- Oct 2017
p.117 - 199. oblique modes are of less effect (have less energy) number of modes increases with frequency.
p111 A table is shown where different frequency bands exhibit how many modes exist for each type of mode.
p112 Reverberation time of the room is shown depending on the frequencies. Reverberation in a room is measured in octave bands. Modes decay at different rates, depending on how absorbing material is distributed in the space. Also beats between neighbouring modes can cause irregular decay. Decay is slow logartithmic.
p115. Each mode has it's own bandwitdh, which is inversely proportional to the reverberation time of the room. The bandwidth of a mode is wider if the room is more absorptive. In studios around 5 Hz Bandwidth.
It is desirable for modes to overlap because (he doesn't say , but I assume they can cancel with each other - maybe it'd be bad because it causes constructive interference)?
p.110 mode identification. The experimenters tie the peaks and valleys of the recording to the table of existing modes created earlier.To see which are prominent.
Modes would boost response if they are in phase and decrease it if they are out of phase. The range of frequencies studied is not that big - i notice. (Up to 322 Hz) Higher frequencies are not comparable to the dimensions of the room, so this makes sense.
Dips in response are narrow. They appear even in carefully designed studios.
p.107 Mode calculations example. When p q and r are integers, modes will exist - creating standing waves. A table identifying all possible modes is included.
p.108 experimental verification. A swept sine wave transmission experiment is described. All room modes terminate in corners in a room. HOW: loudspeaker placed in one low corner. measuring microphone in the diagonal high corner.
Put sine-wave sweep through speaker. The traced recorded response of the microphone is displayed in a figure. Most prominent modes are spikes in the recording. Experiment room is a very absorbent room. (Rev. time = 0.33 seconds)
p.104 There are axial modes
- (involve only two opposite and parallel surfaces)
Tangential modes - involves four surfaces. Oblique modes - involve all surfaces in the room.
Waves vs Rays Waves For low frequencies, in which the wavelength is comparable to the dimension of the room, the ray approach doesn't work. So these are studied as waves.
For higher frequencies, the model in which a sound bounces off with the angle equal to the angle of incidence works.
Wave Acoustics: WE GO INTO MATH B*** > simplified down from 'wave equation'
What are the permissable frequencies based on the modes of the space? See eq. p 106 - folder 'saved images' in 'pictures'. Can tell the frequency of any axial/tangential/oblique mode of rectangular room.
Speed of sound 'c' 1130 ft / sec p q and r are variable LWH are set (dimensions)
If only L participates then we have an axial mode, (or if only W or only H participates) Only one pair of surfaces is involved
If only one zero = tangential mode If no zeros = oblique mode
- (involve only two opposite and parallel surfaces)
p.102 The complexity of the sound dispersion indoors arises because there are several images created by one source. Also, the 'images' can create images of their own! All the reflections contribute to the sound energy at a given point in the room. "The sound at P is built up of the direct sound from S plus single or multiple reflections from all six surfaces"
A room acts as a resonant system, and has various modes of resonance (natural resonant frequency of the space). The fundamental resonant frequency given by the author is 1130/2L (L = distance between two parallel walls).
p101 There are many more reflecting planes indoors, which make sound energy be contained (dissipate slower - stay louder).
An example is given of a source that reflects on a rigid indoor surface, which generates wave fronts. These behave as though they were generated by another source at the opposite side of the wall. (This 'source' is called an 'image').
p100 Sound Indoors is subject to resonance In rectangular enclosures.
STR QT # 5. Arch form. Motivically: Relation of 2. A lot of the phrasing of these motives. Look at the 2nd page - bar 10. Groupings of five.
Motions of 'five' (Rhythmically/ phrasing) tied over.
Look at MV1. Look for motive (similar to start of IV.?) Opening Rhythm - 37 - 59 - 126-159/160 - 193 - 210.
Predominates the Ist movement.
I Sonata form. (Allegro)
> II p.24. Adagio Molto. Ternary. (arch form as well) > III Scherzo and Trio (p.29) Scherzo = p. 29 . Time signature is weird. its an irregular 9 /8 = 4 + 2 + 3 break the time signature.
Bulgarian Style (Influence of folk music).
trio = p.35 divided into 10/8 = 3+2+2+3 It's symmetrical. Smaller scale of symmetry. Not quite stable keep things moving. > IV (p.48) Andante. Ternary (Form relation w II) Slower (tempo) - Relation w/ II Repetition. Dev. of ideas from II with different voicings. Night music w /II. > V FINALE (Allegro Vivace) Sonata Rondo.
A B C B' A' Similar form. Symmetry of form w/ I. (form relations) Allegro.
> 0------------------------------- TEST : Prepare: Study notes: Forms Movements Motives Score
W.b. brown's class.
STR. QT # 4
The Arch form.The first and last movements have connection. The second and fourth have connection. Third one is 'keystone'.
I II III IV V (Symmetrical relationship)
II and IV are both Scherzos. Triple time. Timbral relation. II = instruments have mutes (con Sordino) IV = instruments are pizzicato.
I and V Allegro. Fragmented ideas/ motion.
MOVEMENT WISE I Sonata Form. Exposition (m1-48) Development (m(49 - 91)) Recap(92 - 125) Coda (126- end)
> II Consordino > III p.35 Bartoks night music. Vertical starts. Prominent verticalities. They are double stops. Inversion. > IV Pizzicato. m37. p.42 > V (p.49) Allegro Molto. Vertical. (Bartok-al) Triple/ Quadruple stops. Motivic connections to 1. M. 390 motive shown. See it everywhere first appeareance is Mov 1 measure 7 cello. (Return of the 'agent' motive / or X - agent is derived from X).