On the "Perfect Loudspeaker"
For hi-fi type speakers [where the speakers have a flat frequency response and little or no distortion] with similar design parameters, there really is no such thing as a "perfect loudspeaker." For every reviewer who raves about one speaker, you can find another who hates it, and vice versa. Measuring the parameters for the speakers gets some numbers on paper and verifies that these numbers are within spec, but in the end it's really up to the taste of the listeners as to which speaker sounds "best."
Let's not kid ourselves: the reason why we work so hard to put these [sound reproduction] systems together is to "simulate" live music, or at least live musicians. The only way to really get the full effect of live music is to... listen to live music! In the end, all this fancy stuff we're doing is just simulation.
The problem is that everything in the signal path puts a bias on the original music. For example, if you take a set of microphones and have a person speak into each one, the output from each mike would sound different even though you're amplifying the signal with the same equipment. See, there's no such thing as a "reference" microphone (it's one of those variables a musician can play with when they're recording) and it's difficult to make such comparisons, so I don't really like to talk about speakers that way.
Instead, I like to talk about the "timbre" of a speaker. Basically, the particular mix of materials and choice of design creates a sound unique to that loudspeaker, a signature sound, so to speak. An analogy can be made with pianos. Musicians will tell you that pianos made by Kawai sound different than those from Baldwin, Steinway, and Yamaha, but pianos made by the same manufacturer can sometimes sound very similar. All these different piano brands are fine musical instruments and the question of which "sounds better" becomes a moot point: they're all good interpretations of what a "piano" should sound like.
My advice for consumers has always been to audition the speakers you're considering purchasing. If you like a particular brand name you've purchased before, it's often a good bet you'll like their new stuff because you agree with their speaker designer's idea of what sound presentation a loudspeaker should have. "Good sounding" in the end is very much a matter of personal taste, given that other performance criteria such as distortion and intelligibility are similar. I also think that appearance counts a lot, so you also have to like the way a speaker looks.
On Modern Car Audio Speakers
Car audio speakers of today are definitely much more hi-fi than those from the past. About 15 or so years ago, loudspeaker design was looked at as a "black art" and the design process was mostly trial-and-error, with the good designs coming from individuals with lots of knowledge and experience in the craft. So, even though good designs existed, many of the supposedly "high-end" car audio speakers simply didn't measure well and some just didn't sound all that good.
Advancements in computer aided design (CAD), like Linear X's Loudspeaker Enclosure Analysis Program (LEAP), made designing speakers so much easier since designs could be simulated on the computer to see what performance would be achieved even before any prototyping begins. Before CAD, someone had to build the speaker, then collect data to see what the results were of tweaking these different parameters. What would have taken a team of engineers a month or more to accomplish while testing a series of prototypes takes me usually less than a week using LEAP. However, speaker designers need to be aware that while the CAD results can get you extremely close to a final design, you still need to do the actual prototyping (and sometimes adjust the response of your loudspeaker to get it just right)! These tools really cut down on costs and design time and tend to result in more consistently satisfactory designs from many more manufacturers; in essence, [they] have substantially leveled the playing field. So now I find car audio loudspeakers have overall better fidelity across the board.
The other comment I have about car audio speakers today has to do with the trend for manufacturers to design woofers for small sealed enclosures. The roll-off at or above 40 Hz or so on those enclosures is not really spectacular performance in free-field applications (especially for home theater subwoofers); but for the closed-field of a car (the so-called "cabin gain" that provides as much as 15-20 dB boost in frequencies below about 40 Hz) the small boxes work great. Back in the old days (less than ten years ago!), many cars had a "one-note" bass quality to them as most guys built enclosures that measured flat all the way down to 20 Hz outside the car, so inside the car the cabin gain was just overwhelming. (Okay, maybe some people are into that one-note bass thing, but it doesn't help our "simulation" of a musical performance very much.) It's nice to see the industry go in this direction and produce woofers where the low end is nice and flat once installed. It definitely sounds substantially more musical.
