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Large-scale Higher Order Ambisonic Sound Reinforcement Systems or: SIZE DOES MATTER Jrn Nettingsmeier <nettings@stackingdwarves.net> David Dohrmann <david@adamsonsystems.com> Ambisonics Symposium 2011 June 2-3, Lexington, KY

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Ambisonics Symposium 2011 June 2-3, Lexington, KY

Jörn Nettingsmeier <nettings@stackingdwarves.net>, David Dohrmann <david@adamsonsystems.com>

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Large-scale Higher Order Ambisonic Sound Reinforcement Systems

  • r:

SIZE DOES MATTER

Jörn Nettingsmeier <nettings@stackingdwarves.net> David Dohrmann <david@adamsonsystems.com>

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Ambisonics Symposium 2011 June 2-3, Lexington, KY

Jörn Nettingsmeier <nettings@stackingdwarves.net>, David Dohrmann <david@adamsonsystems.com>

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Large-scale Higher Order Ambisonic Sound Reinforcement Systems

SIZE MATTERS FOR

* large dance clubs * open-air dance events * rock opera shows

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Ambisonics Symposium 2011 June 2-3, Lexington, KY

Jörn Nettingsmeier <nettings@stackingdwarves.net>, David Dohrmann <david@adamsonsystems.com>

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Large-scale Higher Order Ambisonic Sound Reinforcement Systems Introduction:

  • Modern line arrays can be designed to deliver

almost constant SPL over a wide area. Therefore, the only limiting constraint for large systems is run-time.

  • Can we scale HOA systems to hundreds or

thousands of listeners?

  • What happens very far outside the sweet spot?
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Large-scale Higher Order Ambisonic Sound Reinforcement Systems Overview:

  • Previous large-scale Ambi implementations
  • Test system configuration
  • Listening impressions
  • Theoretical analysis
  • Conclusion
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Ambisonics Symposium 2011 June 2-3, Lexington, KY

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Previous implementations:

Malham et al. 1990, “Mediamix 90”, York, UK: 8 horizontal speakers 4 elevated speakers first-order decoder

  • max. radius: ca. 5m

Malham et al. 1992, “York Mystery Plays”: quasi-spherical: 1-4-6-4-1 first-order in-phase decode audience outside the sphere!

  • max. radius: ca. 7m
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Ambisonics Symposium 2011 June 2-3, Lexington, KY

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Previous implementations:

Wiggins/Funktion One 2006-2010, Glastonbury Festival, UK: six horizontal horn arrays second-order decode

  • max. radius:

~20m

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Configuration of the test system:

8 mid-hi stacks: 3x Adamson Metrix 8.5” LF, 3”->1.4” HF 4 sub stacks: 2x Metrix Sub 2x15” X-over 100Hz, 24dB/Oct Linkwitz- Riley

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Configuration of the test system:

slightly oblong layout due to space constraints compensated with delay, effective radius 10.25m nominal coverage angles mid-hi: 120° subs: omni

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Ambisonics Symposium 2011 June 2-3, Lexington, KY

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Configuration of the test system:

slightly oblong layout due to space constraints compensated with delay, effective radius 10.25m nominal coverage angles mid-hi: 120° subs: omni coverage issues!

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Ambisonics Symposium 2011 June 2-3, Lexington, KY

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Configuration of the test system:

Mid-hi decoder: 3rd order, max rV/max rE (x/o 500 Hz) Sub decoder: 1st order, max rV, later sub-cardioid

Decoder: AmbDec (Fons Adriaensen), delay and near-field compensation switched on. Gain calibration w/ pink noise using A-weighted SPL meter at sweet spot, to +/- 0.1 dB

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Listening impressions:

NB: Two subjects only (the authors)!

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Listening impressions:

NB: Two subjects only (the authors)! Yeah, that's unscientific. But try to get people to attend a listening session two days before Christmas, with three days' notice, in a cozy warehouse heated to 12°, from 20-24:00h.

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Listening impressions:

NB: Two subjects only (the authors)! Yeah, that's unscientific. But try to get people to attend a listening session two days before Christmas, with three days' notice, in a cozy warehouse heated to 12°, from 20-24:00h.

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Listening impressions:

First-order material:

  • k'ish for background music, not focused enough

to draw attention to stage or performers Third-order material: stable and focused over a wide area; tested with single sources and hybrid HOA recordings very large perceived source size - irritating with nature recordings, but kind of nice for rock shows ← not specific to Ambisonics

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Listening impressions:

A/B comparison: native Stereo vs. virtual speakers Base angle 45° Stacks T7 and T6 with S4 and S3 used for symmetry reasons. Virtual speakers panned to be congruent with physical stacks.

