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Post by madmanaenewman on Jan 1, 2007 19:48:12 GMT -7
Firstly, let me share my awe and appreciation for a great site. Most of my questions (and a few I never thought to ask) are well answered in you FAQ and related sections. Thank you, and do keep up the great work.
I noticed in all the pictures of peoples' projects only one example of a down-firing transducer. All the other examples mount the transducers with a vertical face orientation. I vaguely remember seeing in another forum a warning about horizontal orientation unless the transducer is specifically designed for it. I do not ever recall a transducer vendor mentioning installation orientation recommendations in their specifications.
My recollection from physics is that waves bend and distort when they reach sharp corners. This would suggest to me that a flush mounted installation would be superior to a recessed installation, given a choice. Of course, ceiling joists at 16" centers renders it impossible to flush-mount 18" speakers, but my ceiling is currently open and I can easily remedy that problem.
So, can one down fire any transducer or only a select few, and what might those select few be?
Another question: I have read in several other sites that a sub-woofer can be placed anywhere providing it is on the floor. Was this just a bit of humor that I missed, referring to the weight of sub-woofers, or is there some benefit to having the sound originate from near the floor boards?
Many thanks for any insight you might offer.
PS, I just noticed that this was the wrong place to post the thread, but I do not know how to move it. Sorry about that.
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Post by ThomasW on Jan 1, 2007 20:07:29 GMT -7
The pictures represent examples of the various type of installations, and nothing else.
The Adire and Parts Express websites have calculators for determining the suitability of a particular driver for down firing application. Up to 5% sag is consider acceptable.
Most drivers are suitable for this orientation but double check should you decide to use a driver we don't have experience with...
18" drivers are only 18" in diameter at the outside of the frame. Their diameter decreases quickly behind that.
A manifold functions like a compression driver.
I have no idea what the floor placement stuff is about. The bulk of IBs are ceiling mounted, and the people with them had floor mounted portable subs before building their IBs.
This forum's software doesn't permit moving of threads.
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Post by chrisbee on Jan 5, 2007 11:05:09 GMT -7
One point that Thomas didn't cover is flexure of the baffle mounting surface.
If your ceiling joists are relatively lightweight the whole ceiling may flex when the IB gets going.
An opposed driver manifold should avoid much of this flexure.
Do not underestimate the flexure induced in the supporting structure by large drivers.
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Post by Darren on Jan 5, 2007 12:24:01 GMT -7
Chrisbee has a very good point. My ceiling joists are 12" lumber and they flex enough to get my can lights all out of shape. My drivers are mounted in an opposing fashion in my manifold which cancells out a lot of the vibration but I tell ya what! It still shakes the room!
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Post by ThomasW on Jan 5, 2007 12:35:07 GMT -7
My ceiling joists are 12" lumber and they flex enough to get my can lights all out of shape. My drivers are mounted in an opposing fashion in my manifold which cancells out a lot of the vibration but I tell ya what! It still shakes the room! Should I put something in the FAQ page about adding bracing that ties the ceiling joists to the top of the trusses, when people have heavy ceiling mounted manifolds?
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Post by Darren on Jan 5, 2007 12:41:39 GMT -7
Adding the bracing surely couldn't hurt for some applications. It might be a good addition to the FAQ for cases where their ceiling joists are less robust and also for array designs. I don't think anything like that would do much for my situation or others with engineered trusses since they are pretty dang stout as is. It would probably help quite a bit when the ceiling structure is less than stout though.
I'm wondering if the resulting vibrations in my setup aren't more from the pressure wave than actual vibrations. Not sure how I can test that.
I have been pondering a rubberized isolation system for my mount just for fun... not necessary for me but I like to tinker.
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Post by ThomasW on Jan 5, 2007 13:13:26 GMT -7
Nousaine set the bottom of his IB in a bed of liquid nails or silicone or something, in an attempt to damp the vibrations. That didn't help.
When I first setup my big IB it wasn't mechanically attached to the floor above. There were multiple layers of thick neoprene tape around the edges of the manifold. A jack under the manifold pushed up sealing the IB. Doing that didn't make any difference either.
