Noise Control: Source, Path and Receiver
Noise control follows one logic: reduce the source, cut the path, protect the receiver, in that order of preference. This page explains the physical tools — mass, decoupling, damping, sealing, absorption, isolation, barriers — where each one works and where it does not, and how a project goes from diagnosis to a verified result. Geonoise designs and verifies these measures; it does not sell them.
Passive control: mass, air gap, decoupling, damping, sealing
- Mass law: doubling the surface mass of a wall gains about 6 dB at mid and high frequencies; heavy single walls are the simplest route to a high rating
- Double leaf with an air gap: two separate leaves on separate studs, with mineral wool in the cavity, out-perform a single wall of the same mass because the leaves are decoupled
- Resilient channels and clips: break the structural path between the board and the stud so vibration does not cross the frame
- Damping and constrained-layer products: suppress resonance in metal, timber and gypsum panels
- Sealing: every gap, penetration and door undercut; a 1 % open area caps the transmission loss near 20 dB regardless of what the wall is made of
Buildings: walls, floors, ceilings, doors, windows and flanking
Walls and partitions
- Double leaf with mineral wool and full-perimeter sealing
- Multiple gypsum layers with a damping layer between them
- Watch for short circuits through beams, columns and continuous slabs
Doors and windows
- Solid, heavy leaves or a double door lobby
- Compression gaskets on all four sides and a drop seal at the threshold
- Laminated or multi-pane glazing with a wide air gap; the glazing sets the ceiling for the whole façade
Ceilings and floors
- Decoupled suspended ceilings on resilient hangers with mineral wool above
- Floating floors or resilient underlays for impact sound
- Treatment of service penetrations and risers
Flanking — sound travelling around the element through the structure or the services — is the usual reason a field result comes out 5–10 points below the laboratory rating. Every junction has to be detailed. For what the numbers mean and how they are verified on site, see what STC is and how it is tested.
Impact sound: floating floors and underlays
- A floating floor on a resilient layer or rubber pads isolates footfall and dropped objects from the slab
- Underlays for timber, laminate and tile floors are chosen by density and dynamic stiffness, not by thickness alone
- Machine bases are isolated from the structure with springs or rubber isolators sized to the machine's speed
HVAC and machinery: silencers, lagging, isolation
- Duct silencers and lined duct: reduce mid and high frequency noise in the airflow and set the NC/NR level in the room
- Lagging and damping: reduce the sound radiated by duct walls, stacks and machine casings
- Vibration isolation: pads, springs and resilient hangers stop vibration entering the structure, where it would otherwise re-radiate as noise rooms away
- Inlet and outlet treatment: acoustic louvres, plenums and lined hoods for fans and generators
- Maintenance: balancing fans, replacing bearings and aligning shafts removes the tonal components that generate complaints
Generators, chillers and rooftop plant have their own page: generator, chiller and rooftop plant noise.
Outdoors: barriers, bunds and site layout
- A barrier or earth bund works only when it is continuous, has no gaps and breaks the line of sight between source and receiver; the gain is typically 5–10 dB and falls off with distance
- Absorptive facing on the source side limits reflection onto other receivers
- Re-orienting a source, raising or lowering it, or re-routing truck traffic often reduces event Lmax more cheaply than any construction
Active noise control: when it applies
Active control cancels sound with an out-of-phase signal. It works at low frequency in confined, stable conditions — ducts, stacks, some cabins and headsets — and needs stable phase and an accurate feedback microphone. In open spaces and at mid and high frequency, barriers, mass and geometry remain more effective.
Administrative controls and PPE
- Schedule and limit the hours of noisy work to reduce dose and TWA
- Zone noisy areas and restrict access; post warning signs where the level exceeds the limit
- PPE: earplugs or earmuffs with attenuation matched to the exposure, avoiding over-protection
- Training and signage so that protectors are actually worn
Thai law requires the engineering route to be tried before PPE is relied on — see Thai noise law.
Project workflow and return on investment
- Diagnose: measure Leq, Lmax and the spectrum; identify the source, the band and the path — with an acoustic camera where several sources compete
- Target: set the KPI, for example Lmax at the receiver down by 6 dB, or DnT,w up by 8
- Design: Good / Better / Best option sets with predicted results and a bill of quantities
- Implement: build to the sealing, mass, decoupling and isolation details — the detail is where most projects lose their decibels
- Verify: measure after the work against the target
- Operate: maintenance, scheduling and PPE training so the result holds
Choosing the measure by situation
| Situation | Main problem | Main measures | Typical result* |
|---|---|---|---|
| Room to room | Speech leakage, flanking | Double leaf + mineral wool + sealing + resilient channels | DnT,w +6 to +12 |
| Floor / ceiling | Impact, structure-borne vibration | Floating floor + underlay + resilient hangers | L'nT,w down 8–15 dB |
| Plant room / ducts | Hum, tones, jet noise | Silencer + lining + isolation + lagging | Room NC/NR brought to target |
| External community | Event Lmax, truck routes | Barrier or bund + routing + scheduling | Lmax at receiver down 5–10 dB |
*Indicative; the result depends on geometry, installation detail and workmanship, which is why every scheme should be verified by measurement.
Frequently asked questions
Which measure should I start with?
Rank the options by decibels gained per baht, and start at the source or the path that gives the most. Sealing and isolation are usually the cheapest decibels; replacing a wall is usually the most expensive.
Does acoustic foam stop sound passing through a wall?
No. Foam and absorbent panels reduce reflection inside a room. Sound insulation between rooms comes from mass, decoupling and sealing; absorbent added to a leaking wall changes almost nothing.
Can active noise control replace a barrier?
Not in general. Active control suits low frequencies in closed or semi-closed systems such as ducts. In the open, barriers, distance and source orientation do more.
Who designs and who supplies the measures?
Geonoise designs the scheme and verifies the result; it does not sell materials or install them, so the recommendation is not tied to any supplier. Materials come from the market; the design and the measurement come from us.