PROC
CEEDINGS of the
23rd Internationa
al Congresss on Acousttics
13 Septemb
ber 2019 in Aachen,A
Gerrmany
9 to 1

Infrasounnd and lo
ow-frequuency nooise immission. S
Structura
aliby indus
strial noiise. Imprroving th
he ISO 19
996vibrations induced
der to pro
opose a plausible standa
ardized p
procedurre for
2:2017 in ord
usin
ng in Leg
gal noise assessm
ment
WalterW
MONT
TANO1; Elena GUSHIKE
EN1
1

ARQUIICUST, Argenntina-Peru

ABSTRAACT
It is welll known thaat dBA measu
urements donn’t are the bestbtool to evaluateean aalleged noise/vibration
disturbannce, mainly when impaccted dwellinggs are in a mixed acou
ustical zoness. The results of themeasuremments, made in Peru insid
de and outsidde dwellings subjected to structural vibbrations, are presented
here. Thee issue is thatt there is not always a sim
mple way to distinguish a specificssoundd from the tottal sound,and methhods recomm
mended in the ISO 1996-2 Standard aree very generaal. An empiriical criterion had to becreated tto find the levvel of specifiic sound conttained withinn the total souund. These accoustic determ
minationsues from a tim
me-history filltering of the total sound. IIn this work, thet author
consist of removing thhe outlier valu
mploying statiistical tools, adapting Pearson’sP
critterion, using
g discrete
proposess a new meethod of em
mathemaatics, inferencce, and acousstics criteria iin order to deevelop a com
mputer prograam to removee spurious
noise witth not compleex algorithmss. The purposee of this Papeer is to share tot the acoustiician commun
nity that itis plausiible to achievve a standardized metho d, in the sen
nse that an algorithmacouould be agreeed amongssoundd contained inn the total
specialistts for having an ”universall computer prrogram” to deetermine the specificsound.
Keywordds: Low frequuency, Noise descriptor, Soound, Standaardization.

1. INT
TRODUCTION
It exxists a plentty publicatioon concerniing about th
hat dBA meeasurements under estim
mate thelow-freqquency conteents and infrasound levells, also. Bothh the WHO anda the I-IN CE (1, 2) waarn about
the probblems of usinng the dBA asa a single deescriptor to measure infrrasound and low-frequen
ncy noisemong acoustticians that globalgdBA measuremenm
nts are insuff
fficient to(ILFN). So, it is weell known amw
le gislation is basedbon thiss descriptor. The problem
m is whenassess a noise probleem, but the worldwide
ns with no pproper training into ILFN
N acoustics problem, th
hey could
a techniccian or untrained person
arrive att mistaken coonclusions by using dBA
A solely.
It hass been obse rved in mosst of the Leggal Noise Protocols around the worrld that the common
practice is using justt dBA measu
urements, annd sometimess the impact on ILFN it iis a separate concept,
w countries haveha specific and logicc way to analyze thelike it iff were a diffferent issue. Only a few
low-freqquency conteent in their Legislation . This Paper covers not only this problem but how todiscrimi nate the speccific sound fromfa total ssound registeered by a SL
LM, because the ISO 1996-2:2017sways too do that, herre the Authoors present one plausible solution.
gives inddication or someThis work presennts the resullts carried oout in a population 2,6000 meters abbove sea lev
vel in the
Andean Mountains in Peru, beccause it is thhe only sourrce of noise/vibration inn the area: a sewagefthe houuse.
treatmennt to 250 m from

2. Objjectives and geogra
aphical chharacteristtics and In
nstrumenttation
The mmost important goal wass to determinne the allegeed noise/vibration disturrbance of the sewage
pumpingg plant. The monitoringmwork
wstarted in May 2016
6 and is still ongoing. Thee other is to know thesound laandscape exissting in the populationpw
with no plant noise; i.e., thhe condition of the enviro
onmental1arquicuust@arquicustt.com

