Just like the price and availability of gas has an effect on the design of cars, wattage has had a big influence on the design of audio systems. Only in the last decade (the ‘90s), have large, high-powered amps become so affordable. In the ‘80s they were around, but they were expensive; and in the ‘70s, they cost an arm and a leg. In the ‘60s they just didn’t exist, period. But even though there have not always been big amps, there have always been audio lovers who want the same thing everyone still wants from their system. And that’s DEEP LOUD BASS!

If you’re addicted to audio and all of a sudden the biggest amp you could get your hands on was 100 measly watts, what would you do? You would do what everybody used to do when building speakers: You would start building big speaker boxes because without LOTS of power there’s no other way to have DEEP LOUD BASS. The problem for audiophiles is that their ability to achieve their goals are so closely tied to the laws of physics.

Many installers fail to realize this simple fact. Designing a speaker system (by speaker system, I mean a woofer in a box) is totally under the influence of the physical laws regarding mass, movement, energy, and a score of other subjects. Unfortunately, much of what many salesmen and installers know has been learned from marketing folks. In many cases, this has led them to believe there are some magic speakers out there. Not so — virtually every speaker on the market is similar in operation. Every manufacturer has access to pretty much the same materials, and until some company starts using “unobtanium” to build speakers, this is not going to change.

So how does this affect our speakers? Designing a speaker is an exercise in making the best compromises. In a woofer, we usually have three things we try to balance: efficiency, bandwidth, and size. Efficiency is a measure of how much electrical power is converted to sound. Bandwidth relates to how deep the bass can go, and, of course, size relates not to speaker diameter, but to box volume. Now, the study of these choices is very interesting and there’s nothing new about them. They have been known for as long as speakers have been around, but they became general knowledge back in the early ‘50s.

In the early ‘50s, there was a really clever designer that popularized what we today call the “acoustic suspension system.” His name was Ed Villchur. Although there are guidelines as to what really constitutes an “acoustic suspension system,” it’s probably safe to say that most sealed car boxes would fit this type. This is usually defined as any sealed system where the compliance of the air in the box is less than that of the speaker. If the compliance of the air in the box is more than the speaker, it’s simply a sealed box. Now Ed did a lot of writing on the subject, and the formulas he used to describe the performance of sealed boxes would more than fill my space for this article. In fact, his writings on the subject would more than fill this entire magazine. But I’m going to make things simple and reduce the entire subject to a simple formula you can always remember. Never forget this formula and you’ll never be misled by marketing nonsense on this subject again. The formula is 3 – 1 = 2. And here is the way to apply the formula: There are three desirable factors to system design: efficiency, deep bass, and small box size. Out of the three, you can have any two, but you have to give up one.

Here’s how it works. Systems with small boxes that have deep bass are inefficient. Small, efficient boxes don’t have deep bass. Big boxes can be efficient and supply deep bass. There are lots of combinations of these parameters, but the physics are always the same — you can only have two of the three. And, incidentally, the rules don’t only apply to sealed boxes, but to all types of speaker systems.

Now, the real blessing for car sound folks is that the price of amps is really cheap. The next time you’re shopping for amps and you don’t believe me, here’s something to think about. Back when gas was 27 cents a gallon, an average amp cost about two to three dollars per watt. And I’m referring to home and pro audio amps — there were no car amps. If the price of amps had kept pace with gas, a typical 100 X 2 amp today would cost about 2000 dollars! That’s why we now have small cars with small engines that get 20, 30, or more miles per gallon instead of driving big gas guzzling V-8 muscle cars!

But wattage is cheap and we can afford wattage-guzzling speakers. Who would care about gas mileage if gas were 27 cents a gallon? Then why do we care about speaker efficiency? I sure don’t care, and to me the choice is clear — speakers that are designed for small boxes do deep bass and to heck with the efficiency. Perhaps in a future article we can cover the design choices speaker manufacturers face when designing speakers to work in small boxes.