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*proceeds to order 1 ton of pillow stuffing to market as my own decoupler*

Glad you got around to this. Thanks.
I wonder how well this would work: take tyvec sheets, cut to match your door card, sew shut on the edges, then fill with synthetic pillow stuffing. Place in between MLV and door.
 

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Yes indeed, a huge thank you to everyone who donated materials for this experiment. We all sincerely appreciate the kindness!
Thanks for taking the time to do this!
 

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I made a mistake regarding closed cell foam thickness, greater than 3/8's gives marginal returns. The only benefit of open cell foam is when it's thickness can be 2" or more in thickness. That's why open cell foam isn't recommended.
 

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Thanks Justin. I always have had my doubts about needing to add the CCF layer. In most cases the MLV is pushed down by the weight of the carpet or tnesion of the trim pieces. Yes its possible MLV could be hung in a way to pick up some vibration, but I would think the vibration of that metal would have to be of significant amplitude to excite the MLV. In 90% of my MLV installs I don't believe that is happening. I've certainly never found a resonance related to my MLV installs . I don't really mind a little extra cost for the CCF, I just minded the extra labor of attaching it. I will no longer be using it. Especially since my product of choice was the RAAM Ensolite which tested very poorly !
 

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Listener of Music
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Products like Ensolite are a good idea. Justin is saying it does not stop the transfer of vibration to the MLV but it certainly stops a panel from buzzing or a clip from slapping against the MLV. I personally will still use it as that was my intention to begin with. I never interpreted the idea in a way that metal transferred vibration to mlv which in turn vibrated causing resonance. I actually always thought that it was to stop stuff from vibrating against each other.
 

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...

Velcro itself has almost no spring-like properties since it is designed to be fairly rigid, so it would not help to decouple the vinyl if used with 100% coverage. However, I think you're suggesting use velcro to hang it on the edges and leave the rest of the vinyl floating which is the recommendation I tried to make in the conclusion. If the vibration along the edge of the vinyl is "far" away from the middle of the vinyl where it is floating, the vibration isolation is excellent.
We should know the stiffness without numbers, but it probably is non linear and very stiff with no movement.

Do I conclude that I want it to hang, or do I still want a layer of something else under it?
And do I still want neoprene layer for the Velcro to attach to?
 

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Wave Shepherd
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Discussion Starter #27
I was trying to recommend letting the vinyl float and not be firmly attached where possible, such as the vertical surfaces on the inside of door trim panels.

Beyond that, it would be ironic if I tried to recommend a certain rule of thumb since the conclusion of this experiment was to disprove a certain rule of thumb. I do not yet have anything better to replace it with other than be practical with both your time and money in terms of what you enjoy about this hobby.
 

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I figure this is a good place to ask this considering it's a similar subject.

Whats your thoughts on FG enclosures like spare tire sub boxes where the box hugs the exact dimensions of the vehicle? In regards to resonance and vibration transfer to the body. Would putting down CCF before laying the Fg be useful or no?


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I figure this is a good place to ask this considering it's a similar subject.

Whats your thoughts on FG enclosures like spare tire sub boxes where the box hugs the exact dimensions of the vehicle? In regards to resonance and vibration transfer to the body. Would putting down CCF before laying the Fg be useful or no?


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Hey Jscoyne2,

I havent done a fiberglass enclosure but I will say that coupling the sub box to the vehicle helps with the sensation of bass throughout the vehicle, especially in the lower octaves because it transfers vibrations to the structure which you will feel. Now obviously you don’t want rattles so that is where using something like CCF along with typical sound deadening methods might help.

I’m no expert but have experimented with this and in my opinion it does make a difference. I will let the fabrication experts chime in on the CCF specifically though.
 

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Wave Shepherd
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Discussion Starter #30 (Edited)
I think it's all about goals. If you enjoy feeling the bass then by all means clamp that enclosure to the car and have fun. Also, the more you bolt it down the less it can become a projectile if you're ever in a crash.

