impedance vs sensitivity

Sensitivity and Efficiency are two specs that try to express the same thing from different points of view. The different points of view are the Voltage Paradigm and the Power Paradigm, which are opposing concepts of how to design and test amplifiers and loudspeakers. For a complete explanation see

http://www.atma-sphere.com/papers/paradigm_paper2.html

Efficiency is 1 watt measured at 1 meter. Sensitivity is 2.83 volts measured at 1 meter. If you work the math, 2.83 volts is 1 watt into 8 ohms. Into 4 ohms it is 2 watts, IOW if you have a speaker that is 92 db 1 watt/1M, it will be 95 db 2.83V/1M, if it is also a 4 ohm device.

The Voltage Paradigm, which mostly describes transistor amplifiers, has no use for the Efficiency measurement, which is a Power Paradigm specification. Amplifier power and impedance are not the same thing; if you have a low impedance speaker that is also high sensitivity, a low power tube amplifier will be able to drive it just fine as long as it is able to get a good match to the speaker.

FWIW these days there is little argument for 4 ohm speakers in high end audio. This because regardless of the amplifier technology (transistor, tube or class D), the amplifier will sound better and perform better on higher impedances. Of course, if you are unconcerned about sound quality, and more interested in sound pressure, than 4 ohm speakers will be more attractive if you also own a solid state amplifier. The other argument against 4 ohms is the speaker cable- they are extremely critical for best results on 4 ohms, while at 16 ohms they are not nearly so. Making a speaker to be higher impedance, all other things being equal, is an easy way to make the speaker appear that it is smoother with greater detail, always a desirable combination.

Atmasphere - I read that speakers, before SS became popular, had much higher impedance (32 Ohm or even higher)?

Yes Kijanki, in the 1950s 16 ohms was common and there were 32 ohm speakers as well. Four ohms really didn't get popular until sometime in the 1970s.

Atmasphere

Regardless the rated impedance of the loudspeaker, doesn't the curve of it's impedance linearity play a more important role?

I mean some speakers, my own included profess an impedance level of 8 ohms... but in practice, delve to far lower means in common usage.

From merely the numbers/specs of an amp or a loudspeaker system, can one derive some methodology for pairing amps to speakers, or vice versa?

For instance, with your amplifiers, do you forewarn anyone as to the speakers with which they are not at their best? ....or are there such speakers?

About the only guidelines I've been able to hang my hat on are these... with 250wpc SS power, there aren't too many speakers such an amp won't drive well. ...and conversely, if a tube amp has 100+ wpc, speaker choices are pretty broad too.

The difficulty I've run into has been matching amps and speakers when the power levels of the amps get below 40 or 50 wpc.... or the speakers have exceptionally tall impedance, and a SS amp is the power plant.

The former interests me greatly, the latter not as much, though I thought to include it as the antithesis of the formers train of thought.

Thanks...

Atmasphere - If you can remember 70's it means you weren't there. I remember The Beatles playing on 30W VOX amps and people tossing LUXMAN tube amps to get beautiful and modern transistor amps. These SS amps often had rated unmeasurable THD and IMD distortions and had a lot of power but sounded like crap because of deep negative feedback and tons of TIM distortions.