Basic Soundwaves
基础声波/
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学习（了解）最基础的声波，是什么使他们不同？
有四种基础种类的声波是通过震荡器生成的，并且这些波有着不同的声音品质。
让我们仔细了解每种波的细节：
它看起来像什么？
一个在两极之间平滑流动的信号。
它听起来像什么？
一个非常平滑圆润的声音。
另外的
典型特征
正弦波是声波种类中最纯的，它的所有能量都被集中在一个基础频率上。
它看起来像什么？
一个信号处于高、低极端之间不停地进行瞬态交替。
它听起来像什么？
一个明亮且更为自信的声音，有着一点刺耳（形状看起来是方形）
另外的
典型特征
方波是由一系列正弦波组成的。但是，它只包含奇次谐波（3、5、7、9…等）。当它们接近基础频率时谐波响度降低（它们是成反比的）。
它看起来像什么？
角信号是两极之间的直线运动所产生的（看起来像三角形）。
它听起来像什么？
我们听到的三角波是一个更为丰满的声音（接近正弦波的特征更似方波）。
另外的
典型特征
三角波是由许多单独的正弦波组成的。像方波、三角波都只包含奇次谐波，但它们振幅的减少比方波快得多（它们与谐波频率的平方成反比）。
它看起来像什么？
锯齿波呈现出一个缓慢上升然后突然下降的参差不齐的波形（看起来像一个锯切割边缘）。
它听起来像什么？
另外的
典型特征
锯齿波是由独立的正弦音调和包含所有谐波的基本频率组成的。这些谐波与相同速率的方波相比振幅减少。
频率和振幅
当一个对象来回振动，在空中产生一种共鸣模式，声波由此产生（参考— Where Do Sounds Come From）
这些共鸣可被测量并可使用示波器观察。
我们可以观察声波特性的变化以及了解影响我们所听的要素。
音高=频率
一个对象振动来回的速度越快，其振动所产生的共鸣频率越高。
频率是用来衡量一秒内振动来回的运动数量（周期）。
振动频率越高，我们听到的音高越高。
观察随着音高的上升其频率的波如何增加。
观察随着音高的下降其频率的波如何减少。
事实
当我们在扬声器上播放低频声音时，我们有时能看见扬声器推子的移动。这是因为扬声器是创作一个低频声音和低速度振动的工具。
当扬声器快速重放高频声音时我们不再能看到共鸣。
响度=振幅
来回振动更远的对象其振幅越大。
声波振幅越大，响度越大。
事实
最安静的声音只需将扬声器推子移动一点点，而最响亮的声音需要将扬声器推子移动很多。
观察波的振幅如何增加以及声音如何渐强。
观察波的振幅如何衰减以及声音如何渐弱。
注意：声音太响会损害你的听力！！！
另外的
声音的速度
有时人们会认为高、低声传播速度不同。
这是错误的。
所有的声音都保持一个固定的速度传播（343m/s空气中(768mph))。需要注意的是，声速是不同频率、速率的声波振荡（来回运动）。
高频率的声音和低频率的声音以相同速度传播，但高频率的声音比低频率的声音包含了更多波形周期。
光的传播速度比声音快得多（299,792,458 m/s (670,616,629 mph))。光的速度是如此之快以至于人类肉眼只能即时看见它。
声速和光速之间的差异，恰恰能解释为什么你经常能看到的东西要经过很长一段时间才可以听到它们，闪电和雷鸣就是一个很好的例子。
闪电和雷鸣=声和光
当闪电和雷鸣同时发生，你知道暴风雨即将到来。当闪电和雷鸣之间存在一定延迟到达于你，你知道暴风雨正在远离。
声速是343m/s，所以如果闪电和雷鸣之间有一秒的延迟，我们知道暴风雨离我们有343米（电平）(1s x 343m = 343m/s)rr。
如果有两秒的延迟，我们知道暴风雨离我们686米(2s x 343m = 686m/s)；如果有十秒的延迟，我们知道暴风雨离我们3430米(10s x 343m = 3430m/s)。
活动
下一次雷雨降临，聆听雷声，并计算闪电和雷声之间的秒数。你能算出暴风雨离你有多远吗？
关键词：
振幅 频率 响度 音高
Learn about the most basic sound waves. What makes them different?
There are four basic types of soundwaves generated by oscillators and each of these waves have a different sound quality.
Let’s examine each wave type in detail:
What does it look like?
