ISBN 978-0-89272-902-9. ↑ Summary of a Finnish government report (1992) on silencers, muzzle brakes and noise levels ↑ (in German) and (in English) Schalldämpfer = Gehörschützer für Jäger, data collected on noise levels Archived 28 March 2009 at the Wayback Machine. ↑ Hearing Protection Basics ↑ Tilstra, Russell C. (2011).