Subwoofer placement - AVS Forum
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post #1 of 18 Old 08-26-2004, 08:30 AM - Thread Starter
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I can't decide whether or not it is a good idea to place one of the subwoofers in my hometheater under the 2nd level riser (see picture). It's 2' off the ground and there is plenty of room, I just don't know what that enclosed space under the riser will do to the sound (if it will make it sound muddy because of proximity to walls)? In part I'm going for rumble affect, but mostly I'm trying to place the two subs in the middle of the room (width wise) following the recommendations at on Harman's white paper about sub placement (two on opposites walls in the middle). I just don't know if placing it under the riser defeats the purpose?!?

Any ideas?? Thanks
LL
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post #2 of 18 Old 08-26-2004, 06:52 PM
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Is the riser on a cement pad or on a riser itself? I always get concerned when a sub sits on cement. Subs sitting on a short riser transmit that bass better then through the air alone. I hate to see you miss out on the rumble. Leave room to experiment and run some cables for the sub so you can move it around and find the best spot.Nuttin' beats experimenting.
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post #3 of 18 Old 08-27-2004, 12:22 PM - Thread Starter
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Quote:
Originally posted by kgveteran
Nuttin' beats experimenting.
I agree, it's just a squeeze for me to fit under there (my four year old son loves it though). I just figured with all the HT geniuses and guros, someone might have a scientific explanation why or why not to place it under there.

And yes, the floor is concrete (I'll place the sub on a piece of carpet for padding.)
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post #4 of 18 Old 08-28-2004, 08:25 AM
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It's not a good idea to put the sub in the riser. If you want to use the Harmon recommendations, just place the rear sub on top of the riser, with some isolation pads underneath it. What you want is transmission through the air, not through room structures.

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post #5 of 18 Old 08-29-2004, 11:21 AM - Thread Starter
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I assumed something like that, but wasn't sure. Thanks!
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post #6 of 18 Old 09-15-2004, 09:11 PM
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Where can "Harman's white paper about sub placement" be found?

And generally speaking it sounds like it's OK to place the sub anywhere in the listening space? The only place I can really put one is behind the couch where the listener would sit.
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post #7 of 18 Old 09-15-2004, 11:51 PM
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Sconicworld:

There are several PDFs at this site, all are worth reading.
I'm not totally sure which one Terry is referring to in this thread.

Todd Welti's (vetted by Sean Olive and Dr. Floyd E. Toole - The famous "let's try 50 subwoofer paper", that ended up recommending 4):
http://www.harman.com/wp/index.jsp?articleId=1003

An amateur built the Ark. Titanic was built by professionals. Of course Noah took a little advice.
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post #8 of 18 Old 09-16-2004, 06:57 AM
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Yes, I believe that's the paper, Bob. The question for this thread was about the recommendation to put a pair of subwoofers in the middle of opposite walls.

Here's a quote from the conclusion of Todd Welti's original paper, "How Many Subwoofers are Enough," given at the May 2002 AES convention:

"How many subwoofers are enough? Four subwoofers are enough to get the best results of any configuration tried. Two subwoofers at the wall midpoints is very nearly as good and has very good low frequency support as well."

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post #9 of 18 Old 09-16-2004, 07:12 AM
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Quote:
Originally posted by Terry Montlick
It's not a good idea to put the sub in the riser. If you want to use the Harmon recommendations, just place the rear sub on top of the riser, with some isolation pads underneath it. What you want is transmission through the air, not through room structures.

- Terry
Not to sound dumb; but why? Also currently i only an 8" Yamaha sub. I will be building my own larger sub eventually. Could i not use my 8" and place it on; say a hollow stage in the corner to make it "louder" until i can build my 15"?
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post #10 of 18 Old 09-16-2004, 07:57 AM
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Not a dumb question at all. The general problem with letting subs vibrate structural parts is that the sound radiation then becomes uncontrolled. You get re-radiation from these parts that can now interact with the direct airborne sound from the sub in unforeseeable ways, and create distortion. Such re-radiation will happen in amounts and at frequencies which are determined by the unknown vibrational characteristics of the structural parts. This defeats the purpose of having a quality, properly designed subwoofer.

