For a musician, playing in a genuine, 30 second reverb is a great adventure – normally, you only get reverb that long by faking it, using digital technology. But NPL’s reverb chamber isn’t designed with music in mind – it’s part of their toolbox for investigating sound and the way it moves through materials.

The ceiling of the National Physical Laboratory reverb chamber

Passing through (transmission)

If you look closely at some of our videos of the chamber, you’ll see a panel in one of the longer walls. Acousticians at NPL put a test material in this panel when they want to measure how much sound will pass through it. The test material might be a new type of wall material, for example. To test this sample, acousticians would make reverberant sound on one side of the panel, then measure how much sound passes through the material to a small chamber on the other side.

Measurements like this are useful if you want to know how to block out unwanted sound. This could be the sound of noisy neighbours or car engine noise, passing through the bulkhead into the cab.

Soaking up (absorption)

Reverb chambers are also used to measure how much a material soaks up sound.

In our short, musical experiments, we could really hear the reverberation time of the room reduce, as more people and instruments were put inside it. Listen to the reverb on the test recordings, which were made with only two people in the room. Compare these to the reverb in the Reverberant Jam No 1, which was recorded with several people present.

If you can measure precisely how much an object reduce’s the room’s reverberation, you can work out how much sound that object absorbs. Some materials, like foam, soak up far more sound than others, such as ceramic tiles. Ahe greater the surface area of an object, the more sound it will soak up. So a small cushion is going to soak up less sound than a large settee; Mike Blow will soak up significantly less sound than Sarah Angliss.

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