4. Architectural (N).pub - Brüel & Kjær

SOUND, VIBRATION, EDUCATION 

Sound and speech are important 

parts of human life and culture. 

In classrooms, meeting rooms, 

cinemas, theatres, concert halls, 

etc. the design has to be such that 

it is easy to speak and comfortable 

to listen with a high degree of 

intelligibility. These issues of 

sound and vibration belong to the 

professional area of a specialist in 

architectural acoustics. 

Architects, interior designers and engineers 

have a responsibility to design 

functional and safe environments. It is 

very difficult, if not impossible, to meet 

these goals without considering acoustics. 

Acoustics are essential to the functioning 

of almost every type of architectural 

environment, from open offices to 

ARCHITECTURAL 

centres of worship. Some environments 

can even become dangerously loud and 

unsafe for the occupants. 

Engineers are working with sound and 

vibration attenuation in buildings and 

the sound quality in theatres, schools, 

cinemas and other large rooms where 

speech must be received clearly and 

intelligible and where music must be 

received undistorted over the entire 

area. Also important is the proper 

acoustic design of work areas in order 

to obtain a suitably low noise level. 

Building Acoustics 

Building Acoustics is the assessment of 

sound insulation in buildings and building 

elements. The acoustics of buildings 

are important for the well-being of people 

in their homes, workplace or public 

ACOUSTICS 

venues and minimum standards are set 

in the building regulations of each country. 

Whether in private homes, at work, 

or at leisure, human lives are constantly 

affected by an ever increasing number 

of noise sources; televisions, kitchen 

appliances, neighbours, traffic, industry. 

Architectural acoustics 

is concerned with: 

• Building acoustics – sound transmission 

in buildings, effects of new 

building materials 

• Room acoustics – room design, 

speech intelligibility, sound reproduction 

in rooms, sound quality 

• Mechanical equipment noise

Sound, Vibration, Education 

Acoustical measurements are used to improve room acoustics in existing buildings 

predicting the effects of changes, and to predict and optimise the room acoustics 

of planned buildings. 

One method of reducing the pollution is 

to reduce the noise source level. However, 

building acoustics takes another 

approach and examines insulation and 

isolation from the source. Building 

acoustic measurements are used to 

validate new constructions and to troubleshoot 

existing ones. They are invaluable 

when designing or examining noise 

control constructions in buildings. Minimum 

requirements are set in the building 

regulations of each country and 

proper measurements should fulfil relevant 

standards such as ISO 140. 

Mechanical Equipment Noise 

Mechanical systems that serve the 

building are sources of noise and vibra- 

2 

Sound 

Source 

tion, both internally and externally. 

Ventilation, transformers, heating etc. 

are increasingly posing challenges for 

mechanical and structural engineers. In 

many countries tighter regulations and 

more demanding specifications are creating 

challenging conditions for adequate 

noise and vibration control. 

Sound power has become the preferred 

quantity to measure when determining 

equipment noise emissions. It is an absolute 

quantity, dependent only on the 

noise source itself, and independent of 

the acoustic environment. Noise emissions 

can be controlled with treatments 

such as insulation, noise barrier 

screens, low-noise fan blades etc. 

Processing 

Unit 

Receiver 

Room Acoustics 

The way sound is created, propagated, 

perceived, measured and modelled inside 

an enclosed space, is called Room 

Acoustics. The enclosed spaces can be 

dwellings, offices, workshops, factory 

halls, lecture rooms, auditoria, concert 

halls, transportation terminals etc. The 

acoustic measurements are used to 

validate new constructions and to troubleshoot 

existing ones. Reverberation 

Time is the single most important parameter 

used to describe Room Acoustics, 

but in addition, parameters describing 

music quality and speech intelligibility 

are important too. 

Testing Enclosures 

Often basic acoustic conditions are 

simulated in rooms or enclosures like 

anechoic chambers or reverberation 

rooms. An anechoic chamber is a 

shielded enclosure designed to suppress 

internal sound reflections. The boundaries 

absorb nearly all the incident 

sound, thereby, creating essentially 

free-field conditions. A reverberation 

room has hard boundaries and long 

reverberation time, and is especially 

designed to make the sound field inside 

it as diffuse (homogeneous) as possible. 

It can be used for measuring sound 

power and sound absorption coefficients. 

