Speaker line transformers match loudspeakers to constant-voltage distributed audio systems such as 25V, 70.7V and 100V paging and commercial sound systems. Compare line voltage, transformer wattage, available taps, speaker impedance, mounting method and frequency requirements when selecting a transformer.
Use the product listings and selection guidance below to compare compatible products by the specifications that matter for the installation.
Speaker line transformers are used in constant-voltage distributed audio systems to connect individual loudspeakers to 25V, 70.7V or 100V amplifier lines. They allow many speakers to share a long speaker circuit while each speaker draws a selected amount of amplifier power. This architecture is widely used for paging, background music, public-address and commercial sound installations.
A line transformer converts the high-voltage, lower-current signal on the distributed speaker line to the lower-voltage signal required by a conventional loudspeaker voice coil. Many transformers provide several wattage taps so the installer can set the acoustic contribution of each speaker and balance the total load across the system.
In a conventional low-impedance system, speaker impedance and series/parallel wiring must be managed carefully as more loudspeakers are added. A constant-voltage system uses a transformer at each speaker. The installer selects a power tap—such as 0.5 W, 1 W, 2 W, 5 W, 10 W or another available value—and totals the selected wattages to determine the amplifier load.
The phrase “70V system†commonly refers to a 70.7V distributed-audio line. Other systems use 25V or 100V depending on the equipment and application. The transformer must support the line voltage being used.
Add the selected wattage tap for every speaker connected to the amplifier channel. The total connected speaker load should remain below the amplifier's rated output, with appropriate design headroom. For example, ten speakers tapped at 5 W represent a nominal 50 W load before adding design margin. Follow the amplifier manufacturer's recommendations for maximum connected load.
Changing a speaker from a 2 W tap to a 5 W tap increases that speaker's electrical load and typically increases its maximum output level. Taps are therefore both a system-load decision and a zone-balancing tool.
When replacing an existing speaker transformer, identify the system line voltage, loudspeaker impedance, required power taps, mounting arrangement and wiring. Do not assume that two transformers with similar wattage ratings are mechanically interchangeable. Physical dimensions and lead arrangements can matter when the transformer installs inside a speaker enclosure or backbox.
A replacement should also meet the performance requirements of the loudspeaker. Voice-only paging may tolerate a narrower bandwidth than a full-range music system. Higher-quality transformers are designed to maintain broader frequency response with lower insertion loss and distortion.
The distributed line voltage is determined by the amplifier and system design. A transformer may support one voltage or multiple line-voltage connections. Never connect a transformer tap intended for one system voltage to another without following the manufacturer's wiring diagram. The selected line-voltage connection and wattage tap together determine the impedance reflected to the amplifier.
Distributed speaker circuits should be installed in accordance with applicable electrical and building codes. Cable type, plenum requirements, fire-alarm or life-safety listings, conduit requirements and separation from other circuits vary by application and jurisdiction. De-energize the amplifier circuit before changing transformer connections.
Is a 70V transformer an amplifier?
No. It is a passive transformer used to match a loudspeaker to a constant-voltage amplifier line.
What does the wattage tap do?
The tap determines how much power that speaker draws from the distributed line at the rated system voltage.
Can I connect an 8-ohm speaker directly to a 70V line?
Normally no. A suitable line transformer or a speaker with an integrated transformer is required.
Can one amplifier run speakers with different tap settings?
Yes. That is one of the primary advantages of a constant-voltage system, provided the sum of the selected taps remains within the amplifier's capacity.
Wallco groups speaker line transformers separately from complete commercial speakers so integrators can compare replacement and system-design components across manufacturers while using line voltage, power, impedance and mounting as the key selection criteria.
