ECHOIC REMNANTS Concerning Preservation_ Which acoustic factor, and to what extent can be it be adapted, can provide an ideal environments for different musical genres and instrument types? What physical measures can be taken to realise this?
Michaela Mallia Architecture and Environmental Engineering Design Studio F_ Technical Study
ECHOIC REMNANTS Concerning Preservation
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ECHOIC REMNANTS Concerning Preservation
“A concerted effort to preserve our heritage is a vital link to our cultural, educational, aesthetic, inspirational, and economic legacies - all of the things that quite literally make us who we are.� - Steve Berry
Musical expression is a reflection of culture and identity. Just as cities strive to preserve art and literature, so should they try to preserve their musical legacy, its history and its instruments.
While the proposal for Echoic Remnants does just this, the aim of this technical study is to explore the ways in which acoustic environments in the building's performance areas can be adapted and idealised for different musical performances.
A transition in acoustic spaces develops in the building, from casual busking spaces, to an adaptable concert hall and, finally, small music chambers in the museum; this study shall focus on the concert hall and the music chambers.
The adaptable concert hall is to provide an acoustically dynamic environment, which can effectively capacitate different musical genres, from rock to Baroque. This is realised through the use of adjustable, ceiling-hung acoustic panels, creating the ability to set the preferred reverberation time for each performance type.
As the journey towards permanence in preservation reaches its apex, instruments from the musical epochs of Britain’s history are exhibited for the public in the museum, where each floor is dedicated to a family of instruments and has its own music chamber. The music chambers allow audiences to experience and gain an educational understanding of individual instruments, which are played by professionals in their ideal acoustic conditions. Again, this will be realised by designing variable acoustic scenes (preferred reverberation time) through the use of adjustable wall hung acoustic panels.
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ECHOIC REMNANTS Concerning Preservation
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ECHOIC REMNANTS Concerning Preservation
C ONTENTS _ 1
INTRODUCTION_ ........................................................................................................................................................................ 7
2
PROPOSAL_ ................................................................................................................................................................................ 9
3
OVERVIEW OF ACOUSTIC CRITERIA_ .......................................................................................................................................10
4
THE ADAPTABLE CONCERT HALL_ ..........................................................................................................................................12
5
6
4.1
Taking Precedence .......................................................................................................................................................12
4.2
The Space Explained ....................................................................................................................................................12
4.3
Reverberation Time ......................................................................................................................................................13
4.3.1
Determining Equivalent Absorption Areas .................................................................................................. 14
4.3.2
Errors .......................................................................................................................................................................17
THE MUSEUM'S MUSIC CHAMBERS_ .......................................................................................................................................18 5.1
Taking Precedence .......................................................................................................................................................18
5.2
The Space Explained ....................................................................................................................................................19
5.3
Reverberation Time ..................................................................................................................................................... 20
5.3.1
Determining Equivalent Absorption Areas .................................................................................................. 22
5.3.2
Errors ...................................................................................................................................................................... 24
INTRODUCING ACOUSTIC PANELLING_ .................................................................................................................................. 26 6.1
The Concert Hall........................................................................................................................................................... 26
6.2
The Music Chambers .................................................................................................................................................. 27
7
CONCLUSION_ ..........................................................................................................................................................................31
8
REFERENCES_ ........................................................................................................................................................................... 33
9
APPENDIX A_ ........................................................................................................................................................................... 35
10
APPENDIX B_............................................................................................................................................................................ 37
11
APPENDIX C_ ........................................................................................................................................................................... 38
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ECHOIC REMNANTS Concerning Preservation
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ECHOIC REMNANTS Concerning Preservation
1
INTRODUCTION_ The acoustic design of musical performance spaces is of principle importance. As such, this report aims to establish the key acoustic criteria required in performance spaces, with particular regard to spaces which resemble the adaptable concert hall and the museum's music chambers.
“Rooms designed for unamplified music are the most visible and interesting spaces in architectural acoustics. It is here that the science of acoustics and the arts of architecture and music are blended.� - Long, 2006, p. 653
While a number of architectural and related acoustical factors should be thoroughly explored in concert hall and music room design, reverberation is considered the "most recognizable parameter associated with concert halls" (Long, 2006, p. 674) since its discovery by Sabine.
Further to this, different types of musical genres and instruments sound their best at different reverberation times. Subsequently, this technical study will primarily focus on the range of reverberation time values required for different acoustic scenes in the concert hall and the museum's music chambers, as well as the methods that would make this achievable.
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ECHOIC REMNANTS Concerning Preservation
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ECHOIC REMNANTS Concerning Preservation
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PROPOSAL_ This investigation will be carried out in four stages:
I. In order to understand what factors contribute towards idealised acoustic environments, a literature review regarding important acoustical factors will be carried out, highlighted reverberation as the principle area of interest.
This will then be followed by an in-depth study of the relationship between reverberation time, musical genres and instruments, along with the acoustic and physical measures which can be taken to enhance these relationships:
II. Firstly, the spectrum of reverberation times required for the adaptable music hall to successfully capacitate different genres of music shall be investigated, using references to support quantitative values. In turn, this allows for consideration of internal material finishes and the variation in equivalent absorption areas required to achieve said reverberation times.
