Seas Excel Diamond tweeter or Plasma?

The plasma tweet is difficult to combine with ATC’s 75 unit -- mechanical compliance will be an issue, before even discussing electronic compatibility.If you wish to improve upon your Tetra, add low-frequency energy maybe even using a couple of 12-15" /channel in open baffle configuration. It will be a bear to cross, but you do say the designer is a master of crossovers.I would also play around with conventional tweeters, metallically coned rather than ceramic.

As a matter of curiosity, what’s wrong with your Tetra 606???

here's no best, there's a best for a specific application and intention.


I would agree with **There is no best,,,*

I've looked at every  SEAS tweet, and wondered if anyone actually employs the Seas Diamond. Most expensve= superior..? I am not convinced .
**Money no object*  may not result in *best ever speaker*. 
Makes sense to build on SEAS drivers only, as i've found SEAS makes the finest, most musical voice coils/cone material, magnet designs. 
Look if your customer wants a  speaker that is superior in musical reproduction,, 1st what is his source and then amplification power. 
A exceptional speaker, hooked up to a  avgerage sounding other components, may only result in just a avg speaker.
laying out that kind of money, synergy is critical. 
I am not convinced, expensive drivers = superior speaker. 
btw I also am interested in Mundorf's AMT Ribbon . But then keep in mind ribbons have that kooky characteristic of The Narrow Sweet Spot, Can't deal with that weakness. In order to have M's ribbon work, is a  row of 3, = $$$$$.
Keep us updated on the final design and give us a  test YT vid. 
We all want to see exotics in action. 

 I have no desire for exotics for the sake of being exotic.

What we are after is natural, uncolored, dynamics, nothing **warm**. 
Warm = coloration, murky lower midrange. 
Of all SEas mid tweets, the only 2 I am interested are the Thor's Millennium and tyheir *Flagship* Cresendo. 
The Millennium is a  incredible midtweet, natural,  voices the human voice with stunning realism. 
a 3 way witha  midrange, would upset this and add warmth, 
The upper midrange of the midwoofer meets perfectly the lower midrange registers of the Millennium, xing ,,, I think 1800hz
Here is a good discussion on xover points. 
To my ears a  3 way sounds blaring/dominate , mushy in the mids, Mids are 80%+ of the music. = a  more simple xover of midwoofer+midtweet is the ideal design for capturing clean, clear critical mid fq's. 
There is no need for a midrange in a  MTM design. 
Midtweet  = superior to   tweeter./midrage combo.  

https://www.diyaudio.com/forums/multi-way/132526-midrange-crossover-choosing-evils.html

I love my Tetra 606s. But I am giving my perspective on this design from a marketing point of view. This is not necessarily a speaker for me to replace my 606s but a commercial product. The 606s are $33k, his 707s are $78k and the piano enclosure Grand Halls should be $88k. My input on this design is relatively minor and superficial.The enclosure will be complex and the crossovers world class and the drivers the best available. And the finish will be carbon fiber piano black. We will get a pair of the Seas Excels to test. The ATC (Volt-same or better, ATC no longer sells its midrange) and 15” TAD both already proven as best. The major task is to make it all work together to truly be an $88k speaker. I am convinced that Adrian Butts is one of the finest speaker designers. Check out his website.
www.TetraSpeakers.com 
If Keith Richards, Herbie Hancock, Winton Marcellus, Ron Carter, etc. will not own any other speaker, who am I to not agree. Do some of the world’s greatest musicians know what is possible in High End Audio? Not necessarily. But they know when their performances sound like they did to them on stage, in studio, etc. Several of these guys own and love their 606s. 707s are a limited edition.