What are Hertz in Sound? [2022]

To understand the science behind soundproofing, you must first understand sound. 

Sound can be a wonderful thing especially if it is transformed into melodious music. 

However, the beauty and melody of sounds often depend on factors such as when, where and how.

Sounds that come into our homes in the form of noise are definitely not welcome.

There are a few things you can do to control the source of these sounds. 

This is why soundproofing is important in the home. 

There are some terms you may encounter when dealing with sounds that can throw you for a loop.

Today,  we’ll take a look at one of the most common terms called Hertz.

What are Hertz in sound exactly?

What is hertz frequency?

Before we dive into Hertz, you’ll need to understand sound, how it behaves and how it is measured.

How sound behaves

Sound travels in waves so you need to understand the characteristics of waves before soundproofing.

You need to understand how sound travels, reflects and transmits through surfaces.

This will tell you if you need to isolate, enclose, diffuse, mask or absorb noise.

Sound wave

Every sound you hear is caused by vibrations that create fluctuations in the air.

These fluctuations are known as sound waves.

Sound waves are a form of energy that can transfer from molecule to molecule through various mediums.

If the medium is dense, the sound energy travels faster than if the molecules are tightly packed together.   

Steel, concrete, wood, and metal are all made of molecular structures.

Sound waves go through certain characteristic changes when it changes mediums.

A portion of the energy will try to pass through the new medium(sound transmission) while the rest will reflect off and away(sound reflection). 

Sound Reflection

Sound waves undergo certain characteristics as they leave one medium and enter another.

Let’s take a look at an airborne wave in a room reaching a brick wall. 

A portion of that wave will try to pass through the wall while the rest of the wave will reflect off the wall. 

Sound wave reflection occurs when that portion of energy stays in the room. 

Sound transmission is the portion of energy that passes through the wall 

Echo vs Reverberation 

The reflection of sound can be measured in the time between the end of the original sound and when its signal starts to reflect into a room. 

The time between these two sound signals can either be an echo or reverberation. 

If the time is greater than .1 seconds then the reflection is referred to as an echo. 

if the time is less than .1 seconds the reflection is then referred to as reverberation. 

the human ear cannot recognize sound signals of less than .1 seconds. 

This is why we hear an echo as two sound signals and reverberation as one prolonged sound. 

Sound Transmission 

When a portion of a sound wave passes through a medium, the energy that survives this transfer is called sound transmission. 

To understand the science behind sound transmission and sound behavior we’ll need to start with the basic understanding of what a medium is. 

a medium is any form of matter that is made up of a molecular structure. 

This can be anything from the air you breathe to the water in a swimming pool to the concrete floor of a factory or the wood studs inside a wall. 

Molecules are tiny invisible cells that make up all the matter in this world. 

The molecules that make up a medium accept vibrations induced by a sound source and pass that energy to its neighboring molecules. 

The fact that molecules make up wood, metal, concrete glass, water and air make it easier to understand how sound can travel through structures as easily as it can through the air.  

How sound is measured

Now that you have a basic understanding of how sound behaves, we can talk and look at how it’s measured.

This is where the term Hertz comes into play.

However, it is not the only measurement used to measure sounds.

There are two other measurements used called Decibels and Sabins. 

All three of these can be used to quantify sound energy. 

They serve to define the noise you’re dealing with and help you to come up with the best soundproofing solutions. 

Decibels

Decibel is the unit of measurement that is used to measure the intensity of a sound.

In other words, it is used to tell how loud a sound is on a scale ranging from 0-194 dB.

The average day is filled with sounds ranging from 30-100dB.

Conversational voice levels fall in the 65 dB range.

However, workers who are exposed to dB rating over 85 for 8 hours a day are required to wear hearing protection.

The dB range where humans begin to experience pain is around 120dB. 

The intensity of sound diminishes over time and distance so the further you are away from the source of the noise, the lower the decibel rating. 

You can control decibel levels by applying soundproofing treatments that attack the source of the noise or the path of the sound wave.