When checking sound insulation in actual 

buildings (field or in situ situations), 

the results are often influenced 

by flanking transmission. In field measurements, 

there may also be trouble 

accessing the site, time constraints or 

background noise. 

For checking constructions such as windows, 

floors and walls, laboratories use 

test suites consisting of two adjoining 

rooms. The test sample is mounted in a 

test opening between the two rooms. 

The two rooms are designed to elimi- 

Investigating the acoustical 

properties of a room, 

a simple clapping of hands 

and listening to the response 

of the room, may give 

a first impression. 

Although it may not be easy 

to describe accurately what is 

heard, this method gives 

an indication of whether music 

would sound pleasant 

or speech would be intelligible 

Brüel & Kjær

ROOM ACOUSTIC PARAMETERS 

There are a large number of acoustical parameters for 

rooms. Their purpose is to describe subjective sound impressions 

in an objective manner. All room acoustical parameters 

can be determined from the room impulse response. 

The room impulse response is the acoustic answer 

of a room excited by a short bang, a Dirac impulse. 

Some basic Room Acoustic Parameters are: 

• Early Decay Time (EDT) 

The EDT parameter is the reverberation time, measured 

over the first 10 dB of the decay. 

• Definition or Deutlichkeit (D50) 

The D50 parameter is the early to total sound energy 

ratio. It is a measure of the intelligibility of a speaker. It 

indicates how well a speaker can be understood by a 

listener in a particular seat of an auditorium. 

• Clarity or Klarheitsmass (C50) 

The parameter of Clarity is the early to late arriving 

sound energy ratio. It is a measure of the clarity of music. 

It is used for large rooms like chamber music and 

concert halls. 

nate the influence of flanking transmission 

– sound that propagates through 

any path other than the test opening - 

and background noise. This ensures that 

the results truly reflect the sound reduction 

of the sample. 

The noise levels in the two rooms under 

investigation are measured and subtracted, 

and the level difference is corrected 

for the influence of the reverberation 

time and background noise 

level in the receiving room. The measurements 

and calculations are made in 

1/1 or 1/3-octave bands and averaged 

over a number of positions in the 

rooms. Finally a single-number index is 

calculated by averaging over all the 

frequency bands. 

Basic Measurements 

The basic architectural acoustic measurements 

that should be dealt with are 

sound insulation, sound absorption, 

reverberation time and sound distribution. 

These measurements will demonstrate 

the effect of room size and 

shape, and acoustic absorption of the 

walls floors and ceilings on the sound 

environment as well as the ability of 

various constructions to attenuate noise 

from one room to another. General 

noise and vibration measurements are 

important because our houses and 

buildings contain ever increasing numbers 

of noise producing installations, 

and ways must be found to attenuate 

their sound emission. 

Soundproofing 

Soundproofing is any 

means of reducing 

the intensity of 

sound with respect 

to a specified source 

and receiver. There 

are several basic 

approaches to reducing 

sound: increasing 

the distance 

between the source 

and receiver; using 

noise barriers to 

block or absorb the 

energy of the sound 

waves, using damping 

structures such 

as sound baffles; or 

using active antinoise 

sound generators. 

Soundproofing affects 

sound in two 

different ways: 

sound reduction and 

sound absorption. 

Sound reduction 

simply blocks the 

passage of sound 

waves through the 

use of distance and 

intervening objects 

in the sound path. 

Sound absorption 

involves suppressing 

echoes, reverberation, 

resonance and 

Architectural Acoustics 

Stage parameters or support parameters (ST), in a variety 

of versions, describe the ensemble conditions or the energy 

fold back to the musicians on stage. They describe 

the ratio between the energy of the reflections and the 

energy of the direct sound. 

• Early Support Early (ST1 or STearly) 

The early reflected energy level relative to the initial 

energy measured at 1.0 m from an omni-directional 

source. It is commonly used to describe the degree of 

the musicians’ mutual hearing. 

• Late Support (STlate) 

The late reflected energy level relative to the initial 

measured at 1.0m from an omni-directional source. It 

describes the degree to which the musician hears the 

late reverberant sound. 

• Total Support (STtotal) 

Total Support describes the support from the room to 

the musicians own instrument. 

Some acoustical parameters are used for rating the understanding 

of speech, among these the Speech Transmission 

Index, STI, and the Percentage Articulation Loss of Consonants, 

%Alcons. 

