Car buyers may be used to sizing up colour, extras and engine power, but research claims there is another big factor in the showroom - the horn.
Tests were carried out on the horns of 25 cars
Scientists at Cardiff University took 25 top-selling cars and rated each horn on their volume, pitch, tension and roughness.
The research found the Ford Mondeo has the most "aggressive" horn on the road.
Professor Theo Van Leeuwen, who carried out the research, said the sound of the horn was becoming important for buyers.
Prof Van Leeuwen, an expert in the semiotics of sound at the university's Centre for Language and Communication, said manufacturers were paying more attention to the sound of the horn, which can be a deciding factor for potential car buyers.
He argued that more car companies were matching the sound of the horn to the "personality" of the car.
TOP FIVE HORNS FOR AGGRESSION
Ford Mondeo: "Strong and assertive"
Honda S200: "Penetrating and aggressive"
Mercedes CLK: "Tense and rough"
Renault Clio: "Very loud and quite aggressive"
Vauxhall Corsa: "Strong and piercing"
Prof Van Leeuwen said: "Automotive industry is paying more and more attention to the sound.
"They design different car horns now for different cars, just as they design the sound the door makes when you close it and so on.
"It's in a lot of areas, you used to have one standard sound in a telephone ring - it's now customised, there's choice.
"If you are buying a car because you want to make a big statement and you have a big, red, sporty car that you want to drive fast in and your horn goes 'beep' that's not quite what you're after.
"I think you can make a fair judgement on how people project themselves as a driver from the horn."
Of the 25 cars surveyed, the Ford Mondeo had the most "aggressive" horn. Its sound was described by Prof Van Leeuwen as "very loud, tense and rough, but not very high. Strong and assertive".
TOP FIVE HORNS FOR DISCRETION
Audi TT Quatro: "Perhaps just a shade too quiet"
CitroŽn Xsara Picasso: "A fairly thin and weak sound"
Fiat Multipla: "Low loudness and pitch levels"
Renault Scenic: "Assertive without being shrill"
Renault Laguna: "A somewhat thin and weak sound"
At the other end of the scale, the horn with the most "discretion" belonged to the Audi TT Quattro.
It was described as "an unusual dual horn, very soft and low, and without tension, but quite rough. "The sound is quietly confident, 'masculine' and 'meaty' - but perhaps just a shade too quiet."
Online car dealership Jamjar, which commissioned the research, said: "Evidence from car buyers suggested some had been disappointed in the past after buying large, imposing cars - only to find a tinny parp emanating from under the bonnet when they sounded their horn.
"Now we're the first to let people test their horns online and experience what they sound like before making the final decision to buy."