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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING The spectrum of the musical signal. Part 6. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers 
A popularized performance of the toccata. Midbass - more, subbass - less, and with the upper frequencies - the story is completely sad. But at the end of the same 60s there was such an ensemble from Holland called Ekseption. (That's not a typo, that's how it's spelled.) They were the first, or almost the first, to popularize classical music, combining philharmonic instruments with modern ones for the 60s. Toccata in D minor (author - J.S. Bach, arranged by R. Van den Linden) has always been the hallmark of Ekseption. The spectrum of their calling card is on the left. It's funny that the nature of the spectrogram is more affected by the traces of progress in sound recording over the past 30 years than by the popularization of performance. The spectrum at lower frequencies is more "intelligible" than in the classical version, there are plenty of midbass that are easy to read with simple equipment, and serious low ones - not even very much at all. But at the upper frequencies, despite the fact that drums were added to the Bach score by the generous hand of Herr Van den Linden, the energy is much more modest than what is being recorded now. And as we used to think from Linden's cymbals, it seemed that there is no wider recording bandwidth. And she, as it turned out, that's what it is, above 10 kHz - tears, and nothing more. Nothing ages like years... However, back to the basses, it was the Dutch and nostalgia distracted by common efforts. So, the first conclusion that we have the right to make is that a real musical signal almost never contains essential components below 30 - 40 Hz. And if so, then the characteristics of the subwoofer must be optimized for a real signal, and not for a mathematical abstraction. In this regard, the bass boost, a common device for boosting bass in amplifiers, which is almost always tuned to frequencies between 40 and 45 Hz, appears in a somewhat new light. At first glance, the device - not of royal blood, such as - for swotting, to the detriment of musicality. Now let's look at it with an open mind: raising frequencies by 40 Hz means they are (relatively) attenuated at frequencies below 40, 30, and so on. So, if you organize the frequency response of the subwoofer with a reasonable drop to 40 Hz, and then raise the frequency response at this level, then there is a chance to get a frequency response that is optimized with respect to the spectrum of a real music signal. In light of the real music spectrum, the common bass boost device is starting to look different... What is wrong with the frequency response of a subwoofer with an excessively wide bandwidth? Yes, here's the thing: very often (including in our tests) you can see the frequency responses of subwoofers extending to the lowest, deep infrasonic frequencies, not just without a drop in amplitude, but also with a rise. This often happens, for example, when installing in free air mode. As a result, such a subwoofer will play God knows how at really bass frequencies (above 35 Hz). But it will start to try inappropriately at frequencies below 30 Hz, where there is no more music, but there is an opportunity to hang out with a large amplitude, causing distortion. But what about the very concept of "subwoofer"? After all, as the name suggests, a "subwoofer" is a link in an acoustic system designed to reproduce not just low, but ultra-low (sub-bass) frequencies. Do they even exist in this world? Let's eat. Such is the sporting life At car audio competitions, the capabilities of an audio system in terms of sub-bass frequencies are evaluated using the same standard soundtrack from the IASCA Competition judges disc. This is a recording of a piece called "The Vikings" performed at the Morton Myerson Music Center in Dallas, Texas, you know. A monstrous size (as reported in the accompanying pamphlet), the organ, played in a very large room, produces majestic sounds. The spectrum reflecting this greatness is at the bottom left. No doubt, sub-bass frequencies are in abundance here. The signal amplitude even at 10 Hz is more than significant. A system capable of effortlessly playing what is recorded on this track of the judges' disc really deserves prizes and awards. But let's look at all this with a practical eye. Moreover, the compilers of the disc themselves helped us in this. On the Setup&Test CD, recorded in the Sheffield Labs also by order of the IASCA, there are two more variants of the Vikings. On one of them, the original recording was subjected to the procedure of "cutting off" the low frequencies by a sixth-order filter with a cutoff frequency of 50 Hz. The result is on track 27 of the IASCA Setup&Test CD. The next track contains what was removed from the original phonogram as a result of a painless procedure. 
"The Vikings": The reference recording for evaluating sub-bass in competitions around the world.
"Vikings" recording, specially processed for the Setup&Test CD. The listener is invited to evaluate how much the sound of his system has changed when playing an untouched phonogram containing the entire spectrum of frequencies, and "cut off". As a rule, the difference is audible. In a large number of cases (not all, but a large number), the filtered recording sounds better. But those who have the best unfiltered sound win, because only it is contained on the referee's disk. Many great-sounding audio systems won't reproduce what's on the IASCA judges' disc. True, it is not recorded anywhere else. Or almost anywhere... But now take a look: the filtered phonogram in its spectral composition is surprisingly close to the spectrum of a "normal" (typical, expected, whatever you want to call it) recording. It turns out that the requirements for a "sports" installation and for a conventional one, to put it mildly, do not quite coincide. On the one hand, this is justified: the referee record places high demands on the system, as it is supposed to at competitions. On the other hand, many great-sounding audio systems will lose in such a competition, because they will not reproduce what is recorded on the judge's disk and is not recorded anywhere else. Or almost nowhere. Now about this "almost". Literature
Author: Andrey Elyutin; Publication: avtozvuk.com
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