What’s difference between time weightings: Slow response and Fast response? 2- Why is the post-calibration for your sound level meter necessary: 3- Briefly explain the main difference and their primary application among three type of sound level meter types according to the ANSI S1.4 standard.

QUESTION

1- What’s difference between time weightings: Slow response and Fast response?

2- Why is the post-calibration for your sound level meter necessary:

3- Briefly explain the main difference and their primary application among three type of sound level meter types according to the ANSI S1.4 standard.

4-A female employee is required to work in different working environments with the following time and noise level: 85 dBA for 4 hrs, 90.5 dB for 2 hrs, and 92.3 dB for 2 hrs. If you use noise dosimeter to monitor her noise exposure, what the reading result (noise dose) will be? Will it be in compliance and explain the reason?

5- Please determine the lower and upper band limits (that is, f1 and f2) for the naming octave band 4,000 Hz.

6- What is the LAS?

7- An acoustic calibrator usually can produce a reference sound level of _____ dB at 1 KHz.

8- If you want to use a sound level meter for noise measurement to comply with OSHA regulations, you need use a meter with setting of ______________ (one of frequency weightings), ______________ (one of time weightings), and __________________ (the level of accuracy / one of ANSI types). Briefly explain why these settings are needed.

9- Why is the pre-calibration for your sound level meter necessary:

10- Most of sound level meters are used to measure __________ (sound power, intensity or pressure).

11- At which frequency (_________Hz), the weighting among A, B and C have the same reading?

12- Noise dosimeter has filter settings for frequency (A/B/C/Z), time response (Slow vs Fast vs Impulse), and ANSI type for accuracy (0, 1 and 2). Using the attached Quest Edge eg5 manual or other credible sources as references, please discuss what filter settings should you use for OSHA compliance, and briefly explain why these settings are needed.

13- Which frequency weighting (A, B, C or F) should you use for octave band analyzer? Briefly explain the reason.

14- Read the two manuals, and explain why you should use windscreen when you use instruments to measure sound level?

15- A computer cooling fan has 5 blades rotating with 6,000 rpm, what is the blade pass frequency?

ANSWER

 Post-calibration for a sound level meter is necessary to ensure accurate and reliable measurements. Over time, the components and sensors of a sound level meter can experience drift or deviations from their initial calibration. Post-calibration involves comparing the meter’s readings to a reference standard and making necessary adjustments or corrections to align the meter’s measurements with the known standard. This process helps maintain the accuracy and reliability of the sound level meter, ensuring that the measurements are traceable and comply with regulatory standards.

According to the ANSI S1.4 standard, there are three main types of sound level meters

   Type 0: Precision sound level meters with high accuracy and wide frequency range. They are typically used in laboratory or research applications where the highest level of accuracy is required.

   Type 1: General-purpose sound level meters suitable for most environmental and occupational noise measurements. They have slightly lower accuracy compared to Type 0 meters but still meet the requirements of most noise measurement standards.

   Type 2: Sound level meters intended for basic industrial and environmental noise measurements. They have lower accuracy compared to Type 1 meters and are suitable for less stringent applications where a lower level of accuracy is acceptable.

The primary application of each type depends on the specific requirements of the measurement scenario, with Type 0 being the most accurate and Type 2 being the least accurate but more cost-effective option for certain applications.

 To calculate the noise dose for the female employee, we need to use the concept of noise dosimetry, which takes into account the duration and intensity of exposure. The noise dose is a measure of cumulative noise exposure over time. It is calculated using the formula:

   Noise Dose (%) = (C1/T1) + (C2/T2) + (C3/T3) + …

   Where C represents the total time of exposure at a given noise level, and T represents the maximum allowable exposure time at that level.

   For the given scenario:

   – 85 dBA for 4 hrs: This contributes (4/8) * 100% = 50% to the noise dose.

   – 90.5 dBA for 2 hrs: This contributes (2/4) * 100% = 50% to the noise dose.

   – 92.3 dBA for 2 hrs: This contributes (2/2) * 100% = 100% to the noise dose.

   Adding up these contributions, the total noise dose would be 50% + 50% + 100% = 200%. Since the total exceeds 100%, it indicates that the employee has exceeded the permissible noise exposure limits. The reading result indicates non-compliance with the noise exposure standards, and appropriate measures should be taken to mitigate the noise exposure or provide suitable hearing protection.

Octave bands are commonly used in sound measurements to analyze the frequency content of sound. The lower and upper band limits for octave band 4,000 Hz can be determined using the center frequency and bandwidth of each octave band. In the case of octave band 4,000 Hz, the lower band limit (f1) would

 be 2,000 Hz, and the upper band limit (f2) would be 8,000 Hz. This means that the band covers the frequency range from 2,000 Hz to 8,000 Hz, with a center frequency of 4,000 Hz.

 LAS stands for “Linearly Averaged Sound Level.” It is a measure of the cumulative sound energy over a specified time period, typically expressed in decibels (dB). LAS takes into account both the steady-state and fluctuating components of sound, providing a more comprehensive representation of the overall sound level.

