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Thinking of trying an IB sub in a difficult room.... all ideas welcome!

post #1 of 32
4/16/07 at 2:57pm
Thread Starter 
I have had real difficulty dialing subs into my room. As you can see from my drawing, the room is 12'-6" X 22'-6" The one 12'-6" wall on the left (the one without the closet) is floor to ceiling stone with a fire place. I don't use the FP, actually my 55" wide screen RPTV is sitting right in front of the hearth area centered along that wall.

I've been using dual subs in that room to try to even out the response and about the only spot that seems to work well at all, is placing the subs side by side centered on the opposite 12'-6" wall (the one WITH the closet) behind the seating position. The WAF on this is poor since we have a very nice wine cabinet/glass rack that really "needs" to go there.

So, I'm considering using my closet (it's built under the stairs leading to the upper level) as an IB sub. For those of you that have experience with IB, what are your thoughts? I was thinking either 4-12" or 4-15" drivers. Will the door and air leakage around/under it cause problems?

I'm just not sure where to begin. All input and advice is appreciated.

TIA


LL
LL
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post #2 of 32
4/16/07 at 3:07pm
Are you sure you have enough volume in the closet for an IB?

"The rule of thumb is that for each driver used, there should be a space no smaller 10 times larger than the Vas of the individual driver. That is then multiplied times the number of drivers. 10 times the total Vas or larger is considered optimal.

I want to add a bit of an addendum to the answer to question #3. For those that can't do a 10 times Vas IB, but can do at least 4 times Vas, go ahead and build it. Now this won't be a true IB (Qts =Qtc) . But anytime you can get a space that's 4 times Vas, you'll have a sub with better sound quality than a standard portable box sub. Note, one will need to use standard sealed box construction techniques with a 4 times Vas box. And be sure to choose low Vas drivers if you take this approach. "

quoted from culf of infinitely baffled....
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post #3 of 32
4/16/07 at 3:10pm
Thread Starter 
Quote:


Are you sure you have enough volume in the closet for an IB?

No, not sure at all. TOTALLY clueless actually...

Driver recommendations would be welcome as well.

edit: And another stupid question.... what is a "low vas" driver?
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post #4 of 32
4/16/07 at 4:26pm
Quote:
Originally Posted by quadriverfalls View Post

No, not sure at all. TOTALLY clueless actually...

Driver recommendations would be welcome as well.

edit: And another stupid question.... what is a "low vas" driver?


Vas/Cms--------Vas represents the volume of air that when compressed to one cubic meter exerts the same force as the compliance (Cms) of the suspension in a particular speaker.

If you look at the parameters listed by the manufacturer of the driver, you will see a listing for Vas. A low vas driver is recommended so you can get 4-10x the volume (Vas) for the driver in the enclosure. So, if your closet in 200L in volume and the driver has a vas of 146L, it will not be suitable for infinite baffle.

You may still be able to use the closet for the enclosre, but maybe not IB. You could go with a LLT or very large ported enclosure with multiple drivers.
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post #5 of 32
4/16/07 at 4:43pm
Move your subs to where you're proposing the IB and see how they sound. If they sound bad there, chances are the IB will too.
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post #6 of 32
4/16/07 at 6:24pm
IMO having the only sub in the room behind the listening position is problematic. I realize this is the opposite of what's suggested by Dr Hsu.

Either the door must be air tight or you must build an air tight enclosure inside the closet.

BTW wine racks don't belong in rooms having vibrations coming from big subs....
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post #7 of 32
4/16/07 at 7:01pm
I would just use the closet, but maybe not as the enclosure per se. I would just build a sub, either sealed or ported, and put the entire sub in the closet and open a space between the studs for the sound to exit. Maybe build in a grill of some sort. This way you can still use the closet and remove the sub when/if necessary.
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post #8 of 32
4/16/07 at 7:10pm
Confirmed that a sub behind you is not the ideal placement. Front and Back great, back only is not good.
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post #9 of 32
4/16/07 at 7:24pm
Don't worry about ideal placement. Just build it and try it. Often people get too hung up having everything perfect. It is just too difficult to tell until you do the experiment youself in your room with your equipment.
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post #10 of 32
4/16/07 at 8:15pm
Thread Starter 
Quote:


Either the door must be air tight or you must build an air tight enclosure inside the closet.

