Basic Tweak & Tune

Question: My question is why did so many companies go away from 3-way components and are 2-way components better for sound competition than the more expensive 3-way components?

The manufacturers will have their own position as to why they shifted away from three-way components—I have my own view, which is based on what happens at the install bay level and how that is translated up the chain to the manufacturers and marketers.

First, from the acoustic science side of the topic, it is accepted as fact that the best speaker is a single point source speaker or emitter. You have one mouth on your face, and when you speak or sing, all frequencies involved emit from the same source. Compare that to a loudspeaker and we hit a couple of snags: a speaker cannot cover all of the audible frequencies, so we need to use a low frequency device called a woofer, and a high frequency device called a tweeter.

Put a woofer and tweeter together, and you can now cover the complete musical band from 20 Hz bass notes to 20,000 Hz at the treble end respectably. Problem solved? Not so fast—the singer has one sound source, which takes two speakers to equal. If you place the speaker components beside each other, the brain can decode the presence of two sound emitters instead of the expected one source. They are duplicating efforts in that the woofer is playing a bit into the tweeter’s range and the tweeter is trying to cover some high bass notes. This duplication of signals causes “phase errors” which is the foundation of how creatures localize the source of a sound whether prey or predator or punk band.

So we add a circuit called a crossover, which is a filter set that blocks high frequencies from the woofer and low frequencies from the tweeter. Now the sound has become more precise but still doesn’t sound exactly like it is from only one emitter, especially when the song transitions from a low note to a high note and the sensitive ear notices that the source of the sound has changed position slightly.

The black art of building a perfect loudspeaker is frustrating enough to drive speaker designers to go postal. The loudspeaker is like a guitar—the longer you play guitar, the more you know that it is impossible to tune and keep in tune. It can be maddening! So far, we have only covered a two-way speaker. Now you want to go three-way? Who needs the aggravation?

From the physical installation side, cars today are just too cramped to offer spaces that are suitable for speaker locations. We prefer to have two locations that are equally distant in path length between the speakers and the ears, forming an equilateral triangle, known as the “imaging triangle”. The speakers must also be “on-axis” or perpendicular to the listener so the speaker is firing directly at the listener. That’s tough to get in cars of the last 20 years. Keep in mind that we also need to ensure the speaker elements are within one-half wavelength at the crossover point according to many, including Vance Dickason, the renowned author of the Loudspeaker Design Cookbook. That means the tweeter, midrange and woofer all must be very close together or you get all kinds of phase and timing problems.

Most installs wind up consisting of a woofer in the door and a tweeter in the dash. According to the half wavelength rule, a woofer and tweeter should be less than an inch or two apart from center to center, depending on the crossover frequency! Where do we put the midrange? Break out the plasma cutter and fiberglass, and let’s fabricate a new dash! It seems that there is little chance of getting naturally good speaker placement in a car. Even the carmaker that has absolute control over the shape of the dash ALWAYS designs the speakers to be in bad positions.

Which sounds better? Audiophile philosophy says that simpler is better, and I agree in the broad sense. It takes more work to make three components work like two, yet never really succeeds. I have heard many stunningly sweet systems using two-way home speakers, and find that if you triple the price tag, you can get a three-way to equal a two-way system if done by a very skilled designer. Just watch out for the voodoo that comes up as an extension of sound physics and true common sense. Those who claim they can hear grass growing are typically found on the Internet forums promoting all kinds of weird concepts as if they are industry veterans.

In the sound competitions I have judged starting with Car Audio Nationals back in the mid 1980’s, two-way systems always seemed to be the most natural and cohesive. The reason always made sense to me: if you drop a stone in a calm lake, you can see circular waves propagate outward from the center. Drop two stones close together and the waves appear to blend into one. Drop several stones and you get a mess. Audio follows a similar parallel in that if we can get the sound wavefronts from a woofer and tweeter to blend in time and phase, it will sound like the highly valued “point source”.

Keeping the woofer and tweeter as close as possible is a major key to success, followed by aligning the voice coils on the same plane. That one is a lot more difficult. If you were able to mount a tweeter in the middle of a woofer (creating, ironically, a coaxial speaker), you would still need to embed the coil of the tweeter back inside the coil for the woofer to approach perfection. This is not possible at the installation level, and even if you did, the coils would induce energy into each other and you are back to having the equivalent of no crossover.

This is where new technology comes in to play. Since we have the ability to digitally delay signals, we could use a processor to delay the signal destined for the tweeter amplifier so it arrives at the voice coil a fraction of a second behind what the woofer receives. Now you have a point source that can be time aligned, resulting in the closest thing to a natural emitter like a musical instrument or voice. Again, in a two-way world, this works, but in three-way speaker systems, it is much more difficult.

Manufacturers recognize that it is important to make things that people want to buy, and speakers have evolved to the point where there are clear preferences. There was a time when “more is better” ruled, resulting in three way, four way, five way 6×9 speakers all feeding off of the enthusiasts mistaken notion that if it had more, it must be better.

Limited speaker mounting options in new cars helps to influence the manufacturers to simplify their offerings, and the additional benefit is passed on in the form of lower installation labor costs to you. Less to build, lighter to ship, more reliability and improved sonic performance all drive the decision. Quality counts—high-grade components are essential whether you choose to build a two way or three-way system but I agree that a two way will always perform better with less work.

