12π basshorn subwoofer

Only one 12π hornsub was measured, but according to models, a pair should run 143dB maximum output at one meter and a group of 4 should provide 149dB, with flat response +/-2dB from 30Hz to 125Hz. Single horn response is very good, but it is improved even more in groups, with deepest 30Hz bass output lifted to the 100Hz level.

See the chart below. Measurements were taken at 10 meters, so add 20dB to find the SPL at 1 meter. The blue line is is output with 65 volts input, roughly 1600 watts. In my recent tests of the heat exchanger, I found that the speaker can handle this level of contstant input power. Also notice the low distortion levels, which are shown by the violet line in the graph. Distortion is low across the entire range, but a particularly intersting feature is the low distortion below the horn flare frequency.

π basshorn subwoofer at 1600 watts

The distortion of most horns rises dramatically below cutoff, but that is not the case with the 12π basshorn subwoofer. Other basshorns make a chuffing sound when driven below cutoff. It sometimes sounds like a helicopter blade. What you hear are actually harmonics of the fundamental without the fundamental being present at all. The 12π does not suffer increased distortion at low frequencies, and is completely dead quiet deep into cutoff below 20Hz. As frequency rises to the 30Hz level and above, output rises steadily. At that point, the bass was loud enough to vibrate the entire countryside, modulating voices to the point that conversation was impossible.

I had already tested the heat exchanger on the woofers in free air, so I had a pretty good idea of what they would do. But while I had performed a destructive test on a woofer having no heat exchanger, I still hadn't seen a failure yet on a device with a heat exchanger. So there were two failure modes I wanted to see, to know the limits of the device. One was failure after extended periods, what I'm calling heat soak failure. The other was an instantaneous failure, one caused by extreme power levels provided to a relatively cool voice coil, one that hadn't been heat soaked.

We had intended to run a 15 minute heat soak period at the Prosound Shootout, which isn't really enough to truly saturate the drivers, but would provide enough heating to see what changes in performance resulted. But we realized after the first battery of tests that we may not have time to do them. So we omited the heat soak test.

Realizing that I could not heat soak, I decided to push the 12π basshorn well above its limits, to find the instantaneous failure level. We were able to run at 73.5v input (roughly 2000 watts), but failed at 80.5 volts input, approximately 2400 watts. From this, I would say the 12π basshorn subwoofer is able to handle 1600 watts RMS continuous, and 2000 watts peak.

Mechanical limits were never reached, with some extreme power sweeps starting at 10Hz. The driver did not sound strained at any power level, and it never reached a point of mechanical interference. The thermal limits were greatly increased using the heat exchanger, and distortion is reduced because of the push-pull configuration and horn loading. Distortion is incredibly low at safe power levels, and even at extreme over-limit power levels averages 30dB below the fundamental (approximately 3%) through the passband.

π basshorn subwoofer at 2000 watts

π basshorn subwoofer at 2400 watts

Are you going to post the rest on the prosound site? I don't want to steal any thunder by putting it on the Fitzmaurice site until you post it up.

Leland

About the power levels, I wanted to see if I could reach a mechanical limit or if failure was always the result of thermal stress. I also want to find what the limits are in various conditions. So far, I have not been able to create a mechanical failure, they've all been thermal whether by heat soak or instantaneous burst.

Is the small dip at 40Hz also present at 1W input? If not that dip may indicate some sort of powerdip. My AJ-horn software shows this powerdip at the same place. But Tako has already shown that computermodels may be off.

Nice to hear the 12pi did very well.

Best regards,

Walt

Sure was good to meet you and hang out. I hope to see you again in May at the Great Plains Audiofest, and also at next year's Prosound Shootout.

I would like to see a graph which compares the 12pi to the Tuba 36. I think the 12pi should be 5-10dB louder in its operating range when driven at full power

Best regards,

Walt