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nyone who’s ever visited a hi-fi show will have worked out in pretty short order which rooms were demonstrating the subwoofers; they were the one with the ceiling tiles and windows rattling, and the exhibitors in the rooms either side cursing. I once stayed overnight at a show hotel, and was unlucky enough to be allocated a room beside which the exhibitors decided to fire up their subwoofers at 7am to get them nicely run in for show opening time.

But fortunately that isn’t the whole story: if you only have space for small speakers, but want a full-range sound, or if you want to avoid annoying the neighbours by running your hi-fi system at high levels, an active subwoofer could well be a sensible buy.

Note that I said an active subwoofer – one complete with onboard amplification and filtering, plus the settings to allow the output to be optimised – as this will not only give you the best bass for your money, but also the best chance of integrating the subwoofer with your main stereo speakers. And integration is what it’s all about, adjusting the frequency band across which the subwoofer operates – more specifically its upper bass roll-off, so it’s not duplicating the effort of your main speakers – and its output level to get a perfect blend.

The intention is that the subwoofer should become part of your speaker system, and to an extent that it shouldn’t be heard, or at least not as a separate entity. If you achieve the effect of your speakers – even small bookshelf models – simply gaining more low-frequency extension you’re on the right track.

Most subwoofers out there are of the active kind, and have either one or two line-level inputs, or sometimes what are called high-level inputs, designed to be connected to the speaker outputs of an amplifier. Which model you choose will be as much about the connections your system offers for a subwoofer as the size and shape of your room: if your amplifier has a dedicated subwoofer output, all well and good, but you might also find some amplifiers with no subwoofer out, but a pair of preamplifier outputs, designed to connect to an external power amplifier, but just as usable for a subwoofer.

If you have an amplifier with neither of these provisions, then a subwoofer with high-level – ie speaker level – inputs will be the answer: you’ll just be running extra speaker cables to the sub rather than interconnects.

I’m talking here about stereo amplification, not multichannel surround systems: the latter always have at least one dedicated subwoofer output, and often more, as surround sound recordings usually have their own low-frequency channel encoded into them, usually referred to as the ‘.1’ channel. Multiple subwoofers are sometimes used in large room surround set-ups: I think the most I have ever seen in an ostensibly ‘domestic’ set-up was four stacked pairs of subwoofers!

So, how do you choose which subwoofer to buy, and indeed do you need a subwoofer? Well, experience suggests that just about any system can benefit from a little assistance in the really low frequencies, with even very large speakers only extending down to around 30Hz, below which a subwoofer can be rolled in. You might need a pair of small subwoofers in a very large room, where they will prove more controllable than one very large sub, but the beauty of many current models is that they’re designed to be very compact – small enough to be hidden away – while still delivering valuable bass. And the fact that very low bass isn’t directional, so it’s hard for the ears to discern where it’s coming from, makes the positioning of your sub(s) even more flexible.

Most loudspeaker manufacturers have subwoofers designed to work alongside their main speaker ranges: for example, the Bowers & Wilkins offering starts with the compact ASW608, a tried and tested design combining a 20cm bass unit with a 200W ICEpower amplifier, and with an in-room frequency response extending down beyond 30Hz. For most compact speaker systems, such as the company’s own 600 series, it will be a fine choice. At the same time, it has the mighty D81B subwoofer, able to complement its 800 series speakers – which are hardly bass-shy themselves – with a 2000W amplifier and 30cm drivers, and able to be controlled via Bluetooth using a dedicated app.

KEF offers a range of compact Kube subwoofers, but perhaps its most striking models are the KC62 and KC92: the KC62, in particular, is a truly tiny unit with a big sound, thanks to powerful amplifiers and the company’s force-cancelling drivers – two bass units mounted back-to-back and firing in opposite directions, thus compensating for each other’s vibrations. Extensive digital processing within allows pre-sets for different room positions, making them simple to set up and operate.

Finally there are subwoofer specialists, and one of the best-known British brands is REL Acoustics, whose late founder Richard Lord was an avid Gramophone reader, and built his subwoofers purely to enhance music. His belief was simple: without deep bass, too much was missing from music and – later – movies. Almost 35 years on, the company is still thinking the same way, as can be seen in models such as the Classic 98, echoing Richard’s original models with its downward-firing bass driver and beautiful real-wood finishes. As the company says, one will enhance your music, but a pair will go even further!

This feature originally appeared in the July 2024 issue of Gramophone. Never miss an issue of the world's leading classical music magazine – subscribe to Gramophone today