A

Write-up

On the

Reverberation in lecture theatresFEDERAL UNIVERSITY OF TECHNOLOGY AKURE,

AKURE, ONDO STATE

NIGERIA.

By

ARC/09/7358 AKINWALE OYINLOLUWA B

ARC/09/7361 OBONGIFREKE AKPAN

Submitted to

THE DEPARTMENT OF ARCHITECTURE

SCHOOL OF ENVIRONMENTAL TECHNOLOGY,

FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE, ONDO STATE.

IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF BACHELOR OF TECHNOLOGY IN ARCHITECTURE

Supervised by

PROF. OLU OLA OGUNSOTE.

JULY 2014

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TABLE OF CONTENTS

COVER PAGE

TABLE OF CONTENTS

ABSTRACT

CHAPTER ONE

Broad –spectrum knowledge of reverberation

1.0 INTRODUCTION

1.1 reverberation and the art of architectural acoustics

1.2 reverberation time

CHAPTER TWO

2.0 REVERBERATION IN LECTURE THEATRES

2.1 reverberation in small lecture theatre, FUTA.

2.2 Reverberation in big lecture theatre, FUTA

3.0 SUMMARY

4.0 REFERENCE

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ABSTRACT

This paper describes our experience with lecture halls/ theatres with regard to the

reverberation within the halls, sound reinforcement and audio frequency induction loops for

persons with hearing impairment.

The optimum reverberation time and geometrical conditions for lecture rooms are well

known. Recent research basically confirms this knowledge but indicates the need for shorter

reverberation times. However, many existing lecture halls do not fulfill these requirements.

Furthermore, too many existing reinforcement systems are deficient in a number of aspects.

This write-up makes a comparison of the level of reverberation in three lecture theatres,

precisely, SMALL LECTURE THEATRE AND BIG LECTURE THEATRE, Federal University

of Technology, Akure, Ondo State, as well as the in finishes and construction materials, furniture

type and arrangements, in other to give an overall analysis of the perceived acoustic properties

of the hall.

In addition, the write up is expected to propose ways of improving the acoustic properties

of the hall with respect to the outcome of the analysis carried out in other to create a long

reverberation time free zone and an acoustic friendly environment for the users.

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CHAPTER ONE

Broad – spectrum knowledge of reverberation

1.0 INTRODUCTION

The question of the reverberation in lecture rooms has been researched internationally in

recent years. The influence of long reverberation time on the students and teachers, for example,

was investigated in an important study by Wallace Sabine (1868-1919).

In various countries the latest knowledge is being incorporated into the respective

standards and recommendations. Of course, good acoustics are also important in lecture halls.

The background noise must be minimized and the room form and materials must be designed so

as to support the acoustics in order to provide high speech intelligibility.

Since the number of seats in a lecture hall is generally higher than in a small classroom

the achievement of good speech acoustics is more complex. In addition, a sound reinforcement

system fulfilling demanding criteria is usually required. Actually, the basics of good acoustics

for lecture halls are well known.

Nevertheless noisy lecture halls with excessive reverberation, echoes or flutter echoes

are common. The speech intelligibility is correspondingly poor. Although high quality

components are generally employed for the sound system, the results, unfortunately, are still

unsatisfactory. Often the specification and reinforcement concept do not adequately consider the

interplay between room and electro acoustics.

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1.1 REVERBERATION AND THE ART OF ARCHITECTURAL ACOUSTICS

In 1895 Harvard University, that school situated on the Charles River, opened its Fogg

Art Museum. This wonderful building, still much used today, contained an equally wonderful,

large lecture hall. Audiences flocked in, eager to experience intellectual enlightenment in

beautiful new surroundings. But there was a large, ugly fly in this intellectual ointment: No one

could understand any of the lectures that were given in Fogg lecture hall. And it wasn't because

the lectures were too esoteric, or because the lecturers mumbled into their beards, or because the

students were too distracted. The problem was acoustics and hearing. For help, Harvard turned to

one of its own, ( , then a 27 year-old Assistant Professor of Physics. To that point in his career,

Sabine had distinguished himself primarily through his teaching; research productivity was not

his strongest suit. Even though Sabine had not previously worked with this sort of problem, his

writings show that he was a remarkably quick study and a truly dedicated scientist. His published

work also provides a model of good, clear scientific prose. After diagnosing and then solving

Harvard's problem with the Fogg lecture room, Sabine devoted the rest of his career to the new

field that he had virtually created in the process: architectural acoustics.

