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General Car Audio
Sound deadening doors for Hybrid Audio Technologies Clarus 61-2
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<blockquote data-quote="keep_hope_alive" data-source="post: 7587091" data-attributes="member: 576029"><p>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.</p><p></p><p>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.</p><p></p><p>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.</p><p></p><p>for information on the benefits of absorption and diffusion - this is a good reference text (and a good read):</p><p></p><p><a href="http://www.rpginc.com/book/index.htm" target="_blank">RPG Diffusor Systems</a></p><p></p><p>here are some free texts (short papers)</p><p></p><p><a href="http://www.rpginc.com/news/library.htm" target="_blank">RPG Diffusor Systems</a></p><p></p><p>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.</p></blockquote><p></p>
[QUOTE="keep_hope_alive, post: 7587091, member: 576029"] 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): [URL="http://www.rpginc.com/book/index.htm"]RPG Diffusor Systems[/URL] here are some free texts (short papers) [URL="http://www.rpginc.com/news/library.htm"]RPG Diffusor Systems[/URL] 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. [/QUOTE]
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