DoAssignment.ca

E1.2 · Assess wave and noise impacts and technologies that reduce them

Learn to assess wave and noise impacts and technologies that reduce them through clear examples and targeted practice.

Ontario Grade 11 Physics

Waves and Sound

Ontario Grade 11 Physics | E1.2

A sound wave carries energy through a material such as air. Sound can help us communicate, notice warnings, and enjoy music. Unwanted or excessive sound is often called noise. Noise can interfere with communication, disturb sleep, make concentration difficult, and, at high levels or after long exposure, harm hearing. In this lesson, the physical system is the sound source, the material carrying the sound, and the people or animals receiving it. Use a stationary room as the reference frame. Sound travels from source to listener; this direction describes the wave’s path, not a positive or negative sign. Sound level is a scalar: it has a size but no direction. The lesson focuses on assessing impacts and choosing ways to reduce them.

What you will learn

1. Prerequisite bridge: sound, waves, and level

A wave is a travelling disturbance that transfers energy. A sound wave is a vibration that travels through a material. Air particles vibrate back and forth as the disturbance passes; they do not travel all the way from the source to the listener. Frequency is the number of vibrations each second, measured in hertz (Hz). It helps describe pitch. Amplitude describes the size of a vibration. A larger sound-wave amplitude is generally associated with a louder sound.
Sound level is commonly reported in decibels (dB). The decibel scale is logarithmic: equal steps in dB do not mean equal additions of sound energy. A rise of 10 dB corresponds to ten times the sound intensity, while a rise of 20 dB corresponds to one hundred times the intensity. Sound intensity is sound power passing through a given area; its SI unit is watts per square metre (W/m2\mathrm{W/m^2}). In many everyday comparisons, a sound-level meter reading is more useful than trying to judge intensity by ear.
A sound-level reading alone does not describe every impact. The result can depend on how loud the sound is, how long someone hears it, how often it occurs, and the situation. A brief sound may interrupt a quiet task. Repeated or long exposure to loud sound can be a hearing risk. Do not treat one dB value as a guaranteed boundary between safe and harmful exposure for every person and setting.
I=PAI=\frac{P}{A}

2. Assessing wave and noise impacts

Noise is not defined only by a high sound level. A sound can be unwanted because it interrupts speech, study, rest, or another activity. A quieter sound that occurs repeatedly at night may be more disruptive than a louder sound that lasts briefly during the day. Wildlife can also be affected when human-made sound interferes with communication or normal behaviour. The effect depends on the receiver and the setting.
Use evidence carefully. A sound-level meter can provide a measured level at a stated location and time. A useful comparison keeps the measurement position and meter conditions consistent. Record whether the sound is continuous, intermittent, or brief, and note the activity affected. A single reading does not establish a person’s full exposure over a day, prove a health outcome, or show that the same sound affects everyone equally.
A proposed investigation could compare readings before and after a barrier is placed between a sound source and a meter. The source, meter position, and other conditions should be kept as similar as possible. These are planned steps, not measured results. A computer simulation can help explore a model, but its output is simulated evidence, not a physical measurement.

3. Technologies and strategies that reduce noise

Noise can be reduced at the source, along the path, or at the receiver. Source controls reduce the sound made in the first place. Examples include maintaining noisy equipment, choosing quieter equipment, or limiting unnecessary operation. Path controls reduce sound travelling from source to receiver. A solid barrier can block some direct sound, while sound-absorbing materials can reduce reflections inside a room. Absorption means that a material takes in some sound energy instead of reflecting it.
At the receiver, well-fitting earplugs or earmuffs reduce the sound that reaches the ears. Their performance depends on correct fit and use. A barrier or protective device does not remove every sound in every situation. Sound may pass around a barrier, and openings can reduce its effectiveness. Different technologies suit different problems: improving a room for speech is not the same task as protecting a worker near loud machinery.
Active noise reduction uses a device that produces a sound designed to reduce some incoming sound. It can work well for certain steady, low-frequency sounds, but it does not cancel every sound in every setting. No one technology should be assumed to eliminate risk. A strong assessment considers the expected reduction, the people and activities involved, practical limits, and whether the solution addresses the source, path, or receiver.

4. Comparing reductions with sound-level differences

When two sound levels are given, subtract the lower level from the higher level to find their difference. The result is in decibels. This subtraction compares levels; it does not mean that the sound energy was reduced by that same percentage. Since the dB scale is logarithmic, a seemingly modest change in dB can correspond to a much larger change in intensity.
A reduction should be judged in context. Compare readings made at the same position and under similar conditions. Then ask whether the change is likely to address the impact: for example, whether speech is easier to hear, whether a quiet activity is less interrupted, or whether exposure at the receiver has been reduced. These observations support an assessment, but they do not by themselves prove a medical result.
ΔL=Lbefore−Lafter\Delta L=L_{\mathrm{before}}-L_{\mathrm{after}}

Worked example

Comparing an intervention

A classroom sound-level meter reads 68 dB before a door is closed and 61 dB after it is closed. Assume both readings are taken at the same position under similar conditions. Find the sound-level reduction and assess what the comparison shows.
  1. Define the comparison
    The system is the classroom sound reaching the meter. The reference frame is the stationary classroom, and the sound travels from the source toward the meter. Sound level is scalar, so no positive or negative direction is needed. The unknown is the reduction in level.
  2. Use the level difference
    Subtract the after-intervention reading from the before-intervention reading. Both values have units of decibels.
    ΔL=68 dB−61 dB=7 dB\Delta L=68\,\mathrm{dB}-61\,\mathrm{dB}=7\,\mathrm{dB}
  3. Interpret the evidence
    The reading is 7 dB lower at the meter after the door is closed. This supports the conclusion that the door reduced the sound reaching that position in these conditions. It does not establish the same reduction everywhere or prove a health effect.
Answer: The measured sound level decreased by 7 dB at the meter.
Check: The units remain dB, and a lower after-reading gives a positive reduction. A 7 dB change is plausible; it must not be described as a 7% energy decrease.

