Re: Aftermarket amps w/DSP HELP(JimL or Bob Hazelw (archive)

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Oh No, Not the DSP system again! ;-)
But seriously. This is a "problem" system, as you are finding out. My information is second-hand, from a handful of Bimwads who have communicated info back to me as we have worked together to solve problems. I have no direct hands-on experience. Therefore, if someone who does, like JimL., contradicts what I have to say take his word for it, not mine.
First. Overall architecture:
1. Two-channels of analog audio pass from front to rear from the radio.
2. The CD signal is a digital bitstream which goes directly to the DSP electronics. All the control and equaliztion is done within the DSP electronics in the rear, so the radio and front of car controls don't do anything to the analog signal. There is also no way to get the CD signal into a "new" amp without first going into the DSP electronics.
3. Even once you get inside the DSP box, there is still no place to get a full-range signal. The crossover is done within the DSP processor IC's, and short of changing the software of these processors, you're stuck with the BMW curves and frequency bands. Summing the outputs of these bands is technically possible, but they may be at different levels to compensate for the different sensitivities of the various transducers, and there is no guarantee that the outputs will sum to flat response.
So, what to do? I can't say with authority, but here's how I would begin to tackle the situation if I were going through the process:
1. Use 11 or 12-channels of amplification (Subwoofer can be mono) to match the BMW frequency bands. Since the Diamond Audio speakers are wider range transducers than the BMW parts, you should be able to use the BMW crossover curves without exceeding the Diamonds capabilities. The Diamond crossovers will just screw things up more in this environment. You don't need a lot of power per channel, since with the limited frequency bands, there will not be a lot of energy in any individual band. 30-50 WPC should be sufficient, with about 200-300 for the sub.
2. In the front, I'd keep the BMW upper midranges, and replace the BMW "woofers" and tweeters with the new components. Replacing the BMW upper mids with the DA tweeters may overdrive the DA tweeters by feeding them frequencies which are too low. There is no danger of this at the higher frequencies delivered by the BMW tweeter crossover. Also, the DA tweeter is not particularly good at low frequencies, so at the very least it will sound a bit edgy if its pushed too low. Unfortunately, you'll need to use the speaker-level connection for all these channels. While this is not ideal, with the proper conversion this will still sound better than the factory amp.
3. Rear and subs are more straight-forward in their replacements, and should present no real obstacles if you follow the same strategy. In the rear, the BMW crossover should be high enough to not present tweeter issues.
4. Before the subwoofer wiring is made permanent, try the subs wired in and out of phase. The BMW uses a bandpass enclosure. There is often so much phase shift in this type of enclosure that the reverse polarity connection yields the smoothest response. If your final system does not have the same phase shift, the connection which looks "right" may in fact result in an acoustic hole between the subwoofer and woofer crossover. Now that I am thinking about it, doing this with all the drivers may be prudent since we don't really know what BMW is doing regarding polarity in the DSP.
5. Phone or write BMW and tell them that while you can understand that a state of the art system may not be commercially feasable for a car manufacturer to offer, at least they should include a set of full-range outputs for add-on capability. It will not add more than a lousy buck to their cost and would prevent a lot of headaches.
BTW, as a somewhat "interesting" anecdote. I was Autocrossing this weekend, getting frustrated by not being able to break below 85 seconds. On my fourth run I left the stereo cranked and made up three seconds! The only thing I can figure is that I was more relaxed, and therefore smoother. And the purists say that an audio system doesn't make your car faster! ;-)

Good luck!

Best regards,
Bob

: My 1999 540i is in the stereo shop getting a sound system overhaul. They've built an awesome fiberglass subwoofer enclosure that replaces the batter compartment cover and it looks GREAT. I am using a single JL Audio 10W6 powered by a PPI PC1800 amp. I am also replacing the front and rear speakers with Diamond Audio, two-way separates up front and two-way coaxials in the rear package shelf all powered by a PPI PC4800 amp.

: However the problem that they encountered is hooking up two PPI amplifiers to the "premium" DSP/amp.

: I have read numerous postings in this board pertaining to this DSP/amp, but I have not found a difinitive solution. The shop tells me that I MUST keep the DSP/amp and use the speaker level outputs from that as the inputs for the new amps. Is this true? They also said that all of the radio controls (tuner etc.) are contained in the DSP/amp and the head unit is really just acting as a remote control. Is this true?
: Is there anyway to bypass the DSP/amp all together and get a clean signal to feed the PPI amps?

: By using the existing DSP/amp, each set of speaker level outs are already crossed over to the BMW crossover specs and therefore a full frequency signal can not be obtained to feed the amp for the mids and highs. They suggested that I add a third amp into the system, so there would be 1 amp for the sub, 1 amp for the mids (front and rear) and 1 amp for the highs (front and rear). However the problem that I see with this is since the premium system in the 99 540 has 3 speakers per side up front, the DSP/amp is crossing over highs, mids and mid bass for the front, but my replacement speakers are only two way, so do I use the mid or the mid-bass from the DSP/amp as the feed for the midrange? Either way I do it there will be a hole in the soundfield.

: The other thing I have read about here and have considered, is if the DSP/amp is indeed Alpine and controlled by the AiNET, could the stock DSP/amp be replaced with an Alpine product such as the PRA-H400 frequency processor? Does anyone know if there is a product that is compatible the signal from the head unit and would work with the head units controls for tonal adjustments as well as the DSP settings?

: As you can see, this is a very frustrating process. If anyone has figured out how to correctly install aftermarket amps with the DSP system, I would love to get your feedback.

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