I've had all the large Lasonics ( 918,920,922,931's, L30, 935,975) except the 951 and still think my 975 has the best bass and sound. But then again my 975 was mine from new and I didn't beat on it at all. As for the 3rd Edition TRC931 with round corners it does have same woofers as all others but does not have same sound as 1st and 2nd Edition. I still say that all Boomboxes of same model sounded the same when new but depending on use through out the years, each one has a different sound now 😉. Most likely the caps have worn greatly causing this.
Bad Boy Bill