Speaker's efficiency, sensitivity and impedance

A speaker's(or speaker system's) efficiency/sensitivity rating is determined by it's SPL output in DB with a 1 Watt(or 2.83v) input, measured on axis at a distance of 1 meter(in an anechoic chamber). The speaker's impedance is not relevant in this measurement.

Looks like you've got an impedance obsession disorder!

Would you buy a car based on the sole parameter of engine displacement? If I told you one vehicle had a 6.2 liter engine and another had a 7.8 liter one, would you be tempted to say which one is the fastest?

The displacement number alone tells you nothing. It is a lot more useful to know the smaller engine goes in a Corvette and the larger one is a diesel from an Isuzu delivery truck.

A speaker's efficiency is due to many factors. Magnet type & strength, precision of voice coil gap, the number of turns on the coil winding, the voice coil gauge, diameter & other physical attributes, cone, spider & suspension materials and design, size, crossover design and cabinet design and more are involved in the performance of a speaker.

I'm curious as to why you are so intent to reduce such a complex issue to such a limited, simplistic view.

Chris,
I feel for you, it appears as if you are hung up on amps lately. I assume for your sound labs- forgive me if I am wrong.

Sensitivity=efficiency= how much power(watt) for how much sound(spl)-typically measured in db/w {decibels(perceived loudness) per watt(measure of power)}.

Impedance is AC (alternating current) resistance and is not related directly to sensitivity. Impedance pertains to the load characteristics of the speaker. A watt is voltage x current and ideally the amplifiers output impedance should match the speakers input impedance for proper power transfer between the two. Sort of like being in the correct gear in a vehicle in so that the motor is in the correct rpm range. Extra horsepower (kph) can overcome being in the wrong gear somewhat, but usually at the expense of "nimbleness"- engine lugging. Ultimately this becomes complex quickly as impedance often varies with frequency. If there were an easy answer someone would have capitalized on it by now. Contrary to what we read in the magazines, there really are very few "new developments" in audio. One of the reasons Western Electric gear is so sought after is they had the budget and the market for doing a lot of R&D. Way mor so than any company since. Often what we see are a rehash of their's and other's experimentations, or that manufacturing technology has advanced in so that their research is affordable to produce for a marketable product. The best amp I know of was never made for consumer use, but as a piece of test equipment not related to audio (and no, I'll not tell what or my friends will hang me for letting the cat out of the bag!). If you are still looking for an amp for your Sound Labs you really ought to give the JC-1's a go. Better yet, Pass Labs if you can afford it. I know you think they are mid fi, and maybe they are. However they offer a lot for the money and are not "clunky" or as you have put it "mechanical".

Well, my answer is a little bit different - so I guess you get to take your pick!

Unfortunately the relevant terms get used inconsistently or imprecisely, leading many people to think that efficiency and sensitivity are the same thing.

Here is the convention that I follow. Some manufacturers also follow this, but not all.

As commonly used in consumer audio, "efficiency" is the 1 meter on-axis broadband anechoic SPL that a speaker delivers with a 1 watt input. Some manufacturers use a non-anechoic measurement (including room contribution), and some use a peak somewhere in the response curve instead of using a broadband average - so comparing two manufacturer's numbers may not really be apples-to-apples.

"Sensitivity" is the 1 meter SPL the speaker delivers from a 2.83 volt input. Sometimes called "voltage sentitivity" to make that clear. The same opportunities for optimistic specs enter the picture - namely, using non-anechoic conditions and/or taking the measurement at a peak rather than using a broadband average.

So, to recap: Efficiency is related to Watts, and Sensitivity is related to Volts.

(Some manufacturers use these terms interchangeably or backwards from this convention, so it's up to you to read carefully and figure out what they're really saying. Look and see whether they are talking about 1 watt input, or 2.83 volts input.)

Now, here is how the two are related: 2.83 volts into 8 ohms is one watt; 2.83 volts into 4 ohms is 2 watts; and 2.83 volts into 16 ohms is one-half watt.

So if you have a 4-ohm, 91-dB/2.83 volt sensitive speaker, it's an 88-dB/1 watt efficient speaker. If you have a 16-ohm, 85 dB/2.83 volt speaker, it is also an 88 dB/1 watt efficient speaker. I prefer to convert back to watts, because you can usually figure out the amplifier's maximum wattage output into a given load more easily than you can figure out its maximum voltage output (which may or may not vary with load, depending on the amplifier), and because if you are interested in power handling then you want to know the wattage going into the speaker.

Hope this helps.

Duke