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You may be able to hear the distinction between high and low-frequency noise, but do you understand how they are different scientifically? Frequency, which is measured in hertz (Hz), refers to the number of times per second that a sound wave repeats itself. When sound waves encounter an object, they can either be absorbed and converted into heat energy or reflected back into the room. Finding the proper balance between absorption and reflection is known as acoustics science.

High-Frequency Noise

Higher frequency sounds contain short sound waves with a frequency of 5,000 HZ or higher. High frequency sound waves are reflected back when they encounter thin objects and don’t bend as much around barriers. High-frequency noise can not endure over a long distance and can quickly dissipate due to higher energy levels. Frequent exposure to high-frequency noise is commonly associated with hearing loss 

Low-Frequency Noise 

Low-frequency noise encompasses sound waves with frequencies below 300 Hertz, often defined as 500 Hz or less on Common Octave Bands. Characterized by deep pitch and long wavelengths, these sounds are highly resilient, capable of traveling vast distances. Unlike higher frequencies primarily perceived by the ear, low-frequency noise is often felt as vibrations. Prolonged exposure to low-frequency noise can lead to adverse health effects including headaches, increased heart rate, anxiety, vertigo, and fatigue.

The noise reduction coefficient (NRC) is an average measurement of how much sound is absorbed by a certain material. Generally, a higher NRC rating means that a product absorbs more sound and a lower NRC rating means a product cannot absorb high levels of sound. However, it is important to remember that this number is an average across a wide frequency range. Determining the frequency range where the most noise is produced is critical to matching up the right product solution to fit the need. 

Comparison Table: High vs. Low-Frequency Noise

FeatureHigh-Frequency NoiseLow-Frequency Noise
Frequency RangeTypically above 5,000 HzTypically below 300 Hz
WavelengthShort (inches or fractions of an inch)Long (5 to 50+ feet)
Physical SensationHeard as a hiss, squeak, or whistleFelt as a rumble, thrum, or vibration
BehaviorHighly directional; easily blocked by line-of-sight barriersOmnidirectional; wraps around objects and passes through walls
Common Industrial SourcesCompressed air leaks, small fans, high-speed motors, whistlesLarge engines, generators, HVAC chillers, heavy transformers
Best Mitigation StrategyAbsorption: Porous materials like open-cell foam insulationMass & Damping: Heavy barriers like mass-loaded vinyl (MLV) insulation
Insulation Material ThicknessCan be treated with thin materials (0.5" - 1")Requires high mass or thick composites (2"+)

Real-World Examples & Material Information

The level of noise frequency produced by a particular item is often determined by its size and its Revolutions Per Minute (RPM). For example, a smaller motor running at high RPM will have a higher noise frequency than a large diesel engine running at a low RPM. With fans, the level of noise frequency is not only determined by its RPM, but also by its number of blades. 

Examples of objects that produce low-frequency sound include:

  • Motors, diesel engines
  • Large fans
  • Large compressors
  • Exhausts 

Examples of objects that emit high-frequency sound include:

  • Small compressors 
  • Small fans
  • Turbochargers
  • Small motors 

Common applications that produce high and low-frequency sound include:

  • Generator enclosures
  • Reciprocating compressor enclosures
  • Oxygen concentrators
  • Vacuum cleaners
  • Ambulances
  • Fire trucks 

When looking for solutions to absorb high and low-frequency sound, Technicon Acoustics offers various products. For low-frequency noise, we offer:

  • NR fabric faced composites foam or fiber
  • Foil or film faced composites
  • Barrier composites
  • Vibration Damping material (if the noise source is structure borne) 

For high-frequency noise, we offer:

  • Absorbers with a lower airflow resistant face(UB, FS)
  • Barrier composites
  • Vibration Damping material (if the noise source is structure borne) 

Working with Technicon Acoustics

As a leading manufacturer of acoustic and thermal products, Technicon Acoustics can provide innovative products for both high and low-frequency noise. Our design and engineering capabilities combined with our ability to problem solve allow us to work with our customers to deliver high-quality acoustic solutions. 

The core values of Technicon Acoustics are to always face challenges head-on while also bringing our A-game and taking pride in what we do. We also believe that a little love and a lot of fun go a long, long way to making this a better place. All of our team members are very engaged in their work and believe in making meaningful contributions. Please contact us or request a quote today for more information about our noise reduction products.

1. Why is low-frequency noise harder to block than high-frequency noise?

The difficulty lies in the wavelength. Low-frequency sounds (like the deep rumble of a large diesel engine) have long wavelengths that can be several feet long. These waves carry more energy and can physically vibrate through solid structures like walls and floors. High-frequency sounds (like a high-pitched whistle) have much shorter wavelengths that are easily absorbed by soft materials or thin barriers. To stop low-frequency noise, you typically need mass and decoupling (creating a physical break), whereas high-frequency noise can often be managed with standard acoustic foam.

2. How can I tell if my noise problem is high or low frequency?

A simple rule of thumb is to determine if you “hear” it or “feel” it. High-frequency noise is typically directional and sounds like a hiss, squeak, or whistle; if you move behind a barrier, the sound often drops significantly. Low-frequency noise is omnidirectional and often felt as a vibration or hum in your chest or under your feet. Scientifically, noise below 300 Hz is considered low frequency, while noise above 5,000 Hz is considered high frequency. For a precise diagnosis, Technicon Acoustics uses acoustic testing to identify the exact Hz peaks.

3. What are the best materials for absorbing low-frequency sounds?

Because low-frequency waves are so resilient, they require thicker, denser materials to be absorbed effectively. Standard thin foams will not work. Effective solutions include thicker composite foams (2 inches or more), mass-loaded vinyl (MLV) barriers, or vibration-damping sheets that convert the mechanical energy of the vibration into low-level heat.

At Technicon Acoustics, using facings or films laminated to porous materials changes the acoustical profile of the materials to help attenuate the lower frequency noise.

4. Can I use the same insulation for both high and low frequencies?

While some materials have a broad Noise Reduction Coefficient (NRC), a one-size-fits-all approach usually fails in industrial settings. If you use a material designed only for high frequencies to treat a low-frequency rumble, you will likely see almost no improvement. However, multilayered composites—which combine a porous absorber for high frequencies and a heavy barrier for low frequencies—are the most effective all-in-one solution for complex machinery that produces a wide range of noise.