A headphone that is especially useful to test the efficacy of an earplug installed in an ear canal, by using the headphone to produce sound and by sensing sound pressure at the ear drum despite the presence of the earplug. Applicant uses the speaker (42) in the headphone to produce a smooth and reasonably “flat” frequency response by reversing the speaker orientation. In the reversed orientation, the front side of the speaker diaphragm (50) faces into the headphone cup and away from the ear. The rear side of the speaker that has a circle of holes (52), faces toward the ear. The headphone frame has a cylindrical passage (40) for carrying sound to the person's ear, which has an outer end (78) that is tapered to encompass the holes in the speaker back side (44). The axial distance (L) from the speaker rear side to the ear, is at least 0.6 inch to accommodate the protruding end of an earplug.