What is the SM137 best suited to? Itís ideal for the professional musician looking to mic up their instrument such as acoustic guitar, cymbals, strings, piano and many others, either in a live or recording environment. What are the characteristics of the SM137? The SM137 uses an ultra-thin diaphragm for quick response, a very smooth high end, and tight bass. It has a transformerless design, low-noise operation and 15dB pad for high SPL sound sources.