5159

noise /vvibration basseline, and thet infrasounnd and low--frequency noisen(ILFNN) levels. Th
his action
manage audittory skills (FForensics Sc ience), wherre low-frequency noise i s a health prroblem.
should m
2.1 Phhysical geo
ography andd weather rreportCons idering the mountains area where the work was
w done, itt is a semi desert enviironment,
opical desertt climate (Bwwk code);accordinng to Köppenn, classificattion is a subttype: Tropicaal and subtro
a subtroopical anticyyclon, or su
ubtropical h igh, inhibitss precipitatiion (becausee of descen
nding air,elevatedd inversions, and clear skies), and w
wind velocityy (See Fig. 1-b) always is below 2 m/s only
during a few daylighht hours (winnd absence oon night).

(b) 48 hhour’s weatheer data
Figurre 1 – (a) View
w of the popu
ulation from tthe plant
It shoould be noteed in Fig. 1-a that the hoouses are at a higher altitude than ppump stationn, and themeasure ments were conductedcinnside a housee near to an undergroundupipeline whhich transportts mining
nt from the hoouse.
affluent to a sewage treatment plant that is 2250 m distan
coustical innstrumentation
2.2 Ac
It is a good practiice to measure both placees simultaneously: at the receiver poiint and near the noise
emitter ((pumps buildding), so the following innstrumentatiion was usedd:a. IIndoor: Sounnd level meter analyzers with one-third-octave band (10 Hz tto 20 kHz), CESVA®
C
iinstruments,, a class 1 SC
C420® modeel. Dry batteery.
b. O
Outdoor: So und level meeter analyzerrs with one-th
hird-octave bandb
(6.8 Hzz to 20 kHz), BSWA®
iinstruments,, a class 1 30
08® model. D
Dry battery and solar panel.
c. V
Vibrometer, CESVA® in
nstruments, a class 1 VC4431® model,, 500 mV/g ttriaxial accellerometerA
AC032® moodel. Dry battteries and soolar panels.
d. A class 1 souund calibratoor, AIHUA®
® AWA6223F
F Multifrequuency model..
e. W
Weather metter, a KESTR
REL® 4500N
NV. Two dig
gital audio reecorders, ZO
OOM® H1.

3. INT
TRODUCIN
NG FORENNSIC SCIEENCE INTOO ACOUSTTICS MEAASUREMENTS
This Paper preseents the resu
ults of one IILFN assessm
ment by means of Forennsic tools ap
pplied tomental acou stic measureements. Thee reason forr this method was becauuse it was notn clearenvironm
whether the noise inside the dweellings was aairborne or frrom the grou
und; also, theere was less certainty
m the industrrial facility underustudy. The work w
was carried out
o near aif the ac oustic emisssion was fromw
is to 200 m from a buuried pipelinne (inside
sewage ttreatment plaant to 250 m away from tthe house, which
which fllows down thhe affluent liiquids and w
water from th
he mine).
Afor noise measu
urements is a new branchh of Forensic Sciences,
It shoould be consiidered that Acoustics
and legaal noise assesssment is intended underr Audit activiity. Thereforre, it is impoortant to get a custody
chain to keep the nooise data saffe, simultaneeously using more than one
o SLM as a way to coorrelate a
mission fromm a specific soundsemitteer.
sound em
The assessment was requessted by thee Authorities, so it waas mandatorry to use just dBA
wever, in ordeer to do a Foorensic Acou
ustics audit, ISO standarrds needed too be usedmeasure ments. Howt alleged annoyance.
a
IIn order to avoidaany
for the nnoise/vibratioon assessmeents in order to rule out the
future coomplaints, thhe study wass conducted dduring contiinuous 48 hoours as follow
w:
T
Table
1 – Inteervals time w
where the plannt was on dutyy and off dutyy

5160

Plant onn duty

Plant off dutyyPlantt on duty

daay #1: 9 am - day #2: 5 amm

day #2: 5 am to 7 pm

day #2: 7 pmm – day #3: 9 am

4. RESULTS OF
F 48-HOUR
R MONITO
ORING NO
OISE/VIBRAATION LE
EVELS
Sincee the assesssment was requestedr
byy the Authoorities, it was
w mandatoory to use justjdBAmeasure ments, but thhis work enh
hanced the leegal requirem
ments because the most im
mportant thinng was to
N immision under low leevels of enviironmental noise;n
Fig 2 sshows the ou
utdoor (a)determinnate the ILFN
and the iindoor (b) siituation.

