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On the Bench The calibrated microphone was placed 12" from either the ports or the driver, depending on which produced the highest SPL. For the frequency response measurement, the microphone was place 1 meter from the driver. All bench tests were conducted with both ports open (a foam plug is supplied that can be used to change the tuning by plugging one of the ports). Using a combination test tone consisting of 20 Hz, 31.5 Hz, and 50 Hz, I was able to get a maximum output SPL of 116 dB without the Turbo, and 115 dB with the Turbo, at 1 meter. At 20 Hz and 100 dB output, THD+N was less than 4% without the Turbo Charger. This is very good.
With the Turbo Charger in place, THD+N went up significantly at 20 Hz. This is the price of the 16 Hz extension that the Turbo gives.
At 25 Hz, THD+N was less than 3% without the Turbo. Again, very, very good performance. This is that new driver technology in action.
With the Turbo in place, THD+N went up to just less than 10%.
At 31.5 Hz, THD+N was 5.5% without the Turbo, and with the Turbo it was . . .
just above 5%. So, by the time you get to 30 Hz and higher frequencies, THD+N with the Turbo is the same as without it.
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