The Maccabeats from Yeshiva University are highly regarded in the acapella world, although I’m sure here are some who will question the “Heimish” creds of YU.
Many poskim forbid listening to fast accapella music during sefira. R’ Belsky, notably, was very against it, and bemoaned the fact that people were lax in observing a period of aveilus, and were al says looking for ways to get around it.
ard: I only heard/read that R’ Scheinberg zt”l allowed classical music, not all recorded music. He held that music which brings someone to increased simcha and/or dancing would be forbidden.
This is also what I was taught growing up, and what my family followed – classical music, or even slow music which won’t lead to dancing is permitted. Fast music, even acapella, is not allowed, as it can bring someone to dance.
ard: You are mistaken. I heard it from Rav Scheinberg himself when he spoke in Boro Park many years ago. He said that classical music is mutar to listen to during sefira as the issur is on dance music.
So dance tunes/beats/music whether acapella, recorded human noises put together to sound like music, electronic keyboards or real instruments should seemingly all be assur during sefira.
Let’s make sefirah a month of classical music appreciation in the yeshivos! Just make sure you find a posek who knows what classical music is. I am pretty sure many people will say: no gedolim listen to Mozart because if a gadol listens to Mozart, he is not a gadol.