Re: Subwoofer comparison SRX728 vs Vertec 4883
TJ,
Sorry for the delay. I'll try to fill in the blanks in this thread as time allows, but this week got really busy.
Regardless of what the marketing department says, the impedance curve doesn't lie 
This is a vented box design tuned to about 40Hz.
A bandpass box has the same general limitations I discussed above as a ported box, as it is one or two Helmholtz resonators in series with the driver.
A sealed vented bandpass box will have the characteristic double-humped impedance curve of a standard vented box, but tuning frequency will be much higher. The sealed vented bandpass will have one excursion minima at this tuning frequency, and the sealed enclosure will reduce the excursion at lower frequencies, with the concomitant reduction in output.
A tapped horn, double vented reflex, or classic "Scoop" enclosure will show a double excursion minima and a triple humped impedance curve. A scoop and a tapped horn will also show additional humps in the impedance curve outside the sub passband at higher frequencies.
Power handling means very little. The AES standard power test rolls off at 50Hz, and therefore is testing primarily for thermal dissipation, as the driver is more than likely not excursion limited at this frequency. Both of the JBL drivers in question have Differential Drive configuration with a 3" voice coil, so that they have the same AES power rating is not surprising.
With real world music signals that extend below 50Hz and have higher crest factors, the excursion limit will be reached before the AES power handling limit. Also, to keep the driver T/S parameters reasonably stable, and therefore the box performance reasonably linear, its is a good idea to limit long term power input to the driver to 5-6dB below AES rating for the typical modern top-shelf driver.