Figuree 2 – (a) Outddoor monitoring station(b) Indoorr monitoring station
The ooutdoor statiion it was jusst above the buried pipelline front thee house acrooss the streett.
4.1 Tiime-history
y of the nois
se and vibra
ation levelss versus afffluent flow
The rreason why it
i is importan
nt to consideerer Forensicc Acoustics, so enhancinng the acousttics study
on IFLN
N, others noisse descriptorrs or vibratioon data will beb imperativ
ve. Fig. 3 shoows, per eachh second,
the time -history of (a)( indoor nooise and (b) indoor vibraation level: ono right axis both correlaated witho weighted Wm (WBB)) rms acceleeration isaffluent flow on lefft axis. The vibration tootal value of( but it waas used dB vvalues referen
nced to 1 µm
m/s2 .
obtainedd according (3),F
Figure 3 – (a)) Noise levelss time-historyy(b) Viibration levells time-historry
Fig. 33-b shows thhat vibrationn immission has a strongg dependencce on mechaanical energy
y emitted
from thee buried pipeeline, but it is
i not the sam
me with noise level imm
mission: althhough the sou
und level
fluctuatees with the affluent floww (Fig. 3-a)), when the plant is offf duty the soound level increases,
because of the urbann noise.
ot informattion of ILFN
N levels by uusing dBA. ILFN immis
ssion from the buried pipeline
4.2 NoBecauuse of the stakeholder’s claim of inddoor hum ann
noyance and rattling winndows, one-th
hird band
spectrumm in two rangges was usedd: (i) Infrasouund range fro
om 10 Hz to 20 Hz (limiteed by the SL
LM used);(ii) low--frequency rangerfrom 16
1 Hz to 2000 Hz accord
ding to (4). There is no audible pum
mp noiseoutside tthe houses, becausebthe plantp
is moree than 250 m away to the affected houuse, for this reason, a
specific ILFN analyssis had been conducted dduring night hours in ord
der to discardd daily urban noise.
m during nighht hours wheen the plant w
was turned off,
o whereFig. 44-a displays,, per each seccond, a zoom
it is inteeresting to see how the sound level in dBA incrreases. Fig. 4-b shows, per each seccond, thetime-his tory of @25 Hz level ev
volution; bothh graphics presentpon rigght axis the ssound level, which isn left axis).
correlateed with affluuent flow (on5161Figure 4 – (a) Indoor dBA noise level - (b) Indoor low-frequency @25 Hz level (re dB 20 µPa)
In Fig. 4-b, the 25 Hz sound level has strong dependence on the acoustic energy radiated from thehouse’s walls, meaning a structural vibration induced by the groundborne mechanical energy fromburied pipeline; when the plant is OFF, the 25 Hz sound level freely oscillates, showing a big varianceamong maximum and minimum because of vehicle pass-by vibrations.

5. HOW TO ESTIMATE THE SPECIFIC SOUND LEVEL USING DISCRETE
MATHEMATICSThe author have been presented a mathematical reasoning (5) in order to simply exclude theunwanted sound from the total sound file by means of discrete mathematics.
5.1

