Airborne sound

Airborne sound accompanies almost every intervention in concrete, rock, and steel. Whether in concrete demolition, the gutting of a structure, tunnel construction, or natural stone extraction – pressure fluctuations arise in the air everywhere and are perceived as noise. For working with product groups from Darda GmbH – such as concrete demolition shears, stone and concrete splitters, hydraulic power packs, combination shears, Multi Cutters, steel shears, or tank cutters – a solid understanding of airborne sound is essential in order to align planning, operation, and protective measures professionally. In addition to technical execution, sound behavior directly affects feasibility, acceptance in the surroundings, and regulatory compliance. Systematic consideration of emission, propagation, and immission enables predictable, verifiable results.

Definition: What is meant by airborne sound?

Airborne sound consists of sound waves that propagate as changes in air pressure. Causes include mechanical processes such as cutting, pressing, splitting, or striking. The sound pressure level is typically given in dB(A) and describes the strength of the perceived noise. Character and impact depend on the frequency spectrum (low, mid, high), temporal structure (continuous noise, impulsive noise), and propagation (distance, reflections, shielding). Airborne sound is distinct from structure-borne sound, which propagates in solid materials and can secondarily radiate airborne sound from surfaces. In practice, the relevant range typically spans from infrasonic low frequencies up to several kilohertz; the speed of sound in air and wavelength determine how well shielding and distances are effective. The metrics LAeq (equivalent continuous level) and LAFmax/LCpeak (maximum and peak) complement the assessment of continuous and impulsive components.

Physical fundamentals and generation of airborne sound

Airborne sound arises when components, tools, or machines set the surrounding air into oscillation periodically or impulsively. In pressing and cutting (e.g., with concrete demolition shears or combination shears), spectra are often broadband but less impulsive. In splitting (e.g., with stone and concrete splitters or rock splitting cylinders), characteristic cracking sounds occur, with peak levels that may rise briefly. Striking methods, by contrast, typically generate pronounced impulses and higher peak levels. Hydraulic power packs contribute valve, pump, and fan noise to the continuous level. Propagation approximately follows the distance law: with each doubling of distance, the level in free field typically decreases by about 6 dB; in practice, reflections, ground characteristics, and wind influence the resulting immission level. Directivity of tools and machine housings, structural coupling into panels, and spectral content at low frequencies explain why the same sound power may be perceived very differently at receivers.

Sources of airborne sound on the construction site and in the quarry

Depending on the work method and construction site layout, the type and level of noise emissions differ. Typical sources include:

• Tools for concrete and steel processing: Concrete demolition shears, combination shears, Multi Cutters, steel shears, and tank cutters generate noise through cutting, pressing, and separating processes on concrete, rebar, and steel components. Contact conditions and feed rates shape the spectral distribution.
• Stone and concrete splitters: Stress build-up in the material and subsequent crack growth lead to short, sometimes abrupt airborne sound events.
• Hydraulic power packs: Pumps, valves, and fans cause broadband continuous noise; housings, lines, and attachments can additionally radiate.
• Peripheral equipment: Transport, feeding, hoists, and material handling generate tonal or impulse-like components.
• Environment-related background noise: Reverberation in interior spaces, tunnel and shaft reflections, facade reflections, meteorological influences.
• Temporary structures: Scaffolds, site fencing, and containers can act as secondary radiators when excited by structure-borne vibration.

Airborne sound in the context of concrete demolition shears and stone and concrete splitters

The choice of method decisively shapes the noise profile. Concrete demolition shears work by cutting and pressing; they generally produce less pronounced impulse peaks than strongly percussive methods. Airborne sound arises primarily from breaking the concrete structure, severing the rebar, and radiation at free edges. Stone and concrete splitters – including rock splitting cylinders – transfer energy into the material via controlled pressure build-up. The acoustic result is short cracking events whose frequency and level depend on geometry, material quality, prestress, and execution of the splitting process. In noise-sensitive environments, a targeted combination of shearing and splitting processes can reduce overall levels, for example by minimizing percussive components and by thoughtful sequence planning. Additional leverage exists in contact geometry (defined clamping points), pre-scoring of surfaces, and segmenting workpieces to control fracture propagation and limit peak levels.

