学习 about the most 基础 声波 波 What makes them different?
There are four 基础 种类 of 声波 生成 by 震荡器 and each of these 波 have a different 声波 品质
Let’s examine each 波 种类 in 细节
What does it look like?
A 平滑 流动 信号 that moves between smoothly between extremes
What does it 声波 like?
A very 平滑 and rounded 声波
Extra
Special Characteristics
A 正弦 波 is the purest 种类 of 声波 波 all the 能量 is focussed at a 基（础） 频率
What does it look like?
A 信号 that 转换 abruptly between extremes in an 交互 fashion
What does it 声波 like?
A brighter more assertive 声波 which is a little 刺耳（粗糙） looks （平）方 in 形状
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Special Characteristics
The （平）方 波 is made up of a 系列 of 正弦 音 BUT it 包含 only odd 谐（泛音） 3 5 7 9… etc These 谐（泛音） 减 in 响度 as they get further from the 基（础） they are 相反 proportional
What does it look like?
An 角 信号 that moves in straight lines between extremes looks 三角 when viewed
What does it 声波 like?
We 听 the 三角 波 as a more rounded 声波 closer in character to the 正弦 波 than the （平）方 波
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Special Characteristics
The 三角 波 is made up of many individual 正弦 波 Like the （平）方 波 the 三角 波 包含 only odd 谐（泛音） but these 减 in 振幅 much faster than in the （平）方 波 they are 相反 proportional to the （平）方 of the 谐/泛音 频率
What does it look like?
A 参差不齐 波 that 斜坡 up slowly and then 突然 drops back looks like the cutting edge of a saw
What does it 声波 like?
Extra
Special Characteristics
The 锯齿 波 is made up of individual 正弦 音 and 包含 all 谐（泛音） of the 基（础） 频率 The 振幅 of these 谐（泛音） 减 at exactly the same 率 as that of the （平）方 波
频率 & Amplitude
声波 波 are 产生 when an 对象 vibrates back and forth 设置 off a 模式 of 共鸣 in the air see also – Where Do 声 Come From
These 共鸣 can be 测量 and viewed by using an Oscilloscope
We can then 观察 how changes in the 属性 of the soundwave 影响 what we 听
音高 = Frequency
The faster an 对象 vibrates back and forth the 较高 its 频率 of 共鸣
频率 is a measure of the 数 of back and forth motions 周期 that take place each second
The 较高 the 频率 of 共鸣 the 较高 the 音高 that we 听
Watch how the 频率 of the 波 增 as the 音高 rises
Watch how the 频率 of the 波 减 as the 音高 falls
Fact
When we play 低 频率 声 on a 扬声器 we can sometimes see the cone of the 扬声器 moving This is because the 扬声器 is 创作 a 低 频率 声波 and is 颤 at a 低 速度
When the 扬声器 is reproducing a 高 频率 声波 it moves so quickly that we are no longer able to see the 共鸣
响度 = Amplitude
The further an 对象 vibrates back and forth the greater the 振幅
The greater the 振幅 of a 声波 波 the 更响 it seems to be
Fact
The quietest 声 move the cone of a 扬声器 only a little bit while the loudest 声 move the cone of a 扬声器 a lot
Watch how the 振幅 of the 波 增 as the 声波 fades in
Watch how the 振幅 of the 波 减 as the 声波 fades out
TAKE CARE 响 声 CAN DAMAGE YOUR 听觉 PERMANENTLY!!!
Extra
The 速度 of Sound
Sometimes 人 think that 高 and 低 声波 travel at different speeds
This is WRONG
All 声 travel at a 固定 速度 343m/s in air 768mph It is 重要 to 音符 that the 速度 of 声波 is different from the 频率 the 率 at which the 声波 波 oscillates moves back and forth
A 高 频率 声波 and a 低 频率 声波 will travel at the same 速度 BUT the 高 频率 声波 will 包含 far more 波 周期 than the 低 频率 声波
Light travels a lot faster than 声波 299 792 458 m/s 670 616 629 mph The 速度 of light is so fast that our 人类 eyes simply see it as instant
The difference between the 速度 of 声波 and the 速度 of light is the reason why you can often see things that are a long way away before you can 听 them Lightening and 雷 are a great 例如 of this
Lightening and 雷 = 声波 and Light
When lightening and 雷 happen at the same 时间 then you know that the storm is above you When there is a 延迟 between the flash of the lightening and the roll of 雷 reaching you you know that the storm is further away from you
声波 travels 343 电平 every second So if there is a one second 延迟 between the lightning flash and the 雷 roll we know that the storm is 343 电平 away from us 1s x 343m = 343m/s rr
If there is a two second 延迟 we know that the storm is 686 电平 away from us 2s x 343m = 686m/s and if there is a ten second 延迟 we know that the storm is 3430 电平 away from us 10s x 343m = 3430m/s
Activity
Next 时间 there is a thunderstorm 听 out for the 声波 of the 雷 and count the 数 of seconds between the flash of lightening and the roll of 雷 Can you 作品 out how far away the storm is from you?
Keywords
振幅 频率 响度 音高