Roger W. Schwenke

Active acoustics and sound reinforcement at TUI Operettenhaus, Hamburg: A case study

TUI Operettenhaus is a proscenium theater with one balcony which is host to drama, musical theater, and concerts. The venue hosts different sound reinforcement systems for different shows, and now has a permanent active acoustic system. The physical acoustics are very dry as is appropriate for modern theater with spatial sound reinforcement, and the active acoustic system allows the reverberation time to be extended as appropriate for different performances. The active acoustic system can also pass through signals to its speakers for spatial surround reproduction. The installation of the active acoustic system in an older building posed many challenges. This case study presents the challenges that were overcome during installation, the integration of the active acoustic system with sound reproduction, and the measured performance of the system.

Electro‐acoustic architecture: Is it Green?

Electro‐acoustic architecture systems offer a means of changing the acoustic properties of a room electronically. They are an alternative to physically variable acoustics, where acoustic properties are changed by retractable curtains and doors opening to reverberant chambers, etc. This paper will address the question of whether electro‐acoustic systems are a Green alternative to physically variable acoustics. In order to have a reverberation time appropriate for symphonic music, a room must have a large cubic volume and hard heavy surfaces. In contrast, in a room with an electro‐acoustic system, the physical reverberation time is desired to be low even at low frequencies. Therefore, the cubic volume can be low and surfaces can be made of a lightweight material over an airspace. This affects the amount of energy needed to deliver materials, construct the building, and operate HVAC and lighting systems. A lower volume building means less pollution and waste during construction, and allows for more open space around the building, and/or higher development density. Electro‐acoustic systems can easily be designed as a renovation, thus recycling existing buildings. Case studies will be reviewed demonstrating these issues.

Prediction and measurement of reverberation increase from electroacoustic architecture systems.

Electroacoustic architecture (EA) systems increase the reverberation time (RT) of rooms by regenerating the physical reverberation of the room, and/or adding electronic reverberation to the direct sound. In regenerative systems, the amount of regeneration is controlled by the loop gain of the system. Increasing loop gain is analogous to reducing the effective absorption in the room. The RT of the electronic reverberator is analogous to the decay time of a physically coupled room, and, therefore, analogous to adding cubic volume to the room. As the electronic RT is increased, there is a point above which the resulting reverberation will begin to be double sloped. This point depends on the gain. The higher the gain, the higher the electronic RT before the resulting reverberation double slopes. In previous work, the gain before feedback of EA systems has been predicted in a statistical approach based on the bulk properties of the room such as RT and cubic volume. This, in turn, can be used to predict the max...

Room acoustics measurements with an approximately spherical source of 120 drivers

An approximately spherical source of 120 individually controlled drivers is used to perform impulse response measurements in a room with a 1.4 s reverberation time and a distinct echo. The signal to the drivers is processed to produce both omni‐directional and unidirectional patterns. The omni‐directional pattern is compared with measurements made with a traditional 12 sided source. The unidirectional patterns are measured both pointed towards and away from the listener position. Intelligibility metrics for the different directionalities and orientations are measured. The unidirectional pattern is aimed in different directions to minimally and maximally excite the distinct echo in the room, and locate its origin.

Rich data trove gathered as a result of a unique opportunity with a capacity audience

When an opportunity arises to perform an occupied room measurement, normally a short time is allotted to acquire data in order to minimize event disruption and audience discomfort. We therefore consider ourselves fortunate if one or two data sets are obtained under those conditions. An extremely rare—perhaps unique—opportunity arose from a confluence of factors: a 1600-seat concert hall at Liberty University, with a purposely over-sized area of movable curtains and banners to adjust the architectural reverberation; an installed active acoustics system, Constellation by Meyer Sound; a concert comprising distinct performances by orchestra, choir, and amplified worship band, with intermission to reset the architectural acoustics; and an interested client. The Constellation system provides 48 microphones distributed throughout the space, so a single set of sweeps through a system loudspeaker results in 48 measurements. The variables tested were (a) adjustable acoustic absorption in and out; (b) full audience ...

