The Lowest Bass Specialists - Part 2

Subwoofers were not always active, were not always closely connected to home theater systems, and did not always serve them in the first place. They began their careers in popular technology in the late 80s, in stereo systems connected to "regular" stereo amplifiers rather than multi-channel receivers - the era of home theater was just approaching.

System 2.1 (subwoofer with a pair of satellites) was an alternative to the traditional pair of speakers (see also: ) without any requirement. This one was supposed to power both the passive low-pass filtered subwoofer and the passive high-pass filtered satellites, but this load is not at all different in terms of the impedance “seen” by the amplifier from that of a multi-way loudspeaker system. It differs only in the physical division of the multi-band system into a subwoofer and satellites, on the electrical side it is basically the same (subwoofers often had two woofers connected independently to two channels, or one two-coil speaker).

The amplifier board with the control section is almost always on the back - we don't have to visit it every day

Systems 2.1 they even gained considerable popularity in this role (Jamo, Bose), later forgotten, because they were suppressed by the ubiquitous home theater systemso, already without fail with subwoofers - but active. These supplanted passive subwoofers, and if today one thinks of a 2.1 system designed for listening to music (most often), one is more likely to consider a system with an active subwoofer.

When did they appear multichannel formats i home theater systems, they launched a special low-frequency channel - LFE. Theoretically, his amplifier could be among the many power amplifiers of an AV amplifier, and then the connected subwoofer would be passive. However, there were many arguments in favor of interpreting this channel differently - this amplifier should be “removed” from the AV device and integrated with a subwoofer. Thanks to this, it is best suited for him not only in terms of power, but also in terms of characteristics. You can fine-tune it and achieve a lower cutoff frequency than a similarly sized passive subwoofer and similar speaker, use an active and adjustable low-pass filter (passive on such bass would be energy-intensive and costly), and now add more features. In this case, the multichannel amplifier (receiver) is “freed” from the power amplifier, which in practice should be the most efficient (in the LFE channel, power is needed that is comparable to the total power of all other channels of the system). !), which would force either to abandon the elegant concept of the same power for all terminals installed in the receiver, or to limit the power of the LFE channel, reducing the capabilities of the entire system. Finally, it allows the user to choose the subwoofer more freely without having to worry about matching it to the amplifier.

Or maybe with music stereo system Is a passive subwoofer better? The answer is this: For multi-channel / cinema systems, an active subwoofer is definitely better, the concept of such a system is correct in all respects, as we have already discussed. For stereo / music systems, an active subwoofer is also a reasonable solution, although there are not many arguments in its favor. A passive subwoofer in such systems makes a little more sense, especially when we have a powerful (stereo) amplifier, but then we have to think carefully and even design the whole thing. Or rather, we will not find ready-made, passive 2.1 systems on the market, so we will be forced to combine them.

How are we going to make the division? The subwoofer must have a low pass filter. But will we introduce a high-pass filter for the main speakers, which will now act as satellites? The feasibility of such a decision depends on many factors - the bandwidth of these speakers, their power, as well as the power of the amplifier and its ability to work with low impedance; it may be difficult to turn on the speakers and subwoofer at the same time (their impedances will be connected in parallel and the resulting impedance will be lower). So… firstly, an active subwoofer is a good and universal solution, and a passive one is in exceptional situations and with great knowledge and experience of an amateur of such a system.

Speaker connection

An extremely rich set of connectors - RCA inputs, loudspeakers and, very rarely, an HPF signal output (second pair of RCA)

This connection, which was once the most important for subwoofers, has lost its importance over time in AV systems, where we most often deliver LFE signal low to one RCA socket, and "just in case" there is a pair of RCA stereo connections. However, connecting with a speaker cable has its advantages and its proponents. Loudspeaker connections become important in stereo systems, both because not all amplifiers have low-level outputs (from a preamplifier) ​​and due to specific signal conditions. But the point is not at all that this is a high-level signal; the subwoofer does not consume power from an external amplifier even with this connection, because high input impedance does not allow; Also, with this connection, similar to the low-level (to RCA connectors), the signal is amplified by the subwoofer circuits.

The fact is that with such a (dynamic) connection, the signal to the subwoofer comes from the same outputs (external amplifier), with the same phase and “character” as the main speakers. This argument is somewhat strained, since the signal changes the subwoofer amplifier further, besides, the phase still needs to be adjusted, but the idea of ​​​​consistency of the signals going to the speakers and the subwoofer appeals to the imagination ... only there are all the necessary outputs.

Liquid phase or jump phase?

