Robert Amour
New Member
I've just got a pair of original 4312s and have recapped them, and I've sort of gone down a rabbit hole looking at the crossover schematic.
It started when I worried I might have reversed the woofer's wiring, seeing that the negative signal to the woofer is wired in directly from the red terminal on the back. This led to a close look at the schematic, the actual crossover, and a series of battery tests on each driver, where I noticed two strange things:
- The woofer goes IN when positive signal is applied to its red terminal
- The mid and tweeter are hard wired such that their phase is opposite of each other
(The woofer's apparent reverse polarity is cancelled out by reverse wiring in the crossover, so positive signal at the speaker's red terminal makes the woofer go OUT as expected.)
After pondering this for a while I realized this means either the woofer and mid can be in phase, with the tweeter being phase reversed, or the woofer and tweeter can be in phase with the mid reversed. Taking a look at the technical manual shows the latter configuration:
During the course of the recap, I took some electrical frequency response measurements before and after to verify that there was an improvement, and looking at the chart I think I might have a clue as to why the mid is phase reversed.
The woofer in the 4312 receives full-scale signal, and signals are sent to the mid and tweeter through high pass filters only. So, it seems like the mid is, by design, phase-cancelling the upper range of the woofer in order to produce a flattish overall response. This design was continued all the way through the 4312a series, but it gets more interesting by the 4312mkII, where the same design is used again, but the with all 3 drivers now in-phase:
I don't see any other discussions of this strange fact out there, but I find it really interesting, so thought I'd put it out there for posterity. It might be that this is a more common design than I think! Any futher info on this design would be appreciated.
It started when I worried I might have reversed the woofer's wiring, seeing that the negative signal to the woofer is wired in directly from the red terminal on the back. This led to a close look at the schematic, the actual crossover, and a series of battery tests on each driver, where I noticed two strange things:
- The woofer goes IN when positive signal is applied to its red terminal
- The mid and tweeter are hard wired such that their phase is opposite of each other
(The woofer's apparent reverse polarity is cancelled out by reverse wiring in the crossover, so positive signal at the speaker's red terminal makes the woofer go OUT as expected.)
After pondering this for a while I realized this means either the woofer and mid can be in phase, with the tweeter being phase reversed, or the woofer and tweeter can be in phase with the mid reversed. Taking a look at the technical manual shows the latter configuration:
During the course of the recap, I took some electrical frequency response measurements before and after to verify that there was an improvement, and looking at the chart I think I might have a clue as to why the mid is phase reversed.
The woofer in the 4312 receives full-scale signal, and signals are sent to the mid and tweeter through high pass filters only. So, it seems like the mid is, by design, phase-cancelling the upper range of the woofer in order to produce a flattish overall response. This design was continued all the way through the 4312a series, but it gets more interesting by the 4312mkII, where the same design is used again, but the with all 3 drivers now in-phase:
I don't see any other discussions of this strange fact out there, but I find it really interesting, so thought I'd put it out there for posterity. It might be that this is a more common design than I think! Any futher info on this design would be appreciated.