car audio

[_paralyzed_]

Thanks everybody!

I always build my own boxes to suit the sub/fit the vehicle.

It will be four old school JL Audio 12w6's. Dual 6 ohm voice coils wired in parallel, then all 4 speakers wired in parallel.

A crossfire 1000d sub amp and a crossfire 402 for mids/highs(4 sets of components)

I have 2 1 farad caps, but I'll lose them.

JL claims a 3db(twice as loud!) increase with a ported box over a sealed, but they sound sooooooooooooo good in a sealed box, thats what they will reside in.

[BrianG]

Yeah, you can get a decent increase in DB in a ported box, but there are tradeoffs.

A sealed box will usually play lower, but you have a 12db/oct (IIRC) rolloff starting at ~60Hz (depending on box style). And, I can't remember the exact figure, but the speaker has to move (excursion) like 4X more each time you half the frequency to get the same output. So, to play low, there is substantial mechanical stress on the speaker suspension. This type of box is usually pretty easy to make though.

A ported box's main advantage is the frequency curve. The speaker's rolloff usually happens about the same point as the sealed box, but the port boosts the output more so the effect is more output. What is really neat is that at the port's tuned frequency, most of the sound comes from the port and not the speaker. Do a frequency sweep and you'll notice the speaker actually moves FAR less at the tuned frequency than it does above or below that. This is what is nice about them: you get good low end without as much mechanical stress on the speaker suspension. Frequency rolloff is 24db/oct below the tuning point though. Also, the port is basically just a hole for frequencies below the port's tuned point. So a subsonic filter is almost necessary. Usually larger than the sealed version. You also have to make sure the port is big enough so you don't get "chuffing", which is the noise the air makes through a port that is too small (air velocity is too high). However, the larger diameter the port, the longer it has to be for a given frequency, and may be difficult to physically fit into the box. And, you have to take the volume the port takes up when figuring out the size of the box.

Even though it is more complicated, I usually prefer a ported box. It usually sounds "punchier" for real music, but those very low (sub-30Hz) notes will not play well.

But, the ideal choice in box type is determined by some ratio (Qms and Qes IIRC), so the ideal box is dependent on the specific speaker. A lot of current speakers generally play well in both box types, so it becomes more user preference.

Not sure if you've seen this, but WinISD is a decent freeware box building program. Enter all your Theille/Small parameters and then you can model a bunch of what-if scenarios before the first board is cut: http://www.subwoofer-builder.com/WinISD.htm

[J57ltr]

Originally Posted by BrianG

A ported box's main advantage is the frequency curve. The speaker's rolloff usually happens about the same point as the sealed box, but the port boosts the output more so the effect is more output. What is really neat is that at the port's tuned frequency, most of the sound comes from the port and not the speaker. Do a frequency sweep and you'll notice the speaker actually moves FAR less at the tuned frequency than it does above or below that. This is what is nice about them: you get good low end without as much mechanical stress on the speaker suspension. Frequency rolloff is 24db/oct below the tuning point though. Also, the port is basically just a hole for frequencies below the port's tuned point. So a subsonic filter is almost necessary.

Another neat thing is that maximum output at the tuning freq the Impedance is highest meaning that it actually takes the least amount of power to produce the highest spl at that frequency. Below the tuning frequency though the ported box basically acts as though the woofer is in free air hence the need for a subsonic filter. The woofer has no "backpressure" or resistance to movment so you can physically damage it.

Ported boxes are my favorite I remember having 2 12" JBL GTI subs in a 3cuft (each) with 2 4" X 8.2" ports and with my 7600 on them we were hitting 141.2 in the 90's that was loud.

Jeff