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In Reply to: RE: Thoughts re. T1-D mid/tweeter (push pull) vs. T-IVa mids? ... posted by andyr on July 23, 2015 at 19:50:56
The tweeters are limited at their lower end to about 1 kHz. The diaphragms are smaller than the T-IVa mids. The diaphragm meassure about 60x1120 mm, T-IVa mid about 80x1450 mm. The moving masses of the T-IVa mids are slightly lower (thinner Mylar devided into small sections).
I could need a pair of tweeters for my Tympanis.... A pity they have the 12 um Mylar and the rather restricting front/rear sheet metal.
Follow Ups:
So not a good idea! :-((
But how do you get " The tweeters are limited at their lower end to about 1KHz "? Sure that's where they extend to, in T1-D & T3-B speakers but that's a function of the XO slope employed, for tweeters?
If they weren't "impeded" by a HP filter, are you saying they would tail off naturally at around 1KHz, because of their thicker mylar?
But re. your comment " the rather restricting front/rear sheet metal " ... 20.1s / 20.7s have this restricting front/rear sheet metal over the mid & bass drivers!
Regards,
Andy
Andy,
it is along time since I was working on Tympani tweeters. As I remember it, there were two fundamental resonant frequencies, one at 450-500 Hz and one quite a bit lower than that. These were very pronounced. The very thin wires on the Mylar makes the tweeters sensitive to heating, that will be the case if letting them produce frequencies bekow 1 kHz. The effective diaphragm is really too small to produce high SPL at lower frequencies, the diaphragm cannot move that much air and there is a limited excursion (as in any Magneplanar type of driver).
Yes, the 20.1 and 20.7 also have restricting magnets/perforated sheet metal. In the case of the old push-pull tweeters the open area is very limited, 11% or so (have not look at for many years). I think the 20.1 and 20.7 are more open. The main reason with the push-pull configuration for mids/tweeters is too increase the efficency while using thing and low mass voicecoils.
Would like to have a wide ribbon from 400 Hz and upwards to compliment he ribbon tweeter
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