noise in schools deserves special attention , as appropriate learning situations depend on good acoustic conditions .
established by the brazilian association of technical standards ( abnt ) , the standard nbr 10152 recommends that noise levels in schools should not exceed 50  db sound pressure level ( spl ) and remain below that of the human voice , which is 60  db ( spl ) at normal intensity1 . in the school environment , children are exposed to several types of noise , such as external noise , environmental noise , and noise generated in the classroom .
previous studies have shown that in children , noise impairs the academic performance related to memory , motivation , and reading ability2 .
thus , in this environment , students can develop difficulties in writing , reading , and maintaining attention and concentration , which can result in disciplinary problems2 .
the presence of noise in the communication process often causes difficulties in speech perception and high levels of stress , even in people with normal hearing3 .
researchers have demonstrated that children are the most affected by background noise both in speech perception and in auditory comprehension4 . with this knowledge of the effects of noise on the learning process ,
it becomes necessary to measure the noise levels in the school environment in order to investigate the factors that may interfere with this process and propose educational and/or environmental modifications to minimize these adverse effects5 .
high levels of background noise are common in the natural environment of children , and are a major contributing factor to learning problems .
a study developed in kindergartens and schools demonstrated that children 's voices produce considerable noise levels . over an 8-hour period , the authors recorded average noise levels of 80.1  db ( a ) near the teacher 's ear and 70.87  db ( a ) in the classroom .
the maximum noise level near the teacher 's ear was 112.55  db ( a ) and that in the classroom was 103.77  db ( a)7 .
thus , the aim of this study was to evaluate the spl to which students are exposed in a municipal preschool .
this study was conducted in a municipal preschool located in a suburb of the city of marlia , whose population is of low socioeconomic status . the project was first presented to the municipal secretary of education , and after receiving approval , it was carried out at the school that had agreed to the study .
are 4 classrooms , the principal 's office , library , toilets and bathroons and courtyard ; there is a covered court and a cafeteria on the second block .
the classrooms are constructed from concrete blocks , have ceramic - tiled floors , padded ceilings , iron doors that open to the outside , and wooden doors that open to the inner courtyard ; 2 rooms face the street and the other 2 face the park .
the cafeteria walls are made of concrete blocks ; it has a plastic ceiling with acoustic treatment and a ceramic - tiled floor .
the school furniture consists of iron cabinets , tables , and chairs with iron legs , and these do not occupy a fixed position in the school .
the spl measurement was performed on 4 different days over a period of 8 hours per day , totaling 1920 minutes .
the measurement was carried out in 2 classes that attended school in the integral period . on the first 2 days
, we followed up the activities of 26 children who were 5 years of age ( preschool ii ) , and on the other 2 days , we followed 28 children who were 4 years old ( preschool i ) .
an audiologist performed the measurements using an audio dosimeter , monitoring the children 's activities at school .
these activities were held in different parts of the school , and most took place outdoors ( court and park ) .
the equipment used for this study was an sv 102 svantek audio dosimeter ; the device was calibrated and checked before the beginning of each measurement according to the technical specification .
a  and with a slow response in order to monitor low levels and continuous sounds in the environment studied according to the recommendations of regulatory standard-15 ( nr-15)8 and the fundacentro standard of occupational hygiene ( nho-01)9 .
measurements were obtained for the following parameters : maximum ( lmax ) , minimum ( lmin ) and equivalent noise level ( leq ) .
the equipment was programmed to operate at nps intervals ( spl ) between 40 and 140 db .
for the offsetting , we used the values proposed in the nr-15 and nho-018 
  9 . in brazil
, 2 standards deal with the measurement of noise and its harmful effects ; they were created to establish the criteria for occupational noise exposure .
1 the limit of tolerance for continuous or intermittent noise , and the other is the nho-01 , which provides criteria for the assessment of personal exposure to noise that are more accurate but does not have legal authority9 .
neither standard specifies changes in measurement parameters and analysis based on an open or enclosed environment .
one difference between the 2 standards is the recommended rate of duplicity : the nr-15 states that it is equal to 5  db , while the nho-01 states that it is equal to 3 db .
we used these 2 standards in this study , articulated with that advocated in the abnt standard nbr 101521 .
the results were analyzed using descriptive statistics based on the spl measurement parameters : lmax , lmin and leq .
complementary analysis was performed to compare the measured values ( as related to both the nho-01 and nr-15 ) for preschool i and ii ; the mann 
whitney test was used , the significance level was 5% ( p  <  0.05 ) , and the confidence interval was constructed with 95% statistical confidence .
there were differences in the spls measured according to the 2 standards . the noise intensity measured at the school ranged between 40.6  db ( a ) and 105.8  db ( a ) on the nr-15 and between 40.6  db ( a ) and 116.6  db ( a ) on the nho-01 ( table 1 ) . 

