Room Acoustics

Wednesday, October 16, 1:30 pm — 5:00 pm (1E10)

Chair:
David Griesinger, David Griesinger Acoustics - Cambridge, MA, USA

P04-1 Use of Wavelet Transform for the Computation of Modal Decay Times in Rooms—Roberto Magalotti, B&C Speakers S.p.A. - Bagno a Ripoli (FI), Italy; Daniele Ponteggia, Audiomatica Srl - Firenze, Italy
The acoustic behavior of small rooms in the modal frequency band can be characterized by the modal decay times MT60. The paper explores a method for computing modal decay times from measurements of Room Impulse Responses (RIR) based on the wavelet transform. Once the resonance frequencies have been selected, the procedure computes a series of wavelet transforms of the Morlet type with decreasing bandwidth, exploiting the property that Morlet wavelets preserve the time history of energy decay. Then decay times can be calculated either by linear regression of the non-noisy portion of the curve or by nonlinear fitting of a model of decay plus noise. Examples of application of the method to real RIR measurements are shown.

P04-2 What's Old Is New Again: Using a Physical Scale Model Echo Chamber as a Real-Time Reverberator—Kevin Delcourt, École Nationale Supérieure Louis Lumière - Saint-Denis, France; Sorbonne Université, Paris - Paris, France; Franck Zagala, Institute d’Alembert, Group Lutheries—Acoustique-Musique - Paris, France; Alan Blum, École Nationale Supérieure Louis Lumière - Saint-Denis, France; Brian F. G. Katz, Sorbonne Université, CNRS, Institut Jean Le Rond d'Alembert - Paris, France
This paper presents a method using physical scale models as echo chambers. The proposed framework creates a partitioned convolution engine where the convolution processing is carried out physically on an up-scaled live audio stream in the model. The resulting reverberated sound is captured and down-scaled, providing the result to the user in real-time. The scale factor can be dynamically changed to explore different room sizes and the reduced dimensions of the scale model make it a tangible reverberation tool. Scale factors up to 1:5 have been tested for full bandwidth, with higher factor possible with improved hardware or in exchange for lowering the upper frequency range, primarily due to driver performance.

P04-3 Synthesis of Binaural Room Impulse Responses for Different Listening Positions Considering the Source Directivity—Ulrike Sloma, Technische Universität Ilmenau - Ilmenau, Germany; Florian Klein, Technische Universität Ilmenau - Ilmenau, Germany; Stephan Werner, Technische Universität Ilmenau - Ilmenau, Germany; Tyson Pappachan Kannookadan, TU- Ilmenau - Ilmenau, Germany
A popular goal in research on virtual and augmented acoustic realities is the implementation of realistic room acoustics and sound source characteristics. Additionally, listeners want to move around, explore the virtual or augmented environments. One way to realize position-dynamic synthesis is the use of binaural technologies on the basis of real measurements. While this approach allows to successfully reproduce the real acoustic environment, many positions need to be measured. To reduce the time effort new methods are invented to calculate binaural room impulse responses from few positions. The presented work enhances existing synthesis methods by including predefined sound source directivities into calculation of binaural room impulse responses. The results are analyzed in a physical and in a perceptive way.

P04-4 Extracting the Fundamental Mode from Sound Pressure Measurements in an Acoustic Tube—Joerg Panzer, R&D Team - Salgen, Germany
Acoustic tubes are used to provide a load to loudspeakers or to measure material properties. If the wavelength is comparable to the diameter of the tube cross-modes can be excited. This paper demonstrates a method that allows to extract only the fundamental mode from the measurement of the sound-pressure response. The only requirement is the use of three microphones mounted into the sides of the tube-wall as well as a circular cross-section.

P04-5 Accurate Reproduction of Binaural Recordings through Individual Headphone Equalization and Time Domain Crosstalk Cancellation—David Griesinger, David Griesinger Acoustics - Cambridge, MA, USA
We have developed software apps that allow a user to non-invasively match headphones to reproduce the identical spectrum at the eardrum as that from a frontal source. The result is correct timbre and forward localization without head tracking. In addition we have developed a non-individual crosstalk cancelling algorithm that creates virtual sound sources just outside a listener’s ears. Both systems reproduce binaural recordings with startling realism. The apps enable researchers and students to hear what acoustical features are essential for clarity, proximity, and preference. Listening to any type of music with our apps is beautiful and highly engaging.

P04-6 Concert Hall Acoustics’ Influence on the Tempo of Musical Performances—Jan Berg, Luleå University of Technology - Piteå, Sweden
The acoustics of a concert hall is an integral and significant part of a musical performance as it affects the artistic decisions made by performer. Still, there are few systematic studies on the phenomenon. In this paper the effect of concert hall acoustics, mainly reverberation, on musical tempo for a selection of different genres and ensemble types is analyzed quantitatively. The study utilizes audio recordings made in a concert hall equipped with a movable ceiling enabling a variable volume and thus a variable reverberation time. The results show that there are cases where the tempo follows a change in acoustics as well as cases where it remains more or less unchanged.

P04-7 Optimum Measurement Locations for Large-Scale Loudspeaker System Tuning Based on First-Order Reflections Analysis—Samuel Moulin, L-Acoustics - Marcoussis, France; Etienne Corteel, L-Acoustics - Marcoussis, France; François Montignies, L-Acoustics - Marcoussis, France
This paper investigates how first-order reflections impact the response of sound reinforcement systems over large audiences. On the field, only few acoustical measurements can be performed to drive tuning decisions. The challenge is then to select the right measurement locations so that it provides an accurate representation of the loudspeaker system response. Simulations of each first-order reflection (e.g., floor or side wall reflection) are performed to characterize the average frequency response and its variability over the target audience area. Then, the representativity of measurements performed at a reduced number of locations is investigated. Results indicate that a subset of eight measurement locations spread over the target audience area represents a rational solution to characterize the loudspeaker system response.