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Old 02-13-2005, 11:26 AM
Kewl X5's Avatar
Kewl X5 Kewl X5 is offline
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Location: X5 World
Join Date: Apr 2002
Posts: 326
Mein Auto: Only BMWs
Smile JL Audio Stealthbox Subs Installed in M3 with HK

Many props to Technic who did this months ago on his M3 down in Florida. (Check out his original post: ).

Well, I had the "SoCal" version done finally this month. With the help of Technic, he designed a special amp bracket to hold the JL Audio 250/1 amp to the right rear corner of the trunk.

Melvin Tool & Die in Fort Lauderdale, FL (e-mail Todd King @ has the original design and they can make the same bracket if you like. It specifically holds the JL Audio 250 amp.

With the help of Custom Cellular (aka CC Wireless) in Irvine (, they helped with the installation of the JL Audio Stealthbox and Amp. If you are in the Orange County area, they can do the same setup (since they already did it in my car). Ask for Bill (949 250-7878).

Bottomline, Technic was right. The M3 with the HK system should have sounded like this from the factory. There is enough sub-bass to enhance your listening pleasure.

The JL Audio subs which are 8" subs replaces the 5" mid-bass HK speakers on both rear corners on the rear deck. The mid-bass is retained by unplugging the "HK Subs" (in reality they are 6x9 speakers) from their amp and sending the signal that was originally meant for the 5" mid-bass to the 6x9 speakers. So you retain the mid-bass, have extra sub-bass ala JL Audio Subs, and the tweeters are still in their stock location in the rear side panel.

I set up the amp to filter cross-over around 60Hz but with a 24dB slope, 48Hz boost around 11-12 dB and turned on the 30Hz filter to prevent damaging the subs since they are free-air subs ported into the trunk space.

The bass is definitely there but without overpowering the stock speakers and actually, it really sounds balanced and nice. Those people looking to waking up the neighborhood need not to apply here.

You can private mail me for more info.
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