Speaker recommendations for Proprius based system?

Hi Phil, you'll be familiar with the name Nyquist? (the sampling theorem guy who didn't live to see his theorem in use - died 1974).

A little known fact is that he also had other theories. One being for push-pull power amplifiers (which all are these days in one way or another).

He reckoned that the output devices only needed to be rated at 1/5th of the rated output power, so I could get away with using 5 watt power transistors. I'm sure old Harry Nyquist was right for a purely resistive load, but speakers are inductors and not pure resitance.

Those following the Frugel Horns and other DIY discussions will have noted the impedance graphs for the drive units. All drive units have impedance graphs and it can be seen that the rated impedance is a nominal figure. It can fluctuate either side.

When two or more drive units are required to span a greater frequency range, a crossover circuit is required, and the outcome is an impedance curve that has dips and peaks. I don't believe any decent loudspeaker manufacturer would make a speaker that dips as low as the scaremongerers tell us... how would they ever sell their wares?

But they do have dips and peaks, and the impedance dips pull more power (unless you use a valve amp where the output transformer won't allow that... think series resistance).

We could go on about inductance and capacitance and phase differences but it all boils down to the impedance curve and the dips caused.

So old Harry didn't factor these dips in... he didn't have to! After all he was talking to engineers in his theories. The engineer understands that the power needs to be high enough to drive these dips, then he can divide that power by 5 and old Harry's theorem of the output devices power rating holds true.

Even so, it's good to over rate output devices for short circuits.

So, in the 25 watt @ 8 Ohm Proprius the dips could demand a lot more than 25 watts. And here I'm going to run through it in reverse engineering...

I use 200 watt output transistors. By Harry's theory they should deliver 1,000 watts.

This is obviously limited by the power supply, which can only do 120 watts, but that's a continuous rating. I don't know exactly what its rupture rating is, and when it detects an overload due to a shorted Proprius output it shuts down.

The belt and braces Proprius back-up fuse is a 2A quick blow which in 0.01 seconds (100Hz) takes 20 Amps to blow remains intact. That suggests the power supply shuts down at getting close to 1,000 watts.

Therefore I would not worry too much about the Proprii's capabilities.

89 dB sensitivity is so close to 90 dB sensitivity as to make little difference. The 6 Ohm 83.5 dB Harbeth's easily fill a 220 sq.ft space, and the 11 Ohm 82dB LS3/5a you've heard. The speakers you're talking about will do more sound pressure level than those.

Graham

Phil,

My speakers are of the following spec:

Sensitivity - SPL/m/2.83V 85 dB
Nominal impedance - 8 Ohm

The Proprius have absolutely no problem driving these. In fact the speakers are now sounding better than I can remember before.
The last amp I used was an Arcam Alpha 10. 100w per channel into an 8 Ohm load.
With an 89dB sensitivity, I wouldn't even bat an eyelid at the thought of a compatibility problem.

msphil wrote: RichW wrote: Phil, if you get the chance do try to hear some Audio Physic speakers. Very musical -  clarity, detail & soundstaging are superb with no excessive brightness. Efficient & easy to drive.       Hi Rich, I think, if I've got it right, the Audio Physic is a German speaker. I did read some good things about them. However, I don't know how I would manage to find a dealer that stocks them near to where I live.