Reflection of sound depends on frecuency?

• idmena
In summary, the conversation discusses the reflection and transmission of acoustic waves on different media, and how it is determined by the characteristic impedance of the wave in each media. It is also noted that in acoustics, the impedance can change with frequency, unlike in light waves. The book being studied also considers the components used to derive characteristic impedance and how it varies with frequency.
idmena
Hi! I need some help understanding something related to sound.

I am currently studying a book called Sound Propagation. An Impedance Based Approach, by Yang-Hann Kim. There is a part where he talks about reflection and transmission of acoustic waves on a flat surface of discontinuity. He gets the coefficients for presure and velocity, and them combines them to get the power reflection and transmission, that is the one that would affect what we can hear. But I find it odd that his equations do not depend on frecuency, only in the characteristic impedance of the two media. In other words. The reflecion and transmission of power do not depend of the frecuency of the wave, all the components of the incoming signal are reflected and transmited by the same factor.

Later on he continues to talk about transmission loss at a partition. In that case he considers a thin wall, and takes into account the mass, the spring constant and the damping coefficient. In that case he doesn't even consider the characteristic impedance of the material that the wall is made of, and that equation does depend on the frecuency of the incident signal. He explained that when the incoming frecuency is much bigger than the resonant frecuency of the wall that's when the well known mass law applies, and continues to consider the other cases.

So tell me, how is this possible? When an acoustic waves enters a different medium all of it's components are reflected by the same factor? If so, how comes the transmission loss depends on the frecuency? The transmission loss is defined in terms of the transmission coeficient, which he stated before that depends only on the characteristic impedance of the media.

Attached are two pictures with the equations I mentioned. Sorry I don't know latex.

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The reflection of a wave from a boundary where there is partial transmission and partial reflection is determined by the characteristic impedance of the wave in each media. Thus when dealing with reflection one starts by determining the impedance. The impedance will change with frequency (dispersion) and hence the reflection changes with frequency. The problem is important in acoustics where it is perfectly possible to have the same impedance (and hence no reflection at the boundary) for two different media and vastly different wave velocities; this does not happen with light waves so one can take short cuts in light waves that might lead one to think that reflection is a function of wave velocity, but light waves actually follow the same rules, but the properties of those media that transmit light waves are restricted, unlike acoustic media.

In your second paragraph, I have not seen the book, but it sounds like he is dealing with those components that are used to derive that characteristic impedance - deriving the characteristic impedance from first principles. So you see the same variation of characteristic impedance with frequency.

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1. How does the frequency of sound affect its reflection?

The frequency of sound refers to the number of vibrations per second that the sound wave produces. As the frequency of sound increases, the wavelength decreases, causing the sound to reflect differently. This can result in changes in the direction, amplitude, and intensity of the reflected sound wave.

2. Can different frequencies of sound be reflected differently?

Yes, different frequencies of sound can be reflected differently. This is because the surface that the sound wave is reflecting off of may have different properties that can affect how the sound wave is reflected. For example, a rough surface may reflect high frequency sounds differently than a smooth surface.

3. How does sound frequency affect the distance that a sound can travel?

The frequency of sound can affect the distance that a sound can travel. High frequency sounds have shorter wavelengths and can therefore travel shorter distances before dissipating. Low frequency sounds, on the other hand, have longer wavelengths and can travel further before dissipating. This can impact how far the sound can be heard.

4. What role does frequency play in the echo of a sound?

The frequency of sound plays a significant role in the echo of a sound. When a sound wave reflects off of a surface, it may experience changes in its frequency. This can result in the creation of an echo, which is a repetition of the original sound. The frequency of the echo may be different than the original sound depending on the surface it reflects off of.

5. Can frequency affect the quality of sound reflection?

Yes, frequency can affect the quality of sound reflection. High frequency sounds tend to reflect more clearly and sharply, while low frequency sounds may be more muffled and distorted when reflected. This is due to the differences in the wavelengths and how they interact with the reflecting surface.

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