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E36 /7 Z3 (1996-2002)
E36/7 Z3 roadster and coupe talk with our gurus here.

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  #1  
Old 06-11-2013, 04:54 PM
AB1945 AB1945 is offline
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Location: The Villages FL
 
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Mein Auto: '01 Z3 & '02 325i Wagon
Hole in subwoofer box

I know this subject has been beaten to death but the PO of my car had the subwoofer replaced in a sound shop. They installed a JL subwoofer which is decent quality but in order to make it fit in the box they cut a hole in the back of the box which they then covered with Dynamat. The speaker does not sound great - kinda vibrating sound - but it looks to be in good condition. I don't know if the sound is bad because of the hole in the box or the speaker going bad.

I'm quite happy to buy a Kicker subwoofer but don't want to wind up with the same problem because the subwoofer box is no good.

Does the subwoofer box have to be airtight?

Is the subwoofer box supposed to be filled with some kind of sound deadening material?

Thanks in advance for any and all suggestions.
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  #2  
Old 06-11-2013, 08:29 PM
Blacklane Blacklane is offline
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Yes. The box needs to be airtight for optimal performance. Plus it needs to be filled about 2/3 full with polyfill or fiberglass.

I know the performance of my Kicker was noticeably worse with even a small pinhole in my enclosure. In your case, I think you're stuck with what you have.
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  #3  
Old 06-12-2013, 12:20 PM
AB1945 AB1945 is offline
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OK - thanks for the reply. Here's my plan:

1. Pull out the subwoofer box and remove the speaker.
2. Seal the hole with plastic about the same thickness as the box
3. Install the Kicker subwoofer.

I'll get back when it is all done and let you know how it worked out.
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  #4  
Old 06-12-2013, 12:31 PM
AustinZ3 AustinZ3 is offline
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The JL subwoofer is probably better than the kicker, so if you can find a way to make it work i would do so.
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  #5  
Old 06-12-2013, 12:41 PM
AB1945 AB1945 is offline
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I like your advice about the JL subwoofer as I would not have to buy another subwoofer. The problem is if I fix the hole in the box then the JL subwoofer won't fit!

I know the subwoofer box has to be airtight but does it have to be rigid? It couldn't have been very rigid before the hole was cut in it as the plastic is not very thick.

Right now I do not have any Polyfill in it - does that make a big difference?
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  #6  
Old 06-12-2013, 03:26 PM
dkindig dkindig is offline
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Quote:
Originally Posted by AB1945 View Post
I like your advice about the JL subwoofer as I would not have to buy another subwoofer. The problem is if I fix the hole in the box then the JL subwoofer won't fit!

I know the subwoofer box has to be airtight but does it have to be rigid? It couldn't have been very rigid before the hole was cut in it as the plastic is not very thick.

Right now I do not have any Polyfill in it - does that make a big difference?
The Kicker sub is pretty much the only one that I'm aware of that will fit the stock enclosure. I got mine to sit ALMOST flush (probably 1/16" shy of the sealing surface, used 1/8" compressible foam gasket under the rim) by dremeling out the reinforcement fins on the back inside surface of the box and removing the rubber cover off of the magnet. Also, the Kicker pole piece is vented to the sides instead of the back. Look for a vent hole on the back of the JL and if it IS on the back of the driver, it will be obstructed by the enclosure.

As far as rigidity goes, in my opinion it's a lost cause with the stock box because of the thin plastic construction. The best you can hope for is airtight. If it were me I would look at layering another piece of plastic with copious sealant on the outside of the back, maybe with rivets to provide a mechanical bond. If you use RTV or something similar that cures with acetic acid (vinegar smell), give the sealant plenty of time to flash off any vapors before you mount the driver. The vapors that outgas from the sealant can attack the rubber parts of the driver and corrode electrical connections.

Polyfill will make a difference. The enclosure comes from the factory with something resembling carpet pad in the box which is really more for damping. It won't do any good at subwoofer frequencies to improve the performance of the system. Loose polyfill (as Blacklane said, about 2/3 full, fluffed up) helps acoustically by slowing down the sound inside the box through both time delay and heat retention (sound is slower through warmer air) and "fools" the sub into performing like it's in a larger enclosure. Typically, comparing a stuffed enclosure to an empty one, the stuffed enclosure will perform acoustically as if it is 20-30% larger than the unstuffed one.

Last edited by dkindig; 06-12-2013 at 03:31 PM.
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  #7  
Old 06-12-2013, 07:53 PM
AustinZ3 AustinZ3 is offline
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And if you go the route of the kicker, as i did, follow dkindig's threads on doing it. Very detailed and made installations much simpler
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  #8  
Old 06-15-2013, 04:46 AM
AB1945 AB1945 is offline
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Well, I took it all apart and found a problem with the JL speaker - there was close to an inch where the speaker cone had come unglued from the foam surround. This was hard to see when the speaker was at rest as there was no gap. It was only when I pushed on the surface of the speaker that I could see it. So I carefully ran the blade of a small knife toward the ends of the gap and another inch or so opened up easily where it appeared to be improperly glued. Anyway, I glued all of that back together and tested it prior to installation and the buzzing sound was gone - alright! I then loosely filled the box with polyfill and installed the speaker using 1/4 inch thick weather strip which reduced the amount of speaker protruding from the hole in the back of the box. Then I covered the hole with Dynamat. The result is that the subwoofer is back in the car and sounds pretty good.

Thanks for all the suggestions - especially about keeping the JL subwoofer and reinstallation instructions.
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