On 07/26/2011 02:18 AM, Marc Lavallée wrote:
Imagine two rooms with proper acoustic characteristics and treatments
for ambisonics reproduction: the first is 3mX4m and the other is four
times larger in surface (9mX12m). In both rooms there's a
horizontal hexagon of speakers, and 5 speakers are against a wall.
regardless of room size, they will require a bit of equalisation. if the
speakers are designed to be close to a boundary surface, the one that's
not against a wall needs (gentle) bass boost. vice versa, if your
speakers are designed to be free-standing, the five speakers need some
attenuation at LF.
if you're still shopping for speakers, i found that the genelec 8030
have a nice built-in bass eq which can be used to deal with this issue.
i was able to even out the bass response of a rig where most speakers
are next to two boundary surfaces and a few only next to one. of course,
you could also do this in software.
When NFC is applied in both rooms, do they sound the same in terms of
distance perception when playing the same recording?
NFC is not a constant. the amount of NFC depends on the distance to the
speaker.
Or is the same
"sound object" appear to be twice as far in the largest room?
actually, if you hope to get distance perception so good that the notion
of "twice as far" begins to make sense, then you're in for some heartache.
that's why i said "distance cues are gimmickry" earlier. the actual
curvature of the soundfield (which is all that NFC does for you) is not
a very robust distance cue. the delay of the (reproduced) floor
reflection is a lot more helpful, as is the ratio of direct to
reverberated sound (but the latter doesn't help soundman john with his
spitfires).
so why get gung-ho about a cue of secondary importance, for a perception
apparatus that doesn't care much anyways...
the problem is that your listening room floor reflection will always be
different from and stronger than the recorded floor reflection, which
pulls the image towards the speaker circle.
if you close your eyes and find yourself able to suspend your disbelief
long enough to actually imagine yourself in a cathedral listening to an
organ, then rejoice and be happy. don't spoil the magic by gauging the
distance. it's not going to happen.
the sad and simple fact is that _no_ surround rig can get the distance
unambiguously right in any but anechoic conditions.
and before you run off to shop for styrofoam, be warned that most
recordings would sound utter crap in anechoic conditions, because nobody
mixes for that.
moreover, the phasing problems of our beloved ambisonic technique would
become very obnoxious indeed.
the deader you make your room, the more hope you have to get precise
distance information. at the same time, the rig will sound less pleasant
and artefacts will become more obvious. since humans suck at absolute
distance perception anyways, your best bet is to be content with some
degree of distance discriminination. that is, you want to hear the
woodwinds _somewhere_behind_ the strings. you wouldn't normally care how
many metres. this usually works well if the recording is ok.
Apart from widening the listening sweet spot, are larger rooms "better"
at reproducing distance cues when using the same speaker configuration?
Is distance perception directly related to speaker distances?
as mentioned before, the floor reflection is a very strong distance cue
at close range under semi-anechoic conditions (i.e. if you want to gauge
the distance of that sabre-toothed tiger or the potential mating
candidate). if you're right next to the sound source, the floor
reflection will have the longest delay. far away, the delay will be
negligible.
the general case is
dly = 340 / (sqrt(ear_height^2 + half_distance^2) * 2)
when a listening room first reflection is strong and early, it will
dominate your sense of distance. in that sense, larger rigs have the
potential to be less intrusive wrt distance perception.
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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