A short, narrow slot parallel to the stud axis that breaks through the face of the horn. Face slots are used to lower the resonant frequencies of nonaxial resonances in wide bar horns and sometimes in radially slotted cylindrical horns.
Face slots are usually machined with a narrow blade. They are often positioned about midway between normal slots. They often extend to a greater depth than the front web length of normal slots.
Where possible, back slots are preferred to face slots because they do not disrupt the working face of the horn.