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Furnace Room Suitable for IB?


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29 replies to this topic

#1 of 30 OFFLINE   Scott Sabin

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Posted May 11 2004 - 08:13 AM

I recently uncovered the subject of IB subs, and am intrigued by all the gushing press on the quality of the sound, as well as the neatness of the packaging.

The only way this would work for me would be to use the "enclosed" furnace room. The back 7 feet of my basement is walled-off and unfinished to enclose the furnace, water heater, and provide shelving for storage. This room has about 1100 cu ft of volume, minus that taken up by the applicances, shelves, and other goods. Being a furnace room, I have vents installed at the top and bottom of the wall making the furnace room enclosure to provide combustion air to the gas appliances.

Would this wall work for an IB installation? Since the room isn't airtight, due to the vents, doorway (which can be closed), and airgaps at the top and bottom of the wall, this means the front and rear of the drivers can't be completely isolated. Is this a deal breaker, or is this a minor non-perfection? What details should I pay attention to in order to maximize the performance of the sub?

Thanks!

#2 of 30 OFFLINE   ThomasW

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Posted May 11 2004 - 09:59 AM

It should work fine. Take a look at the Cult FAQ page for additional info.

Minor openings betweens the adjacent rooms aren't a problem

#3 of 30 OFFLINE   Wayne Ernst

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Posted May 11 2004 - 11:00 AM

Scott,

I have a very similar setup, but a bit smaller. 320 s.f. for the furnace area/water heater area before deducting the area for these appliances. It's essentially the only area that I have to do an I.B.

I'll look into building the I.B. late this summer and then if it doesn't work out, I'll just patch up the drywall and move on.
"My reality check ... just bounced"

#4 of 30 OFFLINE   Scott Sabin

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Posted May 12 2004 - 01:40 AM

I think I'll look into this a bit more, and keep everyone posted on how it goes. However, I'm not sure when I'll get to it - the base finishing work on the basement is not moving very fast, and I still have quite a task ahead of me before I get to purchasing HT equipment. However, I need to have the plan in place.

The wall that will be used for the IB will be my front wall for the theater. It is not a constant height as I have the main HVAC plenums coming through the top of this wall. Any advice on a where to locate the IB in the wall? It will have to be off-center since that is where the screen will be. Looking for advice on positioning it in both directions. I'm figuring I'll want 3 15" drivers. Thanks.

#5 of 30 OFFLINE   ThomasW

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Posted May 12 2004 - 02:14 AM

Probably a better idea to use 4 drivers for ease of wiring. Make a cube 18" on a side, or a rectange with 2 drivers on the long sides. There are multiple examples of these install shown in the IB gallery pages

#6 of 30 OFFLINE   Scott Sabin

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Posted May 12 2004 - 06:45 AM

Thomas,

I assume that is your 12-driver IB sub on those pages. WOW!

When you suggest going with 4 drivers because of ease of wiring, I assume you are saying that provides equal and friendlier amp loading from each driver (assuming 2 pairs hooked up in a serial/parallel fashion, providing an 8-ohm load) versus a 3 driver design? Is that right?

Also sounds like you are suggesting a manifold design. Do these types of IBs have inherent advantages over a flat, in-wall baffle? Is one or the other more forgiving of the vents and door leaks on this wall?

I haven't thought about the manifold design too much. I'm concerned that the added depth into the furnace room might limit where I can locate it. Also, the enlcosure, while simple, seems like more work than a flat baffle. Your thoughts? Thanks.

#7 of 30 OFFLINE   ThomasW

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Posted May 12 2004 - 07:37 AM

Scott,

Yeap the 12 Shiva IB is mine, I also have a smaller one with 4 Shivas.

There's no sonic benefit to using a manifold over a line of drivers. The primary advantage is having to cut just a single hole in the wall. A manifold is more work up front compared to a line array. A baffle for an array can just be a board of 1-1/2" thick material.

Yes the reason for using an even number of drivers is to keep a 4 or 8 ohm load.

#8 of 30 OFFLINE   Scott Sabin

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Posted May 12 2004 - 08:03 AM

Thanks for the info, Thomas. The more I look into this idea, the more I see your name. Seems like I have a true expert answering my questions, so thanks for taking the time to share your knowledge.

Currently, I only have the drywall up on the "closet" side, so at this point in time, there is no tear up involved. I'll have to look at which provides the most centered location option for me - manifold, or line array.

Is bracing required on a "flush mount" baffle? I'm thinking probably not with 1.5" MDF (2 pieces of 3/4" laminated). Does the recommendation for mdf/plywood mixture mainly apply to a manifold, or is it equally important for an array design?

I don't know why I'm even asking this last question from someone who has a 12-driver sub, but, here goes. I'm thinking about the Dayton 15" IB drivers. Would I be missing something with just 2, or would that be adequate for a 6000 cu ft rec room?

Thanks again.

#9 of 30 OFFLINE   ThomasW

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Posted May 12 2004 - 09:15 AM

Yeap I'd use 1-1/2" material for the baffle. Multiple drivers can develop quite a bit of force. I suggest 3/4" MDF glued to 3/4" OSB. Using OSB provides strength, something lacking with MDF. It also does a good job holding T-nuts for mounting the drivers.

