Shrinking Designs, Growing Challenges: Measuring Noise Reduction in Small Structures

Trigun Dinesh Maroo – dr.tmaroo@gmail.com

Donaghey College of Science, Technology, Engineering, and Mathematics, University of Arkansas at Little Rock, Little Rock, Arkansas, 72204, United States

Andrew B Wright

Popular version of 5aAA6 – A Small Reverberation Chamber to Measure Sound Transmission Loss in 3D-Printed Structures
Presented at the 190th ASA Meeting
Read the abstract at https://eppro01.ativ.me/web/planner.php?id=ASASPRING2026

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

Imagine a team of small robots moving through a warehouse, using sound to sense and communicate. The components that control noise in these systems are often around the size of your hand. Yet testing how well these small parts block sound can require a room-sized setup.

While this may sound excessive, it reflects how sound-blocking performance is commonly measured today. The ability of a material to block sound is quantified using Sound Transmission Loss (STL), which is typically evaluated using standardized methods such as the reverberation room and impedance tube.

The reverberation room method requires a large room (>50 m³) to measure the STL of a large sample (approx. 2.4 m). To illustrate this, consider heating a sandwich using an entire room instead of a microwave. Modern 3D printing technology enables the inexpensive production of many designs, but these structures are typically small (approx. 0.02 m³). For such small samples, the reverberation room method cannot be applied directly. One possible workaround is to combine multiple small samples into a larger one, similar to assembling many small sandwiches into one large sandwich. However, this approach is cumbersome, time-consuming, and expensive.

The other impedance tube method can measure the STL of small samples, but only for sound waves that strike the sample perpendicularly. Using the earlier analogy, this is similar to heating a sandwich with a torch from only one direction rather than heating it evenly from all sides.

While both standardized methods are useful, they have limitations when applied to small structures. This research presents the design and validation of a novel small reverberation chamber (0.49 m³, see Figure 1). In the earlier analogy, this chamber functions like a microwave, efficient and suited to the size of the sample.

Left image is large rectangular wooden box placed on a tiled floor. Right image is a top-down view the wooden box open showing two compartments with green cylindrical components attached to the inner walls.Figure 1: The Small Reverberation Chamber (left) closed (right) open

In this setup (see Figure 2), the STL offered by the small sample is measured using a sound input and corresponding waveforms recorded through microphones. A customized programming script developed in this research performs mathematical analysis on the waveform, and the STL is calculated.

Diagram of a small reverberation chamber setup with a speaker, rotating diffuser, sample, microphone, and PC for amplification and processing.Figure 2: Experimental Setup Example

The effectiveness of the chamber is validated by comparing the STL of two known materials against values measured using this system. The observed measurement error was low (±2.75 dB). Although this does not meet ASTM standard’s specifications (±2 dB), it is sufficient as an inexpensive solution for rapid STL characterization. Finally, the STL of four 3D-printed specimens was evaluated under different infills (50% and 100%) and material combinations (PLA, ABS, PLA+TPU, ABS+TPU) across various frequencies.

As modern designs continue to shrink, from small robotic systems to everyday devices, the ability to evaluate sound performance at the same scale becomes essential. The proposed small reverberation chamber enables this shift by allowing compact, noise-controlling components to be tested as they are actually used, supporting more effective noise-reducing designs.

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.

Aerial view with marked GPS points connected by yellow lines showing a tracking path over water channels.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.

Top and side views of green cylindrical samples with varying groove densities labeled by phi and theta angles.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.

Line graph showing alpha values versus frequency from 200 to 1600 Hz for different theta and phi angles, with red and blue curves representing theta 45° and 0° respectively.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.

Graph showing attenuation coefficient versus porosity for frequencies 250, 500, 750, and 1000 Hz with extrapolated curves at 0° and 45° angles.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.