I found that some of the MX500 shells that I just received, have a very small opening between the inside of the shell, and the outer air passage. It's fairly easy to make an opening, to allow the the outer passage to act as a "bass port". I used a 7/64 drill bit, spinning it by hand, at the angle shown in these photos. Once the end of the air passage opens up some, the drill bit can be leaned (to the Right in the photos) but take care not to tear up the end of the cable passage. To make sure the new opening is clear, I used the curved end of a dental pick, holding the opening of the shell up, under a bright light, and looking down the passage (from the Left in the photos) with a magnifying lens. The 3/32 drill bit is the correct size to make sure the end of the cable passage stays clear & open. NOTE: The Helping-Hand was not used for anything other than holding the bit while I was taking the photos.