Selection of single voltage or combination use constant-voltage line transformers includes models for professional and commercial sound and for intercom (45 ohm) applications. Transformers with 8 Or 4 ohm impedance mount standard 4" or 8" loudspeakers without additional hardware except Model HT167 which may require bracket Model CX188329. For convenience and cost savings, Atlas Sound loudspeakers can be ordered with factory-installed transformers. Consult loudspeaker specifications or technical service for proper loudspeaker transformer combinations to meet your installation requirements.