Joseph Audio 'Infinite' crossovers.

[thune]

Measurements on early Joseph speakers show that the Modeffari topology is not enough to tame metal cone resonances. Metal cone resonances still need to be independently notched. Early 2000's Joseph's could definately "bark" on certian content at moderate-high levels.

 

[phase_accurate]

To pinkmouse:
Can't you just copy them to the other thread since they are not that OT here ???

Regards

Charles

 

[PB2]

fntn,

What I meant by "elliptic", is in the mathematical sense - a class of filters with a notch (pair of zeros) in the transition band. His 1 transformer + capacitor lowpass, clearly implements an elliptic filter. Ditto his hipass.

"Magnetic brake" - sounds like a phrase invented by a marketing guy. Woofers "magnetic brake" constantly, as long as they are driven by a fairly low impedance source.

Transformers with tuned coupling coefficients are something I design all day long. In my day job, I design resonant switching power supplies for high volume production. Modafferi's transformers would be cheaper than using 3 inductors.

Peace out.

@jasoncsbb
Hi Jason,
I don't think I've spoken to you since some time in the 1990s and I seem to recall discussing elliptical filters and positioning the notches to align with at least one peak in the metal cone drivers of those days.

It must have been on my mind for some time since I remember speaking face to face with Modafferi at one of the shows in NYC, he was in the Joseph room with Eva Manley, and Vandersteen was in the next room over. I had not read his patent and asked him if they were elliptical filters and he said no, he said that the crossover was simple, a transformer, and cap, and that they produced negative inductance to (approximately?) cancel the voice coil inductance. I think he mentioned Thiele's AES papers and that the negative inductance trick was in there but I never looked into it further. A negative impedance amp, and driver measurement in Fig. 18 (pg 200) seems to hint at what he was talking about. Seems to me he built on it in his ideas but I have not looked closely into his patent:
http://www.readresearch.co.uk/thiele-small_papers/thieles_vented_box_article_2.pdf

The implementation doesn't matter much, what really matters is if his design and something you've used provide the same transfer function equations that can be optimized to provide the same transfer function.

Pete Basel

 

[PB2]

Here is Modaferri's 1988 crossover patent in .pdf:
Multidriver loudspeaker apparatus with improved crossover filter circuits

 

[jackinnj]

This is the Modafferi XO (in LTSpice) of the "improved" Solstice. Modafferi discusses the Joseph in the AX article in which the XO was described (December 2021). Two Morel woofers.