1. ِAcoustics الصوتيات , د. سعود صادق حسن .1 Arch 353
Dr. Abdelrahman Elbakheit
References
الصوتيات , د. سعود صادق حسن .1

2. Acoustical Design of Halls:
In Designing large Halls for speech or Music, (i.e., Auditoriums) the main objective is to deliver the right sound level to the audience.
In order to achieve this aim we need to:
1. Provide enough sound in all parts or the hall in question.
2. Have uniform distribution to sound.
3. Stop intruding noise from outside.
4. Reverberation time should be the optimum for the intended use, (speech or Music).
5. Avoid Long delayed echo.
Volume of Halls:
Before designing a hall, we need to determine the number of the audience in advance.
From the economic point of view, the more the ratio of Volume/Person is small the more economical will be the design of the hall.
From the acoustical point of view the optimum volume is the one with optimum Reverberation time for the required use.
For speech, Reverberation time need to be the least possible and this will determine the right volume.
For Music, Reverberation time need to be longer compared to speech.

3. Shape of the Hall:
There are three main Shapes for Auditoriums: - Rectangular
- Fan Shape
- Horse Shoe
-For Audience less than a 1000, the shape is
Not Critical.
-Rectangular shapes are easier to construct,
it is advisable to have good reflecting surfaces
around the stage to reflect sound to the back.
- ratio of 2:3:5 Height, Width, Length's preferred.
- The more big the hall the more better to use
the Fan Shape.
- it is good to treat the back of the hall with
absorbing material to improve sound quality.

4. Shape of the Hall:
The shape of the back of the hall Ideally is a convex, however, it is Not practical to construct.
It is better to avoid concave surfaces in walls and Ceilings as it focuses sound in focal points inside halls, were sound in it will be louder than surroundings.
Seating Arrangements:
In more than 200 seats It is good to have
gradual sloping in the audience seats.
this will reduce sound absorption from front rows
and allow more sound to reach to the back.
As a rule of thumb, raising each row by mm
will allow for both vision and proper hearing of rows.

5. long Delayed Reflections:
Sound speed can transfer about Syllable per second.
That is one syllable to each 70 mil second (i.e., 0.07 second).
In this 70 mil second sound can travel about 17m.
Therefore in large halls reflected sound from the sides and ceiling that moves more than 8.5m can be delayed by 50 mil seconds and will cause disturbance for direct coming sound.
This can be solved by placing
sound absorption material
at the back and sides of
large halls.

8. Course work:
Students are asked to design an Auditorium of persons capacity for optimum sound performance. They should provide a report describing their design problem and prepare the necessary calculations to minimise reverberations and echo. Students should submit within the report the followings:
Plans of the auditorium detailing on seats layouts and sound proposed directions.
Plans should show locations of reflecting surfaces.
Plans should show locations of absorbing materials.
Sections showing the same information on plans.
Calculate Optimum reverberation time for speech, Music and coral.
Determine the total Required areas or Absorbing material needed for the Optimal reverberation time.