Frank-
I understand what you're saying, and that does solve things, sort of...
There is a difference between a regular two channel stereo setup (left and right channels, or L & R) and the surround setup in the C70 as I understand it (left, right, center, and surround, or L, R, C, & S). The center channel can be ignored as it doesn't receive signal below 100hz and is driven off of a 25w amp internal to the head unit. However, the surround speakers in the rear of the car may receive different information, essentially acting as a left rear and right rear... this leaves us with LF, RF, LR, and RR as our four distinct bass-producing surround channels. This is the only part I wasn't able to verify from dolby and Volvo... those rear speakers MAY be receiving the same information. Still, with a combination of balance and fader controls, it is conceivable that they could be receiving different levels.

Those four speakers in the C70 coupe that reproduce low frequency sound in the 120hz and below range are the two 8" woofers in the front doors, and the two 8" woofers on the rear hat shelf. IF your intent is to have each speaker only receiving the frequencies it is intended to reproduce, then you end up with crossovers and bass blockers and such directing your high freqs to tweeters, your mid range stuff to your mids, etc etc etc. To separate the low frequency into two ranges, woofer (8") and sub-woofer (12-15"), you would probably do something like send the same signal to your woofers and subwoofers, but use bass blockers or an amps internal crossover to keep the right frequencies going to the right speakers. That way, there isn't some sound that doesn't get reproduced at all. Only issue you might have with that is if you ran your rear speakers' signal to your subwoofer, then used your fader to play only out of the front speakers, then you wouldn't hear anything at all out of your subwoofer, and your fronts would be reproducing the whole spectrum. However, usually your fader will be set normal, and you'd be ok. Option two for a regular ol' two channel (L & R) stereo would be something like a five channel amp... I had this setup in my '85 740, my first volvo. The head unit had left and right, front and rear line level outputs. These went into the five channel amp where the low freqs were shaved off and sent to a fifth channel for the subwoofer. Then the four other channels were for the left and right, front and rear. With that setup, no matter what you did with your fader, ANY low freq signals that were going to ANY of your speakers would end up making it to the subwoofer.
That would be a more ideal solution for the surround sound setup, because unlike stereo, you may be getting different musical info sent to your front speakers than what is sent to your rear speakers. SO, in order to accurately have your subs reproducing any and all low frequency music, you'd need to have either a five channel amp like what was described above, or you'd need a FOUR channel mono amp like the one you described (do they make those?) that would combine four distinct inputs (LF, RF, LR, RR) into one output, or you'd need two 2 channel mono amps like the one you use, and have one sub for the front (combining LF and RF) and one for the rear (combining LR and RR), OR one sub for the left (combining LF and LR) and one for the right (combining RF and RR). Any way you went, ANY low frequency bass that went to ANY of your four main speakers would get shaved off and sent to a subwoofer.


In summary- I believe that all four channels of the C70's audio system should be trimmed of their low frequency bass and have that signal sent to a subwoofer. This could be accomplished by a five channel amp designed to shave that signal off and never send it to the main speakers in the first place, OR by a set of crossovers, line level input converters, and mono amps to shave the signal off AFTER it has already left the original amp but before it reaches the speakers.

I'm pretty sure alpine made the amp for volvo, a V12 4X100 watt model. I think I'm going to look into whether or not they have a five channel version...

-Jon



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CPT Jonathan T. Belmont-- '99 C70R 48K 'Valdemar'