FR125S

Years ago I bought a pair of these supposedly full range small drivers and while the bass was impressive the overall sound was slightly lacking. The FR125S was a brave attempt at a full range since it had Dan Wiggins XBL2 motor which gave it a phenomenal X-max for a 4.5in driver. There was a major break-up at about 6.5 kHz which affected the sound for me, anyway. I think it is better for a full range driver to have a smooth if limited response rather than an extended response with holes in it. Also they were lacking in sensitivity, which people who tried to drive them with low power valve designs noticed. I resolved to try them with a tweeter and got an overall nice sound using some NOS (new old stock) Morel MDT41’s. They were a story as well. Even when new, they needed running in. When I took them out of store they seemed to have lost sensitivity and the response was poor until they were run in. But the low sensitivity matched the FR125S. I changed them from a top mount to a flush design. I think the problems are due to the grade of ferrofluid used in the tweeters, having said that my Monitor audio tweeters of the same age work well “straight out of the crate”
The FR125S bass is so good it seems to work in any cabinet, even with the phase plug design giving leakage.
The crossover circuit I used is here, the crossover being at 4.5K and the tweeter needing to be reverse wired. A more sensitive tweeter would need the values of R2 and R3 tweaked.