Speech coherence index with real speech and reverberation

Speech Coherence Index (SCI) is a proposed method of estimating speech intelligibility in real time with program material. The coherence of the complex valued transfer function is used to estimate the signal-to-noise ratio on a per frequency basis. The transfer function is calculated using short time windows at high frequencies and longer time windows at low frequencies to mimic the multi-resolution nature of human hearing. SCI has been shown to produce identical results to Speech Transmission Index (STI) in the case of pure noise interference. Like STI, SCI has been shown to decrease with a single reflection at longer latencies or at greater magnitude. SCI always decreases monotonically with single reflection latency, whereas STI varies up and down at extremely long latencies. For simulated reverberation, both STI and SCI have been shown to decrease with increasing reverberation time and reverberant level. However, SCI is more sensitive to direct-to-reverberant level. This paper will compare SCI to STI u...

A comparison of speech coherence index and measured speech intelligibility

Perceptual tests were taken in real and simulated spaces to determine whether Speech Coherence Index (SCI) predicts human performance better than Speech Transmission Index (STI). SCI is a proposed method of estimating speech intelligibility during event conditions, that is, in real time with program material. The complex valued coherence function is used to estimate the signal-to-noise ratio on a per frequency basis, and is calculated with short time windows at high frequencies and longer time windows at low frequencies to mimic the multi-resolution nature of human hearing. SCI has been shown to track STI very closely under simplified conditions. Under more realistic conditions, SCI is more sensitive to reverberant energy and is always less than STI. Under certain conditions, such as long source to listener distance or low SNR, SCI predicts significantly lower intelligibility values than STI.

Constellation: A hybrid active accoustic system

Constellation is a hybrid active acoustic system that has been used in rooms ranging in size from a virtual reality cave to a sports arena. Constellation has been shown to control both the effective absorption of a room as well as the effective cubic volume. This paper will review how early reflections, effective absorption, and effective cubic volume have been controlled in rooms of various sizes. Recently, there has been a trend of larger classical ensembles performing in smaller venues. If the strength of the room is held constant, but the cubic volume is cut in half, the reverberation time is also cut in half. If a room has exclusively physical acoustics, it is impossible to replicate both the strength and reverberation time of a symphony hall in a space that is considerably smaller (such as a rehearsal room). A special emphasis will be made on how Constellation is uniquely suited to address this challenge.

Reverberation time versus volume for active acoustic systems

If two rooms have the same reverberation time but different cubic volumes, then they will differ in acoustic strength. Many authors have presented recommendations for reverberation time as a function of volume for different purposes. There are many parameters that, if held constant, yield different reverberation times for different cubic volumes: strength, clarity, critical distance, etc. For example, the ITU-R BS.1116 recommendation for reverberation time versus volume corresponds to rooms of constant average absorption per square meter. This paper will review the literature on reverberation time versus volume, show the connection between STI and reverberation versus volume, and propose a recommendation for reverberation versus volume for active acoustic systems.

Stages with high ceilings, pipe organs, and active acoustics

Two case studies are presented of rooms that have a high ceiling over the stage to accommodate a pipe organ. Svetlanov hall is the principal venue of Moscows International Performing Arts Center. It has two to four rows of chorus seating on two levels at stage left and right. The upstage wall is occupied by the largest pipe organ in Russia. It has a physical reverberation time of 1.7 s, which is within the accepted range for symphonic music, but longer reverberation times would be preferred for some pipe organ repertoire. Christopher Cohan Performing Arts Center at California Polytechnic State University has a proscenium and thrust stage. The Forbes Pipe Organ is housed on the stage right wall of the thrust stage. The symphony usually performs on the thrust stage entirely in front of the proscenium with the solid decorative fire curtain down. Both rooms had poor communication on stage between performers, which led them to implement a solution using active acoustics. In both rooms all of the active acoustic elements overhead of the stage are on motors and can be retracted when not in use. Two case studies are presented of rooms that have a high ceiling over the stage to accommodate a pipe organ. Svetlanov hall is the principal venue of Moscows International Performing Arts Center. It has two to four rows of chorus seating on two levels at stage left and right. The upstage wall is occupied by the largest pipe organ in Russia. It has a physical reverberation time of 1.7 s, which is within the accepted range for symphonic music, but longer reverberation times would be preferred for some pipe organ repertoire. Christopher Cohan Performing Arts Center at California Polytechnic State University has a proscenium and thrust stage. The Forbes Pipe Organ is housed on the stage right wall of the thrust stage. The symphony usually performs on the thrust stage entirely in front of the proscenium with the solid decorative fire curtain down. Both rooms had poor communication on stage between performers, which led them to implement a solution using active acoustics. In both rooms all of the active acoust...