Architectural Acoustics | Acoustics.org

2aAAa7 – Gunshot recordings from a criminal incident: who shot first?

Robert C. Maher – rob.maher@montana.edu
Electrical & Computer Engineering Department
Montana State University
P.O. Box 173780
Bozeman, MT 59717-3780

Popular version of paper 2aAAa7, “Gunshot recordings from a criminal incident: Who shot first?”
Presented Tuesday morning, May 24, 2016, 10:20 AM, Salon E
171^st ASA Meeting, Salt Lake City

In the United States, criminal actions involving firearms are of ongoing concern to law enforcement and the public. The FBI’s 2013 National Incident-Based Reporting System (NIBRS) report lists 50,721 assault incidents and 30,915 robbery incidents involving firearms that year [1].

As more and more law enforcement officers wear vest cameras and more and more citizens carry smartphones, the number of investigations involving audio forensic evidence continues to grow—and in some cases the audio recordings may include the sound of gunshots.

Is it possible to analyze a forensic audio recording containing gunshot sounds to discern useful forensic evidence? In many cases the answer is yes.

Audio forensics, or forensic acoustics, involves evaluation of audio evidence for either a court of law or for some other official investigation [2]. Experts in audio forensics typically have special knowledge, training, and experience in the fields of acoustics, electrical engineering, and audio signal processing.

One common request in audio forensic investigations involving gunshots is “who fired first?” There may be a dispute about the circumstances of a firearms incident, such as one party claiming that shots were fired in self-defense after the other party fired first, while the other party has the opposite claim. Sometimes a dispute can arise if a witness reports that a law enforcement officer shot an armed but fleeing suspect without justification, while the officer claims that the suspect had fired.

Figure 1: Muzzle blast recording of a 9mm handgun obtained under controlled conditions [4].

The sound of a gunshot is often depicted in movies and computer games as a very dramatic “BOOM” sound that lasts for as long as a second before diminishing away. But the actual muzzle blast of a common handgun is really only about 1 millisecond (one 1/1000^th of a second) in duration (see Figure 1). More than 20-30 meters away, most of the audible sound of a gunshot is actually sound waves reflected by nearby surfaces [3].

Let’s consider a simplified case example from an investigation in an unnamed jurisdiction. In this case, a shooting incident on a city street involving two perpetrators was recorded by a residential surveillance system located down the street. The camera’s field-of-view did not show the incident, but the microphone picked up the sounds of gunfire. Based on witness reports and the identification of shell casings and other physical evidence at the scene, the police investigators determined that the two perpetrators were several meters apart and fired their handguns toward each other, one pointing north and the other pointing south. Figuring out which gun was fired first could not be determined from the physical evidence at the scene nor from witness testimony, so attorneys for the suspects requested analysis of the audio recording to determine whether or not it could help answer the “who shot first?” question.

The waveform and the corresponding spectrogram from the portion of the recording containing the first two gunshot sounds are shown in Figure 2. The spectrogram is a special kind of graph that depicts time on the horizontal axis and frequency on the vertical axis, with the brightness of the graph indicating the amount of sound energy present at a particular time in a particular frequency range. The sound energy envelope for this same signal is shown in Figure 3. The microphone picked up the direct sound of the gunshots, but also the reflected sound from the street, nearby buildings, and other obstacles, causing the relatively long duration of the two shots in the recording.

In this case, we note that the first gunshot has a distinctive echo (indicated by the arrow), while the second gunshot does not show this feature. What might account for this peculiar difference?

Figure 2: Sound waveform and spectrogram of two gunshots recorded by a residential surveillance system. The arrow indicates the distinctive echo.

Figure 3: Sound energy envelope for the two gunshots depicted in Figure 2. The arrow indicates the echo.

Examining the neighborhood street where the shooting incident took place (Figure 4) revealed that there was a “T” intersection about 90 meters north of the shooting scene with a large building facing the street. The length of the reflected sound path from the shooting site to the large building and back is therefore a little over 180 meters, which corresponds to the 0.54 seconds of time delay between the direct sound of the gunshot an the echo—which would account for the timing of the distinct reflection. The microphone was located 30 meters south of the shooting scene. But why would the observed reflection differ for the two firearms if they were located quite close together at the time of the gunfire?

Figure 4: Sketch of the shooting scene (plan view)

Our conclusion was that the firearm pointing north toward the “T” intersection would likely produce a stronger reflection because the muzzle blast of a handgun is louder in the direction the gun is pointing [5]. Thus, the gun pointing toward the reflecting surface would produce a stronger reflected sound than the gun pointing away from the reflecting surface.

