[thegage]

From what I've read here, it seems that the ideal amount of putty on the PR also results in the lowest distortion. So, wouldn't the best way to tune low-end response be to measure distorion and add/remove putty until the lowest figure was reached? How difficult is it to accurately (usefully) measure woofer distortion?

John K.

[Brian Cheney]

THD (well, 2nd and 3rd harmonics at least) measurements are included in most packages like my SYSID and CLIO. 

You could indeed go by THD measurement alone in adjusting the moving mass of the PR (what's known in these parts as putty pinching) but since it's readily apparent by ear which mass load is optimum I always do it that way.  To me a less than 1/10g change is quite audible.