loud pedal

He enjoys playing the piano with the loud pedal pushed down, singing bass in his cups, playing the fiddle Saturday nights in a parlor orchestra.

From Time Magazine Archive

A bar, L, passing along under all the damper lifters, is raised by depressing the loud pedal.

From How it Works Dealing in simple language with steam, electricity, light, heat, sound, hydraulics, optics, etc., and with their applications to apparatus in common use by Archibald Williams

This is popularly called the loud pedal, and the vulgarest use to which it can be put is to multiply the volume of tone.

From How to Listen to Music, 7th ed. Hints and Suggestions to Untaught Lovers of the Art by Henry Edward Krehbiel

Then, it appeared, Jerry's self-control completely deserted him, and with a hoarse and throaty noise he opened fire with the full force of his starboard broadside; he rammed down the loud pedal and let drive.

From Men, Women and Guns by H. C. (Herman Cyril) McNeile

Let a man with an average ear, however uncultivated, strike the C low down on a good piano-forte, keeping his foot on the loud pedal.

From Peter Ibbetson by George Du Maurier