While the availability of additional acoustic evidence of firearm incidents can only be a positive development for the U.S. justice system, interpreting audio recordings of gunshots remains a challenge for audio forensic examiners for several reasons. First, the acoustical characteristics of gunshots must be studied carefully because the recording is likely to include sound reflections, diffraction, reverberation, background sounds, and other content that can interfere with the analysis. Second, common audio recorders are intended for speech signals, and therefore they are not designed to capture the very brief and very intense sounds of gunfire. Finally, the acoustical similarities and differences among different types of firearms are still the subject of research, so the notion of having a simple database of gunshot sounds to compare with an evidentiary recording is not yet feasible.

[1] U.S. Department of Justice, 2013 National Incident-Based Reporting System (NIBRS) Data Tables (2013). Available at https://www.fbi.gov/about-us/cjis/ucr/nibrs/2013/data-tables . Accessed May 6, 2016.

[2] Maher, R.C., Lending an ear in the courtroom: forensic acoustics, Acoustics Today, vol. 11, no. 3, pp. 22-29, 2015.

[3] Maher, R.C., Acoustical characterization of gunshots, Proceedings of the IEEE SAFE Workshop on Signal Processing Applications for Public Security and Forensics, Washington, DC, pp. 109-113 (2007).

[4] Maher, R.C. and Shaw, S.R., Gunshot recordings from digital voice recorders, Proceedings of the Audio Engineering Society 54th Conference, Audio Forensics—Techniques, Technologies, and Practice, London, UK (2014).

[5] Maher, R.C. and Shaw, S.R., Directional aspects of forensic gunshot recordings, Proceedings of the Audio Engineering Society 39th Conference, Audio Forensics—Practices and Challenges, Hillerød, Denmark (2010).

1pAA6 – Listening for solutions to a speech intelligibility problem

Anthony Hoover, FASA – thoover@mchinc.com
McKay Conant Hoover, Inc.
Acoustics & Media Systems Consultants
5655 Lindero Canyon Road, Suite 325
Westlake Village, CA 91362

Popular version of paper 1pAA6, “Listening for solutions to a speech intelligibility problem”
Presented Monday afternoon, May 23, 2016, 2:45 in Salon E
171st ASA Meeting in Salt Lake City, UT

Loudspeakers for sound reinforcement systems are designed to project their sound in specific directions. Sound system designers take advantage of the “directivity” characteristics of these loudspeakers, aiming their sound uniformly throughout seating areas, while avoiding walls and ceilings and other surfaces from which undesirable reflections could reduce clarity and fidelity.

Many high-quality sound reinforcement loudspeaker systems incorporate horn loudspeakers that provide very good control, but these are relatively large and conspicuous. In recent years, “steerable column arrays” have become available, which are tall but narrow, allowing them to better blend into the architectural design. These are well suited to the frequency range of speech, and to some degree their sound output can be steered up or down using electronic signal processing.

Figure 1. steerable column arrays

Figure 1 illustrates the steering technique, with six individual loudspeakers in a vertical array. Each loudspeaker generates an ever-expanding sphere of sound (in this figure, simplified to show only the horizontal diameter of each sphere), propagating outward at the speed of sound, which is roughly 1 foot per millisecond. In the “not steered” column, all of the loudspeakers are outputting their sound at the same time, with a combined wavefront spreading horizontally, as an ever-expanding cylinder of sound. In the “steered downward” column, the electronic signal to each successively lower loudspeaker is slightly delayed; the top loudspeaker outputs its sound first, while each lower loudspeaker in turn outputs its sound just a little later, so that the sound energy is generally steered slightly downward. This steering allows for some flexibility in positioning the loudspeaker column. However, these systems only offer some vertical control; left-to-right projection is not well controlled.

Steerable column arrays have reasonably resolved speech reinforcement issues in many large, acoustically-problematic spaces. Such arrays were appropriate selections for a large worship space, with a balcony and a huge dome, that had undergone a comprehensive renovation. Unfortunately, in this case, problems with speech intelligibility persisted, even after multiple adjustments by reputable technicians, who had used their instrumentation to identify several sidewall surfaces that appeared to be reflecting sound and causing problematic echoes. They recommended additional sound absorptive treatment that could adversely affect visual aesthetics and negatively impact the popular classical music concerts.