Emission, propagation, and immission of airborne sound

Three levels are relevant for planning: emission at the tool or power pack, propagation over the site, and immission at workplaces and sensitive receivers. Key aspects include:

• Distance and geometry: Doubling the distance significantly reduces the level outdoors. Edges, courtyards, and interiors amplify via reflections. Tunnels and shafts guide and channel sound.
• Frequency dependence: Higher frequencies are more strongly attenuated by air and obstacles; low-frequency components carry farther and are harder to shield.
• Shielding: Massive, dense barriers close to the source reduce line-of-sight and direct sound. Gaps, openings, and leaks diminish the effect.
• Ground and vegetation: Soft ground and vegetation absorb part of the sound; hard surfaces reflect.
• Meteorology: Wind direction and temperature gradients can refract sound upward or focus it near the ground.
• Directivity and source grouping: Many tools radiate more strongly in certain directions; grouping sources can create additive effects that raise levels by several decibels.

For planning, logarithmic addition of levels is decisive: doubling equal sources increases level by approximately 3 dB. Facade transmission and room acoustics determine how much of the exterior level becomes relevant indoors.

Measurement and evaluation of airborne sound

Assessment is performed with sound level meters using A-weighting and suitable measurement periods (e.g., equivalent continuous sound level). In practice, one distinguishes workplace measurements (near the source) and immission measurements (e.g., at property boundaries). Relevant, in addition to Leq, are maximum levels and impulsive events. For comparability, measurement points, time windows, and operating conditions should be clearly documented. Normative details and limits are project-specific and depend on applicable regulations; they must be carefully reviewed in each individual case. Class 1 instrumentation, documented field calibration before and after measurements, and clear notes on operation (tool, load, cycle) improve traceability and reduce uncertainty.

• Use appropriate time weightings (e.g., Fast for LAFmax, Impulse if required by the specification) and capture LCpeak when impulse exposure is relevant.
• Define representative operating modes (start-up, steady operation, peak actions) and avoid mixed, non-comparable states.
• Record meteorological conditions and ground conditions that could bias propagation.
• Where necessary, apply corrections for background and reflections as specified in the applicable method.

Noise-reducing measures in practice

Planning and sequencing

• Schedule work phases with elevated airborne sound in favorable time windows; temporally decouple sensitive tasks.
• Position noise-intensive power packs as far as possible from sensitive areas; minimize paths and lines of sight.
• Plan construction logistics to avoid material handling and idle operations with high levels.
• Bundle similar noisy operations to reduce the number of start-stop cycles and avoid unnecessary peaks.

Method and tool selection

Cutting and pressing methods – such as with concrete demolition shears, combination shears, Multi Cutters, and steel shears – tend to generate less impulsive noise than strongly percussive methods. Stone and concrete splitters as well as rock splitting cylinders operate in a controlled manner; the short cracking events can be influenced by suitable clamping technique, step increments, and material preparation. Tank cutters should be operated with a stable support, constant feed, and decoupled workpieces to reduce vibrational excitation and secondary noise. Selecting appropriate jaw geometries and feed strategies can shift energy input away from resonant conditions and reduce crest factors.

Maintenance, hydraulics, and peripherals

• Check hydraulic power packs: operate pumps, valves, and fans with low noise (e.g., appropriate to speed and temperature), seal housing joints, ensure vibration decoupling.
• Keep tools sharp and free of play; dull cutting edges increase excitation, prolong processes, and raise airborne sound.
• Secure hoses and lines, avoid hard contacts, damp attachments.
• Balance and align rotating components; misalignment can increase tonal components and overall level.

Site setup and shielding

• Place mobile noise barriers or containers as acoustic barriers close to the source.
• Position material stacks, earth berms, and machines strategically to interrupt direct sound paths.
• Indoors: close openings; subdivide reverberant surfaces using fore-placed elements or absorbing building materials.
• Use double-row barriers or staggered screens where geometry allows to improve insertion loss.

Communication and documentation

Transparent information for affected parties, clear operating hours, and traceable measurement and record-keeping support acceptance. Legal requirements are project-specific and must be reviewed; binding statements can only be made within the scope of the relevant standards and permits. Regular feedback loops between site management and measurement personnel ensure that corrective actions are swiftly implemented.

Monitoring and feedback

• Implement periodic spot measurements and maintain a concise noise log for key phases.
• Use clear trigger levels for intervention (e.g., relocate power packs, adjust sequencing) when thresholds are approached.
• After completion of loud phases, review measures and update method statements for subsequent stages.

