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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Subwoofer. Theory and practice. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers Every building must have a proper foundation. Its role in the AV complex is played by a subwoofer. After all, nothing adds more charm to a home theater than deep, powerful bass. Do you know how the law of meanness works? I'll give you an example. After spending a lot of hard-earned money on a home theater system, you buy the latest super-cool action movie. You invite all your friends and acquaintances to "treat yourself" with the achievements of cinematography and computer graphics... But, alas, your efforts are in vain. What's the matter? Well, at least in the fact that the explosion at the beginning of "Lethal Weapon 2" is more like the crackling of a dry branch under the foot of an unlucky trapper from some parody of a Western, and the tread of a tyrannosaurus rex from "Jurassic Park" is more like the timid steps of a baby. And now, after another sip of beer, one of your friends, in a fit of drunken frankness, admits: “Yes, the surround sound is wonderful, but the bass is not enough ...” And this is like salt on the wound: you feel like a complete idiot - and you are ready to give half your life for this same bass. Fatal attraction? "Oh, bass! How much has merged in this sound for the heart of the Russian! .." It is on it, according to the majority of film lovers (especially beginners), that the real sound is based. The rest, in their opinion, is nonsense. To hell with localization and natural tonal balance. Loud, powerful, deafening bass - that's what "catches" amateurs in a full-fledged home theater system. Whether it's a gunshot in John Woo's movie, an explosion in the latest episode of Die Hard, the rumble of Apollo 13 taking off, or the sounds of an orchestra playing a gavotte in Sense and Sensibility, really good bass is the foundation of the soundtrack everywhere. endowing it with a life-giving drama and impact that only the best theaters can offer. The reasons for this are psychoacoustic (that is, related to how the ear hears and how the brain processes this information). In the process of evolution, the human ear has tuned in a certain way. This is why our hearing is particularly sensitive in the mid-frequency region, which includes speech and other human sounds (such as the cry of a baby). In antediluvian times, low, rumbling sounds meant danger (an earthquake, a thunderstorm, the growl of a giant beast with sharp fangs, etc.), so they still make the body release adrenaline. So our love for deep bass is actually a love for thrills. True, there is another explanation for the excessive passion for bass. As a rule, people start to "sick" with a home theater after visiting the corresponding exhibition or trade show, and there they usually turn on the subwoofer to the fullest - in order to make a killer impression on the visitor. Many people think that it should be the same at home. We dance from the stove Sounds are vibrations in the air. They are caused by everything that can set the air in motion - from the explosion of an atomic bomb to the vibration of a mosquito wing - and, of course, the vibration of a loudspeaker cone. Electrical signals cause it to move forward or backward. With each movement, the diffuser compresses or rarefies the air, and this compression/rarefaction propagates at the speed of sound. The faster it happens, the higher the sound. The pitch (or frequency) of a sound is the number of compression and rarefaction cycles per second. They are called hertz (in honor of the famous German physicist Heinrich Hertz, and by no means Herzen, who, according to Lenin, was awakened by the Decembrists). We perceive sounds ranging from approximately 16 Hz to 18 Hz (000 kHz). Meanwhile, most loudspeaker manufacturers list the easier-to-remember range of 18Hz-20kHz, although sounds above 20kHz are picked up only by dogs, bats, and humans, who rarely leave the silence of their homes. Unfortunately for men, the highest part of the spectrum ceases to be available to us in adolescence, with the purchase of the first tube of aftershave cream, while women in middle age retain the ability to hear high frequencies well. But with the opposite end of the spectrum, most people have no problems: even the elderly distinguish frequencies below 18 Hz. The second, and last, physical factor of significance to deep bass hunters is the logarithmic decibel (dB). Decibels, among other things, show the level of sound pressure. True, there is a catch: the measurements of this level are not absolute, but relative. Even worse, when the sound pressure level changes, our hearing changes its sensitivity. However, there is a generally accepted decibel scale, in which the hearing threshold is taken as zero, and the so-called pain threshold is taken as the maximum (it exceeds the