Namaste:
Here is an article by Ramana Maharishi on Sphurana or Sacred Vibrations and I am enjoying relating his concept of Sphurana to the K.S. concept of Spanda in regards to Kevala Nirvikalpa Samadhi.
https://hridaya-yoga.com/hridaya-yog...cles/sphurana/
I hope others get something out of this too.
Om Namah Shivaya