III. The third section shall focus on the five instrument family music rooms in the museum: strings, woodwind, brass, percussion and keyboard, whereby each room is attributed with an example catalogue of instruments. The study will focus on one of these rooms in detail, determining whether the room's reverberation can vary for each instrument through a literature study. Again, the associated equivalent absorption areas for reverberation value ranges will then be determined.
IV. The last section of the study will look at the types of measures, namely acoustic panelling, which are available to realise the design for both types of acoustic spaces. Just as it is common to be able to choose the type of lighting scene or mood in a space, an automated system which would digitally control adjustable acoustic panels would allow for an acoustic scene to be set by the push of a button, creating an ideal acoustic environment.
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ECHOIC REMNANTS Concerning Preservation
3
OVERVIEW OF ACOUSTIC CRITERIA_ A number of factors should be considered in the design of performance venues. Concert halls and music chambers are spaces which are especially designed for music, whereby the acoustic conditions must satisfy both the musicians and the audience (Long, 2006, p. 655). The 'language of music' in concert hall design is described by a number of terms, where “each musical term is associated with one or more acoustical properties of a performance space� (Long, 2006, p. 653). Long (2006, p. 655) provides a list outlining this, whereby the shape, volume and surface materials largely dictate all or the majority of these acoustical factors.
Figure 1: Musical terms and their related acoustical factors Source: Long, 2006, p. 655
It is difficult to specify an 'ideal listening environment', namely because different types of music and instruments sound their best in different environments (Long, 2006, p. 657). Moreover, unlike speech comprehension which is typically measured one-dimensionally, music appreciation is multi-dimensional (Long, 2006, p. 668). In spite of this, Hawkes and Douglas (1971) have set out five principle parameters in musical acoustics: reverberation; clarity; envelopment; intimacy; and loudness. A set of general performance standards in relation to these factors are be listed below:
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ECHOIC REMNANTS Concerning Preservation
I. Reverberation _ By definition, reverberation time is the amount of time it takes for the reverberant sound to decay by 60dB (T60). The reverberant fields below 500Hz should increase as the frequency gets lower; this results in a musical warmth (Long, 2006, p. 657).
II. Envelopment_ All concert halls and musical spaces should provide strong lateral reflections to achieve a sense of envelopment, where a "significant fraction of the energy [arrives] from the side" (Long, 2006, p. 657). Long (2006, p. 658) insists that rectangular halls are the best spaces in achieving this.
III. Loudness_ A space's volume has notable affects on reverberation and room gain, whereby a high volume per seat per 3 -1
3
-1
person, ranging from range from 7m p to 12 m p , is suitable for smaller capacities to control excessive loudness (Long, 2006, 658-659).
IV. Clarity and Intimacy_ Musical scores with rapid passages need clarity in order to be fully appreciated by the audience. As such, the surfaces should facilitate this by creating reflections as near to the source of music or the receiver, creating shorter reverberation times and initial time delay gaps (Long, 2006, p. 657). The latter also creates a sense of intimacy.
Long (2006, p. 657) also provides further good practise standards, namely:
I.
Since instruments generate sounds from frequencies as low as 30Hz and high as 12,000Hz, the acoustic performance of the space should support such a broad bandwidth. As such, the room should not colour (see Figure 1) the natural spectrum of the generated sounds (Long, 2006, p. 657).
II.
The ensemble of the space should be maintained; the musicians must be able to hear each other play, with a "reverberant return that is close to that experienced by the audience� (Long, 2006, p. 657). While all the above criteria are all highly important to consider when designing spaces for acoustic music, Long (2006, p. 674) identifies that reverberation is considered the "most recognizable parameter associated" with acoustic performance of music spaces.
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THE ADAPTABLE CONCERT HALL_ 4.1
TAKING PRECEDENCE
The concept of designing an adaptable concert hall was propelled by the newly built Saffron Walden Music Hall in Saffron Walden. The flexible acoustic space has pioneered as one of Britain’s first state-of-the-art adjustable and versatile auditoria. The space has adjustable acoustic panelling which hangs from the hall's ceiling, thus giving it the ability to adapt the reverberation time to different performances.
Figure 2: Saffron Walden Music Hall Source: Pictures taken off Google Images
4.2
THE SPACE EXPLAINED
The proposed concert hall has a seating capacity of 616 and has been designed in a classic fashion (Long, 2006, p. 655): a normal, hybrid shoebox-diamond configuration [see Appendix A, Figure I] with a single 2
3
balcony. Approximate dimensions for the floor area and volume are 525m and 6300m respectively. As highlight in section 3, the spaces is rectangular in geometry to achieve a good sense of envelopment (Long, 3 -1
2006, p. 658), with a volume per person ratio which lies within the desired volume range - of 10m p (Long, 2006, 658-659).
Figure 3: Lower ground floor plan 12
ECHOIC REMNANTS Concerning Preservation
Figure 4: Long section through concert hall, foyer and courtyard
The space is to have timber internal finishes, with adjustable hanging acoustic panels from the ceiling. Where rooms are designed for unamplified music performance, “the acoustician can only work indirectly with the room surfaces that reflect, diffuse, or absorb the primal energy� (Long, 2006, p. 653); as such, the specification of the internal finishes will be importance and affect the reverberation of the space.
