Seat Dip Effect Research Articles

Investigation of the seat-dip effect using finite-difference time-domain simulations.

The seat-dip effect (SDE) occurs when low-frequency sounds propagate through the seating area of a performance space. The physical aspects governing the effect still puzzle acousticians mostly due to the large variety of seating configurations. In this study, the SDE is investigated in three parameterized hall models using the finite-difference time-domain method to simulate a large number of seat configurations in order to quantify the contribution of different geometric properties related to the seating area. The results show that the step size defining the inclination angle of the seating area and the opening underneath the seats (or underpass) are significant factors contributing to the SDE, whereas the stage height and the source position are found to be less important. The results also demonstrate that with an underpass greater than the step size, the first frequency dip occurring between 80 and 100 Hz is mitigated regardless of the hall type considered. The phenomenon is also found to be predominant in the early part of the room response. Visualizations of spatial and time-frequency evolution in the halls are also provided for the cases where the seat properties are found to visibly affect the magnitude spectrum.

Treating seat-dip with acoustic metamaterials and detuned acoustic resonators

As sound passes over regularly spaced audience seating areas in performance spaces at a grazing angle, the low frequency response of performing arts venues and auditoria is altered. This is due to diffraction based on the regular spacing of the seating. One effect is what is referred to as seat-dip attenuation, which is a reduction in low frequency energy across a bandwidth. Being a low-frequncy phenomenon, it is difficult to treat using conventional acoustic materials such as porous absorbers or Schroeder diffusers. Modern acoustic metamaterials can alter wave propagation using relatively thin layers. This project investigates whether acoutic metamaterials applied to the tops of the seats, the rear of the seats, or the floor can reduce the low-frequency attenuation brought about by the seat-dip effect. This novel approach demonstrates varying levels of succes for remediating low-frequency seat-dip attenuation. The study is carried out using a computer model that is evualted using boundary element method (BEM) in COMSOL Multiphysics. Additionally, a novel approach for reducing the prominence of the seat-dip effect is explored using detuned Helmholtz resonatos placed at the top of the seats.

Mechanism Analysis of the Influence of Seat Attributes on the Seat Dip Effect in Music Halls

The seat dip effect (SDE) is an acoustic phenomenon of low-frequency band attenuation that occurs in the music halls when the sound of the music passes at a near grazing incidence over the seats. In this paper, the numerical simulations on the basis of the finite element method are conducted to study the influence of seat attributes (seat height, seat spacing and seat absorption) on the SDE and the corresponding mechanism. The mapping of sound spatial distribution related to the SDE is employed to observe the behavior of sound between the seats. The results show that the dip frequency of the SDE can be shifted to frequencies lower than theoretical values when the seat height is smaller than the seat spacing. Additionally, the SDE attenuation can be distinctly suppressed in a sequence from the front seats to the rear seats with an absorption improvement to the seat back or cushion, and the seat back absorption is more effective than the cushion absorption. A mechanism analysis reveals that the SDE is highly associated with standing waves inside the seat gaps and with the “diffusion” effect on the grazing incident waves by energy flow vortexes around the top surfaces of the seats.

Measurement verification of reverberation time in seating areas close to the lateral wall in the auditorium

This study started with building a database for existed Jockey Club Auditorium. Using impulse response method to measure numerous seats which cover the whole auditorium. Reverberation time distributed in four range parameters simply look up the hall acoustic performance visualizing by chromatogram. With the hall geometric data and the first lateral reflection path difference calculated from the point of source and receiver in seating areas close to lateral wall, The measurement shows in bass and middle frequency, Early delay time and T20 and T30 exists large fluctuation which reveals seat-dip effect in the front seat area. While in mid and high frequency, T30 presents stable values indicating the direct sound and lateral reflection are predominant in early sound attenuation. Computer simulation is using Pachyderm Acoustical Simulation plug-in based on parametric architectural design software Rhino. Sound attenuation can be calculated with surface shapes defined surface transform efficiency by diffracting energy. However, Reverberation time differences still exist by comparing actual measurement and computer simulation results.

