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Where Should Polyfill Go in a Subwoofer Box? Rear vs. Sides Explained
November 4, 2025 Nathaniel Victor

Where Should Polyfill Go in a Subwoofer Box? Rear vs. Sides Explained

Learn the best polyfill placement for subwoofer enclosures—why the rear wall matters most, when side-wall polyfill helps, and how to avoid over-damping for clean, punchy bass.

NVX empty subwoofer box showing internal polyfill placement on the rear wall NVX unloaded subwoofer enclosure interior illustrating rear-wall damping and side-wall polyfill NVX sealed subwoofer enclosure with internal damping for smooth bass response

Polyfill is one of the most misunderstood enclosure tuning tools. Used correctly, it can improve clarity and smooth response. Used incorrectly, it can reduce output and impact.

Why the Rear Wall Is the Priority

The rear wall is the primary reflection path behind the subwoofer cone. Treating this surface reduces standing waves and internal reflections without hurting efficiency.

When Side-Wall Polyfill Makes Sense

Side-wall polyfill is optional and should be used lightly. It can help slightly undersized enclosures by increasing effective volume and adding damping.

Sealed vs. Ported Enclosures

  • Sealed: Rear wall only (add sides only if needed)
  • Ported: Rear wall only, minimal, never near the port

Watch: Polyfill Placement & Enclosure Tuning

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Filed in: boxes, enclosures, sub box, sub boxes, subwoofer, subwoofers, woofer enclosures
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