First, Sabine noted that when anyone spoke in the Fogg Museum lecture room, even at

normal conversational levels, the sound. of his or her voice remained audible in the room for

several seconds thereafter. You can imagine how difficult this made it to comprehend what the

speaker was saying. The speaker's words first reached the listener directly. Then several,

successive acoustic "copies" of the speaker's words reached the listener. These "copies" were

produced by strong sound reflections from various hard surfaces in the room. If enough surfaces

produced strong, audible reflections, listeners would be bombarded by several versions of

lecture, each version only slightly delayed in time relative to its predecessors. Sabine found that

when a lecturer spoke at a normal conversational level and then stopped, his or her last words

remained audible for about 5.5 seconds. During these 5.5 seconds, if the speaker had not stopped,

he or she might have uttered an

additional 12-15 words. A listener, then, had to contend with a real jumble: a mixture of i)what

the speaker was saying right now, and ii)everything else that the speaker had said during the

previous 5.5 seconds.

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This was a definitely low-tech operation. With just a stop watch, highly trained auditors,

and a portable pipe organ pipe for

equipment, Sabine used compressed air to create sounds of any steady level. Upon shutting off

the compressed air flowing

through the organ pipe, he measured how long it took for the sound to become audible. He found

first that it didn't make

much difference where the auditor stood, or where in the hall the sound source was. As a result,

his findings had considerable generality. We can translate Sabine's basic finding into modern

units. Recall that normal conversational-level speech remained audible for

5.5 seconds. Since normal conversational level is about 1,000,000 times above threshold

intensity, Sabine's measurements

meant that it took 5.5 seconds for the sound level to drop by a factor of 1,000,000 (60 db).

Sabine made thousands of measurements in Fogg Hall. And he made similar numbers of

measurements in other rooms atHarvard. He found that in different rooms, sound took different

amounts of time to die away --to drop by 60 db. Sabine used the term to signify the time that is

needed for a sound's intensity to drop by 60 db. Sabine discovered that reverberation time

increased with a hall's volume; he also found that a hall's reverberation time could be drastically

changed by the hall's contents and building materials.

1.2 REVERBERATION TIME

In October 29, 1898, Sabine derived the expression that relates reverbation time to two key

variables. In his expression, T is

the time required for the residual sound to decay below audible intensity, starting from a

1,000,000 times higher initial intensity:

T = 0.161 V/A

where V is the room's volume in cubic meters, and A is the total absorption in square meters.

More than a century later,

Sabine's equation remains a foundation of architectural acoustics.

Studying various rooms that had been judged to be acoustically good, Sabine discovered that

good halls tended to have reverberation times of 2-2.25 seconds .

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CHAPTER TWO

2.0 REVERBERATION IN LECTURE THEATRES

Reverberation is simply the persistence of sound in an enclosed space in an enclosed

space after the sound source has been removed or the sound has stopped while reverberation

time is the time required for a loud sound to be inaudible after turning off the sound source.

Reverberation is dependent on the total room absorption (a) by the seats and audience as

well as the volume of the room (v). unanimously, the reverberation time (t) is directly

proportional to the volume of the room.

That is

t=0.05v/a

The volume of the lecture theatre accessed by the ceiling height determines the

reverberation time of sounds, which in turns determines speech intelligibility.

Figure 1: chart showing the relationship between reverberation time and volume of space.

However, to expediently have a broad-spectrum of reverberation in lecture theatres, a

comparison of the level of reverberation in various lecture theatres must be carried out.

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2.1 REVERBERATION IN SMALL LECTURE THEATRE, FUTA.

The Small LT. is designed as a bungalow; it functions presently as a lecture hall for all

students according to their fixed lecture hours, accommodating ideally at most 200 students at a

time.

The building consists of the Main hall, main entrance porch, preparation space (back

stage), stores and toilets. The internal dimension of the main hall is 9mx12m long; its headroom

is approximately 7m, it design is such that the seating area slopes downwards towards the stage

or lecture front, giving the hall a theatrical effect.

The stage is raised 0.4m above floor level. The hall is accessible from all four sides, its

main entrance located at the northern part (behind the seats), two side entrances located near the

stage and an entrance to back stage. The roof is in form of a simple gable shape covered with

parapet wall slab.

