Does anyone care to ask an amplifier designer a technical question? My door is open.

@prof 

I could really use some help betting a better grasp of amplifier/speaker interaction. Specifically, in what sense a speaker is "easy to drive" for an amplifier.

This seems to generally relate to two parameters:

1. Speaker sensitivity
2. Speaker impedance (and phase angles etc).

I’ve seen speakers with higher sensitivity but lower or wilder impedance termed "easy to drive" and speakers with lowish sensitivity but higher and smoother impedance being "easy to drive." So I’m trying to get a grasp on what it means...in practical and possibly sonic terms...when a speaker is "easy to drive"for an amplifier and what you get when trading off sensitivity vs smooth impedance.

To turn it in to a practical example:

I owned the Thiel 3.7 speakers. Here are the Stereophile measurements:

https://www.stereophile.com/content/thiel-cs37-loudspeaker-measurements

Note the 90.7dB sensitivity, but with it seems a fairly challenging impedance.

***********GREAT QUESTION, EVERYONE READ THIS**************

Ill take this one speaker at a time. The 3.7 is THE speaker that birthed the RM9-SE and RM-200 designs. Those are AB2 designs that use positive grid voltage to extend the output current range of an AB1 amplifier. We had a MK1 RM-9 customer who was going through output tubes at an alarming rate. The speaker and his love of Miles was driving the tubes hard.

First, JA did not point out, as he now does that 2.83 volts is NOT the proper voltage for a 4 ohm speaker. Its 3 dB too high so the 4 ohm sensitivity of the 3.7 is 87 db. Its even worse because this it a 2.5 ohm speaker so take off another 2 and make it 85 dB. So its really not a very efficient speaker.

I made the RM-200 with taps down to 1 ohm for speakers like this to preserve the damping, reduce the tube stress and lower distortion. The 2 ohm tap on the RM-200 is ideal for this speaker. Mismatching the load on a tube amp makes it work really hard. This is a 2.5 ohm speaker so good luck. Many SS amps will not play this speaker well.

Thats your the gist of question #1. 

#2. Phase angle..

As the phase approaches 90 degrees the output devices have both full voltage and full current across them. The dissipation in SS or tube amps goes wildly high. SS amps are sure to current limit, tube amps just take it. This is why tube amps have a reputation for driving such loads at the 3.7 and ESLs.

Thats all for now. This great question deserves several parts. Anyone please feel free to ask as we go for clairfication.

"Musicality" term used to express a fatigue free listen . Still as resolving as anything but probably not boosting any frequencies . Hence fatigue free . No distortion as well .

Hi Ramtubes,
In response to my query about damping you asked for a link to Hegel
which is:
 https://www.hegel.com/

You will see they describe what they put into their components,  also when looking up integrated amps, the damping factor is specified eg their starter amp H90 is only 2 x 60 watt in 8ohms but the damping factor is over 2000 therefore capable of handling above average difficult speakers (but not mammoth difficult speakers!) As they quote " The grip, or damping factor as it is called, is up to 20 times higher than the industry average. Ensuring a dynamic and powerful bass response, even on larger floor standing loudspeakers."  

i’m late to thread but have a perplexing question. 
i own an expensive ss amp and leave it on 24/7.
i could turn it off when i’m not going to use it for a few hours as well as overnight. for amp longevity what is best? thanks

Are you familiar with Primare's UFPD power technology? Is it pure Class D or something else?