George, yes I saw that figure in the review of the MC275 V.
First, that figure is based on the 16 ohm tap (!), which per JA’s measurements has an output impedance of 0.87 ohms, which is well over twice as much as the 0.33 ohm output impedance of the 4 ohm tap (which is the tap that I presume would generally be used with most Wilson speakers). (Note that references to the 8 ohm tap appear identically in the captions beneath figures 1, 2, and 3, which is obviously a mistake, but the text makes clear which tap each figure applies to).
Second, the frequency response variation that is shown for the simulated speaker load, even with the 16 ohm tap, is within a range of about +0.4/-1.0 db, which doesn’t seem to me to be a big deal. Especially given that the dip of -1.0 db just occurs in a fairly narrow range of frequencies centered at a fairly high frequency, about 5 kHz. And for the 4 ohm tap the variation is within a range of an almost negligible +/- 0.25 db, as stated in the text.
Third, as I mentioned the output impedance of the MC275 VI is probably significantly less than that of the V.
Fourth, 0.33 ohms is a very small fraction of the impedances you quoted from Stereophile for the WP7:
-- Al
First, that figure is based on the 16 ohm tap (!), which per JA’s measurements has an output impedance of 0.87 ohms, which is well over twice as much as the 0.33 ohm output impedance of the 4 ohm tap (which is the tap that I presume would generally be used with most Wilson speakers). (Note that references to the 8 ohm tap appear identically in the captions beneath figures 1, 2, and 3, which is obviously a mistake, but the text makes clear which tap each figure applies to).
Second, the frequency response variation that is shown for the simulated speaker load, even with the 16 ohm tap, is within a range of about +0.4/-1.0 db, which doesn’t seem to me to be a big deal. Especially given that the dip of -1.0 db just occurs in a fairly narrow range of frequencies centered at a fairly high frequency, about 5 kHz. And for the 4 ohm tap the variation is within a range of an almost negligible +/- 0.25 db, as stated in the text.
Third, as I mentioned the output impedance of the MC275 VI is probably significantly less than that of the V.
Fourth, 0.33 ohms is a very small fraction of the impedances you quoted from Stereophile for the WP7:
Its impedance drops to 2.4 ohms at 78Hz and remains below 6 ohms for much of the region where music has its maximum energy (fig.1). In addition, an impedance of 4 ohms at 59Hz is associated with an electrical phase angle of -34 degrees, which will add to the drive difficulty.Finally, as JA said in the review of the V:
... the modification of the McIntosh’s frequency response due to the interaction between this source impedance and the impedance modulus of the loudspeaker was relatively mild.Regards,
-- Al