The acoustical properties of every seat in a concert 

hall may be measured and mapped to ensure the 

best 

Brüel & Kjær 3


reflection. The damping characteristics 

of the materials in the room are important 

in sound absorption. 

Sound Absorption 

It is also important that a student be 

familiar with the measurement of the 

acoustic absorption coefficient of materials, 

as absorbing materials find widespread 

use where noise or sound levels 

have to be regulated. For small samples 

of the material this coefficient can be 

found by means of the Standing Wave 

Apparatus. For measurement on bigger 

samples a different method is used. The 

change in reverberation time of a room 

is measured when a part of a wall in the 

room is covered with the material under 

investigation. 

Sound Insulation 

Sound energy does not remain in the 

room where it is produced, but propa- 

4 

gates throughout the building by any 

available path, intruding into other 

rooms as noise. Each country has its 

own standards of sound insulation in 

buildings, but it is basically measured in 

the same way all over the world. 

Buildings are constructed using many 

elements, and the sound insulation may 

be compromised by defects in materials 

or workmanship. Quite often, the traditional 

measurement will show that the 

sound insulation is not as good as expected 

or required by law. If this is the 

case, a measurement using sound intensity 

can diagnose the fault by showing 

the contribution of each surface 

element to the sound reduction index. If 

a certain weak area is suspected, the 

contribution for that area can be measured 

and checked separately. Or the 

partition can be divided into smaller 

sections and each section checked until 

the fault is found. This measurement 

Sound source and microphone positions 

for measuring airborne sound insulation: 

L1 = Source room level 

L2 = Receiving room level 

B2 = Background level 

T2 = Reverberation Time 

method also eliminates flanking transmission 

(or, by subtraction, provides an 

estimate of its influence), and is ideal 

for detecting and measuring the influence 

of leaks. 

Facade Sound Insulation 

Facade sound insulation is measured 

like sound insulation between rooms, 

except that one "room" is open space. 

The sound level is measured inside the 

Sound pressure levels are used to 

meausre and calculate the sound 

insulation of building facades. 

When measuring sound pressure outside 

and inside a facade simultaniously 2channel 

measurements are required as the 

sound level varies over time. 


eceiving room and outside the façade 

of the building. The level difference is 

then corrected for the influence of the 

reverberation time and background 

noise level in the receiving room. Finally 

a single-number index is calculated by 

averaging over all the frequency bands. 

A loudspeaker source can be used for 

the measurement, providing a choice of 

sound incidence angle. However in practice, 

placing the loudspeaker and getting 

a high enough sound level can be 

difficult. 

Instead of using a loudspeaker source, 

it is sometimes better to use existing 

traffic noise. The measurement then 

relates to actual conditions for source 

type and sound incidence. But since the 

sound level varies over time, the levels 

outside and inside the room must be 

measured at the same time. 

2-channel measurement is essential to 

achieve this. For several measurement 

positions, the average of the outdoorindoor 

level differences is taken rather 

than the difference of the average levels 

in each room. 

As well as being useful for facade sound 

insulation, 2-channel measurement can 

also be used for normal airborne sound 

insulation tasks. By setting up a microphone 

in each room (transmitting and 

receiving), both levels can be measured 

simultaneously. Both microphones can 

then be moved from position to position 

between measurements, or a rotating 

microphone boom can be used for spatial 

averaging in one (or both) rooms. 

Making impulsive excitation measurements 

all that is needed is a Sound 

Level Meter, a tripod and a balloon — 

or an other impulsive source such as a 

starting pistol. 

Reverberation Time 

The sound level is the most important 

parameter to measure when solving 

environmental or occupational noise 

problems. In the open air, or the anechoic 

room, it is often the only measurement 

needed. Indoors, sound reflections 

create standing waves, reverberation, 

which produce natural resonances that 

can be heard as a pleasant sensation or 

an annoying one. 

When sound is produced in a space, a 

large number of echoes build up and 

then gradually decay as the sound is 

absorbed by the walls and air. This is 

most noticeable when the sound source 

stops but the reflections continue, decreasing 

in amplitude, until they can no 

longer be heard. Large chambers, especially 

such as cathedrals, gymnasia, 

indoor swimming pools, large caves, 

etc., are examples of spaces where the 

reverberation time is long and can 

clearly be heard. 

The reverberation time (RT) affects not 

only the understanding of human 

speech or the experience of music, but 

also the level and distribution of sound. 

