What are Decibels? [2022]

We are all subject to some level of noise pollution regardless of where we live.

Traffic sounds, noisy neighbors, etc can become a nuisance over time.

This will have you looking for soundproofing solutions for your home.

However, soundproofing your home from daily noise is no easy task.

What makes it even harder is if you’re trying to do it yourself but have no understanding of how sound works.

In this article, we’ll take a look at the measurement of sound known as decibels and how it can help you with your soundproofing project.

So what are decibels exactly and how can they help in your soundproofing project?

Let’s get right to it.

Decibels meaning

decibel chart meter reader

Decibels are the unit used to measure the intensity of sound. 

Sound is energy that travels in waves. 

It can be measured in two ways.

They are: 

Frequency

Frequency is measured in Hertz(Hz).  

Hertz measures the complete number of sound vibrations in one second. 

In daily life, this translates to how low or high-pitched a sound is. 

A healthy ear can hear sounds at very low frequencies(20hz) to very high-frequency sounds(20,000 Hz).

For more on Hertz, read our what are hertz post.

Amplitude

Amplitude is reported on the decibel scale.

It measures sound pressure or the forcefulness of a sound.

The more amplitude a sound has, the louder it is.

In daily life, this is referred to as the volume of a sound.

What is the decibel scale?

decibel scale reader

The decibel scale is logarithmic which means that it increases by the power of 10 each time.

The quietest audible sound is 0 dB and a sound that is 10 times more powerful is 10 dB.

Meanwhile, a sound 1,000 times more powerful is 30 dB and so on….

Any sound over 140 dB is not safe for the human ears.

However, continued exposure to sounds over 85 dB is unsafe.

These numbers may not mean much if you don’t have something to compare with.

Here’s a list of sounds that you can relate to and use as a rough scale to understand decibel levels.

It is important to understand just how loud something is when looking at dB ratings.

Check out the decibel chart below.

SourceSound Decibel RatingSound Level
Threshold of Audibility0 dBAlmost silent
Breathing10 dBSlightly audible
Rustling of leaves20 dBAudible
Whisper30 dBWhisper-quiet
Refrigerator40 dBFaint
Moderate rainfall50 dBModerate
Conversation60 dBModerate to quiet
Car/ city traffic70 dBLoud
Truck80 dBLoud to very loud
Hairdryer90 dBVery loud
Helicopter100 dBVery loud – extremely loud
Trombone110 dBExtremely loud
Police siren120 dBExtremely loud
Jet engine130 dBExceptionally loud
Fireworks140 dBThreshold of pain

The human ear is incredible and it can distort its sensitivity to lower and higher frequency sounds.

Sound meters try to replicate that process by weighting the readings.

This scale is referred to as the A scale and the ratings taken with this scale are listed as dBA.

There are 3 other scales available; B, C and D.

The B scale is rarely used while the C scale is used to measure very high levels of sound, and the D scale is best used to measure aircraft engine noise.

Measuring sound reduction (Decibels vs. Percentage Reductions)

decibels meaning measuring device

Sound intensities are measured in decibels.

However, decibels cannot be expressed in percentages and this is because of two reasons.

The first is that the decibel scale is open-ended like the Richter scale that is used for measuring earthquake intensities.

To calculate the percentage you’ll need to get the maximum value possible.

Both the decibel and the Richter scale have no limiting maximum value.

This means you cannot calculate a percentage.

Trying to do so will prove futile.

The second reason is that the decibel scale is logarithmic and the percent scale is linear.

Numbers that may appear similar are vastly different.

A decibel isn’t just the intensity of sound but more so a ratio of how many times louder or softer a sound is than a given reference sound level.

This means that 0 dB is not the complete absence of sound.

It is rather an arbitrary 0.

It helps to define the faintest sound that a healthy human ear can hear.

Since the decibel scale is logarithmic, every 10 dB increase in sound intensity increases the sound by ten-fold.

This means a 20 dB rating is not twice as loud as a sound intensity of 10 dB but it is rather 10 times as loud.

On the other hand, a sound intensity of 30 dB is 100 times as loud as a sound level of 10 dB.

Similarly, a dB level of 50 dB would be 100,000 times as loud because it would be 10 x 10 x10 x10 x 10.

This is how the decibel works and it is nothing like the linear percent scale.

The basic rules for working with decibels

sound decibel girl listening

The human ear can distinguish the significant multiplying of the energy of sound.

When the sound is doubled, it increases by 3 dB using the logarithmic scale.

Simply put, it means that every increase of 3 dB means a doubling of sound intensity.

A small increase in the decibel rating can result in huge changes in the amount of noise you hear and can potentially damage your hearing.

The dB unit makes it easy to measure the sound intensity and monitor sound changes if you use these rules.

Check out the table below

Change in dBChange in sound energy
3 dB increaseSound energy is doubled
3 dB decreaseSound energy is halved
10 dB increaseSound energy is increased by a factor of 10
10 dB decreaseSound energy is decreased by a factor of 10
20 dB increaseSound energy is increased by a factor of 100
20 dB decreaseSound energy is decreased by a factor of 100

How to add decibels together

sound level calculator

Sound pressure levels in decibels use a logarithmic scale so we cannot just add 2 dB ratings together.

Let’s take a look at 2 machines in a factory setting.

One machine has a noise level rating of 90 dB(A) and the second machine also has a noise rating of 90 dB, the total noise is not 180 dB(A).

As mentioned before we know 3 dB represents a doubling of noise so this means 90 dB + 90 dB = 93 dB.