legend : max - maximum ; min - minimum ; leq - equivalent noise level .
when we analyzed table 1 , it showed that according to the nr-15 , leq was 73.9  db ( a ) and 75.5  db ( a ) in preschool i , and 76.1  db ( a ) and 82.1  db ( a ) in preschool ii . in this sample ,
the band intensity of a higher recurrence of spl was 5355  db ( a ) and 6580  db ( a ) in preschool i and 5357  db ( a ) and 7185  db ( a ) in preschool ii ( figure 1 ) ; the mann 
whitney test used to compare the standards determined that there were no statistically significant differences ( nr-15 , p  =  0.427 ; nho-01 , p  =  0.186 ) .
this suggests that despite the older children producing a higher spl than the younger children , quantitative analysis determined that this difference was not significant . 

the frequency spectrum of the spl measured in the octave bands was concentrated in the frequency range between 500  hz and 4000  hz ( figure 2 ) . 

distribution of the sound pressure level measured at preschool i and ii according to frequency spectrum ( octave bands ) .
the activities performed by preschool i ( chart 1 ) were related to the spl measurement ( figure 3 ) during the 8-hour period .
the spl varied according to the activity : painting and writing were quieter activities and free activities and games were noisiest ; these activities were carried out in the classroom .
the only time the spl was within the standards was during the childres nap time . 