The problem is usually that the RT is too 

long, but it may also be too short or not 

properly balanced over the frequency 

spectrum. The optimum reverberation 

time depends on the 

use of the room. 

Times about 1.5 to 2 

seconds are needed 

for opera theatres 

and concert halls. For 

broadcasting and 

recording studios and 

conference rooms, 

values below one 

second are frequently 

used. The 

recommended RT is 

always a function of 

the volume of the 

room. 

Reverberation Time 

that is too long will 

muffle speech 

sounds so that one 

sound (or word) cannot 

be distinguished 

from another, making 

it impossible to 

understand what is 


being said. This is critical in classrooms, 

auditoria, churches, theatres and airport 

buildings. On the other hand reverberation 

time that is too short will make 

levels too low at a distance and make 

the sound too "dry". 

The optimal RT for music depends on 

the type of music and the volume of the 

room. Church music requires 2 - 4 seconds 

while concert studios need 1 - 2 

seconds. The RT frequency spectrum 

should be reasonably flat and even. 

Excessive RT will cause the sound level 

Reverberation Decay Curve and Reverberation Time (RT): 

RT is the decay time for sound in a room after the 

excitation stops. It is the time for a 60 dB drop in level, but 

the decay is usually measured over a 10, 20 or 30 dB drop 

and then extrapolated to the 60 dB range 



to rise, causing annoyance or risk of 

impaired hearing. Typical examples are 

concrete stairwells in apartment blocks 

or workplaces with hard reverberant 

walls. 

Reverberation time is usually measured 

using either interrupted noise (pink or 

white) from a loudspeaker source, or 

impulsive noise from a starting pistol. It 

is measured in 1/1 or 1/3-octaves, serially 

or simultaneously. It is usually averaged 

over several positions in the 

room and over several decays in each 

position. Quite often a wide-band average 

is calculated by mathematically 

averaging the RT for a range of frequency 

bands. For critical applications, 

the shape of the decay curve is also 

important. Deviations from the straight 

line can reveal acoustical defects. 

Impact Sound Level 

Impact sound, such as the noise made 

by footsteps, is simulated using a standardised 

tapping machine. The level of 

impact sound insulation can then be 

measured. 

Sound Intensity 

Buildings are constructed using many 

elements, and the sound insulation may 

be compromised by defects in materials 

or workmanship. Quite often, the traditional 

measurement will show that the 

sound insulation is not as good as expected 

or required by law. In this case, 

a measurement using sound intensity 

can diagnose the fault by showing the 

contribution of each surface element to 

PC software may simulate or model the interior acoustics of 

buildings where, from the geometry and properties of surfaces, 

acoustics can be calculated, illustrated and finally 

listened to. 

6 

the sound reduction 

index. If 

a certain area is 

suspected to be 

weak, the contribution 

for that 

area can be 

measured and 

checked separately. 

Or the 

partition can be 

divided into 

smaller sections, 

which are each 

checked until the fault is found. This 

measurement method also eliminates 

flanking transmission (or, by subtraction, 

allows to make an estimate of its 

influence), and is ideal for detecting and 

measuring the influence of leaks. 

Sound 

Distribution 

There is a host of specialized means for 

dampening reverberation ranging from 

special purpose 

rooms such as 

auditoria, concert 

halls, dining areas 

and meeting 

rooms. Many of 

these techniques 

rely upon material 

science applications 

of constructing 

sound baffles 

or using sound 

absorbing liners 

for interior spaces. 

Sound distribution 

measurements are 

especially important 

in theatres 

and cinemas or 

other places 

where sound must 

be reproduced 

clearly over a 

large area. Such 

measurements are 

made by using a 

loudspeaker or a 

public address 

Auralisation combines visual and aural presentation and 

allows sound to be replayed in a model. This gives a fairly 

accurate impression of how the design affects music, 

speech or other acoustic signals — a very powerful tool for 

the designers, architects and engineers. 

(PA) system for excitation and then 

measuring the sound level, which 

should preferably be uniform, at various 

frequencies and at various points in the 

room. 

Modelling 

In acoustic design laboratories, investigations 

are often carried out with special 

software for this purpose. Previously 

investigations were mostly performed 

on model rooms, increasing the frequency 

of the exciting sound in the 

same ratio as that between the size of 

the model and the actual room. Today 

software can simulate the interior 

acoustics of buildings allowing reliable 

predictions in modest calculation times. 

