Hey Clinton. What microphone set up did you use with the RTA and was it calibrated for you or did you use a calibration chart for that model? I noticed the roll off at 20Hz and wondered if that was the mic or the sub
Hi, Thomas. Probably some of both. Since you asked, this was the measurement signal chain:
Outputs:
* MOTU 24I/O (20Hz – 48kHz, +/- 0.2 dB). Why 20 Hz? Assume it rolls off some below that.
* DBX 223 active crossover (20Hz – 20kHz, +/-0.5 dB) / (3 Hz – 90 kHz, +0/-3 dB).
* Peavey 4080HZ (10 Hz – 35kHz, +0/-3 dB at rated 4 ohms power).
Inputs:
* Uncalibrated Behringer ECE8000 measurement mic ("ruler-flat from 15 Hz to 20 kHz"). Yeah, right!
* ART Tube MP preamp (10Hz – 40KHz, +/-1 dB).
* MOTU 24I/O (20Hz – 48kHz, +/- 0.2 dB).
So each of these could have contributed a little roll-off below 20 Hz. So taken all together, the sub is likely much better at 16 Hz than measured.
I designed for a 3 dB roll-off at 16 Hz, so given the above, the measured results aren't too far off. For a more typical box I could have tweaked the port length to flatten the measured curve a little more, but for added strength I fixed the port into the structure of the cabinet. Given the likely measurement errors, I think it's not worth tinkering with.
This configuration models 119 dB at 16 Hz with 1500 watts input. Even if the actual value is a bit less, it's plenty.