4.3
REVERBERATION TIME
According to Beranek (1962, p. 429), reverberation times in concert halls should range between 1.5s and 2.2s. Long (2006, p. 656) refines this by suggesting that preferred values should lie between 1.8 to 2.0 seconds. However, these values applying to halls which provide a single acoustic environment. As such, the appropriateness of reverberation is directly dependent on a space's volume and the type of performance taking place:
Figure 5: Recommended reverberation times Source: Simpson, 2014 13
ECHOIC REMNANTS Concerning Preservation
With this in mind, Table 1 summarises the preferred reverberation ranges for the types of music intended to be played in the proposed design:
Type of Music
T60 (s)
Rock & Pop
0.6 - 1.2
Jazz
0.8 - 1.2
Chamber
1.4 - 1.7
Baroque
1.5 - 1.7
Classical
1.6 - 1.9
Romantic
1.8 - 2.2
Table 1: Suggested T60 values for different types of music Sources: Long, 2006, p. 656; Acoustic control of theatres and concert halls, 2008; Adelman-Larsen, Thompson and Gade, 2010, p. 1
The space will not be able to capacitate music from the Gothic and Renaissance eras, as the polyphonic nature of these genres meant that they were often performed in churches, which can have reverberation times as high as 10s.
As mentioned above, the aim of this concert hall is to be an adaptable one; this is achieved by varying the amount of absorptive surfaces in the space. Thus, the remainder of this section will determine the required difference in equivalent absorption areas that will deliver a reverberation range between 1.2 - 2.0s. With this in mind, the hall should have a smooth reverberant tail, regardless of the reverberation time. This means that the reverberation should have no echoes, no shadowing (particularly under the balcony), colouration or other defects (Long, 2006, p. 657).
4.3.1
DETERMINING EQUIVALENT ABSORPTION AREAS
Reverberation times can be calculated using different equations; namely Sabine's, Eyring's and the Millington Sette formula. Through the Architectural Acoustics and Noise Control module, an understanding of reverberation has been developed; since the space can be considered a 'lively' acoustic environment, Sabine's formula is the most appropriate calculation method, whereby the known T 60 values will be used to find the corresponding equivalent absorption areas. Sabine's equation is as follows:
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ECHOIC REMNANTS Concerning Preservation
Where,
3
V = volume (m ) 2
A = equivalent absorption area (m ) 2
S = surface area (m ) Îą = material absorption coefficient
With the established T60 values and the room volume, the equation was rearranged to determine the A required for different performances. The table below illustrates the variation in A values:
3
2
Performance Genre
Sabine T60 (s)
V (m )
Arequired-mean (m )
Rock, pop & jazz
1.2
6300
845.25
Chamber & baroque
1.5
6300
676.20
Classical
1.8
6300
563.50
Romantic
2.0
6300
507.15
Table 2: Required equivalent absorption areas
In order to calculate the minimum equivalent absorption area of acoustic panelling required over the internal materials of the concert hall, the calculation will initially be carried out to achieve 2s reverberation, 2
therefore using the 507.15m A value.
The equivalent absorption area of the seating (Acoustical Surfaces, 2015) was determined first, as the calculation found from the reference source resulted in a direct equivalent absorption area value for each frequency. Moreover, seating in auditoria should be considered prior to the rest of the materials because it is desirable to have seating which has a similar absorption characteristics to people, so as to maintain a consistent acoustic environment (Long, 2006, p. 660).
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ECHOIC REMNANTS Concerning Preservation Frequency αs per m
2
As
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
0.60
0.74
0.88
0.96
0.93
0.85
180.00
222.00
264.00
288.00
279.00
255.00
Table 3: Upholstered seating/audience equivalent absorption areas
Following this, the surface areas of all the absorptive surfaces in the room were determined. A breakdown of the surface areas can be found in Appendix B, Table I, where the balcony on the upper ground floor was included in the floor, seating and ceiling areas as required. The floors, ceilings and walls of the concert hall will be clad in timber. Long (2006, p. 660) suggests that the use of timber as a surface finish in concert halls should be restricted to a minimum thickness of 25mm (Long, 2006, p. 660). The absorption coefficient values for the floor and ceiling were derived from Acoustical Surfaces (2015), while the other values were all from the excel spreadsheet (Longhurst, 2014a).
Frequency
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
Floor: suspended hardwood boards 2
Sf (m ) αf 2
Af (m )
330.77
330.77
330.77
330.77
330.77
330.77
0.15
0.11
0.10
0.07
0.06
0.07
50
36
33
23
20
23
Ceiling: hanging hardwood panelling 2
Sc (m ) αc 2
Ac (m )
630.77
630.77
630.77
630.77
630.77
630.77
0.15
0.11
0.10
0.07
0.06
0.07
95
69
63
44
38
44
Wall: hardwood panelling 2
Sw (m ) αw 2
Aw (m )
965.44
965.44
965.44
965.44
965.44
965.44
0.14
0.10
0.10
0.08
0.10
0.08
135
97
97
77
97
77
Doors: hardwood veneer with air-gap and insulation 2
Sd (m )
25.60
25.60
25.60
25.60
25.60
25.60
αd
0.35
0.39
0.44
0.49
0.54
0.57
8.96
9.98
11.26
12.54
13.82
14.59
2
Ad (m )
Table 4: Equivalent absorption areas of internal surface materials
The sum of the internal surfaces' equivalent absorption areas were then deducted from the total area required to yield the desired T60 values in each frequency, providing the area of acoustic panelling for each acoustic scene.