hearing threshold by about ten million times and is 140 dB). Perhaps this is an oversimplification, but if you remember that for the most average home movie fan, the norm is 75 - 100 dB, and that according to this scale, adding 6 dB means doubling the volume, you can forget about the rest. Active or passive? To get real bass in a home theater environment, you need a subwoofer, that is, a subwoofer. It can be built into either the two front speakers or their stands, or it can be a separate device that can be installed almost anywhere in the room, since deep bass is non-directional sound radiation. Thanks to the latter factor, there is no need for a stereo pair of subwoofers: to get excellent sound quality, one is often enough. Everything is clear here. The problem lies elsewhere. What should be the subwoofer - active or passive? Passive subwoofers are usually designed for a specific set of loudspeakers and are generally addressed to the low cost system market. Their main advantages are that they allow the use of smaller main speakers (satellites) and do not require additional outputs from the main amplifier. The most serious drawback of passive designs is their elementary inability to reproduce sufficiently deep basses. However, sometimes it is not the subwoofer that should be blamed for this, but the amplifier, which lacks the “strength” in order to swing both the satellites and the subwoofer. That is why Technics has been producing not only five-channel, but also six-channel home theater amplifiers for several years, equipped with the expectation of connecting an inexpensive passive subwoofer (the last example is the SA-AX7 model. We reviewed in No. 3/2000 on page 79 ). The active subwoofer has a built-in amplifier and controls that allow you to change the volume and cutoff frequency, which makes it possible to coordinate the unit with any pair of main speakers. The advantages of an active subwoofer over a passive one are a wagon and a small cart. Since the amplifier in this case is built-in, it is optimal for a particular loudspeaker, which eliminates many potential problems. Active models enhance the sound of any speaker so you don't have to change speakers, and the available controls allow you to take into account the specific features of your room. There are two disadvantages - the relatively high cost and the need for the amplifier to have a separate output. However, prices have come down a lot lately, and if you don't already have an active subwoofer in your home theater, then you're behind the times. Where to lay the foundation? Let me remind you once again: no matter how well your "cinema" is acoustically decorated, it willy-nilly become a kind of equalizer, amplifying some frequencies and weakening others. This effect is determined by the resonant frequencies of the room (in fact, the acoustic properties of the room are determined by many more factors, but in this case the simplification does not affect the essence of the problem), which, in turn, depend on its length, width and height. The fact is that in the room when playing sound, constant areas of high and low sound pressure (standing waves) are created. It is easy to guess that the determination of the optimal place to place the subwoofer (as well as the seat of the viewer) is made either by trial and error, or requires the involvement of huge computer power and a graduate in the field of acoustics.
Optimal subwoofer placement. However, try to move it away from the TV so that it does not affect the kinescope.
A good option for an oblong room - if you can put a subwoofer at least a couple of meters from the place of the audience. General advice: put the sub away from the listeners, but not in a corner (it's not to blame for anything!). The trial and error method is extremely simple, but takes a lot of time. Put on a disc or tape with the deepest bass you can find and play it as you move the subwoofer from place to place. After each permutation, sit down in the "viewing" chair and evaluate the changes that have occurred with the sound. If you are still in doubt, take the manufacturer's recommendations as a basis. When you come to the conclusion that it can't get any better, watch a few movies to make sure you're on the right track, and then enjoy the results. However, I will allow myself to give a few "subtle observations of life." First, most novice theatergoers either turn their subwoofers up too loud or turn up the cutoff frequency. In short, if you find that the sound in the movie "Piano" would be more suitable for the film "Terminator 2" or that the subwoofer emits a frantic growl at the most modest bass note, turn down the volume. Secondly, if possible, try to place the sub near the same wall as the TV to avoid the phase shift of the bass waves from the rest. Thirdly, leave some space between the TV and the subwoofer, because large and destructive magnets for the kinescope are hidden