Quote Originally Posted by charly1944 View Post
Since this is a general recommendation for driver,does it apply as well for a co-axial or is there a correction to be applied when measuring the diameter of a co-ax.
3.Added mass :I have tried to add masses to the back side of the cones but they dont stick long enough to perform the measure till the end.Can i use small magnets without affecting the results of the measures?
A pressure test is required to accurately determine Sd, but buried somewhere in an old Altec technical paper, the 604's effective diameter is ~12.17" Vs a 515's ~12.75". I know of no ~universal 'correction factor' for co-ax.

I'd be reluctant to use magnets except out near the surround where I've had no problems AFAIK. The main thing is to add enough mass to lower Fs > 25% and ideally Fs/1.56, which is the inverse of finding Vas by increasing Fs in a sealed cab by 1.56x.

GM