Quote Originally Posted by cradeldorf View Post
It does seem strange that the 604 is based on a 515 since the specs of a 515 are 20hz to 1000 hz and the specs of a 416 are 20 hz to 1600 hz since the 604 crosses over at 1600? well at least the earlier 604's crossed at 1600 And I think the first ones crossed at 2000 right?
Remember, these are just the electro-acoustic parameters of the driver itself. Those numbers don't tell you how it will actually perform in any particular load/system.

Take a look back historically at how those woofers were implemented. To run a 515 above 500hz or a 416 above 800hz was a rare exception, not a rule of practice. Indeed, running those woofers higher comes with significant caveats.

At 1600-2000hz a 515's dispersion becomes quite narrow and beamy. But, for near field monitoring from a dedicated listening position(exactly how 604's were used), the beaming remains within acceptable limits giving the 604 a pretty amazing presentation overall.

Another thing to remember with the 604 is that the size of the HF horn is what dictates the XO frequency far more than the woofer's ability. Again, another amazing wonder that the 604 plays as well as it does as it's horn is theoretically way to small to be crossed where it is. The whole thing is a big bundle of compromises that just happen to work together pretty magically.

They always told dealers in the 70's the 604 was 515/802 based and the 605 was 416/806 based. Honestly never cared enough to verify it all, so caveats apply.
Lot of truth in basis here since the moving assemblies and much of the motor parts are the same.