Sound deadening doors for Hybrid Audio Technologies Clarus 61-2

[kmoto]

So I want to do this SQ door install right . I don't plan on CLD tiling the whole vehicle just the doors and a couple key areas. I have a 2001 jeep Cherokee XJ . I plan on putting these H.A.T. Clarus in the front doors. I made some oak angled speaker rings out of an old chair (1.5" to 1" angle) then wrapped them in deadener. I plan on using damplifier pro to do the outer skin and the door steel facing the inside of the vehicle. This speaker is made for infinite baffle per the Clarus manual (which is worth the read whether or not you have H.A.T. speakers). My questions regarding the IB enclosure: 1. Is it necessary to sound deaden both inside door surfaces or will just the 1 inside, 1 outside combo be sufficient? 2. Will too much deadener inside the IB hurt the speakers sound ? 3. I have seen most guys just pave right over holes in the door with deadener but is there a better way to seal these holes? I was thinking of just patching the holes with appropriate size pieces of deadener then going over the whole surface with a piece of deadener. 4. I wanted to use SS overkill pro (CCF) too but just a 1' X 3' piece behind the woofer running down the inside of the outer door skin at the bottom. Is this an effective use of this product or will I need more? There seems to be a lot of misinformation out there when it comes to sound deadener. How crazy did you get? Thanks in advance.

[hispls]

Do as much as you can afford. I have never heard of too much hurting mid response.
I cover right over holes with deadener, ideally you can cut some steel or Plexiglas to fill the big holes.

[Rudy]

The important thing to remember about the inner skin is that you are trying to isolate the front and rear waves from each other by closing off the access holes. You aren't trying to create a sealed enclosure. I prefer to hang a barrier on the inner skin to acoustically reinforce that plane. Making it easily removable is a plus either way.

You don't accomplish anything by putting a layer of closed cell foam behind the speaker.

[keep_hope_alive]

2005 Scion tC SQ Hertz Audison Pioneer Build Log

Here is a good how-to. This car is dead and sounds amazing.

I agree the manual is good, Scott is a smart guy.

IB doesn't exist in any car. But the term is general describing a speaker that has sufficient suspension to handle being played without an enclosure providing resistance. A car door is just a resonant, leaky enclosure. Deadener reduces the resonance of the door, meaning you won't hear the door ringing.

Seals are crucial so you don't have phase interference and you don't have the door panel moving. You won't hear midbass without seals due to cancellation.

1. I deaden all metal surfaces until they are sufficiently dead. I do knock tests to listen to the ringing.

2. No real such thing as too much deadener. You just reach a point of diminishing returns. Two layers is as much as I'll usually go.

3. You want to seal the door holes with a rigid panel, paving with deadener will just flex, acting like a passive radiator. Not good if it is not tuned.

4. Foam is absorptive for frequencies who's quarter wavelength is less than the thickness. You can look up absorption coefficients for similar foam products... Not much.

I have used silicone to secure 3" thick sheets of polyfil on the outer door skin, taking care to not interfere with the window. It is inert so I didnt have mold issues, even after 2 years. Fiberglass would be better, but it would need to be treated acoustical duct liner to prevent moisture issues.

[keep_hope_alive]

I have samples of thin film lined fiberglass absorbers, intended for acoustical treatments of swimming pools. I will probably introduce thin plastic encased fiberglass batt into my door cavity, with sufficient thickness to add absorption of midrange frequencies.

I will also introduce Green Glue into my speaker baffles.

[kmoto]

Thanks for the input guys. If I could just bring myself into alignment with the 25% coverage philosophy I would be sold. It makes sense but not many people are doing it with reviews . I did read a couple. I would hate to buy good speakers then fall short of their abilities. Is there a specific pattern to lay your tiles out inside a door for best results? Holes? Cover with aluminum sheet or plexiglass then deaden? Some people recommend egg crate foam behind speaker to disperse wave. Would deadener behind woofer be sufficient?

[keep_hope_alive]

Just rap your knuckles on the metal and you will hear the difference deadener makes. Add more and hear the benefit, it is obvious.

Those that say you only need 25% are not looking at the whole picture.

As you apply patches you also create nodes which can cause issues. It is not like deadener absorbs all vibrations, it adds damping to reduce ringing. Less damping takes longer to squelch resonance.

[kmoto]

film lined fiberglass absorbers? pics? I did not think about 3" thick sheets of polyfil but they use it in home cabinets.

[Rudy]

Just rap your knuckles on the metal and you will hear the difference deadener makes. Add more and hear the benefit, it is obvious.

Those that say you only need 25% are not looking at the whole picture.

As you apply patches you also create nodes which can cause issues. It is not like deadener absorbs all vibrations, it adds damping to reduce ringing. Less damping takes longer to squelch resonance.

