[Reader-list] the space interlude/corridor spaces/6th posting

[Zeenath Hasan]

dear sayandeb

thank you for your post
here are two practitioners/ researchers theorising the  
phenomenological aspect of sound in lived spaces,

Brandon LaBelle, http://www.errantbodies.org/labelle.html
Jacob Kreutzefeldt, http://www.errantbodies.org/sound_house.html

bests,
zeenath

..
Zeenath Hasan
CULTURAL PRODUCER  /  MEDIA ARTIST

Copenhagen +45 3191 5499
Helsinki +358 45 652 3833

w w w . z e e n i a c . n e t


On Sep 27, 2007, at 8:54 PM, sayandeb mukherjee wrote:

> i regret for the delay for it took time to prepare
> scientific and theoretical explanations on
> acoustics/acoustic responses of different kinds of
> corridor spaces
>
>
> 6TH POSTING
>
>
> BEFORE dealing with the psychoacoustics of these
> spaces it is important to give an account on the
> acoustic behavior or acoustic responses of these
> spaces.
> Corridors are generally interspersed with doors which
> are once again the interfaces of individual
> flats/rooms/enclosures. The sounds that are emanated
> from the indoors (i.e. the rooms or flats) are
> transmitted to some extent through the walls and
> closed doors to reach this common passage. If the
> doors are open, like it remains in colleges, hospitals
> or mostly public spaces/unprivatized spaces, the sound
> from the source directly reaches the passage. But a
> person who’s passing through the passage and is away
> from the door also hears a portion of the incidental
> sound. That is due to reasons – a. a portion is
> transmitted through the walls and b. a major portion
> is diffracted at the ends of the opening of the door.
> Unlike optical shadow, sound shadow is not so defined
> because of the diffractive properties of sound. Refer
> to the figures drawn (will be posted later). It shows
> how a listener, in spite being away from the room, is
> able to hear sound sourced from inside the
> rooms/enclosures.
> The diffractive properties differ throughout the
> entire audio-frequency spectrum. A low-frequency / low
> mid-frequency content in the sound is diffracted more
> than the high / high mid-frequencies. Also, the high
> frequency sounds are more directional than the low
> frequency sounds. Hence the high frequency sounds
> generally don’t reach the ears of the listener who is
> off / oblique from the direction of the source. The
> low frequency-content of the source gets more
> scattered and diffracted while reaching the ears of
> the listener distant from the direct opening of the
> room. As the high-frequency content is depleted a
> person perceives a booming or wooly sound of a speech
> when he traverses in the corridor-like-spaces.
> We construct four cases:
>
> CASE A:  Where the corridor is having one side open
>
> This scattered diffracted and transmitted sound passes
> away to the opposite opening unreflected or
> unobstructed. In these kinds of spaces, not much dense
> sound-field is generated.  The sound generated from
> the space doesn’t confront much
> reflections/refractions (for there is no substantial
> reflective surface) and the listener hears it almost
> dry, or without being reverberated. This substantially
> detriments the depth of the sound-field and hence the
> space appears acoustically colorless. In this single
> loaded corridor the property that is distinguishable
> from the double-one is the mammoth interference of the
> extraneous sounds – the environmental sound elements
> that give a characteristic spatial definition to the
> corridor space. In the single loaded corridors, that
> can be called a verandah, the visual attributes along
> with ambient audible qualities provides a positional
> reference to the space. So the listener is not thrown
> into an abstract field with no clues of time and
> space, whereas he is well posited for the re-assurance
> of the environmental associativity. Even if there are
> reflections, reverberations of the sounds generated
> from verandah that would immensely get masked by the
> ambience coming from the open side and the audio
> qualities doesn’t become audible until and unless gets
> diminished to a considerable extent. So when this
> ambience gets diminished, the sonic-scape   of this
> veranda takes a different look/shape. The depth of the
> audio field increases and there happens a resurgence
> of the sounds and its reflections generated from the
> verandah. This happens in the late hours of the night,
> for example in the case of a college which is located
> beside a road with heavy traffic plying during the
> daytime, the acoustic details of the traffic gets
> prominence with the redemption of the traffic during
> night and attains more clarity with the fall of the
> night and as silence prevails in the surrounding. The
