Some of the later 8 inch subwoofers had this. This was supposed to aid in keeping the voice coil from overheating. I don’t know how effective this was.
Yep. I lived in Ballardvale and visited Cizek a few times when it was on Stevens St. in Andover, MA. I remember Sheldon. I also remember getting my first introduction to the idea of a subwoofer. Well, fast forward to today and look what happened.