A smooth flowing signal that moves between smoothly between extremes.
What does it sound like?
A very smooth and rounded sound.
Extra
Special Characteristics
A sine wave is the purest type of sound wave, all the energy is focussed at a fundamental frequency.
What does it look like?
A signal that switches abruptly between extremes in an alternating fashion.
What does it sound like?
A brighter more assertive sound, which is a little harsh (looks square in shape).
Extra
Special Characteristics
The Square wave is made up of a series of sine tones. BUT, it contains only odd Harmonics (3,5,7,9… etc.). These harmonics decrease in loudness as they get further from the fundamental (they are inversely proportional).
What does it look like?
An angular signal that moves in straight lines between extremes (looks triangular when viewed).
What does it sound like?
We hear the triangle wave as a more rounded sound (closer in character to the Sine wave than the Square wave).
Extra
Special Characteristics
The triangle wave is made up of many individual Sine waves. Like the Square wave, the Triangle wave contains only odd harmonics, but these decrease in amplitude much faster than in the square wave (they are inversely proportional to the square of the harmonic frequency).
What does it look like?
A jagged wave that ramps up slowly and then suddenly drops back (looks like the cutting edge of a saw).
What does it sound like?
Extra
Special Characteristics
The Sawtooth wave is made up of individual sine tones and contains all harmonics of the fundamental frequency. The amplitude of these harmonics decreases at exactly the same rate as that of the Square wave.
Frequency & Amplitude
Sound waves are produced when an object vibrates back and forth, setting off a pattern of vibrations in the air (see also – Where Do Sounds Come From).
These vibrations can be measured and viewed by using an Oscilloscope
We can then observe how changes in the properties of the soundwave affect what we hear.
Pitch = Frequency
The faster an object vibrates back and forth, the higher its frequency of vibration.
Frequency is a measure of the number of back and forth motions (cycles) that take place each second.
The higher the frequency of vibration, the higher the pitch that we hear.
Watch how the frequency of the waves increases as the pitch rises
Watch how the frequency of the waves decreases as the pitch falls
Fact
When we play low frequency sounds on a loudspeaker we can sometimes see the cone of the loudspeaker moving. This is because the loudspeaker is creating a low frequency sound and is vibrating at a low speed.
When the loudspeaker is reproducing a high frequency sound it moves so quickly that we are no longer able to see the vibrations.
Loudness = Amplitude
The further an object vibrates back and forth the greater the amplitude.
The greater the amplitude of a sound wave, the louder it seems to be.
Fact
The quietest sounds move the cone of a loudspeaker only a little bit, while the loudest sounds move the cone of a loudspeaker a lot.
Watch how the amplitude of the waves increases as the sound fades in.
Watch how the amplitude of the waves decreases as the sound fades out.
TAKE CARE: LOUD SOUNDS CAN DAMAGE YOUR HEARING PERMANENTLY!!!
Extra
The Speed of Sound
Sometimes people think that high and low sound travel at different speeds.
This is WRONG.
All sounds travel at a fixed speed (343m/s in air (768mph)). It is important to note that the speed of sound is different from the frequency, the rate at which the sound wave oscillates (moves back and forth).
A high frequency sound and a low frequency sound will travel at the same speed. BUT the high frequency sound will contain far more wave cycles than the low frequency sound.
Light travels a lot faster than sound (299,792,458 m/s (670,616,629 mph)). The speed of light is so fast that our human eyes simply see it as instant.
The difference between the speed of sound and the speed of light, is the reason why you can often see things that are a long way away before you can hear them. Lightening and thunder are a great example of this.
Lightening and Thunder = Sound and Light
When lightening and thunder happen at the same time then you know that the storm is above you. When there is a delay between the flash of the lightening and the roll of thunder reaching you, you know that the storm is further away from you.
Sound travels 343 meters every second. So if there is a one second delay between the lightning flash and the thunder roll we know that the storm is 343 meters away from us (1s x 343m = 343m/s)rr.
If there is a two second delay we know that the storm is 686 meters away from us (2s x 343m = 686m/s) and if there is a ten second delay we know that the storm is 3430 meters away from us (10s x 343m = 3430m/s).
Activity
Next time there is a thunderstorm listen out for the sound of the thunder, and count the number of seconds between the flash of lightening and the roll of thunder. Can you work out how far away the storm is from you?
Keywords:
Amplitude, Frequency, Loudness, Pitch
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