 The low weight and high rigidity of beryllium make it useful as a material for high @-@ frequency speaker drivers . Because beryllium is expensive ( many times more than titanium ) , hard to shape due to its brittleness , and toxic if mishandled , beryllium tweeters are limited to high @-@ end home , pro audio , and public address applications . Some high @-@ fidelity products have been fraudulently claimed to be made of the material . 
