Sound secrets

Explore the fascinating world of building acoustics, from echoing clapping telephones to whispering galleries in historical structures.

When you visit a building, you usually experience it visually. Maybe you look at the colours, the shadows dancing on the walls, the sunlight streaming in through the windows.

Have you ever experienced a building in terms of sound? Modern building acoustics deals with controlling sound in buildings like concert halls and cinema theatres. But many old buildings have fascinating acoustics: mysterious echoes and whispers that travel along the walls. 

Imagine you are playing downstairs in your apartment, and see an unexpected guest entering the gates. You want to warn your mother, but you have no phones or devices of any kind. The Golconda Fort in Hyderabad built in the 12th Century had a solution: an echoing clapping telephone. The sound of a clap can travel for more than a kilometre at certain points in the fort: like a secret signalling device. On a visit, a guide will take you to a spot inside, have someone clap at the entrance, and give you a chance to hear it loud and clear. The story goes that this was used to warn the Sultan of oncoming attacks; not unlike the guest you want to warn your mother about! The fort also has a stone chamber that gives a flutter echo, where small sounds like the snapping of fingers get amplified into loud claps. 

In the neighbouring state of Karnataka, tucked away in Bijapur is the Gol Gumbaz, a 17th-century mausoleum. It was built by King Adil Shah as a tomb for himself! It has a massive dome enclosing a single large space where sounds get amplified and echoed. But that’s not all.  

Along the base of the dome runs a narrow walkway: a “whispering gallery”. Whisper a secret into the wall and someone at the other end of the gallery, over 100 feet away, can hear you. Scientists who have studied the phenomenon say that the sound ‘creeps’ along the walls by a process of reflection, where it keeps bouncing off the curvature of the walls. Another famous whispering gallery is at the St. Paul’s Cathedral in London. 

You might think that the architects did some pretty cool stuff to get this effect. We don’t know about the architect of the Gol Gumbaz but the architect of St. Paul’s, Christopher Wren, supposedly never expected this effect when he designed the dome. The gallery ended up being one of the biggest attractions of the building. Think of all the secrets these walls hold! 

Remember, these galleries works only if you whisper; not if you shout to make the job easier. This is because a whisper is a low-intensity sound without interference from echoes and distortions.