On 03/10/2014 11:50 PM, Steve Boardman wrote:
Hi J?rn (not sure what the character '?' is as it always displays
that way)
an o with double dot.
the way i approach it is: * keep the early reflection paths clean
for every speaker, like you would for stereo. no reflections < 10
ms is a good thing, if possible. * keep the diffuse field under
control. off-axis mud adds up as you add more speakers, so proper
bass absorption and diffuse reflection in the treble and upper
midrange are important. * use mild digital room correction in
addition to acoustic treatment, it can do wonders for bass
problems, where mechanical measures are difficult. * if you have to
make compromises, keep the frontal direction as perfect as
possible, and use it as a "magnifying glass" to work on details
even if the respective sound later moves elsewhere.
This is interesting, as I have had various opinions on this. Some
people say that spheres are the best as they have no parallel sides,
so reflections are reduced.
the center of a sphere is absolutely unusuable. all kinds of weird stuff
from in-head localisation to total collapse of localisation, changing
rapidly and erratically with just a few inches of head movement.
the curvature of the walls does not mean that reflections are reduced,
only that they are focused towards the center.
there can even be a flutter echo.
They also only have one room mode, that
can be predicted and treated. Or not excited (depending on the size).
i'd love to hear a spherical room that is not totally abysmal, and be
proven wrong. but i won't buy shares of your studio when you go for a
sphere :)
I do know of speaker box technology that uses this thought to it's
advantage, but I have never considered it for studio construction,
due to complexity and space. It would also have to be very large for
the lowest fundament not to excite it!
think whisper gallery. do you want that in your control room?
I must say, I like dead rooms, although I do agree that they are not
the best places to work. In fact quite disorientating. Listening to
ones own body internally is very off putting. As a consequence I
generally make the front complete dead with absorb-tion materials and
then have the back handle for reflections via random breakup
reflectors. Is this still a good idea?
i guess so. my (modest) experience tells me that overly dead rooms often
call for "freshening up" by thin layers of HF-diffusing surface on top
of the bass absorbers...
A little room correction will of course be needed, especially for
bass.
an off-the-cuff suggestion: * four subs in the corners. * the
fullrange speakers on a horizontal ring, with one speaker in
front, for a decent approximation of ITU 5.1 and 7.1, if
necessary. * the satellites in a lower ring-of-eight, an upper
ring-of-eight, another ring of six, one zenith speaker. then you
have two spares, and they will come in handy some day.
the bass management will be tricky. first of all, each speaker
needs to be perfectly delay-compensated to the listening spot. then
i'd try to create different layers of decoding:
* separate first-order decode for the subs, low-passed at 60,
24dB/oct * fourth-order decode for everything else * horizontal
speakers high-passed at 120/24 * satellites high-passed at 120/24 *
a separate horizontal-only decode (of the same full-sphere input
signal) for the range from 60 to 120 hz, again at 24dB/oct
this lets you drive all speakers to the best of their abilities,
and puts the missing bass frequencies in the correct direction.
$DEITY help you if anything is not perfectly phase-aligned,
though.
disclaimer: i've toyed with such hacked-up multiband setups, but
none of them ever went to production (or had to), so there may be
pitfalls i've overlooked.
First order decode for the four subs in the corners was what I was
thinking. Didn't think about going to fourth order on everything else
though, as I didn't think the increase in channel count was worth the
little improvement. I also want to leave some processing power for
mixing plugs (I use a lot) :)
well, i started from the number of speakers you said you had available.
Agreed on the full range horizontal ring. I was more thinking of a
dodecahedron for the satellites, either only 20 on the vertices, or
get 5 more, and would it be possible to use the edges?
you mean you want to create entirely separate horizontal and full-sphere
systems?
Is it better
to use platonic solids, or doesn't it matter?
with the recent advances in optimizing for irregular layouts by zotter
et al and heller et al, there is no longer a compelling reason to go for
platonic solids, except that they are kind of pretty :)
layouts based on a horizontal ring have the big advantage of better
horizontal-only performance, without much degradation in the 3d case.
Thanks again, and needless to say I will be asking a few more
questions as I progress. The build won't start for another month, and
when it's finished I would love for all you ambisonic heads to have a
listen.
can't wait to. where is your studio located?
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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