Sound Deadener Showdown?

[Bettr n' Revrse 5,000+ posts]

Ooooo shit.... Someone mad bro!

 

[Kangaroux 5,000+ posts]

Oh and starting now every time I get groaned I'm deterring one person from buying AT deadener. Remember nuthuggers your douchebaggery is losing your company business.

And for every time you make a statement like that, I'm going to groan you. A wonderful cycle we have going on, isn't it?

 

[fire_mike 10+ year member]

That's why. If I need to explain the ignorance here, then you really should quit talking about deadener lol

So I'm guessing you are not able to explain your position clearly?

 

[audioholic 5,000+ posts]

because he doesn't know what he is talking about. He thinks a stiff panel will resonate, but it's the weakness in the panel causing it to resonate NOT the stiffness. Try to get stone to resonate it's very stiff.

What? Are you suggesting stone will not resonate? Because it will. Everything in nature can and will resonate. I have used concrete to mass load vehicles before. The concrete didnt stop the panel/vehicle from resonating, it simply lowered the resonant frequency to a point that created less audible problems.

What I think has been lost in the panel resonating debate here is to remember that you will not stop an object from resonating, you will only alter the frequency at which it resonates, and (possibly) the amplitude of the resonating. If a panel is resonating and you want to 'stop' it, you will either mass-load it to lower its resonant frequency, or you will stiffen it to raise its resonating freq. These are your only two options, and neither truly stops the resonating, it merely alters its frequency (which alters its perceived intensity/audibility).

If you want to 'stiffen' a roof, adding a pliable mass loader like deadening mat is a very poor choice. Sure, Ive used deadener mat on panels many times, and then tapped on the outside of it (like a door panel). It appears to be stiffer, but its really just heavier. If you dont believe me, answer one simple question... how will adding a flexible material like butyl rubber make a steel panel "stiffer"?

The best way to stiffen a panel is by using a material that itself is rigid. For the roof example, in say an SUV, a better method of making the roof more stiff would be to apply fiberglass to it, since it will cure into a stiff/rigid state. This will raise its resonant frequency, while covering the roof with mat to mass-load it will lower the resonant freq. To the misinformed observer, both make the same thing happen, the panel moves less at the frequency it use to. To an informed observer, you have either raised the resonant freq ( by stiffening it) or you have lowered it (by mass loading it).

...it's the weakness in the panel causing it to resonate NOT the stiffness.

What are you calling 'weakness' in this statement? The shape of the steel panel, thin and long? If so, why do you then turn around and suggest stone wont resonate, without mentioning the shape/size of the stone in question? You seem very confused about this topic, maybe you should read more and talk less, especially of your talking will be to tell other people that they dont know what they are talking about. Frankly, you dont know what you are talking about. No offense meant, but its true.

 

[fire_mike 10+ year member]

OK, audioholic has explained it quite well. As far as what I said before about deadening helping with SPL, it still can (it can be better than nothing). Ive seen the mass loading effect help to decrease panel movement and increase SPL (not by a ton, but every tenth counts). Again, it's not the ideal choice, but sometimes you work withing rules that limit your options.

 

[Rudy 10+ year member]

So I'm guessing you are not able to explain your position clearly?

No need for this to escalate into a pissing contest. The OP asked if acoustical treatments were worth it. I listed the situations in which I thought they were. I finished by saying that all of the products in this category are worthless to SPL competitors. Some people have taken exception to the statement, but none have provided a reason that went beyond wishful or magical thinking. It seems simple on the face of it that something designed to "deaden" sound would be a good choice for maximizing sound pressure.

This isn't meant as a criticism. 99.9% of what we do as human beings we do because we saw someone else do it first. Add vague and unsupported claims by sellers and governing bodies that have codified the use of the products and you end up where we are.

There is no reasonable justification for the use of vibration damper in a pure SPL installation. If the governing bodies of the organization one competes in limits what can be done to the sheet metal to an adhesive coated aluminum foil, object. I've had discussions with people at the tops of some of these organizations. They agree that the rules haven't been thoroughly thought through in this area and will be improved over time. Compliance should be in the form of the thickest foil allowable with an adhesive that isn't viscoelastic but is as rigid as possible.

Asphalt MIGHT be a reasonable adhesive since I've never seen a dedicated SPL vehicle that hadn't already sacrificed any possible resale value. I'd try to use epoxy of some sort, possibly reinforced. Asphalt remains somewhat flexible until all of the VOC's have out-gassed. That can take a few years so it isn't really a predictable and controllable option.

This is for a disposable vehicle dedicated to SPL competition that must comply with rules that don't make sense to start with. What it sounds like is irrelevant. Impact on the vehicle's value is irrelevant. This is a very rare situation. It's a mistake to extrapolate from this to any other application and from any other application to this.

 

[fish1234 10+ year member]

Never meant to open a can of worms on this subject, but some very helpful ideas going on here. Thank you, all who have posted on this topic. It seems we all can learn a lot from each other.