A new idea of “basal noise” applied to environmental noise measurement
It is common to find the “basal noise” concept in medical jargon, but it is possible to use it inenvironmental noise measurements. According to Cambridge on-line dictionary, basal shall be
understand as “forming the bottom layer of something”.
For years the statistical LA90 (or LA95 ) level has been used as a notion of background noise, or more
recently, representative of the residual sound value, true only when the emitter is off, and the issue is
how to estimate the specific sound which is in the total sound, so a priori, it seems impossible to do it.
Actually, the specific sound level and others noise levels are part of the total sound, so the noisefrom other sources not interested are “mounted” onto the specific sound, because they overlap; then it
is possible to do an empirical statement: Beneath a statistical value, all sound levels are part of thespecific sound and other noises impossible to identify, such as faraway noise sources and natural ones
(birds, pets, weather, etc.).
The environmental basal noise concept appears to be useful for the empirical model presented inthis Paper, it means that the specific sound should be appraised by a statistical value, for instance, all
the sound levels below these reference percentile level belong to environmental basal noise (where thespecific sound is included), on the contrary they will be consider as outliers.
5.2 The ISO series 1996: Measurement and assessment of environmental noise
For years, acousticians have pondered how to eliminate unwanted sound, which is the sound which
doesn’t belong to the noise source of interest. Some of the most common practices have been:a. To conduct measurements on holidays, because of low levels of urban noise.
b. To turn on/off sound sources, though this is impossible to do on industrial sites or withmachines under mandatory continuous work orders.
The ISO 1996 3 rd Edition was established with a group of informative instructions, one of which
has been resolved by the author previously (6, 7): “Record the time history of the noise to be measured
and use statistical or other methods to exclude unwanted sound.” (4).
5.3 Expanding the scope of ISO sound designation to a Venn diagram
ISO 1996-1 (4) presents an important concept to understand the acoustics complexity of the totalsound, in the sense of showing its intrinsic components, but the easy way to find out one possible
solution is transforming the ISO sound designation into a manageable mathematical algorithm; thefirst immediate inferences of their categorical proposition is making a conversion to a Venn diagram,
Fig. 5 shows the assumed obversion.

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Figure 5 – Changing the point of view: ISO concept to the Venn diagram
This categorical logic permits a more convenient way of assessing the specific sound of ISO
categorical propositions by drawing Venn diagrams, the idea showed in Fig. 5 is fairly straightforward,
and the particular affirmative proposition asserts that the total sound is a member of all classes.
Mathematical thinking of the total sound simplified like a set collection, allowing it to be consideredthrough a possible computer program, with low complexity by discrete mathematics. Equation 1 shows
the total sound as an intersection subset, and it is the results of overlapping the others:(1)
Total sound = Residual sound ҏ Specific sound A ҏ Specific sound B ҏ Specific sound C
Using Eq. 1, one can estimate the specific sound as follow:
Specific sound C = {Total sound} – {Residual sound ŀ Specific sound A ŀ Specific sound B}(2)
Eq. 2 shows the specific sound under consideration is the total sound when the others are excluded,
it means that the specific sound should be appraised by a statistical level (such as LA90 ), for instance,
all the sound levels below these reference percentile belong to environmental basal noise, on thecontrary they will be consider as outlier.
5.4

The “unwanted sound” as outlier sound events which need to be extracted
Fig. 6 shows the LA time-history sound level each 125 ms like dots, instead of "seeing" it as acontinuous line, the 60-minute interval between 6 pm and 7 pm, with a working plant. The noise
emissions from the industrial facility under consideration are steady, so one can assume that theenvironmental basal noise (including the specific sound) is beneath a statistical value noise level.

Figure 6 – Normal distribution of total sound: From 2 pm to 3 pm. Plant on duty
In order to explain the inferences, Fig. 6 shows the normal distribution curve of the measurement
but rotated, because in this way it’s easy to see its positive skweness. It can be observed that there is aconcentration of sound levels below LA90 (36.6 dBA), that should be appraised like the specific sound,so for statistical reasons if it is possible to remove the outliers sound levels, then one may considerer
the LA90 value as a threshold of unwanted sound in order to exclude those spikes which don’t belong to
the specific sound under consideration.
In Fig. 6, it is easy to see the environmental basal noise idea: The normal distribution curve doesn’t
have values below 30 dBA, it is not truncated, and this is because it is the minimum sound levelmeasured by SLM; this is the concept of environmental basal noise, so beneath the statistical LA90
value there are high probability to estimate the specific sound level under consideration.