inside the latter. Fourth, most of the recommendations given by the manufacturers of AV amplifiers and processors are wrong in my opinion. These devices are usually equipped with a linear "subwoofer" output, to which the signal is pre-filtered by a low-pass filter. Meanwhile, the active sub itself is equipped with the same filter at the line input. As a result, when connected via a linear signal, two low-pass filters are connected in series, and the total characteristic will be simply unpredictable. It is best to apply a full-range signal from the amplifier's "speaker" output to the special "high-level" input of the subwoofer. And the last tip (it only applies to those who are completely desperate): installing a weak subwoofer in the corner of the room can “pull up” the mids and upper basses a little. bass wisdom Bass What do we mean by this word? The answer will have to be looked for in the Hi-Fi area, because it is she who is the progenitor of the home theater. It turns out that the bass is divided into three octaves, and overlapping. The octave from 20 to 40 Hz includes the deep bass (the lowest notes of the organ fall here), the octave from 40 to 80 Hz is known as the mid-bass range (they are extracted from the bass drum), and the octave from 80 to 160 Hz is called the high bass range ( listen to cello and bassoon). Anything below 20 Hz. we feel rather than hear, here you can no longer distinguish the pitch or repeat the sound, unless, of course, you live in a cathedral. Атака It's actually a quirk of bass terminology. The word "attack" is not entirely appropriate here, but is used because low frequencies are characterized by slower transients compared to highs. Meanwhile, the difference between "slow" and "fast" sounding bass systems, often not otherwise defined, is the difference between a system that "punches the brain" and makes you listen in fascination. Most of the epithets that describe good bass. can be used as a compliment to a skilled drummer. Words that mean the opposite are associated with the concepts of obesity and sluggishness. So, if the sound of an explosion comes to mind with the terms "fast", "distinct", "clear", "live", "tense", "tight" or "precise", then you may be dealing with a decent system. If the words “boomy”, “fat”, “overloaded”, “fat”, “loose”, “fuzzy”, “slow”, “quiet” or “deaf” come to mind, which means it’s time to “get your legs off”. Weight category When it comes to the amount of something, like bass, we're tempted to use the term "weight". If the system lacks bass, it is called "skinny" and "skinny". And if the bass is in excess, they say that the sound of the complex is "fat" and "inflated". When the bass is in order, the system is called "tight" and "muscular". Dynamics If the system is capable of distinguishing loud and soft bass notes, and does not sound "like a barrel", then the words "pop", "bang" and even "energy" are used in relation to it, all in a positive sense. Surprisingly, there are no negative characteristics here. I'll try to come up with something myself. How would you like, say, this: "sounds like chewing glass"? Depth When talking about subwoofers, reviewers often use the term "bass depth". It only means how "deep" the lower end of their frequency range is. A system that is not capable of reproducing the lowest bass is called "slaughtered", and one that can is proudly called "extended". Overlapping Each set of speakers, including tweeter, midrange and subwoofer, has frequency range points where the sound of one speaker overlaps with the sound of another. They are called overlap points. So, if the midrange speaker is "cut off" at 90 Hz. and the subwoofer operates in the range from 40 to 150 Hz, then somewhere around 100 Hz, most of the sound passes from the midrange driver to the subwoofer. This frequency is called the overlap frequency. Most loudspeakers are equipped with circuitry whose components produce a signal that allows for a smooth transition from one speaker to the next. This circuit is called a crossover or crossover. Bass - to taste Without high-quality bass, neither a home theater nor a noteworthy audio system is possible ... If you decide to purchase a sub, approach its choice with all responsibility. An unfortunate model turns out to be practically worthless when it comes to bass reproduction - it's better to spend money on a pair of larger and better main speakers. Luckily, today's stores are littered with great subwoofers for every taste and every price, just reach out. Models under $400 Energy e:XL16 ($300). Despite the not very high price, it has a 40 cm woofer and a 300-watt MOSFET amplifier. The crossover is tuned to any frequency in the range of 50 - 100 Hz. moreover, if desired, you can connect an external equalizer or an active filter, for which there is a separate input. To facilitate coordination with the rest of the acoustics, a phase control is provided in a very wide