Why do subs sound bloated or slow?

I agree that most people don't know how to set up subs properly, but I'm not sure the automatic setup system work any better. They are primarily EQ programs, and do nothing for the transient response. And, frankly, it would be very hard for them to fix transient response because that requires playing the mains and sub(s) at the same time and (usually, because of sub placement and processing delays) delaying the MAINS. The phase control on a sub won't do this either and, to the extent that it is useful at all, can only work when the sub is closer to the listener than the mains.

All of what I'm saying applies to music only. For home theater, it doesn't matter a whole lot if your sub is a full cycle behind the mains. You just need it to be in phase at the crossover point and EQ'ed to avoid the room modes, and it will sound pretty good.

"Why do subs sound bloated or slow?"

I think it's hard to optimize a sub set-up by ear. That approach requires more time, work and patience than most people are willing to invest. If more people used the available tools - real time room analysis - their sub set-ups would sound a helluva lot better, on the whole. If you add room correction to the mix, I suspect that the average set-up would be awfully impressive, with little discussion of "bloated" or "slow".

Just MHO based on personal experience.

Marty

01-23-11: Audiokinesis
Both the bloat and the slowness you describe are primarily frequency response problems; at low frequencies the ear has very poor resolution in the time domain so it doesn't really pick up the transient response in and of itself.

This is precisely what I was hoping to discuss.

Duke - As I mentioned, my theory about frequency response and transient response tending to be a zero sum game is just that - a theory. Which is a way of acknowledging that I very well may be wrong. Having said that, the theory that optimizing frequency response often comes at the expense of transient response, or vice versa, explains many of my experiences with subwoofer setups using frequency response software. Of course, there may be other explanations for my experiences.

IME, small differences in sub placement on the z axis of the room often result in significant audible changes in bass response, EVEN WHEN there are little or no measurable differences in frequency response. Since the audible changes don't seem attributable to differences in frequency response, I eventually concluded that they were attributable to differences in transient response, or more precisely, differences in the system's time alignment, where 'alignment' is understood in terms of the arrival times of the system's various drivers at the listening position. That conclusion is consistent with the audible changes being a function of z axis placement.

Encouraging that conclusion is the impression that, for some z axis sub placements, the bass sounds "in sync," whereas for others, it sounds "out of sync." Again, this is sometimes the case even when two placements have a similar or identical measurable frequency response.

On the basis of these experiences, I concluded that, when two different z axis sub placements measure similarly in frequency response, but one of them sounds significantly better than the other, the reason is because the better-sounding placement has a more ideal time alignment with the other speakers in the system.

Again, I recognize that this conclusion could be a mistake.

Bryon

Transient response is not irrelevant. Many subs have group delays of up to or more than 1 cycle. Of course this is audible. The other factor intrinsically tied to transient response is the resonance.

An underdamped design will keep oscillating after the signal has stopped - this is adding sound after the sound has in fact stopped. Most subs are designed that way. No wonder it sounds bloated.

A good design will be overdamped or critically damped. These will not sound bloated.

As said earlier the crossover point. The crossover point is the main and possibly the only reason for a sub to sound bloated. If your mains go down to 50 and your sub is crossed over at 80 with a very slow slope of 6db you could have a problem. Also having the sub too close to a corner can accentuate humps in the subs frequency response.