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5.5

Inference: Estimating the specific sound using a statistical percentile level
A practical way of appraising the possible sound pressure level of Fig. 6 measurement is to
assume that the LA90 or LA95 have should been the “specific sound level,” it means to use a single
statistical value as the equivalent estimator.
Table 2 – Appraising the specific sound level considering one statistical value (re dB 20 µPa)
Total sound level

Appraised #1 specificAppraised #2 specificmeasured Ӈ LAeq,Tsound level § LA90,T

sound level § LA95,T

LAeq,T

45.2

36.6

35.5

LCeq,T

59.7

unknown

unknown

LZeq,T

63.6

unknown

unknown

The issue is, which one of those two statistical values should be chosen as representative of thespecific sound? Moreover, how should one know the low-frequency level or the infrasound level under
this assumption? It is impossible to know them because it doesn’t have the complete data of the whole
specific sound time-history, but just one single “representative” value?

6. EMPIRICAL METHOD TO DETECT AND REMOVE THE OUTLIERS
This section is a brief explanation of the empiric method applied to develop the functions andprocedures which were programmed into VBA computer language included in Excel®, because it iseasy to use its large library for mathematic and statistical function, no further programming needed.
It is necessary to note that the Empirical method is applied to sound pressure levels data in csv
format resulting to the measurement, not to sound wave.
6.1 Excluding the unwanted sound by means of outliers concept
The simplest procedure to exclude the unwanted sound, it is not consider those sound events which
do not belong to the specific sound, removing them -statistically speaking- as if they were outliers.
There are a number of methods and algorithms to remove the outliers (8, 9, 10), for the particular
procedure presented here, generating and separating a vector with the specific sound noise from thevector containing the total sound data, it will have to consider one threshold value (such as thestatistical value LA90 ) from which all the noise levels that exceed it shall be considered “outliers.” The
resulting vector contains the time-history of the specific sound, and it will be a “smooth signal.”
Other authors (in the field of physics or other sciences) use similar procedure (9, 10), but instead of
deeming it “outlier removal,” they often use other synonymous terms such as “spikes removal,”“removal of spurious,” etc.
6.2 Inference: Estimating the specific sound using a statistical percentile level
A particular macro was written to obtain the equivalent-continuous sound pressure level (using the
spreadsheet with the data measurement) in dBA, dBC and dBZ; the "Percentile" function included in
Excel® was used to calculate the percentiles noise level. The Tab. 3 shows the final results:
Table 3 – Total sound level: From 2 pm to 3 pm. Plant on duty (re dB 20 µPa)

LAeq,T

LA90,T

LA95,T

LCeq,T

LZeq,T

45.2

36.6

35.5

59.7

63.6

The LA90 is the appraised value to be considered as an Estimator; in this case, using it as a thresholdvalue from which each individual LA125ms level exceed it, the LA125ms will be removed from the file.
6.3 Resolving the mathematic empirical model by modular programming
The author presents in (6, 7) a similar set of procedures, in this Paper an updated version ispresented. A new concept about modular programming has been incorporated, because a matrix
structure is more flexible for Set Theory, which is the empirical idea to write automatic software forremoving the outliers.
The SLM generate a data row, each 125 ms, so the resulting array represents a set containing 47

