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    • How We Test

    How We Test Sound Absorbers and Sound Blockers

    At Soundproof Cow, it is our goal to make your soundproofing project as simple as possible.  We spend test our sound absorbption and soundproofing materials to make sure they are the highest quality.

     

    Interested in the sound testing processes? Choose one of the “How We Test” options below to learn how we evaluate the Noise Reduction Coefficient of sound-absorption material using a fully enclosed room, a speaker, and a microphone; learn why it is important that we test our products at a variety of frequencies; and learn the role a tapping machine plays in measuring impact sounds through ceilings. (Plus more!)

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    How We Test Sound Absorbers

    Sound absorption and soundproofing: What's the difference? Soundproofing products block the sound. Sound Absorption products absorb them.

    Sound is like water. It does not 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. Soundproofing products trap the sound. They stop sound from entering or leaving a space, making it difficult for the sound to move to other parts of the building. They also stop unwanted noise from entering the room. Sound absorption products, on the other hand, absorbing the sound waves and prevent them from bouncing off the surfaces of a space. They improve the quality of the sound within a room.

    What is NRC? This is the ability to compare different sound absorption products.

    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.

    How is NRC Determined? Sound absorption material is tested using a speaker and a microphone.

    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%, receiving a score of .3. 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 1-866-949-9269 to find the right product.

    NRC Depends on the Install - To achieve the same results, your product needs to have been installed using the same construction method.

    It is 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 Soundproofing Materials

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

     

    Floors, unlike ceilings or walls, need to dissipate impact sounds (like footfall). A sound that travels through a floor is mostly from the impact on it, and floor soundproofing 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.

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    How We Test Sound Blockers

    What is STC? To be able to compare the performance of different soundproofing products, we rate them by how much sound they can block.

    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.

    How is STC Determined? Two rooms are assembled: the source room and the receiver room.

    To determine an STC rating for a specific material, two rooms are assembled: the source room (where the noise is located) and the receiver room (where the noise is detected). 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).

    Frequencies Play a Role - Our soundproofing products are tested at a variety of frequencies. A product can have different results for each frequency.

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

    If you are not sure the STC rating is for the frequency you are 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

    Defining STC Ratings in a Common Way - Rated by what receivers would hear through a wall that has been treated with soundproofing materials

    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

    Can You Hear Me Now? STC Ratings in Practical Applications - Perceived Loudness

    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.

    STC Depends on the Install - To achieve the same results, your product needs to have been installed using the same construction method.

    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.

    How to Determine the Effectiveness of Soundproofing Material

    The quality and performance of soundproofing products vary widely. Material manufacturers, end-users and others can determine soundproofing effectiveness by assessing several factors.

    How to Determine the Effectiveness of Soundproofing With Laboratory Testing

    Several laboratory tests can gauge soundproofing effectiveness:

    • Transmission loss testing: This test is performed on materials installed between two reverberation rooms. A high-powered sound source generates a continuous random noise stream. The tester measures and subtracts the receiving levels from the source. The results indicate the STC and octave band Transmission Loss (TL) numbers.
    • Absorption testing: With this method, the tester also uses a high-powered sound source to create a loud noise. In this case, the resulting sound and generated random noise stream enable the tester to measure the decay rate with and without the test specimen. The standard for attaining accurate results is a test specimen with a minimum size of 64 square feet, though 72 square feet is optimal.
    • Sound power testing: This testing method quantifies the energy emitted by a sound source. The results provide data that can help manufacturers ensure regulatory compliance.

    Document Reviews

    Conducting a review of resources and references can provide additional insight into the quality and effectiveness of various soundproofing materials. Case studies can be a reliable source, as they provide examples of real-world experiences from actual users.

    How to Test Soundproofing by Comparing

    Another way to gauge soundproofing effectiveness is to measure its performance against similar products. By conducting controlled experiments in a real-world environment or a laboratory setting, you can often note differences in the results that guide the decision-making process.

    DIY Testing Methods

    Use one or more of these do-it-yourself testing methods to gauge the effectiveness of the soundproofing material.

    White Noise

    A whirring fan, steady rain and the hum of an air conditioning unit are examples of white noise in our daily environments. You can use these sounds or a white noise machine to evaluate soundproofing material. Place one of these devices or a white noise-generating machine on one side of a wall and measure the sound levels in an adjoining room. Repeat the process after deploying your soundproofing measures and compare the results.

    Sound Level Meter

    A sound level meter is an acoustic measurement device that uses a handheld microphone to gauge sound intensity. To use the meter:

    1. Place the unit inside the room near the wall.
    2. Use the microphone to collect the sounds and note the measurements from the meter.
    3. Install your soundproofing material and repeat the process.
    4. Observe whether there are any differences in the before-and-after readings.

    How to Judge Soundproofing Quality With Occupant Feedback

    A more subjective method for determining soundproofing effectiveness is to ask the building’s occupants to provide their perception of the material’s quality. This feedback should include their assessment of the noise levels before and after the installation. If the difference is negligible, it likely means that the soundproofing isn’t delivering the desired results.

    Contact Soundproof Cow for More Soundproofing Assessment Ideas

    To learn more about how different sound blockers control impact sound, please call us at 1-866-949-9269 or contact us online.

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