the Vater VMT6 (first one on the list below) looks like it might fit your needs. I have Ludwig Musser mallets, but they are medium not soft. I do like them, but Vater has a good reputation for making excellent mallets.
For symphony gigs, I use Ron Vaughn cymbal mallets, hands down, no comparison. Yarn marimba mallets and timpani mallets work, but using timpani mallets will give you more of a muffled impact.
But, if on a budget, or one needs fewer mallets for the bag, etc... There is always the Louie Bellson mallet/stick.
Disclaimer: I've never tried that but when the hammer felts of a piano become older, the sound of the piano can become a bit piercing. Puncturing the felts with a needle helps to make the sound less aggressive. Maybe this works with felt mallets as well.
I like the John Reilly Mallet- Sticks....I can flip them back around while being able to use the mallet side for cymbals. And the stick size feels like a 5A. Previously I was using the Promark SD12...Too Heavy
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