Best Way To Put Out White Noise Over 70v Speakers?

70 volts? 70 ohms maybe?

Are the speakers existing? If there is already an amp, you can get a white noise generator and connect it to a line level input, or some have built in speaker outputs.

I used to use Lowell or Atlas.

Also, there are specific speaker setups for white noise. Usually they point upwards above a drop ceiling or are suspended if there's no ceiling. If listeners can pinpoint speaker location white noise loses some of its effect.

70V systems don't require a special amp per se, as you can add a transformer to a standard 8 ohm amp to convert it to 70V output. But to be honest, the 70V portion of this audio system isn't really relevant to his question to begin with. It wouldn't matter what amp and speaker system you were using. His question is all about source.

Question is, does this system need to have any other source, or is it solely used for sound masking?

If the sole purpose is sound masking, I would recommend a stand alone system like the Atlas TSD-GPN1200 for "up to six masking loudspeakers tapped at .5W each."

If you already have an amp, or need more than 6 speakers at .5W, and just need a tone generator, then use the same TSD-GPN1200 from Atlas, but use the line level output into your existing amp line level input.

They also make a TSD-GPN1200K Kit that includes the PSU and rack tray, if you need them.