From the geometry and properties of 

surfaces, acoustics can be calculated, 

illustrated and even listened to. 

This calculation method is ideal for the 

prediction of large-room acoustics such 

as concert halls, opera houses, foyers 

underground stations, airport terminals, 


When a sound source in a room is producing noise that is 

intensity modulated by a low frequency sinusoidal 

modulation of 100% depth, the modulation at the receiver 

position will be reduced due to room reflections and 

background noise. 

The Modulation Transfer Function (MTF) describes to what 

extent the modulation m is transferred from source to 

receiver, as a function of the modulation frequency F, 

which ranges from 0.63Hz to 12.5Hz. 

industrial workrooms and various auditoria. 

Similar software has been developed 

for noise prediction of large machinery 

in industrial environments. An 

auditory representation or "imaging" of 

data, an auralisation, can simulate 

sound in the model making it possible to 

actually hear how a specific design will 

affect music, speech or other acoustic 

signals. 

Speech Intelligibility 

In many daily life situations it is important 

to understand what is being said, 

for example over a loudspeaker system, 

and to be able to react to acoustic signals 

of different kinds. However speech 

transmitted across a room by a person 

or a public address system is never received 

at a listening position as an exact 

replica of the original signal. 

Speech Intelligibility is usually expressed 

as a percentage of words, sentences 

or phonemes (speech sounds 

making up words) correctly identified by 

a listener or group of listeners when 

spoken by a speaker or a number of 

speakers. It is an important measure of 

the effectiveness or adequacy of a communication 

system or of the ability of 

people to communicate in noisy environments. 

Intelligibility tests are time 

consuming and consequently expensive, 

but often, at least in the more straightforward 

cases, it is possible to estimate 

speech intelligibility from physical measurements 

and to dispense with the need 

for listeners and speakers. 

Relation between Speech Intelligibility 

Index and speech intelligibility. 

STI SPEECH 

INTELLIGIBILITY 

0.00 - 0.30 Bad 

0.30 - 0.45 Poor 

0.45 - 0.60 Fair 

0.60 - 0.75 Good 

0.75 - 1.00 Excellent 

Speech intelligibility 

is adversely 

affected by 

noise. Most of 

the acoustical 

energy of speech 

is in the frequency 

range of 

100-6000 Hz, 

with the most 

important cuebearing 

energy 

being between 

300 and 3000 Hz 

Speech interference 

is basically 

a masking process, 

in which 

simultaneous 

interfering noise 

renders speech 

unintelligible. 

Environmental 

noise may also 

mask other acoustical signals that are 

important for daily life, such as door 

bells, telephone signals, warning signals 

and music. 

Speech intelligibility in everyday conditions 

is influenced by speech level, 

speech pronunciation, speaker to listener 

distance, sound level and other 

characteristics of the interfering noise, 

hearing acuity and the level of attention. 

Indoors, speech communication is 

also affected by the reverberation characteristics 

of the room. 

To achieve full sentence intelligibility for 

listeners with normal hearing, the signal 

to noise ratio - the difference between 

the speech level and the sound level of 

the interfering noise - should be at least 

15 dB(A). 

Speech measurements can be carried 

out through an artificial mouthdirectional 

loudspeaker sound source or 

through direct injection into a sound 

system, taking into account the impact 

of background noise. 

The standards of the International Electrotechnical 

Commission (IEC) and the 

International Standards Organization 

(ISO) already incorporate objective 

methods for evaluating speech intelligi- 


bility. Evaluation of speech intelligibility 

may use one or more of several methods 

cited in the standards, either objective 

and subjective. 

Speech Transmission Index (STI) is an 

objective measure indicates the quality 

of the transmission of speech. The STI 

value varies from 0 = completely unintelligible 

to 1 = perfect intelligibility. On 

this scale, an STI of at least 0.5 is desirable 

for most applications. It is used 

with reference to public address systems 

as it takes into account the noise 

from external and internal sources. External 

sources are, for example, the 

background noises at a train station. 

Internal sources are, among other 

things, the noise of amplifiers and the 

harmonic distortion of loudspeakers. 

Basic STI-parameters are: 

• STI, Speech Transmission Index 

• STIPA, STI for Public Address Systems 

• RASTI, Room Acoustics STI 

• STITEL, STI for Telecommunication 

Systems 

Another speech intelligibility parameter 

is Percentage Loss of Consonants, 

%ALC. 