> incidental sounds like footsteps with its length
> stretched throughout the verandah, door banging, some
> people talking standing in the verandah acoustically
> establishes that it is a single loaded corridor.
>
> CASE B:   Where the corridor space is having walls on
> both the sides
>
> As discussed earlier, that the sounds generated from
> inside the rooms/enclosures/flats connected to this
> common interface – the corridor undergo 1.transmission
> through the walls of the corridor, 2.diffraction from
> the openings of the rooms (like doors, windows)
> thereby penetrating this double loaded corridor space.
> A major portion of the generated sound remains inside
> the room as they are reflected/bounced back to the
> other walls of the room getting absorbed therein. The
> sounds leaking out from the room, after losing most of
> its high frequency content (as stated earlier) and a
> portion of it being transmitted and diffracted reaches
> the opposite wall of the corridor which acts as a
> reflective surface. The intensity of reflection
> depends on three factors primarily – (i) the intensity
> of the source, (ii) the dimension of the corridor and
> (iii) the reflective properties of the walls.
> The intensity of reflection is directly proportional
> to the intensity of the source and the reflective
> qualities of the wall and is inversely proportional to
> the distance between the walls. The louder the source,
> the more it will undergo reflections from the walls.
> Generally, the sounds are not so impulsive or loud
> (like an explosion) to sufficiently generate higher
> order images.
> Since the sound is being generated at a considerable
> distance from the passage, inside the room and also
> because sound is inversely proportional to the
> distance, its energy content gets appreciably
> diminished by the time it reaches the common space.
> Hence, the reflected image of this leaked out sounds
> is too weak to reach the opposite wall of the
> corridor.
> The possibility of second order images, (i.e.
> reflected images from reflected sounds) further
> reduces as the distance between the corridor walls is
> increased. With the increase in the dimension of these
> spaces, for the sounds arriving from these openings,
> its early reflections from the surfaces will take some
> time to get depleted and a considerable time elapses
> before the sound content decays to an imperceptible
> level.
> The corridor spaces are mostly comprised of masonry
> walls with cemented surfaces sometimes coated with
> plaster of paris. When it is uncoated with plaster of
> paris then the texture is not so regular to produce
> specular reflections like that of light and the
> surface is porous enough to render diffusion for
> certain range of the audio spectrum.
> [About Specular reflection – specular reflection is a
> mirror-type reflection, similar to the reflection of
> light from a mirror.  In specular reflection, the
> incidental sound beam is reflected off the reflecting
> surface as per Snell’s law. For specular reflection to
> occur, the surface irregularities in the texture
> should be smaller than wavelength of sound. And higher
> the frequency of the sound wave, the smaller will be
> its wavelength. So, with surface irregularities of
> smaller dimension specular reflection of high
> frequencies with small wavelength will be affected
> more than low frequencies.
> About Diffuse reflection – in diffuse reflection, the
> incidental sound is reflected equally in all
> directions causing a uniform scattering of sound. For
> diffuse reflections, the reflecting surface must be
> irregular and heavily textured. The dimensions of the
> irregularities should be not less than or
> approximately equal to the wavelength of sound. Thus,
> for a wall to provide diffuse reflection at 1 kHz
> (?=wavelength approximately equal to 0.3m or 1ft), its
> surface irregularities should be of the order of 0.3m
> (1ft). Surface irregularities of a few cm will provide
> specular reflection at 10 kHz frequency. Now a sound
> with a frequency of 100 Hz will have wavelength
> approximately 3m or 10ft. With this wavelength, the
> sound will be specularly reflected from a wall with
> surface irregularity of dimension 0.3m or 1ft. In
> other words, a 100 Hz sound will not see these
> irregularities and the wall will behave as a smooth
> wall. On the other hand, a 1 kHz sound will be
> diffusedly reflected from this surface. At a frequency
> of 10 kHz, with a wavelength of approximately 30mm
> (nearly 1 inch), each individual irregularity will be
> large enough to function as an independent reflector.
> Therefore, sound will be specularly reflected from
> each surface irregularity thereby providing some
