Originally posted by uncle eric
There is a common misconception that small driver equals fast bass and large driver equals slow bass. You often hear reviewers talking about how fast a certain sub-woofer is. If you look at some subwoofer manuafacturers tech blurb they will also suggest the same.
The first thing to understand is that bass itself is not particularly fast. Virtually any woofer, even those with huge heavy high mass cones will reproduce bass frequencies with every ounce of speed present in that bass.
It is in fact nonsense to suggest that small mass woofer cones will give you "super fast bass".
If a driver can produce say 40Hz with low distortion , how fast the woofer starts is almost irrelevant (within reason of course). It only needs to accelerate fast enough to match the rise time of 40Hz at the fastest point along a 40Hz sine wave. If the woofer can do that, it is going as fast as it needs to in order to be as fast as fast can be at 40Hz. The woofer cone does not need to be able to accelerate at 20kHz velocities in order to produce instantaneous 40Hz energy and if you could build a woofer that "fast," 40Hz would sound exactly the same through a "slow" woofer.
Does this mean that there is no such thing as fast bass and slow bass? No. It exists, just not for the reasons and explanations you have been hearing for years, and certainly not for the attributions youve read in some magazines. There are reasons to use lighter, lower-mass woofer cones. They just happen to be different reasons than the ones you think you know.
Smaller woofers dont make faster bass, but they can reproduce higher frequencies than larger woofers can reproduce, and this can be all important when it comes to speaker design. You want your mid-range drivers and the woofer to integrate with spot on symmetry, with perfection and without any problematic interactions throughout their overlap zone.
This is the only reason why you might want smaller, lighter, "faster" woofer cones -- not because they lead to faster bass. Having said that, top quality high end monsters like the Velodynes are so well designed that they have very little problem in achieving this integration or overlap. That "overlap zone" is so incredibly critical to your perception of bass speed that there is little or no tolerance for error. This is a another reason why you should take your time in setting up. The null tolerance for integration error extends to phase, amplitude, frequency, and time. Introduce even slight variations between any part of the woofer and midrange (or panel) overlap zone and you get audible effects in the bass or midbass. This is where all of your perception of bass speed comes from.
In fact, bass speed is virtually 100% a function of how ideally the midrange and woofer are integrated. Bass linearity is just one hugely important factor. Quality bass maestros like Velodyne often talk in terms of their meticulous Linear motion rather than speed for example. Often, you may see a flat frequency-response curve, but the speaker can still sound like it has lumpy bass response because of less-than-ideal phase (or other) relationships between the midrange driver and woofer. Phase can often change with frequency. The woofer and midrange drivers can actually veer off in different directions, phase-wise.
This is especially possible when you mix driver types like panels and dynamic drivers. (Dig up my Martin Logan review from a while back). But large dynamic drivers (woofers) operating at the top of their range and medium-sized dynamic drivers operating at the bottom of their range can often diverge significantly in their phase response. When phase (or other) errors happen, you get comb-filtering effects. This comb filtering results in the complex response of the loudspeaker (to music) being quite different than the response of the speaker when the input is something simple like the sine-wave sweep used to measure "frequency response."
To avoid comb-filtering effects that cause "beating" (reinforcement) and "cancellation" effects in the sound (both are usually partial effects), it is imperative for the phase, time domain, amplitude and frequency performance of the woofer and midrange driver to be "aligned." Get the midrange or woofer a little ahead of or behind the other driver, and comb filtering starts. You can do things to minimize it, but you cant stop it with certain combinations of driver and crossover.
It is fearfully hard to integrate a dynamic woofer with an electrostatic panel because the two drivers are so different from one another. This is in fact just one of the reasons why ML's cost more than Kef Q1's. Your absolute best shot is using an active crossover with infinitely variable phase/frequency, polarity, time domain and amplitude adjustments. Play with it long enough and you could dial in the response of the dynamic woofer and electrostatic panel to achieve perfection in their integration.
Achieving the same thing using a passive crossover is incredibly difficult. Some designers are getting better as they learn from years of trying, but it is still one of the hardest things to do in audio that I can imagine. Just getting a dynamic midrange and dynamic woofer to integrate perfectly is enough of a challenge. You can hear even small errors show up as speed problems in the bass or midbass. These are the kinds of "character" that will remain with a given set-up no matter what happens.
What about amps, preamps or source components that sound like they make the bass faster or slower? There are many ways for this to happen, but they all involve changing some relationship between the midrange driver and woofer so that the integration changes in some way that manifests itself as "faster" or "slower" bass. The component itself is not producing faster or slower bass; it is creating an interaction with the speaker crossover that results in you hearing that. Some of those interactions will be consistent from system to system, while others will be chameleon-like, changing from "fast" bass in one system to "slow" bass in another. Yet if you measure the component electrically, there is nothing in its measurements that indicate that it is anything but perfect, speed-wise, at bass frequencies. It only takes a small loudspeaker-dependent phase shift to occur when using a particular amp to make it so. This would be harder to have happen in a preamp or source component -- their signatures will tend to be more consistent from system to system.
What about bass detail?
Why is it that one speaker has so much more bass detail than another? This to is strictly driver integration and NOT the quality of the woofer itself, as you may have heard.
Let me put this another way. You all know what a water-colour painting looks like. Blotchy with colours running everywhere. In fact, most of the time, until the artist proceeds to "define" the edges of his/her work with something finer like a thin pencil for example, it doesn't look like much at all. In much the same way, bass detail comes from the finer (pencil like) midrange driver. But your ear/brain is so completely fooled by this complex interaction of midrange and bass sound that you believe that it is strictly a bass-related thing. It isnt, and you can prove it.
When you have some time to kill, un-plug your main speakers and play something through your subwoofer alone.
You wont hear anything vaguely resembling speed coming from that slow, soggy-sounding, plodding subwoofer. It has no detail and no speed whatsoever when heard all by itself. However, once re-integrated, if your system is set up well, the subwoofer will appear to have tons of detail. But, and a big but, if the integration is off a little, the bass will sound fast or slow too. All of that sense of speed and detail is coming from the mid-range, not the bass. That is why the integration of the mid-range and bass is so critical to getting a good-sounding set-up.