8 

ROOM ACOUSTICS QUALITY MEASURES 

• Transparency 

• Definition – how well successive 

tones or vowels are distinguishable 

and not “smeared” out in time 

• Spaciousness – experience of a 

large enclosure 

• Intimacy – to what extent it seems 

the orchestra is playing in the same 

room as the listener and not behind 

a sheet of glass 

• Sound colouration – emphasis of 

certain frequencies 

• Speech intelligibility 

• Liveliness – related to the reverberation 

time 

• Loudness 

• Feedback – how well performers 

on stage can hear themselves and 

each other 

NIC - Noise Isolation Class 

A single number rating derived in a 

prescribed manner from the measured 

values of noise reduction between two 

areas, spaces or rooms. It provides an 

evaluation of the sound isolation between 

two enclosed spaces that are 

acoustically connected by one or more 

paths. 

NRC - Noise Reduction Coefficient 

A single-number rating system used 

to compare the sound-absorbing characteristics 

of building materials. A 

measurement of the acoustical absorption 

performance of a material, 

calculated by averaging its sound absorption 

coefficients at 250, 500, 

1000 and 2000 Hz, expressed to the 

nearest multiple of 0.05. 

NR - Noise Reduction 

The numerical difference, in decibels, 

of the average sound pressure levels 

in two areas or rooms. A measurement 

of “noise reduction” combines 

the effect of the sound Transmission 

Loss performance of structures separating 

the two areas or rooms, plus 

the effect of acoustic absorption present 

in the receiving room. 

Consonants play a much more significant 

role in speech intelligibility than 

vowels. If the consonants are heard 

clearly, the speech can be understood 

more easily. Since %ALC expresses loss 

of consonant definition, lower values are 

associated with greater intelligibility. 

Acoustic Quality 

By measuring the acoustics in a room, it 

is possible to predict how listeners will 

judge the acoustic quality of the room. 

For instance, it is possible to determine 

whether the speech intelligibility in a 

church or railway station is sufficient or 

how many loudspeakers are needed to 

raise the speech intelligibility to a satisfactory 

level. Other examples include 

measuring lateral reflections, which are 

important for an agreeable spaciousness, 

and the reverberation time as a 

measure of liveliness. 

All room acoustic parameters can be 

determined from the room’s response to 

an impulsive signal. These so-called 

impulse responses can be viewed in 

many ways, and help, for example, to 

find flutter-echoes in certain frequency 

bands and the walls responsible for 

these echoes. 


Ray or Geometrical Acoustics 

At higher audio frequencies, sound may 

be considered to travel in straight lines, 

or rays, in a direction normal to the 

wave front. It is a fairly simple and effective 

way to consider the propagation 

of sound. 

Wave theory is based on the study of 

wave motion within three-dimensional 

enclosures. It requires the establishment 

of boundary conditions which 

mathematically describe the acoustical 

properties of the walls, ceiling and other 

surfaces in the room. 

The concept of rays has not played the 

same role in the study of sounds as in 

optics. The reason for this is that the 

wavelengths of most audible sounds are 

large compared to the obstacles in the 

path of the sound. Consequently, 

sounds audible to the ear do not travel 

in a straight line or nearly straight line 

paths; they bend around corners and fill 

almost all of the spaces into which they 

are directed. The difficulty involved in 

determining these boundary conditions 

for irregular shapes and rooms containing 

furniture means that true analysis is 

possible for only a small number of idealised 

situations. Although the practical 

application of wave theory is quite limited, 

an understanding of its basis is 

essential in order to appreciate many of 

the problems which arise in room 

acoustics. 

When employing wave theory, a room is 

considered as a complex resonator possessing 

many normal modes of vibration 

which are excited when a sound source 

is introduced to the room. The acoustic 

energy generated by the source acts to 

excite these room modes with the re- 

Acoustic Faults due to Room Geometry 

Most acoustic faults result from the 

geometry of the enclosure. A simple 

geometric analysis can correct most of 

these at the design stage. Some of the 

more common faults are: 

Spurious echoes 

Occur when a strong reflection of the 

original signal can be clearly discerned 

by the listener. This is simply a matter 

of looking at the internal envelope of 

the enclosure and checking for possible 

sound paths which reflect off a sequence 

of large, highly reflective surfaces. 

