The allowable group delay in bass guitar cabinet


Hi,
I'm now trying to build my own bass guitar cab, and have some question about group delay in vented enclosure. Can anyone inform me the maximum allowable group delay in order to get the good bass sound from bass guitar? I have try to design the closed box with my speaker that have a very good transient, but can't get any bottom end from my bass guitar.
Any reply will be appreciated.
Thank's in advance.

Regards,
Gabriel


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