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发表于 2019-8-8 12:36:06
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本帖最后由 Phase 于 2019-8-8 12:38 编辑
因为这些thd失真度其实测的都是一瓦到最大功率，说白了，在实际听音中，只对应最大的那些声音信号，也就是说发布指标thd极低的机器，只是说明能把最大的声音放准确了，而音乐的细节依然可能放的很差。音乐细节一旦放的差，那么余音，韵味，微动态，音色这种东西都是出不来的。
引用一段，有个功放设计师说halcro在极小功率的测试下失真是很严重的。这也说明了halcro为什么不好听。而直热三极管的wavac在极小功率的thd远远好于halcro
MEASURING ULTRA LOW-LEVEL MUSICAL AMPLIFIER SIGNALS
This may be the most important letter I have ever received from a reader. The letter speaks for itself, and is unedited, with my bold. (My "personal comments", plus a sceptical and cautionary perspective from another source, will follow below).
"My name is Steve Keiser, the 'K' of B&K components, and presently design engineer with Luminance Audio. I have developed a measurement system which is able to quantify distortion levels at micropower quantities down to 1/1000th of a watt. These measurement techniques are unprecedented, and have revealed a number of revelations of amplifier distortion characteristics, at micropower levels, which are in direct opposition with traditional and scientific assumptions up unto this point.
The emphasis of my work is to definitively quantify low level signal linearity measurements of power amplifiers, and attempt to correlate these measurements with subjective listening results, as well as establishing the significance of low level distortion. Conventional test equipment generally does not resolve meaningful distortion measurements below 100mw, since the measurements become predominated by noise.
I have modified a spectrum analysis software program, which uses time-averaging to effectively cancel out noise products, leaving an identifiable signal and its related harmonics. This time-averaging approach is to identify extremely weak signals from spacecraft, amid a very high noise ambient background. Using this method, I am able to resolve a standardized total harmonic distortion measurement down to 1/1000 watts, and an approximate measurement down to 1/500,000th of a watt.
My measurement results oppose common engineering supposition, in that it is commonly believed that very low signal linearity is essentially 'virtually perfect', and that only high level signal linearity is a relevant parameter. My measurements indicate exactly the opposite is true of this common held assumption, particularly for amplifiers employing solid state devices.
To give you an example: the Halcro DM58 amplifier measures .007%THD at 2 watts, whereas at 1/1000th watts, THD measures 8.9%! By contrast a Wavac SH833 measures .57%THD at 2 watts and 1.6%THD at 1/1000th watts. The tube Wavac exhibits significantly lower THD at low signal levels by orders of magnitude than the Halcro. I have measured numerous amplifiers, both solid state and tube, which I will provide to you as well as any other information you may want pertaining to this work.
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发表于 2019-8-8 12:21:15
