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. :thumbup:
Very professional looking install! :thumbup: Just wished they made a stealthbox for the X5 :( I ended up with the JL Audio ProWedge enclosed subwoofer instead...which takes up a bit of trunk space (now I just need a way of securing down the sub and still make it easily removable when I need the extra trunk space). But...man, the sub does make a dramatic difference even to a non-DSP system as you've indicated! Now, I don't have to pounce on my door speakers for bass. I love JL subs...worth every extra pennies for them, IMHO!
Great job with the installation, by the way :thumbup:
Technic, would you mind posting your blueprint for your amp bracket? I would like to do the same thing you've done and I have some buddies who work with metal.
Unfortunately, I used a CAD program in the metal shop itself that I do not have access to it other than in their computer.
Now what I can tell you is that I started with a 1:1 sketch of the bottom of the 250/1, got all the attachment holes measurements and from there I created two identical frames bolted together by four 2" standoffs between them. The stand offs are bolted to each of the four attachment holes of the amp, so the order is Amp/frame/standoffs/frame/car.
Sorry that I do not have photos of the frame. I can try to get some sketch that I did in MS Word this week and I will post it.
The amp and the Stealthboxes were bought in a local audio store. There is an online store called Woofers etc that you can get the 250/1 for $299.00. I am not sure if they offer the Stealthboxes, though. Check Ebay for 250/1 auctions too... :thumbup:
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