Architects and urban planners face unique challenges when it comes to acoustics for urban design projects. Cities are noisy places. The variables are endless: transportation, industry, construction, central plants, night life, people. These sounds come together to create either the exciting hum of an energetic streetscape or a bothersome noisescape that results in a huge problem for your client.
Add to that mix the incredible subjectivity of how individuals respond to noise (i.e. What may not be a problem for one client inspires litigation for another). Not only that, but noise ordinances vary greatly from city to city. Then there is the issue that new buildings (or new building equipment) can create a new sound problem for neighbors that hadn’t existed before.
All in all, it’s easy to see why acoustics can be such a headache for urban designers, which is why we want to share some basic resources for architects to make having the conversations about acoustics easier.
1. Simple terms to know and how acoustic issues in urban design get solved.
Acoustics is the umbrella term for several disciplines. Here’s what comes into play for architects working in urban areas:
- Room Acoustics: The discipline of controlling sound within the interior of a space. This is usually accomplished through finish materials, surface shaping, and room shaping.
- Sound Isolation: This discipline focuses on the transfer of sound between spaces or from sources external to the building. For external sources, control is usually accomplished through façade constructions (generally limited by the glazing) and barriers. Internally, this happens through partition and floor/ceiling construction, door seals, and penetration details.
- Noise and Vibration Control: This discipline deals with noise and vibration from mechanical, electrical, and plumbing systems. These issues get solved through strategic locations of mechanical plants and equipment, the equipment chosen, duct layouts and specialty isolation features.
- Environmental Acoustics: This discipline focuses on how the building is impacted (or impacts) the environment around it. Work includes analyzing site conditions through measurements, computer modeling, while also reviewing local noise ordinances local building codes.
2. What does a dB sound like?
Decibels (dB) are a unit of sound measurement that quantifies sound pressure level and sound power level. It’s common for a client (or an acoustician) to talk about sound in terms of a dB measurement when it comes to acoustics for urban design. But what does that mean?
Here’s a handy chart that relates dB levels to real world sounds. It provides a rule of thumb when someone starts talking numbers.
3. Typical noise criterion (NC) for different types of spaces
Noise criterion is a single-number noise rating system used to quantify continuous building system noise in a space. Here is a chart with some good rules of thumb for what different types of spaces should be.
4. Pitfalls in common contract language
Often the acoustic requirements for a building project in an urban area are set by the contract, either between the Developer and Design Team or between the Property Owner and Tenant. Here is the language to watch out for:
“Maximum allowable levels”
Usually this is expressed as a dBA number and refers to noise levels between the tenant space to an adjacent space. The problem is that you can design a project that technically meets the dBA level but still has lots of low frequency energy. (Usually experienced as a thump.) This tends to show up between offices or residences adjacent to a tenant that uses music such as fitness centers, bars, or high-energy retail.
Many contracts contain annoyance clauses related to noise. They use phrases like “should not disrupt business…” or “at a volume that might disturb others.” The challenge with annoyance clauses is that they are highly subjective and therefore difficult to quantify and defend.
Required Noise Criterion (NC)
To quantify noise levels in a space, contracts can require the HVAC system within a space to hit a certain NC level. The challenges come when there is too much other noise for that to happen such as intrusive noise from an environmental noise source.
5. Scale for Speech Privacy (SPP)
Whether you are designing speech privacy for HIPAA (Health Insurance Portability and Accountability Act) or simply trying to provide private conversations in offices, acoustic measures for speech privacy will be another concern to deal with.
Speech privacy is typically measured in terms of SPP, or Speech Privacy Potential. This number is derived from adding the sound isolation component of construction to the background noise level in the receiving room (STCc + NC).
STCc is the composite of value of the separating elements considering the wall, door and/or ceiling construction between two spaces. For more on NC, see item #3 above.
Here’s a scale to help understand what the numbers of SPP mean in terms of the experience in the space:
Want more on this topic? Here’s a link to Cambridge Sound’s document on SPP.
Acoustic design for urban design and mixed use
Acoustics for urban design projects don’t have to be a headache. There are proven strategies to help design teams navigate the challenges.
We hope these resources make having conversations with your clients easier, and if you want to talk about specific challenges, Idibri is here for you.
Courtney Schoedel, LEED AP, INCE Board Cert., is a senior acoustic consultant with Idibri. She has a MArch and an MS in Architectural Acoustics from Rensselaer Polytechnic Institute. Courtney is a theatrical consultant and acoustic designer with depth of experience in the spaces where people gather. Whether auditoria, arenas, healthcare, hospitality, workplace, or mixed-use projects, Courtney is deeply experienced in creating environments that ar
e optimized acoustically to connect and engage people. Courtney regularly speaks to audiences about solving common acoustic issues and on how to solve sound isolation and noise control problems before they ever start. Full bio.
Krisi Hinova serves as an acoustic consultant at Idibri—a team of acousticians, theatre consultants, and technology designers who specialize in spaces where people gather to share an experience. Krisi is a specialist in mechanical noise control, sound isolation, room acoustics, and environmental noise mitigation. With experience in design for the education/arts, hospitality, workplace, government and mixed-use, Krisi also holds an M Eng in Mechanical Engineering from the Rochester Institute of Technology. Full bio.