Picket fence echo 

A result of evenly spaced reflection 

1 

α ) × Air( 

l) 

× ∆Diffr( 

A, 

l, 

cos( θ )) × DirFact( 

Az, 

El) 

× 

4πr 

n 

I n = P n ( 1 s ( )) ( 1 

s s ∏ − θ × −δ 

s 

s= 

1 

sulting sound energy residing in the 

standing waves established in the room. 

The characteristic frequencies of these 

vibrations depend on the room size and 

shape, whereas the damping or absorption 

of the resulting waves depends 

upon the boundary conditions. Thus, 

every room imposes its own characteristics 

on to the sound source present. 

If the dimensions of a room are large 

compared to the wavelength, then 

sound waves may be considered in 

much the same way as light rays are 

treated in optics. This situation frequently 

occurs in architectural acoustics, 

especially in large auditoria. Sound 

rays are reflected from hard planar 

walls in accordance with the laws of 

reflection, i.e.: the incident ray, the 

reflected ray and the surface normal all 

paths, such as the rows of raised seating 

in amphitheatres and the evenly 

spaced curves of compressed fibre 

fencing. Depending on the number of 

steps and the path difference, such 

surfaces can produce a definite pinging 

sound when struck by an impulsive 

sound source. If d is the distance between 

successive steps, then the frequency 

of this ping is given by Fpfe = 

(c / (2d)) where c is the speed of sound 

in air. 

Flutter echo 

Occurs when both the source and receiver 

are between a pair of hard, parallel 

surfaces. Some portion of the 

sound emitted by the source will get 


lie on the same plane and the angle of 

incidence is equal to the angle of reflection. 

In the same way, sound rays incident 

on a curved surface will be either 

focused (for concave) or dispersed (for 

convex). 

The concept of a sound ray and the 

geometrical study of sound ray paths 

play an important role in the design of 

large rooms and auditoria, enabling 

troublesome echoes and flutter effects 

to be detected and dealt with at the 

design stage. A limitation of the geometrical 

approach is that usually only 

primary and possible secondary reflections 

can be studied before the sound 

ray being followed becomes 'lost' in the 

reverberant sound field and, in most 

enclosures, it is restricted to frequencies 

of 500 Hz and above. 

'trapped' between the two reflective 

surfaces and will oscillate back and 

forth, being quite slow to decay. The 

listener will perceive this as a 

'fluttering' noise. If the walls are a distance 

d apart, then the frequency of 

this flutter can be found in the same 

way as picket fence echo. 

Dead spots 

These can occur at positions which are 

far from reflecting surfaces and which 

receive sound only after it has passed 

over an absorbent surface. For example, 

at the rear of a gently raked theatre 

or cinema where the sound must 

pass over the audience and ceiling reflections 

are blocked by a balcony. 

Brüel & Kjær 9 

1 

2


Fundamental measurements 

Sound Pressure Level • • • • 

Reverberation Time • • • • 

Background Noise • • • • • 

Impact Sound Level • • 

Flanking Transmission • • • 

Transmission Loss Factor • • • 

Application 

Absorption Coefficient • • • 

Sound Distribution • • • • • 

Scattering Coefficient 

Sound Intensity • • • • • • 

Time Averaging • • • • • • • • 

Spatial Averaging • • • • • • • • • 

Advanced measurements 

STITEL • 

STIPA • 

STI • • 

ALCON • • 

RB Scattering Coefficient • 

Quick Estimate • • • • • • 

Global Estimate • • • • • • 

Impulse Method • 

Interrupted Noise Method • 

Other techniques 

10 

Architectural 

Acoustics 

Matrix 

Measurement 

/Application 

Airborne Sound Insulation 

Façde Sound Insulation 

Impact Sound Insulation 

Reverberation 

Troubleshooting Sound Insulation 

White Noise • • • • • • • • • 

Pink Noise • • • • • • • • • 

MLS • • • • • • • • 

Sweep / Swept Sine • • • • • • • • 

Speech Intelligibility 

Vibration Isolation / Damping 

Intensity Mapping 

Sound Source Location 

Noise Source Ranking 

Room Acoustics Modification 

Spaciousness 

Transparency 

Definition 

Sound Coloration 

Liveliness 

Room Acoustics Modelling 


Architectural Acoustics Laboratory 

Requires ”Basic Sound and 

Vibration Laboratory” and 

”Enhanced Sound 

Laboratory” 

