Some of the most deeply rooted convictions that hifi fans have do not have solid foundations. In fact, many of them are wrong from a strictly technical point of view. One of the precepts most vehemently defended by some enthusiasts is the convenience of doing without a subwoofer in any equipment designed to reproduce music with the highest possible fidelity, especially if we have full-range speakers that deliver a powerful low end.
In the field of home cinema, on the other hand, we amateurs tend to accept without reservation that a subwoofer it is necessary if we want to reproduce the specific channel that contains most of the information related to the reproduction of low frequencies. However, although it is by no means a popular belief, integrating a subwoofer in a stereo system dedicated to reproducing our music with the highest possible quality is not heresy. Quite the contrary. It’s a great idea, and acoustic theory supports it.
What is surprising is that installing one or more of these loudspeakers will not only help us increase the energy of low frequencies in order to obtain a lower end with more extension and punch. If our stereo equipment incorporates two-way monitors with limited bass delivery capacity, there is no doubt that resorting to a subwoofer will help us restore low frequency information that our speakers are not capable of reproducing. But this is not the only relevant role of a subwoofer.
And it is that, in addition, integrating a subwoofer can help us to solve very effectively a large part of acoustic problems introduced by the room in which we have installed our hi-fi equipment. All the rooms in our houses have their own sound imprint, and they usually take over at certain frequencies below 200 Hz, causing an important part of the musical information contained in these frequencies to be masked by distortion or due to attenuation. of your energy. Fortunately, this serious problem has a solution. And the subwoofers They are very valuable allies that are worth turning to.
The origin of the problem: the modes of our listening room
The rooms in which we music enthusiasts usually install our hi-fi equipment are usually between 7 or 8 and 25 square meters in size, so inevitably our speakers are going to be relatively close to the walls. The sound waves emitted by the loudspeakers of our loudspeakers propagate through the air in the form of pressure changes, and inevitably as they are confined in the closed area that is our listening room. interact with the wallsthe floor and the ceiling of the room, exciting them.
The energy contained in low-frequency sound waves induces the appearance of standing waves, which are those whose wavelength coincides with the physical length of the room in one of its dimensions. And when this happens, and it’s something that always happens in the moderately sized rooms where we usually set up our stereos, those ripples are reinforced, introducing resonances. An intuitive way to identify what a resonance is is to see it as each of the frequencies at which a room is excited by the sound waves emitted by the loudspeakers, causing the room to emit its own sound.
And, precisely, the resonances generated by the standing waves in our room are known as eigenmodes or resonant room modes. From an acoustic point of view, the eigenmodes induce the appearance of two problems. The first of them is that they distort the frequency response of our equipment at the point of listening, so if we place a microphone in this position and take measurements we will not obtain the pure frequency response linked to our equipment; We will measure the interaction that occurs between the loudspeakers and our room. And with certainty in the frequencies that coincide with the own modes of the room there will be attenuations and cancellations that will inevitably mask an important part of the musical information.
The second problem is also serious, although instead of acting on the frequency response alters the time dimension of the music signal. This simply means that the resonances introduced by the room can cause the musical information contained in the frequencies that coincide with the resonant modes to be prolonged in time beyond what is appropriate. In some way, the room emits its own sound when it is excited by the energy of the acoustic waves, and in these conditions, as we can guess, the original musical information is distorted.
Some ‘subwoofers’, the most advanced, incorporate their own DSP, and it is a very valuable tool because it can help us integrate them into our stereo equipment more easily. The model in this photo is the 18S from Dynaudio, and it has its own DSP.
Subwoofers are a valuable acoustic conditioning tool
As we have just seen, the problems we are facing are serious and can cause a good quality stereo equipment to give us a very poor performance due to the interaction of the loudspeakers with our listening room. Fortunately, we have tools to largely overcome this challenge. One way to deal with it is to install elements of passive acoustic conditioningsuch as sound-absorbing panels, bass traps, or diffuser panels.
If we turn to a qualified professional in the field of acoustic treatment, we will probably be able to largely resolve the deficiencies that our room introduces in the musical signal. But it is not always possible to install acoustic correction elements in a room, especially if it is not a room dedicated exclusively to our hi-fi equipment. The presence of a rug, thick curtains and furniture full of books, among other decorative elements, can help us act on the acoustic characteristics of our room in a non-intrusive way, but we have another option. And it works like a charm.
The second strategy that we can choose is to integrate one or, better yet, several subwoofers on our hi-fi. And it is that in addition to extending the frequency response of our equipment ‘from below’ and giving us a more forceful bass, something that many fans like, these speakers specialized in the reproduction of bass frequencies in practice act as an element highly effective active acoustic conditioning.
One or more ‘subwoofers’ can help us control very precisely the modes of our room
And they do it because if we integrate them correctly with our loudspeakers and place them at the ideal points in our room, we can achieve drastically attenuate the resonances and minimize their detrimental impact on the original musical signal. This simply means that one or more subwoofers they can help us to control with great precision the modes of our room, so that our music equipment will be able to express itself much better and give us its full potential.
Fortunately, we have at our disposal a large amount of technical literature that supports this strategy, and one of the books that has helped me the most in this area, and that I enthusiastically recommend if you are interested acoustic theory, is ‘Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms,’ by Floyd E. Toole. Currently it is only available in English, but if this language does not intimidate you, it is well worth reading it because it is a very rigorous and well-founded tool. I also recommend you take a look at the video in which Marc Gras and Jose Almagro They approach this topic in a very didactic way.
The frequency response curve that we can see in this graph reflects the interaction that typically occurs between loudspeakers and the room. As we can see in some frequencies there is a variation in intensity of almost 40 dB, and it is a real outrage that needs to be corrected.
Many of the experts recommend opting for several subwoofers, and not just for one, as long as our budget and the characteristics of our listening room allow us to install them correctly. This is because several of these loudspeakers will help us to control with more precision and flexibility the ways of our room. However, correctly integrating one or more subwoofers in a hi-fi system is not easy.
This procedure is beyond the purpose of this article, but if you are interested in us explaining it, we suggest that you let us know in the comments of this report. If you like the idea in the future we will prepare a didactic article explaining in detail how to use a free and very valuable tool that can help us to integrate one or more subwoofers correctly on our stereo: ‘Room EQ Wizard’popularly known as REW.
Images: Wilson Audio | dynaudio
Bibliography: ‘Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms’, by Floyd E. Toole
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