Originally Posted by kevinzoe
I think the concept of 'group delay' for a subwoofer helps to explain how fast it can stop its motion when an input signal ceases. The longer the group delay the 'boomier' it is likely to be perceived. Also relevant is bass decay (RT60, RT30) within your room which inevitably increases as frequency falls. Without some way of attenuating low bass energy, you will hear more 'boominess.'
group delay is arrival time, not settling time. See http://avtalk.co.uk/showthread.php?t=10999
This is a measure of how the sub delays certain frequencies with respect to others. Typically the extreme bass will arrive at your ears (or our test mic) a few milliseconds after the rest of the frequencies and the extent to which this happens varies from sub to sub. The smaller and more consistent the group delay is across the frequency range, the better the sub should sound. If group delay becomes excessive it may be audible as 'slowness' in the bass or muddiness. For example, if the bass associated with a bass drum beat arrives after the 'thwack', it may sound ponderous and slow. If they arrive more or less in sync then it will sound 'tight'.
"How much group delay is audible? Opinions are divided, but a good rule of thumb is that a time delay of between 1 and 1.5 cycles is just audible. So at 50Hz, group delay should be kept below 20ms (1000/50) and at 20Hz, it should be below 50ms (1000/20) to guarantee inaudibility."