5164

elements (TS[i;j] matrix) with the following format A=[Time stamp; LZ; LC; LA; L10Hz… L20kHz],meaning there are 28,800 rows of 60-minutes’ measurement. Accordingly, the element A(i;4) will
always be the LA value, because all the elements in row i column 4 are the LA sound level of 125 ms
measurement each.
6.3.1 Module A: Excluding the unwanted sound. Outlier’s detection
This Module calculates the LA90 that it will be the threshold value. The simplest procedure to
exclude the unwanted sound is to remove the spikes and not consider those sound events which do notbelong to the specific sound. A decision structure asks whether each TS[i;4] value is greater than thethreshold:- If TS[i;4]ĺ LA > LA90 threshold value: the program discard the actual row and goes to next one, itseeks the TS[i+1;4] asking again the same conditional.
- If TS[i;4] ĺ LA  LA90 threshold value: the program copies its whole row into a SS[i;j] matrix, it
seeks the TS[i+1;4] asking again the same conditional.
When the conditional doesn’t find no more data in TS[i;4], the program activates Module B. So the
only “filtering” used here is to exclude the outlier’s spikes (11) which exceed the LA90 thresholdvalue: There is no frequency filtering; therefore, what is being “filtered” is the LA outliers contained in
the total sound matrix file.
6.3.2 Module B: Building the specific sound time-history. ILFN tones identification
The building-processing algorithm uses the SS[i;j] matrix, which contains all LA125ms values. The
processing is performed consecutively in all 34 frequency one-third-octave bands between 10 and 20
kHz, this Module calculates the equivalent-continuous sound pressure level in dBA, dBC and dBZ; the"Percentile" function included in Excel® was used to calculate the statistical noise level. Tab. 4 shows
the final specific sound results using the SS[i;j] matrix.
Table 4 – Specific sound level: From 2 pm to 3 pm. Plant on duty (re dB 20 µPa)

LAeq,T

LA90,T

LA95,T

LCeq,T

LZeq,T

35.3

32.6

31.5

54.4

60.6

Fig. 7-a shows the resulting specific sound time-history “built”, it is a smooth line because all
outliers and spikes belonging to the unwanted sound were removed.

Figure 7 – (a) Specific sound time-history - (b) Spectrum comparison (re dB 20 µPa)
Fig. 7-b shows a comparison between the specific sound spectrum vs. total sound spectrum of thesame measurement with plant on duty from 2 pm to 3 pm, where it can be seen how, after applicationof the empiric method to remove the outliers, two tonal sounds appear in low-frequency band (after
running the outlier-removal program), those they were masked by urban noise; so, the real specificsound level in the low-frequencies band displays relevance, and the distinct tones contained in the
spectrum can be found distinctively.

7. STRUCTURAL VIBRATION DUE TO GROUNDBORNE ILFN IMMISSION
In order to validate the empirical method as a tool to demonstrate the ILFN immission from theburied pipeline (that produce structural vibration), this empirical method was applied to the matrix
containing the total sound measurement between 2 pm and 3 pm when the plant was out of service (offduty). Fig. 8 show two graphics: (a) it displays the time-history of the residual sound level, after
applying the empirical method to total sound file presented in Fig. 8. (b) It displays a comparison

5165between the specific sound spectrum with plant on duty (it registered on day #1) vs. residual soundspectrum with plant off duty (it registered on day #2).

Figure 7 – Spectrum comparison on different hours. Plant on duty vs. off duty (re dB 20 µPa)

8. CONCLUSIONS
If an inexperienced person, or acoustician without proper training, would give the total sound levelmeasured by the SLM like valid, the Report would be wrong because this value should not be informed
like if were the noise level from the noise source under consideration. An even worse situation would
be if one compares the total sound value in dBA against legal limits.
After using the empirical method, the assessment of LFN radiated from the house’s walls is moreclear because of the structural vibration, and it was reported to the Authorities that: (a) the mechanicalenergy from underground pipeline that propagates through the soil is responsible for this phenomena.
(b) Even the sound levels are below to legal noise limits, because of the low level of environmental
noise, the LFN is possible to produce psychological disturbance but not physical diseases. (c) There is
not airborne sound propagation from the plant to the house at 250 m distance. (d) It should benecessary to install some specific valves to control the affluent flows, in order to reduce their velocity.
This algorithm has been used efficaciously for more than seven years; so the purpose of this Paper
is to share to the acoustician community that it is possible to achieve a standardized method in thesense that an algorithm could be agreed upon among specialists for having an “universal” computer
program to determine the specific sound contained in the total sound.

ACKNOWLEDGEMENT
The authors want to acknowledge to Eng. Federico Miyara for his early commentaries and forallowing us to use his “basal sound” conceptualization.

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