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Adding fiberglass to doors for sound quality/noise reduction
Anyone add fiberglass to their door panels yet? I have two goals: 1) improve sound quality of Bose 10" driver 2) reduce road noise.
I did this in my Accord and made quite a difference both with sound quality as the door is a metal box and with reducing noise that comes through the door skin. Install is pretty easy: purchase fiberglass ceiling tiles, cut to size, wrap in lightweight plastic to keep moisture out, tape between impact beams using aluminum tape. When thinking about a quality speaker enclosure, there's typically material inside to absorb standing sound wave which enhances overall sound reproduction. And, the fiberglass will absorb noise coming through the door skin which should yield a significant reduction in road noise, rain, etc. making the cabin quieter and enhancing sound quality. There's a great tutorial and explanation put together by an audio engineer on the caraudio.com forums.
Dynamat and other similar products deaden panels and reduce noise from vibrations. Peel and stick products won't change the sound quality of the chamber (door cavity) like wool, fiberglass, poly fill, etc. although they can help with road noise. The idea is to make the door cavity more like a speaker enclosure.
did you put acoustic fiberglass in a door? Acoustic fiberglass is fantastic...for an enclosure that is never exposed to the weather. If you must have something similar you should use CLOSED cell foam, since it will not absorb water. Acoustic fiberglass is like a sponge...a sponge that molds and blows off particulates that can lead to mesothelioma when inhaled, even over a short period. With as much vibration and impact (like closing) that a door sees I would never recommend this. Now, I love acoustic glass in sealed enclosures, in any application. It's amazing stuff. But if there's a chance it will ever blow particulates it's a certain no go.
For a door I'd use a damping (not dampening..dampening is to make wet. Damping is to reduce vibration) material like Dymamat, Hushmat, Second Skin...anything like that. They're all essentially the same for daily applications. Just pick the one you like best, and use it. Put it on the inner and outer door skin, and then put closed cell foam on the inside of the door panel. You can also put foam rings around each of the speakers to better isolate the front wave from the rear wave. Additionally, you can add some clay (like modeling clay) between the speaker basket and the metal to decouple the speaker from the door. Seal the inner skin openings with fiberglass or metal panels, and damp them, too. The will create a fairly reliable enclosure that will drastically improve sound.
Yes - I put fiberglass panels in the door, however they are sealed in plastic to keep moisture out and the person that suggested this method has used it for many years without moisture damage to the fiberglass. I understand the implications of using fiberglass but as the material isn't directly exposed I'm not concerned with breathing it.
I also used modeling clay before and I noticed it becomes quite runny at temperatures seen within the door - not sure I'll use it this time.
the point of acoustic fiberglass is for sound to travel through it before it reflects from the sides of the enclosure to reduce standing waves, which cause ringing across the cone and non-linearity in excursion. This makes both bad sound, and leads to the voice coil rubbing against the gap. Wrapping it in plastic defeats the purpose entirely.
the point of acoustic fiberglass is for sound to travel through it before it reflects from the sides of the enclosure to reduce standing waves, which cause ringing across the cone and non-linearity in excursion. This makes both bad sound, and leads to the voice coil rubbing against the gap. Wrapping it in plastic defeats the purpose entirely.
I agree, however this concept was discussed in length on the thread I referenced in my first post. The explanation provided by the engineer who created the thread is that the impact is based on frequency, and as the frequencies I'm working with are lower the plastic has no impact. However, if the targeted frequencies were higher, say in vocals, then the plastic would definitely have an impact. I would invite you to visit the thread to review the conversation as I'm not an acoustical engineer.
I actually drive mostly in town where exterior noise is minimized. However, as quite a bit of noise comes through the doors the fiberglass made a very noticeable difference in the Accord. The sounds of cars/motorcycles/buses driving by were dramatically reduced and even driving in rain was quieter. Plus, the fiberglass does improve the sound of the speakers.
I agree, however this concept was discussed in length on the thread I referenced in my first post. The explanation provided by the engineer who created the thread is that the impact is based on frequency, and as the frequencies I'm working with are lower the plastic has no impact. However, if the targeted frequencies were higher, say in vocals, then the plastic would definitely have an impact. I would invite you to visit the thread to review the conversation as I'm not an acoustical engineer.
-Eric
I am an acoustic and electrical engineer. The plastic has an impact regardless of frequency. There are other products that are safer, more effective, less expensive, and more environmentally appropriate; like closed cell foam over butyl sound damping. The butyl will lower the resonant frequency of the metal to about 4Hz, and the foam will do everything the glass does, and then some. In modern engineering we have moved past things like fiberglass matte and sheep wool because synthetics are more cost effective, and acoustically effective.
You going to do the roof, too? Then there's the road noise transmitted to all the body work, including the firewall.
When I do a full build, then yes, I will do every interior metal surface. This includes removing the entirety of the interior, including the dash and heater core.
05-06-2018, 01:15 PM
