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5\. Loudspeaker A loudspeaker produces a musical sound by means of the oscillation of a diaphragm. If the amplitude of oscillation is limited to \(1.0 \times 10^{-3} \mathrm{~mm}\), what frequencies will result in the magnitude of the diaphragm's acceleration exceeding \(g\) ?

Short Answer

Expert verified
The frequencies will be greater than 498.38 Hz.

Step by step solution

01

Convert the amplitude to meters

Convert the given amplitude from millimeters to meters: Given amplitude: \(A = 1.0 \times 10^{-3} \:mathrm{mm} = 1.0 \times 10^{-6} \:mathrm{m}\)
02

Understand the maximum acceleration condition

The maximum acceleration of the diaphragm is given by the formula: \(a_{max} = A \:cdot \omega^2\) Here, \(\omega\) is the angular frequency, and it is related to the frequency ( \(f\)) by the equation: \(\omega = 2\pi f\)
03

Set up the inequality for acceleration exceeding gravity

Maximum acceleration should exceed gravity ( \(g = 9.8 \:mathrm{m/s^2}\)). Thus, set up the inequality: \(A \cdot (2\pi f)^2 > 9.8\) Solving the above inequality for \(f\):
04

Solve the inequality for frequency

Rearrange the inequality to solve for frequency ( \(f\)): \(1.0 \times 10^{-6} \:mathrm{m} \cdot (2 \pi f)^2 > 9.8\) \((2 \pi f)^2 > \frac{9.8}{1.0 \times 10^{-6}}\) \((2 \pi f)^2 > 9.8 \times 10^6\) \(2 \pi f > \sqrt{9.8 \times 10^6}\) \(f > \frac{\sqrt{9.8 \times 10^6}}{2 \pi}\)
05

Calculate the numerical value for frequency

Calculate the right-hand side of the inequality: \(f > \frac{\sqrt{9.8 \times 10^6}}{2 \pi}\) \(f > \frac{3130.5}{6.2832}\) \(f > 498.38 \:mathrm{Hz}\)

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Key Concepts

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

Oscillation
One fundamental concept in this exercise is **oscillation**. Oscillation refers to any motion that repeats itself at regular intervals. Think of a pendulum swinging back and forth, or a swing at a playground. For loudspeakers, oscillation is the back-and-forth movement of the diaphragm that produces sound by compressing and rarefying the air.

These oscillations are pivotal because they determine the sound's properties. You should understand the relationship between oscillation and sound. Oscillation needs to be consistent with the audio signals sent to the loudspeaker. Without proper oscillation, the quality of the produced sound can suffer.

When studying oscillation, we also consider parameters like amplitude and frequency which we'll explain next.
Diaphragm Amplitude
The **diaphragm amplitude** in a loudspeaker refers to the maximum extent of its movement during oscillation. It is usually measured in millimeters (mm) or meters (m). In this problem, the amplitude is given as a small value: \(1.0 \times 10^{-6} \text{ m}\).

This small measurement is significant. The amplitude determines the loudness and clarity of the sound. A larger amplitude would generally mean a louder sound, but it can also introduce distortion if it exceeds the design constraints. Thus, engineers often limit the diaphragm's maximum amplitude to maintain sound quality.

Remember that amplitude is just one part of the equation. The interplay between amplitude and other factors like frequency makes for a more complex and fascinating study.
Frequency Calculation
Now, let's talk about **frequency calculation**. Frequency (\(f\)) indicates how frequently an oscillation occurs per second. It is measured in Hertz (Hz). According to the problem, we need to calculate frequencies that cause the diaphragm’s acceleration to exceed the acceleration due to gravity (\(g = 9.8 \text{ m/s}^2\)).

Using the formula for maximum acceleration: \( a_{max} = A \times \text{angular frequency}^2 \), we relate amplitude (\(A\)) and angular frequency (\(\text{angular frequency}\)) to figure out the critical frequencies.

We start with the inequality \(1.0 \times 10^{-6} \text{ m} \times (2 \pi f)^2 > 9.8\), which simplifies to \( f > 498.38 \text{ Hz}\). Frequencies higher than this will exceed gravitational acceleration.
Angular Frequency
The concept of **angular frequency** (\(\text{angular frequency}\)) is another key aspect. Angular frequency is related to the linear frequency but adds the rotational aspect to it. It tells us how fast an object rotates or oscillates in radians per second.

The formula for angular frequency is: \( \text{angular frequency} = 2 \pi f \), where \( f \) is the linear frequency. For example, converting a frequency of 1Hz to angular frequency would be \( 2 \pi \text{ radians/second}\).

