofers in the front left and right rear corners, 21' 1.5" apart (according to Pythagoras), but it has occurred to me that I could get longer wavelengths - and thus lower frequency bass - if I used the longer 26' 1" throw from the right front to the left rear.

However, that would put my disk player and other equipment almost directly in line with those standing waves.
The wavelengths coming out of the subwoofer are the same no matter where you place them - they're tied to the frequency being played - so I'm not sure you're going to get "longer" ones by moving the subs further apart. You will change room modes that way, which directly impact peaks and valleys, but it really shouldn't make a difference with regards to how low the subs play.

Unless you're using something like tapped horn subwoofers it's unlikely having your equipment 20+ feet from the subs will cause any problems. Most people have their electronics much closer then that without issue.
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post #3 of 6 Old 07-06-19, 03:56 PM Thread Starter
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Re: Room design question re: dual sub placement

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The wavelengths coming out of the subwoofer are the same no matter where you place them - they're tied to the frequency being played - so I'm not sure you're going to get "longer" ones by moving the subs further apart. You will change room modes that way, which directly impact peaks and valleys, but it really shouldn't make a difference with regards to how low the subs play.

Unless you're using something like tapped horn subwoofers it's unlikely having your equipment 20+ feet from the subs will cause any problems. Most people have their electronics much closer then that without issue.
Remember that the diagram is lying on its side, with the screen wall (the front of the room) on the left in the diagram.

If a sub is placed at the left rear (the bottom right corner of the diagram), it would be about 8 feet behind the equipment stack, firing in a nearly straignt line across the equipment to the opposite corner, where the other sub would be.

If placed at the right rear, that sub would be around the corner from the equipment and seven or so feet away along that wall, playing entirely forward of the equipment.

That's why I'm leaning towards using the shorter throw, to protect the equpment from vibration interfering with playback.
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post #4 of 6 Old 07-11-19, 04:23 AM
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Re: Room design question re: dual sub placement

Philnick
I like your thinking, looking for every advantage and/or parameter. Although sound waves in general do elongate in unrestricted air however there are other considerations to reckon with.

** as waves travel in open areas they will elongate however there is a corresponding
drop in amplitude also a factor for consideration.

For further consideration: a 20hz sound wave length is approximately 56ft long and an 80hz wavelength is approx 16ft. (80hz is a common setting for system low pass crossover point). There is also the consideration of "room gain." Room gain has a varied and inverse relationship with room size with smaller rooms showing increasing amplitude gains.

Bottom line: Your duel subs will fill the room adequately if you want greater detail and/or amplitude buy another subwoofer or two etc etc. When setting up i would consider the time tested "sub-crawl"

If i had a large or small area to cover i would begin by placing the subs in/near corners diagonally opposing each other (facing each other) and move one or the other 6" at a time along the wall, closer or further from each other until sound waves fall in phase enough for a pleasing effect. You may even notice a lowest freq gain.

Its late/early my head hurts - having fun yet...

Last edited by wantAvote; 07-11-19 at 04:50 AM. Reason: resolution
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post #5 of 6 Old 07-11-19, 03:18 PM
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Re: Room design question re: dual sub placement

Yes the old "sub crawl" beats room theory hands down - there are way too many variables beyond room size to predict the placement of one sub, let alone two. On that point, you will have more control over the situation by doing one sub at a time...

Choose one sub and play a swept tone through it. (I've had good results with this tool: http://onlinetonegenerator.com/frequ...generator.html) Move the sub (as the previous poster suggested) by a few inches at a time, and find the spot for the sub that gives the best, solid response at your desired listening position(s). Adjust the crossover frequency to get the best transition to the rest of your system (especally the center channel). Once placed, adjust the phase for the best image in the transition frequency band. (For phase, you can also play pink noise and/or music with lots of energy through the crossover region and set the phase so the sound is "located" solidly.)

Once the first sub is placed and tuned, keep it on, and then add the second sub and repeat the whole placement/tuning process for the second, but listening now for how the pair of subs work together. Don't be disappointed if no placement/tuning sounds better than with just the first sub alone - it happens sometimes! In that case, just unplug the second sub and find another system to put it on.

Note that all of this should be done with no EQ (Audyssey etc.) applied, as that will usually muddy the waters. Get the subs roughed in, and then any further EQ will have more of a chance to do its thing effectively.
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post #6 of 6 Old 09-11-19, 10:45 PM
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Re: Room design question re: dual sub placement

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los153 wrote: View Post
Yes the old "sub crawl" beats room theory hands down - there are way too many variables beyond room size to predict the placement of one sub, let alone two. On that point, you will have more control over the situation by doing one sub at a time...

Choose one sub and play a swept tone through it. (I've had good results with this tool: http://onlinetonegenerator.com/frequ...generator.html) Move the sub (as the previous poster suggested) by a few inches at a time, and find the spot for the sub that gives the best, solid response at your desired listening position(s). Adjust the crossover frequency to get the best transition to the rest of your system (especally the center channel). Once placed, adjust the phase for the best image in the transition frequency band. (For phase, you can also play pink noise and/or music with lots of energy through the crossover region and set the phase so the sound is "located" solidly.)

Once the first sub is placed and tuned, keep it on, and then add the second sub and repeat the whole placement/tuning process for the second, but listening now for how the pair of subs work together. Don't be disappointed if no placement/tuning sounds better than with just the first sub alone - it happens sometimes! In that case, just unplug the second sub and find another system to put it on.

Note that all of this should be done with no EQ (Audyssey etc.) applied, as that will usually muddy the waters. Get the subs roughed in, and then any further EQ will have more of a chance to do its thing effectively.
I'm in the process of acquiring dual subs and I'll be trying to figure this out.

OP, I ponder if you're over thinking it. In both houses I've had my 218 near and far from my equipment w/ no discernable difference in equipment output. I had dual 4k watt SubM's right next to my SR-120 but my decision to keep my 218 was based upon the sound of the Subs but I noticed absolutely no SQ in my full range speakers. The ported vs sealed sounded different but that was it.

To each his own, I'll tweak the out of my turbo but I haven't noticed any SQ difference w/ various HDMI cables, RCA cables, distance etc. I do use https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 under my center channels and my DVD player to keep them from rattling and vibrating off the entertainment stand but that is it.

Good luck!

AVR = Sherbourn SR-120
Speakers = 2 Arx/Chane towers(5.1), dual Arx bookshelves(1.1) as center duty +LR/RR
Subs = Dual JTR 2400's
For sale = JTR 218HT captivator
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