Quote Originally Posted by curtis View Post
If I remember correctly, they were specific to the Sierra-1 and its woofer.
Hopefully Dave will chime-in.
That's true but when I had Sierra-2s mounted up against a corner as surrounds, then the foam inserts helped reduce a little boominess I was getting. I used a measurement mic and REW to verify that the inserts helped flatten the response. But for most applications the inserts wouldn't be needed or desirable.