Sound deadening doors for Hybrid Audio Technologies Clarus 61-2

[GammaRadiation 10+ year member]

Nobody is suggesting that you can't build an inefficient barrier using multiple layers of vibration damper - just that it doesn't make any sense to do it that way.

I'd need to see measurements that showed improvement to believe that was anything more than misunderstanding the purpose of bass traps in a listening room, similar to the: they use foam on the walls of recording studios so I'll put (closed cell) foam on the outer skin of my car door conventional wisdom question I was responding to.

The difference in the closing sound over a single layer and multiple layers of vibration damper is downward resonant frequency shift from the added mass. Nice feature but really nothing to do with the doors' potential as a speaker mounting sytem. It's completely impractical to try to lower a vehicle panel's resonant frequency below the audible range because of the absurd amount of mass required. Since there's some offsetting panel stiffening with vibration damper it's even harder to accomplish.

These are the kind of completely subjective descriptions that make it possible to sell "audiophiles" speaker wire trestles and special magic markers to enhance CD fidelity. The funny thing about claims like these is that they not only don't demonstrate any change they don't even provide enough information to to tell if the claimed change is good or bad.

You may like my "school story" but everything I've said is consistent with the relevant physics and easy to demonstrate. You refuted it with the equivalent of wine tasting cliches.

I wasn't suggesting it was the best way, which is why I have plywood backing.

The physics of it most certainly lends it to a reduction in high frequency road noise and a minor dampening affect, similar to stuffing an enclosure. It dampens reflections. I dont have an RTA and am not in the sound deadening business so I didn't take physical measurements. But my own ears are good enough for me. You may claim that it is a placebo effect. I did the work so it must sound better, right? This might be true, but your blanket statement of "no one has ever" and now claim that the the theory behind it isn't sound physics is a bit reckless. If you're so set in stone about it, post your results of it producing negligible results instead of harping on the many people who feel that foams have a legitimate application in improving sound quality.

 

[Rudy 10+ year member]

I wasn't suggesting it was the best way, which is why I have plywood backing.

Covering just the holes is better than nothing, but not as good as a contiguous barrier across that plane.

The physics of it most certainly lends it to a reduction in high frequency road noise and a minor dampening affect, similar to stuffing an enclosure. It dampens reflections.

Seriously? How? This is a case where an argument can be made on the absolute periphery of the point. That in no way makes it useful or relevant. You've got to clean out the trees before you pick up the last leaf.

"Dampens reflections" may get to the confusion.

I dont have an RTA and am not in the sound deadening business so I didn't take physical measurements. But my own ears are good enough for me. You may claim that it is a placebo effect. I did the work so it must sound better, right?

I'm saying you have no way of knowing whether it's a placebo effect or not but are still using it as a basis to disparage my comments.

This might be true, but your blanket statement of "no one has ever" and now claim that the the theory behind it isn't sound physics is a bit reckless. If you're so set in stone about it, post your results of it producing negligible results instead of harping on the many people who feel that foams have a legitimate application in improving sound quality.

"No one has ever", perhaps, if you're happy to argue distinctions without a difference. I hardly think it rises to the level of being reckless. I'll grant that it would be more accurate to say that "no one has ever and then demonstrated a difference". That includes yours posts on the topics up to this point.

I did a lot of things that didn't pan out as I worked and tested my way to things that did. My belief that some of the things I tried were going to work made me think they did even when they didn't. What people "feel" is going to work means absolutely nothing. Feelings are easily manipulated by expectations or outside influence. I don't think it is reckless to suggest that claiming something makes a difference requires either measurements or the experience of treating dozens or hundreds of doors using different techniques and materials.

The point of these discussions should be to help the people with questions shortcut that process and push our own understanding forward.

 

[keep_hope_alive Premium Member]

I am subscribed, and loving this! (Thanks to the OP and all contributors: its like I am an addict being fed free drugs!)Regarding the above comment, would you then cover this with the same sound dampener that you'd place on the innermost door skin? Or would there be no practical need, at that point, for deadening/dampening the outer door any further?

[Practicality is subjective, I know, but looking at that KILLER Scion install, all I could think is, "Ah, that is the way an install is supposed to be done...so do I have any right to try to do my own build with only a $1500 budget?!?" I was thinking that perhaps I could manage $200 in sound dampening material--- since that is practical for me for my build--- but I couldn't manage even a quarter of what you guys did on the Scion...regardless of whether or not it is justifiable, or an important part of an "ideal" install.]

Adding that absorption would be in addition to deadener. I should take a video of what the outer metal sounds like in that scion. It sounds more dense than MDF. certainy, we have lowered the resonance frequency below where our hearing begins to become less sensitive.

 

[keep_hope_alive Premium Member]

That's an interesting idea with enough potential benefit to be worth trying and measuring. Sealing the surface of the absorbent material (perfectly) will eliminate the moisture problem. It might be better to seal the material in "bags" that completely wrap it and then just bond the bag to the outer skin. Sealing the edges of plastic sheeting to the doors is going to be tricky and doesn't get you any advantage that I can see. This way the only possible point of failure would be the bag material itself. If it doesn't deteriorate with time, the only thing it can do is fall off - no big deal.
In any case, this idea completely gets around the reasons CCF doesn't absorb sound. It's also better than the idea of waterproof open celled foam since that is making it close to CCF.

You still have the thickness/frequency problem. Even 2" isn't going to get you much below 2 kHz the first time through. It's going to get you lower for some of the reflected sound. Not sure how much problem energy we're still dealing with at that point though.

All of this complication should make it clear that if you're willing to go to extremes for speaker performance an enclosure, preferably not in a door, is the way to go.

