The so-called “group delay” is simply the time lag between the envelope of input burst and the envelope of the amplitude of the output burst. So, group delay means a propagation delay through a filter, measured on the envelope of the signal.The selling point of REL as opposed to popular opinion here is it’s speed. But even after going through the “speed” threads here, I am not convinced about the answers. For example like I asked earlier, if I play a 50hz or 80hz signal through the top of the line Kef speaker like the muon and a 20 dollar cheapo speaker for 1 second, would it stop without further swinging at the end of 1 second when the signal is off in the same way. Subjectively I have heard fast and sluggish sounding speakers in my life, never understood what made it sound so.
Transient response is the ability of a speaker to start and stop exactly when the sound going into should start and stop. A bass cab with excellent transient response sounds far more alive and responsive than one with poor transient response and makes it easier to both groove hard and be heard on the gig.
I believe those two will be very different between Muon and 1 dollar speaker, among many other differences.