Sorry. I made a mistake yesterday in haste. The radius of Perseus isn't 2.5Bly. It occurred to me that radius would include the Earth in the cluster, since the Earth is 0.25Bly away. I let it pass in haste, because I came up with a reasonable number for the shock/sound v. That's because the frequency for the wave is not 10
57 octaves below A#. It's 10
48 octaves below a C#4.
Here's a paper that covers the matter: A deep Chandra observation of the Perseus cluster: shocks and ripples" Fig 5 gives a radius of 163kly. The shock/sound velocity is ~0.005-0.02c.