Kebisingan IndustriDefinisi dan pengertian

� Bising = suara-suara yang tidakdikehendaki

� Definisi secara ilmiah = sensasi yang diterima telinga sebagai akibat fluktuasitekanan udara ‘superimposing’ tekananatmosfir/udara yang steady

� Bising = sejenis vibrasi/energi yang dikonduksikan dalam media udara, cairan, padatan, tidak tampak, dan dapatmemasuki telinga serta menimbulkansensasi pada alat dengar

Inside NOISE

�What is noise?– Definition, energy conducted and sensed, properties:

intensity/pressure, frequency, exposure,

�Why unwanted?– Health Effect, age, psychological: annoyed, concentration,

rest/relax problem, communication annoyance, physiological: blood, heart, hearing loss, nausea, muscle control, acoustic trauma (permanent) vs temporary,

�Who are susceptible? – Esp. Industrial workers, determining factors: sensitivity,

age,

�How to evaluate & control?

What is noise?

Definisi: � Suara-suara yang tidak dikehendaki (for

Who? Why?)� Suara: sensasi yang diterima telinga

sebagai akibat fluktuasi tekanan udaraterhadap tekanan udara yang stabil.

� Telinga akan merespons fluktuasi-fluktuasikecil tersebut dengan sensitivitas yang sangat besar.

Properties of noise?

Karakteristik bising

1. Intensitas/tekanan (sound pressure/intensity)

2. Frekuensi3. Durasi eksposur terhadap bisingKetiga karakteristik diperlukan karena:� Semakin keras suara, semakin tinggi

intensitasnya� Frekuensi tinggi lebih berbahaya

terhadap kemampuan dengar. Telingamanusia lebih sensitif terhadapfrekuensi tinggi

� Semakin lama durasi eksposur semakinbesar kerusakan pada mekanismependengaran

Jenis Bising

� Tergantung pada durasi dan frekuensi� Steady wide band noise, bising yang meliputi

suatu jelajah frekuensi yang lebar (bisingdalam ruang mesin)

� Steady narrow band noise, bising darisebagian besar energi bunyi yang terpusatpada beberapa frekuensi saja, contoh gergajibundar.

� Impact noise, kejutan singkat berulang, contoh riveting

� Intermitten noise, bising terputus, contoh lalulintas pesawat

Contoh…

Tekanan = Sound Pressure

� Manusia dapat mendengar suara pada tekananantara 0,0002 dynes/cm2 (ambangdengar/threshold of hearing) sampai 2000 dynes/cm2 ���� range besar sehingga satuanyang dipakai dB (decibel): logaritmik

� Dinyatakan dalam decibel (dB) yang dilengkapiskala A, B, dan C���� sesuai dengan berbagai kegunaan

� Skala A digunakan karena merupakan response yang paling cocok dengan telinga manusia(peka terhadap frekuensi tinggi)

� Skala B dan C untuk evaluasi kebisinganmesin, dan cocok untuk kebisingan frekuensirendah

Intensitas

� Laju aliran energi tiap satuan luas yang dinyatakandalam desibell (dB) – Alexander Graham Bell-

� dB adalah merupakan satuan yang dihasilkan dariperhitungan yang membandingkan suatu tekanansuara yang terukur terhadap suatu tekanan acuan(sebesar 0,0002 dyne/cm2).

� B = log (int.terukur/int.acuan) untuk mendapatkanangka yang lebih akurat ditentukan dengan angkakelipatan 10 (desi)

� Intensity level dB=10 Log (IT/IA)� Sound pressure level (tekanan bunyi) = 20 log

(IT/IA), karena intensitas sebanding dengan kuadrattekanan bunyi.