Exactly what issues are you going to create on a car door using vibration damper? You may create theoretical issues adding mass at points with a resonant material but treat enough doors and you'll see that it isn't a practical concern at all. How are you going to squelch resonance by applying vibration up to the fixed edges of a closed termination system? The real big picture is not doing things that waste money, make future bodywork more complicated than it needs to be and doesn't improve things.

Tapping on sheet metal with your knuckles is a good way to identify resonance in untreated panels and to prove to yourself that you accomplished something with your efforts. Using it as a test as you apply vibration damper is always going to lead you to apply too much.

[Rudy]

film lined fiberglass absorbers? pics? I did not think about 3" thick sheets of polyfil but they use it in home cabinets.

Most vehicles don't have 3" clearance between the outer skin and glass. If yours do, 3" is going to attenuate 1 kHz and above. Is that really where the problem is? If you keep the front and rear waves from interacting, the only problem the rear wave can cause is after it reflects off a concave surface, interacts with the side impact intrusion prevention beams and strikes the back of the cone. The odds of any of that resulting in problems that are audible or measurable in a vehicle are remote. It makes a lot more sense to focus on those things that will make a significant difference.

[kmoto]

Is there any need to put anything else in the door besides sealing so waves don't meet and enough deadener to lower the resonance to a respectable level? CCF,eggcrate,.... it seems to me waves would bounce off of sound deadener because of its density. Wouldn't a material that increases surface area in the IB chamber help this driver reproduce its wide frequency bandwidth? (50-9,000 Hz) crossed over @ 5,200 Hz. Or are the back wave reflections inside the door nothing to worry about SQ wise?

[fish1234]

I have always wondered how the window being down affects the speaker with no deadner or any access holes sealed closed on the door itself?

[keep_hope_alive]

i'm not picking on you here, this is a good discussion for the forum.

Exactly what issues are you going to create on a car door using vibration damper? You may create theoretical issues adding mass at points with a resonant material but treat enough doors and you'll see that it isn't a practical concern at all. How are you going to squelch resonance by applying vibration up to the fixed edges of a closed termination system? The real big picture is not doing things that waste money, make future bodywork more complicated than it needs to be and doesn't improve things.

there is nothing theoretical about physics. finite element analysis is what the industry currently uses to predict resonance frequencies using modal analysis if i had a spare 40 hours, i'd do FEA on a car door. when you sparsely place deadener you create nodes which means you have several resonance frequencies, and all of them are higher in frequency. as you knock across the door skin you hear a change in frequency - all of which will be excited by the speaker. i am in favor of fewer resonance frequencies and having them be lower in frequency.

rapping your knuckles is the cheap way of replicating the ATSM test that automobile manufacturers use when they actually try to make a car quiet. They have a calibrated "hammer" which taps on the metal and records the resulting noise, decay, and resonance frequencies. i have a few acoustics publications on the subject i can look for - some were ASA presentations/research.

the real picture is to make a car sound good and not like a tin can. it's not a cheap process and it requires some sacrifice. besides, even good deadener can be removed with a heat gun - making the theoretical body work a sinch.

"too much" is relative. the strutural deadening in a $100,000 Wilson Audio Alexandria loudspeaker may be considered "excessive" by some, and "neccessary" by others.

the audible benefit of multiple layers of deadner verus sparce placement is very obvious - but some just can't justify spending $800 in deadener. certainly you reach a point of diminishing returns, but you will benefit from additional damping and mass. no debate there.

Most vehicles don't have 3" clearance between the outer skin and glass. If yours do, 3" is going to attenuate 1 kHz and above. Is that really where the problem is? If you keep the front and rear waves from interacting, the only problem the rear wave can cause is after it reflects off a concave surface, interacts with the side impact intrusion prevention beams and strikes the back of the cone. The odds of any of that resulting in problems that are audible or measurable in a vehicle are remote. It makes a lot more sense to focus on those things that will make a significant difference.

available depth depends on the vehicle. i have at least 2" on the door of my accord - the structural steel tubing (for side impact) are about an inch in diameter. some vehicles have even thicker doors, some thinner.

http://www.cmainc.net/ProductDetails...ProductID=1162
Refer to absorption coefficients of the 2"x2# 4.0 mil PVC with A mounting. That's 2" thick of 2 lb/cu.ft. fiberglass encased in 4.0mil thick PVC with type-A mounting (directly to wall). Good absorption down to 250Hz octave band. don't forget the PVC acts as a membrane absorber as well - further enhancing midrange and midbass absorption.

