In counterpoint to Bottlehead's response, some studies have shown that as little as a 0.1 dB difference IS perceptable. Meaning that in an A vs. B choice (this is the same system, but that one choice has 0.1 dB less attenuation), the louder-by-0.1dB choice was preferred because it "sounded better". As far as the "first watt" is concerned, this may be perfectly true for tube amps: Less than 1 watt is dominated entirely by noise, and more than a few watts has high harmonic distortion! So these amps may ONLY sound reasonable when outputting one watt.
how much tube power is needed?
Let's say, for a 86 and a 92 dB efficiency speaker. SE triode fans say 10 W is enough, 20 W is more than you need. They use horns and high-efficiency speakers (> 92 dB sensibility). They say high-powered designs do not sound good at low volumes while driving high-efficiency speakers. Others (mainly push-pull fans) say that even though you have high-sensitivity speakers, the more watts, the better dynamic resolution. I don't want to launch a SE/PP war now. This is not meant to be a pure technical question, it also concerns musical taste. What is your experience with these?
Showing 3 responses by fotopresd4b4
The answer from Mr. Jslager is in error. You only need to double the power for each 3dB increase, not ten times. His table should read: 40 Watts/86dB; 20 Watts/89dB; 10 Watts/92dB. A 10dB increase needs 10 times the power. So with 10 watts RMS a 92 dB/1 watt/1 meter speaker will produce 102dB in SPL (sound pressure level). The three above values will all result in 102 dB peaks. However, musical signals also have 10 dB peaks on the average, so all of the above listed amplifier wattages will produce only a 92dB AVERAGE SPL before clipping on the peaks of 102 dB. Remember that tubes, when driven into clipping, produce THD of over 10%, at best they produce around 1%, so if you wish to put an equalizer, capacitor and distortion unit in series with your loudspeakers then by all means buy a tube amp, the wattage is practically immaterial as they will ALL sound distorted. To figure how much amplifier power you need, take your loudest average listening level, say 102dB, figure the wattage needed and multiply by ten, for the 10dB of overhead needed for the peaks. In the case of a 92dB/watt/m speaker, a 100 watt RMS amplifier is needed. Add to this low distortion like 0.1% or less, low internal resistance (e.g. high damping factor, over 100), reliability and reasonable price, and you will see that no tube amplifier can fill this requirement. Good luck. |
In response to [email protected], I fully agree that a 60 watt tube amplifier will drive the Acoustat 2's to 105dB peaks, but maybe only in the midrange. As this is a discussion forum so that others may understand the issue, the Acoustat 2's, a "full-range" electrostatic which were first introduced in 1980, have an efficiency of 85dB/watt/M. It would take a 100 watt signal to drive these speakers to 105dB, and since a tube amplifier typically has 2 dB peak headroom, the 60 watt tube amplifier can drive the Acoustat at some frequencies to exactly 105dB peaks. This of course, as with all tube amplifiers, with the inevitable high distortion, limited damping and bandwidth, noise, unreliability, inability to match impedence or drive reactive speakers, etc. The 105dB peaks at 20Hz and 20kHz with low distortion that a true "high fidelity" system SHOULD produce are just not possible with user35's system, and that is also a fact. As for testing, a square wave is much more revealing of sonic flaws such as bandwidth limiting or reaction to capacitance, and a spectrum analyzer would allow simple measurement of harmonic distortion and noise. However, the sound of user35's system obviously is his preference, and I certainly respect his right to love his system! But I digress, and to answer zkis' original question of "how much tube power is needed?" my answer is: NONE!!! |