r you talking about the alpine sps-1005 balanced dome tweeters with 120watts and 30RMS cuz i have them.
they sound pretty clean but they don't sound loud. i had to mount them on my headrests so i could hear them.
they're not really 3/8" they are 1" just the metal (the tweeter), plus the plastic surrounding is 1-3/4" and if you use the mount, the cut-out is going to be 1-15/16" and mounting depth is 5/8"
the thing thats 3/8" is a boom on the middel of the tweeter, like almost all tweeters have. i guess it's the voice coil size