If you keep the front and rear waves from interacting, the only problem the rear wave can cause is after it reflects off a concave surface, interacts with the side impact intrusion prevention beams and strikes the back of the cone. The odds of any of that resulting in problems that are audible or measurable in a vehicle are remote.

this is not a remote problem. it is a problem that plagues most cars as well as many home speakers. back wave reflections cause phase interference that takes the form of coloration - it adds to the sound the speaker is trying to reproduce. the problem is clearly audible, and when properly addressed, the difference is striking. the reflecting plane of a door is concave, sure, but the focal point is so far beyond the door it will appear to be a flat surface to most of the frequencies reproduced. the side impact bars will only diffuse a small portion of the rear wave as well as a narrow band of frequencies.

I have always wondered how the window being down affects the speaker with no deadner or any access holes sealed closed on the door itself?

once you lower the window you create a gap in the weatherstripping at the top. you also create a hard reflecting plane behind the driver. the gap at top will reduce measured/heard midbass response and the reflecting plane will increase distortion (in the form of phase interference through the cone).




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Increasing the transmission loss of the speaker enclosure is a good step towards a better sounding system - regardless of the speakers chosen. I would rather spend less on speakers and more on vehicle treatments - because that methodology will result in a better sounding system.

Vehicle doors are about the worst type of speaker enclosure known to man. no one builds speaker enclosures out of thin sheet metal for very good reasons. combating the myriad of automotive issues requires a lot of effort and some financial investment. You don't have to buy name brand deadener. There are dozens of viscoelastic damping compounds on the market, and most are not automotive but for commercial equipment enclosure treatments. while the acoustic benefits of damping is not well tested in the automotive market, the commercial construction market is full of third party transmission loss tests for acoustical products. I have hundreds TL tests that I refer to when making recommendations. looking at the performance of those systems can give you a better idea of what to expect when applying similar materials in an automotive market. having dozens of acoustics texts as reference material helps as well.

we are here to enjoy music. while we will mostly disagree as to what we consider good music, we should be able to agree on the benefits of a good installation and properly treating the vehicle.

in the end, the cheapest and best performing solution is probably sealed enclosures of adequate airspace made from MDF and fiberglass. just eliminate the doors as an enclosure. then seal the openings and introduce a layer of decoupled MLV for transmission loss to control road noise. you still want to seal the doors since the best noise isolation is achieved with dead air space and decoupled surfaces.

[keep_hope_alive]

Is there any need to put anything else in the door besides sealing so waves don't meet and enough deadener to lower the resonance to a respectable level? CCF,eggcrate,.... it seems to me waves would bounce off of sound deadener because of its density. Wouldn't a material that increases surface area in the IB chamber help this driver reproduce its wide frequency bandwidth? (50-9,000 Hz) crossed over @ 5,200 Hz. Or are the back wave reflections inside the door nothing to worry about SQ wise?

you can't prevent the reflection of sound waves in a car door - deadener will try to take out some of the energy in the reflected wave, but your real goal is reducing the audible affect of the door metal resonating. to reduce the strength of the reflected wave you have a few options: 1. let it pass through the rear wall (thin membrane) diffuse it (difficult at mid and lower frequencies) or absorb it (probably the most applicable). sheet metal is just as reflective (if not more) than deadener. i've designed binary quadratic residue diffusers using the classical dr. maxfield schroeder equation for maximum length sequence. they end up being quite large in physical size. absorption goes a long way, but there aren't many good absorber products.

the term Infinite Baffle is misleading. by strict definition it is a sealed enclosure - one in which the rear wave cannot interact with the front wave. the typical application of the term usually refers to increasing the enclosure volume until the overall Q of the system (woofer + enclosure) approaches the total Q of the woofer. this can be achieved by using a large volume - such as a trunk or large door. but without full seals you don't have IB since you have pathways for the rear wave to combine with the front wave.

most people pay no attention to rear wave reflections. not because it doesn't matter but because they don't know they should or they don't want to spend the effort. those that do address rear wave reflections will usually end up with a better performing system than if they hadn't. all it takes is some testing on your own or reading acoustics/loudspeaker design textbooks. in reality, dealing with midrange and midbass reflections is extremely difficult and impractical for most car audio systems.

for information on the benefits of absorption and diffusion - this is a good reference text (and a good read):
RPG Diffusor Systems

here are some free texts (short papers)
RPG Diffusor Systems


when i add absorption to my doors, i will use PVC sheets (available in rolls at any home improvement store, typically for covering your windows in winter). i will sandwich fiberglass batt insulation inside and seal the edges using a tape made for securing the PVC, and secure (probably with silicone) it to the outer door skin along the length of the door in rows (probably three rows since i have two rows of structural tubes). it will be a very cost effective method of adding a substantial amount of absorption - probably $30 per door.

[maylar]

You don't accomplish anything by putting a layer of closed cell foam behind the speaker.

Isn't that the conventional wisdom though? Can it do more harm than good?