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Silencers

Flexible duct silencers for a quieter grow room ventilation

The constant droning of a running extractor fan travels through walls and floors — particularly disruptive at night. A flexible duct silencer tackles this problem at source: the cylindrical metal casing with its 5 cm thick acoustic foam absorbs sound waves and vibrations before they propagate through your ducting. Noise reduction of 25 to 40 percent with no perceptible airflow loss.

Available in five diameters: 100, 125, 150, 160 and 200 mm. Mount directly after your fan where vibrations are strongest. For maximum results, add a second silencer on the intake duct. Fast delivery throughout Belgium.

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Flexible Silencer 100 mm

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Flexible Silencer 125 mm

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Flexible Silencer 160 mm

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Flexible duct silencers: full range for every ventilation system

An extractor fan is essential for climate control in your grow room, but its continuous noise can be the difference between a viable setup and an abandoned project. Especially when your grow space is in a home or apartment, neighbours quickly become an issue. The flexible duct silencer is the most commonly used acoustic solution: a cylindrical metal casing with a thick layer of sound-absorbing foam through which the air flows. No moving parts, no maintenance — just less noise.

How a silencer works: absorption, not blockage

The heart of a flexible silencer is open-cell polyether foam with a density of around 30 kg/m³. When sound waves travel through the silencer, they enter the millions of tiny air channels within the foam. There, the oscillations of air particles convert into heat through friction with the foam walls — a process physicists call acoustic dissipation. The upside: this absorption works particularly well on mid and high frequencies (500-5000 Hz), precisely the range where the irritating "whine" of motor noise sits. For low-frequency hum (under 200 Hz), a soundproof box is more effective. Many growers therefore combine both techniques for complete silence.

Why two silencers make such a difference

A flexible silencer works at one specific point in your circuit. Place one directly after the extractor fan, and you catch the noise output heading toward the exhaust — typically 25 to 40 percent reduction. But your fan also pushes noise upstream, toward the carbon filter and air intake. That noise passes through the filter wall and arrives directly in your grow tent — exactly where you are listening when working. A second silencer between fan and filter, or on the intake, solves that problem. Together you reach 50 to 55 percent reduction: the difference between an audible background sound and a system you barely notice.

Five diameters matched to your installation

Your silencer diameter must exactly match that of your extractor fan and ventilation ducting. A mismatched size creates turbulence at the connection that produces the opposite effect: more noise instead of less.

Flexible silencer 100 mm — for small compact setups with fans up to 150 m³/h
Flexible silencer 125 mm — the most common size for standard grow tents with 250 m³/h fans
Flexible silencer 160 mm — for 120×120 cm tents with 400-550 m³/h fans
Flexible silencer 200 mm — for large setups and fans up to 800 m³/h

Placement and installation tips

The optimal position for a silencer is as close as possible after your extractor fan — that is where sound vibrations are strongest and where dampening works most efficiently. Preferably with a 30-50 cm stretch of flexible aluminium ducting between them, which further dampens mechanical vibrations. Avoid mounting directly against a hard wall or obstacle if the silencer vibrates slightly, as this transfers noise into your building structure. Secure both connection points with duct clamps for an airtight connection without rattling. Note: the internal foam poses no health risks, but do not clean it with water. After 2-3 years, remove dust buildup with a vacuum cleaner on a low setting.

FAQ - Frequently asked questions about flexible silencers

How much noise does a single silencer reduce?

Between 25 and 40 percent, depending on fan type, speed setting and installation quality. That corresponds to 5 to 8 dB on a sound meter. For maximum results, combine two silencers (one on the outlet, one on the intake) and reach 50-55 percent reduction.

Does a silencer reduce my fan's airflow?

Minimally — typically under 5 percent. The internal foam is engineered for open air passage: sound absorption works through the foam structure itself, not by blocking the path. However, always use the exact same diameter as your fan and ducting; otherwise turbulence forms at the connection and produces more noise instead of less.

Where should I place the silencer?

Directly after the extractor fan, on the outlet side — that is where vibrations and sound waves are strongest, so dampening efficiency is optimal. Use a short length of flexible ducting between fan and silencer for extra vibration isolation. Optionally add a second silencer on the air intake to limit upstream noise through the carbon filter.

Difference between a silencer and a soundproof box?

A silencer dampens noise within the air circuit (while air flows through it) — effective against mid and high frequencies. A soundproof box dampens noise the fan radiates outward (in all directions) — effective against low-frequency hum that travels through walls. For maximum silence, combine both solutions.

How long does a flexible silencer last?

Under normal use, at least 5 to 10 years. There are no moving parts to wear out. The only degradation is dust buildup in the foam, which you can remove every 2-3 years with a vacuum cleaner. Only replace if the foam visibly crumbles or shows major mould growth after moisture incidents.

Order your flexible duct silencer today at Plant & Flower. Fast, discreet delivery anywhere in Belgium.