On 03/08/2014 02:13 AM, Steven Boardman wrote:
I have constructed many studios in the past but never one where all the
speaker positions have equal importance. Normally with stereo it is
beneficial for the sides of the space not to be divisible into each other.
still holds for ambisonics. try to get as many different room modes as
possible.
The cube being one of the worst examples of this. It is generally better to
have the mix position at one end of the longest side of a room too, which
helps diffuse reflections before they return to the mix position.
my setup has its front speakers close to a wall, and the remaining short
reflections are compensated with FIR filters to some degree. the sides
are against a bookshelf and free-standing in the room, with very
different acoustic loading and hence vastly different FIRs. the rears
are wedged between sofas.
that makes my front direction the most "analytical", and the system
nowhere near isotropic. but it sounds very good. i just know that when i
want to dissect something in detail, i rotate it to be in front.
unless you can afford a purpose-built room like the (mostly heptagonal!)
listening room at CCRMA (which, despite its very modest speakers, is
quite amazing - goes to show the importance of the room), some
pragmatism is called for :)
Also
completely parallel faces aren't good either, (but they also need to
symmetrical and predictable) as of course this creates more reflections.
symmetry between left and right of the most frequent listener
orientation is still a good thing.
Wider and higher at the back is generally a good thing. The general idea is
to through all errors behind where they have less importance and where they
can lose there energy more. This also applies to 5.1, where front has
dominance.
The problem I have is that this doesn't seem to a good idea with
ambisonics, as the mix position needs to be central and all angle errors
need to be equal.
central to the speaker system, yes. there is no benefit to being in the
exact center of the _room_, though. i'd go for some front-back asymmetry.
This actually leans towards the construction of a perfect
cube for simplicity of build, as creating a perfect sphere would be
difficult and space would be lost.
a sphere would be absolutely disastrous, unless it is anechoic, and then
the shape does not matter anyways. and as aaron pointed out, overly dead
listening rooms lack proper masking of interference artefacts and will
be very irritating to work in.
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.
It will basically be a third order set up, but not sure on the exact amount
of speakers yet. I have 4 subs, 25 satellites (120hz roll off) and 10
nearly full range speakers (60hz roll off). Any advice on room shape, and
speaker positioning would be greatly appreciated.
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.
have fun,
jörn
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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