Investigating the influence of seating area design and enclosure on the seat-dip effect using scale model measurements

The low-frequency attenuation in the direct sound due to the concert hall seats, i.e., the seat-dip effect, is studied with the help of a scale model comprising an adjustable seating area and an enclosed box. More particularly, different seat underpass sizes and floor raking angles are studied, and the results are averaged over multiple source positions. With the measurements on the seating area only, the main seat-dip frequency is found to depend on the seat back rest height, and on the degree of obstruction of the seat underpass. The attenuation bandwidth is found to depend mainly on the floor raking. The differences become less clear when seating area is enclosed by concert hall walls and ceiling because the early reflections from the concert hall geometry compensate the low-frequency attenuation in the direct sound. In addition, the low frequencies below the main seat-dip frequency are found to increase in the presence of unobstructed seat underpasses, and such seats are recommended for the maximal bass response in a concert hall.

Recent studies on the seat-dip effect: Analysis and perception

Recent studies on the seat-dip effect: Analysis and perception

Sampling the sound field in auditoria using large natural-scale array measurements.

Suitable data for spatial wave field analyses in concert halls need to satisfy the sampling theorem and hence requires densely spaced measurement positions over extended regions. The described measurement apparatus is capable of automatically sampling the sound field in auditoria over a surface of 5.30 m × 8.00 m to any appointed resolutions. In addition to discussing design features, a case study based on measured impulse responses is presented. The experimental data allow wave field animations demonstrating how sound propagating at grazing incidence over theater seating is scattered from rows of chairs (seat-dip effect). The visualized data of reflections and scattering from an auditorium's boundaries give insights and opportunities for advanced analyses.

Sampling the sound field in auditoria using a large scale microphone array

Acoustical measurements in auditoria can be laborious with microphones to be placed in large sampling areas that are divided by rows of seating and separated by balconies. As a result, practical studies are often based on measurements of a relatively small number of selected source-receiver combinations. The goal of this paper is to present a new measurement, visualization, and analysis approach for complex wave fields. The measurement apparatus, capable of automatically sampling the sound field in auditoria over a surface of 5.30 m x 8.00 m in high resolution, is described. Based on data collected with the microphone array, a case study of how sound is reflected and scattered from a concert hall’s boundaries is shown. The comparison of repeated measurements with and without the presence of chairs allows a new perspective on grazing sound propagation over theatre seating (“seat dip effect”). The presentation will conclude with the discussion of spatial fluctuations of acoustic properties as a factor of me...

Studies on the perception of bass in four concert halls.

The importance of bass to the overall sound quality in concert halls was highlighted at the opening of the Philharmonic Hall in New York in 1962 (Beranek, Johnson, Schultz, & Watters, 1964). The hall provided almost no immediate lateral reflections, and bass could barely be heard on the stalls (Barron, 2009). The parenthetical comments brought up particularly the weakness of the cellos and the double basses. Apart from critique, this observation led to the discovery of the seat-dip effect (Schultz & Watters, 1964; Sessler & West, 1964). The seat-dip effect is the term assigned for the attenuation at low frequencies due to sound propagating almost parallel, that is, at near-grazing angles to the surface formed by the tops of the seat backs. The seat-dip effect is characterized by a main attenuation dip between 80 and 300 Hz, and an attenuation bandwidth that can extend up to 1 kHz.The seat-dip effect is objectively present in all concert halls with seats, but in many halls no noticeable lack of bass is perceived as such. In particular, the shoebox-shaped hall are generally characterized by a rich bass in the stalls (Schultz, 1965). This indicates that the seat-dip attenuation is corrected as the sound energy distribution in the concert hall develops over time. The lack of bass in the direct sound is compensated by reflections that contain the bass and arrive at the listener at nongrazing angles. This phenomenon is referred to as seat-dip recovery or correction.However, it remains unclear when the bass should arrive at the listener's ears. It was hypothesized that the seat-dip effect could be compensated by increasing the reverberation time at low frequencies (Schultz & Watters, 1964; Barron, 1995). However, Bradley and Soulodre (1997) found that the perceived level of bass is not related to the reverberation time at low frequencies. More recent evidence suggest that the bass should arrive with the early reflections (Beranek, 2011; Davies, Cox, & Lam, 1996; Patynen, Tervo, & Lokki, 2013; Soulodre & Bradley, 1995). Furthermore, Kahle (1995) suggested that sound energy arriving between 80 and 160 ms augments the perception of low frequencies. Additionally, Bradley and Soulodre (1997) linked the perceived level of bass to both the early sound level and late sound level. The phase of the reflections may also alter the perceived level of bass (Laitinen, Disch, & Pulkki, 2013; Lokki, Patynen, Tervo, Siltanen, & Savioja, 2011).It is scarcely understood how the seat-dip effect influences the perception of bass. Orchestral instruments that have their tuning range within the seat-dip attenuation range, such as double bass, tuba, and cello, may lack bass and articulation due to the seat-dip effect. For example, Bradley (1991) estimated that the attenuation of the double bass due to the seat-dip effect can be as much as 6 dB. Barron and Marshall (1981) observed that spatial impression is reduced in the presence of lateral reflections that contain the seat-dip attenuation. Davies et al. (1996) obtained a threshold of audibility for the seat-dip attenuation to be 5.7 dB in the 200 Hz octave band of the early energy over 0 to 40 ms. Although the seat-dip effect is generally considered to hamper the perception of bass, recent psychoacoustic research suggests that if the early reflections retain the bass, the lack of bass in the direct sound may actually enhance the overall perception of bass (Walther, Robinson, & Santala, 2013).In addition to the seat-dip effect, the perception of bass in concert halls is affected by other factors, such as the residual absorption by the seats, walls, floor, and ceiling (Beranek, 2004, 2011). In general, hard thick surfaces absorb less bass than thin panels. Second, the vibrations of the stage floor have been proposed to augment the sound of the double bass and the cello connected to the floor via pins. So far, the augmented bass has been shown to be audible at the stage, but not among the audience (Abercrombie & Braasch, 2010; Wulfrank, Lyon-Caen, Jurkiewicz, Brulez, & Kahle, 2013). …