� Ruang kelas: ?dB� Rumah� Restauran� Berbisik� Berteriak� Jet plane

The decibel

�

SOUND INTENSITY

SOUND SOURCE LINEAR UNITS

Bel

LOGARITHMIC UNITS

Decibel

Lowest limit of hearing 1 0 0

Rustling leaf 10 1 10

Quiet farm setting 100 2 20

Whisper (5 feet) 1,000 3 30

Dripping faucet, quite office 10,000 4 40

Low conversation, residence 100,000 5 50

Ordinary conversation 1,000,000 6 60

Idling car 10,000,000 7 70

Silenced compressor, very noisy restaurant 100,000,000 8 80

Backhoe 1,000,000,000 9 90

Unsilenced compressor 10,000,000,000 10 100

Rock dril, woodworking 100,000,000,000 11 110

Pile driver* 1,000,000,000,000 12 120

Rivet gun* 10,000,000,000,000 13 130

Explosive-actuated tool*, jet plane 100,000,000,000,000 14 140

*Intermittent or "impulse" sound

Source: Construction Safety Association of Ontario, Hearing Protection for the Construction Industry, 1985, page 3

The decibel

� dB = 10 log10 (I1/I0) I = IntensitasdB = 20 log10 (P1/P0) P= Tekanan = 0,0002

dynes/cm2

SP (microbar) SPL (dB) Ratio Intensitas0,0002 0 100

0,002 20 102

Jadi bila SP berubah 10x, maka dB bertambah ? x

PressurePa Bel (B) Decibel (dB)

Threshold of hearing 0,00002 0 0Quiet office 0,002 4 40Ringing alarm clock at 1 m 0,2 8 80Ship's engine room 20 12 120Turbo jet engine 2000 16 160

Sound intensities

Frekuensi

�Adalah jumlah getaran dalam tekanansuara per satuan waktu (Hertz ataucycle per detik), frekuensi dipengaruhiukuran, bentuk dan pergerakansumber, pendengaran normal orangdewasa dapat menangkap bunyi denganfrekuensi 20-15.000 Hz.

Frekuensi

� Dibagi dalam 8 octaf (octave bands), 37.5, 75, 150, 300, 600, 1200, 2400, 4800, 9600 Hz

� Telinga manusia bereaksi beda terhadapberbagai frekuensi

� Kebisingan ‘rata-rata’ mencakup seluruhtaraf kebisingan dari setiap frekuensi ����

dihitung LeqLeq = ekuivalen noise level/ekuivalen energilevelLeq = 10 log 10 (Σ 10 Lpi/10 )

Satuan (Konversi)

�1bar=105Pa=105N/m2

� =105.105dyne/10 4cm 2

� =106dyne/cm 2 atau�1microbar = 1 dyne/cm 2

Sumber > 1…..

�dB=L=20 log(P 1/P2)=10 log(P 1/P2)2

�L/10= log(P 1/P2)2

�10L/10= 10log(P1/P2)^2 =(P1/P2)2

�L=10 log(P 1/P2)2

� =10 log 10 L/10 (satu sumber)

�L =10 log ( Σ10Li/10) (sumber banyak)

� =10 log (10 L1/10+ 10L2/10+…)

Sumber > 1….. (Contoh)

� =10 log (Σ10Li/10) (banyak sumber)

� =10 log (10 L1/10+ 10L2/10+…)

Perbedaanantara sumber

bunyi

ΣdBA yang turunditambah ke

bunyi terbesar

0 3,0

1 2,6

2 2,1

3 1,8

4 1,5

5 1,2

6 1,0

7 0,8

8 0,6

10 0,4

12 0,3

14 0,2

16 0,1

Satuan (Konversi)

�1bar=105Pa=105N/m2

� =105.105dyne/10 4cm 2

� =106dyne/cm 2 atau�1microbar = 1 dyne/cm 2

Sumber > 1…..

�dB=L=20 log(P 1/P2)=10 log(P 1/P2)2

�L/10= log(P 1/P2)2

�10L/10= 10log(P1/P2)^2 =(P1/P2)2

�L=10 log(P 1/P2)2

� =10 log 10 L/10 (satu sumber)

�L =10 log ( Σ10Li/10) (sumber banyak)

� =10 log (10 L1/10+ 10L2/10+…)

Sumber > 1….. (Contoh)

� =10 log (Σ10Li/10) (banyak sumber)

� =10 log (10 L1/10+ 10L2/10+…)

Perbedaanantara sumber

bunyi

ΣdBA yang turunditambah ke

bunyi terbesar

0 3,0

1 2,6

2 2,1

3 1,8

4 1,5

5 1,2

6 1,0

7 0,8

8 0,6

10 0,4

12 0,3

14 0,2

16 0,1

Kebisingan dari 2 sumber

14Perbedaan antara 2 tingkat bising, dB(A)

3

2,5

12108642

0,5

1,5

2

1

Dec

ibel

yan

g di

tam

bahk

anpa

datin

gkat

kebi

sing

anle

bih

tingg

i

Perbedaan(dB)

Tambah pada yglebih tinggi

0 atau 1 3

2 atau 3 2

4 – 9 1

10+ 0

Why unwanted?

