From a loudspeaker’s phase response, we can calculate group delay. Group delay is complex math. It is the first derivative of the phase response (Figure 8).
We can simplify it (but very badly, be warned) by visualizing it as frequency dependent delay which I don’t define and is inaccurate anyway.
Strictly speaking, group delay is the time delay of the amplitude envelopes of the various sinusoidal components.
Figure 9 shows common ways of observing time in an analyzer. For the subwoofer in this article, this particular arrangement enables us to estimate, at best, the way from IR (time domain) via group delay to phase response (frequency domain) and back.
Our “song” begins at the very high frequencies with 0 ms and ends around 40 ms (45 feet/14 meters) later at 31 Hz!
Please remain calm! Just because I slapped a number on it is no reason to panic. Many readers have likely been aware of phase shift and group delay, but until now, very few likely considered them a problem. (Just kidding.)