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"Ideal"/Better Sub-woofer Isolation Strategies? (1 Viewer)

Synergist

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Timothy A. Kogstrom
To Whom it May Concern/Whomever Would Like to Respond-Assist:

I have gifted my two J.L. Dominion 108 sub-woofers to a friend who lives on an upper floor in a condominium, (placement very limited by her desire), such that one is in a corner, the other on a front wall, both on the same plane, very near/below the active monitors, (Adam Audio A5X's), on A.V. cabinet on front wall,

THAT said, due to her concern with vibration transmission through the floor to the condominiums below and around(?) her, I have isolated the sub-woofers by creating a "mass-loaded" foundation below the D-108's...

Each foundation "sandwich" is comprised of TWO, 16 lb., 12" X 8" X 2" concrete blocks. Each sub-woofer, (manufacturer's feet attached), placed on top of the upper concrete block, (26.4 lbs. + 16 lbs. = 42.4 lbs.)...below which are 4, (corner placed), 30 durometer, 1.75" dia., "Sorbothane" hemispheres, (appropriate size to adequately suspend and damp the 42.4 lb. mass)...
Below this is the identical, lower concrete block, which is suspended above the tiled floor by 4, (corner placed), 30 durometer, 2" dia., "Sorbothane" hemispheres, (appropriate size to adequately suspend and damp the 42.4 lbs. + 16 lbs. = 58.4 lbs. of the total mass of the subwoofer + foundation system).

HOWEVER, this now raises the sub-woofer(s) approx. 5 inches off the intended/(engineered for), ground plane...

Questions:
1. By raising the sub-woofers by 5 inches, in what frequency range/(frequencies?), will the subwoofer frequency curve be adversely affected, and how much of a deviation must be corrected?
(J.L. Dominion D-108 Sub: 31 - 112 Hz (±1.5dB), -3 dB at 29 Hz / 119 Hz)

2. Is 32 lbs. of mass-loaded, damped suspension sufficient to isolate these, 24.4 lb. sub-woofers from the floor...(i.e., how much isolation/vibration transmission can I expect?).

3. Is there a better mass or configuration to use...?...(space/placement requirements are VERY restrictive...)

Thank You for you patience if you have read this far!

I thank you in advance for your responses/assistance, and I avidly look forward to your response!

Sincerely,
Timothy A. Kogstrom
 

JohnRice

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Sounds like a solid plan, pun intended. I can't think of any practical way to provide more isolation. Also, it shouldn't have any significant effect on the sound. I mean, everything you do with the placement of a sub will affect it's sound but there's no way to say it will do precisely "this".
 

xx Brian xx

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Why not just get two Auralex SUBDUDE isolation pads and put them under the subs. It would be a lot better looking and they work great.
 

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