Health Effect, age, psychological: annoyed, concentration, rest/relax problem, communication annoyance, physiological: blood, heart, hearing loss, nausea, muscle control, acoustic trauma (permanent) vs temporary,

Efek bising pada manusia

� Psikologis, terkejut, mengganggu danmemutuskan konsentrasi, tidur dansaat istirahat

� Fisiologis, seperti menaikkan tekanandarah dan detak jantung, mengurangiketajaman pendengaran, sakit telinga, mual, kendali otot terganggu, dll.

� Gangguan komunikasi yang mempengaruhi kenyamanan kerjadan keselamatan.

Interference with communication by speech

� When background or ambient noise levels are sufficiently high enough, the background noise can mask the sound levels of speech that wish to be heard.

� Restaurants can often be classic examples of excessive noise interference due to lack of sufficient quality or quantity of sound absorbing materials that prevent excessive noise buildup.

� Diners have to speak louder and louder to be heard and in doing so compete with one another, thereby increasing the sound levels to even greater levels. Appropriate acoustical treatment will prevent the reflected noise buildup and significantly reduce the necessity for diners to speak louder to enjoy conversations with one another.

Mechanics of hearing

�

Mekanisme pendengaran

• Terdiri dari 3 bagian: telinga luar (daun telinga sampai membran timpani) �meneruskan gelombang ke telinga tengah

• Telinga tengah: membran timpani (yang melekat pada 3 tulang kecil sampai membrana ovale) � getaran diteruskan

• Telinga dalam: tube berspiral seperti rumah siput berisi cairan � cairan bervibrasi �stimulasi rambut sel � impuls syaraf otak

Gangguan pendengaran

�Pemaparan pada suara tinggi danperiode/durasi yang lama akanmenyebabkan sel syaraf pendengar danrambut pada corti over aktif sehinggamenimbulkan kehilangan pendengaranpermanen

Pengukuran kebisingan

• Mengukur overall level �sound level meter (satuan dBA)

• Mengukur kebisingan pada setiap level frekuensi �SLM dengan frequency analyzer

• Penentuan eksposur kebisingan padapekerja�noise dosimeter (satuan dBA)

Alat ukur

� Sound level meter, mencatat keseluruhansuara yang dihasilkan tanpamemperhatikan frekuensi yang berhubungan dengan bising total (30-130 d) – (20-20.000Hz)

� Sound level meter dengan octave band analyzer, mengukur level bising padaberbagai batas oktaf di atas range pendengaran manusia denganmempergunakan filter menurut oktaf yang diinginkan (narrow band analyzers untukspektrum sempit 2-200 Hz)

NOISE KALIBRATOR

SOUND LEVEL METER

NOISE MEASUREMENT KIT

NOISE DOSIMETER

PENGUKURAN PADA PEKERJA

DOSEBADGER

Pneumatic chip hammer

103-113 Crane 90-96

Jackhammer 102-111 Hammer 87-95

Concrete joint cutter

99-102 Gradeall 87-94

Skilsaw 88-102Front-end loader

86-94

Stud welder 101 Backhoe 84-93

Bulldozer 93-96Garbage disposal (at 3 ft.)

80

Earth Tamper 90-96Vacuum cleaner

70

�

Pengukuran akibat bising

Untuk mengevaluasi akibatpemaparan terhadap kehilanganpendengaran, kenyamanan, interferensi komunikasi danmengumpulkan informasi untukpengontrolan.

How Does Excessive Noise Damage Your Ears? � Microscopic hair cells of the cochlea are

exposed to intense noise over time � Hair cells become fatigued and less responsive,

losing their ability to recover. � Damage becomes permanent resulting in noise-

induced permanent threshold shift. � Risk of Hearing Loss � Estimated Risk of Incurring Material Hearing

Impairment as a Function of Average Daily Noise Exposure Over a 40-year Working Lifetime (source: NIOSH)

� Average Exposure 90 dBA 29% � Average Exposure 85 dBA 15% � Average Exposure 80 dBA 3%

Ketulian

= berkurangnya ketajaman pendengarandibanding/terhadap orang normal (15 dB)/ gol usia

• Ada 2 macam: - permanen: karena penyakit, usia tua, obat, trauma, dankebisingan- temporer: akibat ekposur bising, dapat pulih setelahistirahat beberapa saat tergantung keparahan

• Ketulian temporer akan menjadi permanen bila terusterekpos bising (dari rumah, tempat umum, rekreasi, musik, industri, dll.)

