In the Asterix books, Cacofonix the bard is forbidden to sing because his voice causes wild boar, villagers, Normans and Romans alike to flee. But Cacofonix does play the carnyx, a long, slender trumpet-like instrument decorated with an animal's head at the top end, and used by the Celts in the last three centuries BC.

The Greek historian Polybius (206-126BC) was so impressed by the clamour of the Gallic army and the sound of the carnyx, he observed that, "there were countless trumpeters and horn blowers and since the whole army was shouting its war cries at the same time there was such a confused sound that the noise seemed to come not only from the trumpeters and the soldiers but also from the countryside which was joining in the echo".

When the remains of seven carnyx were unearthed recently, Christophe Maniquet, an archaeologist at Inrap, the national institute for preventive archaeological research (Institut National de Recherches Archéologiques Préventives), was curious to find out exactly what sound it produced when it drove the Romans mad, or was used to call upon the god Toutatis.

In 2004, more than 500 iron and bronze items placed as offerings to the gods were discovered a small 30cm-deep pit in Tintignac, in the Corrèze department. "These items were deliberately damaged so that they could not be used again by mere mortals," said Maniquet.

Some 40 fragments were identified as being parts of a carnyx, making it possible to restore a tall, 1.8-metre-long instrument with a stylised boar head at the top – a first in archaeology. "Some carnyx pieces were discovered in England, Scotland, Germany and Italy, mainly in the 19th century, but the context was unclear and we have never found so many instruments in one go," said Maniquet.The carnyx is a wind instrument, part of a sub-family of brass instruments defined by the presence of a mouthpiece. The sub-sub family would be natural brass instruments without valves. With its conical shape the carnyx resembles a soft brass instrument like the horn, with a more muffled sound than a cylindrical trumpet-like brass instrument.

Unfortunately since it was impossible to play the instruments the pious Gauls had so carefully dismantled, Maniquet asked an instrument maker to reproduce a brass carnyx of the same size. The archaeologist worked with experts from the acoustics laboratory at the Maine-CNRS University in Le Mans, headed by Joël Gilbert, a brass instruments specialist, who carried out an in-depth analysis of the specimen.

A study presented by a group of researchers and instrument makers in Le Mans last month, revealed that the resonance frequency determined the series of playable notes. In a well-designed instrument this resembles a harmonic series. If the musician had the base note he could easily produce others (mainly octaves, fifths and thirds), by modulating air flow and lip tension.

The carnyx has a fairly low base note because of its length but researchers found that the resonance frequencies obtained with the copy of the carnyx were far from harmonic. According to Gilbert, when he and his colleagues looked into this they suddenly had an idea. "The carnyx is not a primitive instrument and it was known for being very powerful. We therefore worked on the hypothesis that our copy was incomplete," he said.

Maniquet believes that is quite plausible, especially since no one is really sure how the mouthpiece connects to the tube. The acoustics experts have pursued their research by doingsimulations with a mathematical model, this time adding an additional part to a virtual carnyx. They tested two lengths, 10cm and 20cm, which produced a lower sound and altered the resonance harmony.

The simulations showed that the optimum length was achieved by adding a 10cm part, which could match an item in the catalogue of finds from the Tintignac site. Maniquet is now planning to build a second prototype instrument to include the additional 10cm. "That should make this carnyx more powerful and easier to play," said Gilbert, confident that his calculations are correct.

Cacofonix can remain gagged; it seems that relief is on its way.

• This article appeared in Guardian Weekly, which incorporates material from Le Monde