flush mount or manifold for IB...

[CJ Paul]

... if doing a manifold was a compromise. Thomas is probably somewhat aware of my situation as he helped me over at the cult a few months ago but I have a more generic IB question. I have a 16” deep space that I’m going to use for an IB. It is 16” by over 800 square feet so it should be plenty of volume for and IB. But, with only 16” of depth, I’d have to use 12” drivers if I did a manifold. However if I do a surface mount array, I could use 15”s or 18”s.

I know one of the advantages of a manifold is physical, but not audible cancellation. However, if you were in my situation where you would have to user smaller drivers would you forgo that advantage to be able to use smaller drivers? The reason I’m considering doing just that is that my room is going to be about 820sq feet x 8 foot height, so I’ve got a lot of volume to fill with bass.

Many reasonably priced 15” subs model comparably to TWO reasonable 12s so I could save a lot of money going with larger drivers, but I need to know if I’m crazy to try and do an array of four 15s or 18s mounted to the same surface (reinforced of course) with no mechanical cancellation due to a manifold. BTW, another piece of key information is that this space a void in the ceiling, so the subs would all be down-firing into the front of the room between the L/R mains.

[GrahamT]

Sounds cool CJ. Are you asking if four 15s on a baffle is better than 8 12's in a manifold with mechanical cancellation, considering price and space?

[CJ Paul]

Yes, basically my Unibox models bare out that for example, Tempests have nearly the same output as 4 Shivas, yet they are only $25 more per driver. Then you look at something like the Stryke IB15s which I could get 4 for $400 and it seems silly. I mean, maybe I could get by with six Shivas or something, but just for the sake of argument, 8 Shivas is $1000 plus shipping. That starts to not look so great when compared to $400 for 15" drivers.

As my first post indicates though, anything larger than 12" would require all the drivers to be mounted on a baffle in the ceiling.

[GrahamT]

I'm thinking about maybe trying an IB myself, so I am no expert. But, maybe consider the Atlas 15. I think it would have more "clean" output than the Tempest (which I own), although the price is much higher than the Stryke drivers. Just another option.

[CJ Paul]

Yeah, the whole key will be output for the buck. Its tough to beat $100 for a 15" driver. The Atlas drivers would definately excell in a high power, highly eq'd sealed or ported enclosure, but once you hit IB trying to fill a large room, you start looking at cost per liter displacement. Two 18" Avalanches might equal four Stryke IB15s but four Strykes is $200 cheaper, so if you can cut that big a hole in your wall, its tough to justify the "better" woofer.

[jdybnis]

I think this depends on the construction of your house. Could you brace the 15's to something really solid?

If have 16" of depth you can fit the 15's on a trapazoidial manifold with the drivers on angled walls. You should still get at least 50% of the mechanical cancellation you would with the drivers mounted on opposite sides of a cube.

[CJ Paul]

Yes, I could brace the baffle to the ceiling trusses. I would likely build a 1.5" sandwhich of plywood or plywood/MDF to the ceiling and then cut holes for the trivers. The problem with building the trapazoid, which I've thought of, is that I cannot do it myself for sure. I tried something similar for a auto sub box before and ended up with a leaky crappy box. I know I can do a cube manifold, but I think that a cube that accomodates 15" drivers would be too tall to fit up into the ceiling.

[ThomasW]

A pair of 12"s usually has 30+% more swept volume when compared to a single 15". But the 2-12"s are certainly more expensive.

If one has the space for 15"s then the Stryke drivers are the current best bargin IF you buy 4. I don't know how long John will continue this offer...........

Regarding the truss situation unless you can physically measure the space, it's impossible to know if a manifold with 15"s will fit.

One could just so like Mike Knapp did and do a line array in the ceiling. In theory that's the 'best' design from a sound quality standpoint since there's an opening the size of a driver for each driver. The down side is that there's no canceling of the mechanical forces as occurs with a manifold.

[CJ Paul]

The space is EXACTLY 16" high from the top of the dryawall that makes up the ceiling to the bottom of the floor above. I think it would be REALLY tough to do a manifold with 15s. I've done enough measuring to know that there is enough lateral space up there to do a manifold of 15s, its the height that is the problem.

One could just so like Mike Knapp did and do a line array in the ceiling. In theory that's the 'best' design from a sound quality standpoint since there's an opening the size of a driver for each driver. The down side is that there's no canceling of the mechanical forces as occurs with a manifold.

That's exactly my question. I know this in theory, but for someone who has never done and IB, HOW MUCH does not having any mechanical cancellation matter? Is it going to rattle my drywall off the ceiling, etc?

[Paul H]

CJ,

I have no experience whatsover with IB drivers but I cannot resist pointing out that 4 - 15" drivers could very well rattle the drywall off your ceiling no matter how you mount them

Seriously a manifold that offsets physical forces makes a lot of sense.

Try building a box with two sloped sides and two vertical sides - mount 2 drivers in each of the sloped sides. It'll be similar to the trapezoid but much simpler to build.