An acoustic calibrator usually produces a reference sound level of 94 dB at 1 KHz. This standardized sound level serves as a reference point for calibrating sound level meters and ensuring their accuracy. By generating a known sound level, the calibrator allows the sound level meter to be calibrated and adjusted accordingly, ensuring consistent and reliable measurements.

To comply with OSHA (Occupational Safety and Health Administration) regulations for noise measurement, the sound level meter should be set to:

   – Frequency Weighting: A-weighting (dB(A))

   – Time Weighting: Slow response (SLOW)

   – Accuracy Level: Type 2 (or higher, such as Type 1 or Type 0)

   These settings are necessary for several reasons:

   – A-weighting: OSHA regulations specify the use of A-weighting to account for the frequency sensitivity of human hearing. A-weighting emphasizes the mid-range frequencies to align the sound measurements with human perception. It provides a more accurate representation of the potential impact of noise on human hearing.

   – Slow response: OSHA regulations require the use of slow time weighting (typically with a time constant of 1 second) for measuring occupational noise exposure. Slow response provides a more comprehensive and representative measurement of the overall sound level, considering both steady-state and fluctuating components.

   – Accuracy Level: OSHA regulations generally recommend the use of a Type 2 sound level meter or higher for compliance measurements. Type 2 meters provide an acceptable level of accuracy for most occupational noise measurements, ensuring that the measurements align with the required standards.

Pre-calibration for a sound level meter is necessary to establish a baseline calibration reference before its initial use. It involves verifying and adjusting the meter’s readings against a known reference standard. Pre-calibration ensures that the sound level meter is functioning correctly and accurately calibrated before conducting measurements. It provides confidence in the reliability and accuracy of subsequent measurements, reducing measurement uncertainties and ensuring compliance with regulatory standards.

Most sound level meters are used to measure sound pressure levels. Sound pressure is the most common parameter measured, as it directly relates to the intensity and loudness of sound. Sound power and sound intensity are other important quantities in acoustics, but they require specialized equipment and measurement techniques beyond the scope of standard sound level meters.

The frequency at which the A, B, and C weightings have the same reading is at 1,000 Hz. At this frequency, the A-weighting, B-weighting, and C-weighting curves intersect and provide equal readings on a sound level meter. This frequency is often referred to as the “knee frequency” or “cross-over frequency” and is an important reference point for understanding the frequency response characteristics of different weightings.

For OSHA compliance with a noise dosimeter, the recommended filter settings would be:

    – Frequency Weighting: A-weighting (dB(A))

    – Time Response: Slow

    – ANSI Type: Type 2

    These settings are chosen based on OSHA’s guidelines and requirements:

    – A-weighting is used to approximate the frequency response of human hearing and is commonly employed in noise exposure assessments.

    – Slow time response is specified by OSHA for occupational noise measurements to capture both steady-state and fluctuating noise levels over time.

    – Type 2 sound level meters or higher are recommended by OSHA to ensure an acceptable level of accuracy and compliance with regulatory standards.

Octave band analyzers are typically used to analyze the frequency content of sound. The appropriate frequency weighting for an octave band analyzer depends on the purpose of the measurement. In most cases, the frequency weighting used is the flat frequency response, also known as “Z-weighting” or “unweighted.” This weighting does not apply any frequency correction to the measured sound levels and provides an unbiased representation of the sound energy across all frequencies within the analyzed octave band. It is commonly used for octave band analysis to accurately assess the contribution of different frequency bands to the overall sound level.

Using a windscreen when measuring sound levels with instruments is essential to ensure accurate and reliable measurements. Windscreen or wind protection is typically a foam or mesh covering placed over the microphone of the instrument. It serves several purposes:

    – Minimize wind noise: Wind blowing across the microphone can generate turbulence and cause fluctuations in the measured sound levels, resulting in inaccurate readings. A windscreen acts as a physical barrier, reducing the impact of wind on the microphone and minimizing the effect of wind-induced noise.

    – Protect the microphone: Wind can carry dust, debris, or moisture that could potentially damage or affect the performance of the microphone. A windscreen acts as a protective layer, preventing foreign particles from directly reaching the microphone element.

    – Improve measurement accuracy: By reducing wind noise and disturbances, a windscreen allows for more precise and reliable sound level measurements, particularly in outdoor or windy environments.

The blade pass frequency of a fan can be calculated by multiplying the number of blades by the rotational speed (RPM) and dividing by 60 to convert it to Hz. In this case, the computer cooling fan has 5 blades rotating at 6,000 RPM.

   Blade pass frequency = (Number of blades * RPM) / 60

   Blade pass frequency = (5 * 6,000) / 60

   Blade pass frequency = 500 Hz

   Therefore, the blade pass frequency of the computer cooling fan is 500 Hz. The blade pass frequency represents the frequency at which the blades of the fan pass through a fixed point in one second, creating an audible tone or vibration.