Plast-i-Clay or other non-hardening modeling clays damps unwanted resonances very well. Frank Van Alstine wrote about this tweak in his Audio Basics Newsletter, Volume One, Number One, January 1982. All the Audio Basics newsletters are available as a zipped pdf file at the AVA website:
https://avahifi.com/pages/audio-basics-newslettersThe woofers on my old Von Schweikert VR2 speakers had a stamped metal basket so I tried the modeling clay trick. The results were just as Frank described with the sound now clearer, less colored, quicker, and smoother. While playing with the clay I also noticed the housing around the magnet rang like a bell when struck, so I wrapped the housing with some left over VB-2 vibration damping material.
"The test I ran at B&W in Worthing, England years ago was a true double blind test. John Bowers gave me a matched set of their little CM-1 bookshelf speakers to play with in their lab. I had brought a half pound of plasticlay along with me when invited to a factory visit. I pulled the driver assembly from one and damped it thoroughly and then put it back together very privately. Since they had identical cabinets and no serial numbers yet, not even I could tell which one I had worked on.
"We set them side by side in their sound room and A-Bd them with mono material using the balance control of the drive preamp to switch from one to the other.
"The whole tour group got to listen. I asked everyone to write down the answer to two questions. First, can you hear any difference? Second is it a better worse difference and which one do you like better? After everone voted, I opened up one of the speakers again.
"The results, much to B&W's surprise, was that the damped speaker was by far preferred by nearly everyone."- Frank Van Alstine
https://www.audiocircle.com/index.php?topic=63170.msg582865#msg582865
