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Apprentice Q&A · #269

Why can solid metal bracing around a sound attenuator make noise worse?

3rd YearSound Attenuators / FansGREEN · Standard Correction

A sound trap cannot do its job if vibration bypasses it through rigid metal. Separate fan, flex connector, silencer, and supports per the approved acoustic detail.

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Plain-English answer

A sound attenuator reduces airborne noise, but rigid metal tied from the fan casing across the attenuator can carry vibration right around it.

Check whether stiffeners, braces, duct, or hangers are creating a continuous metal path across the acoustic break. The recovery is usually to remove the bridge, restore the flex/vibration break, and keep equipment/supports isolated per detail.

Field checklist

Ask Foreman

The fan/silencer setup has rigid metal bracing crossing the acoustic break. I checked the vibration path. Do you want the bridge removed and the flex isolation restored per detail?

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Verify before acting

Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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