Upon visiting the space as requested to investigate potential acoustical treatments, speech was difficult to understand in various areas on the main floor. While playing a click track (imagine a “pop” every 5 seconds) through the sound system, and listening to the results around the main floor, we heard strong echoes emanating from the direction of the surfaces that had been recommended for sound-absorptive treatment.

Nearby those surfaces, additional column loudspeakers had been installed to augment coverage of the balcony seating area. These balcony loudspeakers were time-delayed (in accordance with common practice, to accommodate the speed of sound) so that they would not produce their sound until the sound from the main loudspeakers had arrived at the balcony. With proper time delay, listeners on the balcony would hear sound from both main and balcony loudspeakers at approximately the same time, and thereby avoid what would otherwise seem like an echo from the main loudspeakers.

With more listening, it became clear that the echo was not due to reflections from the walls at all, but rather from the delayed balcony loudspeakers’ sound inadvertently spraying back to the main seating area. These loudspeakers cannot be steered in a multifaceted manner that would both cover the balcony and avoid the main floor.

We simply turned off the balcony loudspeakers, and the echo disappeared. More importantly, speech intelligibility improved significantly throughout the main floor. Intelligibility throughout the balcony remained acceptable, albeit not quite as good as with the balcony loudspeakers operating.

The general plan is to remove the balcony loudspeakers and relocate them to the same wall as the main loudspeakers, but steer them to cover the balcony.

Adding sound-absorptive treatment on the side walls would not have solved the problem, and would have squandered funds while impacting the visual aesthetics and classical music programming. Listening for solutions proved to be more effective than interpreting test results from sophisticated instrumentation.

1aAA4 – Optimizing the signal to noise ratio in classrooms using passive acoustics

Peter D’Antonio – pdantonio@rpginc.com

RPG Diffusor Systems, Inc.
651 Commerce Dr
Upper Marlboro, MD 20774

Popular version of paper 1aAA4 “Optimizing the signal to noise ratio in classrooms using passive acoustics”
Presented on Monday May 23, 10:20 AM – 5:00 pm, SALON I
171^st ASA Meeting, Salt Lake City

The 2012 Program of International Student Assessment (PISA) has carried out an international comparative trial of student performance in reading comprehension, calculus, and natural science. The US ranks 36th out of 64 countries testing ½ million 15 year olds, as shown in Figure 1.

Figure 1 PISA Study

What is the problem? Existing acoustical designs and products have not evolved to incorporate the current state-of-the-art and the result is schools that are failing to meet their intended goals. Learning areas are only beginning to include adjustable intensity and color lighting, shown to increase reading speeds, reduce testing errors and reduce hyperactivity; existing acoustical designs are limited to conventional absorptive-only acoustical materials, like thin fabric wrapped panels and acoustical ceiling tiles, which cannot address all of the speech intelligibility and music appreciation challenges.

What is the solution? Adopt modern products and designs for core and ancillary learning spaces which utilize binary, ternary, quaternary and other transitional hybrid surfaces, which simultaneously scatter consonant-containing high frequency early reflections and absorb mid-low frequencies to passively improve the signal to noise ratio, adopt recommendations of ANSI 12.6 to control reverberation, background noise and noise intrusion and integrate lighting that adjusts to the task at hand.

Let’s begin by considering how we hear and understand what is being said when information is being delivered via the spoken word. We often hear people say, I can hear what he or she is saying, but I cannot understand what is being said. The understanding of speech is referred to as speech intelligibility. How do we interpret speech? The ear / brain processor can fill in a substantial amount of missing information in music, but requires more detailed information for understanding speech. The speech power is delivered in the vowels (a, e, i, o, u and sometimes y) which are predominantly in the frequency range of 250Hz to 500Hz. The speech intelligibility is delivered in the consonants (b, c, d, f, g, h, j, k, l, m, n, p, q, r, s, t, v, w), which occur in the 2,000Hz to 6,000 Hz frequency range. People who suffer from noise induced hearing loss typically have a 4,000Hz notch, which causes severe degradation of speech intelligibility. I raise the question, “Why would we want to use exclusively absorption on the entire ceiling of a speech room and thin fabric wrapped panels on a significant proportion of wall areas, when these porous materials absorb these important consonant frequencies and prevents them from fusing with the direct sound making it louder and more intelligible?

Exclusive treatment of absorbing material on the ceiling of the room may excessively reduce the high-frequency consonants sound and result in the masking of high-frequency consonants by low-frequency vowel sounds, thereby reducing the signal to noise ratio (SNR).