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Plate 1: Right Side Elevation Plate 2: Rear Facade

Plate 3: 600mm X 600mm Cellotex Plate 4: Leather Finish Cushion Chairs

Ceiling Finish

Plate 5: Heavy Carpet on Concrete Platform

Finishing materials

Floor finish Terrazzo on concrete

Ceiling finish 600mm x 600mm Acoustic ceiling boards

Wall finish Painted Plastered sandcrete block wall

Podium floor finish Heavy carpet on concrete

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Windows Natural anodized frame with 6mm clear float

glass

Figure 2: Table Showing Finishing Materials Used In Small Lecture Theatre.

Figure 3: Floor Plan of Small Lecture Theatre

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Figure 4: reflected ceiling plan of small lecture theatre.

Unanimously, the finishes used in the small lecture theatre goes a long way in

influencing the reverberation time in the lecture hall due to the absorption coefficient of the

materials at various frequencies.

Volume of small lecture theater= length x width x height =

16.1m x 15.1m x 6.0m = 1458.66 cube meters

Reverberation time in small LT= 0.05v/a

Where v= the volume of the lecture hall= 1458.66 cube meters

And a= the total absorption in square meters = 86 square meters

(0.05x 1458.66)/ 86= 0.85seconds

2.2 REVERBERATION BIG LECTURE THEATRE

The building is designed as a lecture theatre with a maximum capacity of 450 persons

seated. It has a rectangular geometry with the longer side parallel to the small lt. On the interior

space, a podium is provided at the front of the theatre for lecture purpose. The theatre is divided

into two rows by middle and two side aisles which provide for easy circulation. There is a

150mm riser demarcating each pews in the sitting area .these is done for direct vision for each

seating arrangement of the students along a row of seats, and also for direct line of auditory

perception for the listeners.

The space has two escape routes at the back of the seating for easy evacuation of users in

case of emergency.

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The front area of the building has a space used as a mini canteen and the business centre. While

the back area of the building has business centres at the lower and upper floor connected with a

geometrical staircase.

The building is properly landscaped with the planting of trees, shrubs, provision of

ramped walkways at the sides i.e. the proper use of hard and soft landscape elements. The

building covers an area of 522450000sq metres. The internal dimensions for the lecture space are

23025m by 17550m: the external dimensions of the building are 29025m by18000m.

Plate 6: picture showing the acoustic ceiling finish plate 7: heavy carpet on podium

Plate 8: clear float glass as window finish plate 9: Students In The Lecture Theater

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Figure 5: Floor Plan of the Big Lecture Theatre

Volume of BIG LT= length x width x height

= 23.1m x 17.6m x 7.2m= 2927.23 cube meters

Reverberation time = 0.05v/a

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= ( 0.05 x 2927.23) /130= 1.12 seconds

Hence, the inference from the study carried out is that, the reverberation time in most lecture

theatres is quite too long and the recommended reverberation time for lecture halls is 0.2 seconds

for the purpose of achieving speech intelligibility.

The chief means of achieving the short reverberation time is to reduce the head room of the

lecture room, and also taking cognizance of the finishes used because the total absorption

coefficient of the materials go a long way in counter – balancing long reverberation time in

lecture halls with large volume.

3.0 SUMMARY

Lecture halls should be designed according to the latest knowledge concerning acoustical

requirements. This can be accomplished with reasonable constructive and instrumental

expenditure.

In the case of renovations, for various reasons the room acoustics of lecture halls often do

not meet the requirements. The reverberation time is much too long. The sound system must then

be especially carefully designed. For most of the seats a fairly good speech intelligibility

can be achieved. However if the acoustical design of the room is poor then today’s requirements

for speech intelligibility often cannot be met for all the seats, even with a very sound good

system.

The problems of hearing impaired persons should be considered routinely by employing

assistive listening technology. For lecture halls, however, this requires careful planning.

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4.0 REFERENCES

D. MacKenzie, S. Airey, ’Classroom Acoustics. A research project. Summery report.’ Heriot-

Watt University, Edinburgh, 1999

J. Seidel, L. Weber, P. Leistner, ’Acoustic properties in German class rooms and their effect

on the cognitive performance of primary school pupils’, ForumAcusticum 2005, Budapest

J. M. Klatte, M. Wegner, J. Hellbrück, ’Noise in the school environment and cognitive

performance in elementary school children. Part B - Cognitive psychological studies’, Forum

Acusticum 2005, Budapest Acoustical Society of America, ASA. ’Classroom acoustics. A

resource for creating learning environments with desirable listening conditions.’. Acoustical

Society of America, 2 Huntington Quadrangle Melville, NY 11747, 2000

DIN 18041:2004-05, ’Hörsamkeit von kleinen und mittleren Räumen. (Acoustical quality in

small to medium-sized rooms.)’, Beuth Verlag G

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