Yeah, I was sort of worried about the air leakage around/under the door.

Quote:


Move your subs to where you're proposing the IB and see how they sound. If they sound bad there, chances are the IB will too.

Duh.... sometimes, some things are just too obvious.... I didn't even think about trying this first. And, that's about the ONLY place I HAVEN'T tried them.
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post #11 of 32
4/18/07 at 4:26am
Thread Starter 
Doing a little math.... the internal volume of the closet is approximately 72,828 cubic inches (34" x 34" X the average height of 63"). 72,828 cubic inches converts into 1,193.437 Liters. http://www.onlineconversion.com/volume.htm

So, if that's the case.... With the VAS on the RL-s12 being 27.65....
http://www.acoustic-visions.com/~aco...rivers/SSRL-s/

Four RL-s12's would have a VAS of 110.6. Ten times VAS would make the internal volume for four RL-s12's 1106 liters. WHich I have almost exactly.

When using multiple drivers. does the VAS remain the same for each driver, or does it increase as each driver is added?
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post #12 of 32
4/18/07 at 5:13am
Vas remains the same for each driver.

Take a look at the 15s as well. You don't necessarily need exactly 10x. I think as long as your Q remains at a reasonable level.
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post #13 of 32
4/18/07 at 5:36am
Thread Starter 
Quote:
Originally Posted by jpmst3 View Post

Vas remains the same for each driver.

Take a look at the 15s as well. You don't necessarily need exactly 10x. I think as long as your Q remains at a reasonable level.


I was surprised at how much "all over the place" this VAS thing is. Of course, I'm just getting started and don't really know what all of these terms are for and how they relate to each other.

For example on the RL-s15, the VAS is 85.37 which means only a single driver would work using the 10 X's calculation.

Then go to the premium series SS drivers and the VAS numbers look like this....
12" 142.7 and 15" 148.8.... which means that neither of those would work at all at 10 X's VAS. Even for a single driver.

Man.... I've got a LOT of research to do, don't I?
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post #14 of 32
4/18/07 at 6:03am
Quote:
Originally Posted by quadriverfalls View Post

I was surprised at how much "all over the place" this VAS thing is. Of course, I'm just getting started and don't really know what all of these terms are for and how they relate to each other.

For example on the RL-s15, the VAS is 85.37 which means only a single driver would work using the 10 X's calculation.

Then go to the premium series SS drivers and the VAS numbers look like this....
12" 142.7 and 15" 148.8.... which means that neither of those would work at all at 10 X's VAS. Even for a single driver.

Man.... I've got a LOT of research to do, don't I?

Hey John,

Take a gander at the "cult of the infinitely baffled" website. There you can find everything you need including detailed pictures and documentation. Best of all they have all the parameters explained and design criteria for IB subs. There is an amazing amount of well thought out docs there.

They provide suggestions for drivers to look for and why....not everything is in layman's terms but you can get the ideas you need if you read enough.

Don't get discouraged and also don't be afraid to just try it. The nice thing about IB is the drivers are CHEAP! If you get say 4 drivers you will probably not have much more than $400 wrapped up. If you don't like it, even if you take a 50% hit reselling them, you are only out $200.

You will need a cheap amp and maybe EQ as well, but not that much money.
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post #15 of 32
4/18/07 at 6:49am
I will recommend some drivers after I get some time tonight to model up a few with your closet space.
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post #16 of 32
4/18/07 at 7:33am
Thread Starter 
Quote:
Originally Posted by HT Nut View Post

I will recommend some drivers after I get some time tonight to model up a few with your closet space.


Wow, guys.... thanks a LOT. Here is another quick render adding to the earlier side view.

I was planning on finshing out the interior stud space with 1/2" or 3/4" plywood (of course, the front baffle could be as many layers thick as is necessary). Then sealing all of the joints with silicone, or even better yet, a tri-polymer sealant.