The signal has two contributions. The direct line-of-sight sound and the early reflections arriving from the walls, ceiling, floor and people and items in the room. So the signal consists of direct sound and early reflection. Our auditory system, our ears and brain, have a unique ability called temporal fusion, which combines or fuses these two signals into one apparently louder and more intelligible signal. The goal then is to utilize these passive early reflections as efficiently as possible to increase the signal. The denominator in the SNR consists of external noise intrusion, occupant noise, HVAC noise and reverberation. These ideas are summarized in Figure 2.

Figure 2 Signal to Noise Ratio

In Figure 3, we illustrate a concept model for an improved speech environment, whether it is a classroom, a lecture hall, a meeting/conference room, essentially any room in which information is being conveyed.

The design includes a reflective front, because the vertical and horizontal divergence of the consonants is roughly 120 degrees, so if a speaker turns away from the audience, the consonants must reflect from the front wall and ceiling overhead. The perimeter of the ceiling is absorptive to control the reverberation (noise). The center of the ceiling is diffusive to provide early reflections to increase the signal and its coverage in the room. The mid third of the walls utilize novel binary, ternary, quaternary and other transitional diffsorptive (diffusive/absorptive) panels, which scatter the information above 1 kHz (the signal) and absorb the sound below 1 kHz (the reverberation=noise). This design suggests that the current exclusive use of acoustical ceiling tile and traditional fabric wrapped panels is counterproductive in improving the SNR, speech intelligibility and coverage.

Figure 3 Concept model for a classroom with a high SNR

3pID2 – The Sound of the Sacred: The State of the Art in Worship Space Acoustics

David T. Bradley – dabradley@vassar.edu
Vassar College
124 Raymond Ave
Poughkeepsie, NY 12604-0745

Erica E. Ryherd – eryherd@unl.edu
Durham School of Architectural Engineering and Construction
University of Nebraska – Lincoln
203C Peter Kiewit Institute
Omaha, NE 68182-0176

Lauren Ronsse – lronsse@colum.edu
Columbia College Chicago
33 E. Congress Parkway, Suite 601
Chicago, IL 60605

Popular version of paper 3pID2, “The state of the art in worship space acoustics”
Presented Wednesday afternoon, May 25, 2016, 1:55 in Salon D
171st ASA Meeting, Salt Lake City

From the clanging of bells to the whisper of burning incense, sound is essential to the worship experience. It follows that the acoustic environment is paramount in the sacred place – the worship space – and thoughtful design is required to achieve a worship experience full of awe and wonder. The first intentional sacred spaces were constructed over 11,000 years ago [1] and, although architectural acoustics design practices have changed immeasurably since then, the primary use of these spaces remains essentially unchanged: to provide a gathering space for communal worship.

Figure 1: Temple YoungIsrael, a 550-seat orthodox synagogue in Brookline, MA designed by Gund Partnership and Cavanaugh Tocci Associates, Inc. (Photo credit: Christopher A. Storch)

Figure 2: Al Farooq Masjid of Atlanta (interior view of main dome), a 1500-seat Islamic mosque designed by Lee Sound Design, Inc. and Design Arts Studio and EDT Constructors, Inc. (Photo credit: Wayne Lee)

To meet this need, the four key acoustical goals that modern worship space designers must consider are to optimize reverberation time, eliminate acoustical defects, minimize ambient noise, and maximize dynamic range. These four goals are imperative in virtually all types of worship spaces around the world, despite vast differences in religious practices and beliefs. In the recent publication, Worship Space Acoustics: 3 Decades of Design [2], the application of these goals is seen in 67 churches, synagogues, mosques, and other worship spaces designed in the past thirty years. Each space and each religion has its own idiosyncratic acoustic challenges, from a visually translucent but acoustically transparent partition required to separate men and women in an orthodox synagogue in Brookline, MA (Figure 1) to the attenuation of a focused acoustic reflection from the dome of a mosque in Atlanta, GA (Figure 2). One space featured in the book, Temple Israel (Figure 3), shows the connectedness of acoustical design in worship spaces. It is part of a special project, the Tri-Faith Initiative, a 14-acre complex in Omaha, NE uniting three Abrahamic faith groups, Temple Israel, Countryside Community Church (United Church of Christ), and The American Muslim Institute. As each of these three worship spaces is constructed on the site, they all must have the four key acoustical goals considered.

Figure 3: Temple Israel, a 900-seat reform synagogue in Omaha, NE designed by Acentech Incorporated and Finegold Alexander + Associates. (Photo credit: Finegold Alexander + Associates)

Figure 4: The Star Performing Arts Centre, a 5000-seat multi-use space in Singapore designed by Arup (completed as Artec) and Andrew Bromberg of Aedas.

