Acoustics · SERVICE · REV 2026-10-06
Sound isolation
Isolation is not treatment. Treatment changes what sound does inside the room. Isolation decides what crosses into the corridor, the next cinema, or the control room. Isolation usually fails at an opening, not for lack of foam.
Definition
Airborne sound isolation is the reduction of energy crossing a partition: wall, slab, door, or glass. The laboratory single number, Rw in the ISO 717-1 family after an ISO 10140 measurement, or STC after ASTM E90 and ASTM E413, describes a specimen in a laboratory. The building adds flanking through a continuous slab, the facade, and the duct. An Rw or an STC is therefore not quoted as a field result.
On-site performance is asked by a field measurement, such as the ISO 16283-1 family, then rated with a figure such as DnT,w through ISO 717-1 if that path is adopted. This page gives no such figure for a project, no absorption coefficient, and no noise level. Internal treatment and RT60 are other subjects: a well isolated room can still be reverberant.
When is this service needed?
Two halls sharing a boundary
A cinema, a lecture hall, or a meeting room behind the stage. The programme in one must not become the noise in the other.
Outside noise entering the show
A street, a mechanical roof, or a public corridor. Isolation here protects speech clarity inside the hall, not only the neighbour’s comfort.
A shared HVAC path
When one duct serves more than one sensitive room. The duct is a hole even if the wall is heavy.
A door in a high-rated partition
An ordinary door, or a gap under it, spends the benefit of the laboratory wall. The door is part of the partition, not a separate joinery item.
Where it is used
Multi-screen cinemas
The partition between two screens, the corridor door, and the projection room. Low-frequency leak from the soundtrack is the usual complaint.
Theatres and rehearsal rooms
A rehearsal next to a performance. Isolation is what allows them to overlap. Treatment inside the rehearsal room does not solve it.
Adjacent conference rooms
Privacy and intelligible speech across the partition. A hearing loop can add magnetic spill. That is a separate path and is checked separately.
The building envelope
Plant on the roof, the fresh-air intake, and the street facade. Incoming noise raises the noise floor and lowers STI.
Parts of the solution
The partition itself
Mass, decoupling, or a lined cavity, as the design requires. The laboratory number of the specimen does not describe the partition after cutting and installation.
Door, frame, and threshold
A designed leaf or a pair of leaves, hinges, and seals that close on four edges. The undercut is an open path.
Glass and the control window
A control room is isolated with a designed glass build-up, not with a single pane because someone must see. Vision is a constraint, not a waiver.
Duct treatment
Silencers, lining, and separate paths for sensitive rooms. A silencer without enough length at the frequency that matters is metal ornament.
Penetration details
A back-box that does not face a back-box on the other side, a seal around the pipe, and a cable that is not left in an open hole.
Engineering considerations
The weakest path governs
Wall, door, glass, duct, and flanking. Energy takes the easiest path. Raising the wall rating alone does not raise the room’s isolation.
Flanking through the structure
A continuous slab or a continuous facade links the two rooms around the partition. Breaking the path or adding mass is an early structural decision.
Low frequency
Music and picture shake the partition where mass and stiffness matter more than a speech seal. A mid-band single number hides that.
Noise floor and STI
Weaker isolation raises incoming noise. IEC 60268-16 rates speech clarity. Isolation is not swapped for an STI target, or the reverse.
Coordination with circulation
An isolating door is heavier and needs a closer and a swing. The corridor and the code see the door as a possible obstruction, not only as an acoustic panel.
Materials
Mass and separation
Heavier layers, separated frames, or a cavity. The material is named on a detail with the joint. A product name without a detail does not isolate.
Seals
A gasket that compresses around the perimeter and is replaced when it takes a set. A seal cut at the lock is a path. No isolation number is stuck to the seal profile on this page.
Duct lining and silencers
Chosen for frequency, pressure drop, and fire performance from the product report. This page gives no decibel insertion loss for a silencer.
Related systems
HVAC
The air path, grille velocity, and the machine body on the roof. Architectural isolation does not include fan noise unless it is designed.
Doors and access control
The lock, the hinge, and the closer have to complete the seal, not defeat it. Coordination with the joiner is electrical and mechanical.
Internal acoustics
Treatment and RT60 come after what noise gets in is known. An internal absorber does not raise the field Rw.
Listening systems
The sound-system level inside the hall, and a hearing loop in the neighbouring wall. Both can be heard outside by a different path.
Design sequence
- 01
Name the noise source and the receiver: from which room to which room, at what hours, and at which frequency the programme dominates.
- 02
Draw every path: partition, door, glass, slab, facade, HVAC, and electrical boxes. An undrawn path will be built open.
- 03
Ask the consultant for a field acceptance criterion, not a copied laboratory number. This page does not propose a DnT,w for the project.
- 04
Detail seals, thresholds, and penetrations at a scale that can be built. The words “acoustic isolation” on a plan are not a detail.
- 05
Review the door against width and against the fire-door requirement if one leaf serves both. The two requirements can conflict and are resolved in the product report, not by guessing.
Delivery sequence
- 01
Penetrations are sealed before the cavity is closed. Reopening after finishes restores the path.
- 02
The door is adjusted to the seals while it is hung, not only on the workshop bench. The hinge settles and the edge changes.
