Originally Posted By: sleddriver
Originally Posted By: grampi
When I was still in the AF, I made my own sealed enclosure using a cheap MTX car audio 15" driver, and a cheap PE 250 watt plate amp. Considering I was using cheap components, and though it was no reference unit by any stretch, it performed surprisingly well. It was made of MDF, which I spray painted flat black...it was an eyesore. So I decided I wanted to make an enclosure that looked like furniture, and I upgraded the driver to a Tempest, while using the same amp in a larger sealed enclosure. We moved before I got to play this sub, and the house we bought here has double the living room area. The output isn't as good as the previous one, and it's real boomy. And then one day the amp just quit working, so I was never able to play with it enough to get it sounding like I want it to, but I do think the Tempest needs more than 250 watts...oh, and it's corner loaded in the living room...and the amp is playing into both 8 ohm VCs paralleled for a 4 ohm load...
This explains a lot.
First, the word "cheap".
Second, "car audio". A 15" driver such as this has a very stiff suspension (spider + surround). It has to for self-protection as it's not designed to fit into a box, much less one that will fit into any car. Instead, the car is it's "box". It's called an "infinite baffle". The outer surface of the sheet metal becomes a secondary radiator. That's why bass can be heard the next block over....
Third, boomy bass is a sure sign of mis-alignment. Many times the box is too small. Anytime you put a driver into any enclosure, its resonant freq. rises. Once several mis-alignments line-up, you get one-note-bass. Sort of like putting a bus engine into a VW. Put such a beast into a corner where you have the intersection of three orthogonal planes, easily exciting all the room modes, will make the sound worse.
Not sure why the amp quit.....
Note regarding "8 Ohms" and such: A voice coil has some wiring resistance (DC), but it's also an inductor, which is fed an AC signal by the amplifier. There should be no DC voltage at all. If there is, somethings wrong. The drivers impedance varies constantly due to frequency. Further, depending on freq., at times it will present a capacitive, inductive or (rarely) resistive load to the amp. Most amp output stages dont like a capacitive load at all. Drives them nuts. The point is there is a lot of freq-dependant interactions going on between amp, any crossover, and the driver. Also, consider that the VC is a generator itself and as such generates a back-EMF that now the amp's output stage must deal with!
Though this may be well over your head, my point in elaborating is to be educational.
That was very educational, but if I had to take a test on the material, I would fail miserably...
Every sub I used in a vehicle was in an enclosure, except a pair of subs that were meant for infinite baffle applications...most of the enclosures I built were sealed, a few were isobaric/ported. All of them sounded good.
The first driver I used, the MTX, was cheap, as was the PE amp. The Tempest is NOT a cheap driver. While it may be made for automotive applications, I have heard them used as HT subs, and when in the proper enclosure, and set up properly, the ones I've heard would hold their own against any of the factory built units. The Tempest is a beast of a sub, and it isn't causing my problem. Like you said, I have other issues, I just have to figure out how to work them out...