An aromatic amine derivative represented by the following formula wherein at least one of Ar1 to Ar4 is a heterocyclic group represented by the following formula wherein X1 is an oxygen atom or a sulfur atom. The barrel has a barrel wall formed with a through hole communicating with a radial vent hole. A carrier attenuation filter passes the attenuated carrier and non-attenuated RF modulation sidebands. The second portions are spaced apart from one another in a second direction substantially perpendicular to the first direction. Similarly, the second switching circuit applies a plurality of pulses to the second output terminal that, in response to the negative samples, have a constant frequency and are pulse-width modulated, and, in response to the positive samples, have a varying frequency and a constant width. In one or more embodiments, the apparatus of the present invention includes a support frame, back box assembly configured for installation on top of a ceiling tile, a ceiling ring configured to be mounted in an opening in a ceiling tile, and a loudspeaker cartridge configured to be mounted to the support frame through the ceiling tile opening.