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How We Test Sound Absorbers and Sound Blockers

Sometimes the effect soundproofing materials have on a room can feel a bit like magic. Now you hear it, now you don’t. At Soundproof Cow, it’s our goal to make your soundproofing project as snag-free as possible, which is why we love this “feels like magic” effect so much, and why we spend so much time testing each of our sound absorbers and blockers to make sure they’re tip-top before they get to you.

Interested in a behind the scenes tour of our testing process? Choose one of the “How We Test” options below to learn how we evaluate the Noise Reduction Coefficient of sound absorbing wall panels using a fully enclosed room, a speaker and a microphone; learn why it’s important that we test our sound blocker products at a variety of frequencies; and learn the role a tapping machine plays in making sure floor sound blockers adequately stop the transfer of impact sounds through ceilings. (Plus more!)

How We Test Sound Absorbers

Sound is like water. It doesn’t have a shape or form, but molds itself to its surroundings. And like water, sound can be absorbed by some materials and contained by others. Click here to learn more sound basics. Soundproofing products trap the sound. They contain the sound within a space, making it impossible for the sound to move to other parts of the building. They also stop unwanted sound from entering the room. Click here to learn more soundproofing basics.

Sound absorption products, on the other hand, soak up sound. They absorb sound waves and prevent them from bouncing off the walls. They improve the quality of the sound within a room. Click here to learn more sound absorption basics.

To be able to compare the performance of different sound absorption products, we rate them by how much sound they can soak up. This rating is called NRC, which stands for Noise Reduction Coefficient. Generally, the higher the NRC rating, the better the product is at absorbing sounds.

The NRC rating is determined by testing the sound absorption material using a speaker and a microphone. A fully enclosed room is set up with a speaker on one end and a microphone on the other. The speaker emits a specific sound at 250 Hertz, 500 Hertz, 1000 Hertz, and 2000 Hertz. These frequencies (pitches) represent the range of the human voice.

The microphone captures readings used to determine the level of sound in the room without a sound absorption product, like Echo Absorber™ Acoustic Panel. After the baseline readings are gathered, the Echo Absorber™ Acoustic Panel is placed on the floor between the speaker and the microphone. The sound level is measured again.

At 250Hz the  Echo Absorber™ Acoustic Panel reduced the amount of sound in the room by 30%.  It receives a score of .3 at 250Hz. Once all frequencies have been tested, they are averaged and rounded to the nearest .05.

Here are the measurements for the
Echo Absorber™ Acoustic Panel:

Frequency:

250

500

1K

2K

Total

Reduction:

.30

.86

1.10

1.05

3.31/4=.85

Echo Absorber™ Acoustic Panel has an NRC (noise reduction coefficient) of .85. Meaning, on average, it absorbs about 85% of the sound it encounters.

Low frequency sounds are created by home theaters, recording studios, and gun ranges. If you have a low frequency application, call us at 1-866-949-9COW to find the right product.

It’s important to note the NRC rating is based on testing a product that has been installed in a specific way. To achieve the same results, your product needs to have been installed using the same construction method. If your product has not been installed properly, it will not be as effective (have as high of an NRC rating).

Before you purchase any sound absorption product, be sure to check the NRC reports to determine if your construction method will achieve the results you want.

How We Test Floor Sound Blockers

Floors are a big contributor to noise problems. Whether they let sound leak in from the room below or transmit the vibrations created from footsteps, floors can be a real sound problem. Floor soundproofing products, like floor joist isolators, work by decoupling (or separating) the flooring from the structural supports. To be able to compare the different floor sound blockers, impact insulation class (IIC) is used. This measurement tells how well a floor blocks sound, just as STC is a sound blocking measurement for walls, and CAC is for ceilings tiles.

Floors, unlike ceilings or walls, need to block impact sounds (like footfall). Sound that travels through a floor is mostly from the impact on it, and floor sound blocking products need to control that sound rather than airborne noise. Instead of a speaker, which is used to test walls and ceilings, engineers use a tapping machine to determine IIC. The tapper hits the floor for regular intervals at 16 different frequencies while a microphone measures the sound pressure level in the lower room. The decibel levels in the top room are compared with those in the bottom room to determine an average difference.