The Dayton IB 15"s are good drivers. Given their relatively low cost (note that they're currently on sale for $100ea), I suggest buying 4. That way you're guaranteed you won't suffer from buyers remorse.... Posted Image

There are numerous benefits to multiple drivers other than higher output levels. Distortion is decreased since each driver is not being worked as hard. And there's plenty of 'headroom' for the various kinds of explosions on DVD soundtracks.

When you think about it $400 for drivers, isn't much for a sub that will humble most $5000+ 'box' subs........

#10 of 30 OFFLINE   Scott Sabin

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Posted May 12 2004 - 03:11 PM

OK, I was thinking the same thing. I've been working on this project for so long that when I'm done, I don't want to feel like I didn't go far enough on something! Using 4 also means (probably) using a manifold design, unless I decide I actually do like the look of the driver array taking up more the half the height of the wall.

Last question, and my plans will be complete. How much extra room should a box side for baffle be? These drivers are 15.125" in diameter. I'm thinking I'd want about an inch at least from the driver to the edge of the board. What's a good board width to use as well as driver spacing?

I'm very much looking forward to hearing this baby. Perhaps if I order the drivers, I'll get down into that basement and get working again!

Thanks again, Thomas.

#11 of 30 OFFLINE   ThomasW

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Posted May 12 2004 - 04:44 PM

I'd use make a cube with OD of 19" or 20". That would give an ID of 16"-17", with an opening into the room that same size.

If you go with a line array you could cover it with grill cloth.

#12 of 30 OFFLINE   Kenneth Harden

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Posted May 13 2004 - 02:37 AM

Hmmm, I have a three car garage below my room (evil grin)

#13 of 30 OFFLINE   Daniel Metcalf

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Posted May 13 2004 - 05:11 AM

I tried my furnace room last night with my single, old, tired JL 12W4-8. It sounds incredible! I know the output is low but the sound quality is exceptional. The only way I could make it work was to fire into a closet from the furnace room, so I either have to crack the door open a bit or put an A/C vent/opening in the door. As soon as I can I'm going to order a Tempest and see if it's enough output, if not, I'll get another. I was afraid it wouldn't work well as the location is to the left and slightly behind my seating, but the distance to the driver is the same as my mains (AV-3's) and I have it crossed over at 40hz 24db/oct.
Oh NOW I hear what your seeing.

#14 of 30 OFFLINE   ThomasW

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Posted May 13 2004 - 06:45 AM

Kenneth,

Go for it Posted Image

Daniel,

I can't really visualize what you're describing....

Trust me a single Tempest just isn't going to cut it unless you listening room is the closet. IB mounted drivers are limited in their output by the excursion limits of the suspension. So a single Tempest is going to bottom with less than 140 watts or so of total power. That's much less that it's thermal rating of 650+ watts when it's mounted in a standard 'box'

Given that the AV3 has a -3dB point of 40Hz you might want to raise your crossover point a bit to avoid a hole in the frequency response....

#15 of 30 OFFLINE   Mike SJ

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Posted May 13 2004 - 07:06 AM

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#16 of 30 OFFLINE   Daniel Metcalf

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Posted May 13 2004 - 07:13 AM

I didn't think I conveyed my situation very well. OK, between my theater and the furnace room is a closet, the driver is mounted in the wall in the back of the closet. I'll try to upload a picture. The door next to the Dyn is the closet, so far if I open it a few inches it sounds fine.Posted Image
Oh NOW I hear what your seeing.

#17 of 30 OFFLINE   Mike SJ

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Posted May 13 2004 - 07:15 AM

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#18 of 30 OFFLINE   Daniel Metcalf

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Posted May 13 2004 - 07:27 AM

When I crack the door a bit I can look directly at the woofer, the closet is for blankets, extra toilet paper, etc. It's only 32" deep, and as stated, the distance to my ear is 8ft (the same as my mains). My wife barely accepted the hole in the wall, so I don't think I could pass a couple woofers hanging from the door!
Oh NOW I hear what your seeing.

#19 of 30 OFFLINE   Mike SJ

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Posted May 13 2004 - 07:30 AM

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#20 of 30 OFFLINE   Scott Sabin

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Posted May 13 2004 - 09:27 AM

Just when I thought I had decided on 4 Dayton IBs (15"), now I'm wondering if 2 isn't just as good in some regard.

I'm thinking bang for the buck here. 2 drivers gives me a 4-ohm load. I could get the PE 250W plate amp to drive it, and get up to about 125W to each driver (250W output into a 4 Ohm load). This is in the ballpark of the max power that each driver can handle without bottoming out (100W max RMS).

If I went with 4, I'd have an 8-ohm load, which means the same amp could only drive 150W total, or 37.5W to each driver. Bass power spread over 4 drivers means less distortion, but I'm thinking I might get little/no additional (even less?) output with 4 of these drivers and this amp, than with 2. So to go with 4, I'd have to get a more expensive amp to realize the benefits. Is this logic correct? Would 2 of these drivers and the 250W amp give me enough oomph in a 21x27x8 rec room? Main listening area is really 21x12 (sweet spot location).

Thanks again.