Group delay of a transmission line?

[454Casull]

How does it rank among sealed, bass reflex, and PR enclosures

 

[rcavictim]

As a trend I think there is more group delay amongst people rushing to build TL speakers than sealed or BR designs.

 

[GM]

It depends on how well stuffed it is. If stuffed to the limit then it will best them all for a given driver/Fb. If no stuffing then it will be the worst of the bunch, so stuff to suit, trading gain for lower group delay.

GM

 

[Bob Brines]

Group Delay

is the second derivative of the frequency response, or in English, the rate of change of the FR curve. So, the answer is -- it depends. The typical QB3 BR box has an abrupt cut-off and high rate of change -- Group Delay. A Qtc=0.7 sealed box has a much more gradual cut-off and hence much lower GD. A Qtc=0.5 sealed box has even more gradual cut-off and lower GD yet.

Now, for TL's. If you have designed a classic TL, very long, gradual taper and stuffed to the gills, the cut-off approaches an infinite baffle and the Qtc= Qts. Very low GD. If you have designed a mass-loaded TL with a cut-off approaching that of a BR, you will get the same high GD. You will need to model your proposed speaker and look at the cut-off characteristics in order to guess at the probable GD.

Bob

 

[rdf]

Though they are related, group delay is properly the rate of change of phase response with frequency. Filters with abrupt frequency response curves generally have abrupt phase variations as well. Regarding transmission lines, it depends what kind of transmission line and its alignment. You're best bet is to download Martin King's MathCad sheets and generate the frequency/phase responses of your line. It doesn't generate group delay but you will see which alignments have severe phase variations.