# Acoustics Design

## Sound Ratings

### STC (Sound Transmission Class)
| STC | Performance | Typical Construction |
|-----|-------------|---------------------|
| 25-30 | Poor - Speech easily understood | Single layer drywall |
| 35-40 | Fair - Loud speech understood | Standard wall |
| 45-50 | Good - Loud speech heard but not understood | Enhanced wall |
| 50-55 | Very good - Loud speech barely audible | Double stud wall |
| 55-60 | Excellent - Most sounds inaudible | Specialized construction |

### IIC (Impact Insulation Class)
| IIC | Performance | Typical Assembly |
|-----|-------------|------------------|
| 25-35 | Poor - Footsteps clearly heard | Bare concrete |
| 40-45 | Fair - Footsteps noticeable | Carpet over concrete |
| 50-55 | Good - Footsteps reduced | Floated floor |
| 55-60 | Very good - Light impact barely audible | Isolated floor |
| 60+ | Excellent - Impact nearly eliminated | Resilient underlayment + topping |

### NRC (Noise Reduction Coefficient)
| NRC | Absorption Level |
|-----|------------------|
| 0.00-0.20 | Reflective (hard surfaces) |
| 0.20-0.50 | Moderate absorption |
| 0.50-0.80 | Good absorption |
| 0.80-1.00 | Excellent absorption |

---

## Code Requirements

### Residential Separations (IBC/IRC)
| Assembly | STC | IIC |
|----------|-----|-----|
| Between dwelling units | 50 | 50 |
| Between unit and corridor | 50 | - |
| Between unit and public space | 50 | - |
| Field tested (ASTC/AIIC) | 45 | 45 |

### Common Target Values
| Space Type | STC Target | NRC Target |
|------------|------------|------------|
| Office (private) | 45-50 | 0.70 |
| Conference room | 50-55 | 0.70 |
| Classroom | 50 | 0.60-0.70 |
| Healthcare (exam) | 45-50 | 0.70 |
| Hotel (guest room) | 50-55 | 0.60 |
| Theater | 60+ | 0.70-0.80 |

---

## Wall Assemblies

### STC Ratings by Assembly
| Assembly | STC |
|----------|-----|
| Single 2×4, 1/2" GWB each side | 33-35 |
| Single 2×4, 5/8" GWB each side | 35-38 |
| Single 2×4, 5/8" GWB + insulation | 38-42 |
| Single 2×4, double 5/8" GWB each side | 45-48 |
| Staggered stud, 5/8" GWB + insulation | 50-55 |
| Double stud (1" gap), 5/8" GWB + insulation | 55-60 |
| Resilient channel + insulation | 50-55 |
| 8" CMU, painted | 50-52 |
| 8" CMU, furred + GWB | 55-58 |

### Improving Wall STC
| Improvement | STC Gain |
|-------------|----------|
| Add insulation to cavity | +3 to +5 |
| Add layer of GWB | +3 to +5 |
| Resilient channel | +5 to +10 |
| Staggered studs | +8 to +12 |
| Double stud wall | +10 to +15 |
| Mass loaded vinyl | +3 to +5 |
| Seal all penetrations | +2 to +5 |

---

## Floor/Ceiling Assemblies

### STC Ratings
| Assembly | STC | IIC |
|----------|-----|-----|
| Wood joist, 5/8" plywood, 5/8" GWB | 38 | 32 |
| Above + R-19 insulation | 43 | 35 |
| Above + resilient channel | 50 | 45 |
| Above + 1-1/2" concrete topping | 52 | 48 |
| 6" concrete slab | 52 | 28 |
| 6" concrete + floating floor | 55 | 55 |
| 6" concrete + carpet | 52 | 52 |

### Improving Floor/Ceiling
| Improvement | STC Gain | IIC Gain |
|-------------|----------|----------|
| Add insulation | +3 to +5 | +3 |
| Resilient channel on ceiling | +5 to +8 | +5 |
| Additional GWB layer | +3 to +5 | +0 |
| Carpet and pad | +0 | +15 to +25 |
| Resilient underlayment | +0 to +3 | +10 to +20 |
| Floating concrete topping | +3 to +5 | +15 to +20 |

---

## Room Acoustics

### Reverberation Time Targets
| Space | RT60 (seconds) |
|-------|----------------|
| Recording studio | 0.2-0.4 |
| Conference room | 0.4-0.6 |
| Classroom | 0.5-0.7 |
| Office (open) | 0.5-0.8 |
| Worship (speech) | 0.8-1.2 |
| Worship (music) | 1.5-2.5 |
| Concert hall | 1.8-2.2 |

### Absorption Coefficients
| Material | 250 Hz | 500 Hz | 1000 Hz | NRC |
|----------|--------|--------|---------|-----|
| Concrete | 0.01 | 0.02 | 0.02 | 0.00 |
| Glass | 0.06 | 0.04 | 0.03 | 0.05 |
| Gypsum board | 0.10 | 0.05 | 0.04 | 0.05 |
| Carpet (heavy) | 0.20 | 0.50 | 0.60 | 0.40 |
| ACT (standard) | 0.50 | 0.70 | 0.75 | 0.55 |
| ACT (high NRC) | 0.70 | 0.90 | 0.95 | 0.80 |
| Fabric panel | 0.50 | 0.75 | 0.90 | 0.75 |

