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Old 10-09-2004, 11:39 AM
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Technic Technic is offline
OEM Audio PnP Integration
Location: Florida
Join Date: Jun 2002
Posts: 7,683
Mein Auto: 2017 M3
JL Audio Stealthbox, 250/1 and the M3


This is, in my opinion, the best upgrade for the BMW audio system for the money, regardless of being HK or not.

This is as best a 90% DIY, 10% will be better taken care of by an installation shop only if your car is equipped with Navigation because the Stealthboxes enclosures are made only for Non Navigation cars thus modification to the left enclosure is required. Other than this, it is a simple DIY if the JL Audio installation instructions are followed directly. One person can do it, however two people is much better.

The installation and location of the 250/1 is a personal decision, in my case I designed a custon bracket in aluminum to fit the Amp in the right cavity just above the battery location for a OEM look and trunk space. The bracket was made to specifications in a metal shop to be bolted on to the existing right fender beam behind the trunk liner by just two bolts (one hole have to be drilled).


1) I used a Peripheral SuperVendetta2 to convert the high level speaker signal to low level, and from wires to RCA. Gains are set to max; absolutely no noise is present.

The main benefit of using this converter is that it allowed me to connect the Harman Kardon subwoofers in parallel with the input of the converter (the converter inputs are op amps so its input impedance is very high). That way I retain the mid bass "fill" and at the same time increase the subwoofer presence in the rear.

2) The 250/1 Signal Sense is not recommended for this configuration, both by JL Audio and personally; use a dedicated remote lead (white wire from the OEM amp). According to JL Audio user manual, the use of signal sense with low level inputs is not recommended because it make the amp unstable. I corroborated this by the amp 25 second shut down phase picking too many signaling "pops and cracks" up from the OEM system.

3) Play around with the settings, on both the 250/1 and from the OEM HU bass level for your optimum sound preference. My configuration is:

a: Input: Low
b: Signal Sense: Off
c: Amp Low Pass Filter: 55 Hz at 12dB
d: Bass Control: 30 Hz (on) at 10 dB
e: Bass contol at HU : 1 "click" up from center
f: SuperVendetta2 input gain: Max

This configuration produces a nice, solid sub bass that is present at all volume levels with no distortion. No rattles, no strange noises, just a way much better sound than the HK system could provide.
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Last edited by Technic; 10-09-2004 at 12:20 PM.
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