Quote:


Thank you for asking!  Two problems... MKIV has too much power for good headphone jack performance and too little power for Harbeth speakers which when converted to a 1 watt / 1 meter sensitivity are about 81dB.  That's 10dB below the recommended minimum.  Below is the performance with the Harbeth/Torii MK IV combination.

1 watt =     81dB @ a distance of 1 meter.
2 watts =   84dB
4 watts =   87dB
8 watts =   90dB
16 watts=  93dB
25 watts=  95dB.

For every meter of distance greater than 1 meter, subtract 3dB.


An alternative approach would be using the 4 watt Mini-Torii with headphone jack paired with the DM945/6 speakers.

1 watt =     94dB @ a distance of 1 meter
2 watts =    97dB
4 watts =   100dB

The last Mini Torii that went out replaced an Audio Note 300B amplifier driving similarly efficient Audio Note speakers and the owner is quite happy.  The DM945/6 speakers are over twice as fast as the Harbeth with the same silky smooth tone, so they too could be an upgrade.

Thanks,

Steve

Fast is the time it takes for the speaker cone to change direction.  The higher the mass of the cone, the harder it will be to stop it from moving in one direction and start it moving in the opposite direction.  Efficient speakers have cones that are low in mass, in extreme cases almost 10 times lower.

A high mass cone requires an amplifier with a lot of power and damping (negative feedback) to help control the cone from overshoot.

There are only two reasons for high mass speakers cones.... makes the driver resonate in a small box and has less peaky response or is more immune to colorations from the enclosure due to the the damping effect of thicker cone material. It's the easy way out.

Part of the speaker power recommendation could come from losses in the crossover that are hard to resolve on paper, and or the damping factor needed to keep the speaker from sounding muddy in the bass.  This damping factor is typically found in push-pull amps with negative feedback in the 50watt or higher range.


-Steve

"I assume the damping factor is a major factor."

Anything above 20 is meaningless.

Yes, it is!

I rarely get it above 1/4 volume on my preamp. However, the sound quality and detail I am getting at very low amperage is amazing. My speakers are known for being difficult to drive.

In conversations with other owners ( after I bought them ) I found out that many people use 400 wpc or even 500 wpc. I heard them with a McKintosh 602 amp, 300wpc, and the dealer told me I really needed a more powerful amp!

Its sort of like using a big block engine vs a small block engine. The torque of the big block just make towing work.

If you have extremely sensitive speakers, you can use a small amp. My first stereo was a Telefunken, class A amp, V250 model. It drove my Telefunken speakers and sounded amazing. All with 25 wpc..

I am now back to the Telefunken sound I had nearly 45 years ago.