Why is good, deep bass so difficult? - Myths and their Busters

Designing and building a woofer system that is theoretically flat to a very low frequency is not that difficult, but it is of academic interest only once that woofer system is placed in a room: At low frequencies, the room’s effects are totally dominant.

There is usually a LOT of room for improvement at low frequencies. Equal-loudness curves predict that the ear is especially sensitive to differences in SPL (peaks and dips) at low frequencies. A 5 dB change at 40 Hz sounds like a doubling of loudness, the same as a 10 dB change at 1 kHz. (This also explains why it takes so long to fine-tune the level control on a subwoofer system - a small change in SPL makes a disproportionate change in perceived loudness.)  Therefore, smoothing the in-room bass makes a greater subjective improvement than we would have expected from eyeballing the before-and-after curves. 

We all want "fast" bass, but what is often not appreciated is that "smooth bass" IS "fast bass". Literally. Because speaker + room = a linear phase system at low frequencies, the time-domain response and frequency response track one another. Fix one, and you have fixed the other. Because room effects are dominant at low frequencies, the most direct path to "fast" bass includes addressing those room effects.

The precise details of the room’s effects differ from room to room, but the basic issue of room-induced, large, highly audible peaks-and-dips is pretty much universal, and there are similarly universal solutions. Remember this is an acoustic problem, so it is most efficiently addressed with an acoustic solution.

One way to get smooth in-room bass is the distributed multi-sub system. Inevitably, each of the subs generates a unique in-room peak-and-dip pattern (and this is true for any listening location within the room). BUT the SUM of these dissimilar peak-and-dip patterns is significantly smoother than any one of them on its own.

An example of a non-acoustic solution would be equalization. When we fix the response of a single subwoofer at a single listening position with EQ, we are (almost inevitably) making the response worse somewhere else. And as we widen the area where we want to make an improvement with EQ, we reduce the amount of improvement that can be made. Distributed multisubs + EQ can work REALLY well, because the multiple subs significantly reduce the spatial variation in frequency response (in addition to making the frequency response significantly smoother), such that if we still need EQ, chances are it will be addressing a global (room-wide) problem, rather than a local one, so it will not be making the response worse elsewhere in the room.

In my experience - which admittedly includes a disproportionate amount of work with distributed multisub systems - a good distributed multisub setup is more effective from a sound quality standpoint than EQ or room treatment alone... though of course the use of one does not preclude the use of the others. Deepest loudest bass for the dollar comes from using a single equalized ubersub, but quantity without quality becomes fatiguing over time.

There are quite a few different ways to implement a distributed multisub system. The main points are, use enough subs (small ones are fine) and get ’em spread out.

Imo, ime, ymmv, etc.

Duke (yeah I got a dog in the fight... four small ones, actually...)

geoffkait wrote: "I hate to judge before all the facts are in but it appears a big advantage of headphones is you can get very good bass performance without all the angst, effort and cost oft required to obtain very good bass performance for speaker systems. And that’s if you’re lucky and don’t actually make matters worse."

Headphones are a lot of fun, but they are not good for accurate bass reproduction. This is at least in part because a) we perceive bass, and in particular deep bass and impact, with our whole bodies - not just our ears; and 2) there is no room reverberation tail on the notes, and room reverberation done right improves our ability to perceive pitch accurately, plus room reverberation is a component of perceived loudness (sounds that last a little bit longer are perceived as being louder).

If headphones were good for bass, they would dominate in the recording industry. Mixing and mastering would be done on headphones. Instead mixing is usually done on small nearfield monitors, and mastering on big main monitors, and if headphones are used at all, they are never relied on to tell the truth in the bass region. Some beginners hope to rely on headphones for mixing in their "budget" home studios, and you can find and follow their painful learning curves on prosound forums... you know, where those other Acme graduates end up...

Duke

One way to get smooth in-room bass is the distributed multi-sub system. Inevitably, each of the subs generates a unique in-room peak-and-dip pattern (and this is true for any listening location within the room). BUT the SUM of these dissimilar peak-and-dip patterns is significantly smoother than any one of them on its own.