This project envolves my 1998 Pontiac Firebird. I bought it new in December of 97'. I really like the stock Monsoon audio system's sound, the features on the head unit are adequate. All I listen to are CD's anyway. From the factory, there are mids and tweets in the doors, mids and tweets in the trunk side panels, and dual voice coil subs in each side panel near the back seats. Each driver has their own 50 watt channel of amplification. But with time, the surround on the subs and the door midranges gave out. I found replacement surround kits for the subs but they didn't last more than a year or so.
I just replaced the door mids with stock drivers; the whole system has 2-ohm drivers just about everywhere. This makes it near impossible to replace anything with aftermarket and still have it sound good. I've always wanted a 'system' in this car, but the monsoon sounded just good enough to not mess with. I also strongly valued the space in the hatchback where the T-tops are stored. The normal box for an f-body takes up the whole area underneath the flap that covers the deep part of the hatchback. I've heard systems with 10's and even 12's firing straight up, placed in a flat rectangular box just behind the back seat. Leaving the deep part of the trunk available. These systems never seem to live up to what a normal set of subs sound like tucked into the very back of a hatchback. I wanted to come up with a design that could use that same flat spot behind the seat and have the drivers firing backwards. And most importantly, leaving space for my T-tops to be stored. 8's where just to tall for this, and until I saw the TangBand 6.5's, no other small speaker really got my attention.
I talked to a Parts Express rep that said he had helped a friend install a pair in a small import car and he was very surprised by the results. He claimed it could move about as much air as a single 10" sub. So I proceeded to purchase four TB 6.5" subs and a small PG amp (R2.5:2). I built a wide flat four chambered box out of half inch 9 ply birtch (weight is an issue). With two 1" ports per rear firing driver. It was a shame to carpet cabinet grade plywood but I have no desire for any wood grain in a sports car. I ran a 10-gage power wire to the battery, and an 8-gage ground wire. The four drivers are wired in 2-ohm stereo. I tied in a passive step-down on the left and right rear channels between the head unit and the monsoon amp in the trunk.
Using the built-in crossover on the PG amp, it took quite a bit of tweaking to get an even sound. What impressed me was how clean the subs where. I could actually run the low pass up to 180hz with out all the typical mid-bass distortion. The stock head unit has the unpopular auto-loudness control, but with responsible use of the eq, I've found it works quite well. Even without using any of the 40hz boost on the amp, the system has unbelievable low end. WinISD software showed me a nice curve down to 34hz, and it is awesome all the way down.
At first I could not believe I was listening to a ported system. Without telling many of my friends what I had installed, I would have them guess what size speakers where back there. Most agreed it was at least a good pair of tens, maybe a pair of twelve's. Everyone, including myself, are just amazed with those four little 6 and a half's. If I had to improve anything, I think I could use a larger amp. I haven't been able to bottom out the cones, and when the system is pushed hard, you can tell it turns soft like the amp just runs out of power.