Designing a new woofer for EPOS
EPOS was always special by using a simple crossover. Of course, also the new EPOS models will use the same target and therefore, a new driver needs to be developed. Like in the original EPOS 14, it’s a 7″, not a 6.5″ and not an 8″. The older EPOS driver used an underhang voice coil and so the new one will follow.
However, in the case of the new driver, it’s not a large and heavy Ferrite type, but a modern radial magnetised Neo magnet with a copper cap for low harmonic distortions and low intermodulation distortion. Since the original EPOS came up, technology improved a lot. Below you can see some of the engineering samples with different magnets
Also, the cone will be very special. Polypropylene with a low Hysteresis Rubber surround has been chosen to combine the clean, open midband of the PP with the snappy dynamics of a low damping rubber. In the older days, a high damping surround has been used to make a flat response curve, today simulation technology let us try countless cone variations without cutting steel.
At the end, we found a cone shape that got a very smooth roll-off. Below you see one of the variations with a large phase plug in place.
The roll-off is well controlled and that gives us a chance to use a simple crossover. Not without any inductor, as it makes good sense to add a simple air core and not adding too much (non-linear) inductance on the driver itself.
Below you can see the difference between two slightly different cone shapes
Below you can see the response curve of a driver with a phase plug on axis and out of axis (90°)
An interesting option is to change the midband with the phase plug. You can use different combinations fo solid material and absorbing material to take out energy in the midband. Why this makes sense? After you mount a driver in a cabinet, you get some diffraction effects that add some energy in the 1kHz area. Yepp, can be removed with a filter, but why not trying to remove it with a phase pug design?
Stay tuned, more to come.