The D104 is a cool looking mic. I have several of them.
The thing about the classic curve that is being discussed is that crystals that are good are getting more rare.
Also, even though they exhibit desirable characteristics, they are very sensitive to load variations, which limits their advantages IMO.
I am attaching an article published in QEX by Jim Tonne for a much more flexible and adjustable speech spectral response.
Jim likes electret elements that are flat and much less load dependent and the response is produced by using a simple active filter with a bump in the 2-3kHz area to provide the enhanced readability to phone modulation and the curve can be varied in center and the amount of bump.
In the old days, the D104 response was connected to speech amps that had no other methods of enhancement.
Jim gives an analog solution that works well.
Of course, modern numeric digital filters can also provide a brick wall above the desirable high frequency and represents the ultimate solution.
The simplicity of Jim’s designs and ease of construction are still a great way to mimic this response curve and his later circuits provide a complete speech chain to provide a complete solution.
73, Mike K9MB
http://tonnesoftware.com/downloads/Tonne-QEX-Sep-Oct-2018.pdf