Long Flutter Echo in Big Hall

In this video, I’m clapping my hands in a big hall. The black surface is acoustically absorbent material. Even though it covers about 80% of the walls, the reverberation time in the space is very long. This is because of flutter echoes between the lower untreated parts of the parallel walls.
After recording this video, I have metrologically assessed the space in more detail by measuring the room impulse response with a class-1 sound level meter as part of my work as an acoustical consultant. BKL, the company I work for, offers world-class sound and vibration monitoring, diagnostics, predictions and assessments to recognized standards and guidelines. We guarantee the highest quality of acoustical services available.
www.bkl.ca/
The video was recorded in February 2021, near Vancouver in Canada.
Camera: iPhone 6S (audio/video has not been adjusted or edited afterwards)

[@egnaro-hm1bd]

Damn thats sick

[@welcomemcnall]

Nice

[@elenalohrey1971]

Dang it I don’t know why but hearing that flutter sends chills of pure satisfaction down my back 🫠

[@mulebeatsdrums]

Cool flutter! I'm an acoustics consultant in the UK and I'm currently writing a paper on flutter echoes, so had to ask: was there any absorption on the ceiling? It looks like there's some metal frames up there, but not enough to create much diffusion - with that much absorption on the walls, the obvious path for the flutter seems to me to be vertically, but I can't see what's up there.

[@Hello.Henning]

Oh that's interesting. I studied acoustics in the UK and used to work for a british company before moving to Canada. The ceiling definitely had absorption. As far as I remember, it had about 50-mm thick fibrous treatment like the parts of the walls higher than 2m. The metal beams below the ceiling are to suspend equipment from them and the acoustical treatment was above those. The flutter was happening between the lower parts of the walls that were completely untreated.

[@alvarojesusnietoillescas8417]

Nice video sir. Did you record the IR at that moment? It would be nice to have such a fx profile for sound design. :)

[@Hello.Henning]

Unfortunately, I can't share any results as they are confidential. Also, for this project, we did just measure the reverberation time - not the full room impulse response (IR). Sorry. :(

[@alexsander471]

​@@Hello.HenningHi, very interesting video. I have a genuine question, what makes this confidential? I know nothing about this field and I got really curious wondering what would make these details almost a military secret haha

[@Hello.Henning]

@@alexsander471 Thank you!. The confidentiallity part is nothing too exciting: It's simply the fact that those were measurements paid by our client and we generally keep any findings confidential. The client might decide to use findings for marketing purposes or keep them to themselves. It's far from a military secret but just the way our business operates. If anyone was willing to pay for the impulse response data of this space, I would have to confirm with the client and go back to do more measurements as, in this case, we had only measured the reverberation time and not the full impulse response.

[@alexsander471]

@@Hello.Henning That makes a lot of sense, thank you for taking your time to reply!!

[@jdickson242]

Is that Shepperton?

[@Hello.Henning]

I had included the location in the description. It's near Vancouver in Canada.