Every commercial building, hospital, data centre, and industrial facility in India that operates a diesel generator set faces a critical regulatory requirement: compliance with CPCB-II noise norms. The Central Pollution Control Board mandates that all DG sets from 7.5 kVA to 2000 kVA must not exceed 75 dB(A) measured at 1 metre from the enclosure surface, with a minimum insertion loss of 25 dB(A).
Yet, a significant number of acoustic enclosures installed across India fail to meet these standards during inspection. The reasons range from inadequate panel construction to poor installation practices — and the consequences include SPCB show-cause notices, operational restrictions, and penalties up to ₹5 lakhs under the Environment Protection Act.
This guide provides MEP consultants, facility managers, and EPC contractors with everything they need to specify, evaluate, and procure CPCB-compliant acoustic enclosures — including ready-to-use BOQ specifications and a manufacturer evaluation framework.
Understanding CPCB-II Noise Norms for DG Sets
The regulatory framework for DG set noise control in India is governed by the Ministry of Environment, Forest and Climate Change (MoEFCC) notification GSR 371(E) dated 17th May 2002 and its subsequent amendments. The key requirements are:
CPCB-II Key Requirements
Additionally, the ambient noise standards under the Noise Pollution (Regulation and Control) Rules, 2000 impose zone-specific limits at the property boundary: 75/70 dB(A) for industrial areas, 65/55 dB(A) for commercial areas, 55/45 dB(A) for residential areas, and 50/40 dB(A) for silence zones (day/night respectively).
Why Acoustic Enclosures Fail CPCB Inspection
Based on field observations across hundreds of installations, the most common reasons for CPCB compliance failure include:
- Insufficient panel thickness and STC rating — panels with STC values below 40 cannot achieve the required 25 dB(A) insertion loss, especially at lower frequencies where DG sets produce maximum noise energy.
- Poor door and access panel sealing — acoustic gaskets degrade over time or are omitted during installation, creating direct sound transmission paths that bypass the enclosure walls entirely.
- Inadequate ventilation design — when ventilation airflow is insufficient, operators prop doors open during summer months, completely negating the acoustic performance of the enclosure.
- Rockwool settling and degradation — low-density mineral wool (below 48 kg/m³) settles under vibration, leaving gaps at the top of panels that transmit noise directly.
- Structural resonance — thin-gauge panels without proper stiffening vibrate sympathetically with the DG set, re-radiating noise instead of attenuating it.
- Disconnected manufacturer and installer — when panels are manufactured by one vendor and installed by a local fabricator unfamiliar with acoustic sealing requirements, joint gaps, missing gaskets, and incorrect assembly are common.
Technical Specification for a Compliant Acoustic Enclosure
The following specifications represent the minimum requirements for an acoustic enclosure that reliably achieves CPCB-II compliance across all DG set sizes from 62.5 kVA to 1010 kVA:
| Parameter | Minimum Specification | Recommended |
|---|---|---|
| Panel STC Rating | STC 40 | STC 45 or higher |
| Outer Skin | 16-gauge CRCA sheet | 14-gauge CRCA with powder coating |
| Inner Skin | 22-gauge perforated GI sheet | 20-gauge perforated GI sheet, 25% open area |
| Acoustic Infill | 50mm rockwool, 48 kg/m³ | 100mm rockwool, 64 kg/m³ density |
| Door Seals | Neoprene gaskets on all edges | Double-lip neoprene with magnetic closure assist |
| Ventilation | Acoustic louvers at intake and exhaust | Acoustically lined duct with attenuator + forced ventilation |
| Insertion Loss | 25 dB(A) | 30 dB(A) or higher |
The ventilation system deserves particular attention. A DG set operating at full load generates substantial heat — typically requiring airflow of 5–8 times the combustion air volume for adequate cooling. If the ventilation design cannot maintain acceptable temperatures inside the enclosure, operators will inevitably open doors, and the enclosure becomes acoustically useless.
BOQ Specification Format for Tender Documents
For MEP consultants and contractors preparing tender documents, the following BOQ format ensures that all critical acoustic parameters are captured in the specification:
Notice that this BOQ format specifies "supply, installation, testing, and commissioning" as a single line item. This is intentional — splitting supply and installation across different vendors is the primary cause of acoustic performance failures in the field.
Manufacturer Selection: What to Look For
When evaluating acoustic enclosure manufacturers for your project, the following checklist helps distinguish between vendors who will deliver compliance and those who won't:
- In-house manufacturing facility — verify that the manufacturer has their own factory with CNC fabrication capability, not just a trading operation that outsources production.
- ISO 9001:2015 certification — confirms that quality management systems are in place for consistent production quality across batches.
- NABL-accredited test reports — ask for third-party acoustic test data, not just manufacturer-declared values. The test should show insertion loss at octave band frequencies, not just a single dB(A) number.
- Own installation teams — the manufacturer should deploy their own trained crews for installation, not subcontract to local fabricators. This single factor accounts for the majority of field failures.
- Reference projects — request a list of completed installations with client contacts for reference checks. Look for projects similar in DG set capacity and application to your requirement.
- Post-installation testing commitment — the manufacturer should guarantee CPCB compliance post-installation and include third-party testing in their scope.
"The difference between an acoustic enclosure that passes CPCB inspection and one that doesn't usually comes down to installation quality — not panel quality. When the same company that designs and manufactures the panels also installs them, accountability is complete and compliance is reliable."
About KBG Group's Acoustic Enclosure Solutions
KBG Group is an ISO 9001:2015 certified manufacturer based in Nashik, Maharashtra, with in-house CNC manufacturing capabilities for acoustic enclosures, acoustic louvers, and noise control systems. We handle the complete scope — from acoustic engineering and panel manufacturing to pan-India delivery and on-site installation with our own trained teams.
Our acoustic enclosures are designed for DG sets ranging from 62.5 kVA to 2000 kVA, with proven CPCB-II compliance across hospitals, data centres, commercial complexes, and industrial facilities. Every installation includes post-commissioning noise testing to verify compliance before handover.
For a turnkey acoustic enclosure quotation — including design, manufacturing, delivery, and installation — contact our technical team with your DG set rating, quantity, and site location.