abwc

A singularly great component in the system is at the mercy of the other components for its greatness, as all the other components are to each other for their own. (Did I violate some law of English with that phrasing ?!)

They are all completely interdependent.

Rare is the magic combination, even when the audiophile has the full palatte of components from which to choose and afford.

I had the guy who sold me my $25K 2-channel system come listen at home after I got it all set up in a spare bedroom (itself another one of those interdependencies).

He was drooling in the chair at the sweetspot, in the dark, when the music stopped and said

Oh my God...
Oh my God...
I don't believe it...
that's the most beautiful thing I've ever heard.

(some faith is required of the reader here; he wasn't just saying that)

When I moved out, I set it up in the new place, and it hasn't sounded the same since...

dxben

Which is why you should always audition audio gear in your own house

abwc

...and then NEVER move!

RI A6

Correct. The efficiency of a speaker is defined to be the acoustic output in dB @ 1 meter with at an electrical power of 1 Watt. Most speakers are not very efficient, with efficiency levels of around 87 dB. To reproduce sound at the level it was originally recorded at requires amplification.

For example the sound pressure level of classical music peaks are around 110 dB. If a speaker has only an efficiency of 87 dB, then it will take 256 Watts of power to reproduce that peak accurately. Rock music peaks can reach 116 dB, and would require close to 1000 Watts with a speaker of 87 dB efficiency.

Now, if we look at speaker design, the efficiency is dependent on two factors. First, the design of the drive (or transducer) itself. In this case, it turns out that higher efficiency, audio clarity and bandwidth go hand-in-hand. High efficiency drivers have lower mass, have heavier magnet structures, and can be accelerated. This also leads to less distortion and better clarity, since the mechanical/electrical system stays in the linear region for a greater range. Second, the efficiency of a speaker is dependent upon the design of the enclosure. I'll get back to that in a moment.

It is true, as you say, that the purpose of a crossover (either passive or active) is to create a flat response. Each driver in a speaker system has an optimal frequency range of operation where the speaker is linear and clean. Outside of this range, frequency response drops off and distortion increases. A crossover is designed to feed each driver individually, only with the frequency range that it is capable of reproducing, and with an "ear" towards an overall flat frequency and group delay response.

Now, when you have low efficiency "gunky" drivers, one way to get the audio output that you desire is to amplifiy the hell out of it. Unfortunately, as can be seen above, it takes a lot of reserve power (or headroom as it's often called by audiofiles) to reproduce those important peaks. This reserve power provides the "punch" that is so characteristic of live music.

Now passive crossovers are generally fairly simple designs, and work with well-behaved speaker drivers (tweeter, mid-range, woofer ... etc) that are reasonably well matched. However, good matching of the individual driver characteristics can be accomplished much better with active equalization and amplification. By adding electronics and amplifiers to each of the drivers in a speaker, it is possibly to do two things at once: better flatten the speaker response, and provide more total amplified power, while spreading that power across each of the drivers.

Now back to the enclosure/efficiency issue. There are two ways to use an enclosure. one way is to direct the sound, as a horn and acoustic lense do, and as a corner horn does. Unfortunately, this requires a great deal of space for low frequency drivers, and even a large amount of space for midrange drivers. You'll see this method used widely in professional sound systems, since space is not as much of an issue as it is in your home or car. But, another way to use the enclosure is as a resonance tuned structure, to reinforce a particular range of frequencies, such as a bass reflex design does. One problem with these approaches is directivity. The sound field becomes highly directive and does not have a "real" quality to it.

Bose saw this as a problem and looked at the problem with the psychoacoustics of sound field imaging. They took this to an art form with the old 901 speakers, which were designed with multiple drivers in an enclosure designed to have multiple tuning and detuning resonances and multiple directivity to simulate a "real" sound field, with direct and reflected sound. This was a good idea, but a very poor implementation, since Bose utilized really crappy drivers with low efficiency. As a result, the sound field was nice, but the speakers lacked any punch at all.

Now, feed forward 30 years. We now have all the electronics we need to do anything we want in audio design. We can choose to use higher efficiency (higher quality) drivers, which require less power to operate, or we can use a brute force method using active equalization, and digital signal processing, and amplification, to create a continuously adaptive sound system. In theory this is a great thing. Theoretticaly we can create any sound image that we want, and we can correct for all non-linearities in the speakers and amplifiers. This is essentially what Bose does in our systems. Some of the music "punch" problems they overcome by using multiple amplifiers, one for each driver in the system, and then controlling them actively with amplification. Unfortunately, Bose (in their arrogance) have decided that the user should have almost no input into the sound quality. They essentially claim that they have created a perfect system, that automatically adapts to the ambient sound environment in the vehicle, and that the sound system has been tuned to the vehicle. Well, if that were the case, it would sound considrably better than it does. It sounds "good enough" for the majority of the population, but is not even close for those of us who know.

Unfortunately, since there are no ***** to twist on the Bose audio system, and there are no published specifications, since Bose deams them "obsolete" for such an advanced system, we have no ability whatsoever to intelligently tune it. I assume that Bose has used cheap crappy inefficient drivers as has been their M.O. for over 30 years. But, since the system has been "tuned" by the factory, there is no recourse to change out the drivers and reequalize the car sound field, even if we had the equipment to do it.

RI A6

The speaker is an imperfect mechanical system. It always has the largest distortion numbers of any other component in the system, by a huge 100:1 margin. Back years ago, before I finished my electrical engineering degree and was working in a high end audio repair store in the DC area, we used to counsel people purchasing new systems to spend 1/2 of their budget on the speakers. We did this because they make the largest impact on the sound of the system. Better speakers are bought for money.

I would tell people to allocate half of the budget on speakers, determine what price they were willing to pay, and then audition them with a sound source they were familiar with in a good high end audio store, and pick the one that sounded best to them. Once that was done, they could go through the options on turntables, amplifiers, etc. I also counseled them to choose the highest efficiency speaker that sounded good to them. Remember that a 3dB increase in speaker efficiency is equivalent to doubling the power output of the amplifier. You get your biggest bank for the buck by increasing speaker efficiency.

It is distortion at high output levels that causes the differences in sound quality between a low end low power and high end high power amplifier. What happens is that many systems drive low efficiency speakers with low power amplifiers/receivers, which drive the audio output into distortion at the sound peaks. The solution is to either provide a higher power amplifier, which can only be done to a point, or to use speakers with higher efficiency (and that sound good to you.) Then you can get away with an amp that has less power, and the overall system still has the same "punch."

Reggie

Reggie

Nice

Reggie

I agree with you