Guest editors’ introduction to the special issue on “performance spaces for music: Acoustical and psychological measurements and their interactions” honoring Dr. Leo Beranek.

This special issue of Psychomusicology: Music, Mind, & Brain, entitled Performance Spaces for Music: Acoustical and Psychological Measurements and Their Interactions, is dedicated to Dr. Leo Beranek not only in acclaim of his 100th birthday in 2014 but also in recognition of his lifelong contributions to the field of architectural acoustics. The significance his work as a researcher, consultant, and author is manifested in countless ways and seems impossible to overestimate. His books, Music, Acoustics, and Architecture (1962), Concert Halls and Opera Houses: How They Sound (1996), and Concert Halls and Opera Houses: Music, Acoustics, and Architecture (2004), represent one of the most important textbook series in concert hall acoustics, and has significance far greater than the sum of its parts. The impetus from reading these works ranges from fuelling an individual's interest and enthusiasm for concert hall acoustics to building bridges between experts from different fields collaborating on concert hall projects, allowing both scientists and practitioners to figuratively stand upon Leo Beranek's giant's shoulders so as to see a little further.There is no doubt that the initial publication of Beranek's book in 1962 on concert hall acoustics triggered ongoing research on how sound is perceived in auditoria. This ranges from the initial works of Hawkes and Douglas (1971) in London, United Kingdom; the works by the Gottingen group (e.g., Gottlob, 1973); and research in Berlin, Germany; (Wilkens, 1977) to more recent works by Barron (1988) in the United Kingdom and Lokki, Patynen, Kuusinen, and Tervo (2012) in Finland. Their studies and many others have refined the fundamental ideas that Leo Beranek had put into discussion.Scientific research on panel reflector arrays, audience absorption of grazing sound (also known as the seat dip effect), and interaural cross correlation as a predictor of spatial perception of sound all carry the distinctive signature of Leo Beranek's work as a consultant on many outstanding projects. Just to name a few, these projects include the Tokyo Opera City Concert Hall, the New National Theater (also in Tokyo), the Philharmonic Hall in New York, The Koussevitzky Music Shed (formerly The Tanglewood Music Shed) in Massachusetts, and the Frederic R. Mann Auditorium in Tel Aviv, Israel.To the present day, Leo Beranek is an active member of the acoustics community and continues to give lectures to an audience that eagerly absorbs the concepts he describes. One of the outstanding characteristics of these talks may be their clarity and the da Vinci-like simplicity that make the distinct multidisciplinarity of architectural acoustics seem easy to grasp. This achievement becomes clear when the diversity of the articles in this special issue are taken as a tangible example.This special issue begins with a biography that briefly chronicles Leo Beranek's life, illustrating the incredible development from his early days in farm-town Iowa to the present day being a world renowned expert of acoustics, a former Massachusetts Institute of Technology professor, and the founder of Bolt, Beranek, and Newman-just to name a few corner points of his multifaceted career. In his article, Leo Beranek shows in an unparalleled way how a long experience in the field allows him to present complex relations in a clear way with a distinct view to the core essentials.The editors of this special issue are in debt to the authors who have provided such a circumferential collection of papers that are worth the reading. Moreover, the support and enduring commitment from all the reviewers was of great assistance to the authors and editors, who together brought this special issue to completion after months of hard work.Organization of the Contributions: The Communication ChainThe order of manuscripts in scientific periodicals is often categorized by the severity of the review process undergone. …

