Creating acoustical comfort in the built environment is our passion; we believe that getting the interior acoustical ‘feel’ right is a key ingredient of good design.
People interact powerfully with sound; it can enhance their performance, happiness and sense of well being, conversely a poor acoustic environment can lead to discomfort, loss of concentration, stress, anxiety and disadvantages people with English as a second language and those with hearing impairments.
We recommend that significant projects employ the professional services of a registered acoustical consultant.

Reverberation control

A major cause of discomfort in buildings is excessive reverberant noise caused by hard reflective surfaces such as painted plasterboard, concrete, ceramic, wood flooring, plastics and glass.

Excessive reverberation raises back ground noise levels and affects speech intelligibility, privacy, the speech development of children and second language speakers, the old and those with hearing difficulties.

Without adequate absorption sound will reflect from surfaces causing long reverberation times (RT 1.0 to 4.0 seconds + ) and because reflected noise travels a longer pathway compared to direct sound it has a time delay and overlaps and masks direct sound creating a confusion for the listener. To compensate people often raise their voices to be heard which rapidly increases the back ground noise levels. This effect is particularly noticeable in rooms > 300 m³ or with hard ceilings, wall and floor finishes. For good communication the signal to noise ratio must be at least 6 dB over back ground noise levels.

Reverberation is easily controlled by use of good quality sound absorbing finishes. Absorbers are classified according to ISO 116 54 and fall into 5 class groups Rated A to E.
Class A absorbers are highest and provide more absorption per sq.m than other finishes which often means less is required. Most of the Asona composite soft fibre panels are Class A. Similar to ASTM C423 NRC 0.85 to 1.00 range.

Care should be taken in selection and placement of acoustical treatment to achieve the desired performance objectives taking note of absorption from 125 Hz to 4000 Hz. Also many budget acoustical products lack the performance to effectively reduce reverberation and it is a mistake to rely on carpet or soft furnishings to try and compensate for poor acoustical performance of walls/ceilings.
New Zealand building designers are encouraged to refer to NZS2107 standard recommendations for reverberation and back ground noise levels in their documentation and employ the services of an acoustical consultant and quality acoustical ceiling and wall finishes to manage the interior acoustic environment.

Click here for a list of NZ acoustical consultants

Classroom Acoustics

Recommended reverberation times and sound levels for educational facilities

Much of what is learnt in school happens through hearing and listening. New Zealand primary school pupils are spending on average 4-5 hours per day in classrooms. It is vital that classroom learning environments have optimal acoustics for ease of listening and good intelligibility for all students.

Children, because they are neurologically immature and lack the experience necessary to predict from context, are inefficient listeners who require optimal conditions in order to hear and understand. Those who continually miss key words, phrases and concepts because of poor listening conditions are significantly disadvantaged.
Classroom design standards must consider what teaching activities occur inside the rooms during the course of a school day. Acoustical considerations must not inhibit teaching styles but facilitate the wide variety of teaching methods used. The ideal classroom should be acoustically friendly for all children regardless of abilities and for all the teaching styles in common practice today. Classrooms should not just be acoustically good when the child has normal-hearing and is sitting quietly on the mat close to the teacher. The room should also be acoustically friendly for the hearing-impaired student when there are high levels of noise because there is group discussion going on.
Noise levels in classrooms are undoubtedly higher than in the past, and this is because children are encouraged to communicate with each other. Educationalists have realised the value of what children learn from each other through gathering information casually, so called ‘incidental learning’, and good hearing conditions are crucial for the children to communicate easily.
The above is extracted from a published research report by Oticon on classroom acoustics

To aide effective communication the room reverberation needs to be controlled to RT0.40 to 0.5 seconds and the signal to noise ratio must be approx 6dB over back ground noise levels
Asona Classroom 60/40 system has been developed specifically for the classroom market, it features 60% Triton 25 NRC 0.95 absorber panels to control reverberation and back gound noise levels and 40% hard Diffusion reflector panel to provide early reflections that aid speech intelligability, both panels are installed on a two way grid for economy and speed of installation. Tested performance show how the 60/40 system helps smooth out the sound absorption curve for optimal acoustics.

More information concerning classroom acoustics is available at the ministry of education web site.
www.minedu.govt.nz
introduction to acoustics (pdf)

Office Acoustics

Recommended reverberation times and sound levels for office buildings

Offices require good control of reverberation to eliminate excessive reflections for improved privacy and comfort. Closed plan office with partitions terminating at the ceiling line will require high STC ceiling panels for room to room privacy.

For general office and closed plan offices designs we recommend our Danoline™ range of perforated acoustic gypsum ceiling systems. Available in economical accessible reveal and concealed edge grid and tile designs as well as screw fixed sheet linings they provide good levels of durability and acoustic control.
Available in 3 perforation styles to suit aesthetic and non perforated panels for borders and over partition heads for room to room privacy.
Danoline™ perforated gypsum ceilings provide an attractive perforated aesthetic and are a healthy and durable alternative to traditional mineral fibre ceilings.