- 03
The duct is installed with the silencer where it was designed. Cutting the silencer to pass a beam deletes its job.
- 04
No back-to-back boxes, and no screws tying both leaves at one point if separation is part of the design.
- 05
The surface is finished before the agreed field measurement. A measurement of an unfinished wall is not an acceptance.
Testing
A named field measurement
A method from the ISO 16283 family, or whatever the brief adopts. One microphone in the corridor is not a test.
Testing the weak paths
Door open then closed, fan running then stopped, until it is known which path governs.
No transfer of the laboratory number
An ISO 10140 report documents the specimen, not the room. This page refuses to write Rw as if it were a site result.
Commissioning
Every seal seated
A door cycle, the lock, and a drop seal if there is one. Handover includes hearing the closure, not only a photograph of the hinge.
HVAC at real duty
Measurement and noise under design airflow, not under a fan that was switched off for the test day.
Recording the condition
Doors closed, the programme, and the hour of the measurement. A figure without a condition cannot be compared later.
Maintenance
Seals take a set
Periodic inspection of frame compression and the threshold. A door that does not latch fully is an open path again.
New penetrations
A later cable drills the partition. Any hole after handover reopens the design unless it is closed to an approved detail.
Silencers
Lining fouls and is sometimes removed in the name of airflow. Replacement is the same type, not an open sheet-metal box.
Common mistakes
Foam inside the room
Treatment does not raise partition isolation. A neighbour-noise complaint is not treated by panels on the inner wall alone.
Quoting Rw as a result
The laboratory figure is not what will be measured between the two rooms. This page does not move any Rw or STC into the field column.
Back-to-back boxes
Two facing penetrations make a hole shorter than the wall thickness. The detail offsets one of them.
A shared duct with no silencer
Air crosses even when the wall is double. HVAC is part of isolation.
Short comparison
The comparison is a way to choose a path. It is not a product recommendation and it is not a code.
| Path | Fits when | Weakens when |
|---|---|---|
| Partition isolation | The programme must not be intelligible next door, or outside noise must not enter. | When the complaint is echo inside the same room. Isolation does not shorten RT60. |
| Internal treatment | Decay, a late echo, or a dead spot inside the volume. | When the neighbour hears speech. Absorber does not close the door. |
| HVAC noise control | The duct or the fan is the governing path. | When the partition itself is weak and the machine is quiet. A silencer does not stiffen a light wall. |
Discussion ranges
Any number here is a preliminary discussion range from practice or a named reference. Replace it with the project criterion, laboratory data, and on-site measurement.
| Item | What is discussed | Limit of this page |
|---|---|---|
| Laboratory Rw or STC | A single number for a specimen to ISO 717-1 after ISO 10140, or STC to ASTM E413. | Not a field result. Flanking, the door, and HVAC drop performance below the laboratory figure. Do not copy it into a quotation as building performance. |
| Field DnT,w | A figure discussed after a measurement in the ISO 16283 family and an ISO 717-1 rating, if that path is adopted. | This page gives no value. Acceptance is written in the brief, and the measurement follows the method. A figure without door and plant conditions is not evidence. |
| Door undercut | Any continuous gap under the leaf is an air path that governs over a high-rated wall. | No millimetre-to-decibel conversion is given here. The verdict is a closed seal and then a field measurement, not an equation on this page. |
| NC or NR curve | A way to compare a room-noise spectrum, not a single decibel. It may be written in the brief as a background limit. | The page imposes no NC number. Noise from HVAC and outside is measured. Isolation and absorption are not deduced from the curve alone. |
What this page does not claim
No fire classification, absorption coefficient, sound pressure level, or legal capacity on this page may be copied into a quotation. Those values come from a product test report, a measurement, or the local code adopted for the project.
Questions designers and owners ask
Why will you not write the Rw we will get?
Because laboratory Rw is not the room result. The site has a field measurement and an acceptance criterion in the brief. Copying the figure misleads.
Is an acoustic door enough?
Only if its seal closes and there is no shorter path through a duct or a continuous slab. The door is one item in a chain of paths.
Does isolation shorten RT60?
No. A heavier wall can reflect more inside the room. Reverberation time is handled by absorption and volume, and in performance spaces it is measured to ISO 3382-1.
What about intelligible speech in the corridor?
That is a failure of the partition, the door, or the duct. Intelligibility for the neighbour is not the audience STI inside the hall, even though the index describes speech transfer on its path.
Is foam on the shared wall isolation?
No. It is internal treatment, and it is weak at low frequency if it is thin. Isolation is mass and a closed path.
Technical sources
- ISO 10140 and ISO 717-1
Laboratory measurement of airborne insulation and its single-number rating. This page does not replace them and does not carry Rw into the field.
- ISO 16283-1
The field-measurement family for airborne insulation. Acceptance is a project figure measured to this method or to what the brief adopts, not an estimate from this page.
- IEC 60268-16
When incoming noise becomes a speech-clarity problem. STI does not replace an isolation rating, and this page does not calculate it.
Last editorial review: 2026-10-06. Review means the text was checked, not that a project was measured.
Turn the question into a brief
A study starts from room volume, use, and existing condition, not from a product name. Fill the brief and copy it.
Project study form