subwoofers

what is the most important thing you look for when buying a woofer?

as far as performance what do you look for?

the reason i am asking is we are deisgning and building subwoofers and amplifiers any input will help

will you use a better product even if it isnt the name brand you like or do you stick with one name?

what do you see as a good fair price for a 5000 watt rms amplifier that would attract you to buy it?

also a 2200 rms amp?

I included in my comprehensive front stage sticky some information for selecting a subwoofer.  Here's a quote:

"So let's start with everyone's favorite, the subwoofer. This write-up is about SQ, so I will ignore the SPL designed system. For the most part you want a driver that will produce a flat frequency response in your vehicle. Although a lot of source material doesn't have it, it is still good to be able to produce even the lowest octaves if possible. So what do we want to look for in a good subwoofer? Well first of all a good amount of excursion is handy. This is because it benefits us two fold. First of all for every halving of frequency, the excursion capability of the subwoofer must quadruple to keep the same output. The second reason for a good amount of excursion has to do with motor linearity and distortion. Earlier I talked about harmonic distortion and how third harmonic distortion is really bad. Well as it turns out this harmonic distortion is mainly caused by motor nonlinearities.

So what are these nonlinearities that were mentioned above? Well a speaker has a fixed magnetic gap with a coil of wire suspended in it. When current is applied to the voice coil it repels from this fixed magnetic flux due to the opposing magnetic polarities. The physical parameter BL (B being the amount of magnetic flux effecting the number of turns L of the coil) is derived from this and is measured in Tesla Meters or Newtons per Ampere. Well about 99% of subwoofers use a motor topography called overhung which is a small magnetic gap with a long voice coil. As it turns out there isn't only magnetic flux between the pole piece and top plate. There is also what is called stray flux or the fringe field that resides above and below the gap. You can see this here: http://www.adireaudio.com/Files/SGLC-Driver.gif   What happens is at rest the BL will generally be at its highest. However as the coil starts moving, it will start to leave some of this stray flux and BL will start to drop. This creates distortion. Here's a DUMAX test of a Kicker Solobaric BL curve: http://www.adireaudio.com/Files/DUMAX/S12D.pdf    You will also notice the Kms curve which is the suspension nonlinearities mentioned earlier (Kms=1/Cms). As you can see, the BL starts to drop off fast with excursion. The more of a change in BL, the higher the distortion will be. So how does having more excursion benefit us? Well a subwoofer with more excursion playing the same frequency as a subwoofer with less excursion and at the same volume level will be in a more linear part of the BL curve. So therefore distortion will be lower.

So what else do you want in a subwoofer? Well despite what many manufacturers want you to believe, a large motor size is not necessarily one of them. In other words, a larger magnet does not necessarily mean a better subwoofer. Huge BL numbers can actually be a hindrance rather than a help. This is because BL directly effects Qes which is a large part of Qts. So when we raise BL, Qes (and along with it Qts) goes down and raises Fb. So too much BL can actually hinder your low frequency extension from the subwoofer. You want just enough BL for the given design goals. Also note that thick magnets aren't as good as wide one's. Adding another slug (doubling the thickness) of magnet generally only increases the available flux by about 10%. It's surface area along the top and bottom plate's that make a difference. Also try to stay away from subs with bumped backplates. The biggest choke point for magnetic flux is at the back plate/pole piece junction. Bumping the backplate throws away a lot of your available flux. This is OK if the design allows for it, but many times it doesn't. For the cone, you want it to be rigid enough to stay pistonic without being too heavy. Now I know that people worry a lot about efficiency. But IMO this is really the last thing you should look for in a subwoofer. Because if you choose to go with an efficient driver, you have to give up either low frequency extension or enclosure size. And neither of those are things I'm willing to give up. Especially since power is cheap and trunk space usually isn't. After all, would you try to hold your breath to conserve oxygen in the middle of the forest? Also if possible look for a higher Qms and lower Qes. This means that Qts is dominated more by the magnetics rather than the suspension where driver tolerances are at their worst. I am also not a big fan of tinsel leads woven into the spider as they will have a negative effect on the life and performance of the suspension on the driver. I also don't recommend dual spiders as they will magnify nonlinearities in the suspension."