How to measure a room's acoustics
Of all of our senses, hearing is one of the most important. It helps us connect to the world and pick up vital information about our environment. However, when it’s impaired, or the quality of sound we’re surrounded by isn’t clear, it puts us all at a disadvantage.
Not being able to hear important information, when sound is muffled or - worse still - when sound bounces around too much, can all be very disconcerting and impair the listening experience. This is why measuring room acoustics is key to assessing how well certain commercial spaces perform.
What exactly is ‘room acoustics’?
The term ‘room acoustics’ describes the acoustic properties of an enclosed space. It’s of particular importance in areas where quality of sound is vital. This includes the sound quality of announcement messages, for example in airport terminals and on station platforms. How many of us have missed an important piece of information because it sounds as if the announcer is speaking far away from the microphone, or even underwater? Other spaces where sound wave transmission is of utmost importance include concert halls, music recording studios and conference halls. Even meeting rooms, restaurants and school classrooms should all be assessed to ensure they’re fit for purpose acoustically.
How is a room’s acoustics assessed?
When it comes to assessing room acoustics, there are three main measurements taken to map and assess the acoustic properties of a room:
Reverberation – This is known as Reverberation Time 60 (RT60). It’s defined as the time required for a sound to diminish by 60 decibels (dB) after a source stops generating sound. This measurement assesses how long it takes for a sound to fade and is crucial for understanding how a room responds to sound.
Speech Intelligibility – Speech is our primary means of communication, it’s therefore essential that what we hear is intelligible. This parameter therefore measures the quality of speech transmission and is known as the Speech Transmission Index, or STI.
Background noise – In order to truly understand how a space performs, it’s vital to assess any disturbing ambient background noise. This is measured using Noise Rating (NR) Curves in Europe and Noise Criterion (NC) Curves in the USA.
Why do room acoustics vary?
If you think about it, there are many factors that can affect a room’s acoustics, it’s not just down to size alone or background noise. Too many hard, reflective surfaces can make conversation sound loud and cold; conversely, soft furnishings such as cushions, curtains and fabric walls will make conversation far softer and warm.
So you need to think about the purpose of the space, and it’s specific sound characteristics. The room acoustics should correspond appropriately; indeed, there’s a ‘sweet spot’ depending on its use. For example, for good acoustics in a concert hall, you’re looking for a reverberation time of 2-3 seconds to ensure a good listening experience; on the other hand, for crisp speech intelligibility (for example in a classroom) the reverberation time should be 1 second or less.
What equipment do you need to measure room acoustics?
In order to measure the acoustics of a room, you need four pieces of equipment:
A sound level meter – this requires a professional sound meter that can measure RT60, STI and Noise Curves.
Microphones – additional omni- or bi-directional microphones can be required to assess a space.
Speakers – an omni-directional sound source and power amplifiers are necessary for emitting sweep test signals.
Analysis software – this is required to create reports that are compliant with international standards. These reports are essential to understand the acoustic landscape, and determine mitigating factors required.
Standards in place for room acoustics
Given the importance of room acoustics, and the damage that can be done when sound levels are too loud, there are international and national standards set down for measuring room acoustics. The most important ones to note are as follows:
RT60 is measured using the ISO 3382 set of standards. ASTM E2235 standard is also used to determining sound decay and sound absorption.
STI is measured using the standard IEC 60268.
Noise Curves are measured in accordance with ISO 1996-2:2007, BS 8233 and ANSI/ASA S12:2-2008.
Who can measure room acoustics?
This is one assessment that needs to be left to the experts. Yes, there are sound measuring Apps available to help you monitor sound levels, but these are only good for getting an indication of noise levels. In order to properly assess sound, you need a good sound level meter, Class 1 or Class 2, with Class 1 being the most sensitive. With costs for a good sound level meter running into the thousands, let alone the other equipment required for measuring room acoustics, you’ll definitely need an Acoustic Consultant to properly determine the acoustic properties of your commercial space.
What can you do to dampen background noise?
The acoustic assessment will be used to determine whether mitigating measures are required, and if so, what you can put in place to improve the sound properties of the space. A variety of materials and products are available to add acoustic absorption into a space, thereby reducing the level of reverberation. These can include ceiling panels, wall panels, hanging acoustic rafts, hanging 3D acoustic absorbers – all available in a variety of finishes, colours, patterns, etc. Your Acoustic Consultant will undertake detailed analysis and modelling to determine the best location and total area of the required treatment.
One common problem, and indeed one of the three key parameters assessed, is disturbing background ambient noise. This can affect everything from what you can hear in a meeting, to the quality of a performance or a music recording.
If, as a result of your assessment, you need to dampen down unwanted background noise coming from external sources, there are several structural steps you can take to improve the acoustics:
Decouple the walls – in this process, two sides of a structure, be that a wall, ceiling or floor, are separated so that they vibrate independently of each other. This prevents transmission of structure-borne sound from external spaces.
Sound dampening – this is the use of specific sound-absorbing materials to reduce sound transmission. It includes installing dead walls and cavity wall insulation.
Install sound-absorbing materials – soft furnishings are also good for deadening unwanted noise. This includes installing curtains, rugs or carpets and solid core doors as well as soundproofing windows. There’s even acoustic paint available if you need to go the full distance with your soundproofing.
Add mass to the walls – obviously, the thicker the walls the more soundproofed a room will be. Methods here include installing plywood on external walls and plasterboard, mass-loaded vinyl or acoustic foam panels on internal walls.
Given the sound-sensitivity of certain commercial spaces, it’s important to get an acoustic consultancy involved at an early stage. This will ensure an optimal acoustic design, and the best user experience possible. If you need help with planning room acoustics then get in touch today. As with most build projects, retrofitting corrective measures can be costly and disruptive, so it’s important to get it right at the design stage. Contact us today at firstname.lastname@example.org and see how our team can help you optimise your business or entertainment space. Alternatively, you can call our London office on 020 7859 4530; for the Reading office that deals with the South East, dial 0118 207 7324.