### Ceiling Coverage Guidelines
| Space | Ceiling NRC | Ceiling Coverage |
|-------|-------------|------------------|
| Open office | 0.80-0.90 | 80-100% |
| Private office | 0.70-0.80 | 60-80% |
| Conference | 0.70-0.80 | 80-100% |
| Classroom | 0.60-0.70 | 80-100% |
| Corridor | 0.50-0.60 | 50-80% |

---

## Mechanical Noise

### NC (Noise Criteria) Targets
| Space | Max NC |
|-------|--------|
| Concert hall | NC-15 to NC-20 |
| Recording studio | NC-15 to NC-20 |
| Theater | NC-20 to NC-25 |
| Conference room | NC-25 to NC-30 |
| Private office | NC-30 to NC-35 |
| Open office | NC-35 to NC-40 |
| Retail | NC-40 to NC-45 |
| Industrial | NC-50 to NC-60 |

### Duct Noise Control
| Strategy | Effect |
|----------|--------|
| Lined duct | -3 to -10 dB per 10' |
| Silencer/attenuator | -10 to -25 dB |
| Duct size increase | Velocity reduction |
| Flexible connection | Vibration isolation |
| Acoustic plenum | -5 to -15 dB |

### Equipment Vibration Isolation
| Equipment | Isolation Efficiency |
|-----------|---------------------|
| Air handler | 95-99% |
| Chiller | 95-99% |
| Pump | 90-95% |
| Cooling tower | 90-95% |
| Generator | 95-99% |

---

## Sound Masking

### Sound Masking Levels
| Environment | dBA Level |
|-------------|-----------|
| Open office | 42-48 dBA |
| Private office | 38-42 dBA |
| Healthcare | 40-45 dBA |

### System Components
- Speakers (above ceiling or direct field)
- Controller/generator
- Zoning capability
- Adjustable spectrum

### Coverage
- One speaker per 200-250 SF (above ceiling)
- More dense for direct field
- Uniform coverage critical

---

## Privacy and Speech Intelligibility

### Articulation Index (AI)
| AI | Privacy Level |
|----|---------------|
| 0.00-0.05 | Confidential (excellent) |
| 0.05-0.15 | Normal privacy (good) |
| 0.15-0.30 | Transitional |
| 0.30-0.50 | Poor privacy |
| 0.50-1.00 | No privacy |

### Factors Affecting Privacy
| Factor | Effect |
|--------|--------|
| Wall STC | Higher = better privacy |
| Ceiling CAC | Higher = better privacy |
| Background noise | Higher = better privacy (masking) |
| Source level | Lower = better privacy |

### CAC (Ceiling Attenuation Class)
| CAC | Performance |
|-----|-------------|
| 25-30 | Poor - Sound easily passes |
| 30-35 | Fair - Some attenuation |
| 35-40 | Good - Significant reduction |
| 40+ | Excellent - High privacy |

---

## Special Spaces

### Music Practice Rooms
| Parameter | Target |
|-----------|--------|
| STC to adjacent | 60-65 |
| Background noise | NC-25 max |
| RT60 | 0.4-0.8 sec |
| Variable acoustics | Recommended |

### Home Theaters
| Parameter | Target |
|-----------|--------|
| STC to adjacent | 55-65 |
| Background noise | NC-25 max |
| RT60 | 0.3-0.5 sec |
| Bass control | Recommended |

### Worship Spaces
| Parameter | Target |
|-----------|--------|
| STC to exterior | 45-55 |
| Background noise | NC-25 to NC-30 |
| RT60 | 1.0-2.5 sec (style dependent) |
| Clarity (C80) | Music: 0 to +3 dB |

---

## Design Strategies

### Noise Control
1. **Source** - Reduce at source (quieter equipment)
2. **Path** - Block transmission (barriers, enclosures)
3. **Receiver** - Protect listener (isolation, distance)

### Room Shaping
- Avoid parallel surfaces (flutter echo)
- Splayed walls (5° minimum)
- Diffusion for even distribution
- Bass traps in corners

### Flanking Paths
| Path | Solution |
|------|----------|
| Above ceiling | Extend partition to deck |
| Through floor | Resilient connections |
| Around doors | Proper gasketing |
| Through ducts | Duct lining, silencers |
| Through electrical | Seal boxes, use putty pads |

---

## Acoustical Details

### Door Seals
- Perimeter gasketing (adjustable)
- Automatic door bottom
- Sound-rated door assembly
- Vestibule for critical spaces

### Window Considerations
- Laminated glass (damping)
- Different thickness panes (staggered resonance)
- Air space (minimum 4")
- Multiple layers for high STC

### Penetration Treatment
- Seal all penetrations airtight
- Mass loaded vinyl wrap
- Putty pads on electrical boxes
- Flexible connections for pipes