> scattering of sound (since the surface irregularities
> are oriented in different directions). ]
> For small little surface irregularities like it
> remains in corridor walls in most cases, the high and
> somewhat high-mid frequencies of the sound spectrum
> are more diffused than the lower end. This attenuates
> the harsh reflections of the higher end (or mutilates
> the acoustic glare caused by the reflectivity of the
> walls). Because of this diffusive property of sound, a
> portion of it is evenly scattered thereby reducing its
> energy so that it doesn’t reach the opposite wall of
> the corridor after being reflected. And as mentioned,
> the high frequencies contained in the sound will be
> more diffused than the lower thereby making the sound
> more muffled giving space to the boomy lower
> frequencies to get partially or fully specularly
> reflected and travel in the walls of the corridor. The
> residual portion of this leakage from individual
> openings gets absorbed in the wall. Now the quantity
> of absorption depends on the absorption coefficient of
> the walls
> contd.
> [Absorption coefficient determines the strength of
> absorption of the walls; this provides a value needed
> for the qualitative analysis of the acoustic materials
> used for acoustic treatment of studios, theatres,
> auditoriums.]
> Mostly for corridor walls, unless it is a special
> case, the walls are made of concrete with a required
> number of coatings and sometimes for affluent/well off
> places it would probably be finally coated with
> plaster of paris. The concrete surface with coarse
> texture and no plaster will have an average absorption
> coefficient 0.34 (0.36 at 125Hz, 0.31 at 500Hz, 0.29
> at 1 kHz, 0.25 at 4 kHz) partially absorbing the
> incidental sound thereby evading unusual reflections
> to happen. The absorption by these kind of walls are
> better than marble or glazed tiles or metallic
> surfaces which will have acoustic glare thereby
> rendering unusual fluttering of the sound and
> sometimes discrete early reflections to happen which
> would be very annoying for the listener.
> When the sound source or the sound-activity is
> happening ‘in’ the corridor then, 1.the intensity of
> the sound would be more in comparison to the sounds
> generated from inside the room and meeting this space.
> When the observer himself is the acoustic centre and
> if he makes an appreciably loud sound, then the sound
> wave instantaneously reaches the opposite walls of the
> corridor. Here the two parallel walls act as two
> parallel reflectors. As we know, when there are two
> parallel reflectors, we will obtain an infinite number
> of images of the source since each image works as a
> source for the other reflector. This may be confirmed
> by standing between two parallel mirrors; an infinite
> number of the self will be seen.
> This is simply another way of stating that the sound
> will be reflected back and forth between two parallel
> reflecting walls infinite number of times before
> exhausting to inaudibility.
> Now imagine a sound source(s) located between two
> reflective parallel walls 15m apart, as shown in
> FIGURE (to be posted later). Obviously, this situation
> produces an infinite number of images of the source.
> The first-order images, image I1 and I2, are behind
> wall 1 and wall 2 respectively. The second order
> image, I12, is the image of I1 and is formed behind
> wall 2. I21 is the image of image I2 behind wall 1.
> Similarly, I121 and I212 represent third order images
> and so on.
> If we determine the distance between images, we find
> that the distance between successive order images
> increases by 30m – twice the distance between walls.
> Thus, the first order images are 30m apart, second
> order images are 60m apart, and third order images are
> 90m apart and so on.
> Since the speed of sound is 344m/s, the time gap
> between each successive reflected sound will be
> 87milliseconds. This, according to the Haas effect,
> will produce echoes. Since these echoes recur after a
> regular interval of 87 milliseconds, they produce a
> flutter effect; hence this phenomenon is called
> flutter echoes.
> If the distance between walls were 5m, successive
> order images would be 10m apart. Therefore the time
> gap successive reflections would be 10/344, i.e. 29
> milliseconds, which (according to the Haas effect)
> should not be perceived as echoes. However, the
> flutter is heard all the same. The reason lies on our
> ears being extremely sensitive to periodic repetition
> of sounds
> ..contd.
>
>
> thanking you
>
> sayandeb mukherjee
>
>
>
>
>
>
>
> SAYANDEB MUKHERJEE
>   FT#308, SUBBARAJU TOWERS,
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>
>
>
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