Valentino skrev:
90 dB/W/m? Hah! Like troverdig som AN/E's 98 dB/W/m.
Peter Qvortrup
Dear Openbaffle!
First of all we do not use the method that John Atkinson uses to measure efficiency (1 meter on axis 2.83 volt pink noise, free field semi anachoic, using a zero impedance amplifier or similar), as R C Daniels correctly says in another post, this type of standardized measurement technique completely fails to take many aspects of speaker behaviour and design into consideration and as result is just as misleading as we are accused of being with our efficiency figures.
Before I start, let me say that the audio industry has become and is now obsessed with simplistic ways of showing off improved or "comparable" performance and John Atkinsons methodology is a fine example of that, the belief that a single simple figure like harmonic distortion, damping factor, efficiency etc. etc. gives us any insight whatsoever into issues as complex and three dimensional as speaker design and performance is just plain ridiculous, the fact that anyone even takes this serious shows how far down the blind alley the combined marketing and lack of education of an industry more concerned with selling product than offering long term quality has lead us.
I think it is relevant to remind ourselves also that a speaker's dispersion affects the total energy presented to the room, the AN-E has exceptionally wide and even dispersion and although standardised measurements have been introduced with good intentions, these measurements are so simplified that they no longer represent reality in a meaningful way. For example, a measurement of two loudspeakers at 1m in an anechoic environment takes no account at all of the power response of the two systems. If, say, both were converting overall 1W
of electrical power into acoustic power, but one were omnidirectional and the other had a tightly constrained beamed output, the omnidirectional speaker would measure as being less efficient, a lot of its output would disappear off the horizon. However, unless you live in a field, this is not the case.
By the way, Martin Colloms asked me the exact same question when he reviewed the AN system 3 - 4 years ago, as he also had difficulty believing the efficiency rating, I showed a quick if somewhat simplified example of how we arrive at the stated efficiency ratings, which is done by combining 2 far field sound pressure measurements to get a room power response which is then used to calculate the efficiency, backwards so to speak.
Martin clearly agreed with the published 96dB/watt efficiency figure having tested the AN-E/SEC Silver, as he does mention in the review.
So here is a brief outline of the procedure, using the highly sensitive system we also use to match the drivers to the crossover and the reference, to get a near perfect match within pairs and to the reference,
1.) With the speakers in the correct corner loaded position, we take two sound pressure measurements at two different output power levels in two positions, using a broadband complex waveform (music), plus a series of sweep tones 15Hz to 25kHz, why use two different powe levels you may ask?
The reason for this is that I have found that many speakers appear to have an optimised behaviour at 2.83 volt input and their efficiency drops disproportionally if presented with less and in some cases more power, why this is, is a whole different question.
2.) We repeat this procedure at 3, 4 and 5 meters, using two speakers and a 2A3 or 45 and a 300B SET amplifier, each time noting the voltage output power from the amplifier and the corresponding sound pressure level.
We then compare to two reference speakers of "known" efficiency, measured the traditional way (as JA did with ours), then repeat the way we measured our speakers, compare the difference in efficiency at listening distance, average for distance and then work their room energy efficiency backwards so to speak.
We add/subtract the difference between these reference speakers and ours to get the figure we publish.
Inconvenient?
Yes, but it gives a far better and more accurate measure of what the real power transfer and equivalent sound pressure level is, and therefore closed to what the actual efficiency of the speaker is likely to be in situ in room, because if you take a 1.5 watt amplifier and you can get 100dB plus out of a speaker measured at 1 meter before audible clipping, then the speaker must be more than 92dB efficient, wouldn't you say, or perhaps it is just the way we measure the amplifier's power that is not correct, it may in reality be more powerful than the measurement shows??
Hope this help a little.
Sincerely,
Peter
Lf