The floor has the same pad and carpet as the room. I can put a rubber sweep on the bottom of the door and a refrigerator door type gasket all the way around the jamb. This "should" give me a fairly tight seal around the door. Not perfect, but a lot better than nothing I would think.

Oh man.... just thought about something else.... there is an HVAC trunk line going from the ceiling of the closet (following the line of risers going to the upper level), that enters the slab on the left side of the closet.... that feeds the main level of the house. I don't think I would need to frame that in, but if I did.....

Trunk line: 10" X 8" X 4' so with 2" X 2" framing and a layer of 1/2" plywood, that would be roughly 14" X 10" X 4' or.... 6,720 cubic inches or approximately 110.121 liters of space needed to be deducted from the inside of the closet. So, guestimating and allowing for any "little" things I missed, I would say, right around 1,000 liters of internal volume.

Thanks so much you guys for all of the help. I REALLY appreciate it!



Edit: Oops.... the file is too large now. But you can get the idea I think from my description. If not, let me know and I'll redo it.
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post #17 of 32
4/18/07 at 7:53am
Quote:
Originally Posted by quadriverfalls View Post

I was surprised at how much "all over the place" this VAS thing is. Of course, I'm just getting started and don't really know what all of these terms are for and how they relate to each other.

For example on the RL-s15, the VAS is 85.37 which means only a single driver would work using the 10 X's calculation.

Then go to the premium series SS drivers and the VAS numbers look like this....
12" 142.7 and 15" 148.8.... which means that neither of those would work at all at 10 X's VAS. Even for a single driver.

Drivers are designed for different applications, as a result the T/S parameters differ.

The RL-s drivers are car audio only drivers, we know this from their high Qts.

The door for any type of closet sub should be solid core wood.
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post #18 of 32
4/18/07 at 7:58am
Thread Starter 
Quote:


The door for any type of closet sub should be solid core wood

Thanks.... it is. I up graded all of my interior doors to solid six panel poplar a couple of years ago.

Quote:


The RL-s drivers are car audio only drivers, we know this from their high Qts.

See? I'm totally clueless. I need to start doing some serious reading not only to learn what all this stuff means (Qts???), but how the different specs all come into play and interact with their surroundings.
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post #19 of 32
4/18/07 at 7:59am
Quote:
Originally Posted by quadriverfalls View Post

Thanks.... it is. I up graded all of my interior doors to solid six panel poplar a couple of years ago.

According to the "cult" you don't need a perfect seal as you elluded to. There can be minimal leaks between cavities....
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post #20 of 32
4/18/07 at 8:04am
Thread Starter 
Quote:
Originally Posted by jpmst3 View Post

According to the "cult" you don't need a perfect seal as you elluded to. There can be minimal leaks between cavities....

Thanks.... I'm going to start some serious research this evening. I've got a LOT of learning to do for sure....

Still though, whether I do the closit thing.... or an entirely different enclosure all together, just perusing the threads on this forum have gotten me excited to "try" something DIY for my HT.

You guys are contageous....
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post #21 of 32
4/18/07 at 8:09am
Quote:
Originally Posted by quadriverfalls View Post

Thanks.... I'm going to start some serious research this evening. I've got a LOT of learning to do for sure....

Still though, whether I do the closit thing.... or an entirely different enclosure all together, just perusing the threads on this forum have gotten me excited to "try" something DIY for my HT.

You guys are contageous....

Ya, just take your time and read.

You can get quite a bit of advice here in these forums, most of it good. But, some of it is not based on facts, or practicallity, or budget for that matter. So, your best bet is to learn as much as possible then get answers to specific questions and conditions.
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post #22 of 32
4/18/07 at 8:45am
Don't close off any openings to volumes not in the listening room. That is just more volume for the IB. For example, don't close in the stud cavities in the closet. You will lose volume. And if that trunk opening vents to some other portion of the house all the better. Extra volume.

If you want to deaden the closet walls, add another layer of drywall on the listening room side glued on with a thick bunch of construction adhesive, the rubbery kind like PL400.
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post #23 of 32
4/18/07 at 8:45am
Quote:
Originally Posted by jpmst3 View Post

According to the "cult" you don't need a perfect seal as you elluded to. There can be minimal leaks between cavities....

