3500 hz. FWIW - It appears as they use the same x-over regardless of 4 ohm or 8 ohm operation.
I bought this a year or so ago when I upgraded my S15D to S15X-D - then discovered that I had one on the shelf - bone head... So this is new, un-mounted as shipped from Modular Sound Systems (aka Bag End) just cheaper...
$55 shipped conus, paypal is OK.