The most common equipment: level and filtration are smooth, phases are stepped; a pair of stereo RCA plus an additional LFE input

Three main active subwoofer controls allow you to change the level (volume), upper frequency limit (so-called cut-off) i phase. The first two are usually liquid, the third - smooth or bouncy (two position). Is this a serious compromise? Many manufacturers decide to do this not only in cheap subwoofers. Setting the correct phase, while very necessary for good alignment, is in practice the least understood and often overlooked task by users. While smooth tuning is theoretically the best way to tune a subwoofer to the satellites, it makes the task much more tedious and therefore difficult and neglected. But with level control and filtering, it’s a real disaster ... By agreeing to such a compromise (a switch instead of a knob), we encourage users to try it in a simple way: just determine which switch position is better (more bass means better phase balance), without the tedious search for the ideal with a large number of handle moves. So if we have smooth control, let's try at least extreme positions, i.e. different by 180°, and we will definitely notice the difference. In the extreme case, an incorrectly set phase means a deep hole in the characteristics, and only “under-adjusted” means attenuation.

Remote control

Until now, only a small number of subwoofers have been equipped with remote control via remote control – for them it is still a luxurious piece of equipment, although very practical, because setting the subwoofer from the listening position helps a lot in achieving the best results. Better to practice any other way than running back and forth between the seat and the subwoofer. However, it is hoped that the remote will become basic equipment, and subwoofer tuning will become easier and more accurate thanks to applications for mobile equipment - this solution is cheaper than adding a remote, and also opens up a lot. more possibilities.

Carefully! Big speaker!

Available subwoofers from big speakers The woofers are a little… dangerous. Making a large loudspeaker is not a great art - a large diameter basket and diaphragm do not cost much, they are most dependent on the quality (and therefore size) of the magnetic system, which determines many important parameters. On this foundation, by appropriate selection of other design features (coil, diaphragm), power, efficiency, low resonance, as well as a good impulse response are built. A large and weak loudspeaker is a disaster, especially in a system bass reflex.

This may be why some people are wary of large woofers (in loudspeakers), usually blaming them for being "slow", as evidenced by a relatively heavy diaphragm. However, if a heavy oscillatory system sets in motion a sufficiently effective "drive", then everything can be in order, both in a passive loudspeaker and in an active subwoofer. But be careful - the weakness of the magnet will not be compensated by the high power of the amplifier or its efficiency (current, etc.), which some manufacturers offer. The current from the booster is like fuel, and even the best fuel will not significantly improve the performance of a weak engine.

The same looking cabinet, loudspeaker (on the outside) and hundreds of watts can produce very different results, depending on the power and configuration of the loudspeaker drive system.

Especially in the case of a phase inverter “broken” by a weak magnet (and / or too small a cabinet volume), the impulse response cannot be “repaired” by the power from the amplifier, which can be used to correct the frequency response, therefore, in active subwoofers - more often than in speakers - it is used closed body. But bass reflex it seduces with its higher efficiency, it can play louder, more spectacular... and the accuracy of explosions is not so important in home theater. It is best to have everything at once, which requires a solid (in all respects) loudspeaker, a lot of power from the amplifier and an enclosure with optimal volume. All this costs money, so large and decent subwoofers are usually not cheap. But there are “reasons”, but to find them, it’s not enough to look at the subwoofer from the outside, read its proprietary characteristics, or even plug in and check a few random settings in a random room. It's best to know the "hard facts"... in our tests and measurements.

Grille - remove?

W multiband loudspeakers The problem of the effect of the mask on processing performance is so serious that we take it into account in our measurements by comparing the situation (on the main axis) with and without the mask. Almost always the difference (to the detriment of the grille) is so obvious that we recommend removing it, sometimes very clearly.

In the case of subwoofers, we don't bother with this at all, because almost no grille changes the performance to a noticeable extent. As we have explained many times, typical gratings they affect the radiation not so much by the material with which the loudspeaker is covered, but by the frame on which this material is stretched. The attenuation introduced by typical tissues is small, but short waves of medium and high frequencies are reflected from the scaffolds, interfere and thereby create additional uneven characteristics. In the case of subwoofers, the low-frequency waves emitted by them are relatively very long (in relation to the thickness of the frames), so they are not reflected from them, but “flow around” such an obstacle as the edges of the cabinet, spreading freely and in all directions. Therefore, subwoofers can be safely left with the grills on, as long as... they are strong and well-fixed so as not to get into vibrations at certain frequencies and higher volume levels, which sometimes happens.

Wireless transmission is often optional, requires the purchase of a special module, but the port in the subwoofer is already waiting for it

Omnidirectional

When measuring subwoofers, we do not take into account directivity characteristics, so we do not measure processing characteristics at different angles. It is difficult to talk about the axis along which the measurement is made, because this is the so-called near-field measurement - (as far as the amplitude of its operation allows). Low frequencies due to the long wavelengths, which are much larger than the size of the large woofer and its enclosure, propagate omnidirectionally (spherical wave), which is the main reason for the use of subwoofer systems in general. So it doesn't really matter if the subwoofer is pointing directly at the listener or slightly to the side, it can even be in the bottom panel ... So there is no need to precisely "aim" the subwoofer at the listening position, which does not mean that it does not matter at all where it is located .