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\(\bullet\) The range of human hearing. A young person with normal hearing can hear sounds ranging from 20 Hz to 20 \(\mathrm{kHz}\) .How many octaves can such a person hear? (Recall that if two tones differ by an octave, the higher frequency is twice the lower frequency.)

Short Answer

Expert verified
A person can hear about 10 octaves.

Step by step solution

01

Understanding the Concept of an Octave

An octave is a doubling of a frequency. For example, if one frequency is 20 Hz and another is 40 Hz, these frequencies are one octave apart. This means for every doubling of frequency, there is an increase of one octave.
02

Initial Frequency Range

We know that the range of human hearing is from 20 Hz to 20,000 Hz (20 kHz). We need to determine how many times the frequency can double (20 Hz doubling to 40 Hz, 40 Hz doubling to 80 Hz, etc.) until it reaches or exceeds 20,000 Hz.
03

Calculate the Number of Octaves

Use the formula to find the number of octaves: the number of octaves between two frequencies is given by \( \log_2(\frac{\text{higher frequency}}{\text{lower frequency}}) \). Here, the higher frequency is 20,000 Hz and the lower frequency is 20 Hz.
04

Apply the Logarithm Formula

Substitute the frequencies into the formula: \[ \log_2(\frac{20000}{20}) \]. This simplifies to \[ \log_2(1000) \].
05

Calculate the Logarithm Base 2

To find \( \log_2(1000) \), we can use the change of base formula: \( \log_2(1000) = \frac{\log_{10}(1000)}{\log_{10}(2)} \). Since \( \log_{10}(1000) = 3 \) (because 1000 is \(10^3\)), and \( \log_{10}(2) \approx 0.3010 \), we calculate \( \frac{3}{0.3010} \approx 9.97 \).
06

Round Off the Result

The calculation yields roughly 9.97 octaves. Since we generally consider full octaves, a person with normal hearing can detect up to 10 octaves, as we round to the nearest whole number.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Octave Calculation
In music and acoustics, an octave represents the interval between one musical pitch and another with double its frequency. When calculating octaves in the context of human hearing, we examine how many times a base frequency can be doubled to reach another frequency within the range of human hearing. For instance, if a sound has a frequency of 20 Hz, the next octave would be 40 Hz, then 80 Hz, and so on. When we consider the human hearing range, which spans from 20 Hz to 20,000 Hz, we aim to determine the number of octaves within this spectrum by seeing how many doubling steps fit in between. To efficiently compute this, we use a logarithmic formula to find the exact number of octaves between two frequencies: - If the higher frequency is 20,000 Hz and the lower is 20 Hz, the number of octaves is computed as: \[\log_2 \left( \frac{20000}{20} \right)\]This method simplifies the process, and understanding it gives us valuable insight into the structure of scales and frequencies that we encounter in various sounds.
Frequency Range
The frequency range defines the span of frequencies that can be perceived or produced by a system, being particularly crucial when discussing the limits of human hearing. Frequencies are measured in Hertz (Hz), which indicate the number of cycles a sound wave completes in one second. Young individuals with normal hearing can generally hear sounds as low as 20 Hz. The upper limit for human hearing is about 20,000 Hz, or 20 kHz. This range from 20 Hz to 20 kHz is significant because it includes sounds from the deepest bass to the highest treble. In practical terms, understanding the full frequency range gives us the ability to - Recognize how different sounds, tones, and music fit within our hearing. - Explore how technologies like audio systems mimic or enhance these sounds within this human-audible range. - Comprehend adaptations in age or exposure that may shrink or alter one's hearing capabilities.
Logarithmic Scale
The concept of a logarithmic scale is vital in comprehending how humans perceive changes in sound, light, and even certain scales in nature. A logarithmic scale represents data that covers a large range of values, compressing them for easier interpretation and understanding. In acoustics, the logarithmic scale highlights proportions rather than linear values because human perception is more sensitive to ratios than to absolute differences. This makes it perfect for measuring things like sound intensity and pitch perception. The octave is naturally well-suited to logarithmic representation because: - It represents a multiplication by a factor of 2 (doubling). - The logarithmic base of 2 aligns with this natural doubling of frequencies. For the calculation of octaves over a frequency range, using a logarithmic scale enables us to view the broad range of human hearing (from 20 Hz to 20 kHz) as a series of manageable steps where each step visually conveys equal "spacing." Moreover, it gives us the tool to precisely calculate the number of octaves regardless of how large or small the frequency range might be.

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Most popular questions from this chapter

The portion of string between the bridge and upper end of the fingerboard (the part of the string that is free to vibrate) of a certain musical instrument is 60.0 cm long and has a mass of 2.00 g. The string sounds an \(\mathrm{A}_{4}\) note \((440 \mathrm{Hz})\) when played. (a) Where must the player put a finger (at what distance \(x\) from the bridge) to play a \(\mathrm{D}_{5}\) note \((587 \mathrm{Hz}) ?\) (See Figure \(12.40 . )\) For both notes, the string vibrates in its fundamental mode. (b) Without retuning, is it possible to play a G \(_{4}\) note \((392\) Hz \()\) on this string? Why or why not?

\(\cdot\) Mapping the ocean floor. The ocean floor is mapped by sending sound waves (sonar) downward and measuring the time it takes for their echo to return. From this information, the ocean depth can be calculated if one knows that sound travels at 1531 \(\mathrm{m} / \mathrm{s}\) in seawater. If a ship sends out sonar pulses and records their echo 3.27 s later, how deep is the ocean floor at that point, assuming that the speed of sound is the same at all depths?

\(\bullet\) The sound source of a ship's sonar system operates at a frequency of 22.0 \(\mathrm{kHz}\) . The speed of sound in water (assumed to be at a uniform \(20^{\circ} \mathrm{C}\) ) is 1482 \(\mathrm{m} / \mathrm{s}\) . (a) What is the wavelength of the waves emitted by the source? (b) What is the difference in frequency between the directly radiated waves andthe waves reflected from a whale traveling straight toward the ship at 4.95 \(\mathrm{m} / \mathrm{s} ?\) The ship is at rest in the water.

\(\cdot\) The electromagnetic spectrum. Electromagnetic waves, which include light, consist of vibrations of electric and magnetic fields, and they all travel at the speed of light. (a) FM radio. Find the wavelength of an FM radio station signal broadcasting at a frequency of 104.5 \(\mathrm{MHz}\) . (b) \(\mathrm{X}\) rays. X rays have a wavelength of about 0.10 \(\mathrm{nm}\) . What is their frequency? (c) The Big Bang. Microwaves with a wavelength of 1.1 \(\mathrm{mm}\) , left over from soon after the Big Bang, have been detected. What is their frequency? (d) Sunburn. Sunburn (and skin cancer) are caused by ultraviolet light waves having a frequency of around \(10^{16} \mathrm{Hz}\) . What is their wavelength? (e) SETI. It has been suggested that extraterrestrial civilizations (if they exist) might try to communicate by using electromagnetic waves having the same frequency as that given off by the spin flip of the electron in hydrogen, which is 1.43 GHz. To what wave-length should we tune our telescopes in order to search for such signals? (f) Microwave ovens. Microwave ovens cook food with electromagnetic waves of frequency around 2.45 \(\mathrm{GHz}\) . What wavelength do these waves have?

\(\cdot\) Two guitarists attempt to play the same note of wavelength 6.50 \(\mathrm{cm}\) at the same time, but one of the instruments is slightly out of tune and plays a note of wavelength 6.52 \(\mathrm{cm}\) instead. What is the frequency of the beat these musicians hear when they play together?

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