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Opinion: Can subwoofers really make music? | StereoNET Australia

Len Wallis examines the pros and cons of integrating a subwoofer into a powerful 2-channel stereo system…

I have never been a fan of subwoofers in a 2-channel environment. At least that was the situation before my stay at the Munich High End Show A few years ago I was looking for a new brand of subwoofer. Several major manufacturers presented their stereo systems with impressive results and I finally decided on one from JL Audio.

My dissatisfaction with subwoofers for stereo systems stems from integration issues. It's hard to find one that will work with a pair of hi-fi speakers without creating its own sound signature. Partly this stems from the speed of the subwoofer itself. Historically, most have been slow, cumbersome units – offering adequate bass response but minimal speed or definition. In a theatrical application, you can get away with this because the senses are so distracted by the action and imagery that you're not as aware of low frequency accuracy. Music is different, as you're fully focused on what the artist is trying to convey. Attack adds to the realism of the performance, and definition is paramount.

Bookshelf speakers have many advantages, but they always have limited bass. Serhan Swift, for example, gets excellent bass out of a small box with the Mu2, but even that speaker struggles with material below 50 Hz, and there is a lot of recorded material down there. A standard grand piano, for example, goes down to 27.5 Hz (A4) and a bass trombone goes as low as 23 Hz. An orchestral double bass manages 32.7 Hz (C3) and even the popular Fender bass manages 41.2 Hz.

All subwoofers can reproduce these frequencies, but many have problems with details. I am a great admirer of the late jazz double bassist Charlie Hayden. When it goes from C sharp (34.6 Hz) to E (41.2 Hz), I expect to hear that as two different notes – and unfortunately, that hasn't always been the case. Far too often, those notes are played as a single monotone. And I expect those notes to be played at the same speed and attack that I get from the speakers that the subwoofer is complementing. If that doesn't happen, if the subwoofer doesn't rhythmically follow what the main speakers are playing, then the magic goes away.

Poor subwoofers compromise the artist's involvement in what they are trying to convey, and many of the benefits gained by using a subwoofer are lost. I would always rather listen to a good bookshelf speaker without a subwoofer – despite the lack of bass response – than one with a second-rate subwoofer. A good pair of bookshelf speakers combined with a quality subwoofer is a whole different story, however…

If your subwoofer is properly integrated into your system, you shouldn't notice it – at least not consciously. It should never draw attention to itself. However, when you turn it off, you should immediately notice that something is missing, as if a dimension of your music has disappeared.

There are three things to consider when buying a subwoofer. First, price, because the good ones aren't cheap. Bass extension isn't the most important thing – if money is tight, go for one that's fast, rather than one with extremely extended bass response, as timing is more important. As always, a proper listening session at the dealer is helpful here. Size is the second consideration, because no matter how clever the design, you can't override the laws of physics. The bigger the subwoofer's enclosure, the more extension you get. And third, there's the question of placement, because where the subwoofer is placed in your listening environment will have a big impact on the end result.

Once you've purchased your chosen subwoofer, you need to get the most out of it. The number one rule is: don't double-use your speakers and subwoofer. In other words, the subwoofer needs to start working at the point where the main speakers start to drop off in bass – so it shouldn't also reproduce the higher bass portions of the recording that the speakers would normally handle. The goal here is to extend the frequency range of your system, not to add extra energy to existing frequencies.

This means that if your stereo amplifier does not have a dedicated subwoofer output, you will need to use the subwoofer's speaker inputs so that it filters out all the high frequencies and does not try to reproduce them. If your amplifier has a direct subwoofer output or preamp output, use that. Most subwoofers are active, meaning you can feed them preamp level signals and they will work optimally.

For a long time, it was thought that the position of the subwoofer was unimportant – based on the assumption that our ears are unable to detect the direction of low frequencies. Today we know that this is not true. Low frequency waves interact with the room they are in – they bounce around and cancel each other out in some places, while doubling their intensity in others. There will be places in your room where the subwoofer sounds too loud, and others where it almost disappears.

Proper placement of your subwoofer – decor, furnishings, power outlets and key partners permitting – is the position where the response is best at your listening position. This is best achieved through trial and error, and the subwoofer should be positioned so that it sounds right in the room. In a typical listening environment, this requires a compromise, that is, finding the best compromise between power and position. You can of course add a second subwoofer, which can do wonders for balancing out different highs and lows in the room, and provide other performance benefits as well. However, a well-positioned and tuned subwoofer will easily outperform two poorly placed and tuned subwoofers. Have fun discovering your bass instinct!

For more information visit Len Wallis Audio