I'm starting this thread to document the journey I've embarked on, namely replacing the mid-range section of my current 3-way loudspeakers:
http://www.homebuilthifi.com/project/9409
Intrigued by a post that I read here a while back:
An interesting JBL driver candidate for diaphragm replacement with Be would be the 2450. This driver was originally developed to accommodate a Be diaphragm as JBL was considering going head to head with TAD with that design. It was the reason for the development of the "Coherent Wave" phase plug. It allows for output from the diaphragm to be recombined in-phase at the driver throat in comparison to the out-of-phase output from a traditional phasing plug with variable length paths. According to JBL, it really only works with a Be diaphragm. The Al and Ti diaphragms are in breakup mode over most of their bandwidth, and as one designer said, are so "phasey" that there is limited benefit from the "Coherent Wave". However, a Be diaphragm, being pistonic for most of its bandwidth, would theoretically benefit the most.
This theoretically in-phase output would be a unique driver attribute compared to the TAD drivers and even JBL's current Be drivers. It would be interesting to have feedback if this two decade old technology actually results in a superior driver with a Be diaphragm.
I decided to purchase a pair of second-hand 2450J drivers and send them to Guido Behringer to have Truextent BeX4016 diaphragms installed in them.
I intend to pair these with Yuichi Arai's A320FL radial horns, which were originally documented in the May 1992 issue of the Japanese magazine "MJ":
This is an interesting design that adopts a Hypex expansion with a cut-off frequency Fc = 320Hz and T = 0.6, resulting in a very linear on-axis frequency response down to Fc when paired with JBL 2441 drivers, as well as good horizontal directivity control to approx. 10 kHz (I intend to use a supertweeter for the last octave or so):
I had the horns made out of baltic birch plywood by a French company specializing in bespoke audio designs:
Another interesting feature of this design is the fact that the throat adaptor operates a very smooth transition from the circular throat of the driver to the rectangular throat of the radial horn, while respecting the same throat exit angle of the "classic" JBL 2" drivers (244x and 2450) in the horizontal plane:
I will post again in the next few days/weeks as I proceed to make the first measurements using my set-up (calibrated Beyerdynamic MM1 microphone + HolmImpulse software)...
Marco
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