According to this small article : https://www.powersonix.com/helicopter.php
In short, this article pretty much supports the brand and model, (Power Sonix's helicopter-mounted speakers). Earlier in the article, Kev (the consumer), rants about how their old speakers sounded horrid and how it also made it incredibly risky for the pilot to give PA instructions clearly (as the pilot had to fly low at 200ft and a slower speed at 20knts), but now that they got these new speakers, they can easily give PA instructions clearly as the pilot can fly at a safe 800ft above the land while going 50knts.
In the bottom you can find a little table going over the specifications (dbc, effective range) of the speaker models you can obtain.
Overall this is an interesting creation that exists and gets the job done according to Kev who ironically used to/still works with San Diego's Police Aviation Unit.