Free Practice Questions for Engineer Noise and Vibration

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Key Facts: Engineer Noise and Vibration Exam

150 Mins

Official written examination time limit for 100 questions across 5 subjects

HRD Korea (한국산업인력공단)

₩19,400

Official written CBT examination application fee in South Korean Won

Q-Net Portal (jmCd 1665)

₩22,600

Official practical (필답형) examination application fee in South Korean Won

HRD Korea fee schedule

40% / 60%

Minimum score per subject to avoid failure (과락) and overall passing average

National Technical Qualification Framework

100 MCQs

Total practice questions in this OpenExamPrep English-language study bank

OpenExamPrep

Prepare for the HRD Korea Engineer Noise and Vibration Examination (소음진동기사) with 100 high-yield practice questions covering wave acoustics, decibel calculations, room reverberation, vibration isolation transmissibility, standard test methods, and the Noise and Vibration Control Act. Note: This practice bank is an independent English-language MCQ study adaptation by OpenExamPrep.

Sample Engineer Noise and Vibration Practice Questions

Try these sample questions to review concepts for the Engineer Noise and Vibration exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1At an ambient air temperature of 20°C, what is the theoretical propagation velocity of sound waves in dry air?

A.331.5 m/s

B.343.7 m/s

C.352.4 m/s

D.360.0 m/s

Explanation: The speed of sound in air (공기 중의 음속 c) is a function of absolute temperature and can be accurately calculated using the empirical linear approximation c ≈ 331.5 + 0.61 * T (where T is the temperature in °C). At T = 20°C: c = 331.5 + 0.61 * 20 = 331.5 + 12.2 = 343.7 m/s.

2An acoustic source emits a pure sinusoidal tone at a frequency of 500 Hz. Assuming the speed of sound in the propagation medium is 340 m/s, what is the acoustic wavelength (파장 λ)?

A.0.340 m

B.0.500 m

C.0.680 m

D.1.471 m

Explanation: Wavelength (파장 λ) is given by the fundamental wave relation λ = c / f, where c is the speed of sound (340 m/s) and f is frequency (500 Hz). Therefore, λ = 340 / 500 = 0.680 m.

3Why do acoustic waves propagate exclusively as longitudinal waves (종파 / 압축파) in non-viscous air and ideal fluid media under normal atmospheric conditions?

A.Air molecules have electrical dipoles that strictly align parallel to gravitational acceleration.

B.Acoustic waves in fluid media undergo total internal reflection that instantaneously cancels transverse particle motions.

C.Longitudinal wave speed in fluids is infinite, whereas transverse wave speed is constrained by the speed of light.

D.Air cannot sustain shear stress and possesses zero shear modulus, permitting only volumetric compression and rarefaction.

Explanation: In fluid media such as air and water, fluids cannot support static shear stresses (전단응력) because their shear modulus (전단탄성계수 G) is effectively zero. Consequently, sound waves cannot propagate as transverse (shear) waves in bulk air; they propagate strictly as longitudinal waves (종파), consisting of alternating compressions and rarefactions along the axis of wave propagation.

4What is the characteristic acoustic impedance (고유음향임피던스 Z0) of air at 20°C and standard atmospheric pressure (air density ρ0 = 1.205 kg/m³, sound velocity c = 343.7 m/s)?

A.285 N·s/m³

B.344 N·s/m³

C.414 N·s/m³

D.1,500 N·s/m³

Explanation: Characteristic acoustic impedance (고유음향임피던스) is defined as the product of the equilibrium density of the medium and the speed of sound: Z0 = ρ0 * c. Substituting ρ0 = 1.205 kg/m³ and c = 343.7 m/s gives Z0 = 1.205 * 343.7 ≈ 414.2 N·s/m³ (Rayls).

5In environmental acoustics, what are the international standard reference sound pressure (기준음압 p0) and reference sound intensity (기준음향세기 I0) for airborne noise?

