---
title: "Sound pressure level (SPL)"
description: "Sound pressure level (SPL) is the logarithmic measure of sound pressure relative to the 20 µPa human-hearing reference, expressed in decibels. It is the primary specification figure for any sonic horn or acoustic cleaner and the metric used to size noise-exposure controls at the work area."
canonical_url: "https://sylio.co/glossary/sound-pressure-level"
last_updated: "2026-06-28T02:29:23.020Z"
---

**Sound pressure level (SPL)** is the logarithmic measure of sound pressure relative to the 20 µPa human-hearing reference, expressed in [decibels](/glossary/decibel). It is the primary specification figure for any [sonic horn](/glossary/sonic-horn) or [acoustic cleaner](/glossary/acoustic-cleaner) and the metric used to size noise-exposure controls at the work area.

## Industrial reference values

<table>
<thead>
  <tr>
    <th>
      SPL (dB)
    </th>
    
    <th>
      Reference
    </th>
  </tr>
</thead>

<tbody>
  <tr>
    <td>
      0
    </td>
    
    <td>
      Threshold of human hearing
    </td>
  </tr>
  
  <tr>
    <td>
      60
    </td>
    
    <td>
      Normal conversation
    </td>
  </tr>
  
  <tr>
    <td>
      120
    </td>
    
    <td>
      Threshold of pain
    </td>
  </tr>
  
  <tr>
    <td>
      140
    </td>
    
    <td>
      Industrial sonic horn (lower-output models)
    </td>
  </tr>
  
  <tr>
    <td>
      160
    </td>
    
    <td>
      Typical cement / ESP sonic horn
    </td>
  </tr>
  
  <tr>
    <td>
      180
    </td>
    
    <td>
      Upper limit of pneumatic industrial sonic horns
    </td>
  </tr>
  
  <tr>
    <td>
      194
    </td>
    
    <td>
      Theoretical maximum for an undistorted sine wave in air
    </td>
  </tr>
</tbody>
</table>

## SPL and cleaning effectiveness

Cleaning energy scales with intensity, which doubles for every 3 dB rise. A 150 dB horn delivers roughly twice the energy of a 147 dB horn at the same distance. SPL is not, however, the only selection criterion: [frequency](/glossary/frequency) determines [wavelength](/glossary/wavelength) and therefore penetration. A 150 dB low-frequency horn typically out-cleans a 160 dB high-frequency horn in a large open vessel.

## SPL and exposure

Reported nameplate SPL is measured at 1 m on the bell axis. Real exposure at the work area falls with distance per the [inverse-square law](/glossary/inverse-square-law) and through enclosure attenuation. Compliance with [OSHA 29 CFR 1910.95](/glossary/osha-29-cfr-1910-95) and [EU Directive 2003/10/EC](/glossary/eu-directive-2003-10-ec) is calculated from exposure, not from nameplate SPL.

## Related terms

- [Decibel](/glossary/decibel)
- [Frequency](/glossary/frequency)
- [Sound power vs sound pressure](/glossary/sound-power-vs-sound-pressure)
- [Inverse-square law](/glossary/inverse-square-law)