In researching this dissertation, I was unable to ascertain a finite limit for acceptable group delay in speaker
design. It appears to be relatively indiscernible, especially when listening to musical content (as opposed to
test tones), and some studies indicate its effects to be partially masked by the reverberant field of the room.
Based on Blauert and Laws work, I hypothesize that a cycle or two of GD will not be audible at low
frequencies, especially when we consider all the GD 'built in" to most all of our source recordings. In my
opinion, other aspects of loudspeaker design, such as flat in room response, and certainly room treatments,
are going to have a much more audible effect.

Addressing the aspect of group delay in vented alignments, it has been demonstrated that lower tuning will
lower the onset of group delay, as well as provide an extended and flat response (when room modes are
considered) over a sealed alignment. The issues of cone excursion and port velocity may be ameliorated by
lower tuning, as compared to a conventional vented alignment.
I'll leave this subject
with two more plots for
you to consider:

First is the group delay
of the driver in a
sealed enclosure with
a transient perfect Qtc
of .5 (dark blue), and
the two vented
alignments discussed
in this article...
...and their respective cone excursions.
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(1) Blauert, J. and Laws, P  "Group Delay Distortions in Electroacoustical
Journal of the Acoustical Society of America
Volume 63, Number 5, pp. 1478-1483 (May 1978)

Copyright 2005 Curt Campbell