70V audio distribution was developed to provide a simple wiring method to connect large quantity of speakers over large area and long distances. This was through the analogy of typical 120 volt house wiring. In your home, all the outlets have 120V present. The amount of power (or watts) drawn by anything you plug into the socket is determined by it's impedance. A high impedance device like a phone charger will only draw a few watts, while a low impedance device like an electric heater will draw lots of power, in some cases a full 1500 watts.
In this way, you can envision a 70V as having a maximum of 70V everywhere on the speaker line. The amount of power drawn when you connect a speaker will be determined by the impedance of the speaker. Now a 4-ohm speaker will draw 1250 watts which would destroy most speakers, so 70-volt transformers are used between the 70V line and the speaker - these are normally inside the speaker so they are not visible. But by using 70V transformers, the power delivered can be varied from under 0.25 watts to hundreds of watts by varying the impedance of the transformer.
The great benefits are you can "plug-in" a speaker anywhere on the line and the max power to the speaker will be set by the transformer. In commercial application, this allows hundreds of speakers to be put on a 70V line if the speakers are run at low power, such as 0.5 watts. These systems are used for low fidelity applications like markets, schools, airports, restaurants etc where sound quality is not important - in most cases voice only. This resulted in very low cost 70V transformers being developed that had limited bandwidth (no bass or highs) and high distortion.
For large high quality landscape systems, James needed the advantage of 70V lines to run 1000's of feet of wire and be able to simply connect a speaker anywhere on the line, yet provide a sound experience to equal James traditional 8 ohm systems. So James engineers attacked the transformer issue - designing high quality, wide bandwidth, low saturation, toroidal wound transformers provided 20-20K Hz response with extremely low levels of distortion. The transformers were many times more expensive to produce than the low-cost E-core type found in your typical 70V ceiling speaker, but in A/B comparisons between James 70V and 8 ohm systems, there is no difference in sound quality.
James 70V Benefits:
- Support for long wire runs
- Speakers can be added easily, at will, anywhere the 70V line is located
- James toroidal transformers provide 8-ohm equivalent fidelity and bandwidth