1985-1998 [Subscribe to Daily Digest] |
Hey 91Aerojr,
I can infer by your thinking about adding a subwoofer, that the improvement you are NOT seeing with the rear speakers, is more bass. This is nothing to be surprised at, I've tried to explain many times, that it doesn't matter how great your rear woofers are, without giving them an enclosure, they aren't going to be capable of putting out high volumes (or even moderate volumes at low frequency) of bass. If the trunk were sealed, as in a 9000CD, this would be a totally different story, though it still wouldn't be great. I also found the stock tweeter location in rear deficient, but it doesn't really hurt anything to keep all the treble in front, in fact Pioneer recently developed a circuit in their decks to do just that (think they call it FLEX). Still, you can do like I did and move the tweeters if you stay with the stock setup of separates/components. But, on to your questions! Oh and I am not sure the stock rating on your stock amp vs. my '87, but I'd be surprised if it was much more than the 20w max x 4. However, even though most 'high power' decks these days have double that power, you won't notice a huge difference. This is because a 3dB increase in acoustic output (which is not that big a difference, often just above the smallest increment on your volume control) requires a doubling in electrical power. To get sound that is twice as loud, you'll need TEN TIMES more power going in.
You can do as you suggest, and wire the subwoofer directly off your rear speakers, so long as you get a subwoofer amp that has speaker inputs. If you go that route, make sure said amp also has a built in low pass crossover, preferably adjustable (as opposed to a set 1, 2, or 3 frequencies), and preferably 18 dB/octave slope or higher. The main disadvantage of this setup, is that you'll still need to run your rear speakers full range, meaning they will still get all the bass they did before, and they can't really handle it. This is not an electrical problem (which is the power handling rating given by the manafacturer), but one of excursion. At frequencies below say, 80Hz, the more you turn up the volume, the further the woofer must move and 6.5" woofers are not known for their high excursion capabilities. But I digress..
The ideal situation would be having two amplifiers (or one three/four channel amplifier), one for your two rear speakers, and one for the subwoofer. Of course this amplifier should have not only a built-in low pass crossover for the subwoofer, but a built-in high pass crossover for the rear speakers. This will remove the majority of the low bass from them, and as a result, greatly improve the midrange quality of their output, at least at higher volumes. This is due to a reduction of the intermodulation distortion in your 6.5" woofers.
As far as a subwoofer interacting adversely with the 6.5" woofers, the answer is no, that is not a problem. First, the trunk is not sealed, so there is an excape path for the high sound pressures generated by the subwoofer. Second, the trunk is so large, that the higher sound pressures created at the cone of the subwoofer driver, dissipate greatly by the time they hit the rear of the 6.5" woofer. And finally, even if the trunk were sealed, the materials used in construction of a back seat, and often even the rear deck, can be largely transparent to the sub-80Hz frequencies the subwoofer is generating. That's why all those riced-out Civics have their subs in a box in the completely sealed trunk and don't need to fold the seat down to get ear-splitting bass to the driver's seat. Of course, it is true that a Civic's rear seat is much less dense than a Saabs, but the principle still applies.
One thing you can do however, if you want to keep it as simple as possible, is to insert some high value capacitors in series with the input to your rear speakers. In this way, you can still get the sub amp that has speaker level inputs and a built-in crossover and have that be your only addition with the sub itself. I think Crutchfield still sells them, they were at one point called 'Bass Blockers', not sure if they still do. However, you don't need to go there. You should be able to get something at Radio Shack or other local place that sells electronic components. I don't know the values off the top of my head, but I am thinking somewhere along the lines of 120 to 200 microfarads of capacitance in line with your rear speakers (note that the input to the sub amp would be taken directly off the stock speaker wire, and the capacitor goes between the stock speaker wire and the input to your rear speakers. You want to make sure the capacitor is a non-polarized, generally it will also be electrolytic (as opposed to Mylar, Polypropylene, or other special material). Come to think of it, I may have some of those caps lying around, I'll get back to you on that..
Let me know if any of this is not too clear... :)
Aaron Gilbert
1987 9000T 247k miles 460 watts RMS 137.2 peak dB
A
Way too much stereo stuff in one Saab!
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