Originally posted by Diabolik
Oh yes, the box is everything. I have always made my box to the specs given by the sub manufacturer and never been disappointed. Some points:
- Always use at least 3/4" MDF or thicker for a box.
- Never buy prefab. They are made with cheap ass particleboard and are never properly designed.
- Only mess with a box outside of the manufacturer's specs if you really know what you're doing. Even a 0.5 cubic foot variance can make a huge difference.
Bass Mechanic: A ported box will not go lower than a sealed box, quite the opposite. A ported box cannot go lower than the tuning frequency of the port you put into the box as you lose cone control below that frequency and can blow your sub. That's why many D-class amps come with a switchable subsonic filter now. Sealed boxes go way lower than a ported box, but a car's resonant frequency is generally around 40 to 45 Hz so for SPL it's a moot point. Most SQ setups use sealed boxes as you have a smoother response curve and can go a lot lower, which really helps in RTA.
-Diabolik
ummm NO! your compleatly wrong about that statement.
a ported box goes considerably lower than a sealed box and has far less cone travel than a sealed box. also has less distortion because of less cone movement and has more SPL than a sealed box because of the added area of the port.
here is a responce graph that has a JL audio sub as an example. notice that the sealed box has an F3 of 50 hz while the ported box has an F3 of 34hz if my math is correct i belive the ported box has considerably lower frequency responce than the sealed box. it also has a gain of 3db over the sealed box over about 75% of the usable frequencies.
if i showed you an incar responce (and i can) of this example you would find that the ported box maintains the SPL at 35 hz with a 5-6db gain over the sealed box.
also the point of porting a box is not to tune it to some off the wall frequency. you pick a frequency that compliments the woofer and the box. as you can see in this example the tuning frequency is at 29.31hz but it still has more output and less cone travel than the sealed box until it comes to about 22 hz. this is where a subsonic filter is used to prevent the cone from getting excessive travel. also notice that the cone travel does not even reach the xmax limit until 20 hz. there is still mechanical limit available below 20hz.
unless you plan to listen to elephant calls in the sub 20hz zone there is really no need for a subsonic filter in this example. most all music does not contain program material that falls below 20 hz. a subsonic filter is good added protection but not a requirement if you design the box correctly.
just a little FYI.. i have been building boxes for over 15 years. and have recently designed a subwoofer box that has broken all the rules for what typically you expect from different types of boxes.
usually a sealed box is the tight accurate box design, ported are known for extended LOW frequency responce and bandpass boxes are known for good SPL but not so good of SQ.
my computer designed subwoofers and computer designed bandpass boxes have combined all 3 aspects into one box. the box happens to be a bandpass but if you ask anyone that has heard it they will all tell you the same thing.. it is simply awesome!
i belive there is are 2 members on this board that will attest to that fact.
thanks for your time.
Kevin