Why do subs sound bloated or slow?

I currently have my subs next to my mains, slightly forward. They are sensitive to movements of one inch. I can play a passage and it will sound right, but if I move the subs an inch forward or back, and it's out, and stays out if I move it farther. In previous setups, I've been able to introduce a delay to the mains relative to the subs (in Pure Music, for example), and I had the same results: the coherence of the sound was sensitive to delays that were a fraction of a millisecond.

So time alignment is crucial, and I don't think the subs will ever be truly integrated in a system until that is achieved. I think once it is tackled, EQ is available to deal with the frequency response of the room. That's my current approach, and I don't think I've sacrificed much, except that there are subwoofers sitting in not-inconspicuous locations in my living room.

Crossing over to full range speakers....at too high a frequency, is guaranteed to give you that bloated feeling.

Certainly group delay and frequency response are intertwined.

I suspect that "masking" is what makes the effects audible. What I mean is that you can't perceive accurately what is happening to the bass response except by what it "masks" in the higher frequencies.

If a 20 Hz signal suffers a group delay of say 30 msecs - what happens to the harmonic distortion associated with that sound...are they also delayed by 30 msecs?

If the harmonic distortion is significant and delayed by 30 msecs then you may have a very audible 80 Hz harmonic that is audibly delayed by 30 feet. I cannot help but suspect that this harmonic will make the bass sound "slow", "bloated" or "muddy" by masking higher frequencies.

In essence, just consider the entire harmonic distortion from low frequencies (below 50 Hz) all delayed by the group delay - this smears out the bass response and masks transients to the ear.

I agree that a hump in the frequency response will ALSO cause masking by emphasizing certain frequencies by as much as 5 dB more than they should be and making the balance of sound such that you do not properly hear the higher frequencies (sound of the high frequency hit from the stick hitting the drum head).

Sound Engineers know that they can change the "speed" or attack of bass notes by altering the higher frequencies - emphasis is added for greater attack and de-emphasis to make the sound more laid back - in my opinion they are playing with teh amount of bass "masking" when they do this

You shouldn't really "hear" the sub. If you do, they are too LOUD!!!

There's an element of "When did you stop beating your wife?" to this discussion. It starts with the presumption of guilt (for subwoofers) and asks for proof of innocence.

I can (and have) set up subs that sound somewhat overdamped - producing a lean sounding tonal balance (to my ear) despite flat on-axis measurements at/around the listening position on my RTA unit. My Rythmik subs allow for adjustable Q and I have backed off the most highly damped setting for just this reason. I have also heard many extended/full range speakers that sound underdamped, bloated and "slow".

The question of properly damped bass isn't unique to subs. As to group delay issues attendent to placement, endless screwing around with varying placement of subs relative to mains leads me to believe that it's a non-issue, but that would have to be qualified for related variables, including:

Crossover frequency and slope. IF these issues are actually audible at higher frequencies (and, as a practical matter, I have my doubts) , a lower crossover frequency and steeper slope would largely determine how audible they are in a given system. It would also allow increasingly greater separation as the crossover point drops and/or the sub's high cut slope is steepened. IOW, generalizations would be misleading.

The relative damping of the subs and mains at/near the x-over point. IME, there is a pretty good chance that the (sealed) sub is more highly damped than the main speaker (if not matched with care) and the qualitative result of this mismatch is hard to predict. Incidentally, this one is -again- not unique to subs. Many a 3 way full range speaker can exhibit problems in the lower crossover region.

and

The sensitivity of a given listener, among others.

Bottom line, it will be VERY difficult to prove inocence (or guilt) using the math cited here, but much easier using your ears.

Just MHO, as usual.

Marty