The first step is to choose a subwoofer that fits your setup. Sometimes it’s not that hard. If you build a surround setup based on speakers from a reputable manufacturer that also focuses on home cinema, there is a good chance that a suitable subwoofer is available. In theory, it should fit perfectly with the speakers you choose…
But with a manufacturer that is more focused on stereo, you will often have to look for a subwoofer elsewhere. That in itself is not a problem. You can safely combine a subwoofer from one brand with speakers from another. With the other surround speakers, it is best to stay within the brand and even within the speaker family, because then you have good timbre matching (read: the speakers are similarly tuned).
Really good subwoofers are difficult to make, which also explains why some loudspeaker manufacturers prefer not to try them. That’s why there are certain specialized brands that just have a huge reputation in the field of subwoofers. Often these are lesser known North American brands because you have a greater tradition of home cinema installations there. SVS and the British REL are good examples, as are Velodyne and Sunfire. There are still some. Mainstream brands that have developed good reputations for subs include Bowers & Wilkins, Dali, ELAC, KEF, Klipsch, Monitor Audio, PSB and – if you want to tap into your piggy bank – Paradigm and Wilson Audio.
Whichever brand you choose, choose a model that allows you to adjust sufficiently. What you need is an auto power mode, a crossover frequency control (which determines the upper limit in terms of frequencies the sub plays), a volume control and a phase knob. If you want to add a subwoofer to a stereo setup, a music mode is handy and a cinch or XLR input. After all, with a stereo amplifier without a dedicated sub output you will have to use a pre-out output.
In practice, you will have to choose a sub with dimensions that (may) fit in your living room. But size should not be the determining factor. Our rule of thumb: the bigger, the better. And also: the more solid, the better. A dancing sub is funny – but not good. Be warned: a subwoofer is often a heavy thing for this reason.
How much power?
Don’t focus on wattages. You may never really use that 1,000 watts and the numbers you read are a bit like the official fuel consumption figures for cars. At the same time, a sub must have some power (see our background piece on subwoofers), especially if your space is a bit larger.
Deeper is better
The frequency range specified by a manufacturer is only an indication. Unless it is specified at which frequencies the response falls below -3 dB, for example. That’s a bit more concrete. The rule of thumb here is that a larger woofer will often produce a deeper bass – although smaller subwoofers can still play lower thanks to bass reflexes.
Control is important for music playback
In movies, tight bass is better than slow or woolly bass. But with music, it’s simply crucial, otherwise any sense of speed and rhythm can disappear from songs. This is the secret of more expensive subwoofers: a tight, controlled sound, which is reflected in a short impulse response. The impulse response indicates how long a loudspeaker ‘vibrates’ when it plays a sound.
Choose the right crossover
You have to choose the point at which the subwoofer stops working and the other speakers take over. Too high, and you will notice certain sounds coming from your subwoofer. That undermines the stereo or surround image. Too low, and you’re left with a ‘gap’ between what your speakers can reproduce and when your subwoofer starts.
The crossover point is best determined by your AV receiver, with a stereo amplifier you should look at the frequency range of your stereo speakers. A rule of thumb: let the sub take over everything around 80 Hz, even if those floorstanders can go even lower. Ideally, you work with an amplifier that has a high-pass filter that ensures that those lower frequencies are no longer sent to your stereo speakers. If there is no setting to do this, it is best to experiment with the crossover. You may have to set the crossover on the sub lower to prevent a certain low frequency coming from the stereo speakers from counteracting the same frequency from the sub – paradoxically, you experience just less bass.
With bookshelf speakers, you may have to adjust the subwoofer higher than 80 Hz, because the small speakers cannot go that low. It is then definitely recommended to place the sub at the front of the room.
The placement of a sub is extremely important. It is often advised to place the sub at the front of the room, not near a corner and not against a wall. That’s not bad advice, but not always feasible. Sometimes the subwoofer has to be in the back of the room. Then don’t set the crossover too high. If you have a small sub and you want exaggerated bass, you can of course place the device in the corner. This is still possible for movies, but it is not recommended for music.
Do not build in subwoofer
You never put a regular subwoofer in a cabinet. It’s very tempting to hide that ugly thing, but you’re just creating an extra enclosure around your subwoofer. One that was not designed acoustically and can therefore only deteriorate the sound. If hiding the sub is really a necessity, look at other options. Like subs that are built into the wall, which works surprisingly well. You also have models that fit under seats, although those are also compromise devices.
You can solve many problems in the room with measuring systems. But maybe you don’t have the time or money for that. But you can already make a start with a simple app on your tablet or smartphone. Before your inner audiophile kicks in: it’s a rudimentary solution. But you can detect a pronounced room mode in an app like RHA Audio, as in the screenshot with this article. We played a sweep test tone through the receiver (playing consecutive frequencies at the same volume, possibly through some apps) and then quickly see a noticeable peak around 50Hz. If you listen carefully, you will notice this too. Based on this measurement, you can experiment with a different placement of the subwoofer or with the equalizer on the receiver. If you’re ready for a more advanced approach, the free REW is definitely worth exploring!