Features: 

• Building Acoustics 

• Room Acoustics 

• Reverberation Time 

• Room Acoustics Modelling 

• Acoustic Material Testing 

Building Acoustics and Building Material 

Testing (Field and Laboratory) 

2270-K-001 Dual Channel Building Acoustics 

System including Type 2270-K, 

OmniPower Sound Source and Amplifier 

2 x 2734-B Power Amplifier with wireless 

receiver 

2 x 4292 OmniPower Omnidirectional Sound 

Source (tripod and loudspeaker cable 

included) 

3207 Tapping Machine for impact insulation 

assessment 

EN-2228 Laboratory measurement of vibroacoustic 

properties of material - Extended 

ISO set 

SENNEHEISER Kfhkdlkofmofk Kfhkdlkofmofk 

• Material Transmission Loss 

• Room Qualification 

• Sound Propagation 

• Sound Absorption 

• Sound Insulation 

3 x UA-1426 Mounting Kit for Wireless 

Transmission for 2260D/2716/4296 requires 

receiver/pocket transmitter 

UA-1476 Wireless Remote Control for 3207 

3923 Rotating Microphone Boom 

4224 Portable Battery & Mains Powered 

Sound Source 

7758--N PULSE Material Testing, Nodelocked 

License 

4206-T Transmission Loss Tube Kit (50 Hz - 

6.4 kHz) 

2 x M1-7758-N Annual Software Maintenance 

and Support Agreement for 

PULSE Material Testing, Node-locked 

License 


• Sound Source Location 

• Noise Source Ranking 

• Speech Intelligibility 

M1-3560-005 PULSE Software Agreement 

for Educational Partners, 5 years 

Room Acoustic Modelling 

7837 ODEON Combined: Room acoustics 

Modelling Software version 9.2, MS1 

contract included 

2 x 7837-X-300 Extra Odeon 7837 combined 

license, MS1 contract included 

Computers and other accessories 

3 x 7201-D-GB2 Dell High End Notebook w 

Office Pro 

4128-C Head and Torso Simulator 


Sound and Vibration 

in Education 

Sound and vibration reach into almost every aspect of everyday life. In 

every sector of industry, in every part of the scientific community and in 

all aspects of daily life, people are working with challenges of sound and 

vibration. Industry, trade and public services demand new solutions, 

more knowledge and more education. 

Effective sound and vibration solutions in modern society require engineering 

education providing a fundamental understanding of the generation, 

transmission and radiation mechanisms associated with sound and 

vibration: Multi-disciplinary knowledge ranging from applied mathematics 

and mechanics to sound perception and signal processing. 

Apart from an understanding of theories, students of engineering and 

physics require knowledge of the techniques of testing and measuring 

used in industry and research laboratories. Measuring and testing that 

can prove the validity of calculations, simulate practical environments 

and create models, and allow experiments where calculations are not 

possible. 

In technical colleges and universities, electronic measuring instruments 

are used in demonstrations, exercises, and student projects. They also 

provide the teacher with an indispensable tool to demonstrate the validity 

of theory taught. Measuring equipment is essential to modern education 

and learning. Appropriate and flexible sound and vibration laboratories 

are needed. From the basic laboratory to advanced and specialised 

solutions — Brüel & Kjær is a world leading manufacturer and supplier. 

Sound and Vibration Laboratory Packages 

From basic laboratory to advanced solutions 

The Brüel & Kjær publication series ”Sound, Vibration, Education” 

includes seven documents describing measurements, applications and 

laboratory packages in different fields of sound and vibration. 

Each document describes a particular line in engineering education or a 

special focus area in sound and vibration and lists the matching set-up of 

Brüel & Kjær products — the experimental laboratory equipment suitable 

for these specialised purposes: a laboratory package. 

HEADQUARTERS: Brüel & Kjær Sound & Vibration Measurement A/S · DK-2850 Nærum · Denmark 

Telephone: +45 77 41 20 00 · Fax: +45 45 80 14 05 · www.bksv.com · info@bksv.com 

SOUND LEVEL METERS 

TRANSDUCERS 

ANALYSERS 

TEST AND MEASUREMENT 

SOLUTIONS

4. Architectural (N).pub - Brüel & Kjær

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