The ES-58 offered by GLS Audio is an even more affordable version of Shure’s ubiquitous SM58. Just like the SM58 (as well as the SM57 and GLS’s version, the ES-57) the ES-58 has an acoustic resonator disc that boosts upper midrange frequencies to add presence. While this boost is often welcome on sources like snare drums and guitars, sometimes a dynamic mic with a flatter response is more welcome. Removing the resonator disc is a free, reversible modification that removes this presence boost.
Full instructions for the mod are available from the article on Michael Joly’s website.