I use two low cost equalizer...
One was the Douk tube equaliser TB pro 7 levels for my low cost powered speakers... With success at peanuts cost... Great immediate improvement...
( i add others improvements at no cost but it is impossible now to communicate some experiments without being mocked )
I use the internal equalizer of my Hidizs to improve greatly the AKG K340 hibtyd...
Not only that but i use the tone control of the Sansui alpha...
Why ?
Because there is 2 cells working in the K340, one electrostatic and one dynamic with a crossover at 4,000 Hertz...
I max the highs on the tone control and the highs already good become celestial...
Not only i had deep clear bass as the heaviest organ tone, but the violin put me in ectasy... The mids are totally natural...
It takes me 6 months of research and experiment with 6 optimizations modifications even reading the patent of Dr. Gorike to understand how this TOP headphone can work with his 5 resonators and his dual acoustic chamber volume. (it is the more complex ever designed because most use only one type of cell ,planar dynamic or electrostatic...)
Tone controls and equalization for a better S.Q. is as claimed by
may help most and helped especially me because this K340 puzzle...
It was not necessary to pay big money....In my case....