A.p0 = 1 × 10⁻⁶ N/m² (Pa) and I0 = 10⁻¹⁰ W/m²

B.p0 = 1.0 N/m² (Pa) and I0 = 1.0 W/m²

C.p0 = 2 × 10⁻⁴ N/m² (Pa) and I0 = 10⁻¹⁴ W/m²

D.p0 = 2 × 10⁻⁵ N/m² (Pa) and I0 = 10⁻¹² W/m²

Explanation: The internationally standardized reference sound pressure for airborne sound is p0 = 20 μPa = 2 × 10⁻⁵ N/m² (the threshold of human hearing at 1,000 Hz). The corresponding reference sound intensity in free air is I0 = 10⁻¹² W/m² (1 pW/m²), based on I0 = p0² / (ρ0 * c).

6If the measured root-mean-square (RMS) acoustic pressure in air is 0.2 Pa (N/m²), what is the corresponding Sound Pressure Level (음압레벨 SPL) in decibels relative to 2 × 10⁻⁵ Pa?

A.60 dB

B.70 dB

C.80 dB

D.90 dB

Explanation: Sound Pressure Level (SPL) is calculated using SPL = 20 * log10(p / p0). Here, p = 0.2 Pa and p0 = 2 × 10⁻⁵ Pa. Then p / p0 = 0.2 / (2 × 10⁻⁵) = 10⁴ = 10,000. Therefore, SPL = 20 * log10(10,000) = 20 * 4 = 80 dB.

7Two independent, uncorrelated acoustic sources operate simultaneously in a factory workshop, producing sound pressure levels of 80 dB and 83 dB at a given worker location. What is the combined total sound pressure level (합성 음압레벨)?

A.81.5 dB

B.83.0 dB

C.84.8 dB

D.163.0 dB

Explanation: When combining uncorrelated sound pressure levels: L_total = 10 * log10(10^(L1/10) + 10^(L2/10)) = 10 * log10(10^(8.0) + 10^(8.3)) = 10 * log10(10^8 * (1 + 10^0.3)) = 10 * log10(10^8 * (1 + 1.995)) ≈ 10 * log10(2.995 × 10^8) = 80 + 4.76 ≈ 84.8 dB.

8During an acoustic test of a blower, the total combined sound pressure level (target source plus background noise) is measured at 86.0 dB. When the blower is switched off, the ambient background noise (암소음) alone is 83.0 dB. What is the true sound pressure level generated solely by the blower?

A.3.0 dB

B.80.0 dB

C.83.0 dB

D.84.8 dB

Explanation: To isolate the target sound source from background noise: L_source = 10 * log10(10^(L_total/10) - 10^(L_bg/10)) = 10 * log10(10^8.6 - 10^8.3) = 10 * log10(3.981 × 10^8 - 1.995 × 10^8) = 10 * log10(1.986 × 10^8) = 80 + 10 * log10(1.986) ≈ 80 + 2.98 = 82.98 dB ≈ 83.0 dB.

9Under free-field spherical divergence conditions (자유음장), a small omnidirectional point sound source produces a sound pressure level of 76 dB at a distance of 10 m. What will be the sound pressure level at a distance of 40 m?

A.64 dB

B.70 dB

C.72 dB

D.73 dB

Explanation: For an ideal point source emitting spherical waves in a free field, geometric divergence follows the inverse square law: SPL2 = SPL1 - 20 * log10(r2 / r1). Here r1 = 10 m and r2 = 40 m, so r2 / r1 = 4. Since 20 * log10(4) = 20 * 0.602 = 12.04 dB, SPL2 = 76 - 12.04 ≈ 64 dB. This embodies the rule of a 6 dB reduction per doubling of distance.

10For an infinitely long, continuous highway line source (무한 선음원) exhibiting cylindrical wave divergence in a free acoustic field, what is the statutory rate of sound level reduction per doubling of distance?

A.1.5 dB per doubling of distance

B.2.0 dB per doubling of distance

C.3.0 dB per doubling of distance

D.6.0 dB per doubling of distance

Explanation: An ideal infinite line source emits cylindrical acoustic waves whose wavefront area expands proportionally to distance r (A = 2πrL). Acoustic intensity therefore diminishes as 1/r, leading to distance attenuation ΔSPL = 10 * log10(r2 / r1). For a doubling of distance (r2 / r1 = 2): ΔSPL = 10 * log10(2) ≈ 3.01 dB (3 dB reduction per doubling).