Paul

[ThomasW]

You'd make a cutout and remove a section of the drywall. Then install a 1.5" board that has the cutouts for the drivers.

The inherent strength of the truss system should easily handle the mechanical stress created by 4-15"s

[robertwb70]

I'd try 15s in a manifold-butt the sides right up against the overhead floor and it should just fit I think-you know the saying-where there's a will,there's a way...sometimes you just have to be creative

[jdybnis]

Another thought, you could hang the mainifold for the 15's down into the room a couple of inches. It will look good if you finish the edges well.

[CJ Paul]

You'd make a cutout and remove a section of the drywall. Then install a 1.5" board that has the cutouts for the drivers.

The inherent strength of the truss system should easily handle the mechanical stress created by 4-15"s

Thanks, I think this is the plan. I truly have thought a lot about doing trapazoidal boxes, inverted manifolds (cant hang down too far as I have a FP system), and all kinds of crazy things. I think I will go with 15s and when I build it, if there is a way to do a manifold, I will, but if it wont fit, I'll be screwing a 1.5" wooden baffle to the trusses and going that way.

[cjd]

Any reason you couldn't mount drivers on a manifold with angled sides? You do tend to lose some of the mechanical cancellation aspects but you do keep the hidden aspects which for some is somewhat important (you want to put how many of those big ugly round things in the WALL?!). In your case where 15's would almost fit it wouldn't even take a lot of angle.

Of course, if this would be sensible, it opens up some options for me as well. :B The downside (problem?) I see in my situation is the drivers would need to be mounted inside the manifold. And it would have to slide not in the space between trusses, but throug the side - so, it would have to be just the right size to slide in.

C

[CJ Paul]

cjd, that has been mentioned. The biggest problem would be building the box, but its not completely un-doable. My main thing now is that if there is no compelling reason not to do a baffle, then I'll go with 15s and just make them work however, but if everyone had replied, "OH GOD, no, dont do that, you MUST use a manifold in your case" then I would have ordered 12s just to be SURE I could fit them in a manifold. Since that's not the case, I'll order 15s and make them work one way or another.

[Andrew Pratt]

Is it going to rattle my drywall off the ceiling, etc?

That will happen no matter what you do...4 15" drivers are going to rattle everything in your house as the whole house frame is going to vibrate. Besides if its working for Knapp I'm sure it'll be just fine.

[CJ Paul]

Besides if its working for Knapp I'm sure it'll be just fine.

yeah, buy his are vertical in a wall. I'm sure it doesn't matter from a physics stanpoint. The woofers dont know that. It just "seems" like it would be different in the ceiling. Plus, what am I supposed to think? After all the reasoned, logical responses here, the general concesus seems to be do a manifold if AT ALL possible. The question: why?

[Andrew Pratt]

Actually I'd guess ceiling would be better as the joists are going to be thicker then what's in Mike walls so it should have a better foundation in the ceiling.

[CJ Paul]

Cool. So someone needs to dare me to order them now (I wont be using them until we move in this summer but I dont want to miss the pricing)

[JonMarsh]

I triple double dip dare you....

:rofl:


~Jon

[Andrew Pratt]

Resistance is futile :assimilate:

[Evil Twin]

Cool. So someone needs to dare me to order them now (I wont be using them until we move in this summer but I dont want to miss the pricing)

Join us, CJ... come over to the dark side.... feel the power of this IB design... the force is strong in this one...

[CJ Paul]

Hehe. One more quick question. So will this design be efficient enough for my monoblock amp to drive it to good levels. It is 250W RMS at 4 ohms.

[PMazz]

Hi CJ. As you know, I just installed 4 AV12s in my HT and am feeding them 1500W. If you're worried that it's not enough output, rest assured it is. And my room is 24'x18' opening to a larger open area. I was worried that my pro amp may not be able to push a 2 ohm load, but so far, so good. If you choose to go with the AV series, make sure you have plenty of power.

Also, having had 2 Tempests mounted horizontally for years, I would try to avoid it. The suspension definitely sags over time.

Pete

[CJ Paul]

Dang Pete. Well, like I said, I'll probably order them and try to do a manifold if at all possible. Mike has a 2-Adire ceiling mounted IB now too, so he has some downfiring woofers as well as the vertically mounted Tempests.

Check this plan though. I was thinking I could just butt two panels up and make a 90 degree angel and it would be mounted in the ceiling with the apex pointing straight up. According to my highschool geometry, 20" sides would give me only about 14" height so. How much cancellation would I get mounting the woofers at 45 degrees to the plane of the ceiling, 90 degrees from each other? I'm still working out all the angles.

[CJ Paul]

All right, I ordered four of the woofers. Dang you guys are bad influence.

[Evil Twin]

Yes, even you can feel the power of the dark side...

Excellent; as you give in to it, it's strength will lead you to a new mastery of your HT and music empire.

[CJ Paul]

Hehehehe

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