Speaker efficiency is the measure of how effectively a speaker can turn electrical energy in sound pressure. This is usually specified as db/watt. In simplistic terms, you can expect to have a specific sound pressure level for a specific power level applied to the speaker. Your power amplifier can pass more power into a 4 ohm load than an 8 ohm load, therefore, the higher power level presented to your 4 ohm speaker would result in a higher sound pressure level even though the efficiency is the same.
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"Efficiency" is commonly mistaken for "sensitivity", as shown by the above poster. Efficiency is expressed in percent, representing how much electrical energy is converted into acoustic output. Both above postings are concerned with sensitivity, which is usually expressed as dB of output measured at 1M from a particular point of the source, with 1 watt input. This is complex, as different measuring points for the pick-up microphone will produce different results. Also the source's radiation pattern affects its rate of attenuation as a function of distance. The difference in output could be attributable to mistaken manufacturer specifications or a result of the 4 ohm speaker drawing twice the voltage of the 8 ohm speaker, or both. The question of whether or not the sub will match output is best answered by trying it out.
Efficiency is almost never (correctly) used anymore. It's useage in general has become less common since approximately the late 1960's. I know useage determines definition, but this is something serious students of the loudspeaker art & science would defend steadfastly, & the differences are worth noting. Sound & Vision Buyer's Guide 2001 (Glossary page 338) defines "efficiency" as "The percentage of electrical input power going to a speaker that is converted into acoustic energy; often used synonomously with the related concept of sensitivity." Not "is a synonym", and not "always interchangeable with", but rather "used synonmously". A girlfriend who has performed "wifely" functions can not successfully sue for divorce. Also it does not say "identical concept" or "same concept", but rather "related concept". The measurement units "percent" & "dB/watt/meter" are not always interchangeable, & not in this case. In this case "percent" expresses how much of an amplifier's power is converted into acoustic energy, while "dB/watt/meter" expresses a specific unit of sound pressure measured at a particular distance from the source with a specific measure of power applied. For instance 87% can not be compared to 87dB/watt/meter for (I hope) obvious reasons. In the former, 13% of the applied power is not converted into acoustic energy, whereas in the later, that percentage is unknown & undecipherable (form the information given, anyway). I respectfully request poster Gm to list the specific Vandersteen literature mentioned. Richard V. or anyone in his tech. dept. would agree with me & Sound & Vision. Likely the copy, if published by Richard's company, was written by an ad person who does not even know what absolute polarity is. Other reliable sources would be Brian Cheney, the San Francisco Bay Area Chapter secretary of the Audio Engineering Society ([email protected]) or Galen Carol at Galen Carol Audio, who was in the technical dept. at JBL when it was known as James B. Lansing Co. If this all seems too trivial, I apologize, but as the great Jack Webb used to say, "Just the facts, m'am. Just the facts". This is a good thing about which hobbyists should know & agree upon the differences. Cheers.
I, being the lovable audiophile with some degree of Scotch-Filipino temper to control, will do my best to keep this all civil. Will forward reply from Galen Carol (ex-JBL factory speaker driver techcician) upon receipt. There are eight Stereo Review/Sound & Vision Equipment Directories nearby going back to 1980 (twenty years ago) that agree with me & the secretary of the local Acoustical Engineering Society, & disagree with the above posters & (at least partially, keep reading) the Vandersteen website's useage of the term "efficiency". Here is the response from Brian Cheney, sec. of the local AES: "Sensitivity is measured in dB SPL per W input at distance. Efficiency is the ratio of acoustic output to electrical input. Low efficiency might be around 1%, high efficiency around 5%. Vandersteen is being sloppy. B" Here is the summary of my phone conversation with Richard Vandersteen this morning: Richard admitted to me that he has never seen efficiency measured in percent, & that he only started in the business in the mid-'70's. This is consistent with my earlier post that "effficiency" has fallen into more recent misuse. When he was told of the "classical definition" & "unit of measure for efficiency", he admitted he "may be wrong". He is wrong, as are the above posters. He also said he would not charge customers a "2%" surcharge just to fix all the literature. He got snippity & used the term "bullshit". I proposed changing the website. You will have a hard time finding another speaker company using "efficiency" the way he does because I know of none, & I do a lot of reading on this subject. It will take a little more weight than one speaker company & website posters to change it's accurate technical meaning. I use the following information to further impeach Mr. Vandersteen: am I the only one who notices a lot of photos of boxes next to the word "boxless" describing Vandersteen's products? Does "boxless" mean the same as "box", or is Richard just generally careless with his website content? He also admitted that sensitivity is misleading & that it gives the customer little to no indication of output, which means he is presenting misleading information to readers. Also, I know none of the above posters have seen efficiency units as percent, but no one has presented evidence contradicting my above proof that there is such a thing as an audio definition relative to speakers which is: the percent or ratio if acoustic output to electrical input. I propose the term for which this is a definition is "efficiency". If you disagree, what is the term for which this is a definition? Jim Romeyn, Petaluma CA
A light when on when you first mentioned Vandersteen. I remembered in the early '80's seeing Vandersteen use "efficiency" incorectly. "Efficiency" (measured in percent) was, as I said, fairly commonly used in the early days with lower-output tube amps & high sensitivity speakers. This was later inverted. Solid state made watts cheaper, so speaker designers had the freedom to make lower-sensitivity speakers. "Sensitivity" became the term of choice. But the true original meaning of efficiency & its unit of measure (percent) has never changed. Since then people have come along unfamiliar with it. Peace. Jim
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.
I read somewhere that the reason that the term "efficiency" has fallen into disuse and "sensitivity" has supplanted it as the preferred terminology for describing a speaker's ability to convert an electrical signal to sound, is simply because, as stated by one of the above posters, normal efficiency for dynamic loudspeakers is between 1% and 5%. Supposedly, in the 70's, many speaker manufacturers decided, for marketing reasons, that an "efficiency" rating in the low single digits would cast a negative light on their products. Even combustion engines are more efficient, by somehing like an order of magnitude. Apparently, all but a small portion of the power output from our amplifiers is irretrievably lost. Sensitivity, expressed in Decibels relative to a watt input, is a more nebulous and tricky concept for the average audio consumer to grasp, but at least carries with it a nice high number. People (Consumers) like high numbers..... except in golf. I don't know if all of this is true. It would be interesting if someone could comment on it. Interesting thread. - Jim, I think you are definitely correct. Shame on R. V.... his speakers still sound good, though!