• Secara mekanisme: ketulian ada 2:- konduktif: peralatan konduksi suara rusak akibattrauma atau sakit- sensorinueral: akibat persyarafan pendengaran rusak

Audiometric test

�

Audiometric test

�

Audiometric test

Current OSHA Standards•1926.52 Occupational Noise Exposure

•TABLE D-2 - PERMISSIBLE NOISE EXPOSURES

Duration per day, hoursSound Level dBA slow response

8 90

6 92

4 95

3 97

2 100

1 1/2 102

1 105

1/2 110

1/4 or less 115

What Is The Purpose of Having a Hearing Test on a Regular Basis?

� An audiometric testing program is used to track your ability to hear over time. – Baseline and annual

� Test records provide the only data that can be used to determine whether the program is preventing noise-induced permanent threshold shifts. It is an integral part of the hearing conservation program.

� Case Study 1. Teenage Girl From the American Academy of Family Physicians website, Rabinowitz article

FIGURE 1. Audiogram findings in the patient in case 1.

The area below the curves represents sound levels that the patient could still hear. (X = left ear; O = right ear)

Case Study 1 Conclusion

� "Temporary threshold shift" example � Common in persons exposed to high

noise � Represents transient hair cell

dysfunction � Complete recovery can occur � Repeated episodes of such shifts

causes permanent threshold shifts because hair cells in the cochlea are progressively lost.

Case Study 2 Factory Worker Age 55

Case Study 2 Conclusion

� Noise Induced Hearing Loss – Speech discrimination and social function

interference – Difficulty in perceiving and differentiating consona nt

sounds – Sounds such as a baby crying or a distant telephone

ringing, may not be heard at all.

� Tinnitus – Common symptom of noise overexposure – Further interferes with hearing acuity, sleep and

concentration.

� These impairments have been associated with depression and an increased risk of accidents.

Carpenter Hearing Losses by Age

Damage risk criteria

� Variation in individual susceptibility� The total energy of the sound� The frequency distribution of the sound� Other characteristics of the noise

exposure, such as whether it is continuous, intermittent, or made up of a series of impacts

� The total daily time of exposure� The length of employment in the noise

environment.

Noise control

�A source radiating sound energy�A path along which the sound

energy travels�A receiver such as the human ear

Pengendalian kebisingan

Pengendalian dilakukan di 3 bagian: SUMBER, RUANG ANTARA sumber dan penerima/pekerja, pada PENERIMA/PEKERJA

Urutan pengendalian paling efektif:• Kurangi/hilangkan sumber bising• Pengendalian pathway: jarak diperjauh dengan

perisai/isolator/automatisasi• Perlindungan penerima dari bising (APD)

SUMBER PATHWAY/MEDIA PENERIMA/RECEIVER

•Cara teknis:

APDPerpanjang jarak

Reduksi waktuPerisaiInsulasi sumber

Isolasi pekerjaAbsorpsi/dampingSubstitusi

PENERIMAPATHWAYSUMBER

•Cara medis:Pemeriksaan ketajaman pendengaran secara periodikPenempatan pekerja sesuai dengan kepekaan thd bisingMonitor ketulian temporer

•Cara manajemen:Reduksi waktu eksposurDiklat pemakaian dan pemeliharaan APD

Noise control

�Source: modification or redesigning of the source.– The modification of compressed air jets for parts

ejection, to reduce noise by altering the jet flow.– Multiple-opening air ejection nozzel: less noise tha n

single-opening.

Noise control

� Noise can be controlled at the source, along the path or at the worker.

� At the source, equipment may be replaced by quieter models, or less noisy work procedures can be adopted. - In general, less friction and vibration mean less noise. Maintenance procedures such as lubrication may sometimes reduce noise by reducing friction. - Equipment can sometimes be modified to reduce the amount of noise that is generated. Sound-absorbing material may be attached to the noise source. Or the frequency of the noise may be shifted to one that is less hazardous.

