19
Interesting exercise in scale modelling for acoustics
https://www.sciencedirect.com/science/article/pii/S0305440320301394
They found a slight enhancement in sound, in small areas inside the henge, but news headlines are slightly more hyped (vs if you read the original paper)
https://www.sciencenews.org/article/stonehenge-acoustics-sounds-voices-music
I used to work with a guy who did a lot of fascinating historic soundscape modelling--it opens up a whole new way to understand historic sites. There is an old video floating around of people drumming in Stonehenge (on their own, not as part of the solstice ceremonies!) and moving around the site, to hear how the sound changes in different positions.
A few things about Stonehenge for anyone interested--first, I'm told that because there's now little to no international tourism and Stonehenge was largely a place for international tourists to visit, it's extremely quiet now, so if you haven't been now might be a good time. Second, it's not that well known, but it's possible to have the stone circle to yourself before or after regular visiting times--a friend arranged for us to have the space to ourselves one summer morning for my birthday. There is, or was, a form on the site to fill out to arrange for an out of hours visit, and it costs something like £20. Third, the circle itself is only one small part of the entire World Heritage site, which is full of other Neolithic monuments and which you can wander around for free.
I had never thought about this in terms of open outdoor sites. Caves and cathedrals, obviously (and there's the aspect of trying to reproduce the acoustics of those spaces for digital music too).
Out of hours visits to Stonehenge sounds great.