Re: [Sursound] Construction of purpose built ambisonic studio. (Aaron Heller)

[Fons Adriaensen]

On Mon, Mar 10, 2014 at 09:50:43PM +, Steve Boardman wrote:
 
> Stanford's CCRMA room does look (and undoubtably sound) good, but
> the space below is maybe a bit over board for what I want to achieve,
> in the space I have. The actual area of the build space is probably
> around 180 square foot within a bigger space of 700 square foot on
> two floors.

As an example of what can be done without digging holes in the ground
have a look a this: .

This is at the conservatory of Pesaro, Italy, and the best sounding
and most accurate higher order Ambisonics studio I know of. Size
should be comparable to your 180 sq.ft. Shape is approximately a
square, but with no parallel walls. The space has a very low RT60
down to LF (bass traps are planned but not yet operational), the idea
being that in AMB mixes most of the space should be provided by the
signal and not by the room (which makes sense, creating virtual spaces
is one reason to use full surround). The control desk, shown against
the wall in the panaromic picture, can be moved to the center.

The speaker system consist of

* a ring of six at elevation -33 degrees (ideally this should
  be -45 degrees, but this requires an elevated listening 
  position),
* a ring of eight at ear height,
* a ring of six at +45 degrees
* a speaker at the zenith.
* one subwoofer

for a total of 21+1 speakers. This is an excellent setup for
third order, in the sense that the decoder matrix is very
well-conditioned (it doesn't rely on signals that would cancel
acoustically).

If you have four subs there's no reason for not using them
(put them in the corners, with a dedicated decoder).

One thing that could be improved is that the current ring of
eight is oriented such that there is no front speaker. The
alternative, rotating it 22.5 degrees, would provide a layout
that is more compatible with formats such as 5.1 or 7.1.

One point not yet mentioned in the replies so far is that for
lower order (and in particular first) you should use less
speakers. Also for this the rotated ring of eight would
be better - the subset used for first order at the moment
does not have L-R symmetry.

Ciao,

-- 
FA

A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)

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Re: [Sursound] Construction of purpose built ambisonic studio. (Aaron Heller)

[Steve Boardman]

Hi Aaron

Thanks for your response.

What I meant by 'angle errors', was that if the speakers are placed in a 
different part of the room that was structurally different, the sound waves 
would not be the same as the any of the others (due to reflection/absorbs-ion 
phase errors altering frequency/transient response). This can be improved 
through dsp, but it is never as good as getting it right at source. Maybe 
'angle errors' was not the correct term.

Stanford's CCRMA room does look (and undoubtably sound) good, but the space 
below is maybe a bit over board for what I want to achieve, in the space I 
have. The actual area of the build space is probably around 180 square foot 
within a bigger space of 700 square foot on two floors. It does have high 
ceiling though, with an apex over 4 metres (6.8 metres from ground floor to 
apex). This does dictate to a certain extent the shape of the room, as the room 
will be built on a mezzanine above the ground floor. This means the 'front' 
already slopes down to1.80 metres, rising to the back 4.5 vertical wall (that 
meets the apex). A box could still be constructed though, ignoring the slopes, 
but as I mentioned earlier this would actually be beneficial in front dominant 
mixing. I will probably go for a raised listening position to achieve more down 
positions, although to get a fully central head position standing may be 
required.

I will be very interested in your forth coming paper on partial coverage 
speaker arrays, as to date I have only used the platonic solids, or only 
horizontal decodes.

Cheers

Steve

> Message: 10
> Date: Sat, 8 Mar 2014 20:26:17 -0800
> From: Aaron Heller 
> To: Surround Sound discussion group 
> Subject: Re: [Sursound] Construction of purpose built ambisonic
>   studio.
> Message-ID:
>   
> Content-Type: text/plain; charset="utf-8"
> 
> Steve,
> 
> I'm not sure I follow everything you're saying about angle errors, but
> there are a few installations that work well here in the SF Bay area that I
> have personal experience with. The Listening Room at Stanford's CCRMA
> is a 3rd-order periphonic facility, described here
> 
>   https://ccrma.stanford.edu/room-guides/listening-room/
> 
> The others are in private homes, so I'll let the owners to chime in if they
> please. They're good sounding rooms, but without special acoustic
> treatment.  (unlike my living room, which is glass on three sides).  There
> are several accounts of Ambisonic reproduction not working well in very
> dead rooms, such as an anechoic chamber.
> 
> Also, for 3rd order periphonic you need to place a number of speakers below
> the listener, which can be a challenge.  The acoustically transparent floor
> in CCRMA's Listening Room is one solution.Eric Benjamin and I have a
> paper in the upcoming Linux Audio Conference on designing HOA decoders for
> partial coverage speaker arrays, such as domes and rings.
> 
> Aaron (hel...@ai.sri.com)
> Menlo Park, CA  US
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