To learn more about how different floor sound blockers control impact sound, please call us at 1-866-949-9COW or contact us online.

How We Test Sound Blockers

Sound is like water. It doesn’t have a shape or form, but molds itself to its surroundings. And like water, sound can be absorbed by some materials and contained by others. Click here to learn more sound basics.

Sound absorption products soak up sound. They absorb sound waves and prevent them from bouncing off the walls. They improve the quality of the sound within a room. Click here to learn more sound absorption basics.

Soundproofing products, on the other hand, trap the sound. They contain the sound within a space, making it impossible for the sound to move to other parts of the building. They also stop unwanted sound from entering the room. Click here to learn more soundproofing basics.

To be able to compare the performance of different soundproofing products, we rate them by how much sound they can block. This rating is called STC, which stands for Sound Transmission Class. Generally, the higher the STC rating, the better the material is at blocking sound.

To determine a STC rating for a sound blocking product, two rooms are assembled: the source room (where the noise is located) and the receiver room (where the noise is detected). Sound blocking material is installed on the wall that joins the two rooms. A large speaker in the source room emits a sound at a variety of frequencies (pitches) and at certain dB (volume) levels.

The receiver room has a microphone and a diffuser. The diffuser is used to distribute the sound energy evenly within the receiver room. The microphone is used to measure the amount of sound that is detected. The sound travels from the speaker in the source room, through the sound blocking material on the shared wall, and into the receiver room. The microphone measures the dB (volume) for each frequency (pitch).

One soundproofing product is tested at a variety of frequencies. A product can have different results for each frequency. It’s important to verify the STC rating advertised is for the frequency you’re trying to treat. Some products with low STC ratings perform better than those with higher STC ratings for certain frequencies.

If you’re not sure the STC rating is for the frequency you’re trying to eliminate, request a copy of the Transmission Loss data. The Transmission Loss data provides details on the sound blocking product’s performance at each frequency level tested.

Sample STC Rating at Varying Frequencies

5000

4000

3150

2500

2000

1600

1250

1000

800

630

500

400

315

250

200

160

125

100

80

Frequency (Hz)

Specimen Transmission Loss (dB)

24

26

33

33

37

42

45

46

49

52

55

57

60

60

56

56

62

67

72

The table below defines STC ratings by what the receiver would hear through a wall that has been treated with soundproofing materials. Please note: these descriptions are based on subjective definitions and may vary by the person hearing the sound.

STC Rating of the Soundproofing Material

What the Receiver Would Hear through the Wall (How Effective the Product Is)

30-35

36-40

41-45

51-55

56-60

61-65

66-70

71+

most sentences heard clearly

words and phrases heard occasionally

loud speech audible, music and TV’s heard

speech barely audible, loud music and TV audible

loud speech inaudible, loud music faintly heard but bass is still audible

music faintly heard, bass still audible, power tools heard

music heard if very loud, power tools still audible

most airborne noise is blocked

Each time a structure is treated with soundproofing materials, the amount of sound that is transferred through the structure is reduced. Each time the STC Rating of a structure is increased by 10, the sound transfer is reduced by 50%.

For example: a wall had an STC of 35. A sound barrier material was added and it improved the wall to an STC of 45. This means that sound leakage was decreased by up to 50%. The chart below illustrates how changes in STC impact the actual sound transmission property of a wall. Please note: these descriptions are based on subjective definitions and may vary by the person hearing the sound.

Changes in STC Rating

Changes in Perceived Loudness

+/-10

+/-5

+/-3

+/-1

almost imperceptible

just perceptible

clearly noticeable

twice (or half) as loud

Since STC and dB (volume) levels are directly related, the same is true for drops in Transmission Loss data, expressed in dB. For example, a +/- 5 dB change is also clearly noticeable, just like a +/- 5 STC change is clearly noticeable.

It’s important to note the STC rating is based on testing a product that has been installed in a specific way. To achieve the same results, your product needs to have been installed using the same construction method. If your product has not been installed properly, it will not be as effective (have as high of an STC rating). Before you purchase any sound blocking product, be sure to check the STC reports to determine if your construction method will achieve the results you want.

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