That info relates to when LARGE spaces are being used for the rearware. His closet sub needs to be airtight.
Quote:
Originally Posted by quadriverfalls View Post

See? I'm totally clueless. I need to start doing some serious reading not only to learn what all this stuff means (Qts???), but how the different specs all come into play and interact with their surroundings.

This is something that takes quite a while to learn. It's probably most expedient to use drivers recommended by someone who already knows this stuff.
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post #24 of 32
4/18/07 at 6:44pm
The Ficar Audio Q15 would be a good choice. Two drivers in an outtie manifold vented into the closet. About 4 times Vas

Tell us more about the other outlets that the closet has. How much room is there around that duct? Could that be made larger?
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post #25 of 32
4/18/07 at 8:24pm
Thread Starter 
Quote:


Tell us more about the other outlets that the closet has. How much room is there around that duct? Could that be made larger?

No other openings at all. The trunk line (olive green) comes into the top of the closet from the room, angles down directly under the stair risers and then goes into the solid concrete (dark grey) wall on the left where it then feeds the main level of the house from the slab.
LL
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post #26 of 32
4/18/07 at 8:59pm
You might want to do an SLLT using that closet. That is a vented alignment meaning there are ducts that act as resonators at a given frequency which "tune" the volume to interact with the driver. You would have to seal up the closet, which would probably entail a nice solid door with some devices similar to the turn knobs on a window which draw it together, a cam arrangement.

Steve Callas here is a big help with that kind of project.
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post #27 of 32
4/19/07 at 5:15am
I dunno guys,

I think it is going to be a tall order to get that closet to work for anything related to IB.

IMO, his best bet, if he still wants to use the closet in some fashion, he should just place a traditional sealed or vented sub in the closet.

This eliminates the need for sealing the room off and allows more flexibility in design.
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post #28 of 32
4/19/07 at 4:27pm
Thread Starter 
Quote:
Originally Posted by jpmst3 View Post

I dunno guys,

I think it is going to be a tall order to get that closet to work for anything related to IB.

IMO, his best bet, if he still wants to use the closet in some fashion, he should just place a traditional sealed or vented sub in the closet.

This eliminates the need for sealing the room off and allows more flexibility in design.

Yeah.... after doing a LOT of reading over on the IB forum.... I think I'm beginning to agree.

I just picked up a brand new RDES unit from AV123 (well, from a former owner who never used it). I'm also looking seriously at some bass treatments. I think between the two, I should be able to at least improve my over-all response a bit.

I still need to address extension though. The subs I have right now, while VERY expensive in their day (Harmon/Kardon Citation 7.4 THX passive subs with 14" PRO JBL drivers that have 18#.... yes, EIGHTEEN POUND magnets)... they retailed new for $1150 each back in the early 2000's.... just don't go that deep with any authority.

I don't know, it may be my amp.... I'm using a vintage DENON POA-2200 two channel (200 wpc @ 8 ohms/ 350 wpc @ 4 ohms) amp to drive the pair of subs. The JBL PRO drivers are rated at 6 ohms, so the amp never breaks a sweat (doesn't even get that warm really) pushing them. I guess more power wouldn't hurt, but power doesn't necissarily equal extension.... right?

Sigh.... maybe just a big 'ole DIY box is the way to go. I'm just not sure at this point. The closet though, I think is out.

Thanks so much for all of the reply's and information guys.
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post #29 of 32
4/19/07 at 4:31pm
Well, you would have hut to cut a hole in the closet for the IB. So, you could easily do the same for even a DIY too. If you want a better sub you will need to build of buy anyway. If you build one, leave the box(es) unfinished and try them in or near the closet and see if it works. If does you are golden...
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post #30 of 32
4/19/07 at 5:29pm
So you do you have a basement underneath this? That is another possibility for IB, you just need to stick to 15" or smaller drivers, this would only work if there was something for the baffle to go underneath, a couch, a coffee table, something along the edge of the room that would never get walked on with a bit of space for it to breathe.
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