Achieving Better Bass Impact from Your Audio System

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!