70.7v is probably more common that 100v, but look up "constant voltage speakers" on google or for that matter "70.7v speakers", which is just one specific voltage for CV speakers.
Constant-voltage speaker system - Wikipedia
When you have two or four speakers, you can wire them in series, parallel, or series/parallel so the impedance suits your amp. But trying to do that for 100 speakers scattered all over the ceilings is impossible. So they came up with CV speaker systems. Now the amp cranks out a high voltage signal, and it is wired to all the speakers in parallel. But at each speaker, there is a small transformer to step that large signal down to an appropriate level. Typical in restaurants would be small 8-10 inch speakers and the transformers have taps at 10, 5, 2.5, 1.25, 0.75 watts. The taps get wired to the speaker itself. Those are the wattages the speaker will see when the amp is full bore.
And really, in a restaurant 1 watt is plenty. So instead of impedance, you simply add up the tap wattages of all the speakers, and keep it within the power of the amp. If you think of it, this is like the mains wiring in your house. No one adds up the impedances of table lamps.
This also lets them balance speakers. They may want 5 watts all over the bar, but right near the waitress station, they might set that speaker down to only 1 watt. That way they can hear orders at the bar.