najaf Auditorium project IRAQ



400 Bed General Hospitals Project
Enoshmink Technology & Media Services



Project Acoustical Design :: Auditorium/Theater

Goal: To properly balance absorption and reflection to provide a favorable acoustical environment. One must address both the need to hear and understand speech, and the desire to have a pleasant space for music.

  • Tips/Considerations
    • Recommended reverberation time is 1.0-1.5 seconds (might be higher for some auditoriums).
    • Although the seating area will provide absorption, thereby reducing the reverberation time, you will most likely need to add absorptive materials to the other surfaces within the space.
    • It is vital to control the reflections from the back wall. If you don’t control them, the presentation could reflect off the back wall and “slap back” to the presenter(s). This won’t necessarily impact the audience, but could be disastrous and distracting for the people on stage. Because of this, it’s usually necessary to treat the back wall with an absorptive material. A concave back wall could compound this problem. If you can’t avoid a concave back wall, it’s imperative that it be treated with absorptive material.
    • Splay or use irregular surfaces on the walls to avoid flutter echoes. Parallel reflective surfaces can allow sound to “ricochet” back and forth between the surfaces. This potentially annoying condition is referred to as standing wave or flutter echo. It is avoided by constructing non-parallel surfaces or by adding absorptive materials to the surface(s).
    • Consider faceting the ceiling to help with sound dispersion.
    • Control the reverberation time on the stage. Ideally, the reverberation time in the stage area should be the same as in the house. Since the stage area might have a higher ceiling than the rest of the auditorium, more absorptive materials might be required in this area. Frequently, the back wall of the stage, and possibly one or two of the side walls, is treated with an acoustically absorptive material, typically black in color.
    • Remember the space will be less absorptive when only half full, since the audience itself is absorptive. By using absorptive seating areas, the reverberation time will remain more consistent regardless of the audience size.
    • Noise from the lobby area can be disruptive. Be sure openings such as doorways are properly sealed. Consider a vestibule door system.
    • Persons seated deep under a balcony might experience auditory distortion. To avoid this, the balcony should be no deeper than twice its height. Ideally, the balcony should not be any deeper than its height.
    • Even if everything else is controlled perfectly, the space might not be usable if the background noise (e.g. HVAC system) is too loud. To help protect your design, the NC level should not exceed 20 to 35. When specifying NC, specify an actual rating, such as NC 20, rather than a range, such as NC 20-30. Although specifying a lower number will ensure minimal background noise, it might be cost prohibitive to achieve. Be realistic about the amount of acceptable noise and the project’s budget when specifying an NC level.
    • Beware of potential outdoor noise impacting your space. For example, is your location near a flight path, a railroad or freeway? If so, you might have to pay critical attention to blocking this noise. To do so effectively, you must address not only the STC or isolation quality of the exterior wall, but also for the possibly weaker building elements, such as the

Auditorium sound transmission loss:


Wall 1 and 3


Wall 2 and 4



Wall sound Isolation Thickness ( wall damping concept ):

Recommended ANSI Levels for Large auditoriums, (for very good speech articulation) :  35   db

Used material :    Rock wool

Material density:   80    m3/Kg

SPL:   85   db











Wall 1                                                                       


0.0120975198718746  m


Wall 2

0.0217294161921501  m


Wall 3

0.0120975198718746  m


Wall 4

0.0217294161921501  m



0.00532148967971023  m













2- Reverberation time before sound treatment calc


Reverberation time of the auditorium before sound treatment


Frequencies (HZ)















RT 60
















Length:     24.5     m

Width:       13.64     m

Height:      6     m

Volume:   2005.08    m3














Front Wall




Back Wall


Right Wall


Left Wall
















3-Reverberation time after sound treatment calc


Enosh Ceiling:


Length:     < enosh_ceiling>           m

Width:       9             m

Material:   1”       m     


Eonsh pallet:


Number: 10

Area:  37.5      m2

Material: 2”









RT 60 at different frequencies (after adding enosh materials):




Frequencies (HZ)















RT 60















4-Critical area after sound treatment  





5- calc of Standing Waves:



Frequency Length Width Height    
F1 7 12.5733137829912 28.5833333333333    
F2 14 25.1466275659824 57.1666666666667    
F3 21 37.7199413489736 85.75    
F4 28 50.2932551319648 114.333333333333    
F5 35 62.866568914956 142.916666666667    
F6 42 75.4398826979472 171.5    
F7 49 88.0131964809384 200.083333333333    
F8 56 100.58651026393 228.666666666667    
F9 63 113.159824046921 257.25    
F10 70 125.733137829912 285.833333333333    












6- the shape of the diffuser to remove standing wave 


Length: 1.5

Width:  0.3


   0.0571666666666667                  0.228666666666667                0.228666666666667

   0.0571666666666667                  0


The application of the diffuser will be in the wall panel




7-Codes & Testing :: Sound Transmission Class (STC)

Code: STC rates a partition’s or material’s ability to block airborne sound.