In the past three decades, worship spaces have seen an increased need for multi-functionality, often hosting religious services with varying acoustical needs. For example, the Star Performing Arts Centre (Figure 4) in Singapore serves as the home of the New Creation Church, seats 5000 people, and supports programing ranging from traditional worship services to pop music concerts to televised national events. Some spaces must even serve more than one religion, such as the Sacred Space (Figure 5), a multi-faith house of worship constructed in the shell of an old Boston chapel that caught fire in the mid-90s, now used for meditation, private worship, and small gatherings. These varying usage requirements require careful consideration of the acoustic design, often relying on variable acoustics such as retractable sound absorption and the use of sophisticated electroacoustics systems.

Figure 5: The Sacred Space, 150-seat multifaith house of worship in Boston, MA designed by Acentech Incorporated and Office dA.

Figure 6: Mean reverberation times at 500 Hz octave band center frequency for 67 worship spaces of varying seating capacity.

Although the use of each space may vary, the most important acoustic goal remains to optimize the reverberation time. This is the time necessary for sound in a space to decay to one-millionth of its original intensity. Essentially, it describes how the sound energy decays, perceived as the fading away of sound over time. Typically, reverberation time decreases as more sound absorption is added, and increases as the size of the space increases. Figure 6 shows the mean reverberation times (500 Hz) for the various seating capacities of the 67 worship spaces. Seating capacity is generally directly proportional to size of the space, and the reverberation times here show the general trend of increasing with increasing size up to about 2000 seats. For 2000 seats and beyond, the data show a marked decrease in reverberation time. For these larger spaces, there tends to be a higher proportion of sound absorbing material used in the design, typically to allow for the use of electroacoustics systems that require a large number of loudspeakers. Spaces that rely heavily on electroacoustics to achieve the desired sonic environment require non-reflective surfaces and lower reverberation times for the microphone-loudspeaker systems to work properly.

Regardless of reverberation time, the goal remains the same, to create a gathering space for worship where the sound is sacred.

K. Schmidt, “Göbekli Tepe, Southeastern Turkey: A Preliminary Report on the 1995-1999 Excavations,” Paléorient, 26(1), 45-54, 2000.
D. T. Bradley, E. E. Ryherd, and L. Ronsse (Eds.), Worship Spaces Acoustics: 3 Decades of Design, (New York, NY, Springer, 2016).

4aAA5 – Conversion of an acoustically dead opera hall in a live one

Wolfgang Ahnert¹, Tobias Behrens¹ (info@ada-amc.eu) and Radu Pana²(pana.radu@gmail.com)

1 ADA Acoustics & Media Consultants GmbH, Arkonastr. 45-49, D-13189 Berlin / Germany
2 University of Architecture and Urbanism “Ion Mincu”, Str. Academiei 18-20, RO-010014 Bucuresti / Romania

Popular version of paper 4aAA5, “The National Opera in Bucharest – Update of the room-acoustical properties”
Presented Thursday morning, November 5, 2015, 10:35 AM, Grand ballroom 3
170th ASA Meeting, Jacksonville

The acoustics of an opera hall has changed dramatically within the last 100 years. Until the end of the 19^th century, mostly horseshoe-shaped halls were built with acoustically high-absorbing wall and even floor areas. Likewise, the often used boxes had fully absorbing claddings. That way the reverberation in these venues was made low and the hall was perceived as acoustically dry, e.g. the opera hall in Milan. 100 years later, the trend shows opera halls with more live and higher reverberation, preferred now for music reproduction, e.g. Semper Opera in Dresden.

This desire to enhance the acoustic liveliness in the Opera House in Bucharest led to renovation work in 2013-2014. The Opera House was built in 1952-1953 for around 2200 spectators and it followed a so-called style of “socialist realism”. This type of architecture was popular at the time, when communism was new to Romania, and the building has therefore a neoclassical design. The house was looking inside the hall like a theatre of the late 19th century. The conditions in the orchestra pit for the musicians, as far as mutual hearing is concerned, were bad as well. So, construction works took place in order to improve room acoustical properties for musicians and audience.

