Acoustic wall or earthen berm: which one to choose?
An earthen berm and a vertical acoustic wall both work by interrupting the direct sound path between source and receiver. Yet their performance, footprint and total cost differ widely. In this guide, our acoustic experts compare both systems on geometry, dB reduction, surface area, aesthetics, cost and maintenance. Want the basics first? Read our explanation on how an acoustic wall works or check our application against traffic noise along motorways and ring roads.
Two solutions, the same acoustic principle
Both an earthen berm and an acoustic wall work according to the Path Length Difference principle: they force sound waves to take a detour over the top edge of the obstruction. The greater the difference between the direct line and the detour, the more sound energy is lost along the way.
The distinction is not in the mechanism itself, but in the geometry of the obstruction. A berm has a wide foot and a sloped flank, a wall stands vertically on a narrow foundation. Those differences determine how efficiently each system removes sound and how much space it requires.
Why a vertical wall outperforms a berm at equal height
The position of the top edge determines how much detour the sound must take. With a vertical wall, that top edge sits directly above the foundation, as close as possible to the direct sound path between source and receiver. This delivers a large path length difference and therefore a strong reduction.
With a berm, the slope shifts the top edge tens of centimetres or even several metres away from the sound path. The effective path length difference drops, and so does the reduction. In addition, sound follows the sloped flank upwards and slides down the other side, causing some of the energy to "creep" around the obstacle instead of being sharply deflected. A vertical top edge creates a much sharper diffraction angle.
Sound barrier vs. earth berm at equal height
The orange path shows the detour the sound must take. The longer this detour compared to the direct line, the greater the reduction.
- Top close to the direct sound path → large path length difference
- Narrow foundation, modular and demountable
- Absorbent core prevents reflections
- Slopes shift the top away from the source and receiver
- Requires a large footprint (1:1.5 to 1:2)
- Reflects sound instead of absorbing it
Schematic representation. In practice, a berm typically needs to be 1.5 to 2 times higher to achieve the same reduction as a vertical sound barrier in the same location.
- At equal height: a vertical wall yields a greater path length difference than a berm, hence more dB reduction
- For the same reduction, an earthen berm typically needs to be 1.5 to 2 times higher than an acoustic wall
- A straight top edge deflects sound more sharply than a rounded or wide berm crest
- An absorbent acoustic wall also prevents reflections towards the opposite side, while a bare-earth or grass berm acts mainly as a reflector
Footprint and ground surface
The most practical difference is the space each system occupies. A berm requires a slope on both sides, typically between 1:1.5 and 1:2. A 3 m berm quickly takes up 9 to 12 m of width. An acoustic wall of the same height needs only a foundation of 30 to 60 cm wide.
In most gardens, along regional roads, on business parks or near sports facilities, this difference is decisive. A berm often simply does not fit on a typical plot, whereas an acoustic wall can be placed right on the property line without sacrificing usable surface area.
- Berm: slope of 1:1.5 to 1:2, so 3 to 4 times more width than height
- Acoustic wall: narrow strip foundation, 30 to 60 cm depending on height and soil type
- A 3 m berm requires roughly 9 to 12 m of total width, a 3 m wall about 0.5 m
- On a property line or in a narrow garden, a berm is usually not a viable option
Cost, construction and timeline
The total cost of both solutions varies significantly and depends on many factors: soil supply, earthworks, retention works, planting and maintenance for a berm, versus production, foundation and installation for an acoustic wall. At first glance soil seems cheap, but supplying hundreds of cubic metres of topsoil or sandy soil, compacting in layers, drainage and planting add up quickly.
An acoustic wall is prefabricated in our workshops and assembled on site on a light foundation. The lead time is usually limited to a few days or weeks, while a berm requires weeks to months of earthworks and settlement time before it is truly stable.
- Berm: cost is often underestimated due to soil supply, compaction, drainage and planting
- Acoustic wall: higher material cost per linear metre, but lighter foundation and quick installation
- Lead time berm: weeks to months, including settlement time before the soil stabilises
- Lead time acoustic wall: usually a few days to weeks, immediately acoustically effective
Aesthetics, maintenance and lifespan
A berm can be visually integrated into a green setting and looks natural, but requires ongoing maintenance: mowing, pruning, drainage checks and replenishing soil where erosion occurs. Slopes steeper than 1:2 also need retention works to prevent landslides.
A modern acoustic wall such as the vegetated Kokowall coconut fibre barrier looks like a green hedge after a few years. Maintenance is limited to occasional pruning of the vegetation. The structure itself lasts 20 to 25 years and can be dismantled and reused during renovation or relocation, while a berm is a permanent earthwork.
- Berm: looks green when planted, but requires annual mowing, pruning and erosion checks
- Acoustic wall: vegetated versions (such as Kokowall) look like a green hedge after 2 to 3 years
- Acoustic wall lifespan: 20 to 25 years, with a 10-year warranty on construction and materials
- An acoustic wall is modular and reusable during renovation, a berm is permanent
When to choose a berm, when to choose a wall?
Both systems have their use case. A berm can make sense on large infrastructure projects with surplus soil, in landscape-sensitive zones where a natural profile is desired, or where ample space is available and the cost of soil supply remains negligible. In most practical situations for private clients, businesses and sports facilities, a custom acoustic wall comes out as the clear winner, both acoustically and in terms of space and economics.
Our acoustic experts assess each project to find the right combination. Sometimes a hybrid solution is optimal: a lower berm at the base, with an acoustic wall on top for the extra height that truly makes the difference. Request tailored acoustic advice.
- Berm: useful when there is surplus soil, wide zones along motorways, or landscape integration is needed
- Acoustic wall: default choice for limited space, higher reduction targets or short delivery times
- Hybrid solution: a lower berm with an acoustic wall on top, for maximum height in limited space
- A definitive choice always requires an on-site analysis by our acoustic experts
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Our experts will be happy to advise you on the best solution for your situation. Contact us for a non-binding conversation.