Soundproofing Studios

Studios are critical listening spaces. The noise levels have to be as low as 10-20 dB.  The hum of the HVAC, the rumble of the ceiling fan, the structural vibrations of all the houses/buildings nearby, the rumble of trucks on the road, the cross talk through the HVAC duct, the hum of the machines, all make a rather big difference to the quality of the sound. Also, since most studios are rather small spaces, the the bass response must be carefully evened out.

One of the projects I worked on involved two studios (A and B), located one above the other. Both A and B were located on top of a full fledged household. So the ceiling fan of the house was hung from a metal hook, and that ceiling formed the floor of Studio A. That made a rather audible rumbling noise, despite carpeting in Studio A. The glasswool in both studios was filled in more than 15 years ago, and was clearly sagging. When you played sound loud in Studio A, it could be heard in Studio B’s recording room. This is otherwise not a problem, only, in this case, when they increased the gain of the mic for singers with feeble voices, the sound coming out of the other studio got recorded.

Both studios were built with good isolation in mind, with double doors, corridors lining the rooms, etc. But the structural vibrations caused by the HVAC unit on top of the terrace was a problem, as was the motor run by the next house for pumping water to their overhead tank.  The recording room in studio B was exactly 11 ft along one size, and the bass frequency formed clear dips and peaks in the room. Any surprise that the problem frequency was exactly 100 Hz? The monitor speakers were placed at accurate angles, but despite that, the recording console had a big dip, and right behind that, where the producer of the movie and his cronies sit, there was a boom.  They were also not able to use the air conditioning when the recording was in progress. They only used it for post production. So in terms of scope of work, it was a rather big project. But as with all acoustics projects in Bangalore, the budget was rather limited 🙂

The purpose of outlining this scenario is to mention common issues faced by a lot of studios in this area. Structural vibration is the biggest grouse. And increasingly, pavements are laid joining the road and residential areas. This, despite there being a mandate not to do so for longer than a certain width ( wide enough for your car to roll out of your house). This leads to added coupling.

That said, in India, the advantage is that most structures are still brickwork/RCC, unlike gyp/wood partitions in the west. Internal walls are usually 4 inches wide, and external walls are 8 inches. Older houses have thicker external walls.  So, a decent amount of isolation exists between rooms, if you ignore flanging.

All this is was about the sound isolation bit. Now when it comes to reverberation treatment, and the frequency response of the room,  studios again are the most critical sound spaces.  It is vital to avoid shadow zones for bass frequencies, and diffusers must be optimally used. Faulty room acoustics leads to the sound engineer falsely believing the sound spectrum to be something it is not, and equalizing to correct what they think they’re hearing.

Sound technical help should make sure that you avoid all these pitfalls, and the expensive corrections they entail. The right treatment should make the ambient sound crisp and clear, with accurate and predictable colouration from the room.   The quality of sound you hear can then safely be subject only to the quality of the equipment. I have a personal affinity towards sound studios, because these test so much of our skills, and these are also the places where some of the best works of art are immortalized. As someone whose interest in music primarily led her to acoustics, I do have a thing for these little rooms.  🙂

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