Viscoelastic Layers and Transmission Loss: ALTA Integra's RECAV 2017 Panel Research

Adding a viscoelastic material layer in a periodic configuration raised a sound insulation panel's transmission loss from 7–16 dB to 14–20 dB across the 125–250 Hz range — roughly a doubling at the low frequencies where lightweight partitions are weakest. That measurement is the core finding of the paper ALTA Integra presented at RECAV 2017, authored by Herwin Gunawan with I.B. Ardhana Putra and Joko Sarwono as co-authors. It matters in practice because 125–250 Hz is exactly where an STC rating starts to lose descriptive power, and where added mass alone gives poor value per kilogram.

Measured Transmission Loss by Sample Type

All three sample types were measured and then compared against theoretical calculation, so the study validated a transmission loss prediction equation rather than only reporting a result.

What a Viscoelastic Material Does in a Panel

A viscoelastic material combines the properties of an elastic solid and a viscous fluid. That combination lets it absorb and dissipate vibration energy as heat instead of passing it onward through the panel — the same principle behind the damping loss factor used to characterise vibration control materials generally.

The variable this paper examined was arrangement rather than quantity. Three periodic configurations were tested — orthogonal, diagonal and striped — on the premise that how a damping layer is distributed across a panel changes its effect, not just how much of it is present. That distinction is what makes the result useful to a specifier: it suggests performance can be bought through geometry as well as through material volume.

Method: Three Samples, Measured Against Theory

Transmission loss was measured across three sample types: a single panel, a single panel fitted with viscoelastic material, and a sound insulation panel incorporating viscoelastic material. Measured results for each were then compared against theoretical calculation to validate the transmission loss prediction equation — which is the part of the study with the longest useful life, since a validated prediction method outlasts any single measured value.

Why the 125–250 Hz Range Is the Interesting One

The improvement was measured in a frequency band that causes disproportionate trouble on real projects. Standard airborne insulation ratings such as STC cover 125 Hz to 4,000 Hz, and performance at the bottom of that range is where lightweight construction typically underperforms its single-number rating. A partition that measures well overall can still pass bass-heavy music, mechanical rumble or traffic noise, because the rating averages across a range in which the low end contributes least to the number and most to the complaint.

Raising low-frequency transmission loss without a proportional increase in mass is therefore worth more than the same improvement higher up the spectrum — both acoustically and structurally, since added partition mass has to be carried by something.

Why This Research Still Informs Project Work

Presenting at RECAV 2017 reflects ALTA Integra's intent to ground its consulting in tested research rather than convention. The transmission loss principles examined in this paper continue to inform how the firm specifies sound insulation panels for partitions in studios, performance spaces and other isolation-critical environments through its acoustic engineering and design practice. It was one of two papers ALTA Integra submitted to the conference that year, alongside a study on splaying walls and room mode distribution.

FAQ

Sources

1. H. Gunawan, I. B. Ardhana Putra and J. Sarwono, "Transmission Loss Improvement of Sound Insulation Panel with Viscoelastic Material in Periodic Configuration," RECAV 2017, Denpasar, Bali.
2. ISO 10140-2:2021, Laboratory measurement of sound insulation of building elements — Part 2: Measurement of airborne sound insulation.