Know the difference between intelligent and indulgent acoustic design

Why do we need intelligent acoustic design?

Acoustic consultants aim to design spaces where the acoustic experience is comfortable, productive and sustainable. This is also known as acoustic engineering.

• User wellbeing – if an acoustic engineer has a good understanding of the user and takes into consideration the ambient noise and other desired acoustic qualities, then they’re mindful of an occupant’s wellbeing. They design to create comfort and minimise disturbance, stress and agitation.

• Productivity – acoustics is important in workplace design as it can facilitate concentration, connection, meetings, presentations and downtime. When sound insulation and sound absorption quality is poor in a workplace, employees are less able to perform.

• Sustainability – considered use of acoustic materials, reduced maintenance costs, greater use by tenants and happier occupants all contribute to a more sustainable space.

What is intelligent acoustic design?

The foundations of intelligent acoustic design lie in a genuine understanding of the user and their needs. For example, are they a visitor, resident, office worker, hotel guest or patient? Will the listeners be young, old or multigenerational? Is the space going to be for a performance or one-on-one conversations? How long is someone going to be in this space?

Further pillars of intelligent acoustic design:

• Knowledge that spans engineering disciplines – acoustic engineers need a good understanding of the other engineering disciplines involved in a project, for example, structural, mechanical, fire and hydraulic engineering. This enables a holistic approach.

• Good knowledge of materials – new acoustic materials come onto the market every day and it’s important to understand their efficacy for different spaces alongside their environmental impact.

• Balancing of reward and environmental impact – acoustic consultants always need to ask the question – when is enough, enough? The more material that’s used for sound proofing, room reverberation and noise control, the greater the energy needed in manufacturing and the more waste generated.

A good example of intelligent acoustic design is the use of sound masking in open plan offices to improve speech privacy between desks. By subtly raising the background noise using loudspeakers playing artificial noise (similar to white noise) across an office, you can effectively mask the speech signals, without adding distracting sounds or introducing physical barriers.

How do you reach beyond acoustic design into intelligent acoustic design?

As experienced acoustical engineers with a solid appreciation of sustainability and other engineering disciplines, we’re always looking for ways to improve our design. We recognise the value of trying new things, making mistakes, and developing new solutions. Our industry connections have opened up opportunities for us to test new products and solutions, before we take them to a client.

Recently, we’ve really been pushing the limits in other ways too – with the development of an aural simulation (auralisation) tool.

Here’s how we developed our intelligent approach to acoustics

Over the last couple of years we’ve been developing AiHear, an auralisation app that shows you how something will sound before it’s built. It’s a portable system that replaces in-situ acoustic demonstrations. Using an iPad, headphones and the environment of your choice, the app saves having to set up physical in-situ demonstrations with loudspeakers in a suitable listening room.

We were surprised to learn that, through this app, we could deliver auralisations much easier than traditional methods. This would translate to considerable cost savings for both ourselves and our clients, without compromising on audio quality of the sound simulation.

It’s been a huge journey developing AiHear and we’ve learned a lot along the way. We were proven wrong on a few things, and developed intelligence we didn’t know we needed. Here’s a snapshot of the knowledge we developed in producing AiHear.

Most people don’t care about ‘just noticeable differences’ in sound levels and room reverberation

Sound levels

Most people can only just notice a change in sound level of 3 decibels (dB). This is known as the ‘just noticeable difference’ in the field of acoustics.

In mathematical terms, a 3dB change is significant because it equates to a doubling or halving of sound power. However, how we actually perceive that increase in sound is less significant. For example, if you turn your stereo up by 3dB, you literally double the electrical power required but produce only a very slightly noticeable increase in volume.

Acoustical engineers can get lost in the detail of small decibel changes. When written on paper, the difference between 40dB and 43dB might seem worthy of a greater investment in acoustic design. However, there’s a major inequality between the effort required to increase or decrease a sound – costly materials that increase a building’s environmental footprint – and how we perceive that change.

While developing AiHear, and presenting auralisations to clients, we confirmed that people only tend to appreciate changes in sound level of at least 4dB or more. This proven observation has notably influenced the way we approach acoustic design for our clients. AiHear has helped us, and our clients, gain a better understanding of design that truly makes a difference.

