Shallow LLT Possible?

7636 Views 35 Replies 9 Participants Last post by looneybomber, Jul 12, 2008

polhub

Discussion Starter · May 30, 2008

Well I thought I would try my hand at an LLC sub. Of course I can't have something simple because, well, suffice to say a big box in the corner is not an option (if you know what I mean) .

I have a fairly narrow HT (12x22x8). On the narrow end is a 65" RP DLP flanked by a couple of DIY speakers that sit on an old pair of Velodyne F1200 subs.

My thought is to utilize the space behind the TV (40"H x 70"W x 14"D). I would mount the sub to the wall behind the TV. There is quite a bit of play in the above dimensions but I don't want to go higher than the TV (40") nor deeper (14") off the wall. I can go as wide as I need.

There may be an opportunity to use some of the sloping area at the top of the TV to gain more depth, however, this complicates construction and aesthetics. Another possible option is to increase the depth where the speaker is mounted, kind of like a bump out. and then build back to the 14" depth (12" would be better) for the rest of the box.

I envision a front firing sub (either SDX15 or, if the box is large enough, a pair of Tempest-X's) with a side firing port. The SDX15 is pretty deep so that may be out.

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Mike P.

· #2 · May 30, 2008

The box dimensions give a net volume of 18 cubic feet. I'm not sure what effect the sub will have on the 65" RP DLP though.

polhub

Discussion Starter · #3 · May 30, 2008

The more I think about it I think it would be best to make the box wider (and not as high) so that the speaker does not fire into the back of the TV. If the speaker fired into the TV is could cause premature lamp failure.

Blaser

· #4 · May 31, 2008

Welcome Polhub!

Not so sure about that. And I am also not sure if a DLP TV would be afftected by magnetic field. I hope someone with better knowledge in this field will shime in.

polhub

Discussion Starter · #5 · May 31, 2008

I can vouch for that and say that the magnetic fields from a speaker WILL NOT effect a DLP TV. Even an MRI has no effect on LCD or DLP technology. CRT and to a small amount plasma show any effect from magnetic fields from the likes of a speaker.

My greatest concern is the shallow depth of the proposed box and how it may adversely effect the speaker, tuning, etc.

Thanks for the greeting. Lots of knowledge here.

eyekode

· #6 · May 31, 2008

My concern would be the dimensions of the side panels. It will be hard to adequately brace a 40"x70" panel. But then again, plywood/mdf is cheap. Let us know how it turns out!

SteveCallas

· #7 · May 31, 2008

This definitely sounds do-able with a side firing port, you'll just need to find a driver that isn't all that tall.

polhub

Discussion Starter · #8 · Jun 1, 2008 (Edited)

2

I have actually decided on a triangular box that will fit behind the TV. I will use the CSS SDX15 and the box will be 8 cuft, 6" port a little under 24.5" in length.

I will be putting some more bracing in there but at least this can get me started.

I hope the wall will hold it.

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polhub

Discussion Starter · #9 · Jun 11, 2008

In thinking further about this box I am considering if the speaker and port are in the correct orientation. The speaker and port oppose each other similar to a horizontal sonosub. ~ 4' from the speaker is a window and ~ 4' from the port is a window (see above post for illustration). Will this cause the window to rattle excessively (I know it depends on how loud I listen)?

The other option I would have is to mount the speaker pointed up towards the ceiling ~3' above and still port out the side. Would this be a better option?

I have started construction of the above box but I can easily alter the speaker orientation.

Any help is appreciated.

Mike P.

· #10 · Jun 11, 2008

I don't see a problem with your side firing configuration. Some build pics would be nice to see.

Blaser

· #11 · Jun 11, 2008

Will this cause the window to rattle excessively (I know it depends on how loud I listen)?.

Not necessarily. Rattling will depend more on the amplitude of the wave (loudness) that corresponds to the natural frequency of the window.... more than being close or far.

The other option I would have is to mount the speaker pointed up towards the ceiling ~3' above and still port out the side. Would this be a better option?

You will only be able to tell by experimentation. So just chose a configuration and go ahead.

polhub

Discussion Starter · #12 · Jun 12, 2008

Ok, I'll go with the original plan. I will get some build photos together

Is damping material subtracted from the total volume? If so, how is it calculated?

Mike P.

· #13 · Jun 12, 2008

You don't subtract the dampening material. Only the sub, port and bracing.

polhub

Discussion Starter · #14 · Jun 16, 2008

4

Well, here is how far I've gotten on my sub project. The triangles have made this a bit more complicated than a rectangle but I think i't coming along ok.

Let me know what you think (not that I can change much now).

Layout

Adding bracing

Two outta three sides done. Still have some more bracing and need to cut the baffle.

Port point of view

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Mike P.

· #15 · Jun 16, 2008

Looking good! What tuning frequency are you planning on?

polhub

Discussion Starter · #16 · Jun 16, 2008

I was planning on 18Hz. In the 8 cuft box that looked best.

SteveCallas

· #17 · Jun 16, 2008

Nice, reminds me of Sonnie's LLT behind his couch.

eyekode

· #18 · Jun 16, 2008

Woah... so you are going to attach this to the wall with the "thick" part on top? This is what you meant by taking advantage of the sloping of the back of your TV?

Cool/crazy idea

. How do you plan on affixing the cabinet to the wall? Metal L brackets? Or are you going to mount the third side to the wall then screw the cabinet to the third wall?

polhub

Discussion Starter · #19 · Jun 16, 2008

I was planning on a French cleat to hold it.

http://benchmark.20m.com/plans/FrenchCleat.pdf

eyekode

· #20 · Jun 17, 2008

Ah, I have used these to hang cabinets. It might work or it might be a noisy interface because only gravity holds the cleat and the cabinet together. But then again there is alot of gravity going on with that sized box

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