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aperiodic concept for midrange in doors


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krazylegs 
Member - Posts: 8
Member spacespace
Joined: March 20, 2007
Location: Texas, United States
Posted: February 11, 2011 at 12:36 AM / IP Logged  
that acoustiblok stuff is only good with a air baffle its no better than any other sound deadening material for cars in fact its possibly less effective due to no adhesive to seal it and its rigidity it is better than nothing i guess but as for your enclosure very impressed ive never dealt with ap systems before i have an suv where space is abundant though i have acquired a small car that i now have fantastic ideas for
chevy korsica build progress
00%]--------exterior
00%]--------interior
00%]--------engine
15%-]-------sound system
00%]--------computer
just your average redneck kustomizer
teenkertoy 
Copper - Posts: 112
Copper spacespace
Joined: April 01, 2008
Location: California, United States
Posted: February 11, 2011 at 1:03 AM / IP Logged  
krazylegs wrote:
that acoustiblok stuff is only good with a air baffle
Please explain more, I don't know what you're talking about yet.
krazylegs wrote:
as for your enclosure very impressed ive never dealt with ap systems before i have an suv where space is abundant though i have acquired a small car that i now have fantastic ideas for
Thanks, glad you could gain something from reading.
-J
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.
krazylegs 
Member - Posts: 8
Member spacespace
Joined: March 20, 2007
Location: Texas, United States
Posted: February 13, 2011 at 5:16 PM / IP Logged  
you need an air space between two layers of material to allow for the sound to dissipate the transfer of sound waves between mediums is where energy is lost sound waves travel easiest through solids next liquids and last gas or air dynamat is sponge like it has small microscopic air bubbles sandwiched between hard rubber so its constantly changing between mediums in a small distance killing the sound
chevy korsica build progress
00%]--------exterior
00%]--------interior
00%]--------engine
15%-]-------sound system
00%]--------computer
just your average redneck kustomizer
teenkertoy 
Copper - Posts: 112
Copper spacespace
Joined: April 01, 2008
Location: California, United States
Posted: February 13, 2011 at 9:07 PM / IP Logged  
I don't claim to be an authority on the subject, but I think I have a good grasp of what's happening. This is as much in reply to you as it is for me to learn. I see three things.
Damping a surface (applying dynamat to sheet metal) reduces that surface's tendency resonate. This is accomplished by adding mass to flat sections of sheet metal where it is least stiff and most likely to resonate. Mechanical vibrations of the car (including the vibrations caused by speakers mounted in the doors) are less likely to be turned into acoustical energy, reducing one source of unwanted noise. One analogy would be a heatsink; the heatsink dissipates thermal energy (small-scale vibrations) as heat, instead of allowing the thermal energy to build up and be released as radiation and light (like the sun).
Sound barriers like mass loaded vinyl, lead sheeting, acoustiblok and others, reduce sound from passing from one pocket of air to another by reflecting it. They are used to keep road noise, traffic, engine, exhaust, and other noises outside of the cabin from crossing into the cabin. In addition, they are used in doors and trunks to keep the rear wave of a speaker from entering the cabin or interfering with the front wave of the speaker. Essentially the material becomes part of the infinite baffle in some installations. One analogy would be a mirror for light waves; the mirror does not absorb or drastically alter the light, it just prevents it from passing through by reflecting it.
Absorbent material is the type I think you are describing. Sound waves in the air are converted into mechanical energy by the material and are dissipated as small amounts of heat. Unlike a sound barrier, absorbents reduce the acoustic energy of a system instead of simply deflecting it. This is why anechoic chambers must use absorbent materials, otherwise acoustic energy would stay in the room defeating the entire purpose. For car audio, absorbent material is easy to use for higher frequencies (dashboard covers), but for lower frequencies it becomes unpractical, and thus barriers are preferred.
The separate air chambers I think you refer to would be similar to what is found in double-pane windows, or to the extreme found in recording studios.
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.
krazylegs 
Member - Posts: 8
Member spacespace
Joined: March 20, 2007
Location: Texas, United States
Posted: March 28, 2011 at 5:43 PM / IP Logged  
i agree this discussion should be explored to give people the truth about noise control and the application of it
as for the discussion dynamat is a damping material true reducing resonance on the panels but are working in conjunction with its absorbency you need both on almost all applications as for
as for sound barriers the metal door panels covered in dynamat would do a much better job because the practical application of akoustiblok mounting it and all in such a small space but even sound barriers cant be totally rigid or they would just relay the sound through it the best application would be all three noise reducing mediums but in wich order is another discussion too
chevy korsica build progress
00%]--------exterior
00%]--------interior
00%]--------engine
15%-]-------sound system
00%]--------computer
just your average redneck kustomizer
teenkertoy 
Copper - Posts: 112
Copper spacespace
Joined: April 01, 2008
Location: California, United States
Posted: March 28, 2011 at 5:58 PM / IP Logged  
I don't want to kill the discussion by complaining about your grammar, but I can only guess what you're trying to say. It would make much more sense if you use things like periods, commas and the like.
Dynamat and other damping materials have (nearly) no absorbent properties, I'm not sure what you mean about that. The metal doors covered in a damping material is perhaps a decent sound barrier, sure. However mild damping of the door panels (25%-50% area) with a mass loaded, sealed, mechanically isolated, floating sound barrier like MLV is better from experience. I agree though it can be very tight to fit all of this material behind a door panel, especially some that have limited to no extra space back there.
I think we're both trying to say the same thing here, that all three materials used intelligently is the best method.
-J
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.
teenkertoy 
Copper - Posts: 112
Copper spacespace
Joined: April 01, 2008
Location: California, United States
Posted: March 28, 2011 at 6:01 PM / IP Logged  
For anyone else still curious about the enclosures, they certainly did what they claimed. The impedance peak is minimized, though the bass is severely reduced. I believe with some very fine tuning of the membrane material I could get it "just right", though I've decided to leave the woofers in the doors like stock, infinite baffle style.
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.
krazylegs 
Member - Posts: 8
Member spacespace
Joined: March 20, 2007
Location: Texas, United States
Posted: April 03, 2011 at 11:44 PM / IP Logged  
i think we are trying to say the same thing i was under the impression you were only going to use the mlv as dampening
chevy korsica build progress
00%]--------exterior
00%]--------interior
00%]--------engine
15%-]-------sound system
00%]--------computer
just your average redneck kustomizer
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