 

[Rudy 10+ year member]

What? Are you suggesting stone will not resonate? Because it will. Everything in nature can and will resonate. I have used concrete to mass load vehicles before. The concrete didnt stop the panel/vehicle from resonating, it simply lowered the resonant frequency to a point that created less audible problems.
What I think has been lost in the panel resonating debate here is to remember that you will not stop an object from resonating, you will only alter the frequency at which it resonates, and (possibly) the amplitude of the resonating. If a panel is resonating and you want to 'stop' it, you will either mass-load it to lower its resonant frequency, or you will stiffen it to raise its resonating freq. These are your only two options, and neither truly stops the resonating, it merely alters its frequency (which alters its perceived intensity/audibility).

If you want to 'stiffen' a roof, adding a pliable mass loader like deadening mat is a very poor choice. Sure, Ive used deadener mat on panels many times, and then tapped on the outside of it (like a door panel). It appears to be stiffer, but its really just heavier. If you dont believe me, answer one simple question... how will adding a flexible material like butyl rubber make a steel panel "stiffer"?

The best way to stiffen a panel is by using a material that itself is rigid. For the roof example, in say an SUV, a better method of making the roof more stiff would be to apply fiberglass to it, since it will cure into a stiff/rigid state. This will raise its resonant frequency, while covering the roof with mat to mass-load it will lower the resonant freq. To the misinformed observer, both make the same thing happen, the panel moves less at the frequency it use to. To an informed observer, you have either raised the resonant freq ( by stiffening it0 or you have lowered it (by mass loading it).

What are you calling 'weakness' in this statement? The shape of the steel panel, thin and long? If so, why do you then turn around and suggest stone wont resonate, without mentioning the shape/size of the stone in question? You seem very confused about this topic, maybe you should read more and talk less, especially of your talking will be to tell other people that they dont know what they are talking about. Frankly, you dont know what you are talking about. No offense meant, but its true.

Exactly. The problem for SPL goes beyond resonance though. If you care how what's being reproduced sounds, you don't want any audible resonance since that is reinforcing the music with the mishmash of resonant frequencies and harmonics coming from all of the bodies whose resonance is audible.

Adding mass and stiffening panels is important for SPL because it limits the expansion of the interior volume under pressure. It's like forcing air into a balloon and a bottle. The balloon expands to accommodate the increasing pressure until it can expand no more and bursts. The bottle holds, allowing pressure to increase until the bottle bursts. Even if the interior pressure is the same when both the balloon and bottle burst, maximum pressure will have been reached in the bottle first.

Adding mass reinforcement increases the pressure required to distort the sheet metal. Air leaks are the next issue and distorted panels can make that worse too.

Given the choice between raising and lowering a panel's resonant frequency, I'd probably raise it for SPL. An object's resonant frequency is basically a free pass band for sound. I'd want the highest energy frequencies to be reflected.

 

[audioholic 5,000+ posts]

We also need to remember something about this whole SPL competition discussion... the final reading on the meter occurs from a fairly complex set of circumstances. Leaks, frequency os the mid, position of the mic, etc... all play roles in the final SPL measurement. Sometimes a flapping panel might increase your SPL score for several reasons.

Move the microphone from the kick panel area to the headrest, dash, windshield, rear parcel shelf, rear floor, etc... and you will experience vast differences in your SPL score. Alter thew mic's measuring frequency by a half octave and you will experience vast differences in your SPL scores. Crack a window, have your friends lean against the doors, turn the AC on to cool the vehicle's interior space... all these things can and (usually) will alter an SPL score. This topic is not so simple as many people here make it out to be, simply 'losing' energy to panel flex. Hell, a roof flexing to the point it vibrates against its 'stiffening ribs' might make an audible noise in the correct freq band to actually raise your SPL score, even though technically you are losing acoustical energy to the panel's motion.

Its this complexity of the situation that makes it true that the only real way to maximize your SPL score is by thorough testing. Its impossible to quantify every factor that will affect the final SPL reading. If it was as simple as making your vehicle as rigid as possible, to conserve acoustical energy, it would be quite easy to build an SPL rig that does very close to maximum potential right out of the gate, without much/any testing prior. So lets try to keep that in mind while we are discussing this topic, and not over-generalize our positions/opinions based on what common sense would tell us works or fails.

 

[audioholic 5,000+ posts]

Given the choice between raising and lowering a panel's resonant frequency, I'd probably raise it for SPL. An object's resonant frequency is basically a free pass band for sound. I'd want the highest energy frequencies to be reflected.

Given that chose, Id chose whichever method alters the resonant frequency outside of the freq band that is being recorded/measured in the easiest and most practical manner. Its similar to building an enclosure, you simply want to make the enclosure resonate at a frequency that is outside the passband that it will be expected to produce. Neither raising nor lowering the frequency outside this range is 'best', they both accomplish the same final result (less energy lost at the specified freq band), so the 'best' choice is whichever method is the easiest, most economical, and has the least impact on the functionality of the vehicle. In other words, building a (relatively) light enclosure that resonates above the passband it will reproduce is no better than building an enclosure that will resonate below it. But it makes a lot more sense to build a (relatively) lightweight enclosure whose rigidity pushes the resonating freq above the useable passband (by using methods such as extensive internal bracing), instead of building a concrete enclosure that will resonate below the useable passband, but weights 2,000 lbs and ruins your vehicle's ability to function as a mobile mechanism.