Analysis of the Seat-Dip Effect in Twelve European Concert Halls

Analysis of the Seat-Dip Effect in Twelve European Concert Halls

Effect of spectral overlap on the echo suppression threshold for single reflection conditions

In performing arts venues, the spectra of direct and reflected sound at a receiving location differ, due to seat dip effect, diffusive and absorptive surfaces, and source directivity. This paper examines the influence of differing lead and lag spectral contents on echo suppression threshold. The results indicate, that for a highpass filtered direct sound and a broadband reflection, attenuation of low frequencies initially results in an increase in echo suppression threshold, while for higher cutoff frequencies echo suppression threshold drastically decreases. For broadband direct sound and filtered reflections, the echo suppression threshold is inversely related to high frequency content.

Analysis of concert hall acoustics via visualizations of time-frequency and spatiotemporal responses

Acousticians and other practitioners alike often describe acoustic conditions in performance spaces with standard objective parameters. Apart from a few exceptions, the parameters are calculated by integrating the sound energy of the impulse responses over time; this makes them inadequate for researching the acoustics in detail, especially in the early part of the room impulse response. This paper proposes a method based on time-frequency and spatiotemporal presentations to overcome the lack of detail in the standard analysis. In brief, the proposed methods visualize the cumulative development of the sound field as a function of frequency or direction by forward-integrating the energy in the impulse response in short time frames. Analysis on the measurements from six concert halls concentrates particularly on interpreting the results in light of the seat dip effect. Earlier research has concluded that the seat dip effect is reduced by reflection from low overhead surfaces. In contrast, the current results indicate that the seat dip attenuation in the frequency response is corrected the best when the hall provides most lateral reflections. These findings suggest that the proposed analysis is suitable for explaining concert hall acoustics in detail.

Analysis of concert hall acoustics using time-frequency and time-spatial responses

A set of objective parameters (ISO3382-1:2009) is widely used for describing acoustic conditions in performance spaces. With few exceptions, they are based on integrating sound energy within moderate time intervals. In practice, different acoustic conditions can yield similar values for objective measures. A presented method of analyzing concert hall acoustics with respect to the time-frequency features aims to overcome the deficiencies of the objective parameters by conveying considerably more information in an uncomplicated form. This is achieved by visualizing the contribution of short time frames in the impulse response to the cumulative sound energy as a function of frequency. Particularly the early part of the room impulse response, including the influence of the seat dip effect is efficiently visualized. The method is applied to acoustic measurements conducted at five corresponding positions in six concert halls. It is shown that in addition to communicating standard monaural objective parameters, the visualizations from the method are connected with several features regarding the subjective impression of the acoustics. The time-frequency analysis is further extended into utilizing a recent sound direction estimation technique. Resulting time-directional visualization enables the accurate analysis of early reflections and their contribution to spatial sound.

Predicted and experimental results of acoustic parameters in the new Symphony Hall in Pamplona, Spain

Two room acoustical simulation software have been used to predict the main acoustic parameters of a Symphony Hall in the planning stage, when only drawings were available. The modelled room is the Symphony Hall of the Conference Hall of Navarre, in Pamplona, Spain. Although the values of the calculation parameters (number of rays, reflection order, etc.) recommended by each software are slightly different, in this work the same values were used for both programs. Once the Hall was built, experimental results were obtained using the MLS-measurement technique. The values predicted and measured for several parameters defined in ISO 3382 at 9 receiver positions are compared. Even though the values predicted by both software are very similar for most of the acoustic parameters, there are notable differences at particular values, mainly when evaluating energy ratios. Different statistical corrections for late reflections between both programs seem to be the main reason for these differences. A more exhaustive knowledge of scattering coefficients is required to improve predictive accuracy. Important differences at 250 Hz frequency band were found between calculated and measured values probably due to the yet to be implemented seat dip effect in room simulation software. The comparison of calculated and measured impulse responses seems to be the first choice for the assessment of room simulation software. However, it should be kept in mind that its usability is also determined by many additional features. This work is not only a comparison of software dealing with the same object as well as equal input data but also shows the power of this kind of tool to predict the acoustic parameters of a room before its construction.

