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

All about the tools and techniques involved in capturing sound, in the studio or on location.

Moderator: Moderators

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

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?
TheLegit
Regular
Posts: 130
Joined: Wed Jun 27, 2018 1:16 pm

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

Til it's not a room.

Tomás Mulcahy
Frequent Poster (Level2)
Posts: 2007
Joined: Wed Apr 25, 2001 12:00 am
Location: Cork, Ireland.

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

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.
merlyn
Regular
Posts: 304
Joined: Thu Nov 07, 2019 3:15 am
It ain't what you don't know. It's what you know that ain't so.

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

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

... or an anechoic chamber...

Hugh Robjohns
Moderator
Posts: 31027
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound
In my world, things get less strange when I read the manual...

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

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.
forumuser840717
Regular
Posts: 294
Joined: Thu Jun 16, 2016 5:20 pm

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

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.

Hugh Robjohns
Moderator
Posts: 31027
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound
In my world, things get less strange when I read the manual...

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

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.
forumuser840717
Regular
Posts: 294
Joined: Thu Jun 16, 2016 5:20 pm

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

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.

Yes, I've had that experience too. Mindblowing!

Hugh Robjohns
Moderator
Posts: 31027
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound
In my world, things get less strange when I read the manual...

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

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

RichardT
Frequent Poster
Posts: 933
Joined: Fri Aug 13, 2004 12:00 am
Location: London UK

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

with no walls - of course outdoors with nature and birds and stuff - there would be stratospheric bouncing
Airfix
Frequent Poster
Posts: 743
Joined: Mon May 07, 2012 12:00 am

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

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 ).
forumuser840717
Regular
Posts: 294
Joined: Thu Jun 16, 2016 5:20 pm

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

One could have a large marshall stack on stack pointed at the stratosphere - lying above the troposphere - with amp heads
Airfix
Frequent Poster
Posts: 743
Joined: Mon May 07, 2012 12:00 am

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

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.

Arpangel
Jedi Poster
Posts: 7742
Joined: Sat Jul 12, 2003 12:00 am
That would be an ecumenical matter.

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

The pointed rib-arch - vaulting. I'm thinking might have something to do with it
Airfix
Frequent Poster
Posts: 743
Joined: Mon May 07, 2012 12:00 am