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Post by moonfly on Sept 1, 2010 11:22:56 GMT -7
Hi everyone. Having seemingly upset Thomas with some apparent misunderstandings on the way IB's work, I have joined with the hope to fix this. I would like to use this thread to discuss my own install, as well as some of the finer points of IB installs at large. I have read all the FAQ's, but thats not to say I fully understand them, which is never that unlikely if I'm honest  . Anyway, my build is basically as follows. My room is 4.1 x 3.6, with a layout that doesnt lend itself to having 2 DIY subs in there. This naturally leads me to the IB, and the chance of no cabinet in my room at all, whilst at the same time theoretically enjoying the best bass I possibly can. My room has a suspended wooden floor and I plan to use the void underneath as the IB. The volume of the space is roughly 7100 litres, or 260ish cu ft. For this I have come to the conclusion (with the help of Chrisbee) that a pair of Fi Audio IB318 drivers will work best. I modelled them in WinISD with 500 watts input power which seems to be pretty optimal. A couple concerns I have are that I ideally would like to have the drivers non-co located, as this fills out a bit of a dip in the response my room dictates. Second is that this means no possibility of dual opposed drivers in a box manifold. Third is the obvious impact of a powerful sub and a flexible floor. I have already experienced a slight lack of detail and composure due to this floor (compared with a concrete one), and the dual subs seemed to help with this for whatever reason. So far I am at the thinking stage, trying to work out the very best way forward, so if there are any glaring issues I have missed I would appreciate some input. Hopefully the ensuing discussion will reveal my knowledge on the subject, where that knowledge is correct and incorrect, and how best to move forward. Cheers Dan |
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Post by jman on Sept 1, 2010 19:30:55 GMT -7
Can you afford a pair of 18's in each of the locations? A pair is not bulletproof even in a small room. 7000L is enough VAS for 4 drivers.
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Post by chrisbee on Sept 1, 2010 22:48:18 GMT -7
If your floor is more flexible than mine I'll eat my hat. I relish the free vibes when the floor "melts" under my chair. It did this even with my old SVS cyinder. The only real downside is when my wife starts tapping her feet on the floor to the music over the film credits. I'm always rather disappointed that it wasn't the subwoofer having this effect.  More seriously: You could try bracing the floor with a pillar of some kind. Though you would have to ensure absolutely no damp can rise through any added structure. Use another subwoofer to test the effects of floor bracing with REW. Naturally you'd have to brace under the floor joists. Not under the floorboards themselves. A screw "bottle" car jack and a length of RSJ to bridge several joists would be useful to test the effects of a very gentle lift. Just to see if the idea is worth pursuing. I suppose I should have asked if you have physical access to the crawl space? |
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Post by moonfly on Sept 2, 2010 11:00:53 GMT -7
I cant really access under the floor unless I make a hatch, and TBH I think a bit of floor bounce would be fun. Whether I go IB or any sub, that floor is going to be there, so the cleanest design possible is best either way. Ive considered the 4 driver question, but I can easily add 2 later, not so easy to sell 2 without making a loss, so might hold off on the 4, especially as work has all but dried up on me out of the blue again, ruining a planned speaker upgrade and possibly postponing this project. I'm feeling a bit exhausted of late, so might just take a break for a bit  |
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Wull
Junior Member
Posts: 84
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Post by Wull on Sept 2, 2010 11:48:36 GMT -7
I wandered if you could of used an inflatable jack for this... I'm not surprised, all that typing  |
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Post by ThomasW on Sept 2, 2010 12:25:01 GMT -7
Dan, I think your wedge box idea will work fine. The hole in the floor needs to be as big as the bottom of the box. The back wall of the box should have a layer of fiberglass batting or whatever damping material you have ready access to.. I like floor bounce, people's eye's bug out when really low bass waves roll across the floor....  |
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Post by moonfly on Sept 3, 2010 1:58:34 GMT -7
Dan, I think your wedge box idea will work fine. The hole in the floor needs to be as big as the bottom of the box. The back wall of the box should have a layer of fiberglass batting or whatever damping material you have ready access to.. I like floor bounce, people's eye's bug out when really low bass waves roll across the floor.... I am considering a pyrosorb lining. Its a kind of closed cell foam used in the ventilation industry as an acoustic lining to help reduce mechanical noise in ventilation systems. Not sure how well it will work in this application though, I know the properties of the material well, just not if it should be used in this application. On the box, yes the larger end of the box that will be the opening between the manifold and the listening room (or IB chamber, depending on which way round I build it. |
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Post by ThomasW on Sept 4, 2010 6:30:19 GMT -7
I'm not familiar with that material. Sounds like it's designed to damp vibrations in the metal as opposed to absorb sound waves.
