MoFi Sourcepoint 8 or Q Acoustice Concept 50s

An amp with a high damping factor(almost every solid state amp) will not have any frequency variation due to wide speaker impedance swings in the speaker load. However as stated tube gear will show frequency variation because they always have low to very low damping factor.

By the way there will be frequency variation in the bass with low damping where there are impedance peaks from box resonance and port resonance.

@lanx0003 well luckily their amp isn’t a high output impedance tube amp. it is solid state AB amp with high damping factor so impedance mismatch isn’t going to be an issue here

@maam522a get the Sourcepoint 8. 

Have you had a chance to listen to either pair of speakers at your local dealers, or at a show?  Me, personally, I wouldn’t purchase the most critical component in my audio system (speakers) without first being able to hear them in person somewhere, somehow.  Seeing as it my be impossible for you to be granted an in-home audition, I would even travel a reasonable distance in order to audition.  Once I decided on the speakers, then I’d purchase, trade, exchange, amplification that synergizes with your speakers of choice.  Or, you could buy based solely on what you think would synergize best with what you already have.  You have subs, so you don’t have to worry about low bass extension.  Good luck.  Happy listening.         

@dynamiclinearity @kofibaffour   Well, it’s not as immediately obvious to me as it is to you two (and probably many others) why a higher-damping-factor amplifier is more resilient to frequency variation. I had to spend some time thinking it through and convincing myself.

By the voltage divider law (for two series resistors), Vi = Vo Zi / (Zi+Zo), where i = input (source) and o = output (load).  For a tube amp, assume Zo = 2 ohm. When impedance of load (on speaker) rises from 8 ohm (150hz) to 75 ohm (1.9khz), the voltage drop Vi/Vo = 8/(8+2) = 0.8 and the change in volume level = 20log(0.8) = -1.94dB, and then transitioned to 20log(75/(75+2)) = -0.23dB.  This transition leads to an increase in sound pressure level of 1.71dB.  The perceived increase in loudness = 2^(1.71/10) = 13%.

By contrast, for a SS amp, assume Zo = 0.05 ohm, performing the same calc. leads to an increase in SPL of 0.04dB, the perceived increase in loudness = 0.3%.  It’s immediately clear that the perceived sound-level variation caused by this impedance transition is much smaller for a solid-state amplifier than for a tube amplifier.

On the low end, the impedance transition from 8 Ω to 21 Ω results in about an 8.3% increase in loudness for a tube amplifier. It’s still an increase, but the perceived change in bass loudness is relatively less noticeable to the human ear. That might be why no attenuator is provided for it.