There are many factors that contribute to the development of a growing child. The act of listening is among the most important when it comes to the child’s comprehension of the world from the earliest stages and throughout his/her education. Good listening conditions are directly related to academic performance and, indirectly, they affect the overall well being of the student. It has been proven that poor listening conditions lead to tiredness, attention deficits and irritability. Poor listening conditions also affect teachers who thus need to raise their voices, leading to stress, fatigue, and even voice impairment.
So, what creates good listening conditions indoors, in spaces such as classrooms, gymnasia, auditoria or even cafeterias?
There are three main acoustical attributes that control the listening conditions and determine the degree of speech intelligibility in a learning environment. These are the sound reflections and reverberation within the space, the background noise levels (mostly from the mechanical systems serving the building), and sound isolation between adjacent spaces and from outdoors.
In a space designed for music, such as a concert hall, a long reverberation time is a desired acoustical effect. It creates a sense of envelopment and of immersion in the musical act. When it comes to speech, however, sound reflections bouncing back and forth from the room surfaces for a long period of time mask the information contained by the direct sound. Listeners have to strain their hearing to extract the information contained in speech when it is clouded in reverberation.
The reverberation time of any space is directly proportional with its volume and inversely proportional with the amount of sound absorptive treatment added to the room’s surfaces. Since the room volume is generally set by capacity needs or architectural intent, a key acoustical design tool is to strategically distribute sound absorptive treatment in the space to ensure that reverberation is sufficiently controlled and to ensure good intelligibility.
To demonstrate the variations in a room’s acoustical response when different degrees of sound absorptive treatment are employed, we created a series of auralizations – three-dimensional acoustical simulations, based on acoustical computer models. A rather recent and innovative tool in the acoustical consultant’s repertoire, the auralization technique has various benefits; it allows, for instance, hearing how a space will sound before it is built. For this demonstration, the use of auralizations provides the opportunity to make an immediate comparison between two acoustical designs of the same space, allowing one to assess clearly the advantage of one acoustical treatment approach over another.
Please use headphones or high quality loudspeakers when listening to the following sounds to hear their full effect.
The following example is an auralization of activity noise in a gymnasium that has a large volume and no sound absorptive treatment on any of its walls or ceiling:
By strategically distributing sound absorptive treatment to parts of the Gymnasium ceiling and walls we can improve the aural environment in the same Gymnasium, as follows:
The next factor to ensure good listening conditions is a quiet background noise level. New schools, designed in compliance with modern classroom standards, achieve background noise levels between 35 and 40 “A weighted” decibels (dBA). Although some standards allow background noise levels as high as 45 dB, these are less desired toward achieving good acoustics in the classrooms. In comparison, older schools or schools that do not observe such standards and/or did not receive advice from an acoustical consultant during facility design, are oftentimes characterized by background noise that exceeds these levels significantly. In these cases the noise is found to be excessive for any occupant, and it is particularly detrimental for young children whose hearing system is not yet developed to segregate sound sources based on spectral differences, and who are not able to put together missing pieces of information, and are overall less efficient listeners.
To demonstrate a child’s poor listening capabilities in the presence of masking noise we created a series of auralizations based on research in the audiology and psychoacoustics field (Werner & Bargones, 1991; Werner & Boike, 2001).
The first auralization in the series presents a speech sample as heard by an adult in the presence of high-frequency masking noise:
The second auralization consists of the same speech sample in the presence of the same amount of noise, as heard by an infant. Since an infant’s listening is not frequency selective, the noise provides more effective masking and interferes greatly with intelligibility:
Additionally, infants detect speech less well than noise, resulting in yet more effective masking and poorer intelligibility, as shown in the third auralization:
Careful selection and installation of the mechanical equipment, and a thoughtful low-noise mechanical design are critical factors toward achieving a low background noise level, suitable for a learning environment for young students.
Finally, it is important to provide good sound isolation with appropriate demising constructions to eliminate other sources of listening distraction. A student’s attention can be easily distracted by activities that take place in the corridor or in an adjacent classroom, if the sound is effectively transmitted through the walls or communicating doors. Moreover, sound transmitting from a Band Room or other loud environment is not only distracting but can interfere with speech intelligibility in the classroom, not unlike the noise from the mechanical systems. Careful selection and installation of the building’s construction elements (walls, ceilings, doors and windows) is essential to provide adequate sound isolation and allow for suitable listening conditions in the learning environment.
Several standards are available to help set suitable acoustical goals in a school environment. Among them are the ANSI Standard for Classroom Acoustics S12.60, LEED for Schools, and the Collaborative for High Performance Schools.
Excellent acoustical conditions can be achieved in the learning environment by setting suitable acoustical criteria during the early design stages of a new school project, and by encouraging strong collaboration between the acoustical consultant, the architect, and mechanical engineer. Most importantly, good classroom acoustics can bring substantial improvement to the academic performance within a school.
Acentech would like to thank Professor Peggy Nelson of the University of Minnesota for her guidance in creating the noise impact auralizations.