SPL, or sound pressure level, is a measurement of the intensity of a sound pressure wave. Measured in decibels, it provides us with a relative scale of loudness which is useful in determining proper mic selection and placement. High sound pressure levels can damage some ribbons, and will stretch any ribbon mic over time. But Royer ribbons are tough! Through our patented work-hardened corrugation process, our pure aluminum ribbons will stand up to years of high SPL before they exhibit any signs of fatigue. That said, it is a good idea to limit exposure to unnecessary high SPL to insure the longevity of your investment. Please note that dynamics and condensers are also susceptible to the effects of sound pressure and like any physical membrane, their diaphragms will stretch over time leading to degraded performance.