sub in crawl space venting to HT?

[mizedog]

Hey all,
I'm your consummate newby in DIY (never done it, but planning my attack). Due to the small size of my HT (and my huge couches), I'm really looking to get all the speakers behind an AT screen. This would gain back floor space that is now being taken up by my Klipsh 12" sub, and my ancient-but-free Fisher monkey coffins. I'm planning on in wall Nat P's, Khahncenters, or Aviatrix for the LCRs.

Here's my question for you:
Can I put a sub in the crawls space behind the screen wall and vent it into the HT? In other words, something like an IB, but enclosed to keep the sound out of the rest of the house.

Here's a sketch of the wall and crawlspace:


Here's a dark pic of the wall from inside the room:



Here's the wall before sound board and drywall:



Whadyathink? Can I put a big box in the crawlspace, and run a vent into the HT? If so, is the vent format/size/material critical, or could I just build a rectangular MDF vent through the wall?

I've considered building small subs into the two ottomans, but they only have room for a cabinet 6-7" high by 25 to 35" wide.
Thank you for your input.

[capww8]

Do whatever you like, it's your house! ;-)

Look at the 'custom series' servo woofers here, I think it would suit your application nicely, and they're pretty inexpensive.

http://www.rythmikaudio.com/products2.html

[rdrowley]

I couldn't tell from your pictures, but are you going to have the speaker firing into the room, and the port venting into the room? If you do that you should be good. You could get away with not venting the port into the room as well, but it would be better if you did IMO. Though I'm not sure what that will do to the phase etc. with sounds coming out of the port and speaker differently. If you have lots of space and are just worried about sound throughout the rest of the house why not make a huge sealed box? You'll get near IB performance without the stray sound. I would also be careful venting into the crawl space as it will allow a way for moisture/bugs to get into the box and neither is good for your speaker.

Along those lines, make sure you don't hide the amp in the crawl space...

Looks like a fun project! It's exciting to design/build a room around what you really want.

[ThomasW]

Sell the Klipsch and build an IB sub

[mizedog]

Sell the Klipsch and build an IB sub

Thank all for the suggestions.

I'm not in love with the Klipsch and would sell it, or augment it with an addition sub.

Re: IBs (which I'm still learning about), doesn't this design mean there is nothing on the back side to keep the sound from filling the crawl space? I would like to keep the sound isolated to the HT room.

[Hdale85]

Well the crawl space isn't open to your house? So shouldn't really be that big of an issue. You'll likely never have it 100% isolated to the HT anyways.

[mizedog]

I couldn't tell from your pictures, but are you going to have the speaker firing into the room, and the port venting into the room? If you have lots of space and are just worried about sound throughout the rest of the house why not make a huge sealed box? Looks like a fun project! It's exciting to design/build a room around what you really want.

House about this? It would have to fit between 16" center studs but could be as deep as needed due to crawlspace area. I would keep it decoupled from the wall to avoid transmitting the sound of the sub through the studs.



Here's the link to this very slow and budget build.

https://www.avsforum.com/avs-vb/showthread.php?t=1223611

Today I'm picking up the wood for the rack cabinet that will fill the whole to the right of the wet bar. This hole, by the way, is plenty big enough to hide a sub (24" deep, by more than 28" wide). While I know a corner is not ideal placement for the sub, it would make a nice hiding place for a sub.

[cjd]

Re: IBs (which I'm still learning about), doesn't this design mean there is nothing on the back side to keep the sound from filling the crawl space? I would like to keep the sound isolated to the HT room.

You don't want a sub if you want to keep the sound isolated to the HT room. At least, not a real one. Low frequency just carries. I've had sound from the basement rattle the floor of the 2nd floor office when my wife is watching a movie (which means it's QUIET, by the way... 70dB@2.5M usually) - and that's opposed-mounted drivers in a floating wall (i.e. the chance that it's mechanical energy transfer from the drivers is something negative - that's pure sound energy)

But more to the point - If I hear a movie playing while I'm upstairs (even standing directly above where the sub lives,) it's the high frequency stuff or the really really low stuff. And if you do a good system without the usual problems of "center on its side stuffed in a cubby" that make things inaudible, you'll find you can get comfortably loud most times and hear everything, feel everything, and noise will not be an issue elsewhere in the house - and that's WITH a good IB setup.

