[LAU] ambisonics: fons ambdec and muse.demon.co.uk ambidec

Jörn Nettingsmeier nettings at folkwang-hochschule.de
Sat Jan 8 00:39:17 UTC 2011


On 01/07/2011 12:58 PM, fons at kokkinizita.net wrote:
> On Fri, Jan 07, 2011 at 11:10:41AM +0100, Jörn Nettingsmeier wrote:
>
>> for those non-ambiheads wishing to follow this discussion:
>> the near-field effect in ambisonics results in a bass boost. it's
>> caused by the speakers. ambisonic theory (without NFC) assumes plane
>> waves, i.e. speakers that are very far away, so that the wave fronts
>> are not curved. since they are curved in practice, you get the bass
>> boost. the same thing is responsible for the well-known proximity
>> effect on directional microphones.
>
> Not exactly. For a well-designed decoder the pressure at LF will
> be proportional to W, even without NFC, and should not have any
> bass boost.

need to double check, but iirc i did hear a very pronounced (read: 
unbearable) boominess on my organ recordings when listening to them on 
my <4m array in second order without NFC...

> What you get in that case is a velocity field that
> does not match the pressure in level,

this i understand.

> and more important - in
> phase, and this sounds very unnatural.

this is news to me. where does this phase delay come from?

> I'm pretty sure that uncompensated NF effects in reproduction
> systems are partly to blame for the 'you can't hear the direction
> of LF sources' myth.

interesting hypothesis.

i guess the myth is more correctly formulated as "you can't localize 
anything except some select and very obvious mid-frequency cues in AB 
stereo". of course, bose and friends would jump on this to sell 
ridiculously small satellites with woofers going up to 300 hz :)



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