The spectrum of the musical signal. Part 2. Scheme, description

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The spectrum of the musical signal. Part 2. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Speakers

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Tops can't...

Now the third condition of measurement, which, alas, turned out to be quite expensive for too many. This applies to HF emitters. Squeaker, in short. The third page (out of seven) of the official text of the IEC standard contains the phrase: "for radiators intended to operate within a part of the audio range, the power measurement is made at the input of a filter that selects the required frequency band." Terribly said, no doubt. But the point is this. Let's assume that you have a tweeter, for which it is indicated: the operating frequency band is 2 - 20 kHz. According to the standard (the standard is sacred, especially if the numbers become prettier as a result of its application), it is necessary to connect the tweeter through a filter that passes frequencies above 2 kHz, and measure the amplitude (and power, therefore) at the INPUT of the filter. Then it will turn out: at the input - all the power corresponding to the standard distribution curve over the spectrum, as in the graph. That is, there are many on the middle ones, on the lower ones too, and the upper frequencies of the spectrum have a gulkin nose. This nose gets on the squeaker, and she feels great.

The most competent (and, as a result, the most conscientious) manufacturers give power ratings both at the inlet and outlet of a standard filter. And they indicate (hereinafter - a quote from Philips professional technical documentation): "The maximum allowable power (at the input / output of the filter) is 20/4 W (filter 2000 Hz, 12 dB / oct.) or 50/6 W (filter 4000 Hz, 12 dB/oct.)". For specialists it is clear: in the numerator - at the input of the filter, in the denominator - at the output. Did you feel the difference, or what? In a piece of paper attached to the speaker, please be so kind as to write only the numerator. The numerator is the fierce power of the broadband signal coming to the crossover filter, which selects the signal for the tweeter. The filter from all this at the input cuts out (in accordance with its characteristics) a small fraction of the high-frequency components intended for reproduction by the HF head.

Already thanks to the standardized spectrum, there is not God knows how much remains of the total power. And after the filter - well, attach the ruler to the chart yourself and see how much. The dynamics will have to be digested and taken out just the denominator of the fraction given by an honest manufacturer. But it is impossible to say how many tweeters were burned during this eternal war of the numerator with the denominator, and it is even more difficult to pay the damage. Practical conclusion: ceteris paribus, the viability of the tweeter is directly related to the characteristics of the filter through which it is connected. To a greater extent than with the characteristics of the tweeter itself as an example of engineering.

How many tweeters were burned during the eternal war of the numerator with the denominator ...

Well, this is a standard, a standard, a principle and an average guideline. But as in life, in the sense - "purely concrete", on the basis of live musical material. Let's see: here's the spectral distribution of the signal amplitude, averaged over about 20 CDs of classical music, mostly performed by a full symphony orchestra.

The average spectrum of classical music "of all times and peoples" in comparison with its standardized representation.

On the graph - the average spectrum of classical music (saved and averaged for a long time) - this is the blue curve. Red - spectral characteristic of pink noise. It will be present everywhere on further charts to serve as a guide. Because the spectrum of pink noise is a sample of a uniform distribution of energy over octave bands. The spectrum of pink noise in our experiments was taken from the same CD player as the rest of the phonograms, so there is confidence that the path passes all the frequencies of the studied range. (The pink noise recording was used from the IASCA Competition disc. The signal quality needs no comment - and that's all you can see. For the information of experimenters: we tried several recordings on test discs marked as pink noise, but a truly uniform characteristic was found only on IASCA, Competition or Setup&Test, it doesn't matter, the entry is the same.)

Returning to the chart. Look: indeed, the distribution of power over the spectrum is very similar to what was proposed (until 1969) by the International Electrotechnical Institute at high frequencies, although modern recordings give more amplitude than expected, but we will evaluate this factor later, on special material. Now - to rock, under the pressure of which in 1969 the "music of all times" curve was corrected.

"Races" performed by Yello is the benchmark for even distribution of energy.

Music signal spectrum

The average spectrum of rock music and the standard DIN spectral curve.

Averaged, by our efforts, the spectral response of rock records (from Dire Straits to AC / DC) - on the graph. Here, at the upper frequencies, the music even falls short of the "disciplining" curve of the standard spectrum. But on the lower ones it shows: the power of a real signal can be noticeably higher than expected by the standard.

A little, perhaps, digressing from the general plan of the narrative, we will show one more frequency response, it turned out to be very characteristic. Few presentations, shows or other image and prize performances are taking place now without Yello's "Races" being performed. Indeed - very emotional and exciting. We always include this phonogram in the repertoire during test listening to equipment, since a lot is heard on it. However, only after taking the spectrogram, it became clear, at least in part, where such fullness came from. Look, it's rare.

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Literature

Magazine "Autosound" № 11 / 2000

Author: Andrey Elyutin; Publication: avtozvuk.com

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