About the Engineer Noise and Vibration Exam

Comprehensive practice bank and engineering reference for the Engineer Noise and Vibration Examination (소음진동기사 자격시험), administered under qualification code 1665 by HRD Korea (한국산업인력공단) under the Ministry of Environment (환경부). This preparation bank features 100 verified multiple-choice questions across all 5 official subjects: 1) Introduction to Noise and Vibration (소음진동개론: wave propagation, decibel math, human audiology, weighting networks, simple harmonic motion), 2) Noise Control Technology (소음방지기술: acoustic absorption, room reverberation Sabine/Eyring, partition sound transmission loss, coincidence effect, acoustic barriers, and silencer design), 3) Noise and Vibration Standard Test Methods (소음진동공정시험기준: sound and vibration level meter specifications, microphone calibration, background noise corrections, industrial, traffic, and construction noise measurement procedures), 4) Vibration Control Technology (진동방지기술: single and multi-DOF dynamics, resonance, damping, vibration transmissibility TR, vibration isolators, and dynamic absorbers), and 5) Noise and Vibration Regulations (소음진동관계법규: Noise and Vibration Control Act 소음·진동관리법, factory emissions standards, construction noise limits, traffic control zones, and administrative compliance penalties). Note: This practice bank is an independent English-language MCQ study adaptation by OpenExamPrep.

Exam sponsor: Human Resources Development Service of Korea (HRD Korea / 한국산업인력공단 / Q-Net) under Ministry of Environment (환경부). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

Written CBT examination (1차 필기): 5 subjects of 20 four-option MCQs each — 소음진동개론, 소음방지기술, 소음진동 공정시험기준, 진동방지기술 and 소음진동 관계법규 — 100 questions in 150 minutes, passing with at least 40 points in every subject and 60 points overall. Practical examination (2차 실기): 소음진동방지 실무, a written-answer paper (필답형) of 3 hours marked out of 100, passed at 60 points. Note: Q-Net has published a revised 출제기준 that takes effect for sittings from 1 January 2027; the structure above is the one in force for 2026 sittings.

Time Limit

Written: 150 minutes (2.5 hours; 30 minutes per subject). Practical: 3 hours (written-answer)

Passing Score

Written: 40% floor per subject (과락 40점 미만 방지) and 60% overall average (전과목 평균 60점 이상); Practical: 60% or higher

Exam / Certification Fees

Written examination: ₩19,400 KRW; practical examination: ₩22,600 KRW

Exam sponsor website

Reported exam pass rate: ~30–40% (Written), ~35–50% (Practical). Annual pass rates vary by cycle based on the difficulty of quantitative vibration engineering calculations and practical descriptive problems. This describes exam candidates, not OpenExamPrep users or results from using our resources. Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Official sources

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

20%

Introduction to Noise and Vibration (소음진동개론)

Fundamental wave physics, sound velocity in air (c = 331.5 + 0.61 * T m/s) and structural media, characteristic acoustic impedance (Z = rho * c), reference thresholds for sound pressure (p0 = 2 x 10^-5 Pa) and power (W0 = 10^-12 W), logarithmic decibel addition and subtraction, spherical point-source and cylindrical line-source geometric attenuation, human hearing range (20 to 20,000 Hz), equal loudness contours, Fletcher-Munson curves, phon and sone loudness scaling, A-, B-, C-, and D-weighting filter networks, and vibration kinematics (displacement x, velocity v, acceleration a) in simple harmonic motion.

20%

Noise Control Technology (소음방지기술)

Sound absorption mechanisms and materials including porous fibrous media, resonant panel/membrane absorbers, and perforated cavity Helmholtz resonators. Architectural room acoustics, diffuse field energy density, room constant (R), reverberation time calculations via Sabine (T60 = 0.161 * V / A) and Eyring-Norris formulas. Sound transmission loss (TL) of partitions, theoretical Mass Law (TL = 20 * log10(m * f) - 48), critical frequency and coincidence effect (일치효과 / 맹점), composite partition average transmission loss, outdoor sound barrier diffraction attenuation (Maekawa method and Fresnel number), reactive (expansion chamber, side-branch) and dissipative (absorptive lining) silencer acoustics, and acoustic enclosures.