range (from 0 to 180 degrees). This subwoofer doesn't have many competitors, and those are either designed for midi systems (Aiwa TS-W5) or cost about 35% more (Velodyne CT-80). For those on a tight budget, I would suggest getting the largest possible size main speakers, however if you have a small room and have recently purchased new compact speakers, the e:XL16 is the way to go in most cases. <$ 600 REL Q-50 ($500). Today it is the most inexpensive model produced by REL. It is unpretentious, but reproduces deep basses very well. Its closest rival, the more elegant KEF 20V (also $500), is equipped with a built-in 70-watt amplifier and, unlike the 0-50, has magnetic protection. Polk's PSW120 ($480) also demonstrates good bass. It is somewhat preferable due to its better quality/price ratio, as it will make any home theater system rumble at full power. <$ 900 REL Q-100 ($850). Beautiful, deep bass, good quality/price ratio, acceptable appearance and a big name - that's what this device combines. It's capable of reaching such bass depths that your home theater system will growl and rumble. REL should be warned, however, that it has formidable rivals here in the form of the exquisite Tannoy 625 ALFie ($900), the simple but bassy Mission 75AS ($800), and the small but otherwise great M&K VX-7B ($675). Each of these models is a worthy alternative. When the price doesn't matter Be careful, very careful. "Price doesn't matter" - these four short words can mean more than anything to a designer. If you're looking for the best subwoofer in the world, check out the REL Studio ($4000), M&K MX-100 ($2200), KEF AV1 ($3500), Revel Sub 15 ($2800 - 5200), B&W, Bag End, Linn, Meridian and Muse. The cheapest of these subwoofers will lighten your wallet by at least $2000, but if you really want to overspend, you can spend twice as much. In the event that you need to save not money, but space, pay attention to EnergyMicrostar 12.1 ($1600). This cube with a side of 40 cm can bark so that it doesn’t seem a little - its power is one and a half kilowatts! Kevlar woofer, digital amplifier plus all sorts of sonic and custom bells and whistles make it extremely attractive for high class theaters. RELation to REL In the UK, among bass masters, one firm occupies a special position - it is not one, but several heads higher than the rest. This is REL. Perhaps no other subwoofer manufacturer has been so welcome here and won so many prizes. Why is this so and who is the creator of REL's success? Let's look at the end of the eighties. A man named Richard Lord is resigned with full honors. And instead of starting a measured life and resting on his laurels, Richard Lord uses his savings to design and build the simplest woofers for Hi-Fi systems. This is how the first REL subwoofers were born. Of course, the inherently conservative Hi-Fi industry refused to recognize the usefulness of such devices, and the opinion was formed that, although they were not the devil's spawn, they were only slightly better. Therefore, back in early 1990, Richard Lord's dream of a bass, of a bass everywhere and everywhere, seemed unrealizable. Thankfully, home theater suddenly burst into life in need of oceans of bass, and the REL subwoofer's place in history was sealed. The REL formula is simple yet deadly effective. Each subwoofer has a large bass driver, a heavy, well-knit cabinet, and a MOSFET power amplifier. capable of receiving a signal either from the corresponding line output of the amplifier, or directly from the "speaker" outputs. The subwoofer has very few controls - they only control volume, cutoff frequency and phase. You can safely forget about the latter after the initial installation. There are also four "heels" that prevent the device from staggering, no matter what is on top of it. - so the subwoofer looks more like a makeshift table than part of an AV system. The formula remains the same at all levels of the REL hierarchy: it's just that each "superior" model is larger, more powerful and of better quality. Most subwoofers from other companies are omitted, at least. one of the elements of the REL formula and is often done in an attempt to keep the retail price in check. This approach inevitably leads to a decrease in quality and turns the product into another mediocrity. By refusing to make such compromises, REL is making its family more and more popular. And finally, we should not forget that REL is such a success in Russia, since the real competition for its products can be mainly American devices, and the journey of such a solid person as a subwoofer is not cheap. In the meantime, there are a lot of very cool subs out in the USA (by Miller&Kriesel, Bag End. Muse and others), and if it weren't for the shipping costs, we would recommend them to you more insistently. Author: Vyacheslav Savvov, Salon AV; Publication: audio.ru/salonav/home.php
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