---
title: "Piston-whistle horn"
description: "A piston-whistle horn is a sonic horn whose sound is generated by a reciprocating piston or rotating slotted disc inside the driver, rather than by a flexing diaphragm. The mechanism is closer to a steam-whistle or ship's siren scaled to industrial duty, and tends to occupy the upper end of the audible cleaning band — 250 to 450 Hz."
canonical_url: "https://sylio.co/glossary/piston-whistle-horn"
last_updated: "2026-06-28T02:29:29.535Z"
---

A **piston-whistle horn** is a [sonic horn](/glossary/sonic-horn) whose sound is generated by a reciprocating piston or rotating slotted disc inside the driver, rather than by a flexing [diaphragm](/glossary/diaphragm-horn). The mechanism is closer to a steam-whistle or ship's siren scaled to industrial duty, and tends to occupy the upper end of the audible cleaning band — 250 to 450 Hz.

## Where piston-whistle horns are preferred

Higher frequencies carry more acoustic energy per unit volume and couple efficiently into compact internal geometries. That makes piston-whistle and related high-frequency designs the usual choice for:

- [Fabric-filter](/glossary/fabric-filter) compartments where filter bag spacing is tight
- [Catalyst layers](/glossary/honeycomb-catalyst) in [SCR reactors](/glossary/selective-catalytic-reduction) where ash needs to be lifted from cell faces rather than projected across a large open volume
- Small [hoppers](/glossary/hopper) and [cyclones](/glossary/cyclone-separator) where wavelength matching benefits from shorter waves

In larger open vessels — [ESP fields](/glossary/esp-field-bus-section), [preheater cyclones](/glossary/preheater-cyclone), [recovery-boiler superheaters](/glossary/recovery-boiler) — long-wavelength [low-frequency](/glossary/low-frequency-acoustic-cleaner) diaphragm horns penetrate further and are usually preferred.

## Trade-offs versus diaphragm horns

<table>
<thead>
  <tr>
    <th>
      Attribute
    </th>
    
    <th>
      Piston-whistle horn
    </th>
    
    <th>
      <a href="/glossary/diaphragm-horn">
        Diaphragm horn
      </a>
    </th>
  </tr>
</thead>

<tbody>
  <tr>
    <td>
      Typical frequency band
    </td>
    
    <td>
      250–450 Hz
    </td>
    
    <td>
      60–250 Hz
    </td>
  </tr>
  
  <tr>
    <td>
      Penetration in large vessels
    </td>
    
    <td>
      Limited
    </td>
    
    <td>
      Excellent
    </td>
  </tr>
  
  <tr>
    <td>
      Energy density at the target
    </td>
    
    <td>
      High at short range
    </td>
    
    <td>
      Moderate over longer range
    </td>
  </tr>
  
  <tr>
    <td>
      Wear part
    </td>
    
    <td>
      Piston, seals, slot disc
    </td>
    
    <td>
      Single diaphragm
    </td>
  </tr>
  
  <tr>
    <td>
      Best suited to
    </td>
    
    <td>
      Fine dust, dense catalyst, small geometries
    </td>
    
    <td>
      Open vessels, bulk solids
    </td>
  </tr>
</tbody>
</table>

## Related terms

- [Sonic horn](/glossary/sonic-horn)
- [Diaphragm horn](/glossary/diaphragm-horn)
- [High-frequency acoustic cleaner](/glossary/high-frequency-acoustic-cleaner)
- [Bell horn](/glossary/bell-horn)