Consideration of the propagation loss of the direct sound with change in seat conditions

Reviewing excess attenuation of the direct sound by seats in concert hall acoustics gives the propagation loss by the performers absorption on the stage platform and diffraction of the front seats as well as seat dip effect in low frequency spectrum. Scale model experiments with 1/10 scale model in anechoic chamber were conducted at YAMAHA Acoustic Research Laboratories, Hamamatsu, focusing on propagation loss by (1) diffraction due to various geometrical conditions of the seating row in front of the listening position and (2) attenuation by the seat rows in front of the listening point. The results show the excess attenuation in middle and high frequency spectra. The optimum height between two adjacent seating rows is more than 1.3 feet and the number of seat rows are less than five seats. Normalized SPL referenced to SPL measured at 6.6 feet over the listening point is presented to be effective for evaluating excess attenuation. Concert Hall at Niigata Performing Arts Center was designed with consideration of these scale model experiments. Measurement data of normalized SPL and power spectra of orchestra sound in this hall are presented. 2284,2284

Reducing seat dip attenuation

Strategies for reducing seat dip attenuation in concert halls are considered. It is shown that the dip is established 4 ms after the direct sound from the stage arrives at the listener. Sound scattered from the seats and floor is the main cause of the dip. By controlling these very early reflections the attenuation can be reduced to below its subjective threshold. With this in mind, changes to the shape and impedance of the seats and floor are trialed using a boundary element model and a physical scale model. It is found that the seat dip effect can be rendered inaudible by introducing a 1-m pit under the seats. Smaller improvements are produced by changing the impedance of the seat squab.

Seat dip effect: The phenomena and the mechanism

The phenomenon of excess attenuation due to audience seating, which is called “seat dip effect (SDE),” have been discussed in the case of a rather short-time interval including a direct sound and early arriving sound. However, it may be expected that the effect is diminished as the time interval increases, owing to the supplement of other arriving sounds. The first aim of this investigation is to clarify the effect of time interval on the SDE as well as the effect of other arriving sounds, by means of 110-scale model experiments. For the mechanism of the phenomenon, a clear explanation has not yet been given. The second aim is to clarify the fundamental mechanism of the SDE. For this aim, a wave-scattering theory for a periodic surface and a simple wave reflection theory for a layered boundary surface are applied, and discussed in comparison with the experimental results. From this investigation, it became clear that the mechanism of the SDE can be easily explained by using these simple analytical models.

Modeling of the seat dip effect using the finite-difference time-domain method

In this paper the use of the finite-difference time-domain technique for the modeling of the seat dip effect in concert halls is demonstrated. The linear time-domain acoustic partial differential equations are discretized using a finite-difference technique. The second-order accurate differencing scheme is time–space centered, and the velocity and pressure are solved on an interlaced mesh. First- and second-order Mur absorbing boundary conditions, originally formulated for electromagnetic problems, are adapted to the acoustics case and used to truncate the numerical grid. The technique is first verified by comparing the numerical results to the analytic solution of a simple point source. Results from computer simulations of the seat dip phenomena are compared with the findings of previous studies where measurements had been made on scale models and in real concert halls. The computer model successfully predicts the effects associated with the source–receiver distance, the height of the receiver, and the height of the source.

Investigation of the fundamental mechanism of the seat-dip effect. Using measurements on a parallel barrier scale-model.

The mechanism of seat-dip attenuation was examined using a simplified parallel barrier model representing rows of auditorium seats. From the results measured in the fullscale auditoria, seat-dip attenuation was thought to be caused by interference between the direct sound wave and the successive waves forming a negative-positive sequence in the impulse response immediately after the direct sound. The negative pressure wave was found to be caused by barrier (seat back) top diffraction and not to be reasonable to apply local reactive hypothesis. The measurement arrangements altering the geometry of the parallel barrier on the floor enabled to clarify the effect and cause of the positive wave. The diffraction at the barrier tops reflected off the floor, resulted in positive wave in the impulse response, caused the excessive attenuation at low frequencies interfering with the direct sound, and the arrival time of the positive wave determined the frequency of the maximum attenuation. The phase relationships depending on the diffraction angle were found to be crucial in order to explain the mechanism of the seatdip attenuation, and these can not be explained by vertical resonance alone suggested by the previous study