Generally speaking acoustic foams are open cell.
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Post by moonfly on Sept 4, 2010 12:41:57 GMT -7
I'm not familiar with that material. Sounds like it's designed to damp vibrations in the metal as opposed to absorb sound waves. Generally speaking acoustic foams are open cell. I may be mistaken then, maybe it open cell, will ave to check on that. Its use is for making sound attenuators, basically reducing the sound of the fans in air vent systems. I could try some to test its properties, but it could muffle the bass, or at least that what I'm thinking. |
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Post by chrisbee on Sept 4, 2010 13:37:53 GMT -7
Dan
Given the wavelengths involved, multiple bounces into deep, fibrous insulation are more likely to attenuate reflected sound waves. Since there is no room for such materials in a manifold it might be best to ensure that no nearby reflective surfaces exist. So dump the manifold altogether.
I'd ask Fi if horizontal mounting is acceptable with the IB range. Then lay them flat and point them up at the ceiling with a nice pile of rockwool on the crawl space floor beneath the drivers.
I really can't remember what their answer is to horizontal mounting. Many of their other drivers sit flat on the parcel shelves of cars. Whether the IBs can tolerate this I don't know. But it would be the ideal SQ choice IMO. No underfloor access required either. Just a hole in the floor and a stiffening baffle. You could add a shallow frame to carry a strong grill just above maximum excursion. Or sink the driver below floor level and have a flush grill capable of accepting foot traffic.
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Post by moonfly on Sept 5, 2010 6:19:37 GMT -7
I already asked about Horizontal mounting and Am from Blade Ice said it would be absolutely fine. I can see a whole bunch of benefits from going that route, as long as the floor doesnt move enough to cause lost output. Some bracing could likely help.
Ive got some time to decide now anyway, funding has dried up for the minute and I wont be getting the drivers till I get some more work in now.
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Post by chrisbee on Sept 5, 2010 7:52:30 GMT -7
Floors are usually much stiffer than stud walls and ceilings. The structural timbers (floor joists) are normally much deeper than non-structural, room surfaces. If they weren't strong enough they wouldn't support a bunch of people holding a party. (for example) Keep smiling, more work is bound to come along soon. |
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Post by moonfly on Sept 5, 2010 12:30:08 GMT -7
Well, I figured a load of people weighting the floor down would help ensure no lost output, its playing on my mind though, just one of those things where physics gets into your brain.
I'm sure the floor mounting would be superior to the wedge 'outie' boxes though. I could also brace the joists with UniStrut directly where the driver is. With the clamping action of strut braces against the weight of the floor, I reckon I could get them pretty darn solid.
This will certainly be the easiest and quickest install, will possibly be the cleanest, and would offer the maximum amount of placement options as well. I've got a loan sub as a put me on, so I may take the time to take a load of measurements. I could use REW's auto eq projection graphs to simulate possible twin sub position interaction as well, so a bit of time might be a good thing too. I think getting the drivers below the floor so I can put a grill over them is the way forward though. I'm thinking a 3" thick baffle plate from ply or MDF set so the face is flush with the underside of the floor boards (driver mounted so its set in the baffle) will be best. The driver will then be flush with the underside of the boards when at full excursion, and give a floor boards thickness of clearance to the grill.
I need to work on a grill design though I think.
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