Different dispersion patterns of different drivers may not be a decoder
question only, but should be solved in the acoustic domain. That has been the
whole idea of so called waveguides, to match the directivity of a higher
frequency driver - MF or HF - to the directivity of the lower frequency driver
around crossover. Otherwise there will be a bump in power response as the
higher frequency driver is practically omnidirectional at its low end while the
lower frequency driver gets directive in its upper end.
Ilpo
> On 16 Oct 2015, at 19:27, David McGriffy <da...@mcgriffy.com> wrote:
>
> 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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