For open plan office space and call centres with lower reverberation time requirements we recommend our ISO class A absorbers, Triton 25, Triton 50, Triton Duo 35, Triton Duo 60 ceiling absorber panels.

For meeting rooms with parallel walls we recommended that at least one wall be lined with our Sound Soft high impact/ tackable stretch fabric acoustic panels to prevent flutter reflections and reduce reverberation.

For premium office space we recommend our ATKAR™ brand perforated decorative acoustic panels for wall panels, column covers, quiet rooms, receptions, feature ceilings.

Geometry and Placement of Acoustical Treatment

The positioning of sound absorbing finishes has a great bearing on the effectiveness of the acoustic properties. Incorrect placement can reveal and accentuate unwanted sounds. Examples of room shapes and good positions for sound absorbents are given below.

In lecture halls projections in the ceiling surface should not be used, as this can produce a delayed echo unless absorbent.
Mutually acute angled surfaces should both be fitted with sound absorbents.
In rooms with large ceiling height, both ceiling and wall surfaces located above normal storey height must be treated. To prevent flutter echo between parallel walls absorbers should be used on the whole wall surface of at least one wall in large rooms.
Adjoining rooms with shared opening may act as sound amplifiers in relation to each other. Sound absorbent treatment need to be fitted in both rooms.
Don’t position quiet rooms next to active spaces with long reverberation times. Use a transitional room to act as an acoustic buffer and treat it with absorbent finishes.
Conference rooms or auditoria must not only emphasize the speaker's sound but also attenuate unwanted reflections. Use hard reflective panels above the speaker and position absorbent surfaces opposite the speaker.
Domes, rotundas or cradle vaults have strong focal points and normal sound can be heard as powerful echoes. In order to limit this effect place the focal point high over head or treat the surface with sound absorbing finishes to eliminate reflections.

Glossary of Terms

Direct Sound
Direct sound is a single path from source to receiver and it’s clarity is beneficial for speech intelligibility and music tone quality as it is unaffected by room surfaces.

Reflected Sound
Reflected sound is sound that is has reflected from one or more room surfaces. Reflected sound takes longer to reach the ear than direct sound because its path is longer, it is useful or problematic depending on the delay and overlap with direct sound. Reflected sound can be controlled by altering the surface absorbent or reflective qualities and Asona manufactures a wide range of ceiling and wall finishes to suit the many different applications.

Reverberation Time
This is the time in seconds that it takes for a sound to decay 60dB. Hard surfaces reflect sound and can lead to long reverberation times, porous surfaces absorb sound and help shorten reverberation times. For good speech intelligibility reverberation times of RT 0.4 to 0.8 seconds and a signal to noise ratio of 6dB are required.

Background Noise
This is any sound that is heard, it can be from air conditioning, traffic noise, noise from other people etc. Combined they add up to the back ground noise levels. Excessive back ground is a common problem in interiors.

NRC
Sound absorption of material finishes can be classified according to NRC (noise reduction co-efficient) as tested per ASTM C423 standard and is the average absorption of a material at 250, 500, 1000, 4000 Hz rounded to the nearest 5%
The NRC gives no information as to how absorptive a material is in the low and high frequencies, nor does it have anything to do with the material’s barrier effect (STC).
We strongly advise using full scale test data to assess individual frequency sound absorption data. In New Zealand NRC is superseded by ∂W per ISO 11654

∂W
Sound absorption of material finishes are classified according to ISO 11654 as tested to ISO 354 test method. It is the weighted average absorption of a material and is a good indicator of a product performance. ∂W numbers can have L M,H after the number as an indicator as to the shape of the absorption curve. L means the curve is higher at the low frequencies ( 125-250Hz) M means the curve is higher at the mid frequencies (500 – 1000 Hz) and H means the curve is higher at the high frequencies (2000 – 4000 Hz).

Satisfactory Design Sound Level
The level of noise that has found to be acceptable to most people for an environment question and also not to be intrusive. Reported in weighted average sound pressure rating dB(A)

Sound Transmission Coefficient ( STC)
STC) is a single-number rating of a material’s or assembly’s barrier effect. Higher STC values are more efficient for reducing sound transmission. The rating assesses the airborne sound transmission performance at a range of frequencies from 125 Hertz to 4000 Hertz. This range is consistent with the frequency range of speech. The STC rating does not assess the low frequency sound transfer. Special consideration must be given to spaces where the noise transfer concern is other than speech, such as mechanical equipment or music.

Flanking Sound
If you are disturbed by unwanted noise it can be caused by flanking sound.
Flanking sound can be air borne or structural borne and can seriously degrade room privacy ratings.