How Subwoofer Became a Dirty Word

Whatever their differences, many professionals and audiophiles share a common experience – a subwoofer dalliance. However, after much trial and turd-polishing they often conclude that mo’ bass isn’t worth the downside: the sub can’t keep pace with the mains, bass is bloated, locatable and not integrated; dual analog outputs are needed, etc. Thus ends the subwoofer episode: better to have tuneful upper bass, unspoilt by the crudeness of a dedicated LF box. Quality not quantity. Lesson learned: subs are OK for sofa-quaking movies; not so much for music.

Wrong. You tapped out too soon. And you didn’t think big enough. Here’s five points to consider . . .

First, there’s a reason why a domestic floorstander or 2-way studio monitor is widely accepted as being not-too-awful: they naturally roll off at 40-80Hz. One of the more destructive artefacts of an untreated room is a  5-15dB room mode peak somewhere in the 30-100Hz region. Therefore the natural limitations of such speakers often leans rather happily into the properties of the room . . . .

Throw a subwoofer into the mix, with ruler flat response from 20-80Hz crossing over one-sidedly into mains, and LF room issues are amplified.

Second – related to the above – a subwoofer is a powerful demonstrator of the room mode created by placement of an LF emitter in a given location. Rooms ring with a static pattern of peaks and nulls. Two or more subwoofers interfere with these ‘standing’ waves and smooth response, averaging out room modes. For more on this, see here >.

One subwoofer is simply a bad idea: it’s not possible to genuinely integrate a single sub. The integration that matters most is not the crossover between the subs and the mains, it’s the interface between the sub and the room. Get that right, and you’re half-way there. Using two, or four, subwoofers is a major step in the right direction.

Third – corollary to the above – subwoofers are useless without EQ. Ideally, DSP/EQ lives on-board and allows its performance to be profied in response to in-room measurements for flat, in-room response. Alternatively, in-line DSP or the kind of room correction common in AV processors can be very effective, though somewhat lossy.

Fourth: subwoofers have to be really big and really powerful, or they’re a waste of time – given that your mains have useful in-room response down to 50Hz. Consider the logarithmic progression of energy required to produce lower and lower frequencies . . .

As a rule of thumb, if you’re serious about authentic bass reproduction, forget about anything less than a 15-inch driver and half a kilowatt of amplification. Nothing weedier is man enough,  and will only lead to dissatisfaction. Because huge energies are needed to propel a cone to generate 20Hz tones, big, efficient drivers have a head start. However, equally huge magnets and amplifier damping is needed to stop the driver as rapidly as it starts, and avoid the dreaded ‘one-note’ thrum of cheap subwoofers.

It’s worth mentioning that porting a subwoofer is probably a bad idea, too. Efficiency gains hit performance benchmarks of bigger and more powerful subs (re: SPL and frequency extension), but they always sound relatively sluggish and tend to be compromised in other ways. Designs vary in sophistication too widely to make a general rule hold fast, but it tends to be true that open-baffle (no box) or sealed (all box) subs stop and start more realistically than ported designs.

Whatever sub you choose, of course, you need at least two, which leads to our final point . . .

Five: location. It’s helpful to think about the sub-80-100Hz performance of your listening room as an entirely different issue to it’s performance above that point. Rooms have strong preferences for the correct location of subs (plural). Get that wrong and you’re snookered. Consider this as unrelated to the position of your mid/treble emitters, which have to be sited with increasing precision as you ascend the scale to co-ordinate the arrival of higher frequencies with your ears and create a soundstage centred on a listening triangle.

If you stop and think about it, it’s a terrible idea to lock sub-80Hz frequencies into the same cabinet as higher frequency emitters: where do you put that box? In a spot that steers treble information correctly, but creates major bass issues, or vice versa?

The only solution is multiple bass emitters of the right size, in the right location, properly harnessed with smart, room-responsive EQ.

So, if you’ve heard a single, dumb, underpowered, ported 12-inch subwoofer and concluded that a subwoofer can’t live with the speed of your electrostatics, you’re partly right but almost entirely wrong: doing it like that will never work. Go big or go home. If you hear dual, sealed 18-inch subs driven by a kilowatt of amplification each and tamed by DSP for flat in-room response, there’s no going back.

Music needs bass. But bass needs smartly applied power. Short-change it, and you’re just irritating the bass (and your room). Respect the bass with proper subs and you will be  rewarded: not only in terms of full-spectrum FR but also greater dynamic range and lower distortion from the drivers and cabinets you’ve unloaded with that high-pass filter.

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