speaker effiency

Jim, you seem to be very knowlegeable in this field. Please read my post in the "Sound Advice" catagory labeled Speaker Enclosure and let me know what you think. I have a bunch of scrap black granite from scrapped counter tops and wondered if it would be feasible to make the material into speaker enclosures. I have downloaded some software and done some preliminary calculations to see if I have enough material. It seems that I have more than enough so I was just curious if there are any caveats with the fabrication. I may try it as a winter project but thought I would run it by some people who are more knowlegeable than I before investing any time. Thanks in advance for the help.

They are quite distinct from each other. dB/watt is the sound pressure level converted from 1 watt of electrical power signal. For 'speaker specifying purposes a 'speaker of 90dB/watt is said to be more efficient than another of 85dB/watt. The numbers have little relation to the quality of sound produced. This parameter is used by audio engineers to design their products and similarly applied to audiophiles to mix and match their different choice of poweramp/speaker combination in a less haphazard manner.

Okay, I wan't to pose an honest (as opposed to rhetorical or provocative question) regarding efficiency vs. sensitivity. When comparing two speakers driven by the exact same amplifier, would the more efficient speaker (as cogently defined by Spkrplus) also be the more sensitive one? Logically, this would seem so, but I'm not sure if I'm missing another fundamental part of the equation. Would there be a circumstance where a speaker that is less efficient at converting electrical to acoustic energy is in fact more sensitive than a speaker that is less efficient? Thanks in advance for the enlightenment.

All things being equal, the more efficient speaker will also produce a higher sensitivity rating. The only reason that it would actually produce a lower SPL is if it was a very low impedance and the amp could not properly drive it. While most amps do not have a problem with higher impedance loads, dropping the impedance or using a speaker that is highly reactive can give some amps fits. The more difficult the speaker load, the less options that you have in amplifiers. Thiel's have always been known as "power suckers" even though their sensitivity rating is reasonable. They are a little tougher to drive than most other speakers and as such, require an amp with TRUE "hi-current" output. As to Jim's statements about efficiency being measured as a percentage, he is correct. As we've all seen, sensitivity and efficiency are often incorrectly interchanged for each other. Most speakers are VERY, VERY low in terms of efficiency even though you might see what we normally think of as being a very high sensitivity rating for them. Sean >

Spkrplus is correct in his differentiation of efficiency and sensitivity. Ask a speaker manufacturer what the "efficiency" of a model is, and in all likelihood, THEY DO NOT KNOW. It is a very complex thing to ascertain. I recommend that when you are seeking specs on a loudspeaker, you look at sensitivity, an impedence plot(rather than a nominal value), AND a plot of the phase angle. Phase angle is the most underappreciated spec in this whole argument. By, looking at the impedence and phase angle plots, you can often garner more information than you realized. By looking at a few specs provided by a manufacturer, we are often misled that a given loudspeaker will be easy or difficult to drive. In the real world, many speakers play a lot different than the spec in the literature. Another thing, if you can find out which drivers are used in the speaker, you can often go look at an spl(and impedance) plot(from the driver manufacturer). While this doesn't factor in the effects of the crossover, it can often tell you a lot. Example, if a driver's sensitivity is 88 dB/2.83V over most of its operating range, peaking at 92 dB/2.83V @ 1500 Hz, you can best believe the number you will be fed will be 92, when actually the number is more like 88.