the results demonstrated that most of the time , the noise level at school is higher than that recommended by the abnt and the world health organization1 
 10 .
a study conducted in a school showed that the noise levels measured in the classrooms and the school yard were the same as that caused by heavy traffic , race cars , and subway trains , ranging from 80  db to 110  db10 , and this shows that the measurements obtained in this study are not appropriate for the school environment , the physical and mental health of children in this learning phase , and for other school professionals11 . in this study ,
the average spl , determined from 4 days ' measurement , was 73.9  db ( a ) and 75.5  db ( a ) in preschool i and 76.1  db ( a ) and 82.1  db ( a ) in preschool ii ; these results are similar to those found in the literature .
in other studies involving schools , the spls in classrooms ranged 4975  db ( a ) , 59.571.3  db ( a ) , 5987  db ( a ) , and 71.196.2  db ( a)12 
 13 
 14 
  15 . in daycare centers and schools ,
children 's voices produce considerable levels of noise ; the equivalent noise levels ( leq ) measured over 8 hours were 80.1  db ( a ) near the teachers ' ears and 70.87  db ( a ) in the classroom .
the lmax was 112.55  db ( a ) near the teachers ' ears and 103.77  db ( a ) in the classroom7 .
a study that measured the influence of external noise in an empty classroom obtained a leq of 56.2  db ( a ) when there was activity in only one classroom in the school and 63.3  db ( a ) when activity was carried out in another 3 classrooms16 .
this difference in spls observed in the literature can be explained by the influence of different factors , such as equipment position , the number of children in the classroom and/or activity , type of activity performed , the environment acoustic characteristics , and school location .
the noise levels in schools should not exceed 50  db ( spl ) , remaining below the human voice , which is 60  db ( spl ) at normal intensity1 .
measurements in the classroom demonstrated that excessive noise is a more relevant issue than the poor acoustics of the room , and the levels of environmental noise are almost always higher than the 35  db ( a ) recommended by the abnt , even in empty rooms1 .
the spl measured at the school in octave band was concentrated in the frequency range between 500  hz and 4000  hz , the frequencies that favor speech perception .
this finding suggests the interference of spl in the understanding of speech due to the signal - to - noise ratio .
several studies have indicated that the contribution to the intelligibility of speech is specific to certain frequency bands , and speech sounds consist of low and high frequencies that vary continuously in intensity17 . for sounds below 500  hz
, there is a concentration of 60% of the energy ; however , only 5% contributes to speech intelligibility . at frequencies of 5001000  hz
, the energy and intelligibility are around 35% , and finally , at frequencies above 1000  hz , only 5% of the acoustic energy is responsible for 60% of the intelligibility and information18 .
research has shown that children are the most affected by background noise , either in speech perception or in listening4 . regarding the recommendations for noise in schools
, we observe that concern has increased because noise from internal sources ( conversations , furniture , and equipment ) and external sources ( traffic , movement of people , and proximity to urban centers ) has increased .
thus , the teaching  learning process suffers interference , as the environment does not favor concentration and understanding of speech19 . in this study ,
the spls in the classroom reached values above 80  db ( a ) according to the activity performed , where painting and writing were the quietest activities . during free activities periods and games that took place on the covered court and playground ,
the spl exceeded 90  db ( a ) , and these were the noisiest activities in this sample .
these findings contradict the recommendations endorsing the classroom - tolerated limit of 4050  db1 .
in the literature , studies have reported that the spl depended on the activity performed in the classroom12 
 20 
 21 . in elementary schools ,
the noise levels measured were 44  db ( a ) when the children were silent , 56  db ( a ) when they were carrying out some activity in silence ( silent reading ) , 65  db ( a ) when they were carrying out individual work in a noisy environment ( conversation ) , and 7077  db ( a ) when group work was being done20 
 21 .
students ' activities are a dominant source of noise in the classroom , even when they are quiet and well behaved . in this environment , any activity can increase the noise level by 510  db ( a)19 . a recent study measured noise during recess , demonstrating that the noise was excessive during both periods ( morning and afternoon ) , reaching maximum values of 88.7  db ( a ) in the morning and 102  db ( a ) in the afternoon15 .
the authors stated that these peaks are caused by the objects falling or being used , furniture being moved , or students shouting .
the peaks interrupted the teacher 's activity and the student group lost its focus19 . in this study , the children of preschool ii , aged between 5 and 6 years , produced a higher level of noise than the younger children did .
it has been reported that kindergarten rooms frequented by children aged 5 years were noisier than rooms frequented by high school students22 .
we used 2 different standards ( nr-15 and nho-01 ) to analyze the results and observed differences in the measurements obtained , and these differences were justified by the parameters used , for example , the duplicity rate of the dose .
it is worth mentioning that the rules that deal with noise measurement and its harmful effects were created to establish criteria for occupational noise exposure .
however , as there are no specific rules in brazil for noise measurement in schools , we decided to use these standards1 .
the criteria established by the nho-01 are based on modern concepts and scientific and technical parameters , follow current international trends , but without the commitment of equivalence with the legal criteria .
thus , the results obtained and their interpretation when applying this standard may differ from those compared against the nr-15 .
when we consider the high spls found in schools and their negative impact in this environment , it is essential to implement actions that aim to minimize this disadvantage
. it is important to remember that a good acoustic design ensures efficient distribution of the desirable sounds , as well as the exclusion of unwanted noise ( noise from the roof , floor , ceiling , and walls)23 .
the high level of noise in the school environment was reported as a disturbing finding in a study because it impairs the academic activities of students .
this problem goes beyond the perception of the discomfort caused by noise : it demands reflection about the physical layout of the school environment , classroom acoustics , and student and staff awareness of the noise generated at school24 .
researchers have stated that noise should be considered a risk factor in the school environment .
once the acceptable noise levels for classrooms are exceeded , it is necessary to reduce them within the legal and medical scope .
smaller classes built with acoustic materials and suitable furniture could be examples of immediate actions14 .
changes in students ' attitudes , such as behavior in the classroom , will affect the noise level . a reduced noise level combined with treatment for the acoustic environment would produce a significant beneficial effect19 .
the spls measured at the school were higher and exceeded the maximum permitted level according to the reference standards .
therefore , the implementation of actions that aim to minimize the negative impact of noise in this environment thus becomes essential .
 summary 
 aim :  to evaluate the sound pressure level to which preschool students are exposed . 
 method :  this was a prospective , quantitative , nonexperimental , and descriptive study . to achieve the aim of the study we used an audio dosimeter 
 . the sound pressure level ( spl ) measurements were obtained for 2 age based classrooms . 
 preschool i and ii . 
 the measurements were obtained over 4 days in 8-hour sessions , totaling 1920 minutes . 
 
 results :  compared with established standards , the spl measured ranged from 40.6  db ( a ) to 105.8  db ( a ) . 
 the frequency spectrum of the spl was concentrated in the frequency range between 500  hz and 4000 hz . the older children produced higher spls than the younger ones , and the levels varied according to the activity performed . 
 painting and writing were the quietest activities , while free activities period and games were the noisiest . 
 
 conclusion :  the spls measured at the preschool were higher and exceeded the maximum permitted level according to the reference standards . 
 therefore , the implementation of actions that aim to minimize the negative impact of noise in this environment is essential . 