car audio

[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