A recent project that illustrates sound levels is a large public library the NDY acoustics team consulted on. The project was well over budget and looking to reduce material costs where possible. The sound absorbing materials on the ceiling were identified as being a major cost item, due to the sheer quantity required to cover the entire ceiling area of the large open plan spaces. Initially, we were reluctant to reduce our proposed acoustic treatment for fear that the ambient noise levels might become uncomfortably loud. However, after AiHear modelling, and various ceiling treatment reductions, we were confident we could reduce the treatment with little noticeable adverse effect. Halving the amount of absorption increased the ambient noise level by roughly 3dB.

Several different treatment scenarios were presented to the client who concurred that the treatment reduction would be acceptable and elected to take the cost savings, keeping the project on-track with a more efficient, sustainable design.

Room reverberation

Similar concepts apply to room reverberation, where people generally only appreciate quite significant changes to the reverberation time inside a space.

Reverberation time is quantified in terms of how quickly sound takes to dissipate in a room, like when you clap inside an empty hall and then wait for the sound to disappear. Smaller spaces, or those with more sound absorbing materials, tend to have a short reverberation time, while larger spaces with hard surfaces tend to have long reverberation times.

While developing AiHear, we investigated the ‘just noticeable difference’ for room reverberation in offices. A private office might have a reverberation time of 0.6 seconds. If the amount of sound absorbing materials increases in the space by 20%, the reverberation time would decrease to 0.5 seconds. Is that a significant, or even noticeable, change?

We’ve learned that such a change is barely perceptible, and that most people would need much more than a 20% increase in sound-absorbing materials to think it was worthwhile.

Based on our findings from developing and using AiHear, we’ve evolved our design approach to ensure we make smart and strategic acoustic decisions which reflect real-world benefits rather than on-paper gains.

It can’t just sound good, it’s got to look good too

During the early development of AiHear we just focused on the technical and audio side of the app and how we could make this ambitious idea happen. We drilled down into augmented reality, technical specifications, processing power and sound output. And then we took to testing.

Oh, how we failed! Although we were happy with the audio accuracy, we found out that people still need a strong visual aesthetic – something intuitive and easy to use. We hadn’t realised the importance of how visuals could affect people’s perception of a presentation, and influence their decision-making process.

So, we came back to the table and added in features – an interface that was user-friendly, with more intuitive controls. Our marketing team built in our brand style to make it appealing to our clients. We also added more features like being able to import models of furniture and 360-degree panoramic photos into the auralisation.

Background noise can be simulated even when wearing headphones

Normally, when you put headphones on, you want to block out background noise. However, background noise is vitally important for providing accuracy in an auralisation. We need to control and simulate different types of background noise for different scenarios, as you would experience in a real-life environment.

We soon discovered this was actually much easier to do with headphones, rather than without. We could accurately recreate the acoustic environment needed to test designs for a range of places like:

• private hotel rooms with very low background noise
• open office spaces with ambient worker sounds
• libraries with patron noise
• classrooms with the background of children working or playing.

Using headphones is integral to using AiHear. This has proven to be much more effective than setting up a loudspeaker-based auralisation where there are huge levels of uncertainty around the acoustics of the room we present in and existing ambient noise level.

The journey to develop acoustic intelligence was daunting

When our Acoustics Director first came to us with the idea of developing a portable auralisation app, we thought it was too ambitious a plan. The enormity of the task in coding and using cutting edge augmented reality technology was significant and we didn’t initially believe it was possible. Some of our doubts included the following:

• How could we develop an auralisation app that responded in real-time when a person wearing headphones moved around a room?

• How could we implement this on a portable device with limited processing power instead of a high-performance desktop computer?

• How could we build a natural-sounding one-third octave band filter set which spanned the entire audible frequency range and could be adjusted in real-time?

• If a person turned their head to the side, how could we track the location of the source accurately to demonstrate the panning effect of the sound?

• If we only had a two-person team to develop the app, how were we going to make it work in a realistic timeframe?

Well, after many hours of hard work and exploring a lot of acoustic theory, we managed to build a system that crushed these doubts.

Bridging the gap between acoustic consultants and anyone else with ears

As the creators of AiHear, Jack Wong and I are both very proud of our achievements, both technically, and for creating a tool that bridges the – sometimes very wide – gap between acoustic consultants and anyone else with ears. While we always knew about the importance of acoustics in building design, along this journey we’ve taught ourselves a few things we didn’t know about acoustics – like how to use our intelligence to indulge less and achieve more.