On Listening Responsibly
I have nothing against loud music: rock-and-roll wouldn't be rock-and-roll without being loud (hey, I played keyboards in a very loud rock band for five years)! However, there's a trend in car audio that I'm concerned about. More and more, I'm seeing manufacturers producing ultra long excursion woofers that can handle a tremendous amount of power. These designs are coming out because there's a large demand for it, and if I were a manufacturer I'd crank them out by the truckload, too. The problem is that these woofers are being installed in the closed field environment of a car. The sound pressure level in a car can get ridiculously high, and can happen without any appreciable distortion from this current generation of high performance woofers and amps. Distortion is how we judge if we're pushing the limits of a system and we can say, oh that's too loud I should turn it down. Without these previous limitations, the new state-of-the-art system sounds so much better at high volume; and we no longer have that audible cue on the loudness of the music we're playing. Extended listening at such high SPLs can lead to significant hearing loss in the long term.
My angle on this issue is from the professional audio end. Sound engineers that mix concerts are exposed to incredibly high sound pressure levels when they're working. Many of these guys end up losing a lot of their hearing by their mid-to-late 30s. I have on several occasions published information in Voice Coil from groups that are organized to help the professional sound community address this problem.
So when I advise people to listen responsibly, I mean for them to be aware that sound can be seriously damaging to hearing in the enclosed space of a car. I'd like to see consumers become more aware of this issue, and maybe the manufacturers address it in some way. In the end, I don't think there's anything wrong with designing loud systems and cranking it up, but there needs to be more education in how loud sounds affect your hearing in the long term.
On the Future of Car Audio
Car audio is definitely heading to 5.1 [or surround sound] in the future, both audio and video. That's six channels of sound information (front left, front right, front center, rear left, rear right, and a subwoofer channel) simulating the musical performance. Over the past five years I have designed some of the best reviewed surround sound home theater systems in the industry, so I am very enthusiastic for the medium. Obviously, the possibilities of using this new format for music are just incredible, and I'm very excited by it.
Car audio really is ready for a surround format. Most cars already have the four locations for front/rear, left/right; and subwoofers in cars are a standard thing. The center channel is all that is needed to complete the 5.1 music or video system. Center channel installation can be tricky, but I've seen installers solve this problem by placing center speakers in the dashboard or console; and some manufacturers actually make center channel speakers for the car now. With the surround format, the center channel generates sounds that are purposely mixed for the center, rather than some derived center extracted from the old two-channel format; so getting those left and right speakers to image perfectly wouldn't be quite so critical as it was for two-channel. The main criterion will be to make certain that the left/right image coincides with the center channel. As for amps, many aftermarket installations already have six- or eight-channels to play audio and there is a big selection of multi-channel amps available. The most subtle problem is the same for surround systems in cars or in the home: the timbres of the speakers need to be closely matched so, as objects "travel" from one speaker to the other, the same tonal quality is maintained. Image location is also important, so as the object moves it isn't distorted spatially. Achieving that balance across these different speakers mostly means using the same drivers (mids and tweeters) in all five locations.
So far home theater has been advancing surround multi-channel technology, but a couple of things needed to happen for DVD audio to take off in either home or car. First, the new DVD audio format needed to be established and it has been. DVD-Audio players are now shipping and software is starting to show up, but so far it's just a trickle. So the second and most important thing is that musicians must accept this new format as a creative medium. Not only are most musicians only just recently learning about this technology, but studios that are able to record DVD audio are few and far between. However, once the music community gets a chance to play around with surround sound a little and learn different ways of exploiting this medium, I expect that these guys will gladly make the switch and start cranking out most everything in a surround format. Home theater will still drive the technology in the future -- I just don't see that cooling off -- but once these musicians "get it," surround audio will definitely follow suit, first in the home then in the car, although it may end being a parallel development.