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ECHOIC REMNANTS Concerning Preservation Frequency
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
Mean
Romantic Arequied
507.15
507.15
507.15
507.15
507.15
507.15
Ainternal surfaces
468.35
434.30
467.96
445.09
447.06
414.13
Aacoustic panels
38.80
72.85
39.19
62.06
60.09
93.02
61.00
Classical Arequied
563.50
563.50
563.50
563.50
563.50
563.50
Ainternal surfaces
468.35
434.30
467.96
445.09
447.06
414.13
Aacoustic panels
95.15
129.20
95.54
118.41
116.44
149.37
117.35
Chamber & Baroque Arequied
676.20
676.20
676.20
676.20
676.20
676.20
Ainternal surfaces
468.35
434.30
467.96
445.09
447.06
414.13
Aacoustic panels
207.85
241.90
208.24
231.11
229.14
262.07
230.05
Rock, Pop & Jazz Arequied
845.25
845.25
845.25
845.25
845.25
845.25
Ainternal surfaces
468.35
434.30
467.96
445.09
447.06
414.13
Aacoustic panels
376.90
410.95
377.29
400.16
398.19
431.12
399.10
Table 5: Determining the four mean values of required acoustic panel equivalent absorption areas
Performance Genre
Sabine T60
Arequired-mean
AAP-mean
Rock, pop & jazz
1.2
845.25
399
Chamber & Baroque
1.5
676.20
230
Classical
1.8
563.50
117
Romantic
2.0
507.15
61
Table 6: Resulting equivalent absorption area values for four acoustic scenes
4.3.2
ERRORS
A significant issue in the calculations was the limited range of frequencies used for both the reverberation time. While sounds produced by instruments range between 30Hz - 12000Hz, the availability of data was limited to 125Hz -4000Hz. This is likely because the latter range lies within the realm of speech.
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ECHOIC REMNANTS Concerning Preservation
5
T H E M U S E U M ' S M U S I C C H A MB E R S _ 5.1
TAKING PRECEDENCE "It is highly recommended that the ability to vary the reverberation times in the room be incorporated as this will provide a versatile music room and can be used for various musical instruments". - Osman (2010, p. 7)
Once again, the idea of the specialised music chambers was inspired by a precedent - The Sonorous Museum in Copenhagen. As described by ArchDaily Magazine, "The Sonorous Museum is comprised of four sound regulated studios, acoustically adapted to a specific instrumental group: strings, brass, percussion and mixed instruments." (ArchDaily, 2014). The spaces are described as "four delicately detailed sound spaces" (ArchDaily, 2014), which create an opportunity to experience instruments being played by professionals in their sound spectre, creating an optimal acoustic setting for a specific instrumental family.
Figure 6: The Sonorous Museum rooms Source: Dezeen, 2014
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ECHOIC REMNANTS Concerning Preservation
While these rooms provide idealised acoustic environments by providing "unique acoustics and pared-back aesthetics" (Dezeen, 2014), the idea of idealised room's for instruments was adapted for the project, once again by providing ideal reverberation for each instrument. This is, however, suggested in the plan of the percussion room where opening acoustic panels on the walls can be seen:
Figure 7: Sonorous Museum percussion room Source: Dezeen, 2014
5.2
THE SPACE EXPLAINED
The museum has five permanent exhibition (floors 2 to 6); each level is dedicated to one instrument group and has a music chamber in which the instruments can be performed by professional musicians. A catalogue of typical instruments which would be exhibited is illustrated in Figure 9. Each of the proposed music chambers has a seating capacity of 30 people. The dimensions of the floor area and volume are 2
3
3 -1
112.5m and 337.5m respectively; the room's volume to person ratio is 11m p , which is on the higher end of the accepted range (Long, 2006, 658-659). Once again, the space is to have timber internal finishes.
Figure 8: Typical permanent exhibition floor plan
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ECHOIC REMNANTS Concerning Preservation
Figure 9: Instrument catalogue
5.3
REVERBERATION TIME
While the study set out to determine ideal reverberation times for different instruments in a single instrument group, literature on the subject was hard to come by. Osman (2010, p.4) does, however, provide general guidelines to preferred ranges for the different families.
