Yes that is it!
Incidentally, I would like to add a (nonmathematical)
point. I think dipoles are more or less a disaster for Ambisonics
Bass is one thing, but what dipoles mostly do is bounce sound off
the back walls(unless you were using them as subwoofers only)
in a way that creates "spaciousness", so beloved of stereo loving
audiophlies, but that blurs the actual spatial information.
About the last thing one wants with a surround system that actually
workss is a lot of time delayed sound bouncing off the walls behind.
People sometimes argue that if the dipoles are far from the walls
that the wall reflection is so long delayed so as not to mess up the
stereo. I do not believe this but it is not flat out silly.
But the idea of having all that extra reflected energy(above the bass)
for Ambisonics seems to me really wrong. Moreover to put the dipoles the
seven feet or so from the wall behind that they need in order to be
reasonably uncolored one would need a HUGE room for an Ambisonic setup.
Forget dipoles, would be my suggestion, unless you want to use them in the
bass only and something more precise in the higher frequencies(eg
like the Gradient Revolution)
Many years ago in issue 3 of The Absolute Sound, Jon Dahlquist
wrote an article where he said the perfect speaker for use in an actual
room would be dipole in the bass and forward radiating about the bass.
(Never mind that he went on to build the DQ10 which was exactly the
reverse of that). He had a point!
But fullrange dipoles are no so good for Ambisonics I think unless
you have enormous space to work with.
Robert
On Sat, 11 Jun 2011, Martin Leese wrote:
Marc Lavall?e <[email protected]> wrote:
...
In an article I mentioned earlier ("Spatial auditory display using
multiple sub-woofers in two different reverberant reproduction
environments"), tests were made in an anechoic chamber where the
detection was much better than in a small room. The test tones were one
octave wide with centre frequencies varying between 40Hz and 100Hz.
Would such tones have high frequency components in an anechoic chamber?
I believe the point that Robert was trying to
make was that *everything* has high
frequency components. To avoid these the
audio signal would have had to have been
playing since the dawn of time. Robert also
pointed out this doesn't necessarilly mean that
they matter. The problem is in trying to prove
that they don't.
Dipole and cardioid subs excite less room modes than omni subs:
http://www.kirchner-elektronik.de/~kirchner/DIPOL-CARDIOIDeng.pdf
http://www.linkwitzlab.com/Woofer%20accuracy.rtf
Would they be a better choice for Ambisonics?
The difference is not between Ambisonics and
5.1 (or whatever), but between the number of
subs you have. If you have more than one
sub then, if you feed them different signals,
you have the possibility of localising the audio
they produce. With such a goal, you want to
avoid exciting standing waves in the room, and
so directional subs would be preferable.
I understand that with ambisonics bass management is not required,
although a dedicated decoder for 3 or more subs could be considered
like bass management (when full range speakers are not available).
The difference is not between Ambisonics and
5.1 (or whatever), but between the capabilities
of the main speakers and the subs. The
purpose of bass management is to direct bass
to speakers that can handle it. If not all of
your speakers are equally capable of
reproducing bass (and the fact that you have
a sub at all suggests this is the case) then you
would benefit from bass management.
There is nothing magical about Ambisonics
with respect to bass.
Regards,
Martin
--
Martin J Leese
E-mail: martin.leese stanfordalumni.org
Web: http://members.tripod.com/martin_leese/
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