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I would expect both amplifiers to have a sufficiently high damping factor that the difference in output would be negligible. After looking through a bunch of Stereophile measurements, I am seeing at most a 0.25 dB difference between typical Class-AB and Class D frequency responses due to load. The SMSL SA-50 amp uses the TDA7492 chip. The datasheet does have the frequency response curve showing -0.5 dB down at 40 Hz and -2 dB down at 20 Hz. IIRC Frank's solid-state amplifier designs try to push the -3 dB point very low, like single Hz range. It seems more likely that the difference in excursion is related to the amplifier AC coupling at low frequencies.If I knew more about speakers, I would attempt to calculate the difference in excursion for woofer when given a 0.5 dB difference in signal. Though I am sure it is not that easy without knowing specific driver characteristics and box/port loading of the speaker.Cheers,Curtis
Seems these amps have different damping factors what lead to different behavior on bass freq.
It would have to be a very large difference indeed to have any affect. (or on second thought maybe it's effect)
It might very well be the high upswing at 70hz?
No, the port damps the cone very strongly at frequencies around the port tuning frequency, so you won't see much cone movement there......and both of these low-impedance SS amps will totally ignore the load impedance of the speaker, so those tall peaks around the port resonance won't affect FR at all. But it's good practice to make the speaker load impedance flat and smooth as possible because that makes life easier for amps with higher source impedance (tube amps) which are more sensitive to load impedance, so that a flat FR can still be achieved no matter what amp. Not so common practice anymore, kudos to Philharmonic.
The origin of the phenomenon has been explained by other members.