Enforcement: Appendix Chapter 35 of the ’88 and ’91 UBC, Appendix Chapter 12, Division II of the ’94 and ’97 UBC will be contained in the forthcoming IBC. Although not all municipalities have adopted this appendix chapter, it is still recognized as an industry standard.

General Information: The Uniform Building Code (UBC) contains requirements for sound isolation for dwelling units in Group-R occupancies (including hotels, motels, apartments, condominiums, monasteries and convents).

UBC requirements for walls: STC rating of 50 (if tested in a laboratory) or 45 (if tested in the field*).

UBC requirements for floor/ceiling assemblies: STC ratings of 50 (if tested in a laboratory) or 45 (if tested in the field*).

* The field test evaluates the dwelling’s actual construction and includes all sound paths.


  • Sound Transmission Class rates a partition’s resistance to airborne sound transfer at the speech frequencies (125-4000 Hz). The higher the number, the better the isolation.

STC Strength: Classifies an assembly’s resistance to airborne sound transmission in a single number.

STC Weakness: This rating only assesses isolation in the speech frequencies and provides no evaluation of the barrier’s ability to block low frequency noise, such as the bass in music or the noise of some mechanical equipment.

Recommended Isolation Level
An assembly rated at STC 50 will satisfy the building code requirement, however, residents could still be subject to awareness, if not understanding, of loud speech. It is typically argued that luxury accommodations require a more stringent design goal (as much as 10dB better – STC 60). Regardless of what STC is selected, all air-gaps and penetrations must be carefully controlled and sealed. Even a small air-gap can degrade the isolation integrity of an assembly.



8-Codes & Testing :: Reverberation Time (RT60)

Test: RT60 measures the reverberance within a room.

Related Code: RT60 is soon to be adopted under ADA for classroom acoustic criteria.

General Information: Reverberation Time is the time required, in seconds, for the average sound pressure level in a room to decrease 60 decibels after a source stops generating sound. This test is standard on certain projects, such as “THX” movie theaters and various government buildings. Normally, in the design phase, you must demonstrate (through calculations) that a space will achieve the stipulated reverberation time. Often times, measurements are required to verify results.

Strength: Because RT60 is void of variables, unlike many other tests, it is straightforward and clear-cut.

Weakness: RT60 does not account for problematic and potentially annoying reflections. Often times, there is still a need for expert analysis.




9-Codes & Testing :: Noise Criteria (NC)

Code: This industry standard (also an ANSI standard) usually pertains to HVAC or mechanical noise impact.

Enforcement: This standard is often required for certain certifications (such as government medical facilities) or included in client specifications/standards (for example, some companies have NC standards that their buildings must meet).

General Information: An NC level is a standard that describes the relative loudness of a space, examining a range of frequencies (rather than simply recording the decibel level). This level illustrates the extent to which noise interferes with speech intelligibility. NC should be considered for any project where excessive noise would be irritating to the users, especially where speech intelligibility is important. There are a few spaces where speech intelligibility is absolutely crucial, including:

For some areas, such as machine shops or kitchens, it is not essential to maintain a particularly low NC level.

NC Level Strength: It is important for design professionals to specify NC ratings to protect their designs (within reason – specifying an acceptable NC level does not have to be a burden on the budget). Doing so speaks to your reputation as a responsible architect or designer and limits your liability.

NC Level Weakness: NC does not account for sound at very low frequencies. In spite of numerous efforts to establish a widely accepted, useful, single-number rating method for evaluating noise in a structure, a variety of techniques exist today. The vast majority of acoustic professionals use the NC standard, but it is still important to be aware of the other acceptable methods that do account for low frequency levels, including (but not limited to):

  • Room Criteria (RC) measures background sound in a building over the frequency range 16 Hz to 4000 Hz. This rating system requires two steps: determining the mid-frequency average level and determining the perceived balance between high and low frequency sound. To view the recommended ANSI levels for room criteria for various activity areas.
  • Balanced Noise Criteria (NCB) is based on the ANSI threshold of audibility for pure-tones and is defined as the range of audibility for continuous sound in a specified field from 16 Hz to 8000 Hz.



1-   Wall damping system theckinss 14 to 15cm

2- Wall treatment using acoustics panel NRC UP to 1.15

3- Ceiling treatment using acoustics panel NRC up to .80

4-  Floor treatment using bright surface to balance the RT of room

5- Standing wave are detect by 10 frequency

6- Must diffuse all wall by two thickness panel

7- theater seats must be foam injection not


this stady according to American standard

ASTM E90-2009″ Standard Test Method for Laboratory Measurement

Of Airborne Sound Transmission loss of Building Partitions”

ASTM E4I3-2004″ Classification for Rating Sound insulation”

Dr. Ibrahim elnoshokaty

Member acoustical society of America

Member acoustical society of Egypt










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