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For some, it is the most important piece of a home theater system, for others a huge and unnecessary box that gives them headaches in domestic installations. For most one more element of our home cinema that allows us to improve the overall quality of the sound at low frequencies.
The subwoofer or woofer has two basic missions: play without distortion frequencies to which the rest of the speakers are not able to reach and play the sound stored in the audio tracks. 1 of the multichannel formats.
This 1 is also known as the low-frequency effects channel or LFE, and in it we find subwoofer sounds (below about 40 Hz) whose objective is to make the spectator vibrate in effects like explosions and shots, but also to recreate a realistic environment Reproducing the very low frequency sounds of motors, closed stays, outdoor scenarios, etc.
The first audio tracks that were part of this LFE channel were used sporadically and only to highlight certain key moments in action. However, most films currently use it almost continuously not only to reinforce some sounds but rather to recreate a realistic sound scene.
This has made them become an almost essential element of every good home theater system that boasts. And we say almost because it can be replaced in some cases by the front speakers if they can reproduce low frequencies without problems and the receiver A/V supports the option to pass the LFE channel to the front.
We can distinguish fundamentally two types of subwoofers (without entering into shapes, colors, power, formats or typology of boxes, etc.), liabilities and assets.
The first ones, as its name implies, do not have active amplification elements that endow them with sufficient power to produce sound. They are, as it were, a transducer stuck in a box, something similar to the rest of the frontal, central and effects speakers that we have commented on throughout the special, but focused on the exclusive reproduction of low frequencies.
Liabilities, therefore, will need an external amplifier that provides them with the electrical power needed to move their membrane and produce the sound. They do not have volume or phase or frequency controls, something that we will have to manage from the A/V receiver or from the amplifier that we use to feed them. A clear example of how to build a passive subwoofer step by step you can see it in our special Sub Delta project.
The active subwoofers, on the other hand, have an amplification stage that is integrated into the loudspeaker itself. They are usually the most frequent to find in the market, since they incorporate everything necessary to put them to work from the first minute, with only connecting them to the electrical outlet and the receiver.
Also, they often incorporate extra features such as volume control, phase control, cut-off frequency management, boosting of certain bass frequencies, including automatic on/off systems, remote control or wireless communication with the Receiver.
Characteristics of a good subwoofer
A good bass speaker should be able to ideally reproduce all frequencies up to almost zero Hz without distortion and with sufficient acoustic pressure. As you imagine this does not usually happen, because playing frequencies below 10 or even 20 Hz without distortion (or with an undetectable distortion) is quite difficult.
So much so that most of the market receivers filter the low-frequency signals with which they work (many put the actual limit in about 5 or 10 Hz) and a large part of the active subwoofers that we can find in stores have subsonic filters that work with S Danger up to 20 or 25 Hz to protect the speaker from the lowest frequencies.
And is that working at smaller frequencies makes the loudspeakers have to work very hard to give a sound without distortion, and that is relatively simple to leave the linear operating area, depending on their characteristics and how Built the box, favoring the possible breakage of the loudspeaker (or reducing its useful life) if we put it to high volumes.
This is not to say that a subwoofer filtered at 20 or 25 Hz is bad, it is more, in most home installations The result may be more satisfactory than a full-range one, as the latter will tend to produce unwanted vibrations in objects and elements Decorative rooms (furniture, shelves, lamps, paintings, and even floor and walls) that although eye-catching in a first listen, eventually we will get tired.
If you ask me my opinion, a good subwoofer for home theater should be able to lower passively, without having the acoustics of the room and without problems of distortion to frequencies of about 30-35 Hz with drops of about 3-6 DB and reach about 20 Hz with maximum falls of about 9 DB (of course then all this is equalize).
To achieve these requirements we will have to have a driver of at least 8 inches, being advisable one (the optimal would be to have 2 or 4 subwoofers, although this escapes the possibilities of most of the domestic rooms not dedicated) of 10, 12 and even 15 flea As if we can afford to install it.
As for the shape of the box, when playing very low frequencies, the wavelengths will be higher than the size of the box, so they serve perfectly cubic and rectangular shapes.
With regard to the design format, the usual thing in the market is to find subwoofers of type bass-reflex (especially in the ones of fewer inches) or with passive elements that allow to lower more often, but they have the counterpart to enter a group delay in the Final sound that can sometimes be annoying by giving the sensation of a softer, less glued sound, or even hindering the location of the box in the room.
In my opinion, if you can choose, better a sealed box subwoofer with a driver as large as your budget and room size will allow. With it usually, we will get a sound with more impact, with more glued, although we probably lose some extension in low frequencies (something that is otherwise solvable with equalization and that is not necessary if as we said before We arrived well up to 30-35 Hz).
With respect to high-frequency cutting, it is normal to work up to frequencies between 100 and 200 Hz, point from which the LFE signal of the audio tracks ceases to have content in most cases (although in recent years I have seen editions of tracks whose CA NAL LFE reaches well above 500-600 Hz, something unusual and does not make much sense of the truth.
What power do I need?
And the power, how much will I need? Well, it depends on the result we want to get. Especially since the audio tracks in the cinema have a dynamic range quite high at the level of the LFE channel that makes in the ideal case a lot of power is necessary to be able to offer the acoustic pressure demanded by the soundtrack.
However, as in most cases we do not have a dedicated room or a bomb-proof ears (if you are looking for the Internet you can see cases of people who configure their home computers to have sound pressures of more than 115 or even 120 DB, something exaggerated that can be detrimental to our ears), it is normal to lower the expectations of sound pressure of the subwoofer up to levels with which we will feel comfortable in the nearly two hours that usually lasts the movies.
In general, for an average size room of about 20-25 square meters, with about 150-250 Watts RMS should be sufficient for our subwoofer, although of course, this will depend on multiple internal and external factors. Among the first, we will logically have the sensitivity of the loudspeaker, something that we can not vary and in function of which we obtain for the same power a greater or less sound pressure (more sensitivity greater sound pressure for the same power of excitation).
And among the external factors, we will have to consider how the room is asylum acoustically, the position of the subwoofer in it and especially how are the other speakers of our home cinema. If you have followed the special, you will notice that I got very heavy with that all the speakers reach at least 40 Hz (and that the fronts to be possible are the full band).
One of the reasons for this personal mania is that if the rest of the speakers can go down a lot in frequency, the range of these that we will have to send to the subwoofer will be reduced, minimizing the necessary power in the sub-woofer at the same time we facilitate s or installation in the room.
If on the contrary our main speakers are small and unable to play frequencies below 80 or even 100 or 150 Hz (as the typical 3-inch effects speakers that sell us with the 5.1 kits), all those frequencies will have to be Send to the subwoofer, needing it to support more power and obtaining a less localized sound.