Figure 10: Preferred mid frequency reverberation times for various instrument types Source: Osman, 2010, p. 4
Building upon this, literature concerning ideal reverberation times in small performance spaces is somewhat less limited; rather than small performance spaces, sources typically refer to rehearsal rooms or practice rooms. As such, SkĂĽlevik (2014, p. 2) provides a table with guidelines reverberation times for different sized music rooms: 20
ECHOIC REMNANTS Concerning Preservation
Figure 11: Examples of T30 values in different sized rooms Source: Skålevik, 2014, p. 2
3
The proposed music rooms fall between the first two listings, with a volume of 337.5m and musician numbers which will range between 1-5. As exhibited in Figure 13, the smaller rooms have a low reverberation times of 0.4s and 0.8s, which can be considered as somewhat 'dry' spaces. This, however, is due to the necessary control of the reverberant gain (Gr), a key factor which must be considered in rooms of this size. According to Skålevik (2014, p. 1), "this question calls for a discussion over the conflict between the wish for proper reverberance versus the wish for a proper loudness, in rehearsal rooms that are a lot smaller than the performance room." Skålevik explains that if a rehearsal room, or in the proposal's case a small performance chamber, had a reverberation time that was equal to a concert hall, the acoustics would be too loud. On the other hand, a small chamber with an ideal reverberant gain would result in a space that is too dry. This is supported by Rindel (2014, p. 126), who suggests that reverberation in small volumes must be reduced to avoid excessively loud sound levels. What is interesting about literature concerning practice rooms, is that equal emphasis is given to the acoustic impression of the musician as well as the audience, and "when it comes to musicians’ acoustical environment, the literature leaves more focus on the features of sound levels than on decay times" (Skålevik, 2014, p. 3).
Figure 12: Principle influence of reverberation and strength in perceived music Source: Rindel, 2014, p. 126
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ECHOIC REMNANTS Concerning Preservation
SkĂĽlevik's paper, thus, suggests that the variation in reverberation is dependent on the loudness of the instrument and the limiting reverberant gain desired when the volume is constant. Once again, this is supported by Rindel, who explains that "during the work on the standard NS 8178, several models for this volume-dependence were considered" (Rindel, 2014, p. 126), with particular interest in the consequence of room gains. It was found that 25-26dB was a suitable limiting Gr value in small performance spaces. Rindel (2014, p. 126) brings an equation to light, which creates a relationship between the reverberation and the this limited Gr value:
Where a and b are constants are constants which vary to achieve reverberation time range limits.
Figure 13: a, b and volume range for reverberation time range limits Source: Rindel, 2014, p. 126
Unfortunately, the equation does consider the sound pressure level of individual instruments; rather, the reverberation limits are defined for three types of instruments: amplified instruments; loud musical instruments; and weak musical instruments (Rindel, 2014, p. 126) [see Figure II, Appendix A for sound power level breakdowns of individual instruments]. As such, specific reverberation values for individual instruments were able to be found in the scope of this report; empirical testing within the actual rooms would need to take place, to gain the sound power levels, the corresponding sound pressure levels and, thus, the room gain for each instrument.
5.3.1
DETERMINING EQUIVALENT ABSORPTION AREAS 3
Using the highlights values in Figure 15, appropriate T60 values were found for the room volume 337.5m .
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ECHOIC REMNANTS Concerning Preservation Instrument type
a
b
T60 (s)
Amplified (average)
0.304
0.204
0.56
Powerful acoustic
0.404
0.304
0.72
Mixed acoustic
0.600
0.500
1.02
Weak acoustic
0.750
0.650
1.25
Table 7: T60 values for limiting Gr of 25dB
Once again, using , the established T60 values and the room volume in Sabine's equation provided the required equivalent absorption areas for the different instrument types. The table below illustrates the variation in A values:
Instrument type
Sabine T60
A
required-mean
Amplified (average)
0.6
96.24
Powerful acoustic
0.7
75.74
Mixed acoustic
1.0
53.43
Weak acoustic
1.2
43.60
Table 8: Required equivalent absorption areas
The same procedure used in the Section 4.3.1 was carried out to determine the range of equivalent absorption areas required by acoustic panels. A breakdown of the room's surface areas and the equivalent absorption areas of all the internal materials can be found in Appendix C, Table I and Table II respectively. The sum of the internal surfaces' equivalent absorption areas were then deducted from the total area required to yield the desired T60 values in each frequency, providing the area of acoustic panelling needed for each acoustic scene.
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ECHOIC REMNANTS Concerning Preservation Frequency
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
Mean
Amplified instruments Atotal
96.24
96.24
96.24
96.24
96.24
96.24
Ainternal surfaces
59.08
46.34
44.94
37.87
40.78
42.33
Aacoustic panels
37.17
49.91
51.30
58.38
55.46
53.92
51.02
Acoustic instruments, powerful Atotal
75.74
75.74
75.74
75.74
75.74
75.74
Ainternal surfaces
59.08
46.34
44.94
37.87
40.78
42.33
Aacoustic panels
16.66
29.40
30.80
37.87
34.96
33.41
30.52
Acoustic instruments, mixed Atotal
53.43
53.43
53.43
53.43
53.43
53.43
Ainternal surfaces
59.08
46.34
44.94
37.87
40.78
42.33
Aacoustic panels
-5.64
7.10
8.49
15.57
12.65
11.11
8.21
Acoustic instruments, weak Atotal
43.60
43.60
43.60
43.60
43.60
43.60
Ainternal surfaces
59.08
46.34
44.94
37.87
40.78
42.33
Aacoustic panels
-15.47
-2.73
-1.34
5.74
2.82
1.28
-1.62
Table 9: Determining the four mean values of required acoustic panel equivalent absorption areas
Instrument type
Sabine T60
Arequired-mean
AAP-mean
Amplified (average)
0.6
96.24
51.02
Powerful acoustic
0.7
75.74
30.52
Mixed acoustic
1.0
53.43
8.21
Weak acoustic
1.2
43.60
-1.62
Table 10: Resulting equivalent absorption area values for four acoustic scenes
Thus, taking the string music chamber as an example, three acoustic scenes would be useful in this room: a 1.2s reverberation time for a single violin with a k value of 0.8 (Rindel, 2014, p. 124), 1s reverberation time for a string quartet with a k value of 3.1 (Rindel, 2014, p. 127) and 0.6s for electric (amplified) guitars.
