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The factory 10-speaker non-Harmon Kardon audio system in the BMW E36 leaves much to be desired.
The head unit (which is usually the first thing replaced) has a horrible frequency response and the speakers, especially the rears, do not provide enough bass for even the most conservative listeners.
The rear speakers are plastic enclosures that contain a 1" tweeter and a 4" woofer, which is too small for any type of low frequency reproduction.
To achieve better bass output, a pair of adapter plates were fabricated from 3/4" MDF to allow a pair of 6"x9" speakers to be mounted in the rear deck and used as small subwoofers (using passive crossovers) to reproduce the lower frequencies, while still utilizing the factory amplifier and front speakers.
While not as earth-shaking as a dedicated subwoofer/amp setup, this combination provides a considerable amount of bass compared to the factory setup, but does not take up any trunk space nor require the purchase of any expensive aftermarket audio equipment.
Click here to view the Installation FAQ!
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Speakers Compared
A pair of used 3-way 6"x9" speakers were purchased for only $10 that had damaged midrange drivers.
The midrange/tweeter pedestals were disconnected and removed from each 6"x9" speaker so that only the woofers will be used as subwoofers.
The surface area of the 6"x9" woofers will provide a lot more bass output than the 4" woofers in the factory rear speakers.
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Adapter Plates
Adapter plates were fabricated using 3/4" MDF to allow the 6"x9" woofers to be mounted in the OEM rear locations.
The plates are a two piece design that are positioned together in a specific configuration. |
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Plates Assembled
The two pieces of each plate are positioned and permanently mounted together using wood glue and screws.
You can see from this photo how the sound from the 6"x9" woofers will pass through the plates into the passenger compartment.
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Plates Painted
The plates are painted black to make them less conspicuous when viewed from the trunk and 3/8" foam weather stripping is placed around the top lip to provide an air-tight seal against the car's rear deck.
The plates are mounted using the existing mounting holes for the factory speakers, so no drilling or cutting is necessary to install the plates. |
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Speakers Mounted
The 6"x9" woofers are mounted to the plates, and a 5.1mHy low pass coil (125Hz at 4ohms) is mounted to the side of each plate and wired to the woofer.
The coils will allow only the lower bass frequencies to be reproduced by the 6"x9" woofers.
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Plates Installed
The plates/woofers are installed into the car and wired up to the factory amplifier using the speakers leads that were for the factory 4" woofers.
The factory amplifier has enough power to drive the 6"x9" woofers and produce plenty of loud, clean bass (without distortion) that compliments the front speakers nicely. |
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Front Speakers
Each of the front 5 1/4" kick panel speakers are re-wired with a 265mfd high pass capacitor (150Hz at 4ohms), so that they aren't trying to reproduce the same lower frequencies that the 6"x9" woofers are now providing.
The factory front speakers combined with the 6"x9" woofers provide a balanced overall sound with a solid front stage, a hint of rear fill, and plenty of bass for a factory non-HK system.
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Click here to view the Installation FAQ!
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