Acoustic and Vibration Consultants

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R&D at DOT Acoustics includes the development of acoustic criteria for classroom acoustics, the development of hardware and software for acoustic measurements and models, the development of new materials and assemblies for sound control, the development of a methodology for laboratory measurements of reflectivity along with the applied metric and research in speech intelligibility in the learning environment.

Since 1998 we have been actively involved in acoustic designs that optimize rooms for speech intelligibility. Our focus has been on classrooms, lecture halls, amphitheatres, conference rooms, public meeting rooms, town halls, churches, video conference rooms, and distant learning in real time interactive communication. The main objectives were to create acoustically comfortable environments that allow extended periods of concentration while listening to speech. In smaller rooms <120m² the speech can usually be reinforced with passive designs, while in larger rooms >120m², various forms of non distractive speech amplification can be introduced along with passive designs with excellent results.

During our work at the CNRS with the CAAPS group (2002-2005), our mission was specifically to optimize rooms for all levels of hearing impairment. This included subjective comparative surveys to determine how each system or technique was judged through various hearing aids. The CAAPS (Cellule Acoustique et Audition de Paris-Sud, Orsay), directed by Paul-Marie Guyon and assisted by Béatrice Bremont were indefatigably committed to the communication of the importance of acoustically comfortable public spaces for the HoH community.

Our current studies:

In the challenging quest to define both how classrooms can be optimized acoustically to assist learning and how to measure the results, one important factor is how the level of fatigue invoked due to the difficulty of listening through noise in classrooms reduces the attention of the students over time. Learning involves multiple thought streams and extended mental effort requiring cognitive processing that must be shared with aural processing when listening in an environment that is generally noisy. The results of our studies indicate that addressing occupied noise levels vs. speech levels on a seat by seat basis, by combining early reflections up to 50ms with the direct energy speech levels, and subsequently considering reverberation to be a component of the total noise figure offers real and significant support to extended attending in classrooms.
Optimizing classrooms and lecture halls has been the center of our studies since 2003, and in this work we have included the development of treatments for all public spaces used for speaking and hearing impaired as well as normal hearing occupants.
Below you will find several articles that describe many of the key features of our directions in developing new criteria for acoustic designs for classrooms.

The need for a dedicated system to quickly measure the acoustic properties of a room used for learning has been long recognized yet today the only commercially available tools or techniques offer only noise measurements and reverberation time measurements. In that the majority of international recommendations only recognize unoccupied noise values and reverberation time values there is no need to collect data beyond these values. Our research concludes, as does the literature, that reverberation time should not be used as a target for classrooms or lecture hall design, and measurements of unoccupied noise do not represent values of occupied noise. The only index appropriate for classrooms that describes the limits of speech comprehension in noise that is widely agreed upon today is the speech to noise ratio (S/N). Much research has been done on this subject and there is general consensus that values greater then +10dB S/N in an occupied classroom at the furthest seats from the teacher can be considered good for speech intelligibility. We are developing a system that would allow 1 person to thoroughly measure one classroom in 1 hour. Results are presented on a seat by seat basis for occupied noise, speech levels, occupied early reflections, occupied late energy noise, intrusion noise, and ambient noise.
Below you will find several articles that describe some of the criteria that we find essential for acoustic measurements for classrooms.

As a compliment to reverberation time (RTxx) as a metric for the control of sound fields in rooms, reflectivity has been suggested to be a potentially important tool for noise control, for the enhancement of speech, and for the control of levels of clarity and envelopment in music. Though it is widely recognized that first and second order reflections are extremely influential in our perception of the sound fields that surround us in all built environments, a laboratory measurement system and associated metric to classify the reflectivity of common building materials or assemblies has yet to be accepted in architecture.

“A laboratory measurement methodology for the classification of reflectivity” refers to the characterization of the reflected field in regards to spectra, magnitude and eventually phase based on the incident angle, and distance of the source point and reception point. Wall surfaces whether porous, solid, perforated, textured, periodic, continuous or layered assemblies have characteristic impedances, characteristic admittance, absorption coefficients, reflective coefficients, transmission coefficients and possibly significant resonances. Among these attributes reflectivity stands out as the logical compliment to absorption and plays the dominant role in the resulting reflected sound field in small to medium size rooms. If reflectivity data were mandatory along with the absorption coefficient, they as a pair would offer enormous help to the architectural acoustic design teams in their quest to accurately predict sound fields.
We are actively involved in the development of such a system and will be publishing a paper on the subject by the end of 2010.

Listening, thinking, understanding a new concept, preparing a question, accessing short, mid and long term memories, are only a few of the many nearly simultaneous thought processes that immerse students while learning in classrooms. The relationships between binaural perception of speech in noise and the actual cognitive processes involved in memory access, multiple tasks, selective and divided listening has been a main concern in our studies for the last 10 years.
The following article briefly describes studies involving cognition, listening, memory, multiple tasks and selective listening.

"Speech Comprehension while learning in classrooms" - September 2010

Over the years we have been involved in the development of materials and strategies that respond to specific acoustic problems using common or recycled materials. For example felts made from recycled cotton fibers, surface materials that enhance reflections for speech, isolation and resonance reduction strategies using recycled gravel, shock and impact reduction using critical damping. Below you will find several articles that describe some of the materials and products our design team has developed.

As part of the InteliCAAPS work group at the CNRS (2002-2005), we formulated a speech intelligibility test strategy that introduced complexity, divided and selective attending and short term memory as variables. The point here was an attempt to match levels of difficulty of speech comprehension encountered in noisy classrooms using a paradigm of forced attending and short term memory retrieval that controlled levels of complexity. Successful comprehension regularly diminished over time as a natural result of fatigue and focused listening was reduced. The very nature and complexity of speech comprehension while learning imposed fatigue as a function of time. Therefore it seems natural that speech intelligibility in classrooms would have a time function, and not be related to a static metric. Time, task complexity and fatigue therefore have been shown to be critical in any speech intelligibility test that intends to be valid in a learning environment. Articles presenting key points of this work will be available here soon.

DOT Acoustics : 121 Rue d’Aguesseau 92100 Boulogne, France ; Administration Fax: 01 46 84 00 68 ; contact@dotacoustics.com
Tel : Sooch SanSouci 33 (0)6 61 76 18 03 ; s.sansouci@dotacoustics.com ; Line Guerra 33 (0)6 68 52 98 28 ; line.guerra@dotacoustics.com Telephone/Fax for Technical Services: 33 (0)1 64 29 64 78