5.3.2
ERRORS
Once again, the issue of the limited frequency band widths (125Hz - 4000Hz) in the data found means that the entire sound spectra of instruments (30Hz - 12000Hz) could not be analysed.
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ECHOIC REMNANTS Concerning Preservation
Moreover, the 125Hz band for the weak and mixed acoustic scenarios, as well as the 250Hz and 500Hz bands in the weak scenario, resulted in a negative equivalent absorption areas; this would obviously not be possible and these values must be assumed to be 0. As such, the room will actually be less than the 1.2s in the weak scene and 1.0s in the mixed scene, creating a slightly dryer acoustic conditions.
Frequency
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
Mean
Acoustic instruments, weak 2
Aacoustic panels (m )
0
0
0
5.74
2.82
1.28
2
59.075
46.335
44.940
43.60
43.60
43.60
V (m )
337.5
337.5
337.5
337.5
337.5
337.5
T60 (s)
0.92
1.17
1.21
1.25
1.25
1.25
Atotal (m ) 3
1.17
Acoustic instruments, mixed 2
Aacoustic panels (m )
0
7.10
8.49
15.57
12.65
11.11
2
59.075
53.43
53.43
53.43
53.43
53.43
V (m )
337.5
337.5
337.5
337.5
337.5
337.5
T60 (s)
0.92
1.02
1.02
1.02
1.02
1.02
Atotal (m ) 3
1.00
Table 11: Revised T60 values for weak and mixed acoustic instruments
The revised calculations suggest that the replacing the negative value in the 125Hz band with 0 creates not difference to the mean T60 value. The new T60 value for the weak acoustic scene is 1.17s, once again suggesting that the replacing the negative values with 0 has a minimal effect on the resultant reverberation time. Moreover, comparing this value to the recommendations in Figures 10 and 11, which have reverberation ranges between 0.3s and 0.9s, suggests that this slight reduction will render the acoustic condition too dry.
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ECHOIC REMNANTS Concerning Preservation
6
INTRODUCING ACOUSTIC PANELLING_ 6.1
THE CONCERT HALL
In order to achieve the desired acoustic scenes, ceiling hung adjustable acoustic panelling would be used, as seen in the Saffron Walden Concert Hall. The ability to control the acoustic environment, that is alter the surface area of exposed acoustic panelling, would take place in the tech rooms. Precedents, such as the movable ceiling panels in Figure 2 (Saffron Walden Concert Hall) provide an idea of how this would work.
Figure 14: Example visualisation of acoustic scene panel
Technologies such as the Transcend Active Acoustic System or Wenger's Interactive Acoustic panels would be appropriate. The latter provides a range of panel sizes, from 59 x 59 x 8cm to 119 x 119 x 8cm in a variety of colours to achieve the desired aesthetic in the concert hall (Wegner, 2008, p. 1).
Figure 15: Wenger's Interactive Source: Wenger, 2015
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ECHOIC REMNANTS Concerning Preservation
Technical data on the panels' absorption coefficients was obtained (Wegner, 2008, p. 4), to determine whether the resulting surface areas at all frequencies were relatively similar [see Appendix A, Figure III for technical data sheet].
125Hz
250Hz
500Hz
T60 of 1.2s
1000Hz
2000Hz
4000Hz
Contemporary Scene
Required A
376.90
410.95
377.29
400.16
398.19
431.12
Wenger Tunable APs α
0.65
1.1
1.31
1.23
1.2
1.09
Resulting surface area
580
374
288
325
332
396
T60 of 1.5s
Baroque Scene
Required A
207.85
241.90
208.24
231.11
229.14
262.07
Wenger Tunable APs α
0.65
1.1
1.31
1.23
1.2
1.09
Resulting surface area
320
220
159
188
191
240
T60 of 1.8s
Classical Scene
Required A
95.15
129.20
95.54
118.41
116.44
149.37
Wenger Tunable APs α
0.65
1.1
1.31
1.23
1.2
1.09
Resulting surface area
146
117
73
96
97
137
T60 of 2.0s
Romantic Scene
Required A
38.80
72.85
39.19
62.06
60.09
93.02
Wenger Tunable APs α
0.65
1.1
1.31
1.23
1.2
1.09
Resulting surface area
60
66
30
50
50
85
Table 12: Resulting equivalent absorption area values for four acoustic scenes
As can be seen from the results, the panels would perform adequately in the Romantic acoustic setting, however large area variations are apparently in the 500Hz and 4000Hz frequencies. However, the surface area ranges for the other three scenes with larger reverberant fields are unsatisfactory, as the difference in surface for each frequency is too great to provide satisfactory acoustics. As such, acoustic panels with a better specification, that is, more constant absorption coefficients across the frequency band, would need to be specified by working with manufacturers to achieve the best results possible. This would probably, however, prove costly and time consuming.
