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-   -   2 15" on a baffle against ceiling corner (open ends) (http://www.diyaudio.com/forums/subwoofers/111374-2-15-baffle-against-ceiling-corner-open-ends.html)

OTMOPO3OK 5th November 2007 06:04 PM

2 15" on a baffle against ceiling corner (open ends)
 
Hello guys,

Preface:
I built a nice 12" 8cu.ft MLTL sub 4 years ago that served well both for movies and music. Now i built new OB mains with 15" drivers and they go down to 30Hz and I'm amazed by OB bass and now the TL sub sounds boomy. Plus for movies it's very weak (I now realize that) So i'm on a quest to build a new pair of subs with couple 15-18" drivers. I need something that goes down to 10Hz (mainly for movies, since i'm happy with just mains for music) with authority but does not 'boom' in the room. I don't like ported or radiator ideas, so it's either sealed or OB.
My apartment room is 191sq.ft. , 1750 cu.ft. (not large at all) I listen along the long wall (so the PJ screen can fit). I also have no space on the floor and will be removing my current 'refrigerator' sub. The only available space i have a above the screen along the whole length of the front wall (16.5 ft).

Idea:
I wanted to know if it's possible to put couple of 15-18" subwoofers on a baffle and mount that baffle at 45 degrees angle between front wall and ceiling and have open ends. It will be like OB/TL mix, but the problem is I don't know how it will behave and how to model that. Since i have 16 ft of space i can make the TL pretty long and have openings facing the listener.

Tell me if this idea is totally crazy (since I haven't seen anyone do that)?
I was also thinking of putting 4 drivers on OB and setting them in the front like Bob in St.Luise did, but they will be at most 1ft from the back wall and will probably not go down that low.

If i want the lowest extension MUST i go with sealed then?

I was thinking of couple RL-p15, RL-p18, CSS SDX15 or Tempest-X 15". If I'm going with the sealed than i'll need the smallest Vas driver. If OB/TL then largest Vas.

Any comments on any of the issues.
Thanks.

Bluto 6th November 2007 05:09 PM

Otmo ... -

Not much help at all but I know it's been done. Guy down South somewhere as I recall and He has a pretty decent site with alot of how-to's and pics.

He had switched from standard sub boxes to this system and said this design beat his boxes hands down. I recall he used some pretty expensive drivers and it was his own hit or miss design. He did a great looking install.

Seems to me I also ran into him a month or so back on an infinite baffle site as a poster with a link to his site.

He's saved on my Computer but so is The Library of Congress. If I see his place on a run through of my files I'll repost.

At least a place to start search if you get no answers here.

Bluto

OTMOPO3OK 6th November 2007 10:16 PM

Thomas from infinite baffle forum corrected me that OB and TL are oxymorons and he is absolutely correct. I only called it TL because it's rather long and if i close one end there will be a standing wave of rather low freq. there.
I imagine it to function somewhere close to Ripoles where driver is sitting in a tight space and is not completely free OB but has some air resistance (due to smaller volume than optimal). Since the air behind the drive gets compressed somewhat due to small volume but the air still escapes it lowers the Fb of the whole system, just like Ripoles do.
The other thing that I think happens in my idea is once the back wave enters the room from both sides it starts canceling with the front wave. So i imagine it would have a 90 degree radiation pattern.

________/^\________
............/....\
.......... /.......\
........../..........\

Doesn't look like 90* but u get the idea. If you are sitting in the front (and i do) you would get the benefit of whole front wave but closer to the sides and corners they would cancel out. It's JUST my speculation, i really have no idea.



By varying the space behind woofers I can lower Fb.

Also I'm not sure if I should select high Vas drivers (dipole oriented) since it's kind of OB and to get the benefit of compressing them with smaller space.

OR should I get low Vas driver (box oriented) since there is little space behind the woofers. But then to make them 'uncomfortable' (to lower Fb) I have to make the space behind them even smaller.




What do you think? Am i on the right path with these ideas?

W,H,U frames require space around them and do not go as low as Ripoles (which are an evolution of W frame in a sense (evolution towards lower Fb i mean)) . But think about it, all W,H,U baffle does is separate front wave from the back wave a certain distance, same as in my idea. Ripoles compress back wave somewhat to achieve lower Fb, so does decreasing the space behind woofers in my idea will.

PS: I'm using term Fb incorrectly here since it relates to boxed design but i think everybody understands that i mean the -3db point of the whole system.


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