Well, the snow stopped early this afternoon and it turned into a bright, sunny day. Back at it, can’t let frozen sky-water stand in the way of science!
To start off, I added another terminal cup and converted the box to two 2ohm loads.
Step one: cut a hole in a box.
Rewired, and verified with dmm:
I also used the 9v battery test to confirm all drivers are correct polarity.
Haul everything back outside and get it all set up again:
I unbridged the amp, and put each 2ohm load on one channel. I used the dmm to measure voltage on one channel. I set up the minidsp to send identical signals to both channels.
Performed the same sweep test. Once again, ran into mic clipping and bad noises at the same time. This time, reran the trouble sweep while standing up at the cab. I discovered that what I took to be driver distress was actually the whole cab rattling on the dolly. I was able to stop it by putting my weight on the cab. Great, there goes yesterday’s results.
Continued running sweeps. The peak got cut off due to mic clipping, but the rest of the sweep continued to increase linearly. Eventually, increase stopped and voltage readings bounced around, I ran out of amp. I never heard driver distress.
I didn’t export this graph, I do still have the data. I consider it to be of limited use due to mic clipping.
I moved the mic to 4 meters, and started up again with the sweeps. I started at higher level this time, knowing it was safe from the 2m testing. 1db increments on sweeps.
I calculated the wattage for each channel using the RMS voltage displayed by the DMM, and the Re of 1.7ohm. I multiplied by 2 to account for both channels. I didn’t convert voltage to peak.
P = V^2 / 1.7 * 2
Here’s the resulting graph:
I left off the final sweep where the amp gave out.
Since I had invalidated my stopping point from yesterday, I popped the hatch and set it back up series/parallel. I verified polarity again with 9v battery test.
I set the amp up bridged, and performed the sweeps again. Started in 3db increments, switched to 1db as levels got high. Once again, I was able to increase until hitting the limit of the amplifier. This time, I just hit mic clipping on the final clean sweep.
Again, RMS voltage was used for wattage calculation. Re of 3.4ohm was used.
Once again, I left off the final sweep where the amp gave up.
Here’s a comparison of the final clean sweeps for both wiring methods:
What did I learn from this data?
Nothing definite. Other than the fact that this cabinet can put out some serious noise.
It doesn’t seem to be hampered by the over-excursion predicted in AkAbak for series/parallel operation. Or at least isn’t showing it.
The wattages I’m recording make me doubt my voltage measurement technique. Unless my amp is highly underrated, or just high distortion at these output levels. I wish I had a an oscilloscope to check waveform.
The spl I’m recording doesn’t jive with the model at all. If I’m correct, 4m mic distance should be down 12db.
Apparently my model-output level match from yesterday was just chance, from where the mic clipped at 2m.
Hopefully someone more experienced can help me interpret this data. As of now I’m pretty lost on what I’ve measured, and where to go from here.