The last spec sheet I was able to obtain is a 4 page folder that was put out when the T35A was put under the University Sound division of Mark IV. The sensitivity is 105db 1 meter averaged pink noise 3000-15000 hz. This agrees with all the older spec sheets I have going back to the 60's. I have only seen the no phase plug version in very old material. I have used very many of these tweeters, but now use the Eminence units. If you ever want I will scan this sheet for you.