If you want to float it and decouple it, you have the same challenge as mass loaded vinyl. You should find a decoupling material that is soft enough to isolate it, relative to how heavy it is. Most materials used in car audio do not have published stiffness values so the only advice I could offer is grab something like a set of rubber anti-vibration mounts from an industrial supply company, something used to isolate small power generators or small machinery. Those are usually specified with stiffness or with how much weight they are designed to decouple and at what frequency etc..

I doubt any of that would work for a custom molded enclosure like a JL Audio Stealthbox because they are designed to be fitted exactly one way and you'll have a crazy challenge trying to do something different. Even if you could fit something squishy between the box and the car, it still gets clamped to the car with bolts so that defeats the purpose of trying to float it.

A much much easier thing would be to mount two speakers opposing so they cancel the vibrations of eachother and then you don't need to worry about anything else.

See the Sonos home subwoofer for example:

 

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I do my best to totally decouple enclosures from the car as much as possible. The last thing you want to do is transfer the vibration from the enclosure to the rest of the car.

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For large home theater subwoofers I use 3 layers of 1/8” rubber from Tractor Supply (roll) interspersed with a pair of 1/2” plywood sheets. For a car I’d probably try thinner rubber like maybe multiple layers of the rubber used for drawer liners. And you can also get rolls of cork at a hardware or office supply.

And if you’re trying to do a complex shape, you might want to look into cans of Plastidip or Flexseal that can be applied with a brush, which would give you a rubberized coating. Maybe you could use strips of cork above that and even apply them while the rubber is wet so the cork is adhered, which would provide some spacing/isolation for your enclosure. But as soon as you bolt the enclosure to the car, unless you use an isolation mount, you’re going to transfer vibrations into the cars structure.
 

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Feeling the bass as well as hearing it is an important part of the equation. High end theaters use bass shakers for this very reason because the sensation of bass is just as important as hearing it. Sound traveling through air also loses energy much faster than it does traveling through a solid. I deal with that when we design buildings and don’t want sound to travel through walls or floors. In those cases, decoupling the walls is more effective than adding mass or insulation to increase the STC ratings. I also renovated the Bose research and development building years ago and learned a lot. Those engineers do some amazing shit in that building. My crew was the first to construct a sound room for them that didn’t rattle in years.

In car audio, the school of thought is “we don’t want rattles” and from an installers point of view I can understand this as you don’t want customers coming back complaining about a rattle in the door or similar. For me, the trick is to couple the subwoofer to the structure of the vehicle AND deaden all the rattles that it might produce. The above mentioned securing the box down to prevent that the box from becoming a skull crushing projectile in an accident is also important and obviously when you do this you’ve just coupled the box to the car. Build a fiberglass enclosure, even with foam between the car metal and sub box and guess what, you’ve just coupled the box to the frame of the car. I think you guys do it all the time and may not even know you are coupling the box to the car. It’s a balancing act between rattles and feeling the bass. Going with huge cone area and thousands of watts is another way to feel the bass too but that costs much more. :laugh:
 

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Wave Shepherd
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Discussion Starter #35
Hummm, find this just before I re-do all my car interior. Does this means I'd better use 3M Thinsulate rather than CCF + MLV?
Please re-read the last sentence of the conclusion.
 

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I'm a little confused by the testing & report... that the MLV samples were 1.5" square, and the wavelength of the sound frequency is long, on the order of feet. The MLV functions to deflect with the sound pressure, and by virtue of internal coulomb friction turn that displacement energy into heat and not just act as a fixed mass against an undamped CCF spring? Would we see much different results from a large coupon? I only have questions, not answers!
 

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New project this weekend - angrily rip out all of the ensolite I painstakingly applied to my whole car!!!!

Great job on the research.


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If I might add a question to this debate:

If most of MLV sheet's surface is secured to a vertical panel (like a plastic trim card on a side door) using glue or plenty of velcro strips, I don't see a need to use any decoupler between the MLV and the trim card.
The only way for MLV to vibrate in that setup is if the entire trim card would vibrate with it, and that would take a lot of force to "excite".


Is this thinking correct?


By the way, has anyone used an automotive-grade glue (example: roof upholstery glue) instead of velcro strips to secure an MLV sheet to a vertical surface? Did it hold up in the long term?
 

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Wave Shepherd
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Discussion Starter #40
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