I'm not entirely sure what you are after and not entirely sure what you mean by 'luxurious' car horn... Are you wanting to describe the timbre of a certain car horn sound using words? And do you have any examples of a particular type of horn you are able to post a link to?

Timbre, or 'how something sounds', is usually described using words you'd normally relate with other senses, such as vision and touch. For example, a sound can be described as warm or cold, sharp or soft, bright or dull.

Words I'd use to describe a typical car horn would be things like 'sharp', 'bright', maybe 'harsh'. The point of a car horn is to act as a warning so will tend to be be disharmonic and cutting so as to stand out and catch our attention.

Again, if you post a link to a more specific example of what you're attempting to describe, we might be able to give you more assistance!!