I've managed to carry out some low frequency (15Hz to 300Hz) on two different subs placed in the same location to gauge the difference in THD measurements.
The setup included placing the subs in the front left corner of the room - same location. The sub distance is the about the same (off by 0.1 ft) as advised by the AVR. The volume levels were different depending on the amp plate settings. The noise floor as advised by the calibrated UMIK-1 mic from CSL is just under 70 dB, a bit high as the handheld meter says 55dB.
KEF E301c center speaker was used in both instances. Main Volume kept constant at -15dB. Audyssey was engaged, Dynamic EQ and Dynamic Vol were OFF.
The first graph is that of the new Rythmik F12G. The maximum THD is just below the noise floor of 70dB with a maximum value of about 6.5%.
The second graph is that of the old HTIB boom box (Minstral). Notice that the THD is really high, with maximum value in the 270%. This is audible and the sound quality is very objectionable.
While these are two extreme examples of THD measurements for the sub, I'm not sure where to draw the line in terms of acceptability. I do prefer the sub that has the lower THD in sound reproduction.
Marantz SR-7009, Oppo BPD-93, MTV 7000D, aTV, Harmony Home Control remote, KEF E301+T101, MiniDSP (2x4)+(10x10HD)+(DDRC-88A), Emotiva 2xXPA-5 (Gen2), Rythmik 2xF12G+2xF8, HiMedia Q16, LG 55EC9300.
Last edited by steveting99; 07-02-2014 at 12:54 AM.