Hear With Mumbli: Reverberation Time With Karishma Prasad

September 9, 2022

We do bang on a bit about how the world is too noisy. But did you know that our experience of noise isn’t just about Decibel levels?

What is reverberation time?

Reverberation time is the time it takes for a sound to ‘fade away’ or ‘decay’ after the sound source has stopped. Think about it: if you’re sat across from your friend in an echoey restaurant, it’s going to be so much harder to hear what they’re saying –  regardless of how loud it actually is!

Thanks to the University of Salford and Eden Smith Group’s Nurture Programme, we were able to work with data science student (and Mumbli intern!) Karishma Prasad to analyse the reverberation times in London social spaces. The aim was to come up with a model that could predict reverberation times in empty and busy venues.

We caught up with Karishma to ask her all about the project, reverberation times and why it matters.

Related research: How the Pandemic Silence Project Is Making Noise

Reverberation Time With Karishma Prasad

Why do you think this project on reverberation time is important?

This project sits right in the middle of data science, engineering and wellness, so it grabbed my attention straight away.

I believe that every enclosed space should have an optimal level of reverberation time to reduce reverberant noise level and make for better speech intelligibility. If a space’s reverberation time is too high or too low level, that can disrupt its acoustic quality.

For instance, a reverberation time that’s too high could make it difficult for students to hear what their teacher’s saying in the classroom or for workers to conduct a meeting in a meeting room. At the same time, a reverberation time that’s too low could disrupt the rich sound experience of musicians in a concert hall.  

Traditionally, the reverberation time of venues could only be calculated using mathematical equations or computed using software like ODEON or FEM. These computations need complex equipment, skill and time.

The idea behind this project is to explore the different Machine Learning models that can be used to estimate reverberation time with higher accuracy, using inputs like the volume of the venues, the materials used, the number of people present and the surface area that those people occupy.

In this way, the project provides a great starting point to understanding the acoustics of a venue and makes it possible to make complex data available to a wider audience in a user-friendly way (which ultimately, we hope to do using the Mumbli app).

What’s the most surprising thing you discovered?

I’ve learned an awful lot from both a data science and acoustics point of view. But more than anything, it never occurred to me until this project quite how much a venue’s interiors can affect how you hear your peers.

I was surprised to find out that for a well-architected building like a concert hall, each material present in the room is there for two purposes – to add to the venue’s aesthetics, and to enhance the sound experience! From the balcony to the beautiful curtains, every material inside the hall contributes to the acoustic experience. Visiting places like this will never be the same again.

Related research: Hearing Sensitivity With Kaveh Kiani

What tips would you give someone who’s looking to optimise their venue’s reverberation time?

The most important thing is to understand that a venue’s interiors aren’t just there to make it look nice. They can also enhance or deteriorate a customer’s hearing experience.

High reflective materials like tiles, glass, and marble correspond to a high reverberation time since they have the least absorptivity for sound. Meanwhile, low reflective materials like curtains, carpets, and padded chairs correspond to low reverberation time, since they’re highly sound absorptive.

So, to optimise reverberation time, a venue shouldn’t be so heavily carpeted that the sound dies. But at the same time, it shouldn’t be so heavily tiled or glassed that you can hear your own conversations echoing back at you. Instead, the venue should be made up of an amalgamation of different materials optimised for reverberation time.

Do you ever have difficulty hearing others or being heard because the space is too noisy?

Sadly, yes! It’s not rare for me to have difficulty hearing or being heard when I’m in a space that’s too noisy, which can often lead to incomplete or half-understood conversations.

I find this kind of situation really unpleasant – especially when it has the potential to lead to misunderstandings (just as bad whether I’m in a meeting or casually hanging out with friends!).

Ultimately, in today’s world, communication is the key to everything.

As you can see, there’s a lot more resting on a venue’s interiors than what many of us give them credit for. So, next time you enter social space, take a look around – what are the venue’s furnishings like?

How do they affect your ability to have a conversation?

Let us know your thoughts.

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