To learn more, check out this sound attenuation and what are decibels posts.

Sabin

Sabin measures how well one square foot of a given surface of any texture is able to absorb sound reflections. 

All surfaces are ranked from 0 to 1.0 on the NRC(Noise Rating Coefficient) scale.

A ranking of “0” indicates a lack of absorption while a ranking of “1.0” is perfect for absorption.

Hertz

We’re now going to look at the term that we are going to be focusing on in this article.

What are Hertz?

hertz sound waves wiggly lines

What are Hz?

Understanding Sound Hertz is important, especially in soundproofing situations.

Soundwaves are movements of air molecules that our ears translate to sound. 

One complete oscillation of a sound wave is referred to as a cycle.

Hertz measures the frequency of the cycle.

Frequency refers to the number of cycles sound waves complete in a second. 

This measurement of cycles per second is expressed in Hertz(Hz). 

1 Hertz is equal to one cycle per second.

Cycles, in this instance, can also be referred to as vibrations.

On average human voice falls on a frequency band of 1000 hertz or 1 kilohertz(kHz).

This equals 1000 vibrations per second.

The higher the number of cycles per second, the higher the frequency as well as the pitch of the sound.

Human ears can register sound from somewhere around 20Hz in frequency up to 20,000 Hz.

However, this varies from person to person.

People suffering from some form of hearing loss have trouble hearing sounds in the higher frequency range.

There are three types of sound waves and you can figure which is which using Hertz.

Hertz sound waves

The three types of soundwaves are:

Low-frequency sound waves

Low-frequency sound waves are any sound that is 500 Hz or lower.

These sound waves sound lower to the human ear.

Let’s look at an example.

When you turn up the bass on our stereo, you are creating low-frequency sounds. 

These are the types of rumbling sounds that you can hear and feel.

Medium frequency soundwaves

Medium frequency sounds usually fall between the 500 HZ and 1000 Hz range.

This is the range where you can decipher human speech.

Sounds in this range ten to have a tin or horn-like quality.

High-frequency soundwaves

High-frequency sounds start somewhere above 2000 HZ.

However, there is a wide range of audible sounds in this range.

At 2000 Hz, it is said that sound gives presence to speech.

What this means is that speech sounds more authentic. 

At 10,000 Hz, you can hear sounds from cymbals crashing or birds chirping.

History of Hertz

The measurement Hertz wasn’t always called Hertz.

It was referred to as cycles per second (cps), kilocycles per second (kc/s) and megacycles per second (Mc/s), and occasionally kilo megacycles per second (kMc/s). 

In some cases, the “per second” was omitted and  “megacycles” (Mc) was used as an abbreviation for “megacycles per second” which translates to megahertz (MHz)).

Before we get to that, let’s go back in time for a bit.

The measurement “Hertz” was named after a German physicist Heinrich Hertz.

Heinrich Hertz was born in 1857 in Hamburg which was then the German Confederation.

He was born into a wealthy family and received his Ph.D. from the University of Berlin in 1880.

Later on, he became a physics professor in Karlsruhe and Bonn.

At the time, he was also involved in several studies.

He was particularly interested in English scientist James Clerk Maxwell’s theory regarding the interaction between electric and magnetic fields.

Maxwell believed that while the fields are static on their own, they could come together to create something dynamic.

Maxwell published the paper “ A Dynamic Theory of the Electromagnetic Field” in 1865.

The paper posited that when electric and magnetic fields converge, they take the form of waves moving through space at the speed of light.

It also stated that light was an expression of electromagnetic waves that happen at a specific wavelength.

Maxwell was also the one to predict the existence of radio waves.

However, we won’t get into that much in this article.

Maxwell’s paper presented several complex mathematical formulas to support his theories about electromagnetic fields.

The first problem was that there was no experimental proof to support his theories and the second was that no one seemed to understand the paper.

This was where Heinrich Hertz played a major role.