Noise control

� Noise can often be controlled along the path to the worker with:- the use of sound-absorbing paneling on walls or ceilings, and - enclosures around noisy machinery.

� Controls at the worker include both administrative controls and personal protective equipment. – Administrative controls modify how the work

is carried out. – The time employees spend in noisy areas

may be reduced. – Workers in noisy areas may be rotated to

less noisy areas.

As the distance from the noise source increases, the pressure (or intensity) of the noise decreases faster than its sound level.

Noise control

�Noisy operations may be conducted outside normal working hours to reduce the number of people exposed.

�Where noise exposures cannot be reduced by other methods, hearing protection is required. This includes ear plugs and ear muffs.

Insulation of the workers

�A separate noise insulated room provides effective control (up to 30 dB noise reduction).

Machine insulation

�Machine: on floors and walls ����vibrate them ����sound radiationproper use of machine mountings insulates the machine and reduce the transmission of vibration

Control of noise by absorption

�Travels out in all direction�When encounter walls ����reflected�Total noise exposure within the

room = direct + reflected noise�Application of sound absorption

material (However, limited: no effect on direct noise).

Reduction of exposure time

�Limiting the total daily exposure reduces the noise hazard.

�See TLV

Personal protection against noise

�Many operations cannot be quieted by engineering methods.Therefore ���� protection: ear plugs

�Properly worn: 25 – 400 dB protection

�Degree of discomfort ���� employee education is adequate

Example….

� Durasi tingkat bising yang diijinkan dapat dilihat daritabel di bawah ini:

� Kebisingan yang terukur disuatu area adalah 90 dB selama 2 jam sehari, 97 dB selama 2 jam, dan sisa 4 jam berikutnya terdapat variasi tingkat bising secara bergantian 95 dB selama 10 menit dan 80 dB selama 10 menit. Tentukan apakah tingkat kebisingan yang terukur masih dalam batas yang diijinkan atau tidak.

Durasi per hari

Tingkatbising

86432

1,51¾½¼

90929597

100102105107110115

Faktor-faktor yang mempengaruhibising

�Tipe bising: menerus dan terputus�Lokasi pekerja�Waktu kerja

NAB Kebisingan di lingkungan kerja

USA (TLV ACGHI)t (eksposur) jam dB(A)

8 906 924 953 972 100

1,5 1021 105

0,5 110<0,25 115

kebisingan impulsif < 140 dB

t dBA8 854 882 911 94

30 mnt 9715 mnt 1007,5 mnt 103

3,75 mnt 1061,88 mnt 109

dstdilarang > 140 dB

INDONESIA Permen 51/1999

Waktu pemaparan vs dB (TLV)

WaktuWaktuWaktuWaktu pemaparanpemaparanpemaparanpemaparan (jam)(jam)(jam)(jam) dBdBdBdB

8888

6666

4444

2222

1,51,51,51,5

1111

0,50,50,50,5

<0,25<0,25<0,25<0,25

90909090

92929292

95959595

100100100100

102102102102

105105105105

110110110110

115115115115

((((SumberSumberSumberSumber: FHI): FHI): FHI): FHI)

Steps aiming to control noise at work� Assess risks to develop a noise control plan

� Reduce risks for all employees

� Investigate and implement good practice for control of noise

� Prioritise noise control measures

� Use hearing protection for residual risks

� Carry out a noise dosimetry program to check the effectiveness of noise control measures

Some simple noise control techniques� Application of damping material to

chutes, hoppers, machine guards etc.,

can give a 5-25 dB reduction in the noise

radiated

� Cabin internal noise can be reduced by

10-12 dB by applying damping pads and

sound barrier mats to floor and engine

bulkhead

� Reduce fan speed by 30% to achieve a

noise reduction of 8 dB

BARRIER-BARIER ATAU PANEL

ISOLASI PEKERJA/MESIN DI TEMPAT BISING

BAHAN ABSORBER BAHAN BARRIER

Noise control can be complex

Use noise control

consultants to

help solve your

problems if

complex

Engage

employees in

process

Hearing protectors

� Selected for protection, user preference

and work activity

� Guard against over-protection — isolation

can lead to under-use and safety risks

� Require information, instruction,

training, supervision and motivation

�Will only protect if worn all the time and

properly

Rating hearing protectors

The sound level conversion (SLC80 ) rating of a hearing protector, ear plugs or headset is a simple number and class rating that is derived from a test procedure as outlined in the Australian/New Zealand Standard AS/NZS 1270:2002

