I have never been a fan of using subwoofers in a 2-channel environment. At least that was the situation prior to spending time at the Munich High End Show a few years back, looking for a new brand of sub. Several of the major manufacturers were demonstrating their offerings in stereo systems with impressive results, and I finally settled on one by JL Audio.
My dissatisfaction with subwoofers for stereo stems from the problems of integration. It’s hard to find one that works with a pair of hi-fi speakers without introducing its own sonic signature. Part of this stems from the speed of the sub itself. Historically most have been slow, ponderous devices – providing sufficient levels of bass response but with the bare minimum of speed or definition. You can get away with this in a theatre application because your senses are so distracted by the storyline and the visuals that you’re not as conscious of accuracy in the low-frequency department. For music, this is different, as you are fully concentrating on what the artist is trying to convey. Attack adds to the realism of the performance, and definition is paramount.
Bookshelf speakers may have many things going for them, but they will always have limited bass. Serhan Swift, for example, gets excellent low-end out of a small box with the Mu2, but even it struggles with material below 50Hz, and there is much recorded content down there. For example, a standard grand piano reaches down to 27.5Hz (A4), and a bass trombone dives even lower to 23Hz. An orchestral double-bass is capable of 32.7Hz (C3), and even the much-loved Fender Bass is capable of 41.2Hz.
All subwoofers can reproduce these frequencies, but many struggle with detail. I am a great admirer of the late jazz double-bass player Charlie Hayden. As he moves from C-sharp (34.6Hz) to E (41.2Hz), I expect to hear this as two distinct notes – and unfortunately, this has not always been the case. Far too often, these notes are reproduced as a single monotone. And I expect these notes to be played with the same speed and attack that I am getting from the speakers the sub is supplementing. If this does not happen, if the subwoofer does not rhythmically follow what the main speakers are reproducing, then the magic disappears.
With poor subwoofers, the involvement with what the artist is trying to convey is impacted, and many of the gains achieved by adding a sub in the first place are lost. I would always prefer listening to a good bookshelf speaker without a sub – despite the lack of low-frequency response – than one with a second-grade subwoofer. However, a good pair of bookshelf speakers paired with a quality sub is a different story…
If your subwoofer is correctly integrated with your system, you should not be aware of it – not consciously at least. It should never draw attention to itself. However when you turn it off, it should be immediately apparent that something is missing, as if a dimension to your music has disappeared.
There are three things that need to be considered, when buying a sub. The first is the cost because the good ones aren’t cheap. Bass extension isn’t paramount – if funds are tight, go for one that’s fast as opposed to ultra-extended, as timing is more important. As ever, a proper dealer audition is helpful here. Size is the second consideration, as no matter how clever the design is, you cannot buck the laws of physics. The larger the subwoofer’s cabinet, the more extension you’ll get. And third is the issue of placement, as where the sub goes in your listening environment seriously impacts the final result.
When you’ve bought your chosen subwoofer, you need to get the best out of it. The prime directive is – don’t double up your speakers and your sub. In other words, the sub needs to start working at the point that the main speakers tail off in the bass – so it shouldn’t also be playing the higher bass parts of the recording that the speakers normally handle. The object here is to extend the frequency range of your system, not to add additional energy to existing frequencies.
This means that if your stereo amplifier doesn’t have a dedicated subwoofer output, then you need to use the sub’s speaker inputs, so it filters out all of the high frequencies and doesn’t attempt to reproduce them. If you do have a direct sub output or preamp output on your amplifier, then use this. Most subwoofers are active, meaning that you can feed them preamp-level signals, and they’ll work optimally.
There was a long-held belief that the position of the sub is unimportant – based on the assumption that your ears do not have the ability to detect the direction of low frequencies. We now recognise that this is incorrect. Low-frequency waves interact with the room they are in – bouncing around and cancelling themselves in some places and doubling in intensity in other areas. There will be a position in your room where the subwoofer will sound too loud, and others where it almost disappears.
The correct placement of your subwoofer – décor, furnishing, power points, and significant partners allowing – is where the response is best at your listening position. This is best done by trial and error, and the sub should be positioned where it sounds right in the room. In a typical listening environment this calls for a compromise, which is to find the best trade-off between performance and position. You can, of course, also add a second subwoofer, which can work wonders for balancing various peaks and troughs throughout the room and deliver other performance advantages, too. However, one well-positioned and adjusted sub will easily outperform two poorly placed and set-up ones. Have fun discovering your bass-ic instinct!
**This article by Len Wallis originally appeared on StereoNET on the 3/7/2024**
