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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING The spectrum of the musical signal. Part 1. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers The musical signal is food for the audio system. More precisely - not so. Speakers do not listen to music, our brain restores it, receiving a complex signal containing many frequency components. The task of the speakers (not without the help, of course, of everything that precedes them - amplifiers, signal sources, etc.) is to convey these frequency components to the listener's ears in the form of air vibrations. Convey carefully, preserving everything that was in the recording, but without foolish amateur performance, that is, without introducing into the signal what was not there. It would seem, what is easier. However, everything that thousands of people around the world have been tirelessly doing for a hundred years is aimed at solving this problem, which is so simple in words. But before demanding from the audio system conscientious assimilation of the proposed musical dishes, it does not interfere with understanding what is included in the diet. The data that we have collected (for quite a long time) and, to the extent possible, generalized (also not immediately), owe their birth and concentration in the hands of the author to simple and sincere curiosity - the most powerful driving mechanism of human actions. However, the provoking factor was the questions "from the public", which the public asks with constancy and interest, worthy of a much better application, honestly. We are talking about the power of the speakers - a characteristic that leads the audience into great and very often inappropriate excitement. "I have 100 watts on my speakers, but you only have 80 watts, weakling, that's for sure." And what do these watts mean, if only we discard the case when they do not mean anything (a 45-degree bow towards the rising sun, which rises not only over the slopes of Fujiyama, but also over the banks of the Yangtze). So here you are, gentlemen, the terrible truth, to start the conversation. The definition and conditions for measuring the power of speakers, given in their technical descriptions, even the most detailed, are never deciphered. And the decoding of this characteristic is given only in the dry and boring texts of industrial standards. According to current regulations, the maximum allowable power of a speaker is considered to be such power (in rms measurement), which, when applied to it, after 100 hours of operation, will not cause its failure or irreversible changes in the parameters of more than the allowable one. For example, a 40% reduction in resonant frequency after such a test is considered acceptable. Normal, right? Such a half-swinging speaker is considered to have passed the test for maximum power. This is measurement condition number one. Condition number two: what signal is given to the speaker during the painful test. We look at the text of the standard: "when applying a signal with a pink noise characteristic that has passed through a filter with a frequency response corresponding to the standard power distribution over the spectrum of a musical signal." That is - it's understandable, not just a noise or, God forbid, a sinusoidal signal, but some conditionally averaged one, depicting the spectral image of "music of all times and peoples" in one dish. The characteristics of this filter can be found in special literature, certainly not in the one that is put into a box with speakers like "100 W, but you want 200!". This frequency response even has its own history. Until the end of the 60s, the curve proposed by the International Electrotechnical Commission (in our opinion - IEC, in their language - IEC) was considered the standard. The music of "all times and peoples" was averaged by the international commission into the curve depicted in green on the graph. Should be nearby, find it. The curve itself is quite expressive. International experts have established that in a real musical signal the content of the lower frequencies is lower in level than the level of the middle ones, by an average of 10 decibels, and the upper ones - you can see for yourself how much. 
Curves of standard spectral density: old, "philharmonic" (green) and new (violet). In the pastoral early 60s, experts looked mainly in the philharmonic direction, and the standard curve of the spectrum of musical recordings, approved by high signatures and seals, was mostly based on classical music recordings. In the late 60s, when the Beatles had already played almost all of them, and others had just dispersed in earnest, it became clear that the music had changed. That is, not all, but the one that was the main burden for the record companies and the main diet for the speakers. "Modern" (for the time) music demanded a greater tolerance for high-end content, hairy, fuzz-stomping guitarists and sweaty percussionists with twenty cymbals per head took care of that. The new, post-revolutionary curve was approved by the IEC, and a little later the holy inquisition of international standardization, the German office of industrial standards DIN, adopted it. What is accepted by DIN is accepted by everyone, it has been tested repeatedly. The progressive curve of the standard DIN spectrum, now accepted by everyone, is on the same graph, in purple. The Cultural Revolution in the late 60s changed the frequency response. An understanding of these curves, whether past, classic, or new, hippie, in itself sheds light on the promises of manufacturers about power. 100 watts (or whatever) the maximum power specified for a speaker does not, did not mean, and never, until the next cultural revolution, will mean that it can be fed a signal of any frequency within the declared operating band with the power declared by the manufacturer, and expect everything to be ok. At some frequencies, most likely, it will be so. But on others - no, but now you know that you were not promised this, the case will not go through in court. Literature
Author: Andrey Elyutin; Publication: avtozvuk.com
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