Critical subwoofer tip

That is achieved by time and phase alignment of the sub, LF, mid and HF drivers. Full Stop.

@ieales Yours is not the first mention in the discussion referring to the importance of time alignment. I don’t think I understand this in the context of low frequency behavior in a closed room.

For example, if my listening position is 10ft away from my main speakers, all frequencies above about 113Hz are arriving at the listening position from the speakers directly because all the frequencies at this level and higher have wavelengths of less than 10 feet. In contrast, frequencies below this threshold will require more than 10 ft to reach full amplitude because their wavelengths are longer than this. This means, to hear these lower frequencies, they have to bounce off at least one or more room boundaries. This would seem to indicate that all these lower frequencies arrive at the listening position later than the higher ones. In other words the higher frequencies would arrive at my listening position after traveling 10 ft, the 30 Hz frequency had to travel at least 37.5 ft, the 40 Hz traveled over 28 ft., etc. Since all the frequencies travel at about 1,125 ft/sec, the lower, reflected frequencies are all going to lag behind direct ones from the mains.

There was some suggestion that a delay could be applied to the subwoofer but it would seem for exact time alignment, you would have to apply a variable delay to all frequencies except for the lowest the system can produce to have them all arrive at the listening position at the same time. This seems pretty involved to me. Or have I missed the whole point again?

ieales, Trikustik-this is a trip! thanks 

Consider a kick drum on an open field where there are no reflections. The higher frequencies of the beater hitting the head arrive before the full amplitude of the head deflection, yet you still identify it as a kick.
 You can see a kick waveform here
http://192.168.1.160/assets/CblSnkOil/Signal_vs_ACLine.png

Putting the same kick drum in a room does not change your identification as a kick, but you are fully aware it is now a kick in a room

In a multi driver speaker the frequencies which make up a kick are reproduced by different drivers. The sound begins when the electrical signal starts and in the voice coil plane. The ≈50Hz fundamental starts propagating from the woofer at the same time as the [say] ≈2250Hz beater whack does from the mid. If the voice coil of the woofer is 3 inches back from the mid, the whack is ≈180° out of phase by the time the fundamental starts to reach your ear.

Time aligning attempts to minimize these displacement artifacts. Nothing is ever perfect and there are crossover affects to consider as well, but properly aligned systems have a coherence missing in others. Our brain can correct for frequency variation but cannot shift time. 

Compared to live acoustic sound, all playback sucks. But as Nietzsche opined "Without music, life would be a mistake." So we put up with it.

@ieales 

The ≈50Hz fundamental starts propagating from the woofer at the same time as the [say] ≈2250Hz beater whack does from the mid. If the voice coil of the woofer is 3 inches back from the mid, the whack is ≈180° out of phase by the time the fundamental starts to reach your ear.

The waves would not reach your ears at the time even if they started at the same point as they are different lengths. And bass takes a few cycles to be heard anyway.

The waves would not reach your ears at the time even if they started at the same point as they are different lengths.

When I was in the Navy, this was known as a gross conceptual error (GCE). You get zero points for the answer. Better luck next time.