Most people will tell you this is wrong, but I can say from doing it on several bows, it works very well for me. I put on a endless loop dacron string.
I have tested it thru the chrono, this string slows the speed about 4-5 ft per second, but the noise level is greatly reduced. My most recent Widow, a PSR was noisy with the fast flight. With the endless loop dacron, it is now the quietest bow I have ever shot. The biggest draw back is you may have to switch to a lighter spined shaft. I am a stickler on shooting perfectly spined shafts. And with the dacron endless loop, it requires a lighter spine than the flemish fast flight or 97.
Also, the dacron endless loop sells for about $6.