I didn't explain well. Yes, I invisioned making sealed bags and not sealing against the walls. We use a similar method when lowering reverberation time in buildings, adding bagged fiberglass in areas that have high humidity, as you can see from the CMA link earlier, good absorption can be achieved down to 250Hz (depending on the size of the sample)

We will be building an impedance tube to do our own absorption tests at work soon.

Thanks for your contributions.

 

[GammaRadiation 10+ year member]

Seriously? How? This is a case where an argument can be made on the absolute periphery of the point. That in no way makes it useful or relevant. You've got to clean out the trees before you pick up the last leaf.

"Dampens reflections" may get to the confusion.

If flexible porous materials dampen sound then the addition of such materials to a sound cavity moves its properties towards an anecho environment. You can not deny this. That is sound, proven scientific theory. Then we should, at some point, be able to apply this to our doors and obtain measurable results. If what you're saying is that 0.5" neoprene foam hanging against the door skin does not make an appreciable difference, it's possible. I dont disagree. However, my point is just because YOU haven't seen the data doesn't mean it doesn't exist and when a large number of parties believe the same result you have to leave it in the realm of plausibility. If you're already in your door, why not spend $25 to improve its acoustic properties regardless of whether the result is placebo or truly distinguishable?

 

[GammaRadiation 10+ year member]

And it does reduce high frequency road noise which lowers the noise floor.

 

[Rudy 10+ year member]

Closed cell foam is not porous in the way that matters. You are assuming that the functionally absorbent volume is the material's thickness. With CCF, it isn't. Here's an electron microscope image of CCF:

http://www.sounddeadenershowdown.com/_forum_images/SDS-ccf.jpg

What you are seeing is the cut open top layer of cells that happens when the sheets are sliced out of a bun. Below that top surface, the cells are completely sealed. Air can't pass beyond the the top layer, there's no resistance, energy isn't converted to heat, absorption doesn't happen. You are literally talking about a few mils of effective depth.

 

[keep_hope_alive Premium Member]

I am with Rudy on this. CCF is not porous and is not an absorber by very definition since it is closed cell foam. Open cell foam is an absorber but we don't put it in a door since it absrobs moisture. CCF performs like a membrane.

http://books.google.com/books?id=y0d9VA0lkogC&pg=PA78&lpg=PA78&dq=sound+engineers+handbook+closed+cell+foam&source=bl&ots=AQo88HbbqM&sig=rnnq_F6MZC8rYKOFjiieJxvJwBo&hl=en&sa=X&ei=RjMHT-K8OcaRgQerluy3Ag&ved=0CD8Q6AEwAQ

PVC encased fiberglass is cheaper and way more effective. Bags of it could be placed othe bottom of the door and along the outer door skin.

Does it hurt anything to install CCF in a door? Not as long as it is not trapping moisture and causing rust.

 

[maylar 10+ year member]

This is an outstanding reference thread. Thank you to all who have contributed.

I have a roll of 1/2" polyurethane foam that I bought from McMaster Carr:

McMaster-Carr sound absorbing foam

I had intended to put a pad of it behind my speakers and perhaps line the door panels with it instead of the foam rubber noise barrier the car came with. Now I'm wondering if it'd be a waste of time.

 

[keep_hope_alive Premium Member]

THe best use for CCF

Cover deadener and metal to eliminate plastic door panel rattle

Put it on the trim panels, we cut CCF into strips

 

[Rudy 10+ year member]

Two best uses for CCF in this context. One is isolating trim panels as illustrated above (the treatment in photos 3 and 4 makes much more practical sense than the full coverage in photos 1 an 2). The second is as a durable and resilient decoupler for a barrier layer - critical if you're interested in reducing noise levels in the passenger compartment.

 

[R34P3R 10+ year member]

This was a great read but it really makes me want to ask one question. Why go through hundreds of dollars to isolate the rear wave and completely deaden a door when a tiny fiberglass/mdf enclosure would be more suitable? I understand some depth issues occur with the window and outer panel, but wouldn't you be able to build something asymmetrical out of fiberglass that would be able to work around those limitations?

 

[Rudy 10+ year member]

This was a great read but it really makes me want to ask one question. Why go through hundreds of dollars to isolate the rear wave and completely deaden a door when a tiny fiberglass/mdf enclosure would be more suitable? I understand some depth issues occur with the window and outer panel, but wouldn't you be able to build something asymmetrical out of fiberglass that would be able to work around those limitations?

That's a good question with a few answers. In some cases an enclosure inside the door would make a lot of sense. In many cases. it's going to be very difficult to fit in the space available. Depth can also be a problem - in my car, even with as much spacer as I can fit and still get a ground down trim panel back on, I have 1 mm clearance between the magnet and window.

Why stop there though? Sometimes kick panel enclosures make more sense than doors. You can get the speakers farther away from your head and have better control over the enclosure. You may also be able to get the speakers more on axis. That's not an option for me because I drive a manual, have long legs and can't lose any space.

If we're going to use the doors - an often practical but never ideal solution, there's something else to consider. Many people use speakers intended for car audio. Most of them are designed for the leaky enclosure volumes of a vehicle door.

Several hundred dollars is sort of high for treating two doors. Can certainly be more than a hundred so I'm not dismissing the concern out of hand. Many of us are as interested in reducing noise levels while we drive as we are in improving speaker performance. I wouldn't do anything that only impacts the vehicle's ability to host a sound system when parked. Others have different priorities. The important point is that noise reduction and improving speaker performance overlap.

Putting a barrier on the inner skin will improve the speaker's performance. It's also the ideal placement for noise attenuation. A surprising amount of noise enters the door from the front, rear, top and bottom. Blocking at the inner skin puts all of those sources behind the barrier.