[Sursound] Ambisonic Cube reverberation attenuation with foam

[Tommaso Perego]

Hello Everyone
I was wondering if you could please help me solve the following problem.

I have encountered reverberation issues with an Ambisonic installation,
of dimension 5x5x2.5 meters (a squashed cube, so to speak).

I have noticed that reverberation is due to the proximity to the surrounding 
walls (7x12x6), causing 
imperfect appreciation of the spatial sound designs when heard in the middle of 
the cube.
Assuming that this is the correct understanding of the problem I was wondering 
if:

- surrounding  the cube with the following foam material

http://www.anyfoam.co.uk/sheet-foam.php 
  (the acoustic foam)

 would significantly reduce reverberation effect to better the definition 
inside the cube?

- where exactly would be best to put the foam? Would just the sides (excluding 
floor and ceiling) of the cube be enough ?

- should reducing the overall sound power improve the situation?


Looking forward to hear your opinion, I would greatly appreciate your help
Thank you

kind Regards

Tommaso
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Re: [Sursound] Sweet spot precise measurement

[Tommaso Perego]

Well thank you so much Martin, Jorn and Fons.
That confirmed my hypothesis and very kindly you gave me a lot more information 
very interesting.

I'm a bit concerned now, as I would not know for sure if eight speakers and 3rd 
Order could provide quite accurately a soundfield for an area of 5x5 meters. 

Accordingly to what you wrote, it doesn't really matter in Ambisonics if I 
place the loudspeakers at 6, 8 or 10 meters diameter... (as long as the 
loudspeakers are powerful enough). Is that correct?

Do you have any suggestions? How differently would you do?

Many thanks again, I love this list

tom



> 
>   1. Re: Sweet spot precise measurement (Martin Leese)
>   2. Re: Sweet spot precise measurement (J?rn Nettingsmeier)
>   3. Re: Sweet spot precise measurement (Fons Adriaensen)
> 
> 
> 
> --
> 
> Message: 1
> Date: Wed, 7 Nov 2012 10:51:50 -0700
> From: Martin Leese 
> Subject: Re: [Sursound] Sweet spot precise measurement
> To: sursound@music.vt.edu
> Message-ID:
>   
> Content-Type: text/plain; charset=ISO-8859-1
> 
> Tommaso Perego wrote:
>> Dear all,
>> I was wondering how, knowing the diameter of a speaker octagon,
>> using 1st or 3rd Order ambisonics,  to calculate precisely the dimensions of
>> the sweet spot area.
>> Any ideas?
> 
> If you want to make calculations of area then
> your first problem will be defining precisely
> what you mean by the sweet spot.
> 
> Your second smaller problem will be that the
> area will have fuzzy edges.
> 
> Regards,
> Martin
> -- 
> Martin J Leese
> E-mail: martin.leese  stanfordalumni.org
> Web: http://members.tripod.com/martin_leese/
> 
> 
> --
> 
> Message: 2
> Date: Wed, 07 Nov 2012 19:08:59 +0100
> From: J?rn Nettingsmeier  
> Subject: Re: [Sursound] Sweet spot precise measurement
> To: Surround Sound discussion group 
> Message-ID: <509aa3bb.5060...@stackingdwarves.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> On 11/07/2012 10:04 AM, Tommaso Perego wrote:
>> Dear all,
>> I was wondering how, knowing the diameter of a speaker octagon,
>> using 1st or 3rd Order ambisonics,  to calculate precisely the dimensions of 
>> the sweet spot area.
>> Any ideas?
>> Many thanks
> 
> 
> the strict sweet spot is only a function of order and frequency, not of 
> the array diameter.
> r < N/2 * c/f is an approximation i saw mentioned in one of franz 
> zotter's papers, where N is the order, c is the speed of sound and f is 
> the frequency. in words, the order N is the number of zero-crossings of 
> a given frequency which are correctly reproduced.
> 
> that sounds pretty dire until you realize that at frequencies above a 
> few hundred hertz, phase relationships are not that important anymore...
> 
> 
> in practise, a larger diameter does help, because of two factors:
> a) the sound pressure level varies much more slowly in the far field of 
> a loudspeaker. e.g. the level halves when you move from 2 to 4 meters 
> (i.e. over 2 meters), and again when you move from 4 to 8 meters (same 
> drop, but over 4 meters). that means that while the phase relationships 
> are quite wrong outside the sweet spot, the intensity ratios of the 
> speakers are more or less correct, which helps with rE localisation.
> even more so if you can use highly directional speakers such as line arrays.
> b) more distant loudspeakers excite more reverb and have a lower 
> direct-to-reverb ratio, which helps to mask some of the oddities of 
> ambisonic playback.
> 
> but these perceptional advantages do not change the basic fact that the 
> soundfield reconstruction is incorrect outside the sweet spot.
> 
> 
> best,
> 
> 
> j?rn
> 
> -- 
> J?rn Nettingsmeier
> Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
> 
> Meister f?r Veranstaltungstechnik (B?hne/Studio)
> Tonmeister VDT
> 
> http://stackingdwarves.net
> 
> 
> 
> --
> 
> Message: 3
> Date: Wed, 7 Nov 2012 20:43:57 +
> From: Fons Adriaensen 
> Subject: Re: [Sursound] Sweet spot precise measurement
> To: sursound@music.vt.edu
> Message-ID: <20121107204357.ga17...@linuxaudio.org>
> Content-Type: text/plain; charset=iso-8859-1
> 
> On Wed, Nov 07, 2012 at 07:08:59PM +0100, J?rn Nettingsmeier wrote:
> 
>> On 11/07/2012 10:04 AM, Tommaso Perego wrote:
> 
>>> I was wondering how, knowing the diameter of a speaker octagon,
>>> using 1st or 3rd Order ambisonics,  to calculate precisely the dimensions 
>>> of the sweet spot area.
> 
>> the stric

