Re: [LAU] ambisonics and number of speakers

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From: <fons@...>
To: <linux-audio-user@...>
Date: Sunday, February 28, 2010 - 2:05 pm

On Sun, Feb 28, 2010 at 02:21:08PM +0100, Jörn Nettingsmeier wrote:

> hmm. i still don't see from this explanation why 1st order horizontal

Have a look at the Bessel functions (either spherical
or cylindrical, they are different but similar).

The degree N Bessel function determines how much an
order N component contributes to the pressure field,
in function of distance from the reference point
(= the sweet spot).
The argument is 2 * pi * distance / wavelenght.

With some imagination you'll see that for each
distance their is a set of orders that dominate
the reconstruction. If these harmonics are missing
then field reconstruction at that distance will
be impaired.

As an extreme case, just imagine that all harmonics
except the zero and first order ones are absent, as
would be the case for first order reproduction with
a very large number of speakers. So the field is
reconstructed according to the J0 and J1 functions
only, and it decays rapidly as you move away from
the reference point. In fact this would be some form
of focussing on the sweet spot.

The 'area of reconstruction' is the one were field
reconstruction is dominated by those harmonics that
are reproduced exactly rather than aliased.
Its radius is expressed in wavelengths, so for all
except LF, at least one of your ears it out of it.
At real HF this doesn't matter so much, at least
not if you have the usual random distance errors.
But there is a mid frequency range where the effect
of incorrect field reconstruction can be very marked.

Ciao,

--
FA

O tu, che porte, correndo si ?
E guerra e morte !
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Messages in current thread:
[LAU] more than 4 channels for listening? Really?, Bearcat M. Sandor, (Thu Feb 25, 6:27 pm)
Re: [LAU] more than 4 channels for listening? Really?, Ken Restivo, (Fri Feb 26, 4:21 am)
Re: [LAU] more than 4 channels for listening? Really?, Jörn Nettingsmeier, (Sun Feb 28, 11:19 am)
Re: [LAU] more than 4 channels for listening? Really?, Arnold Krille, (Thu Feb 25, 8:41 pm)
Re: [LAU] more than 4 channels for listening? Really?, Bearcat M. Sandor, (Thu Feb 25, 9:21 pm)
Re: [LAU] more than 4 channels for listening? Really?, Arnold Krille, (Thu Feb 25, 10:01 pm)
[LAU] ambisonics and number of speakers, Jörn Nettingsmeier, (Sun Feb 28, 11:04 am)
Re: [LAU] ambisonics and number of speakers, Jörn Nettingsmeier, (Sun Feb 28, 1:21 pm)
Re: [LAU] ambisonics and number of speakers, , (Sun Feb 28, 2:05 pm)
Re: [LAU] more than 4 channels for listening? Really?, Bearcat M. Sandor, (Fri Feb 26, 12:41 am)
Re: [LAU] more than 4 channels for listening? Really?, Jörn Nettingsmeier, (Sun Feb 28, 11:13 am)
Re: [LAU] more than 4 channels for listening? Really?, Bearcat M. Sandor, (Sun Feb 28, 9:54 pm)
Re: [LAU] more than 4 channels for listening? Really?, Arnold Krille, (Fri Feb 26, 9:47 am)
Re: [LAU] more than 4 channels for listening? Really?, Florian Faber, (Fri Feb 26, 10:06 am)
Re: [LAU] more than 4 channels for listening? Really?, Jörn Nettingsmeier, (Sun Feb 28, 11:09 am)
Re: [LAU] more than 4 channels for listening? Really?, Fernando Lopez-Lezcano, (Mon Mar 1, 1:39 am)
Re: [LAU] more than 4 channels for listening? Really?, Jörn Nettingsmeier, (Mon Mar 1, 1:50 am)
Re: [LAU] more than 4 channels for listening? Really?, Fernando Lopez-Lezcano, (Mon Mar 1, 4:08 am)
Re: [LAU] more than 4 channels for listening? Really?, Jörn Nettingsmeier, (Mon Mar 1, 8:54 am)
Re: [LAU] more than 4 channels for listening? Really?, Fernando Lopez-Lezcano, (Mon Mar 1, 7:42 pm)
Re: [LAU] more than 4 channels for listening? Really?, Monty Montgomery, (Fri Feb 26, 10:41 am)
Re: [LAU] more than 4 channels for listening? Really?, Monty Montgomery, (Thu Feb 25, 10:53 pm)
Re: [LAU] more than 4 channels for listening? Really?, Ken Restivo, (Fri Feb 26, 9:47 pm)
Re: [LAU] more than 4 channels for listening? Really?, Fernando Lopez-Lezcano, (Thu Feb 25, 8:24 pm)
Re: [LAU] more than 4 channels for listening? Really?, Bearcat M. Sandor, (Thu Feb 25, 9:24 pm)
Re: [LAU] more than 4 channels for listening? Really?, Jörn Nettingsmeier, (Sun Feb 28, 10:52 am)
Re: [LAU] more than 4 channels for listening? Really?, Bearcat M. Sandor, (Sun Feb 28, 9:15 pm)
Re: [LAU] more than 4 channels for listening? Really?, Florian Faber, (Thu Feb 25, 6:32 pm)
Re: [LAU] more than 4 channels for listening? Really?, Arnold Krille, (Thu Feb 25, 8:35 pm)
Re: [LAU] Quipping at people's equipment choices (was more t..., Bearcat M. Sandor, (Thu Feb 25, 9:04 pm)
Re: [LAU] Quipping at people's equipment choices (was more t..., Gordon JC Pearce, (Sun Feb 28, 10:23 am)
Re: [LAU] Quipping at people's equipment choices (was more t..., Bearcat M. Sandor, (Thu Feb 25, 9:20 pm)
Re: [LAU] Quipping at people's equipment choices (was more t..., Bearcat M. Sandor, (Fri Feb 26, 5:53 am)