# Exercise involving acoustics physics engineering

• louisnach
In summary, to reject a disturbance signal propagating in a ventilation duct with a fundamental frequency of 250Hz and odd harmonics in its spectrum, the appropriate filter option is to use an expansion chamber with dimensions that will attenuate the signal by 20dB. This is possible because the expansion chamber has been proven to attenuate each odd harmonic by the same amount as the fundamental frequency. Another option, using a helmotz band stop resonator, would allow for complete attenuation of the 250Hz frequency, but this is not necessary for the given problem.
louisnach

## Homework Statement

A disturbance signal propagates in a ventilation duct with cross-sectional area A=0,04m2. The fundamental frequency of the disturbance signal is 250Hz and its spectrum consists of odd harmonics only.

Choose the appropriate filter options for rejecting this particular disturbance.
Choose the dimension of your filter in order to attenuate by 20 dB

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## The Attempt at a Solution

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I hesitate between two approachs: using a expansion chamber with transmitted power formula
= 4 / ( 4cos²(kl)+ (A1/A2 +A2/A1)²sin²(kl) ) where A area of the duct and A2 area of the chamber and l length of the chamber, and getting a transmitted value in order to attenuate 20dB, in the lectures the expansion chamber was not presented as a filter so maybe it is completely stupid thie approach

the other idea is using a helmotz band stop resonnator but then it become possible to attenuate completely 250Hz by designing a helmotz resonnator with resonnance frequency equal to 250Hz, so i don't understand why it is asked to attenuate 20dB

In both case i don't know what means "its spectrum consists of odd harmonics only" and how to use this.

Happy end of year for everybody (sorry for my english i am not a native english speacker)

Sorry I can't quite make the leap to acoustics just now, but if it were a problem in electrical engineering, involving a transmission line, we might use a stub of transmission line shunted across the main line. By choosing a suitable length, the fundamental and odd harmonics can be reduced greatly.

It's okay i solved it by using expansion chamber, when it attenuates a frequency f0 (at maximum attenuation) it is possible to show that it attenuates the same each odd harmonics (2n+1)*f0, so the expansion chamber is the good filter

## 1. What is the purpose of using acoustics in exercise?

The purpose of using acoustics in exercise is to improve the overall experience and effectiveness of the workout. Acoustics can be used to create an energizing and motivating atmosphere, reduce distracting noises, and enhance the clarity of instructions or music.

## 2. How does physics play a role in exercise involving acoustics?

Physics plays a role in exercise involving acoustics by determining how sound waves travel and interact with different materials. Understanding the principles of sound waves, such as frequency and amplitude, can help engineers design better acoustics systems for exercise spaces.

## 3. What engineering techniques are used to improve acoustics in workout spaces?

Some engineering techniques used to improve acoustics in workout spaces include sound absorption, diffusion, and isolation. Sound absorption materials, such as acoustic foam, can reduce echoes and reverberation. Diffusion panels can scatter sound waves to create a more balanced and natural sound. Isolation techniques, such as soundproofing, can prevent outside noise from entering the workout space.

## 4. How can acoustics affect the safety of an exercise environment?

Acoustics can affect the safety of an exercise environment in several ways. Excessive noise levels can cause hearing damage, especially in high-intensity workouts where participants are exposed to loud music for extended periods. Poor acoustics can also make it difficult to hear instructions or emergency announcements, posing a safety risk.

## 5. Are there any specific guidelines for designing acoustics in exercise spaces?

Yes, there are specific guidelines for designing acoustics in exercise spaces. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has published standards for acoustical design in fitness facilities, which cover factors such as noise control, sound isolation, and speech intelligibility. Additionally, organizations like the Acoustical Society of America (ASA) and the National Strength and Conditioning Association (NSCA) provide resources and recommendations for designing acoustics in exercise spaces.

• General Engineering
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