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Listening impressions:

A/B comparison: native Stereo vs. virtual speakers slight loss of presence and dryness with virtual speakers in direct comparison; still very enjoyable

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Listening impressions:

A/B comparison: native Stereo vs. virtual speakers wider virtual stereo (90-120°) prefered by both testers over native stereo; very immersive, no “hole- in-the-middle” effect, stereo localization remains stable → an improvement even for standard stereo material

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Listening impressions:

Sub decode: Max rV means out-of-phase components: → loss of “punch”, less efficient → no perceptible gain in localization Sub-cardioid or even mono decode is better suited to rock'n'roll settings, unless → the crossover frequency is very high, or → the system is installed in a small room (less excitation of room modes with hypercard decode).

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Listening impressions:

* very good localization over a wide area * no evident coloration * only very subtle phasing artifacts * no collapse until within 1-1.5m of the opposite speaker even with hypercardioid decode * confirmed usable area: 180m² → 360 tickets for dance floor, easily more if you provide lounge area around the listening zone. We are confident that 600 people will have a satisfactory listening experience with adequate localisation.

possibly masked by room reverberation!

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Listening impressions:

* very good localization over a wide area * no evident coloration * only very subtle phasing artifacts * no collapse until within 1-1.5m of the opposite speaker even with hypercardioid decode * confirmed usable area: 180m² → 360 tickets for dance floor, easily more if you provide lounge area around the listening zone. We are confident that 500 people will have a satisfactory listening experience with adequate localisation.

possibly masked by room reverberation!

Slight problem: Slight problem: This is This is too good too good to be true. to be true.

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Theoretical considerations:

Almost everybody is outside the sweet spot. Therefore, the ITD cues will be incorrect. As the listener moves away from the center, the ITDs will shift out of phase. It seems those inconsistent cues are being discarded by the brain and do not cause noticeable confusion, as long as robust ILD cues are available.

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Theoretical considerations:

Our best metric is therefore rE. Consequently, it might be best to use a max rE decode throughout the spectrum, perhaps excluding the subs (not tested).

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Theoretical considerations:

Worst-case scenario: a source from 0°, listener at 180°, 7m away from center

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Theoretical considerations:

relative levels and timings at listening position (assuming constant SPL, normalized to first incoming wave front)

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Theoretical considerations:

Applying stereophonic theory (summing localization, precedence effect, echo threshold):

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Theoretical considerations:

1st phantom source at 180°

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Theoretical considerations:

1st phantom source at 180° 2nd p.s. at 0°, +3dB, +16ms

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Theoretical considerations:

1st phantom source at 180° 2nd p.s. at 0°, +3dB, +16ms 3rd p.s. at 0°, +8dB, +29ms

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Theoretical considerations:

1st phantom source at 180° 2nd p.s. at 0°, +3dB, +16ms 3rd p.s. at 0°, +8dB, +29ms 4th p.s. at 0°, +18dB, +36ms

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Theoretical considerations:

1st phantom source at 180° 2nd p.s. at 0°, +3dB, +16ms 3rd p.s. at 0°, +8dB, +29ms 4th p.s. at 0°, +18dB, +36ms

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Theoretical considerations:

1st phantom source at 180° 2nd p.s. at 0°, +3dB, +16ms 3rd p.s. at 0°, +8dB, +29ms 4th p.s. at 0°, +18dB, +36ms ! ECHO threshold !

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Theoretical considerations:

We did not perceive any echoes. The sonic events were fused into one auditory event (→ listening expect- ation on large system is totally different from studio monitoring).

! ECHO threshold !

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Conclusion:

It works very well, although we don't quite understand why. Backward masking? Reduced precedence effect when confounded by multiple sonic events with rising level? Trading effect of echo threshold vs. number of sonic events? Further rigorous listening tests are necessary.

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Conclusion:

It works very well, although we don't quite understand why. Backward masking? Reduced precedence effect when confounded by multiple sonic events with rising level? Trading effect of echo threshold vs. number of sonic events? Further rigorous listening tests are necessary.

In practice, we feel In practice, we feel confident that a 3rd-order confident that a 3rd-order Ambisonic system will Ambisonic system will deliver good results for at deliver good results for at least 600 people least 600 people (300m² or r~10m). (300m² or r~10m).

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Acknowledgements:

Thanks to: Adamson Europe for the speaker systems

http://adamsonsystems.com

Cobra Sound Hamburg for the space

http://cobrasound.de

The Linux Audio community for the software.

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Thank you.

I'm looking forward to your questions.

The paper is available at http://stackingdwarves.net/public_stuff/linux_audio/ambisonic_symposium_2011/AmbiSym2011-Nettingsmeier-Dohrmann_Large-scale_HOA_Systems.pdf