20%

Noise and Vibration Standard Test Methods (소음진동공정시험기준)

Statutory instrument standards for sound level meters (Type 1 precision and Type 2 general) and vibration level meters under KS and IEC specifications. Microphone characteristics, angle of incidence, and wind screen requirements (> 2 m/s). Strict background noise evaluation and logarithmic correction protocols (difference < 3 dB remeasurement, 3 to 9 dB correction, >= 10 dB no correction). Field measurement protocols: factory site boundary line evaluation, construction site equivalent noise levels (LAeq, 5min), road traffic noise sampling, railway noise maximum levels (LAmax), and aircraft noise evaluation metrics (Lden / WECPNL). Vibration transducer mounting methods (rigid stud mounting, magnetic base, mounting wax, and ground spikes).

20%

Vibration Control Technology (진동방지기술)

Lumped-parameter mechanical dynamics of 1-degree-of-freedom (1-DOF) and 2-degree-of-freedom (2-DOF) oscillatory systems. Free undamped, damped, and forced steady-state vibration response. Natural frequency calculation (fn = (1 / 2pi) * sqrt(k / m) ≈ 5 / sqrt(static deflection)), critical damping coefficient (cc = 2 * sqrt(k * m)), damping ratio (zeta), and logarithmic decrement (delta). Dynamic vibration transmissibility (TR) curves, active vs passive vibration isolation criteria (frequency ratio r = omega / omega_n > sqrt(2)), isolation efficiency (I = 1 - TR). Engineering design and selection of vibration isolators: elastomeric rubber mounts, steel helical coil springs, pneumatic air mounts, damping materials, and Frahm dynamic vibration absorbers.

20%

Noise and Vibration Regulations (소음진동관계법규)

Statutory mandates under the Noise and Vibration Control Act (소음·진동관리법), its Enforcement Decree, and Enforcement Regulations. Legal definitions of noise emission facilities, vibration emission facilities, and quiet machinery. Factory noise emission standards across General, Semi-Industrial, and Industrial zones for daytime (07:00-18:00), evening (18:00-22:00), and nighttime (22:00-07:00). Regulatory standards for construction work noise and traffic noise regulation areas. Statutory appointment, qualifications, and operational responsibilities of Environmental Technical Managers (환경기술인). Administrative enforcement procedures: improvement orders, orders to suspend operations, facility closure orders, and administrative fines (과태료 / 벌칙).

Preparing for the Engineer Noise and Vibration Exam

What You Need to Know

Passing score: Written: 40% floor per subject (과락 40점 미만 방지) and 60% overall average (전과목 평균 60점 이상); Practical: 60% or higher
Assessment: Written CBT examination (1차 필기): 5 subjects of 20 four-option MCQs each — 소음진동개론, 소음방지기술, 소음진동 공정시험기준, 진동방지기술 and 소음진동 관계법규 — 100 questions in 150 minutes, passing with at least 40 points in every subject and 60 points overall. Practical examination (2차 실기): 소음진동방지 실무, a written-answer paper (필답형) of 3 hours marked out of 100, passed at 60 points. Note: Q-Net has published a revised 출제기준 that takes effect for sittings from 1 January 2027; the structure above is the one in force for 2026 sittings.
Time limit: Written: 150 minutes (2.5 hours; 30 minutes per subject). Practical: 3 hours (written-answer)
Exam / certification fees: Written examination: ₩19,400 KRW; practical examination: ₩22,600 KRW Official sources

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Engineer Noise and Vibration: Suggested Study Strategy

1Master Decibel Arithmetic and Geometric Attenuation: Ensure you can rapidly perform logarithmic operations without hesitation: calculating combined sound pressure levels (L_total = 10 * log10(sum 10^(Li/10))), subtracting background noise (Ls = 10 * log10(10^(Lc/10) - 10^(Lb/10))), and calculating distance attenuation for point sources (-6 dB per doubling of distance) vs line sources (-3 dB per doubling of distance).

