Can Grass Quiet the Shore? Lab Experiments Reveal How Coastal Vegetation Muffles Sound

Christian Di Nicolantonio – dinicolantonio@cua.edu

Instagram: c.dinic
The Catholic University of America, 620 Michigan Ave., N.E., Washington, DC, 20064, United States

Diego Turo
Christopher Crognale
Ariel Wise
Teresa Ryan
Joseph Vignola
John Judge

Popular version of 5aPA6 – Modeling sound attenuation of near shore tall vegetation
Presented at the 190th ASA Meeting
Read the abstract at https://eppro01.ativ.me/web/index.php?page=IntHtml&project=ASASPRING2026&id=4065520

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Coastal marsh grass does more than just breed mosquitos, it can act as a natural sound barrier. Researchers at The Catholic University of America (CUA) have developed a laboratory method to measure and predict how fields of tall grass reduce sound levels near shorelines, with results that closely match outdoor measurements taken at Manteo, North Carolina.

Figure 1: Satellite image of the Manteo, NC field site alongside a photo of the Long Range Acoustic Device (LRAD) source and receiver setup in the marsh grass field (Receiver height highlighted in red).

Predicting how sound travels near coastlines is important for a range of applications, from understanding the acoustic environment to military and environmental monitoring. Tall grass fields that line riverbanks and coastlines absorb and scatter sound as it passes through them, but running outdoor experiments every time is not always possible, so researchers at CUA looked into alternatives.

The research team designed miniature 3D printed replicas of grass blade arrangements and tested them inside an impedance tube, a hollow cylinder used to make precise acoustic measurements. Think of it as a controlled, repeatable grass field measurement that fits on a desk.

Figure 2: All 3D printed samples (left) and a sample mounted within the impedance tube (right)

Seven different sample configurations were tested, varying two things: the porosity of the samples, meaning how tightly packed they are, and the angle at which the blades were oriented relative to the incoming sound. One set had blades straight at 0 degrees while the other set had blades tilted at 45 degrees, mimicking the natural variation found in real grass fields. The porosity of blades ranged from 0.5 to 0.8, meaning between half and four fifths of the sample volume was open air.

Both the porosity and the angle of the blades matter. Denser blade arrangements slow sound down more and shift the frequency at which sound is most strongly absorbed. The straight 0 degree blades consistently absorbed more sound than the tilted 45 degree blades at the same porosity, because the straight blades forced the sound to travel a longer, more winding path through the sample, a property known as tortuosity.

Figure 3: Absorption coefficient for all configurations, showing the shift in peak absorption with porosity and the difference between blade orientations.

By measuring how sound behaves across a range of sample thicknesses, the team estimated two key properties of each grass configuration: how fast sound travels through the medium and how quickly it loses energy, a quantity known as attenuation. These values were then extrapolated to predict how a much more open natural grass field would behave. When extended to porosities of 96% to 99%, the predicted attenuation matched the field measured value of 0.02 per meter closely.

Figure 4: Extrapolated attenuation coefficients for both blade orientations, with the field measured reference value shown for comparison.

This confirms that a simple laboratory experiment on small printed samples can successfully predict the acoustic behavior of a real coastal grass field, offering a practical and repeatable tool for understanding how nature quietly does its job.