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Post by Darren on Jan 5, 2007 13:59:33 GMT -7
Nousaine set the bottom of his IB in a bed of liquid nails or silicone or something, in an attempt to damp the vibrations. That didn't help. When I first setup my big IB it wasn't mechanically attached to the floor above. There were multiple layers of thick neoprene tape around the edges of the manifold. A jack under the manifold pushed up sealing the IB. Doing that didn't make any difference either. Sounds like the majority of the vibrations are due to sound pressure rather than mechanical transfer.
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Post by chrisbee on Jan 6, 2007 1:46:32 GMT -7
If you tie the ceiling joists to the sloping rafter of a pitched roof it should increase the mass helping to resist vibration in the ceiling. Roof coverings vary enormously in kilos per square meter. Whether the ceiling vibrations are the result of mechanical or acoustic excitation coupling struts to the rafters should help. I don't suppose we have any architects or structural engineers onboard who might warn us against such roof modifications?
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brady
Full Member
Posts: 238
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Post by brady on Jan 6, 2007 7:26:13 GMT -7
Chris is correct adding something to tie the ceiling joists to the roof joists will make it stiffer and add some mass.
Truss manufactures usually engineer the product to meet the minimum standards for that application so it isn't that hard to improve.
On many of the new construction jobs a plumber or hvac has to cut through a large part of the truss and a engineer has to approve a method to strengthen it. It's always the same, add plywood to both sides glued and nailed. I always add some screws to draw it tight but nails are required because any movement could cause the brittle screws to fail.
I'm not sure if simply adding plywood to a rafter or truss would void warranty on a new house, but if it were my house I wouldn't worry.
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Post by chrisbee on Jan 6, 2007 9:36:48 GMT -7
I always add some screws to draw it tight but nails are required because any movement could cause the brittle screws to fail. I didn't know there was a problem when using screws. If the screws can be hardened for socket heads I always assumed the material would have a higher carbon content and so be tougher than ordinary mild steel nails. I've used screws on nailing plates sometimes to avoid shocking the structure which would normally occur when hammering nails home.
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Post by Darren on Jan 6, 2007 10:24:08 GMT -7
In certain situations tying the ceiling joists to the roof trusses can introduce stress cracks in the drywall as the seasons go by. This would happen in my situation so I don't tie them together. If mine were engineered trusses it would be another story and wouldn't need the additional support anyway. This is why they used 2 x 12 lumber in my ceiling. If I were to tie the sloping roof to my ceiling the family room ceiling would be subject to any load or expansion and contraction that my roof joists are subject to which would lead to cracking drywall. You need to be sure you aren't introducing any transference of load when you tie things together up there
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brady
Full Member
Posts: 238
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Post by brady on Jan 6, 2007 23:09:07 GMT -7
Good point Darren, transferring a load someplace else could cause some problems. I have vaulted ceilings in my house and when I moved in there was a gap between the trim around the top of a support post and the ceiling. So I moved the trim up tight and nailed it in. Summer came and the trusses moved down about 2 inches and crushed the sheetrock. This is called truss uplift and is caused by the lower cord in the truss being warmer than the upper cord, one shrinks and one swells. Had to fasten the trim to the ceiling so it could move with it through the seasons Chris, drive a screw half way into a board and whack it with a hammer, it's easy to snap. But I do the same thing as you do all the time for the same reasons. Sometimes I wonder how the state comes up with some of the building codes like this one.
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REK
New Member
Now building a home theater !
Posts: 11
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Post by REK on Feb 25, 2007 10:41:54 GMT -7
I noticed in all the pictures of peoples' projects only one example of a down-firing transducer. All the other examples mount the transducers with a vertical face orientation. I vaguely remember seeing in another forum a warning about horizontal orientation See nousaine.com and other areas of this site for sub-woofer location. Down firing subs will not work with soft suspension speakers. The old Audio Concepts DV12, and the JBL 128, 2235 and 2245 were susceptible to this phenomena, i.e.sagging with age. A soft suspension yields a lower Fs, but more sagging. The best bet is to ask the speaker manufacturer about horizontal mounting.
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