Fig. 1: Opera hall after reconstruction

The acoustic task was to enhance the room acoustic properties significantly by substituting absorptive faces (as carpet, fabric wall linings, etc.) by reflective materials:

Carpet on all floor areas, upholstered back- and undersides of chairs
Textile wall linings at walls/ceilings in boxes, upholstered hand rails
Textile wall linings at balustrades, upholstered hand rails in the galleries

All the absorbing wall and ceiling parts were substituted by reflecting wood panels, the carpet was removed and a parquet floor was introduced. As a result, the sound does not fade out anymore as in an open-air theatre but spaciousness may be perceived now.

The primary and secondary structures of the orchestra pit were changed as well in order to improve mutual hearing in the pit and between stage and pit. The orchestra pit had the following acoustically disadvantageous properties:

Insufficient ratio between open and covered area (depth of opening 3.5 m, depth of cover 4.7 m)
The height within the pit in the covered area was very small.
The space in the covered area of the pit was highly overdamped by too much absorber.

Fig. 2: new orchestra pit, section

The following changes have been applied:

The ratio between open area and covered area is now better by shifting the front edge of the stage floor to the back: Depth of opening is now 5.1 m, depth of cover only 3.1 m.
The height within the pit in the covered area is increased by lowering the new movable podium.
The walls and soffit in the pit are now generally reflective, broadband absorbers can be placed variably at the back wall in the pit.

After an elaborate investigation by measurements and simulation on site a prolongation of the reverberation time of 0.2-0.3 s was reached to actual values of about 1.3 to 1.4 s.

Together with alterations of the geometric situation of pit, the acoustic properties of the hall are now very satisfactory for musicians, singers and the audience.

Beside the reverberation time, other room acoustical measures such as C80, Support, Strength, etc. have been improved significantly.

2pAAa4 – Does it sound better behind Miles Davis’ back? What would it sound like face-to-face? Rushing through a holographic sound image of the trumpet

Franz Zotter – zotter@iem.at
Matthias Frank – frank@iem.at

University of Music and Performing Arts Graz
Institute of Electronic Music and Acoustics (IEM)
Inffeldgasse 10/3, 8010 Graz, Austria

Popular version of paper 2pAAa4, “Challenges of musical instrument reproduction including directivity”
Presented Tuesday afternoon, November 3, 2015, 2:25 PM, Grand Ballroom 3
170^th ASA Meeting, Jacksonville

In many of his concerts, Miles Davis used to play his trumpet facing away from the audience. Would it have made a difference had he faced the audience

Unplugged acoustical instruments can feature a tremendously different timbre for different orientations. Musicians experience such effects while playing their instrument in different environments. Those lacking such experience can only learn about the so-called directivity of musical instruments from publications showing diagrams of measured timbral changes. Comprehensive publications from the nineteen sixties deliver remarkably detailed descriptions. And yet, it requires training to imagine how the timbral changes sound like by just looking at these diagrams.

microphone_sphere_trumpet - holographic sound

Figure 1: A surrounding sphere of 64 microphone was built at IEM (Fabian Hohl, 2009) to record holographic sound images of musical instruments. The photo (Fabian Hohl, 2009) shows Silvio Rether playing the trumpet.

In the new millennium, researchers built surrounding spheres of microphones that allow to record a holographic sound image of any musical instrument (Figure 1). This was done to get a more natural representation of instruments in virtual acoustic environments for games or computer-aided acoustic design. Alternatively, the holographic sound image can be played back in real environments using a compact spherical loudspeaker array (Figure 2).

Figure 2: The photo (Franz Zotter, 2010) shows the icosahedral loudspeaker during concert rehearsals.

Such a recording allows, for instance, to convey a tangible experience of how strongly the timbre and loudness of a trumpet changes with orientation. (Audio example 1) is an excerpt from a corresponding holographic sound image using 64 surrounding microphones. With each repetition of the excerpt, the recording position gradually moves from behind the instrumentalist to the face-to-face orientation.

While what was shown above was done under the exclusion of acoustical influences of the room, the new kind of holographic sound imagery is a key technology used to reproduce a fully convincing experience of a musical instrument within arbitrary rooms it is played in.

The icosahedron as a housing of 20 loudspeakers (a compact spherial loudspeaker array) was built 2006 at IEM. It is a device to play back holographic sound images of musical instruments. Currently, it is used as a new tool in computer music to project sound into rooms utilizing wall reflections from different directions.

Audio Example:

In the example, one can clearly hear the orientation-related timbral changes of the trumpet. The short excerpt is played in 7 repetitions, each time recorded at another position, moving from behind the trumpet player to the front. The piece “Gaelforce” by Peter Graham is performed by Silvio Rether, and the recording was done by Fabian Hohl at IEM using the sphere shown in Figure 1.

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