Second Exam:

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• Second Exam
• revised exam date Thursday 4/11/2002 (instead
  of 4/9/2002)
• study guide handed out today (answers on
  Thursday 4/4/2002)
• covers Ch4-9 and Homework 4-8
• (homework 8 will be handed out on Thursday
  4/4/2002)
• back copies of old homework and answers available

• Topics for paper
• guide to select a topic was handed out 3/18/2002
  -

• Old homework and exams
• if not picked up will be discarded at end of week

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Physics 371 April 2, 2002
Acoustics for Musicians

• Room Acoustics (cont)
• smoothness of decay, diffusers
• early reflection, canopies
• bad and good concert halls
• criteria and shape of hall
• (shoe box, vineyard terrace)
• noise reduction
• Excitation of steady tones

New Tokyo Opera
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decay 20dB in 0.4 s reverberation time RT 1.2 s
smooth decay of reverb good
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undesirable echo
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Good room acoustics Strong early lateral
reflection
direct sound same signal in both ears
lateral reflection difference in intensity in
L and R ear and difference arrival time!
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Birmingham, U.K large adjustable canopy over
orchestra increases early reflection adds to
performer satisfaction
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Shape of concert halls the classic shoe
box hall Vienna Musikverein Saal (1870)
- RT 2.05 sec. used by J. Brahms, A.
Bruckner and G.Mahler
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Symphony Hall, Boston (1900)- good show
box dimensions 45m long, 24m wide, 17m
high early lateral reflection distance to side
wall 12m 35msec shallow balconies. reverb
time (1000Hz) 2.05 sec example calculate average
absorption of walls 2.05 sec 0.161V/A A
Saave V 18740 m3 -gt A 1472 m2 surface area
of walls, ceiling, floor approx S4500 m2 thus
ave absorption of walls a A/S 1472/4500
0.32 example of application what is effect of
carpeting the aisles? a increases from 0.03
(concrete) to 0.37 (heavy carpet on concrete)
over about 15 of floor area (homework)
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Another shoe box Royal Festival Hall London
(1951) 3000 seats elevated stage, shallow
balconies
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(No Transcript)
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Fan-shaped halls are rareley very
good lack of intense lateral reflections
(Liverpool Philharmonic)
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New Ideas Vineyard Terrace (e.g.
Berlin Philharmonic - Hans Sharoun,
Architect) advantage more seats close to stage -
more direct sound
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Berlin Philharmonic
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among the famous failures NY Philharmonic 1962
16M 2M in attempted improvements
- problems related to bulging concave side
walls to provide more seating elimination
of sound-diffusing elements () sound
absorption by plywood panels on balconies led
to understanding of need for early lateral
reflection (rebuilt as Avery Fisher Hall 1974)
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Electronic Enhancement of Concert Halls

• compensate lack of loudness at rear of hall and
  , improve uniformity
• loudspeakers permit fine tuning of room
  acoustics
• provides some flexibility for different
  performances
• difficult audience should be unaware of it
• essential direct sound must come first! (delay
  speaker signal)
• for speech directional speakers toward audience
  improves intelligibility

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Unwanted background sounds and vibration
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Examples of noise suppression
Bridgewater concert hall in Manchester, England
is immediately adjacent to a railroad track
The entire building is supported on
shock absorbers
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• Suppression of ventilation system noise

• large ducts (low air velocity)
• flexible coupling
• new electronic noise cancellation

• electronic noise compensation
• useful for periodic noise

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• known elements of successful concert hall design
• loud sound, early lateral reflection, smooth
  reverberation
• solid construction walls of concrete and
  plaster on wire lath
• yields good bass
  reflection (warmth)
• strong lateral reflection yields envelopment
• short initial time delay gap yields intimacy
• direct path from source to listener gives
  presence
• raised musician platform, raked seating, raked
  shallow balconies,
• careful placement of diffuser improves
  uniformity
• attention to construction details (including
  noise reduction)
• use electronic enhancement sparingly
• models are of benefit
• advantages of computer design(rational design)
  still disputed
• .but anotherproblem
• how objective is the quality judgment of
  concert halls?

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Importance of concert hall acoustics for
composers, conductors and musicians
different composers (and conductors) prefer
different acoustics examples Mozart, Beethoven
preferred to conduct in Wiener Hofburg with 1.4
sec reverberation time Brahms, Bruckner Mahler
preferred Musikvereinsaal Vienna with 2.1 sec
reverberation time.
Wagner assisted in acoustic design of Bayreuth
Theater
Insertion of galleries in Thomaskirche, Leipzig
reduced reverb time. This permitted articulation
of fast passages -gt resulted in Bach Mass in
B-minor and St.Mathew Passion.
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Performers and Conductors consider problem that
audience does not hear the same as the
preformers examples directionality of
sound Bruckner 4th Symphony asks for raised
trumpets makes 15 dB
difference! Sound reflection off floor can make
important difference Arrangement of instruments
in orchestra