If you need help you can use this table below when you need to add noise levels together.

Difference between two noise levelsAmounts to add to the higher of the two noise levels (dB or dB(A)
03.0
0.1-0.92.5
1.0-2.42.0
2.4-4.01.5
4.1-6.01.0
6.1-100.5
100.0

The first step is to try and figure out the difference between the two noise levels.

Once you have that figured out, find the corresponding row in the left column of the table.

The second step is to find the corresponding number in dB in the right column of the table.

The third and final step is adding the number in the right column to the highest of the two-decibel measurements you have.

If the difference between the two-decibel measurements is 10 dB and over, the amount you have to add is zero.

This is because the contribution to the overall noise of the lower reading is not perceived by the human ear so no adjustment is needed.

Let’s say your workspace noise level is 95 dB(A) and a machine has a rating of 80 dB(A) on its own, the workplace noise level will remain at 95 dB(A).

Soundproofing and Decibels

db and soundproofing man finger lips

Sound is energy that travels in two ways. 

The most common is airborne noise like people conversion, tv sounds, etc.

The second is impact/vibration noise like footsteps or vibrating appliances, etc.

To soundproof, you can choose from 3 different methods.

The first method you can try is to block the noise by adding mass to a structure until sound energy is reflected or converted to heat. 

The second method is to decouple one structure from the other.

This will stop sound vibrations from traveling through the second structure.

The third is sound absorption.

This is when sound energy gets absorbed by a material and reduces the amount of sound that travels through a structure.

Think of soundproofing like waterproofing.

It is only as good as its weakest point.

For example, when you’re in a car and the window is open just a tiny bit, you can hear all the sounds from outside really well.

However, if you close the window all the way, the sounds become muffled or reduced greatly. 

Just like the car window, there should be no gaps when soundproofing your home.

So how do you soundproof airborne and impact noise?

Airborne Noise

Airborne sound is energy that travels through the air.

It is measured in decibels which are shown on a logarithmic scale.

The dB scale measures the increase in the energy created by sounds.

For every increase of 3 dB in the scale, it measures a doubling of that energy.

As humans, it is quite hard for us to detect this level of increase easily.

This is why it is better to use the dB scale.

A 10 dB increase equates to a doubling of perceived noise.

This means the higher the dB reduction for airborne noise, the better.

Impact Noise

Impact noise is also measured in decibels.

However, it measures the amount of impact energy that transfers from structure to structure.

The lower the dB rating for impact noise, the better.

We all live with a certain level of background noise and a normal dB reading for a standard domestic quiet room falls around 30-40 dB.

We’ll use this rating as a target figure for soundproofing.

To figure out the correct dB rating for soundproofing your room, you’ll need to take a reading on both sides of the structure while the noise is happening.

This will help to tell you what level of soundproofing the existing structure provides.

However, this can prove to be difficult especially if you share a wall with your neighbor or so.

That being said, most times you won’t have to access your neighbor’s apartment as the dB rating on your side of the structure will tell you the level of sound you need to block.

Just take a reading on your side when the noise is at its loudest.

You can then deduct that from the normal dB background noise to get your target figure.

Once you know the level of decibels you need to reduce, you can try any of the soundproofing methods.

You’ll find that some soundproofing materials on the market will have a dB rating.

The decibels ratings listed will be a measurement of the total sound reduction achieved after testing the material on a standard construction.

The manufacturer tests the product by passing sounds through all existing materials in a standard construction and the soundproofing material as well.

The sound decibel rating listed is how much sound reduction you will achieve when you use the soundproofing material on any standard construction wall, floor or ceiling.

It’s quick to get caught up in false advertising so be sure you check out the table below so you don’t get caught up with these popular soundproofing myths.

ItemExpected ResultsActual results
Use egg cartons to fill the wallSuppose to improve loss by 10 dBNo effect
Acoustic insulation in the wallFixes everythingAbout 3 – 4 dB improvement
Install mass loaded vinyl under drywallWill prove loss by 27 dBAround 3 – 9 dB
Add another layer of drywallWill stop bass sounds2 – 3 dB per layer
Use foam as a barrierGets rid of all sounds< 2 dB

If you’re trying to make a 30 dB improvement, it cannot be achieved using egg cartons and vinyl as the table clearly shows.

Check out this article for the best soundproofing materials you can use for your soundproofing project.

Frequently Asked Questions

decibels ratings reading meter

1. Why is it called decibel?

The unit was named after Alexander Graham Bell.

It originated during the 20th century in the Bell systems in the United States.

At that time, referred to simply as “bel”, it was used to measure the transmission and loss in telephony.

Bel refers to the amount of increase in the loudness of a sound when its intensity increases ten times.

However, the bel was hardly used because it is a huge number.

The decibel (dB)which is one-tenth of a Bel was introduced and is more frequently used as the unit of measurement.

How can I measure sound at home?

You can use a device called a decibel meter.

It samples and measures sound, giving you a readout.

You can also access sound level meters on your smartphone using various apps.

There are apps available for both Android and iOS phones.

This is one of the best ways that you can get a decibel reading at home.

2. How many decibels is too loud?

Any sound over 70 dB over a prolonged period of time can begin to damage your hearing.

Extremely loud sounds at 120 dB and over can cause harm to your ears immediately.

3. What is an acceptable noise level?

Sounds at or below 70 dBA are considered safe.

Any sound with a higher decibel rating can damage your hearing over time.

4. How much louder is 20 dB compared to 10 dB?

A sound with a reading of 20 dB is 10 times louder than a sound with a rating of 10 dB. 

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