i am perplexed, sub boxes

I have been perplexed for some time now. Why is it a growing trend to attempt to engineer sub boxes that are not capable of high output at low frequencies? From what I have seen many people are building enclosures that rely on the vehicles transfer function to bring the low end response to an equal level for a flat response. Of coarse there is a definite rise, but its not as predicted. Here are a few problems that I see with this thinking. 1.     By limiting a subs acoustic output at low frequencies you are also eliminating any Acoustic head room. I guess this is fine if you never plan to use any kind of bass control. Ever! 2.     In order to achieve a theoretical flat in car response, people are using subs that have high resonance frequencies. This means that you are expecting your sub to perform accurately well below resonance. Unless you own your own Kippel distortion analyzer you can not accurately predict just how severely out of wack your phase response will be. Bl and consequently Qts is not constant at high power levels. Enclosure modeling programs have there limitations and this is one of them. 3.     The theoretical 12 db per octave rise due to cabin loading dose not exist. Due to various panels flexing and responding at various frequencies, as well as trunks and foot wells and wind shields all interacting acoustically this is not an exact science. Its not even a good science. I always measure a vehicles transfer function before building a serious enclosure (hundreds) and I know from first hand experience that this generic rise is GOPy (Good enough On Paper) If accuracy is what you are after, your best bet is to perform an actual in car measurement to determine the transfer function. Look closely at your software most let you do this. Then design your enclosure taking that information into account. Designing in this manner will enable you to achieve a sub system that has better cone excursion, phase, group delay, frequency, and output abilities. As a bonus you are likely to end up with a good amount of efficiency and acoustic head room (when did that become a bad thing?). This will allow you to crank up the bass when you want to (or not you decide) and the cannon shots in the 1812th overture will not destroy your sub. The solution to flat frequency response over the pass band is careful planning and making good use of an equalizer. Its not difficult to bring those peaks down with moderate adjustments. Remember that a box program is just a big hand calculator, and thank God for them. But if you are attempting to make a science out of this stuff you have to keep in mind the variables outside of your software and account for them. The 12 db rise utility that most box programs have is a valuable tool. I use it. As a guide, but that’s the extent of it. I wish I had a buck for every person that I have seen design or purchase one of these boxes only to cry an moan that it dose not have the sound that they were looking for. That’s my piece.

One more thing. Many “one note wonder” boxes are a direct result of the rise occurring at a frequency other than what the designer predicted. Also worth mentioning is the fact that reliable pc based test equipment is very affordable and available. So the excuse that measuring a cars transfer function is out of reach for normal people is not valid. Worst comes to worst you can always plan and prepare the test, then visit your local Audiocontrol dealer and pay them for some RTA time to conduct your test. Audiocontrol dealers are required to have an RTA to be a dealer. If you have already done your home work and spent dozens of hours getting familiar with box programs and spent thousands of dollars on equipment why stop short of the finish line? And if you do decide to settle for the theoretical in car response, that’s fine to. Just admit that you have officially compromised. Don’t claim that you have the definitive answer. What’s today’s date? Because I am feeling kinda cranky.

One way of creating aggressive fast sounding bass is to make a peak in the bass response at 40-50hz. A peak of 3-6 db that is set to match the frequency that the vehicles cabin starts gain starts to rise will create a wider ripple extending down to 35-40hz. Bass guitar and kick drum fundamentals come from this range. By creating a peak in this region you can fool your brain into thinking that you are hearing lower bass than you are. Increasing the illusion of hearing lower harmonics of those instruments. That all means that the music will sound more convincing and more exiting to listen to. Use this trick in moderation and with a subsonic filter for best results. Also an additional peak around 30hz if your sub and amp can handle that (with out compression, distortion or amplitude issues) will reinforce this effect.