Maybe Im splitting hairs here, because I know you already know this information Don, but I felt it was worth discussing for any reader who may misunderstand your previous statement.

 

[Rudy 10+ year member]

Given that chose, Id chose whichever method alters the resonant frequency outside of the freq band that is being recorded/measured in the easiest and most practical manner. Its similar to building an enclosure, you simply want to make the enclosure resonate at a frequency that is outside the passband that it will be expected to produce. Neither raising nor lowering the frequency outside this range is 'best', they both accomplish the same final result (less energy lost at the specified freq band), so the 'best' choice is whichever method is the easiest, most economical, and has the least impact on the functionality of the vehicle. In other words, building a (relatively) light enclosure that resonates above the passband it will reproduce is no better than building an enclosure that will resonate below it. But it makes a lot more sense to build a (relatively) lightweight enclosure whose rigidity pushes the resonating freq above the useable passband (by using methods such as extensive internal bracing), instead of building a concrete enclosure that will resonate below the useable passband, but weights 2,000 lbs and ruins your vehicle's ability to function as a mobile mechanism.
Maybe Im splitting hairs here, because I know you already know this information Don, but I felt it was worth discussing for any reader who may misunderstand your previous statement.

I'm for any discussions that end up with us better understanding the topic. 100% includes me. It's definitely not as simple as the bottle balloon illustration but it's a very common oversight for something that fundamental. I've been to competitions where gas tank filler covers where flapping under pressure.

There's a really important distinction that needs to be made. We're dealing with both motion inside the panel (resonance) and gross motion of the panel relative to a fixed point in space. A roof is a perfect illustration. A roof that's flexing in and out in response to pressure changes inside the vehicle isn't doing so because of panel resonance gone mad, it's acting as a piston - a passive radiator that's perfectly out of phase with the signal it's responding to. There's no question about what's happening to energy in that scenario.

 

[fish1234 10+ year member]

I'm for any discussions that end up with us better understanding the topic. 100% includes me. It's definitely not as simple as the bottle balloon illustration but it's a very common oversight for something that fundamental. I've been to competitions where gas tank filler covers where flapping under pressure.
There's a really important distinction that needs to be made. We're dealing with both motion inside the panel (resonance) and gross motion of the panel relative to a fixed point in space. A roof is a perfect illustration. A roof that's flexing in and out in response to pressure changes inside the vehicle isn't doing so because of panel resonance gone mad, it's acting as a piston - a passive radiator that's perfectly out of phase with the signal it's responding to. There's no question about what's happening to energy in that scenario.

So.... would the CCF on the top of the roof braces be the best applied deadener for the roof to keep it from rattling? To me that sounds the easiest and cheapest way about it.

 

[audioholic 5,000+ posts]

A roof that's flexing in and out in response to pressure changes inside the vehicle isn't doing so because of panel resonance gone mad, it's acting as a piston - a passive radiator that's perfectly out of phase with the signal it's responding to. There's no question about what's happening to energy in that scenario.

Absolutely, no question. But what is in question is whether or not that loss of acoustical energy will affect your SPL score. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif This is exactly why these threads get so heated, science is still at work (obviously), but the over all situation is more complex than the bottle/balloon parallel. Its true that science is and always will be the key factor in building a well performing SPL setup, but the complexity of the over all scenario makes it impossible to predict all the possible factors, so testing becomes a necessity. Some people take that necessity to mean we can ignore some basic scientific principles (not saying anyone in this thread is doing this, just saying why the science versus seemingly random testing argument always occurs)

 

[Rudy 10+ year member]

... but the complexity of the over all scenario makes it impossible to predict all the possible factors, so testing becomes a necessity ...

Just to pick the last nit, with sufficient inputs and processing power, it would be possible to perfectly predict outcomes. Not saying this is practical or even possible for all but a few very fortunate people, just that every possible combinations is a knowable thing. Trial and error is a substitute for millions of dollars.

 

[Rudy 10+ year member]

So.... would the CCF on the top of the roof braces be the best applied deadener for the roof to keep it from rattling? To me that sounds the easiest and cheapest way about it.

It depends what you're trying to accomplish. CCF between the objects that are the making contact would be the most direct way to eliminate the rattles. It wouldn't do much to control resonance - if faithful reproduction is important or to limit gross movement.

Newer Ford and Mercury large SUV's have a hybrid product in that space. It's a stuff butyl compound with particles that out-gas when heated. It's installed prior to the paint bake where the heat causes the stuff to expand. Stops rattles and does some vibration damping. Reinforces the roof by adding contact between the roof and cross beams.