When I was first getting interested in all things audio, home subwoofers were rather specialist devices that were only of interest to two groups of hi-fi enthusiasts: those who listened to large pipe organ recitals and those who enjoyed reggae! Things have moved on a great deal since those distant days, and today subwoofers are now considered — more for the ‘domestic acceptance’ factor than any potential sonic benefits — to be an almost standard part of modern hi-fi and studio monitoring systems.
It is therefore becoming increasingly common to have smaller ‘satellite’ left and right subwoofers speakers, plus one or more subwoofers — a format often referred to as 2.1. The two refers to the main pair of stereo (left and right) speakers, while the ‘.1’ refers to the limited-bandwidth subwoofer. In the same way, a surround sound system is often denoted as 5.1, meaning five main channels plus a subwoofer to handle the low frequency effects channel (LFE).
However, in the case of 5.1 home theatre and surround sound systems, a dedicated subwoofer is required specifically to handle the low frequency effects (LFE) channel. The fact that this sub usually also doubles up, through the use of bass management (explained later), to handle the bass content of all five main channels as well, is just a convenience that allows the use of smaller satellite speakers. Again, I’ll come back to this topic later, but I first want to consider 2.1 stereo monitoring arrangements.
The Subwoofer Advantage
When designed and used appropriately, subwoofers can be extremely effective and very convenient. Equally, though, it is very easy to destroy any chance of good monitoring quality with an inappropriate or badly set-up subwoofer — and it is worth stating that I have probably seen nine unsatisfactory installations for every good one!
Poor subwoofer installations usually suffer from too much, or poorly defined, bass. Often there is an obvious ‘hole’ in the frequency spectrum in the crossover region between the satellite speakers and the subwoofer. It is the ‘integration’ through this crossover region that really makes or breaks the system as a whole.
The worst kind of subwoofer system will only provide a boomy or monotonal ‘woomf’ of energy, regardless of the pitch or dynamics of the bass instrument, and the bass might thus appear to be slow or late relative to the main speakers. On the other hand, a well-designed and well-configured system will usually enable more accurate imaging, and have a clearer, more transparent mid-range (thanks to lower distortion and intermodulation levels) and higher overall output than could be achieved with the satellites alone.
From a practical point of view, a satellite and subwoofer combination is much easier to site and to move around. The individual speaker cabinets are more compact and lighter than full-range speakers, and that is often an important consideration — especially in small home studios and for location-recording rigs.
So the aim of this article is to try to explain the hows and whys of choosing and using a subwoofer, in the context of both stereo and surround sound applications.