Tom Danley wrote on Sun, 04 November 2007 19:18 |
As you might be aware, at the Michigan subwoofer shoot out, where the labs were measured, they had the lowest distortion of all the speakers there. (look up the curves on line). That same driver linearity is how people have been able to use them in living rooms eq’d to extend the bottom.
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I did a quick search of the internet to find the distortion measurements from the Michigan shootout in 2003. There are some differences between the Tulsa data and the Michigan data that make this less than an "apples to apples" comparison, but I think it is still good information.
The graph below is distortion of four LABhorns measured with "9-12 volts input". I'm not sure why the voltage wasn't recorded more precisely than that, but in any case,
that's less than 40 watts.Since the LABhorn presents about 4Ω load impedance, 9 volts is 20 watts and 12 volts is 36 watts. We're only talking about 10 to 20 watts per woofer being sent for the distortion measurements. I wouldn't expect much distortion at these power levels, because they're so low.
Having four horns is an advantage too, since loading is better at low frequencies than what you would get having just one horn. So again, this comparison heavily favors the LABhorn, with the very low drive voltage and the use of four horns instead of just one.
As you can see, even at just 10v, distortion at 25Hz is already at 10%, rising rapidly at frequency falls. As one would expect from a basshorn, it is lowest in the passband, but rises rapidly at the cutoff frequency. From 35Hz down, distortion ramps up heavily, already above 3% at 30Hz even at the low drive level of 10v. By 20Hz, it is at 30% distortion, again, at only 10v input signal.
These figures aren't unexpected. If you double the drive signal, you'd see that distortion would be louder than the fundamental at 20Hz, probably also at 25Hz. At 30Hz, distortion might be about equal to the fundamental, or maybe slightly less. If you increase drive even more, nearing maximum power, distortion of the LABhorn would be even worse. This is no slam of the LABhorn, all basshorns are like this. They work best when used in their passbands, and as you get close to their lower cutoff frequency, distortion rises rapidly. That's just the way it is.
Except for the 12Pi with its push-pull drive. Look at the charts below. The blue line is SPL and the violet line is distortion. This is a single horn, run at 28.3v -
three times the drive voltage as was used to test a group of four LABhorns.
Notice that distortion doesn't rise at low frequencies like it does on other basshorns without push-pull drive. This makes a cleaner, tighter sounding bass. Everyone notices it right away. The distortion is so low at this 28.3v drive level that we really can't see it - it's mostly below the noise floor.
The distortion curve is shown in decibels, and to convert these values to percentages use the chart at the link below. The noise floor was about 70dB, so anything below that is indeterminate.
Now the real nut cutter. How does it perform at higher power levels? See the link below: