Changing of surrounds on Sony APM woofers.

The APM are very high quality speakers but they are very fragile. I decided to repair them as close as possible from the original but with an additional constraint: the repair must be durable.

Exit polyurethane foam surrounds which depending on the use and the storage conditions last from 5 to 10 years. The idea that the surrounds’ mechanical specs could be altered in time and that a new repair would need to be done later is unacceptable to me.

I systematically repair APM loudspeakers with the fabric surrounds I developed over lengthy research. I am lucky to have found a pair of NOS APM-66ES woofers in their original cardboard boxes and plastics, both never opened: thoses surrounds are intact as the day they were made.

It allowed me to make T&S measurements and to develop my own fabric surrounds with a sound reference. Looking at speakers with fabric surrounds from my collection and with iterations using different materials, I found a satisfying compromise - look at the Fs comparison below.

Also, many tests and trials were needed to find the proper molding process so a lot of mold prototypes were made, too!

I show here woofers repairs from Sony APM-33W, APM-55, APM-66ES.

(Repairs of Sony APM-8, APM-6, APM-4, APM-77 will be introduced in dedicated sections.)

The repairs of these loudspeakers is extremely sensitive and requires a lot of experience: a lot of traps are to be avoided to preserve their integrity.

One can find on the internet many attempts, easy, but I sincerely think that none could possibly reach for the same level of perfection.

These surrounds have better damping characteristics than the original foam ones, they have low mechanical fluctuations and they will last forever.