AES Paris 2016
Paper Session P3
P3 - Instrumentation and Measurement
Saturday, June 4, 13:30 — 17:00 (Room 353)
Chair:
Bert Kraaijpoel, Dutch Film Academy (NFA) - Amsterdam, Netherlands; Royal Conservatory - The Hague, Netherlands
P3-1 Characterization and Measurement of Wind Noise around Microphones—Chris Woolf, Broadcast Engineering Systems - Cornwall, UK
Producing wind noise measurements for microphones that correlate well with practical use has always proved difficult. Characterizing the noise numerically, rather than spectrally, has proved even harder. This paper explores some novel approaches to both problems. The airflow patterns of a newly designed wind generator are mapped, and a simple method of producing turbulent flow from a laminar stream is demonstrated. In order to characterize the wind noise numerically a dual number approach is explored as a possibility. This takes the spectral curves for a protected and unprotected microphone in an airstream, and produces two numbers: one for the level of noise reduction, and a second one for the accuracy with which the two curves track, duly corrected for audibility.
Convention Paper 9495 (Purchase now)
P3-2 Rocking Modes (Part 2: Diagnostics)—William Cardenas, Klippel GmbH - Dresden, Germany; Wolfgang Klippel, Klippel GmbH - Dresden, Germany
The rocking behavior of the diaphragm is a severe problem in headphones, micro-speakers, and other kinds of loudspeakers causing voice coil rubbing that limits the maximum acoustical output at low frequencies. The root causes of this problem are small imbalances in the distribution of the stiffness, mass, and force factor in the gap. Based on lumped parameter modeling, modal decomposition and signal flow charts presented in a previous paper (Part 1) this paper focuses on the practical measurement using laser vibrometry, parameter identification, and root cause analysis. New characteristics are presented that simplify the interpretation of the identified parameters. The new technique has been validated by numerical simulations and systematic modifications of a real transducer. The diagnostic value of the new measurement technique has been illustrated on a transducer used in headphones
Convention Paper 9496 (Purchase now)
P3-3 Harmonic Distortion Measurement for Nonlinear System Identification—John Vanderkooy, University of Waterloo - Waterloo, ON, Canada; Sean Thomson, Bowers & Wilkins - Steyning, West Sussex, UK
In order to model nonlinearities in loudspeakers, accurate measurement of harmonic distortion is necessary with particular attention to the relative phases of fundamental and harmonics. This paper outlines several ways that logarithmic sweeps can be used to achieve this goal. It is shown that Novak’s redesign of the logsweep is not strictly necessary, if proper account is taken of the phase relationships of the various harmonics. We study several other types of sweeps and methods to extract precise harmonic amplitudes and phases, using tracking filter concepts. The paper also deals with measurement systems that may have fractional-sample delays between excitation, reference, and data channels. Such details are important for accurate phase characterization of transfer functions. An intermodulation example is given for which sweeps with a single instantaneous frequency are inadequate.
Also a poster—see session P8-5]
Convention Paper 9497 (Purchase now)
P3-4 Evaluation of a Fast HRTF Measurement System—Jan-Gerrit Richter, Institute of Technical Acoustics, RWTH Aachen University - Aachen, Germany; Gottfried Behler, RWTH Aachen University - Aachen, Germany; Janina Fels, RWTH Aachen University - Aachen, Germany
This paper describes and evaluates a measurement setup for individual Head-Related Transfer Functions (HRTFs) in high spatial resolution in a short time period. The setup is constructed to have as little impact on the measurement as possible. It consists of a circular arc segment of approximately 160 degrees on which a large number of broadband loudspeakers are placed forming one continuous surface. By rotating the subject or the arc horizontally, HRTFs are acquired along a spherical surface. To evaluate the influence of the measurement setup a solid sphere and an artificial head are measured and are compared with both the presented system, simulation data using Boundary Element Method, and a traditional, well evaluated HRTF measurement system with only one loudspeaker.
Convention Paper 9498 (Purchase now)
P3-5 Efficiency of Switch-Mode Power Audio Amplifiers—Test Signals and Measurement Techniques—Niels Elkjær Iversen, Technical University of Denmark - Kogens Lyngby, Denmark; Arnold Knott, Technical University of Denmark - Kgs. Lyngby, Denmark; Michael A. E. Andersen, Technical University of Denmark - Kgs. Lyngby, Denmark
Switch-mode technology is greatly used for audio amplification. This is mainly due to the great efficiency this technology offers. Normally the efficiency of a switch-mode audio amplifier is measured using a sine wave input. However this paper shows that sine waves represent real audio very poorly. An alternative signal is proposed for test purposes. The efficiency of a switch-mode power audio amplifier is modelled and measured with both sine wave and the proposed test signal as inputs. The results show that the choice of switching devices with low on resistances are unfairly favored when measuring the efficiency with sine waves. A 10% efficiency improvement was found for low power outputs. It is therefore of great importance to use proper test signals when measuring the efficiency.
Convention Paper 9499 (Purchase now)
P3-6 ITU-R BS.1770 Based Loudness for Immersive Audio—Scott Norcross, Dolby Laboratories - San Francisco, CA, USA; Sachin Nanda, Dolby Laboratories - San Francisco, CA, USA; Zack Cohen, Dolby Laboratories - San Francisco, CA, USA
With the adoption of ITU-R BS.1770 and the creation of numerous loudness recommendations, measuring and controlling the loudness of audio for broadcast is now a standard practice for legacy (5.1 and stereo) content. With new immersive and personalized audio content, the measurement and controlling of loudness is still in its infancy. While ITU-R BS.1770 has recently been revised to support an arbitrary number of audio channels. However dynamic object-based audio measurement is not explicitly covered in this revision, though the revision can be used to measured the rendered object-based audio. This paper summarizes the results of subjective loudness matching tests that were conducted using rendered dynamic object-based audio to verify the revision of ITU-R BS.1770.
Convention Paper 9500 (Purchase now)
P3-7 Metrics for Constant Directivity—Rahulram Sridhar, Princeton University - Princeton, NJ, USA; Joseph G. Tylka, Princeton University - Princeton, NJ, USA; Edgar Choueiri, Princeton University - Princeton, NJ, USA
It is often desired that a transducer have a polar radiation pattern that is invariant with frequency, but there is currently no way of quantifying the extent to which a transducer possesses this quality (often called “constant directivity” or “controlled directivity”). To address the problem, commonly-accepted criteria are used to propose two definitions of constant directivity. The first, stricter definition, is that the polar radiation pattern of a transducer should be invariant over a specified frequency range, whereas the second definition is that the directivity factor (i.e., the ratio between the on-axis power spectrum and the average power spectrum over all directions), or index when expressed in dB, should be invariant with frequency. Furthermore, to quantify each criterion, five metrics are derived: (1) Fourier analysis of contour lines (i.e., lines of constant sensitivity over frequency and angle), (2) directional average of frequency response distortions, (3) distortion thresholding of polar responses, (4) standard deviation of directivity index, and (5) cross-correlation of polar responses. Measured polar radiation data for four loudspeakers are used to compute all five metrics that are then evaluated based on their ability to quantify constant directivity. Results show that all five metrics are able to quantify constant directivity according to the criterion on which each is based, while only two of them, metrics 4 and 5, are able to adequately quantify both proposed definitions of constant directivity.
[Also a poster—see session P8-6]
Convention Paper 9501 (Purchase now)