2Focus Heavily on Vibration Isolation Mechanics: Natural frequency (fn = (1 / 2pi) * sqrt(k/m) ≈ 5 / sqrt(static deflection)), transmissibility (TR), and isolation efficiency (I = 1 - TR) appear extensively on both the written and practical examinations. Understand why isolation only occurs when the frequency ratio r = omega / omega_n > sqrt(2), and how damping reduces peak resonance amplitude but slightly impairs isolation at high frequencies (r > sqrt(2)).

3Memorize Standard Test Method Background Noise Correction Rules: Know the exact criteria under the official Korean standard (소음진동공정시험기준): if the difference between measured noise and background noise is less than 3 dB, the measurement is invalid and must be retaken; if between 3.0 dB and 9.9 dB, apply the statutory correction table or equation; if 10 dB or greater, no correction is applied.

4Internalize Room Reverberation and Partition Sound Insulation: Practice Sabine's formula (T60 = 0.161 * V / A) and Eyring's formula, composite wall transmission loss calculations (TL_comp = 10 * log10(S / sum(Si * tau_i))), and the coincidence effect (fc inversely proportional to wall thickness h) where bending wavelength matches acoustic wavelength in air.

5Review Key Regulatory Emission Standards: Memorize the daytime (07:00-18:00), evening (18:00-22:00), and nighttime (22:00-07:00) factory noise emission limits for General Residential (50 / 45 / 40 dB(A)) and Quasi-Industrial (60 / 55 / 50 dB(A)) zones, construction site limits (65 dB(A) daytime in residential zones), and administrative penalty progressions.

Frequently Asked Questions

What is the Engineer Noise and Vibration (소음진동기사) qualification?

The Engineer Noise and Vibration (소음진동기사, Qualification Code 1665) is a Republic of Korea national technical qualification administered by HRD Korea under the authority of the Ministry of Environment. It certifies engineering competence in acoustic design, machinery vibration isolation, environmental noise/vibration monitoring, and regulatory compliance under the Noise and Vibration Control Act.

What are the exam subjects and passing requirements?

The written examination (1차 필기시험) tests 5 subjects: 1) Introduction to Noise and Vibration, 2) Noise Control Technology, 3) Noise and Vibration Standard Test Methods, 4) Vibration Control Technology, and 5) Noise and Vibration Regulations. Each subject contains 20 multiple-choice questions (100 total, 150 minutes). Candidates must score at least 40% in each subject to avoid automatic disqualification (과락 40점 미만 방지) and achieve an overall average score of 60% or higher across all 100 questions.

What is the structure of the practical examination (2차 실기시험)?

The practical examination (소음진동 실무) is a 2.5-hour written descriptive test (필답형, 100 points). Candidates solve advanced engineering calculation problems, acoustic barrier dimensioning, vibration isolation design, room reverberation adjustments, and statutory compliance scenarios. A score of 60 points or higher is required to pass.

What are the examination fees and scheduling timeline?

As set by HRD Korea, the written CBT examination fee is ₩19,400 KRW and the practical descriptive examination fee is ₩22,600 KRW. The examination is administered 3 times annually (Regular Engineer Cycles 1, 2, and 3). Online registration and slot reservations are managed through the official Q-Net portal (q-net.or.kr).

What career roles legally require an Engineer Noise and Vibration holder?

Under Article 19 of the Noise and Vibration Control Act, designated business establishments operating noise and vibration emission facilities must appoint an Environmental Technical Manager (환경기술인). Certified engineers are also legally required for environmental impact assessment consulting, acoustic consulting firms, architectural design offices, construction environmental monitoring teams, automotive NVH engineering, and public environmental research institutes.

Is this OpenExamPrep question bank an official examination simulation?

No. This practice bank is an independent English-language multiple-choice study adaptation developed by OpenExamPrep. It includes official Korean technical terms and statutory phrasing in parentheses to enable bilingual engineers, international practitioners, and environmental specialists to master the quantitative calculations, standard measurement methods, and regulatory frameworks of the Korean national exam.