You can always check out more installation pics at www.northfield.com.au

Many thanks to www.caraudiomag.com

Full custom installation done by Northfield Car Sound. Head unit is Eclipse AVX7000, boot is packed full of Eclipse amplifiers and Eclipse Speakers and Subwoofers finish the system.
Full custom interior including customized dash, suede seat trim with monogrammed logos and new custom floor mats and door trims. More www.facebook.com/pages/Northfield-Car-Sound-Head-Office/115125265176155 or on the web at www.northfield.com.au

Ask anyone what is he or she looking for in their auto sound systems and nine times out of then they will say bass, lots of bass. So what do we do? We normally start with one 10″ woofer, rapidly followed by two 12s, only to swap them for even larger subs, typically installed in Free Air or Infinite Baffle configuration. We all start that way only to discover, some sooner than others, that besides size and number, there are other aspects that have a huge influence in the final sound and output, like the enclosure in which they work in, the direction the woofers are firing and their relative position inside the car.

Ask again anyone how should their loud bass systems behave and they will reply right away that they expect them to slam them, feel the impact like a kick in the chest. Problem is woofers don’t do that! Not the way we normally use them in car audio, with a low pass filter around 100 Hertz. All this behavior, all this “hitting stuff”, is the midrange responsibility. Have you ever heard a drummer, live, with no amplifier and loudspeaker interface, 5 feet away? If not, please give it a try; it will change the way you think about bass forever. When you stand right in front of a good and powerful drummer performing on a high quality drum kit, the bass waves hit you in the chest so hard, you may think they will leave you bruises. The words sound pressure, kick, impact and fullness simply acquire new meanings. If you don’t know someone who plays it, go visit a music academy.

The Importance of Mid-Bass
Now, if you analyze carefully those beautiful and inspiring sounds, what do we get? An almost full range signal, with lots of energy in the mid-bass region, frequencies between 100 and 500 Hz, all of them within the working range of the midranges. That’s where the “kick” comes from! Of course those huge woofers you already own are very important. They produce the “body”, the energy, the envelopment, but they are only a part of the equation. If you don’t believe it then ask a friend with an awesome sound system to temporarily shut down all his speakers but the woofers, and listen to what’s left. You will only hear hollow sounds, with absolutely no impact, lifeless, like a thunder heard from many miles away. So, if you crave for great bass, go for great midrange.

Speaker Enclosure
Now, if you want those midranges to really perform, they will need a real enclosure. By now it should be clear that the box a woofer is working in is almost as important as the woofer itself. That a woofer with no box, simply won’t be able to produce bass. When a cone moves, it produces exactly the same wave on its front and back sides, but the wave in its back is 180 degrees out of phase, so, if we let them combine, they will cancel each other and produce nothing. This may seem like an old story to you, but what you may have not yet realized is that those 6 inch drivers, part of the component system you just installed in the front of your car, ARE woofers, so all those old rules apply the same! No box, no bass, period! So, the car door is not a proper enclosure, even if you try covering it with damping material. That small piece of wood you used to mount the driver is not a proper enclosure, that beautiful fiberglass mounting pod, if not perfectly sealed and strengthened is not a proper enclosure, etc. No kick, no impact, no fun.

It should be clear now that the only way to produce awesome bass is with awesome mids and that this will only happen if they are also working from a properly executed enclosure. The preferred enclosure for this use is a sealed box. The reasons are many. First, they are the smallest and most forgiving with regards to the calculated internal volume. This is important because we usually don’t have much space there. Also, they behave very naturally, have good transient response, soft roll off and, compared with a door or a free air format, can greatly increase power handling—the trapped air inside won’t let the cone move as far, greatly reducing excursion. It should also be noted that the goal of more exotic designs is usually to extend low bass reach, which is not necessary here.

Size of Enclosure
So how big that sealed box should be? Ideally we would like to calculate that enclosure with a computer program, but it would be necessary to have its Thiele-Small parameters, which usually are not available for this type of drivers. The solution would be to ask the manufacturer or, better yet, measure them ourselves. If our goal is not some sound competition finals, let me save you time and effort and suggest a leak-free, solid sealed box, as big as the car permits, and if it permits a lot, around 9 liters of internal net volume would do wonders. If this is not possible, don’t worry, almost any box will do a lot better than no box at all. Just to check this out, load any woofer in an enclosure design computer program and study how the frequency response changes as the internal volume is decreased from the theoretical optimum Qtc of 0.707. You will note that the smaller the box, the more deep bass you give away in exchange of output in the upper region. Also, the smaller the enclosure the higher the power handling because of the stiffness increase of the trapped air, which may not sound as a bad idea. So, if we are forced to use a very small enclosure, this may not be that bad as we are not actually looking for deep bass from this driver. That will be the job of the subwoofers, so we definitely won’t miss that. On the other hand, the extra mid-band output may produce more kick, which is exactly what we were supposed to be after, so this may not be such a bad trade off. I’m mentioning “trade-off” here because any good installer or enthusiast knows that a very high Qtc sealed enclosure will not be very musical; but let me repeat here that this, nevertheless, will be way better than no enclosure at all.

Shape, Size of Enclosure
Hoping that I have already convinced you to try these enclosures and discover what your system is really capable of, let me give you a few extra recommendations. First, in general, shape doesn’t matter as long as the required internal volume is accomplished. The only shapes that should be avoided are squares or rectangles with dimensions that are multiples, say 3 x 6 inches or the like, as this would produce coincident standing waves. Also, it’s a good idea to try to build both sides as identical in internal volume as possible, so both sides may sound the same. Use wool or any other high quality absorbing material inside, taking care that it doesn’t get extremely close to the driver. Use a gasket to mount the driver. If the tweeter will work side by side with the midrange, be sure to seal it completely or leave it outside of the enclosure, as many tweeter mounting kits leak air. And last but not least, attach the enclosure to the car as securely and firmly as possible, as this will greatly improve impact and clarity, in addition to avoiding dangerous flying objects during an accident. Have fun!

Thanks to Car Audio Mag USA for the article.. www.caraudiomag.com