Special application areas: targeted control of airborne sound

Concrete demolition and special deconstruction

During the deconstruction of massive structural elements, airborne sound components arise from separation, crushing, and fracture processes. Alternating between concrete demolition shears for selective separation and targeted splitting for volume-reducing measures can reduce impulse components and limit sound duration. Short free paths between the source and outside air, as well as using existing structural elements as shielding, are important. Where feasible, pre-relieving cuts and stepwise load introduction stabilize the process acoustically.

Building gutting and cutting

During gutting, reverberation and decay times in rooms are particularly pronounced. Cutting methods with combination shears, Multi Cutters, or steel shears benefit from decoupled support of the workpieces and segmented procedures to smooth airborne sound peaks. For tank cutters, the following applies: stable seating, controlled feed, and avoidance of resonances through defined clamping points. Additional absorbent linings on temporary partitions reduce buildup of reverberation in corridors and shafts.

Rock excavation and tunnel construction

In tunnel bores, airborne sound is channeled; reflections increase levels in certain zones. Stone and concrete splitters as well as rock splitting cylinders act directly in the rock; the elastic energy released manifests as a short cracking sound. Coordinated pacing, acoustic shielding behind the working face, and routing power packs into side adits reduce immission. The use of bends and rough surfaces in access ways disrupts line-of-sight propagation and lowers levels further down the tunnel.

Natural stone extraction

In quarries, topography determines propagation: free-field conditions favor distance attenuation, rock faces reflect. Controlled splitting enables large-block extraction with manageable airborne sound. Hydraulic power packs should be operated in depressions, behind berms, or barriers to interrupt direct sound. Orienting operations away from reflecting faces and exploiting wind direction can yield additional attenuation in practice.

Special operations

In sensitive environments – such as near protected facilities – a combination of low-noise methods, tight time planning, and consistent shielding is effective. Short, plannable noise events are often easier to control than long-lasting continuous levels. Early coordination with stakeholders helps align windows for unavoidable peak events.

Health and occupational safety when dealing with airborne sound

At workplaces with elevated airborne sound, suitable protective measures must be provided. These include personal protective equipment (e.g., hearing protection), break arrangements, and minimizing exposure through task rotation and distance. The specific design is based on applicable regulations, operating instructions, and risk assessments for the respective project. Selection of hearing protection should consider octave-band attenuation to avoid under- or overprotection; in high-impulse environments, combined protection (earmuffs plus plugs) and clear signage for demarcated zones are advisable. Fit checks and regular instruction maintain effectiveness over the course of the project.

Practical guide: step by step to a quieter construction site

1. Identify sound sources: tools, power packs, and handling processes; prioritize them.
2. Process analysis: evaluate cutting, pressing, and splitting with respect to impulse and continuous components.
3. Optimize layout: increase distances, place barriers near sources, break lines of sight.
4. Align tool selection: where possible, combine cutting/pressing methods (e.g., concrete demolition shears) sensibly with splitting processes.
5. Dampen power packs: encapsulate hydraulic power packs, optimize fan guidance, decouple vibrations.
6. Cadence operations: cluster noise peaks, avoid sensitive times, synchronize workflows.
7. Ensure maintenance: keep cutting edges sharp, avoid leaks, check fastenings.
8. Verify effectiveness: document measurements, fine-tune measures.
9. Stabilize routines: integrate noise checks into daily briefings and update action plans as conditions change.
10. Close the loop: compare results with targets, capture lessons learned, and transfer measures to subsequent sites.

Typical misconceptions about airborne sound

• “Only the dB value matters.” – Time structure, frequency content, and impulse peaks also significantly shape perception.
• “Just placing barriers somewhere is enough.” – Effectiveness primarily arises from short source-to-barrier distance and closed shielding.
• “Hydraulic power packs are secondary.” – Continuous levels from power packs often shape overall exposure more than brief tool operations.
• “Low frequencies are harmless.” – Low-frequency sound carries far and is harder to attenuate; planning and positioning are critical.
• “Twice the distance halves the level.” – Level reduction with distance is logarithmic; halving is not achieved by a simple twofold increase in distance.
• “If it is short, it is safe.” – Even brief impulsive events can dominate exposure and annoyance; peak control is essential.