How do you make a subwoofer?

[Carlman]

I would like to add a pair of subwoofers to my audio system and have a sub dedicated to HT as well.

Ideally, I'd use the same 2 for both purposes but.. I will have 2 separate systems and I can't easily do that.

There will be 2 platforms, first is 6" tall, 4' x 8', second is 12" tall, also 4' x 8'.  I was thinking it'd be nice to build all 3 subs into these platforms.  That way, I could have the audio subs pointing to the left and right of the main seating area and the HT sub exiting rear.  I have ~30 cubic feet of space, 10 cf for each sub, if I use the larger of the 2 platforms.

How do I know which sub works in a 10cf box?  I would prefer to do 1 15 for the HT and 2 12's for the audio... but I don't know how to fit those.  I do plan on slanting the face of the boxes back so the effective height is less than 12". 

I have been considering the Rhythmik subs for a while now... but I don't know if this will work... because I don't know how a sub is designed.

Any help is appreciated.

-C

[TomS]

Carl,

This might be interesting for a raised platform...

http://www.danleysoundlabs.com/pdf/SPUD%20intro.pdf

Tom

[Carlman]

Yes, something like that, at least functionally, but not specifically.
Very cool, thanks for the link, it provides a nice visual of what I'm doing.

The differences in that implementation and mine are that I need the drivers to fire directly left and right and then 1 firing to the rear. 

I cannot find the article I read where they determined the best placement of subs was the middle of the walls, directly opposed from one another.  That's why I want the subs firing left and right.  Since there will be a shorter platform and another row of seating in front of this one, I'd prefer the HT sub to fire out of the rear.

I also read an article about building a sub that had a long, skinny box that fit  under a sofa that increased the box size tremendously but tucked away hidden... So, I've got all these ideas... and then there's Shane with his big blowout sale on sub amps and such.. and I had to get to thinking on this idea...

-C

[bpape]

The main issue with something like that is that you can't exactly move it around to find a place to get nice flat response.  Building it into a platform is kind of a crap shoot with regard to the response that you're going to get - unless you can build test boxes first and see what works and what doesn't that's also going to overlap within the given envelope of the riser.

Bryan

[miklorsmith]

Can the subs be on an EQ?

[Black Sand Cable]

When I built my Rythmik's, I followed Brian's plans to the letter and have had zero regrets. The subs do everything well and given I went with dual subs, I have a ton of placement options.

I tried them stacked, on opposite sides of the room, and finally with both subs sitting on the back wall in the middle facing away from each other. This offered up the best performance with not only HT, but with audio also.

One was enough but two of them is icing on the cake!

[attachment deleted by admin based on 2 year limit]

[richidoo]

Carl you sent me an email last year about a sub cabinet which increased its own interior sealed volume with a long flat box appendage that squirted out the side to fit under a couch. You emailed it to me once, so check you sent messages. I don't have it anymore because.... errr.... ahhhhh..... ummmm..... Oh yeah! Now I remember, I printed it and put it in the safe deposit box for safe keeping, along with all of your other emails.

I found this while searching:
http://www.harman.com/wp/pdf/multsubs.pdf
http://www.soundandvisionmag.com/features/1944/why-you-need-four-subwoofers.html
http://www.harman.com/about_harman/technology_leadership.aspx  (See white papers and scientific pubs to left in "Tech Leadership" box.) That article about middle of wall placement is in there somewhere. I remember it was Harmon Research that wrote it.

There are a lot of subwoofers that can fit inside a 2x4 wall. Since your walls are rubber suspended you would want one that has minimal vibration, or isolate it from the wall and mount to the concrete behind.
http://www.definitivetech.com/loudspeakers/inwall_/inwall_subs_.html#subref    You should determine best location for subs using a portable sub, then bury it in the wall if desired.

Last year or two years ago a large speaker company introduced a design of subwoofer that had two drivers firing in opposite directions, creating a pressure zone between the driver cones that was exposed to the room. It is designed to be zero vibration and in wall installation. It is not infinity or deftech, thiel or paradigm. but I can't remember who! Any ideas?  I threw out all my old HT mags.   It had white frame.

[Black Sand Cable]

What about twin 10in's mounted in the wall?

http://www.psbspeakers.com/products/In-Wall-In-Ceiling-Speakers/CWS10-In-Wall-Subwoofer

[Carlman]

I might be able to use those inwall subs for the platforms but it looks like they're in pretty small enclosures which probably compromises their overall output... I don't know.  Thanks for the links and thoughts.

I just have this huge box under the seats that I thought would be perfect for some subs... And I'd definitely consider an EQ or something like the Velodyne SMS unit.

-C

[richidoo]

The riser boxes are large volume which would be good for sealed subs, but thin walls of the riser if not structurally reinforced to prevent flexing will displace as much air as the cone, making it sound very bad. Reinforcing them adequately to reduce flex and distortion adequately would be a big expensive job. You would need two layers of MDF with aluminum bar frame, or something to that degree. It would need a bottom to remain sealed. All that thickness would make a 6" riser impossible to fit a sub inside if 3" of that height is wall thickness. A good 12" driver is 6+" tall. Rhythmik drivers are extra tall to accomodate the 2nd sense coil. You could build a smaller box of such construction that won't flex under pressure to put inside the taller riser, but they are still not very tall so it would be a design challenge - pancake sub. The closer to a cube shape, the smaller the unsupported wall surface the less reinforcement you need. If it were a sphere you would need no reinforcement (in theory...) The surface tension alone would prevent flexing, but there would still be wobble. B&W makes a spherical sub that looks pretty enough to hang in a ceiling corner, that might be a better wtg than hiding, performance-wise.

GR Research has plans for ryhtmik sub cabinet on line. We could make a couple of these easily and cheap.
http://www.gr-research.com/pdf/singleservo.pdf

In-walls can perform very well when designed to, = $$. I will try to find the model I was referring too. But it won't beat a DIY price.

[Carlman]

Ah, I see.  My plan was to build a box for each sub and put it under the platform... I figured I had 12" of clearance due to it being a 12" tall platform.. It would be somewhat of a pancake but I didn't think too bad... Plus, I was thinking I could slant the speaker.  The platform (w/ carpet and such on it) would just be a shell over the subs... to cover them.

In any case, building 2 Rhthmik's is starting to make a lot more sense.  However... I still may do 1 sub for HT and put it under the platform, firing backwards.

That solves the planning stages, too... I don't need to run anymore wires under the platform.  Thanks!!!

-Carl

[richidoo]

I think this is the in-wall I was talking about. http://www.artisonusa.com/artison_009.htm