Sensitivity and frequency response (A-level only) Flashcards – AQA A-level Physics (7408)

What is sound intensity, and what is its SI unit?

Sound power transmitted per unit area normal to the direction of propagation; $\mathrm{W\,m^{-2}}$.

What is the formula for sound intensity level $L_I$ in terms of intensity $I$ and reference intensity $I_0$?

$L_I=10\log_{10}\left(\frac{I}{I_0}\right)\,\mathrm{dB}$

What reference intensity is used for sound intensity level, and what does it represent?

$I_0=1.0\times10^{-12}\,\mathrm{W\,m^{-2}}$, the threshold of hearing.

What intensity does a sound intensity level of $0\,\mathrm{dB}$ represent?

The reference intensity $I_0$, not zero intensity.

What is the formula for the intensity-level difference between two sounds with intensities $I_1$ and $I_2$?

$L_1-L_2=10\log_{10}\left(\frac{I_1}{I_2}\right)\,\mathrm{dB}$

What do equal changes in sound intensity level imply about the corresponding intensities?

They imply equal ratios of intensity, not equal intensity differences.

Why is a logarithmic scale useful for expressing sound levels?

Human perception responds to relative intensity changes over a very large range.

Why does sound intensity level alone not fully determine perceived loudness?

Perceived loudness also depends on frequency.

How does a sound level meter detect and display sound?

It uses a microphone to detect sound and displays a level in decibels.

What does a decibel sound-level reading express?

A logarithmic level relative to a reference.

What must be considered when interpreting a sound-level meter’s dB reading?

The frequency weighting used.

What does A-weighting do to a sound-level reading?

It reduces the contribution of frequencies to which hearing is less sensitive. A dBA reading is therefore not just a unit conversion of an unweighted reading.

Does a dBA reading give an exact measure of perceived loudness in every situation?

No. A-weighting accounts for frequency-dependent hearing sensitivity, but does not measure perceived loudness exactly in every situation.