preliminary results on the acoustic environment in ...€¢national campaign launched in 2013 by the...

Preliminary results on the

acoustic environment in

classrooms in France

Simon Bailhache and Catherine Guigou-Carter

S.Bailhache and C. Guigou-Carter: Preliminary results on the acoustic environment in classrooms in France

Context & goals

• Acoustic environment in schools • Strong influence on the learning process

• American Speech-Language-Hearing Association (ASHA): recommendations on noise levels, signal-to-noise ratio, sound reverberation

• Interaction with indoor air quality, thermal conditions, etc.

• French acoustic regulation • Extension to schools in 2003

• Limits on the performance of buildings,

not on noise levels inside the premises

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Source: www.ai-media.tv


Context & goals

• National campaign launched in 2013 by the Indoor Air Quality Observatory (OQAI) • Field investigations • Issues addressed:

• Indoor air quality • Visual comfort • Thermal comfort • Acoustic comfort

• 300 pre-schools and primary schools to be investigated by 2016 • 1-3 classrooms in each school • Results from 136 classrooms (84 schools) analyzed so far

Unique opportunity to evaluate the acoustic conditions in French schools

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Methods

• Questionnaires • Teachers

• Perception of the acoustic environment • E.g. global satisfaction, types of noise heard, etc.

• Information on the survey’s conditions • E.g. students’ grade, timetable, heating system on/off?

• School administrator and surveyor • Description of the building and rooms

• E.g. date of construction, number of classes, dimensions and construction details

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Methods

• “Long-term” noise monitoring • Duration: 1 week

• Collected data: • LAeq

• LAFmax

• LASmax

• LCeq

• LZeq

• Etc.

• One sample every 2 seconds

• Statistical analysis • Semi-automatic post-processing

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Sound level meter

Air pollutants monitoring devices (including pump!)


Methods

• Estimation of building acoustic performance • Simplified model based on EN 12354

• Single number ratings according to ISO 717

• Calculations: • Indoor airborne sound insulation

• Façade sound insulation

• Impact noise level

• Reverberation time

• Input data: room descriptions from the questionnaires

• Validation: field measurements in 4 schools

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Results: noise exposure

• Analyzed data from noise monitoring experiments

• ASHA’s recommendations • Background noise level = 35 dB(A) exceeded in 9% of classrooms

• Signal-to-noise ratio ≥ 15 dB not fulfilled in only 1 case; SNR ≥ 25 dB in 75% of classrooms • Hypotheses: RT = 0.5 s and teacher’s voice level defined in ISO 3382-3

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Results: building acoustic characteristics

• Indoor airborne sound insulation

• French regulatory limits • Between 2 classrooms (with door in separating wall): DnT,A ≥ 40 dB never fulfilled!

• Between classroom and hallway: DnT,A ≥ 30 dB fulfilled in 96% of classrooms

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• Façade sound insulation

• French regulatory limits • Depend on the exposure to noise from ground and air transportation infrastructures

• Minimum requirement: DnT,A,tr ≥ 30 dB not met in 14% of all classrooms

• Individual requirements not met in 29% of all classrooms

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• Impact noise

• French regulatory limit • L’nT,w ≤ 60 dB exceeded in 3 cases

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• Sound reverberation

• French regulatory limits • Depend on room volume fulfilled in 72% of all classes

• Unrealistic high values • Too simple calculation method new calculations with ray-tracing software ICARE

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Results: teachers’ perception

• Questionnaires filled by 155 teachers

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Results: teachers’ perception

• Speech transmission

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Results: comparisons

• Noise exposure and teachers’ overall perception

• LAeq and LA10 during class closely related to the teacher’s responses

• LAeq during class ≥ 70 dB(A) at least “rather noisy” environment for most teachers

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• Façade sound insulation and teachers’ annoyance due to exterior noise

• DnT,A,tr within 2 dB of legal requirement almost 50% of teachers at least “slightly annoyed” by exterior noise • 3 dB tolerance in the French acoustic regulation!

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• Indoor airborne sound insulation and teachers’ annoyance due to interior noise

• Better correlation when considering hallways as emission rooms • Noise from neighboring classrooms is less heard on average


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2 responses out of 3



• Impact sound insulation and teachers’ annoyance due to noise from rattling furniture

• No clear trend identified (not often heard)

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1 response only


Conclusions

• Teachers’ overall perception • More than 50% consider their classroom as « rather noisy » to « very noisy »

• Transmission of speech • Noise measurement results show rather moderate background noise levels

• Questionnaire results do not indicate any particular influence of indoor design or architectural shape

• Noise from outside the building • Not heard so often, although estimated values of façade sound insulation do not meet

legal requirements in almost 30% of classrooms

• Rather annoying when heard

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Conclusions

• Airborne noise from neighboring classrooms • More heard but less annoying

• Sound insulation between classrooms below regulatory limits • Presence of doors in the separating wall in 70% of all cases

• Most schools were probably built before the acoustic regulation

• Airborne noise from common hallways • More heard and considered as the most annoying type of noise

• Most estimated values of DnT,A meet regulatory limits…

• Impact noise • Least heard and least annoying type of noise

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Future work

• Ongoing campaign • Analysis of data from 300 schools in total

• Analysis of timetable • Correlation between activities and noise levels

• Improve estimation of RT

• Consider more acoustic criteria • Noise from service equipment

• Speech Transmission Index (STI)

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Thank you for your

attention

preliminary results on the acoustic environment in ...€¢national campaign launched in 2013 by the...

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