Class and specification of hearing protectors

SLC80Class May be used up to this

noise exposure level

10 to 13 1 90 dB(A)

14 to 17 2 95 dB(A)

18 to 21 3 100 dB(A)

22 to 25 4 105 dB(A)

26 or greater

5 110 dB(A)

Ear plugs

Properly fitted Wrongly fitted

Ear muffs

Proper clamping force Worn-out head band

Reduction in protection provided by hearing protectors with decreased wearing time

Example:

Effectiveness of

wearing an ear

muff with a rating

of 30 dB for an

exposure time of

one hour

Wear timeEffective

attenuation

60 minutes 30 dB

55 minutes 11 dB

50 minutes 8 dB

45 minutes 6 dB

Our challenge

Away from …

� Noise assessment as the end point

� Reliance on hearing protection

Towards …

� Control of noise risks through prioritised action plans

� Introducing equipment with good noise and vibration characteristics – ‘Buy Quiet’

TWA untuk kebisingan: berdasarkan standarkebisingan.

Jumlah jam dB(A)

1,5 102

1,0 105

0,75 107

0,5 110

0,25 115

Jumlah jam dB(A)

8 90

6 92

4 95

3 97

2 100

dB(A) 80 90 95 97 100

1 T ukur 2 jam 4 jam 2 jam

T TLV tt 8 jam 4 jam 3 jam

TWA 0 4/8 2/4 = 1 < batas aman

2 T ukur 0 2 jam

2 jam 2 jam

T TLV tt 8 jam 4 jam 3 jam

TWA 0 2/8 2/4 2/3 = 17/12 >batas aman

STANDAR KEBISINGAN

Noise3. 4 orang pekerja printer di unit percetakan dimana

terdapatoffset press. Masing-masing terpapar sbb:

Berapa dosis harian yang diterimanya? dan Equivalent 8-hour Sound Pressure Level (SPL) yang dialamipekerja percetakan tersebut?

No. of presses operating

Average Sound Pressure Level (dBA)

Average daily time in operation

(hours)

0 81 4.5

1 93 2.1

2 96 1.0

3 98 0.4

Jawab:

5/)90(max 2

8−=

LT

5/)9081(max 2

881@ −=dBAT = 27.858 jam

Untuk SPL 81 dBA:

5/)9093(max 2

893@ −=dBAT = 5.278 jam

Untuk SPL 93 dBA:

5/)9096(max 2

896@ −=dBAT = 3.482 jam

Untuk SPL 96 dBA:

5/)9098(max 2

898@ −=dBAT = 2.639 jam

Untuk SPL 98 dBA:

Noise

niT

C

T

C

T

C

T

CD n

n

i

i

max1 max

2

max

1

max

....21

+++==∑=

639.2

4.0

482.3

0.1

278.5

1.2

858.27

5.4int +++=erprD = 0.998

Now, expressing this result as a percentage as required by the problem statement, we have: Dprinter= 99.8%

The Printing Company that employs these four Printers is not in violation of any established OSHA SPL dosage standards.

Noise

Lequivalent= 90 + 16.61 log[D]

Lequivalent= 90 + 16.61 log[0.998]= 89.987 ~ 90 dBA

These Printers experience an equivalent SPL of ~ 90 dBA

Noise

4. How much longer is an individual, without hearing protection, permitted to work at a location where the noise level has just been reduced from 104 dBA to 92 dBA?

To answer this question, we must first determine the OSHA permitted duration, in hours, for each of the two identified noise levels.

Tmax = 8 / [2(L-90)/5]

For an SPL of 104 dBA: Tmax @ 104 dBA= 8 / [2(104-90)/5] = 1.149 hours

For an SPL of 92 dBA: Tmax @ 92 dBA= 8 / [2(92-90)/5] = 6.063 hours

The additional time permitted at the lesser noise level of 92 dBA, ∆Tmax, is simply the difference between these two OSHA permitted time intervals; thus:

∆Tmax=6.063 – 1.149 = 4.914 hours

This individual can spend an additional 4.9 hours at a 92 dBAnoise level