[Sursound] Sweet spot precise measurement

[Tommaso Perego]

Dear all,
I was wondering how, knowing the diameter of a speaker octagon,
using 1st or 3rd Order ambisonics,  to calculate precisely the dimensions of 
the sweet spot area.
Any ideas?
Many thanks

tom


On 6 Nov 2012, at 17:00, sursound-requ...@music.vt.edu wrote:

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> Today's Topics:
> 
>   1. Which order (but not extactly high order)? (Eric Carmichel)
>   2. Re: Vestibular response, HRTF database, and now with added
>  height... (Peter Lennox)
>   3. Re: Vestibular response, HRTF database,and now with added
>  height... (Dave Malham)
>   4. Re: Vestibular response, HRTF database, and now with added
>  height... (Peter Lennox)
> 
> 
> --
> 
> Message: 1
> Date: Mon, 5 Nov 2012 15:59:19 -0800 (PST)
> From: Eric Carmichel 
> Subject: [Sursound] Which order (but not extactly high order)?
> To: "sursound@music.vt.edu" 
> Message-ID:
><1352159959.33851.yahoomail...@web2802.biz.mail.ne1.yahoo.com>
> Content-Type: text/plain; charset="us-ascii"
> 
> Greetings,
> I would like to model microphone pickup patterns in conjunction with HRTFs 
> and Ambisonic recordings that I've made. To give a specific example, I would 
> like model a miniature supercardiod mic, pointed forward, that is located 
> proximal (or superior) to the pinna. This would be akin to a directional mic 
> on a hearing aid or CI processor. The HRTF can be approximate, as the mic is 
> likely to be placed slightly above the pinna and close to the head, not right 
> at the opening of the ear canal. Some mics, however, are located in the 
> concha, so the IRs from the Listen Project would approximate the mic 
> placement, but not the mic's polar pattern.
> I have recordings of cafeterias and public spaces that I made using a 
> TetraMic. VVMic allows me to create first-order mic patterns that can be 
> rotated in space. This alone is useful, but does not include the acoustic 
> shadow that would be created by a hearing aid wearer's head. I have the 
> Harpex VST, too. Harpex includes the HRIRs from the Listen Project (Svein, 
> please correct me if I'm wrong on this), thus making binaural simulations a 
> snap. But to get an HRTF that includes a specific mic pick-up pattern is a 
> little trickier.
> I had initially used VVMic to create the mic pattern I wanted, and then aimed 
> it to the direction I wanted. Input was B-formatted wav files. The resulting 
> output is a single channel, or N identical channels if I want to create N 
> tracks. I created 4 tracks and used these as pseudo B-formatted material in 
> Harpex.
> The other "order" would be to create a stereo (binaural) output via Harpex 
> from the original (authentic) B-formatted material. Then one of the two 
> channels, L or R, could be made into four identical tracks that can be fed to 
> VVMic to get the intended polar response. The four tracks, of course, are not 
> B-format.
> A bit of head scratching tells me neither method outlined above is correct. 
> At least the binaural output from Harpex should be equivalent to an 
> omnidirectional mic placed at an ear's concha (ITE hearing aids), and that 
> could be used for simulations of electric listening. But I'd really like to 
> model hybrid devices that combine both electric (cochlear implant) and 
> acoustic (hearing aid) stimulation. It seems that using Ambisonic recordings 
> without the need for loudspeakers would be an elegant way to simulate CI 
> listening in 3-D environments, but using normal-hearing listeners.
> 
> Regarding my recent post (vestibular-auditory interactions and HRTFs): Thanks 
> to Peter L. for making my clumsy wording clearer and to Dave M. for making 
> the idea more direct and to the point. I have to be careful when referencing 
> the anatomical horizontal plane versus the horizontal plane that lies 
> perpendicular to gravity. Although a bit off topic of Ambisonics, the post 
> did directly relate to spatial hearing. Because it's easy to do virtual mic 
> rotations with Ambisonic material, Ambisonics could be a useful tool for 
> studying vestibular-auditory interactions.
> Thank