Loudspeaker Resonance

An open-cone dynamic loudspeaker will generally exhibit a single resonant frequency at which it most readily responds to an electronic signal. The purpose of this experiment is to measure the resonant frequency of a speaker and plot the response curve of the speaker over the audible frequency range.

一个开口型动态扬声器通常会在某个共振频率下最容易响应电子信号。本实验的目的是测量扬声器的共振频率，并绘制出扬声器在可听频率范围内的响应曲线。

In many applications, resonance is desirable because it provides an enhanced response to a particular frequency, but in loudspeaker design it is in general not desirable. An ideal speaker should respond equally to all audible sound-frequencies so that it will accurately reproduce the sound programming supplied to it. Any change in the relative intensities of the various frequencies present in the sound will change the quality (timbre) of the sound and therefore represents a distortion. Much of the effort in designing a good speaker system is directed toward broadening and smoothing of the open-cone resonance so that the speaker will respond more uniformly to a broad range of frequencies.

在许多应用中，共振是期望的，因为它能增强对特定频率的响应，但在扬声器设计中通常不希望出现共振。一个理想的扬声器应该对所有可听频率有相等的响应，以便能够准确地再现输入的音频节目。任何声音中各种频率相对强度的变化都会改变声音的品质（音色），因此代表一种失真。设计一个良好的扬声器系统所做的大量努力都是为了拓宽和平滑开放型锥体的共振，使扬声器对宽范围的频率有更加均匀的响应。

In this experiment an audio frequency oscillator (signal generator) will be used to drive the speaker and an oscilloscope will be used to measure the voltage supplied to the speaker coil. The connections are shown in the sketch.

在这个实验中，将使用音频频率振荡器（信号发生器）驱动扬声器，并用示波器测量加在扬声器线圈上的电压。连接方式如图所示。

A resistor is to be placed in series with the speaker as indicated in the diagram. Its purpose is to maintain a more nearly constant "load" on the signal generator. The speaker impedance is nominally some value like 4 ohms, 8 ohms, etc., but it varies considerably near resonance. The oscilloscope will be used to measure the voltage across the speaker. The voltage will reach its maximum value at the resonant frequency of the speaker.

一个电阻应按图示与扬声器串联。其目的是保持信号发生器上的“负载”尽可能接近恒定。扬声器的阻抗通常为某个值，如4欧姆、8欧姆等，但在共振附近变化较大。示波器将用来测量扬声器上的电压。电压将在扬声器的共振频率处达到最大值。

PROCEDURE 1. Wire up the circuit as shown and get a sine wave display on the oscilloscope. The lab instructor will explain the oscilloscope controls.

1. 按图连接电路，并在示波器上显示正弦波。实验室指导教师将解释示波器的控制按钮。

2. With the signal generator output set to its maximum range, adjust the frequency to 20 Hz using the frequency dial and the multiplier switch. Sweep the frequency up slowly to 1000 Hz, watching the oscilloscope display. When the vertical height (voltage) of the display peaks and then diminishes, you have passed through the resonant frequency. Adjust the oscilloscope control labelled 'volts/cm' until the vertical height nearly fills the screen. Be sure you know what scale factor you are using on this control. Record the voltage (height in cm times the scale factor in volts/cm) and the resonant frequency.

2. 将信号发生器的输出设置为其最大量程，使用频率旋钮和倍率开关将频率调整到20 Hz。缓慢地将频率扫到1000 Hz，观察示波器显示。当显示的垂直高度（电压）达到峰值然后逐渐减小时，说明已通过共振频率。调整示波器上标有'伏特/厘米'的控制旋钮，直到垂直高度几乎填满屏幕。确保你清楚正在使用该控制旋钮的量程因素。记录电压（高度以厘米乘以量程因素伏特/厘米）和共振频率。

3. Reset the frequency to 20 Hz and record the voltage from the oscilloscope. (Do not adjust any of the controls on the signal generator except the frequency for the remainder of the experiment).

将频率重置为20 Hz，并记录示波器上的电压。（在实验剩余部分，除频率外，不要调整信号发生器上的任何控制。）

4. Take voltage readings at one-half octave intervals over the frequency range 20 - 8,000 Hz as outlined on the data sheet. Take additional measurements at several frequencies near the resonant frequency, so that the behavior near resonance can be followed more closely.

4. 在20至8000Hz的频率范围内，按数据表上说明的半 octave 间隔取电压读数。在共振频率附近几个频率处取额外测量，以便更精确地跟踪共振附近的特性。

5. On the semi-log paper provided, plot your measured frequency and voltage data. The frequency is to be placed on the logarithmic axis. On the other axis, choose a scale such that the voltage at resonance will nearly reach the top of the scale. Draw small circles around your plotted points and then draw a smooth curve through your points to produce a frequency response for your speaker.

Equipment: Loudspeaker Resonance

设备：扬声器共振

在提供的半对数纸上，绘制你测量的频率和电压数据。频率应放在对数轴上。在另一根轴上选择一个刻度，使得共振时的电压几乎达到刻度的顶部。在所绘点周围画小圆圈，然后画一条平滑的曲线通过这些点，以得到扬声器的频率响应曲线。