I can't tell you just yet what I have been up to, but give it another month and I will able to reveal what kept me busy in my spare time: as they say, if you want something done, talk to a busy person...
A side effect of the research I have done on this project, commissioned by one of my day job client, is that I had to do a lot of research on which drivers are available today. One area where I found an interesting improvement
is tweeters. Well, obviously we have all heard of diamond, beryllium, various other metals but interestingly enough, the more mundane silk or "plastic" variety has been completely revamped with the view of extending the frequency range beyond 20KHz and often also extending the range at the bottom of the range, with resonant frequencies lowered as low as 1kHz and with a often a very low raise in impedance around that frequency. The result is that, even though I like to use a cut-off frequency around 5kHz, the resonant frequency is now two octaves below that cutoff and then in theory 24db down, basically not audible anymore.
The proprietary Audax boomer we used in the Microphase SATs is basically flat to 10kHz, so any breakup modes would be at least one octave over the cutoff frequency and then 12 db down let say around 15 to 20kHz, way beyond what most people can hear.
Another interesting new parameter is the consumer demand for a much better sound in their cars, right from the start and with the manufacturer's pre-installed gear. This new market has driven a lot of research by Tymphany (Vifa+SEAS+Peerless) to produce very affordable tweeters with a very small footprint.
The next challenge was to find a driver that would work without modifying the existing filter. I wanted the potential client - you, dear reader - to be able to unsolder the current Audax TW51 and fit the new driver in minutes and be assured the results would be consistent with my tests here in Sydney..
I then had my new speaker cabinet supplier to make me a quantity of new flanges that would "simulate" the flange of the TW51. This was achieved with a 3mm birth plywood CNCed to fit both the original flange and the new VIFA tweeter. Final touch is the replacement of the rather "cheap" screws on the original product with cap screws similar to the one used on the boomer. Et voilà!
Once the wiring is done, flip the tweeter over and screw it in place using the Allen key provided. You will have to use some strength about halfway through, as the screw needs to make it way into the timber. The new screws are longer and slightly bigger than the original ones. Be careful not to touch the dome or scratch the timber edge of the boomer baffle. Also, hold on to the Allen key firmly to prevent the very strong magnet to attract the key and possibly crash it on to the dome. If this were to happen, just wait for the dome to come back to its original shape and you should be OK, but don't try your luck unnecessarily! Repeat on the other unit.