8.3 Sound levels

• Natuurkunde / Scheikunde
• Middelbare school
• havo, vwo
• Leerjaar 2

8.3 Sound levels

Schedule for this lesson

Starting with a fun fact about sound

Explanation 

Ending with the fun fact

Learning objectives 1/2

- You can use a graph to explain the relationship between the sound intensity and the amplitude of a vibration 

- You can explain how the sound intensity depends on the distance of the sound source 

- You can describe how the threshhold and the pain threshold depend on the frequency

Learning objectives 2/2

- You can explain the difference between the dB (A) scale and the dB scale

- You can do calculations using the relationship between the sound intensity and the number of sound sources 

Starting with a fun fact!

The loudest sound recorderd in history came from a vulcanic eruption

(1883)

The sound was estimated to be around 180 decibel 

Here is a picture of the vulcano 

on the indonesion island Krakatoa 

Starting with a fun fact!

What is a decibel and how loud is this? 

If this happened today, could we hear it?

that is what we will learn today!

Explanation

Here we see a sound sample which is used to make music

We can see that the lines are high and low

This indicates the

sound intensity

Explanation

We can look at the amplitude

to determine the sound intensity

Explanation

The unit of sound intensity is decibel (dB)

The device we use to measure 

the sound intensity is called a decibel meter

You could also use a phone app to measure

the sound intensity

Explanation

Most decibel meters have a filter

This way the meter allows the sound to be

perceived the same way as we hear it

With this filter you have to mark the decibels as

dB(A)

Explanation

Here we can see different

sound sources

with their sound intensity

The sound intensity will increase when 

you move closer to the sound source

Explanation

Our ears are not equally sensitive to all frequencies 

We have a limit of hearing

As you can see,

most things we are able to

hear are greater than 0 dB

Explanation

Our hearing is sensitive around 4000Hz

The sound intensity does not have

to be high to damage our hearing

The range makes it seems less 

loud than the sound really is

Explanation

We are also able to calculate with decibels

But the scale is a bit different than most units

Explanation

As the number of sources increase (for example double), the sound intensity does not seems twice as loud

If one persons plays guitar at 60dB

2 people do not reach 120dB

Explanation

On the decibel scale if sound sources are doubled

The amount of decibel increases with 3

Explanation

On the decibel scale if sound sources are doubled

The amount of decibel increases with 3

Example, a group of 6 singers, sing with a sound intensity of 70dB

So a group of 24 singers, sing at a sound intensity of 70 + 3 + 3 = 76dB

The sound source doubles twice

Going back to our fun fact

So our vulcano that erupted with 180 decibel

A plane has a sound intensity of 130dB at 30m 

So imagine how many planes you need

to simulate this 180 decibel

Going back to our fun fact

People who where 3000km away from the eruption were able to hear it!

Making exercises 

Start with the exercises of paragraph 8.3

End of the lesson