- Written by John E. Johnson, Jr.
- Published on 18 June 2014
The Bryston Middle T Speakers On the Bench
For distortion measurments, the test microphone was placed 1 foot from the respective driver. For the low frequencies, the microphone was pointed between the two 8" woofers.
At 20 Hz, and 90 dB output, distortion was less than 10%. This is a number that many dedicated subwoofers cannot produce.
The ports are tuned to 28 Hz, so the test at 25 Hz showed 21% THD+N. At this frequency most of the sound is coming from the rear ports. However, we listen to music from the front, so I measured it that way, and the speakers were 6 feet away from any wall. In your home, the speakers would likely be a foot or so out from the wall, and the bass from the ports would reflect from the wall. Distortion at 25 Hz and 90 dB in front where you sit, taking into account the wall reflection, would likely be midway between what it would be at 20 Hz and 30 Hz.
At 30 Hz, distortion was less than 5%, which, again, is excellent.
A 40 Hz test signal produced only 1.2% distortion.
And at 50 Hz, less than 1%.
So much for the woofers. Let's move on to the midrange driver. At 1 kHz, distortion was less than 1%.
And for the tweeter, a 10 kHz test signal. Distortion was really low, at 0.3%.
The room frequency response, at 2 meters, is shown below. First is an on-axis response, and then a 450 off-axis response. You can see that the off-axis response attenuates some of the very high frequencies above 18 kHz, but the midrange comes up a bit, actually making the overall response flatter. So, I would suggest not toeing in these speakers, as the sweet spot is off-axis, in my opinion. Since my favorite listening chair is off-axis, that's just fine with me.
The impedance/phase plot is shown below. The impedance spread would suggest the Middle T to be a nominal 8 ohms rather than the 4 ohms specified (Bryston tends to be conservative). This is a very easy speaker to drive. The phase is + 300 to - 100, which is very good performance.