Road Noise Frequency

Road noise is one of the most annoying interior noises in any vehicle. This problem is even more accentuated in an electric vehicle, leaving road noise, aero acoustic noise and, at certain conditions, heating, ventilation and air conditioning (HVAC) noise to be the dominating noise sources. External tire noise is also increasingly critical for fulfilling pass-by noise regulations. Read about electric applications here.

The road surface excitation is the source in road noise testing, and the cabin noise is both structure-borne and airborne. Frequencies below ~300 Hz are mostly structure-borne and above this frequency more airborne.

The noise is caused by the tire tread and road surface interaction. The tire tread design and tire sidewall stiﬀness have a lot of inﬂuence on cavity resonances that cause tonal noise around 200-250 Hz. The vehicle verification is done by analysis of sound pressure level (SPL), third octave band spectra, narrow band spectra and Articulation Index (AI) at diﬀerent vehicle speeds and welldefined road surface types for noise, vibration and harshness (NVH) testing, e.g. smooth, coarse, grooved and standardized surface for pass-by noise measurements. Transient noise and comfort while driving over bumps must also be evaluated.

Learn more about the challenges and how to select the right microphone

Learn more about Road Noise Frequency here

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Selected products

GRAS 146AE
A rugged and versatile microphone thoroughly protected for maximum performance in conditions with shock, dirt and moisture
GRAS 147AX
Makes ATF testing easy thanks to its small size and the possibility of mounting it even in the most difficult places
GRAS 42AG
The ideal solution for calibration

Road Noise on Electric Vehicles

Road noise is an important noise source in EVs and constitutes approx. 40% of the entire sound field. In a traditional ICE, the noise from the powertrain will often mask the road noise. This of course is not the case in EVs.

Road noise is an annoying interior noise in any vehicle, but in EVs often becomes a problem at lower speeds – often at an interval between 40-100 km/25-62 mph.

For road noise application testing, we recommend GRAS 147AX CCP Rugged Pressure Microphone together with GRAS 146AE ½'' CCP Free-field Microphone Set.

See our complete application offering within electric vehicles here.

Acoustic Test Types Within Road Noise Testing

Vehicle interior noise testing

A vehicle test on an NVH test track typically includes two to four microphones inside the vehicle distributed between the driver's and passenger seats. External microphones with high-performance windshield or intensity probes with nose cones can be used for measurement of tire near-field noise. Impact noise is measured on a dedicated test track with impact bars.

These tests together with sound power measurements can also be performed on a NVH chassis dynamometer equipped with road surface or impact bars during development. A test rig for the wheel only, adapted for the test track or the NVH chassis dynamometer, can be used for acoustic source measurements or pure tire development.

Structural testing is used for determination of the vehicle chassis sensitivity. Excitation is done with an impact hammer or shaker as well as a force transducer, and the acoustic response is measured with a measurement microphone at ear position. These tests in combination with vehicle tests and spindle force measurements will explain, if improvements are needed for vibration isolation to reduce low frequency road noise and/or tire cavity tonal noise.

Acoustic transfer function (ATF) testing

Acoustic transfer functions are measured between several positions in front of and behind the tire to understand the noise insulation from the wheelhouse to the cabin. This is done either with the direct method or reciprocally. The direct method involves using a calibrated omnidirectional sound source located at the tire, while the response is measured with one or more measurement microphones at ear position. For reciprocal measurements, the sound source is at ear position and the response is measured at the tire.

These measurements must be performed at several positions to include the source as well as the response. The result of such tests can show, if the acoustic pack needs improvement or, if there is a sound leakage. Pass-by noise is measured with dedicated microphones at a pass-by test track where all test equipment and facilities are thoroughly specified in the applicable standards.

FAQ for Road Noise Frequency

What is the typical road noise frequency range in modern vehicles?
Road noise in modern vehicles typically occurs between about 20 Hz and 1,000 Hz, with most tire and road interaction noise concentrated in the 100–500 Hz range. Engineers analyze this range to improve cabin comfort and reduce unwanted noise.

What is the frequency of road traffic noise?
Road traffic noise generally spans a wide frequency range from low frequencies around 20 Hz up to several kilohertz, depending on the vehicle type, tire interaction, and driving speed. Low-frequency components are usually dominant in cabin perception.

How do you measure road noise frequency in electric vehicles?
Road noise frequency in electric vehicles is measured using cabin microphones and vibration sensors during controlled tests or on-road driving. Engineers analyze the recorded signals using frequency analysis to identify dominant tire and road noise components.

Why is frequency analysis important for tire noise development?
Frequency analysis helps engineers identify the specific frequency bands where tire noise is generated. This allows tire and vehicle designers to optimize tread patterns, materials, and vehicle insulation to reduce unwanted noise and improve ride comfort.

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