Worked example

Interpreting a larger difference

At a listening position, one condition measures 80 dB and a quieter condition measures 60 dB. How does the sound intensity compare, using the rule that each 10 dB increase corresponds to ten times the intensity?
  1. Define the comparison
    The system is sound reaching the same listening position. Use the stationary room as the reference frame. Sound travels from the source to the listener, but the level and intensity comparisons are scalar. The unknown is the intensity ratio.
  2. Find the level difference
    The higher-level condition exceeds the quieter condition by 20 dB.
    80 dB−60 dB=20 dB80\,\mathrm{dB}-60\,\mathrm{dB}=20\,\mathrm{dB}
  3. Apply the stated rule
    A 20 dB rise contains two 10 dB steps. Each step multiplies intensity by ten, so the total ratio is one hundred to one.
    10×10=10010\times10=100
Answer: The 80 dB condition has 100 times the sound intensity of the 60 dB condition.
Check: The ratio has no units because it compares two intensities. A higher level gives a larger intensity, and a 20 dB difference correctly represents two tenfold steps.

Worked example

Choosing a control for a specific impact

A steady machine sound makes conversation difficult at a nearby desk. The sound is measured at 74 dB at the desk. A proposed enclosure is expected to reduce the measured level there by 8 dB. What level is expected, and what else should be assessed?
  1. Define the system and direction
    The system is the machine sound travelling through the room to the desk. The room is the reference frame. The direction of travel is from machine to desk; level itself has no direction. The unknown is the expected level after the enclosure.
  2. Subtract the proposed reduction
    A reduction means the after-level is lower than the original level. Keep the level units through the calculation.
    74 dB−8 dB=66 dB74\,\mathrm{dB}-8\,\mathrm{dB}=66\,\mathrm{dB}
  3. Assess the proposal
    The estimate is 66 dB at the desk if the expected reduction is achieved. The enclosure acts near the source and along the sound path. A fair assessment would measure at the same desk position under comparable conditions and check whether conversation is less interrupted.
Answer: The expected level is 66 dB at the desk, if the proposed 8 dB reduction is achieved.
Check: The result is in dB and is lower than 74 dB, as a reduction requires. The value is an estimate, not measured evidence, and the impact on conversation still needs assessment.

Common mistakes and how to avoid them

Treating a 10 dB increase as only ten percent more sound energy.
Correction: A 10 dB increase corresponds to ten times the sound intensity. Decibels use a logarithmic scale.
Assuming one sound-level reading proves that a sound is harmless or harmful to everyone.
Correction: Consider duration, repetition, context, and the receiver. A reading is evidence about sound level at a place and time, not a complete health assessment.
Assuming any wall or hearing protector removes all noise.
Correction: Controls have limits. Sound can pass around barriers, and protection depends on fit and use.
Calling a planned test or simulation a measured result.
Correction: Identify proposed procedures as plans and simulation outputs as model results. Only actual instrument readings are physical measurements.

Lesson summary

Check your understanding

Question 1

A sound level rises from 50 dB to 60 dB. According to the lesson’s rule, how does intensity change?
  1. It doubles.
  2. It becomes ten times as large.
  3. It increases by ten percent.
  4. It remains the same.
Show answer and explanation
It becomes ten times as large.
A 10 dB increase corresponds to ten times the sound intensity.

Question 2

Which is the strongest assessment of a proposed room barrier?
  1. Assume it works because it is thick.
  2. Measure before and after at the same position under similar conditions, then consider the activity affected.
  3. Use one reading from a different room.
  4. Treat a computer simulation as a physical measurement.
Show answer and explanation
Measure before and after at the same position under similar conditions, then consider the activity affected.
Consistent measurement conditions make the comparison more meaningful, and the assessment should connect the change to the real impact.

Question 3

A source measures 72 dB before a control and 66 dB after it. What is the reduction?
  1. 6 dB
  2. 12 dB
  3. 66 dB
  4. 138 dB
Show answer and explanation
6 dB
Subtract the after-level from the before-level: 72 dB−66 dB=6 dB72\,\mathrm{dB}-66\,\mathrm{dB}=6\,\mathrm{dB}.

Key terms

Amplitude
A measure of the size of a wave’s vibration.
Decibel (dB)
A unit used to report sound level on a logarithmic scale.
Frequency
The number of vibrations each second, measured in hertz.
Intensity
Sound power passing through a given area; measured in watts per square metre.
Noise
Sound that is unwanted or disruptive in a particular situation.
Sound absorption
The taking in of some sound energy by a material rather than reflecting it.
Sound wave
A travelling vibration that transfers energy through a material.

Continue through SPH3U

View the complete SPH3U Ontario Grade 11 Physics curriculum and lessons

About this lesson and its review

Published by DoAssignment. This AI-assisted lesson follows Ontario Grade 11 Physics (SPH3U), expectation E1.2. It is a study resource, not an official curriculum publication.

Before publication, the draft is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability, and then requires administrator approval. Errors can still occur, so corrections are welcomed.

Official curriculum reference

Report a correction or ask a question