Of course, if all you want to do is make a lot of noise, all bets are off. :)

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post #11 of 18 Old 09-17-2004, 07:55 AM
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Quote:
Originally posted by Terry Montlick
Not a dumb question at all. The general problem with letting subs vibrate structural parts is that the sound radiation then becomes uncontrolled. You get re-radiation from these parts that can now interact with the direct airborne sound from the sub in unforeseeable ways, and create distortion. Such re-radiation will happen in amounts and at frequencies which are determined by the unknown vibrational characteristics of the structural parts. This defeats the purpose of having a quality, properly designed subwoofer.

Of course, if all you want to do is make a lot of noise, all bets are off.

Regards,
Terry
Hi Terry,

How about putting a compact subwoofer in a column?

Attached is a concept drawing.

I was thinking of building the base of the column out of a three-sided MDF box attached to the wall. The top of the box would have a shelf that the subwoofer would sit on at about 4 feet off the floor. A frame would extend from the shelf to the ceiling soffit. It would be wrapped in acoustically transparent fabric and would conceal both the subwoofer and a side surround speaker. The base would be stuffed with fibreglass insulation.

Since the subwoofer is front-firing, sits on top of the structure rather than inside, and is designed for in-cabinet applications, I was hoping that unwanted vibrations might be kept to an acceptable level, especially if I used rubber feet. What do you think?

Thanks.

Larry
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post #12 of 18 Old 09-17-2004, 08:35 AM
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Hi Larry,

I think that this is a viable concept, provided the column is really solid and unable to rattle. Just make sure you maintain access to the sub through a panel or easily removable fabric. Then, if you find you need more isolation than the rubber feet provide, or if the sub has vibrated itself to one side, you can do something about it!

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post #13 of 18 Old 09-17-2004, 09:02 AM
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Quote:
Originally posted by Terry Montlick
Hi Larry,

I think that this is a viable concept, provided the column is really solid and unable to rattle. Just make sure you maintain access to the sub through a panel or easily removable fabric. Then, if you find you need more isolation than the rubber feet provide, or if the sub has vibrated itself to one side, you can do something about it!

Regards,
Terry
Hi Terry,

Thanks very much for the prompt response.

I plan on building a removable frame panel wrapped in acoustically tranparent fabric to serve as the face of the upper portion of the column.

In a previous version of this concept, I had toyed with the idea of having an adjustable shelf to "optimize" the performance of the subwoofer. However, I received a message from a forum member pointing out what a bad idea that would be for the reasons you alude to. He suggested that I build a tray filled with sand to sit the subwoofer in. I think that would be the next upgrade to this arrangement if I was getting too much extraneous reradiation, or if the subwoofer started to dance across the shelf.

Larry
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post #14 of 18 Old 09-17-2004, 12:31 PM
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Quote:
Originally posted by BasementBob
Sconicworld:

There are several PDFs at this site, all are worth reading.
I'm not totally sure which one Terry is referring to in this thread.

Todd Welti's (vetted by Sean Olive and Dr. Floyd E. Toole - The famous "let's try 50 subwoofer paper", that ended up recommending 4):
http://www.harman.com/wp/index.jsp?articleId=1003
That's it! Thanks BasementBob.

Nice drawing LarryChanin. What program did you use to do that?
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post #15 of 18 Old 09-17-2004, 12:40 PM
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Quote:
Originally posted by sonicworld
Nice drawing LarryChanin. What program did you use to do that?
Hi sonic,

Thanks. I used Microsoft Visio to do the drawing as well as the concept drawings shown in my signature links below.

Larry
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post #16 of 18 Old 09-17-2004, 01:14 PM
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Larry

You may want to decouple the sub from your proposed shelf to reduce any unwanted enclosure interaction. Auralex makes some useful products in that regard.

http://www.auralex.com/sound_isolati...tion_mopad.asp

Just a thought.
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post #17 of 18 Old 09-17-2004, 06:02 PM
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Hi cmont,

Thanks for the response. As I mentioned I do plan to decouple the subwoofer from the shelf. I plan to start with rubber feet which have worked well for me in the past.

I will keep Auralex products in mind. Do you know how much how much the MoPAD isolators list for?

Thanks.

Larry
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post #18 of 18 Old 09-20-2004, 11:34 AM
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Hey Larry

I noticed you mentioned rubber feet but I think you may encounter some interaction with just those. Certainly worth a shot initially of course.

Unfortunately I do not know the price of the MoPads. I should know soon as I am seriously considering Auralex for treating my room. I do know their large subwoofer elevator retails for around $60 or so. Based on that I suspect the MoPads are quite a bit cheaper.
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