6.2
THE MUSIC CHAMBERS
Due to the scope of this study, it will not be possible to analyse suitable acoustic panel options in all five rooms. As such, the strings room will be used as an example for acoustic panel integration.
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ECHOIC REMNANTS Concerning Preservation
Figure 1: Example visualisation of acoustic scene panel
Once again, Wenger's Interactive Acoustic panels would be appropriate as the manufacturers also provide wall hung panels, with a large range of panel sizes. The absorption panels were tested, to determine whether the sound absorption coefficients (Wegner, 2008, p. 4) resulted in similar surface areas in each frequency.
125Hz
250Hz
T60 of 0.6s
500Hz
1000Hz
2000Hz
4000Hz
Average
Amplified Scene
Required A
37.17
49.91
51.30
58.38
55.46
53.92
Wenger Tunable APs α
0.65
1.1
1.31
1.23
1.2
1.09
Resulting surface area
57
45
39
47
46
49
T60 of 1.0s
47
Mixed Acoustic Scene
Required A
0
7.10
8.49
15.57
12.65
11.11
Wenger Tunable APs α
0.65
1.1
1.31
1.23
1.2
1.09
Resulting surface area
0
6
6
13
11
10
T60 of 1.2s
8
Weak Acoustic Scene
Required A
0
0
0
5.74
2.82
1.28
Wenger Tunable APs α
0.65
1.1
1.31
1.23
1.2
1.09
Resulting surface area
0
0
0
5
2
1
1
Table 13: Resulting equivalent absorption area values for four acoustic scenes
The panels would work relatively well in the music room even though, once again, there is a moderate discrepancy in the 500Hz and 125Hz frequency ranges in the amplified scene. In addition to this, it is possible to assume that the weak acoustic scene would not require any panels, as only a mean value of 1m
2
is required. The following calculation disregarded any acoustic panelling, only using the total internal finishes equivalent absorption areas to determine the resulting T60 value:
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ECHOIC REMNANTS Concerning Preservation Frequency
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
Mean
Acoustic instruments, weak 2
59.075
46.335
44.940
37.87
40.78
42.33
V (m )
3
337.5
337.5
337.5
337.5
337.5
337.5
T60 (s)
0.92
1.17
1.21
1.44
1.33
1.28
A (m )
1.23
Table 14: Resulting equivalent absorption area values for four acoustic scenes
The calculation yields a slightly higher reverberant field of 1.23s; as the change is slight, it shall be assumed that this value is acceptable. However, if the space proved to be too muddy, the room would have to be designed to have a smaller volume.
A total of 16 119 x 241 x 8 cm panels would be required in the space to provide the desired amplified scene. The results suggest that the room's internal finishes alone would provide an acceptable absorptive surface for the weak acoustic scene (as discussed in Section 5.3.2). As such, a mechanism that would be able to slid the panels in and out of a designed wall gap would need to be developed further, however it goes beyond the scope of this study.
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ECHOIC REMNANTS Concerning Preservation
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ECHOIC REMNANTS Concerning Preservation
7
CONCLUSION_ This report set out to determine the principle acoustic factor which, when adapted, provides various ideal acoustic environments. Reverberation was found to be the dominant factor, whereby different reverberation times are preferred for different musical genres; these values were applied to the desired acoustic environments in the proposed adaptable acoustic hall, resulting in four acoustic scenes: contemporary with a T60 value of 1.2s; Baroque with a T60 value of 1.5s; Classical with a T60 value of 1.8s; and lastly, Romantic with a T60 value of 2.0s. With this, the variation in equivalent absorption area to be provided by adjustable acoustic panels was deduced.
Different preferred reverberation times were also found for different types of instruments, namely: weak acoustic with T60 of 1.2s; mixed acoustic with T60 of 1.0s; powerful acoustic with T60 of 0.7s; and amplified instruments with T60 of 0.6s. The applicability of these four acoustic environments will need to be considered when designing each music chamber in the museum, that is, the strength classification of the exhibited instruments. The strings rooms was taken as an example, whereby the required variation in equivalent absorption areas for three applicable acoustic scenes (weak, mixed and amplified) was determined.
The final section of the report tested the effectiveness of a manufacturer's panels in achieving the desired acoustic scenes in both spaces through technical data on sound absorption coefficients. The concert hall would use ceiling hung acoustic panels, however, the results did not provide a consistent surface area in each frequency. As such, further investigation into different manufacturers or custom made panels would need to be undertaken. The manufacturer's wall hung panels were investigated in the strings music chamber, where they proved more effective by providing fairly consistent surface areas throughout the frequency band.
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ECHOIC REMNANTS Concerning Preservation
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ECHOIC REMNANTS Concerning Preservation
8
REFERENCES_ Acoustic control of theatres and concert halls (2008). [pdf]. Carmen: Custom-made acoustics. Available at: http://www.cstb.fr/fileadmin/documents/webzines/2008-09/acoustique_10_ans_labe/panosgb/217_carmen_gb.pdf [Accessed 24 Mar. 2015].
Acoustical Surfaces, (2015). Sound Absorption Coefficients. [online] Available at: http://www.acousticalsurfaces.com/acoustic_IOI/101_13.htm [Accessed 25 Mar. 2015].
