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The 01
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intro
Acoustics regulations are national, hence the different legislations. They work with standards,
where they say what you have to achieve to achieve acoustic comfort.
To measure acoustic comfort, they are European standards.
Exam: written, 5 questions 1)
materials: properties of a material 2) theory
question: e.g. explain the MSM system, what is the difference between a double wall or single wall
(answer is 1 A4) 3) multiple choice, 6 questions with 4 possible answers each, no correction for
guessing 4) draw the curve of different systems, sound insulation curve of 20cm concrete wall, 1àm
concrete wall, double wall made out of gipson 5) drawa a complete detail of a construction, e.g. junction
floor and wall, indicate the different materials and thicknesses, so that it complies with thermal and
acoustic regulations
Chapter one: The basics
acoustics are directly linked to the construction materials. So this should be taken into account from
the start. For thermal insulation, the material does not matter much, a layer is added to it. So DO NOT
confuse insulation with acoustic insulation.
Acoustic insulation must be done correctly and everywhere. If the acoustic insulation is
interrupted, this has an impact on the whole.
Acoustics can be 18 dimensional.
Frequency is the tone one hears, there are 18 different frequency bands, each with their own
characteristics. Low – medium – high frequency.
Low frequency passes very easily through structures, very difficult to block. They are a problem
within acoustics. Higher frequency are easy to block. That is why it is difficult to build next to an
airport, for example. These are very strong low frequencies. Best solution to convert a glass building
to an airport, a double glass facade. With an air gap in between.
Airtightness is linked to the high frequencies. If your building is not airtight, the high frequencies will
also pass through the structure. High frequencies come through small holes/slits/…
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Structure born sound = knocking on the board
Airborn sound = praten
Sound is much faster in the structure, the forces of the molecules in a structure are much stronger, in the air they are
much looser.
For example, moving a chair on the floor, sound travels through the material through the building. We don't want the
materials to connect directly, we want disconnections. The floor must be decoupled from the surrounding walls/structure.
Otherwise you will hear the footsteps through the building. Let the floor float with a resilient material underneath. It is
mandatory! We call this a floating screed. (eg PE foil 4mm, rock wool 2cm).
Damping = lowering the amplitude of the vibration, the faster one can damper the better
Airborn sound collides with the wall and becomes structure born sound, in turn passes to the other room and becomes
airborn sound again
Sound is a vibration in time of the air pressure.
The highest point of the wave, we call it the wave front. It doesn't move in that direction, it moves up and down,
compare it to the mexcian wave, people move up and down but don't weigh in the direction of the wave. This is called
the transverse wave.
This is NOT the case with sound
With sound, the particles move in the same direction as the wave!! Longitudinal wave, the motion of the particles are
parallel to the motion of the wave.
Structure born sound has both types of waves, transverse and longitudinal.
Frequency = number of waves that pass at 1 point per second how many
times it goes from plus to minus When one talks, one mixes different
frequencies.
Different vibrations at the same time.
The sound wave can be decomposed into all kinds of different waves, 18 different frequencies.
Spectrum is the decomposition. Sound spectrum, all different tones
An analysis of the sound over time is interesting for larger sounds, airports, factories, …
The bigger the amplitude, the energy it has. = sound pressure
1030hPa
Red line = connect all points furthest from the zero point
Wave length = the distance between the red lines lambda lambda
* f (frequency) = C (celerity, speed of sound)
C Air = 340 m/s
C Liquids = 1400m/s
C Solids = 5000 m/s
T=1/f
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Aantal vibrations/second = frequency f ÿ 1/s=Hz
100Hz is low frequentie, 5000Hz is high frequency
Energy of sound wave = amplitude = sound pressure ÿ Pa sound
pressure = very low pascale max sound pressure that we can
generate is 20Pa = enormously loud, 50m next to an airplane
The left note on a piano is 28 Hz, so it goes 28 times left and right in 1 second. In building acoustics
we are not going to work with all the different types of hertz, we are going to
grouping up
an octave is doubling an octave, each octave consists of 3 bands 1/3 oct. Band, with this we analyze
the acoustics in a building
To analyze a building we use the green frame, starting at 100Hz and ending at 5000Hz.
Our hearing can hear between 25Hz and 20k Hz, we cannot hear ultrasounds (>20k Hz), but bats
and dogs can.
We only analyze the green frame because the sounds outside are blocked far too easily. infrasounds
(<25Hz) whales etc, sounds that go over km and kms (speaking sounds = 500 to 2K HZ)
Rode kader = lage frequentie
lange golflengte: lambda = ongeveer 6m ÿ high
error of measurements, the lower you go, the more difficult it becomes to measure the quantity.
The table would normally continue downwards, but we do not measure those Hz, they do not occur
often
Always better to analyze with 1/3 octave bands, more resolution, more data points (18 points in the green box). If we
analyze with octave bands, we only have 6 points of information. know numbers in green box! Often double
Decibel is the value we use for the sounds pressure level Lp = 10log(p²/p²0) (p =
pascale) (p0 = 2*10^-5) sounds pressure level has no 'unit' (unit is something like
meter, cm, liter, kg,…)
Decibel is not a unit!! It just gives an indication that you calculated that
If you go from 50dB to 60dB, this feels like a doubling facade should drop
at least 10dB
2 boxes of 80dB each gives a volume of 83dB
KNOW
Log X * Y = log x + log y
Log X/Y = log x – log y = n* log
Log x^n x
Log x = A ÿ 10^A = x
10log(10) = 10dB 10log(1) = 0dB 10log(2) = 3dB 10log(4) = 6dB
10log(8) = 9dB
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Exercise: rock concert, people shout at 70dB, total sound pressure level is 120dB How many
people are at the concert?
120dB = 10log (10^7 + 10^7 + … + 10^7)
120dB = 10log (n * 10^7)
120dB = 10log(n) + 10log(10^7)
120dB = 10log(n) + 7*10log(10)
50dB = 10log(n)
10log(10^5) = 50dB
10log(10^5) = 10log(n)
10^5 = n = 100 000 people
If sound is disturbing, it is noise (noise)
- 1 line on the spectrum is artificial anyway
- The rich feeling of a sound comes from the overtones, eg violin, with an expensive violin the
overtones very powerful
Fletch and Munson curves = analysis of our ear
Each curve is called an isophon, iso = equal, phon = sound each
curve represents the same loudness
If one follows the curve, one will experience this as the same loudness, even though the frequency and volume
change
Anything on the 50dB curve will be perceived as 50dB
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