I've been thinking about how this discussion might apply to a couple of
things I'm working on and it seems to me there are two different problems
here.
First, there is the issue of higher order mics often not really being
higher order at low frequencies. But isn't this really a problem of
encoding and not decoding? It seems like we shouldn't have to know
anything about the mic once we are in B-format. And such considerations
would not apply to synthetically panned higher order signals, right?
The other issues around cost of low frequency drivers, the ability to place
the physically larger, heavier speakers, dispersion patterns of different
drivers, etc. are certainly decoder questions. With simple, linear
decoders, one would have an 'ambisonic crossover' that not only divides
frequency bands but takes care of scaling the different order components,
followed by two or more decoders. Since a parametric decoder is already
working in the frequency domain, one could just vary the decode parameters
on a bin by bin basis, thus generating all the outputs from a single set of
input FFT's.
But these issues are about really decoding to speakers, which would not
apply to creating say 7.1 stems to be later mixed and sent to a bass
managed theater system, right? Or to put it another way, crossed over
decoders are doing the bass management in the ambisonic domain.
David
VVAudio
On Fri, Oct 16, 2015 at 8:19 AM, Peter Lennox <p.len...@derby.ac.uk> wrote:
> plus, with the large numbers of speakers, it's cheaper and easier to cross
> over in the b-format 'pinchpoint' than in the speaker feeds.
> ppl
>
> Dr. Peter Lennox
> Senior Fellow of the Higher Education Academy
> Senior Lecturer in Perception
> College of Arts
> University of Derby
>
> Tel: 01332 593155
> ________________________________________
> From: Sursound [sursound-boun...@music.vt.edu] On Behalf Of Steven
> Boardman [boardroomout...@gmail.com]
> Sent: 16 October 2015 14:14
> To: Surround Sound discussion group
> Subject: Re: [Sursound] Advice on new loudspeaker array... Genelec 8010
> speakers?
>
> This is something I have alluded to before.
> There is no need to have multiple transducers in the same box with
> ambisonics.. In fact it should be more accurate, economical, aesthetic, and
> space saving to have each transducer at its own separate point in space.
> Tweeters are more directional so more are needed, they are also cheaper.
> Going all the way down the frequency range to the least directional and
> most expensive, woofers and subs.
> Separate decodes could be done for each transducer bandwidth, rotating the
> soundfield to align. This would also benefit the transducer crossover
> point, as there would be less interference from proximity. It would also
> help room response, as crossovers could be tweaked and balanced on the fly.
> Which is also alot of fun!
>
> Steve
> On 16 Oct 2015 12:47, "Peter Lennox" <p.len...@derby.ac.uk> wrote:
>
> > we used a much cruder version of this back in 2002 - decoding a
> > hemispherical 32 speaker array to second order, but crossed over the
> > B-format at 90Hz (I think) to a horizontal-only 8-sub array, decoded in
> 1st
> > order. This was on the basis that we couldn't fly the subs, and anyway,
> > elevation discernment, being largely due to pinnae affects, was not
> > appealed to by the subs anyway. Had to work on the time alignment (the
> sub
> > decoder was analogue, the mid'n'tops 32 speaker array done in software)
> and
> > spatial alignment (rotating the subfield to match t'other, in the
> b-format
> > feed). It worked well, though could have been further refined; it was a
> > one-off installation.
> > But the principle of using decreasing order with decreasing frequency
> made
> > sense from the point of view of efficient use of transducers.
> >
> > It made me wonder whether the same principle extends the other way -
> > increasing order with increasing frequency, to make up for the
> deficiencies
> > in spatial resolution of lower orders at HF.
> > Given that it should now be reasonably 'easy' to align the fields of
> > multiple cells - even having differnt numbers of speakers for each
> > frequency band, there might be less reason to assume that point source
> > speakers are strictly necessary.
> > We're still using speakers designed as stereo projection systems, and it
> > could even be that starting again, thinking about real-world usages of
> > ambisonics, that one could revisit the speaker design theories.
> >
> > Going off on a tangent, it might be that (as others have experimented
> > with, before) that the trasnducer design for the programme material which
> > is 'ambient' (reflected sound, from no particular source, and therefor
> not
> > requiring precision in phantom imagery) might differ than that for
> > the'virtual sources' ('images')
> >
> > So I experimented with 12 very modest nxt-type flat panels which were
> > rotated thru' 90 deg. to what you'd expect, as it were - that is, they
> > didn't 'face' the centre but were at right angles to it. The results
> (given
> > the modest set up) were better than they had any right to be - most
> > especially for ambient and distant sounds.
> > I know they used to use multiple dipoles on the walls in cinemas for
> > conveying the surround channels of 5.1 material (they might still do, I
> > never go to the cinema because of the loud, poor sound) - so this seems
> to
> > be a similar principle.
> >
> > Just a few ramblings
> > cheers
> > Dr. Peter Lennox
> > Senior Fellow of the Higher Education Academy
> > Senior Lecturer in Perception
> > College of Arts
> > University of Derby
> >
> > Tel: 01332 593155
> > ________________________________________
> > From: Sursound [sursound-boun...@music.vt.edu] On Behalf Of Jörn
> > Nettingsmeier [netti...@stackingdwarves.net]
> > Sent: 16 October 2015 12:15
> > To: sursound@music.vt.edu
> > Subject: Re: [Sursound] Advice on new loudspeaker array... Genelec 8010
> > speakers?
> >
> > On 10/15/2015 10:51 PM, Dave Malham wrote:
> > > One of the things that should be investigated in conjunction with
> higher
> > > order Ambisonics material would be to "fade down" the higher order
> > > components as the frequency drops, thus spreading the bass over more
> > > speakers, reducing the strain on the individual speakers whilst
> > maintaining
> > > the spectral balance - hey, wasn't that Richard Lee's Powered
> Integrated
> > > Sub concept from several years ago?? Doesn't help with first order
> > materiel
> > > but....
> > >
> >
> > <ears pricked up>
> >
> > Intriguing idea, that. So we would apply zero-phase high-pass filters to
> > the second and higher components?
> > Should be nice for a test run, but how to keep latency down for live
> > electronics and A/V sync? How would we phase-align an IIR filter?
> > Allpasses on the lower components?
> >
> > The spectral balance would be maintained despite the filters, since
> > we're in LF, where each new order "takes away" as much as it "adds", so
> > to say. Unlike at HF, where we have to add energies and any such
> > filtering throws the spectral balance of kilter, as Eigenmike users will
> > know...
> >
> > --
> > Jörn Nettingsmeier
> > Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
> >
> > Meister für Veranstaltungstechnik (Bühne/Studio)
> > Tonmeister VDT
> >
> > http://stackingdwarves.net
> >
> > _______________________________________________
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