---
title: "Attenuation (acoustic)"
description: "Attenuation is the loss of acoustic energy as a sound wave propagates through a medium. It combines geometric spreading (the inverse-square law) with absorption losses to viscosity, heat conduction and molecular relaxation. Attenuation rises sharply with frequency, which is the physical reason low-frequency acoustic cleaners reach further into large industrial vessels than their high-frequency counterparts."
canonical_url: "https://sylio.co/glossary/attenuation-acoustic"
last_updated: "2026-06-28T02:29:22.975Z"
---

**Attenuation** is the loss of acoustic energy as a sound wave propagates through a medium. It combines geometric spreading (the [inverse-square law](/glossary/inverse-square-law)) with absorption losses to viscosity, heat conduction and molecular relaxation. Attenuation rises sharply with [frequency](/glossary/frequency), which is the physical reason [low-frequency acoustic cleaners](/glossary/low-frequency-acoustic-cleaner) reach further into large industrial vessels than their high-frequency counterparts.

## Implications for cleaning reach

A 60 Hz wave loses very little energy per metre of air travel; a 400 Hz wave loses substantially more. In hot flue gas the absolute losses change but the frequency dependence remains the same. The result is that a 60 Hz horn can clean fly-ash deposits 8–10 metres from the bell, while a 400 Hz horn is generally effective only within 3–4 metres at the same nameplate SPL.

## Implications for noise control

The same physics that lets a low-frequency horn reach deep into a vessel also lets it travel further outside the vessel. Operator-station noise control is therefore harder for low-frequency installations, and [sound-attenuation enclosures](/glossary/sound-attenuation-enclosure-sonic-horn) are sometimes added at the bell.

## Related terms

- [Wavelength](/glossary/wavelength)
- [Frequency](/glossary/frequency)
- [Inverse-square law](/glossary/inverse-square-law)
- [Sound-attenuation enclosure (sonic horn)](/glossary/sound-attenuation-enclosure-sonic-horn)