I worked for BOSE in the late '80's as a Manufacturing Engineer, and now that I have a '90 NA Coupe, I thought I'd attempt a single comprehensive discussion to address all the BOSE questions I often see here.
As for power output, I'm embarrassed that I don't have the exact spec, but it's not much more than 15-20 watts rms per speaker. Unless already familiar with the required math, though, these figures can't really be compared with other aftermarket equipment. BOSE generally uses speakers with an impedence of roughly 1 ohm, compared to the common 4-ohm rating on most widely available components. The BOSE speaker places far less load on the amplifier, allowing lower power output to be used to achieve a given volume level. A BOSE power spec would be rated at the lower impedence, but if connected to a 4-ohm speaker, the actual output would drop significantly. If BOSE speakers are connected to a conventional amp, it'll most likely destroy the speaker AND fry the amp. Most conventional amps can't handle the 1-ohm load. DO NOT TEST THIS THEORY UNLESS YOU HAVE DISPOSABLE COMPONENTS!
If considering upgrading the stereo, understand some of the system design elements. Each BOSE amplifier contains active equalization circuitry tailored to the specific driver (not you, the speaker!) characteristics and the location of each original BOSE speaker. In addition, the speakers are mounted in ported enclosures (the big, odd-shaped black plastic boxes). The air volume and port tube (hole in box where the air comes out when the speaker's working) size are designed to resonate at a specific frequency to enhance the bass response of the BOSE driver. If mounting aftermarket speakers in the stock enclosures, use aftermarket amplification, and it'll take a fair amount of effort to achieve a good physical fit due to BOSE's unique speaker sizing.
The rear 6 1/2" isn't bad, although because the speaker is covered up so much, it won't get very good highs without a separate tweeter placement. Luckily, unless using rear speakers only, most of the stereo imaging in a well-designed system should come from the front speakers anyway. This produces the desired front-biased soundstage, and a good coaxial will suffice for rear fill. Note that these are simply the most commonly held opinions of how car audio should sound. There are many other theories, so use your own ears. I personally prefer the sharp detail of separates all around!
The front 3 1/2" presents more of a problem, and doesn't allow for an easy direct replacement. With modification, 4", 5", or 6 1/2" speakers can fit, preferably with separate tweeters mounted in the dash (better imaging than door-mounted tweeters). Experiment with plugging the port tubes to see what gives the best sound with the new speakers. Due to these unique aspects of the BOSE design, simply adding 4-ohm aftermarket speakers to the BOSE system doesn't work very well. The sound would be weak and have terrible frequency response. Spend a little money and avoid the hassle, these installation difficulties are easily overcome by any good professional installer.
BOSE manufactures their own speaker drivers, enclosures, and amplifiers from scratch, using their own proprietary specifications, which make them incompatible with the general aftermarket. The head units however, are relatively standard DIN chassis, sourced from quality manufacturers like Panasonic (the heads BOSE used to sell in their old BOSE-branded retail systems), and Clarion for Nissans and Alpine for Hondas (It's been awhile, so I might be wrong on one or two of these, but they're all familiar brands). They're not high-end components, but they're certainly solid enough for a modest system if they're still working properly. It's possible to get adapters for these through stereo shops to keep the stock head unit and upgrade the amps and speakers.
In creating their OEM systems, BOSE designs each system individually for the intended model. A special dummy head with electronic "ears" is actually placed in each seat at proper listening height to gather acoustic data that's processed by computer in an effort to achieve the desired sound curve. The Z's particular interior acoustic characteristics were analyzed, and equalization curves are set on the individual amplifiers to provide proper frequency response and stereo imaging for the occupants' listening positions. Some systems, like our Z's, even use a fifth speaker as a front center channel. This compensates for the loss in imaging that occurs due to the fact that the speaker on the door is much closer to your ears than the speaker on the opposite door!
In general, the BOSE system is a decent quality OE system that uses some interesting acoustic technology to achieve reasonably good frequency response and nice stereo imaging at low-to-moderate volume levels, but its "crankability" is pretty weak. The end result is technically, pretty good sound, but not everyone necessarily agrees with BOSE's (as defined by Dr. Amar Bose himself) definition of goodness. It is definitely NOT, nor was it intended to be, as kick-ass as with aftermarket components, but IF everything is still working properly, it's a pretty good system for those with modest audio needs. For those that want to make truly satisfying upgrades, plan on replacing the entire system, like I am.
Oh, I almost forgot, the loud scratch and pop sounds that occur when turning any electronic volume knob are almost always due to oxidatation of the volume pot (potentiometer). Huh? The internals of the volume control get dirty or corroded and can't make good electrical contact. Get some 'Tuner Cleaner' from any electronics store (Radio Shack), then remove the volume knob and try spraying a LITTLE bit down along the volume shaft. It needs to get inside the part that actually rotates when turning the volume knob. I haven't done this on my Z yet, so I don't know how difficult it is to get enough fluid into the right places (and out of the wrong places!), but I do have the symptom, and I know the sound well from my guitar amps. This is a common electrical problem in many devices, and tuner cleaner is usually the best fix short of dis-assembly.
gordman
