A union of truck and taxi drivers in Ghana's capital, Accra, has turned the mundane honking of horns into music.

Steven Feld, a professor at the University of New Mexico and self-described "anthropologist of sound," has spent three years recording the sound of these horns, known in the West African nation as por por horns after the sound they make.

Antiques from the 1930s and '40s, the honk horns have a rubber squeeze bulb at one end and are either straight or curved. Drivers used to hang them off their side mirrors.

Feld has produced a CD of the music, Por Por: Honk Horn Music of Ghana, to coincide with the 50th anniversary of Ghana's independence earlier this month. The CD features the unique combination of drums, singing, bells and squeeze-bulb horns.

The music originated for very practical reasons, Feld tells Melissa Block.

Punctured tires were common on Ghanaian roads in the past. At night, as they pumped air back into their tires, the drivers — fearful of animals that might lurk in the darkness — also banged on tire rims with wrenches and honked their horns "like crazy" to scare any potential predators away.

"And then somebody got the idea to start taking bell rhythms and horn rhythms from different kinds of music in the country, and transposing them onto the horns and the tire rims, and that was the birth of the music," Feld says.

Although por por originated 60 years ago, Feld says it has been largely unknown until recently because it is performed only at the funerals of truck drivers.

"The idea is kind of like a New Orleans jazz funeral: a real rejoice-when-you-die kind of party, where you are sent up by a honking of horns," explains Feld. "The drivers' road to heaven paved with car horns and a whole lot of honking."

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