You might find a small-box sub is actually worse, but that's harder to quantify without a direct comparison. But... I've heard a crappy sub-in-a-car driveby in the basement, watching a movie. Pushing to ~110dB@2.5M I can just hear my HT standing outside - and that's not even inside a car, on the street: it's on my front porch. Quality vs crap. Crap is louder at the same SPL, I swear.

[dpc rep]

FWIW, I have an IB sub and spent some time on the Cult before building it, and I like it very much. It is definitely not your average sub, nor does it sound like it. Oddly enough, when I am up in my attic it is not nearly as loud as it is in my family room ... I cant actually explain why. My point is that the backwave from the sub shouldnt affect your house as much as you are thinking that it will. As was already stated, if the sub is functioning properly, the LFE will be heard and felt throughout the house anyway. The only technical requirement for an IB sub is to completely isolate the front soundwaves of the speaker from the rear soundwaves with a rear volume as close to or greater than 10 times the VAS of the driver. After the fact, there can be many other mitigating circumstances, but these would be no different than any other sub.

And an IB has absolutely awesome WAF!

All that being said, my IB doesnt boom at all. It is very accurate, and deceptively powerful. I have way too much power driving the four 18's in a manifold in my attic, but it reproduces the absolute lowest of frequencies with a frightening ease. It has the capability of actually making 10 Hz audible, not just felt. IB's have been referred to before as a "20 pound feather", and I feel that description is very accurate.

With all that said, I think you know the direction I believe that you should take. Build yourself an IB and you will never look back.

[mizedog]

You don't want a sub if you want to keep the sound isolated to the HT room. At least, not a real one. Low frequency just carries. I've had sound from the basement rattle the floor of the 2nd floor office when my wife is watching a movie (which means it's QUIET, by the way... 70dB@2.5M usually) - and that's opposed-mounted drivers in a floating wall (i.e. the chance that it's mechanical energy transfer from the drivers is something negative - that's pure sound energy)

But more to the point - If I hear a movie playing while I'm upstairs (even standing directly above where the sub lives,) it's the high frequency stuff or the really really low stuff. And if you do a good system without the usual problems of "center on its side stuffed in a cubby" that make things inaudible, you'll find you can get comfortably loud most times and hear everything, feel everything, and noise will not be an issue elsewhere in the house - and that's WITH a good IB setup.

You might find a small-box sub is actually worse, but that's harder to quantify without a direct comparison. But... I've heard a crappy sub-in-a-car driveby in the basement, watching a movie. Pushing to ~110dB@2.5M I can just hear my HT standing outside - and that's not even inside a car, on the street: it's on my front porch. Quality vs crap. Crap is louder at the same SPL, I swear.

Thanks for the insight, and for inspiring me to try diy. The nice thing about this room is that WAF is not really too much of a factor - my wife wants a dedicated HT room (halleluiah!). The wall I'm referring to is kind of a pseudo-false wall, there's just not wall behind it. One thing I could do if necessary is build another wall in the crawl space behind the speakers to somewhat encase them. I don't think it's necessary, though. The room is fairly isolated now, and we're on a 1/2 acre lot, and it's in the basement. In an effort to keep the AT screen as far from the front row as possible, I'd like to set the LCRs into the wall behind the screen. Getting the sub off the floor would just give the illusion of a bigger room. I'm also struggling with the fact that I really need in-wall speakers for the surrounds and rears too. The right surround sticks out far enough to get in the way. The back row is right up against the back wall. So, in walls would seem to give the back row a chance to hear the rears. I just want to avoid buying mass produced in-wall speakers.

Choices, choices. Thanks again for the insight!

[cjd]

The surrounds I use in my HT may suit - pretty flexible on where they can go... for that matter, so may the fronts I use, or Khanspires (which have been on-wall mounted with success). And that's just the start of the possibilities - there are many good designs out there that probably can get you where you want to go.