He created a device in 1886 that proved the existence of electromagnetic waves and determined their varying lengths.

Hertz was also able to measure the velocity of electromagnetic radiation and figured out it was the same as the speed of light as Maxwell predicted.

With his discoveries, Hertz opened the doors for research into electromagnetism.

This later led to the practical application in telegraphs, radios, televisions, and speakers.

Let’s take a look at speakers for example.

Electromagnetism is used to generate sound in speakers.

It corresponds to the electric charge being fed to the system as an alternating current.

This is the audio signal which is an electrical image of the acoustic waveform.

When the audio signal is passed through the voice coil, it creates an electromagnetic field that causes the direction of the field to change quickly. 

This causes the coil to vibrate with a frequency and intensity determined by the audio signal.

When this is amplified by a cone, the vibrations create sound waves. 

Although sounds are generated by an electromagnetic field in speakers, the sound does not consist of any electromagnetic waves. 

This is because the waves travel much slower than the speed of light and require air as a medium to move. 

However, much like an electromagnetic wave, sound occurs as a series of sine waves or oscillations with a waveform that can be defined as a sine curve. 

This allows for the measure of frequency or Hertz to be applied. 

Heinrich Hertz pointed the way towards the practical applications of electromagnetic fields. 

He also gave us a way to measure one of the most important aspects of sound. 

To give him credit for all the work done,  the International Electrotechnical Commission (IEC) honored him in 1935 by naming the unit used to measure frequency, Hertz.

It was later adopted by the General Conference on Weights and Measures (CGPM) in 1960 and by 1970 “Hertz had largely replaced the term “cycles per second”

Soundproofing and soundwaves

sound hertz acoustic foam

The pitch of the noise plays a key role in selecting the right products when trying to soundproof your home. 

wavelengths are longer and flatter for lower pitch sounds with lower Hertz values. 

This means that they require less distance and time to travel through a surface. 

Unfortunately, these are the most difficult sound sources to deal with. 

This is why you might be able to hear the bass tones from your neighbor’s stereo but not the conversation from his television. 

Be sure to take notice in advance as to the frequency of your noise source before you start your soundproofing project. 

For example, if you want the control reverberations the thicker the soundproofing material, the better the results if you’re dealing with low bass tones. 

If you use 2-inch-thick acoustic pyramid-designed panels, long flat sound waves will have to force their way through more material. 

This gives the pyramids more time and distance to capture the energy and convert it. 

Check out our best soundproofing materials article for some of the best soundproofing materials you can find on the market.

You can also read this how to soundproof a room for the best results.

Sound Standards

There are three basic standards used in the acoustic industry to measure soundproofing results.

These are NRC, STC and IIC.

They are all used to measure the effectiveness of sound control.

When purchasing soundproofing products, you may come across these ratings.

Let’s take a brief look at all 3.

NRC

NRC stands for Noise Reduction Coefficient.

It is used to measure the amount of energy that gets absorbed when it hits a surface.

In other words, i9t describes how well a product absorbs sound in a given space.

NRC is measured from 0 to 1. 

If the NRC rating is 0, it indicates perfect reflection which means the product will bounce 100% of the sound back into the room.

On the other hand, if the NRC is 1, it means perfect absorption which means the product will absorb 100% of the sound.

STC  

STC refers to the Sound Transmission Class.

It represents a product’s ability to block sounds from traveling through a medium like a wall, ceiling and floor.

The STC rating tells you how much a product can block airborne sounds from traveling from place to place.

The higher the STC rating, the higher the product’s ability to block out sound.

However, STC has some limitations with one being that it only measures certain frequencies; 125 Hz-4000 Hz.

This means it doesn’t accurately tell you how well a product can block low-frequency sounds below 125Hz.

IIC

Impact isolation Class or IIC measures a product’s ability to absorb impact noises.

It is represented with an integer or whole number.

The larger the number, the better as it means more sound is being blocked.

IIC is calculated based on sound reduction in 16 frequencies; 100-3150 Hz. 

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