# "Ideal"/Better Subwoofer Isolation Strategies?



## Synergist1 (12 mo ago)

To Whom it May Concern/Whomever Wishes 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!

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

Sincerely,
Timothy A. Kogstrom


----------



## Da Wiz (May 8, 2019)

Raising the subwoofer 5 inches does the same things as moving the sub fore-aft 5 inches or right-left 5 inches. Which is "not much" in the big scheme of things. "Stopping" bass from bothering other residents in multi-unit homes is **** near impossible. Getting the subs off the floor directly is only a small part of the issue. Stopping bass takes a LOT of material. Layers of dissimilar materials works best...alternate layers of hard and soft. Dry play sand makes a good soft layer, bricks and cinder blocks make good hard layers (the deader the hard material sounds when tapped, the better. But the soundwaves produced by the subwoofer still interact with 100% of the floors, walls, and ceiling. All those surfaces being exposed to bass will put some bass energy into the structure and into other units... it is unavoidable unless you construct an entire soundproofed room INSIDE the existing unit. As for current isolation work under subs... have a slft layer against the floor and a soft layer below the sub, and alternate hard and soft layers between sub and floor. Mix wood, concrete/stone, sand (inside durable plastic bags of the proper sizes), and other materials like drywall or particle board or strand board. I would encourage sound checks inside the adjoining units (assuming neighbors are OK with it, of course). Have someone adjusting the sound level of the subs while a second person is in the neighboring unit listening with the residents to agree when the sound is getting annoying... the person on the volume control and the person listening in other units can talk on the phone to get the volume raised/lowered. This will help you figure out how loud is too loud for the subs as far as the neighbors are concerned. Once you know that, you'll have a much better idea of whether the isolation of the subwoofer is useful or not. It may turn out that the subwoofers just aren't practical in multi-unit housing if you are interested in being a good neighbor--that should be one of the possible "solutions".


----------



## 1Michael (Nov 2, 2006)

Isolating the box from the floor will have no effect on stopping the sound waves from going through the building. Only turning the sub volume down can do that. Or maybe enclosing the room in 4 feet of concrete...A properly built box will not vibrate except when it is pushed hard.


----------



## wantAvote (Dec 2, 2018)

The alternating of hard and soft materials is an excellent suggestion along with Sorbothane and mass loading i believe is the best one can do to decouple the sub from the building framework.
Next, controlling sound pressure waves. Sub frequencies are long and/or wide and will fill the room regardless of what you will do. I suggest carpet and rug for the floors and in attempts to minimize direct reflections use acoustic baffles suspended immediately behind the sub or attached to the back wall. As for direct first reflections find a heavy wool tapestry (lol). The low frequencies are larger than the room is tall, wide etc. You know the answer as well as i do - anything you do, short of a complete soundproofing renovation will only reduce sound wave volume and propagation.
I think what you've done already will allow you to raise the spl a little without waking the neighbors - cause that is the real concern (during normal sleep hours sound travels so much more efficiently) during evening hours any sound greater than what is in the immediate vicinity becomes obvious..., then maybe annoying.
You could make an acoustic baffle or several with - picture framed, rock wool and covered with ??? whatever. 
I believe each of your projects will give you a little of what you're hoping for
Happy Days


----------



## Da Wiz (May 8, 2019)

The post that says isolating the subwoofer will have no effect on sound transmission... that's not correct. Isolation WILL improve the situation by transmitting less mechanical energy (vibrations) from the subwoofers to the structure. That said, the bass radiating through the air is VERY DIFFICULT to manage to prevent escape to neighboring units. It requires actual sound-proofing (again, multiple layers of dissimilar materials, soft, hard, granular, solid, rubbery, and dead). And that sound-proofing includes HVAC ducts that may run in the walls between units allowing sound to propagate easily, up/down or left/right or front/back. The walls will be "excited" into vibration by bass sounds and those vibrations will go straight across the barriers between units unless the walls are concrete or brick between units and assuming the units do not share HVAC systems. If the whole building is on a single HVAC system and the ducts run into all rooms in every unit... it is going to be very hard to quiet the bass without the major expense of soundproofing the floor, walls, and ceiling. One thing a speaker manufacturer told me YEARS ago was that if you feel like the speakers or subwoofer aren't producing the amount of bass they should be able to produce, is that it's very possible the missing bass will appear in some other part of the house. Sure enough, when I setup in my new room after a move, there seemed to be very little bass in the room at first. I walked around the house (finished basement, 1800 sq ft on the main level, 800 sq. ft, finished in the basement, and another 700 sq. ft on the 2nd floor) and found all the missing bass in the jack-and-jill bathroom shared by 2 bedrooms up stairs and in one of the unfinished corners of the basement. Moving things got the bass back into the room.

Isolating the sub(s) from the floor is probably only a 15% solution to reducing how much bass is transmitted to other units. So it's not a waste of time, but it's not the major part of the bass transmission issue either.


----------



## AndrewOrnellas765 (10 mo ago)

Synergist1 said:


> To Whom it May Concern/Whomever Wishes 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,
> 
> ...


If you just isolate the box from the floor, then the musical waves will still pass through the floor. It seems to me that it’s worth just making a properly built box, then everything will be cool.


----------



## BP1Fanatic (Mar 28, 2011)

Move the corner sub to a wall also. Ideally, you want a sub on each wall to cancel room nodes.


----------



## acousticsman (Jan 21, 2009)

For Structural isolation, these are by far the best available EVP Equipment Vibration Protectors | A/V RoomService, Ltd.


----------



## gplracerx (Nov 9, 2010)

Low frequency sound waves travel a long way. That's why elephants communicate with infrasound, frequencies below 20Hz. I remember going to see a Star Wars movie many years ago and hearing the low frequency sound effects in the parking lot. So yes, the most important thing is the sound pressure level in the room. However, minimizing the coupling of the enclosure to the floor can help some. You definitely don't want to mount your subwoofer on spikes.


----------