Adelman-Larsen, N. W., Thompson, E. R. and Gade, A. C., (2010). Suitable reverberation times for halls for rock and pop music. Acoustical Society of America, [online] 127(1). Available at: http://flexac.com/wpcontent/uploads/2014/05/JASA.pdf [Accessed 24 Mar. 2015].
ArchDaily, (2014). Sonorous Museum/ADEPT. [online] Available at: http://www.archdaily.com/572043/sonorous-museum-adept/ [Accessed 20 Apr. 2015].
Beranek, L. L., (1962). Music, Acoustics & Architecture. London: John Wiley & Sons.
Dezeen, (2014). Adept creates timber-lined music rooms that each suit different instruments. Dezeen. [online] Available at: http://www.dezeen.com/2014/12/02/adept-danish-music-museum-music-roomscopenhagen/ [Accessed 20 Apr. 2015].
Hawkes, R.J. and Douglas, H., (1971). Subjective acoustic experience in concert auditoria. Acustica, 24.
Long, M., (2006). Architectural Acoustics [online]. London: Elsevier Academic Press. [Accessed 20 March 2015].
Longhurst, M., (2014a). BB93 SRI and absorption coefficient data v1.1March2004.xls. Architectural Acoustics and Noise Control Engineering [online]. Available from: https://blackboard.uwe.ac.uk/
Osman, R., (2010). Designing small music practice rooms for sound quality. International Congress on Acoustics. [online] Available at: http://www.acoustics.asn.au/conference_proceedings/ICA2010/cdromICA2010/papers/p754.pdf [Accessed 1 May 2015].
Rindel, J. (2014). Rooms for music – Acoustical needs and requirements. akuTEK. [online] Available at: http://www.akutek.info/Papers/JHR_MusicRooms_Requirements [Accessed 21 Apr. 2015].
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ECHOIC REMNANTS Concerning Preservation
SkĂĽlevik, M., (2014). Rehearsal room acoustics for the orchestra musician. akuTEK. [online] Available at: http://www.akutek.info/Papers/MS_Orchestra_Musician [Accessed 28 Apr. 2015].
Simpson, S., (2014). Measurement and Assessment methods for room acoustics. Architectural Acoustics and Noise Control Engineering [online]. Available from: https://blackboard.uwe.ac.uk/
Wenger, (2008). Interactive Acoustic Panels. [pdf] Wenger. Available at: http://www.wengercorp.com/Lit/Wenger%20Acoustical%20Wall%20&%20Ceiling%20Panels-TS.pdf [Accessed 4 May 2015].
Wenger, (2015). Performance Space Acoustical Treatments. [online] Available at: https://www.wengercorp.com/acoustics/performance-space-acoustical-treatments.php [Accessed 4 May 2015].
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ECHOIC REMNANTS Concerning Preservation
9
A P P E N D I X A_
Figure I: Simple plan forms concert halls in normal and surround configurations Source: Long, 2006, p. 659
Figure II: Examples of sound power levels for different instruments Source: Rindel, 2014, p. 124
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ECHOIC REMNANTS Concerning Preservation
Figure III: Wenger Interactive Acoustic Panels sound absorption coefficients Source: Wenger, 2008, p. 4
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ECHOIC REMNANTS Concerning Preservation
10
A P P E N D I X B_ Room Dimensions 6300
m
3
Seating area
300.00
m
2
Floor area
330.77
m
2
Ceiling area
630.77
m
2
Wall area
965.44
m
2
Door area
25.60
m
2
Volume
Table I: Breakdown of absorptive surface areas
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ECHOIC REMNANTS Concerning Preservation
11
A P P E N D I X C_ Room Dimensions Volume
337.5
m
3
Seating area
35.00
m
2
Floor area
105.00
m
2
Ceiling area
112.50
m
2
Wall area
125.00
m
2
Glazing area
6.00
m
2
Door area
4.00
m
2
Table I: Breakdown of absorptive surface areas
Frequency
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
Seating: Occupied and Unoccupied αs per m As
2
0.19
0.23
0.25
0.30
0.37
0.42
6.65
8.05
8.75
10.50
12.95
14.70
Floor: Wood 2
Sf (m ) αf 2
Af (m )
105.00
105.00
105.00
105.00
105.00
105.00
0.15
0.11
0.1
0.07
0.06
0.07
16
12
11
7
6
7
Ceiling: Wood 2
Sc (m ) αc 2
Ac (m )
112.50
112.50
112.50
112.50
112.50
112.50
0.15
0.11
0.1
0.07
0.06
0.07
17
12
11
8
7
8
Wall: Wood 2
Sw (m ) αw 2
Aw (m )
125.00
125.00
125.00
125.00
125.00
125.00
0.14
0.10
0.10
0.08
0.10
0.08
18
13
13
10
13
10
Doors: Wood 2
Sd (m )
4.00
4.00
4.00
4.00
4.00
4.00
αd
0.35
0.39
0.44
0.49
0.54
0.57
1.4
1.56
1.76
1.96
2.16
2.28
2
Ad (m )
Windows: Triple glazing 2
Sw (m )
6.00
6.00
6.00
6.00
6.00
6.00
αw
0.15
0.05
0.03
0.03
0.02
0.02
0.9
0.3
0.18
0.18
0.12
0.12
2
Aw (m )
Table II: Equivalent absorption areas of internal surface materials
38