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Theoretically speaking how big would a room have to be until reflections are no longer an issue

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Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby TheLegit » Thu May 13, 2021 4:04 pm

If you think about it if a room is big enough reflections could be taken out of the equation, but the question is how big would it need to be?
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby Tomás Mulcahy » Thu May 13, 2021 4:11 pm

Til it's not a room.
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby merlyn » Thu May 13, 2021 4:23 pm

Cathedrals are pretty big and they have a massive reverb.

There are two things going on -- standing waves and reverb. If the room was big enough the standing waves (the modes of the room) would be below audibility. That wouldn't mean there would no reflections, though, as a cathedral shows.

Even outside there can be reflections from a hard surface, like hearing an echo in the mountains as sound waves bounce off a rock face and come back.
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby Hugh Robjohns » Thu May 13, 2021 4:35 pm

Bigger than your average cathedral or concert hall....

... or an anechoic chamber...:lol:
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby forumuser840717 » Thu May 13, 2021 4:50 pm

TheLegit wrote:If you think about it if a room is big enough reflections could be taken out of the equation, but the question is how big would it need to be?

Depends.

If you mean how big would it need to be for there to be no reflections then that's either a space so big that any reflective surfaces are so far away that the energy of the source is absorbed by the air before hitting a boundary, or big enough that any energy reflected at a boundary is absorbed before it can reach a receiver (either way, a very big space!), or it's a space in which no energy is reflected at boundaries - so an anechoic chamber / total absorption type space.

If you mean how big would a space need to be to have no problematic reflections off whatever surfaces are unavoidable in a practically functional and buildable space (like floors/walls/room contents/etc.) rather than a mathematically conceptual theoretical space, then it's probably smaller than one might think but would need careful design to manage/control angles, timings, dispersions, and relative strengths of reflections.
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby Hugh Robjohns » Thu May 13, 2021 4:59 pm

I recall Bob Walker at the Beeb's R&D department designed what was called the 'Controlled Image Design' control room in the mid-90s. It employed carefully angled surfaces on the walls and ceiling around the console and monitors with the idea that incident sound waves would be directed away from the listening position to create, as the title suggested, a listening area free from local reflections and with improved stereo imaging a result.

After a lot of evaluation at Kingswood Warren (the beeb's R&D centre at the time) a couple of studios were converted to the format in Broadcasting house as a practical test bed... but as I recall the implementations weren't that successful or popular with the users and I believe the concept was abandoned.

There's a white paper on it here: http://downloads.bbc.co.uk/rd/pubs/reports/1995-04.pdf
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby forumuser840717 » Thu May 13, 2021 5:11 pm

I remember reading somewhere about those experiments but I never heard the room. Someone who worked in one did tell me that it was 'potentially very good but rather odd' and made him a little uncomfortable compared to what he was used to.

I was thinking of the Hidley Non-Environment rooms like Nomis and Bop, amongst others - probably a similar concept to the BBC room but a bit earlier. They take a bit of getting used to but once you get your head around what's going on they're incredible spaces to work in. They're a bit like the difference between top end moving coil headphones and electrostatics or, in some ways, the difference between headphones and speakers. The imaging is incredible, as is the clarity.

They sound/feel like much bigger spaces which creates an odd, and initially rather unsettling, dichotomy between what one sees and hears and it takes some getting used to. As does managing monitoring levels. All the Hidley rooms I've worked in have the extreme acoustic clarity combined with monitoring systems capable of massive headroom and clean delivery at seriously high levels. Until one gets the hang of the room, the acoustic clarity and lack of monitoring distortion or other acoustic clues can lead to the monitoring levels creeping upwards. It only becomes noticable when one tries to speak to someone without shouting!

One of the most memorable things, though, is how switching from nearfield to midfield to main monitors just led to more level and more LF as the speakers got bigger. The reflection profiles were so well managed that imaging remained the almost identical betwen systems and, until one got used to really detailed listening, if the levels were matched between the systems and running within the capabilities of the smaller systems, the only way easily to tell which system was working was to listen to the LF. On programme which wasn't LF heavy, or which didn't extend really low, it could be quite hard to tell without checking which monitor selector switch was lit up on the desk.
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby Hugh Robjohns » Thu May 13, 2021 6:38 pm

forumuser840717 wrote:Someone who worked in one did tell me that it was 'potentially very good but rather odd' and made him a little uncomfortable compared to what he was used to.

Yes, that sums up my impression of the KW test room as well. But the version I tried at BH (studio B13?) didn't seem to work in the same way. I think they decided it was due to reflections from the console (which I think was a large Neve 66?).

I was thinking of the Hidley Non-Environment rooms like Nomis and Bop, amongst others

Truly awesome rooms. I've been in quite a few around the world now and they are always absolutely stunning! But they do take some getting used to, and you do need to be careful with monitoring levels as you say.

One of the most memorable things, though, is how switching from nearfield to midfield to main monitors just led to more level and more LF as the speakers got bigger.

:D Yes, I've had that experience too. Mindblowing!
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issu

Postby RichardT » Thu May 13, 2021 7:35 pm

the Inchindown oil tanks have an amazing reverb - not surprising as they are almost 800 feet long!

https://m.youtube.com/watch?v=lLUcOFwZvyY
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby Airfix » Thu May 13, 2021 10:17 pm

with no walls - of course outdoors with nature and birds and stuff - there would be stratospheric bouncing
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby forumuser840717 » Fri May 14, 2021 12:27 am

Airfix wrote:with no walls - of course outdoors with nature and birds and stuff - there would be stratospheric bouncing

At radio frequencies maybe but not at audible frequencies. The temperature and pressure gradations arent rapid enough to cause audio to bounce back. (Except, maybe, at certain types of extremely high level events like hypersonic pressure shocks, at which point they'd be more shock waves than audio waveforms and aren't necessarily audible :think: ).
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby Airfix » Fri May 14, 2021 2:17 am

One could have a large marshall stack on stack pointed at the stratosphere - lying above the troposphere - with amp heads
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Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby Arpangel » Fri May 14, 2021 8:42 am

There is an amazing room in Osterley Park House, in the basement, a gothic chapel, it’s very small, about 30ft in diameter, with a ceiling, about 15ft high, it’s always amazed me, the reverb in there is phenomenally long, for such a small space, your mind can’t reconcile where you are with the sound you are hearing, I don’t know what makes this happen, if you could apply this structure to a studio reverb chamber you’d have access to amazingly long and dense reverbs in a modest sized room.
If you ever get the chance to go there, try it out, it’s totally amazing.
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That would be an ecumenical matter.

Re: Theoretically speaking how big would a room have to be until reflections are no longer an issue

Postby Airfix » Sat May 15, 2021 3:38 pm

The pointed rib-arch - vaulting. I'm thinking might have something to do with it
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