Angular frequency helps us understand the oscillatory motion in circular terms. It was particularly useful in this problem to set up our inequality for acceleration.
Acceleration Inequality
Finally, let’s dive into the **acceleration inequality**. This part is crucial to ensure the diaphragm’s acceleration does not exceed safe limits.

The maximum acceleration, which comes from the oscillation of the diaphragm, should be more than the acceleration due to gravity (\(g = 9.8 \text{ m/s}^2\)). The formula used is: \( A \times (2 \pi f)^2 > 9.8\).

By solving this inequality, you figure out the threshold frequency. Only frequencies beyond this will cause the diaphragm to exceed this acceleration limit. Thus, defining this frequency is essential for protecting the loudspeaker from potential damage.

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Most popular questions from this chapter

55\. Block Suspended from Spring A \(4.0 \mathrm{~kg}\) block is suspended from a spring with a spring constant of \(500 \mathrm{~N} / \mathrm{m}\). A \(50 \mathrm{~g}\) bullet is fired into the block from directly below with a speed of \(150 \mathrm{~m} / \mathrm{s}\) and becomes embedded in the block. (a) Find the amplitude of the resulting simple harmonic motion. (b) What fraction of the original kinetic energy of the bullet is transferred to mechanical energy of the harmonic oscillator?

14\. BMMD Astronauts sometimes use a device called a body-mass measuring device (BMMD). Designed for use on orbiting space vehicles, its purpose is to allow astronauts to measure their mass in the "weightless" conditions in Earth orbit. The BMMD is a springmounted chair; an astronaut measures his or her period of oscillation in the chair; the mass follows from the formula for the period of an oscillating block-spring system. (a) If \(M\) is the mass of the astronaut and \(m\) the effective mass of that part of the BMMD that also oscillates, show that $$ M=\left(k / 4 \pi^{2}\right) T^{2}-m $$ where \(T\) is the period of oscillation and \(k\) is the spring constant. (b) The spring constant was \(k=605.6 \mathrm{~N} / \mathrm{m}\) for the BMMD on Skylab Mission Two; the period of oscillation of the empty chair was \(0.90149 \mathrm{~s}\). Calculate the effective mass of the chair. (c) With an astronaut in the chair, the period of oscillation became \(2.08832 \mathrm{~s}\). Calculate the mass of the astronaut.

69\. To What Angle? A small metal ball of mass \(m\) hangs from a pivot by a rigid, light metal rod of length \(R .\) The ball is swinging back and forth with an amplitude that remains small throughout its motion, \(\theta^{\max } \leq 5^{\circ} .\) Ignore all damping. (a) The equation of motion of this ideal pendulum can be derived in a variety of ways and is $$ \frac{d^{2} \theta}{d t^{2}}=-\frac{g}{R} \sin \theta $$ For small angles, show how this can be replaced by an approximate equation of motion that can be solved more easily than the one given. (b) Write a general solution for the approximate equation of motion you obtained in (a) that works for any starting angle and angular velocity (as long as the angles stay in the range where the approximation is OK). Demonstrate that what you have written is a solution and show that at a time \(t=0\) your solution can have any given starting position and velocity. (c) If the length of the rod is \(0.3 \mathrm{~m}\), the mass of the ball is \(0.2 \mathrm{~kg}\), and the clock is started at a time when the ball is passing through the center \((\theta=0)\) and is moving with an angular speed of \(0.1 \mathrm{rad} / \mathrm{s}\), find the maximum angle your solution says the ball will reach. Can you use the approximate equation of motion for this motion? If the starting angle is not small, you cannot easily solve the equation of motion without a computer. But there are still things you can do. (d) Derive the energy conservation equation for the motion of the pendulum. (Do not use the small-amplitude approximation.) (e) If the pendulum is released from a starting angle of \(\theta_{1}\), what will be the maximum speed it travels at any point on its swing?

18\. Block and Piston A block rides on a piston that is moving vertically with simple harmonic motion. (a) If the SHM has period \(1.0 \mathrm{~s}\), at what amplitude of motion will the block and piston separate? (b) If the piston has an amplitude of \(5.0 \mathrm{~cm}\), what is the maximum frequency for which the block and piston will be in contact continuously?

32\. Flat Disk A flat uniform circular disk has a mass of \(3.00 \mathrm{~kg}\) and a radius of \(70.0 \mathrm{~cm}\). It is suspended in a horizontal plane by a vertical wire attached to its center. If the disk is rotated \(2.50\) rad about the wire, a torque of \(0.0600 \mathrm{~N} \cdot \mathrm{m}\) is required to maintain that orientation. Calculate (a) the rotational inertia of the disk about the wire, (b) the torsion constant, and (c) the angular frequency of this torsion pendulum when it is set oscillating.

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