Hola Tony

The use of "ruidosísimos" in the sentence "Los conciertos de la calle son ruidosísimos" is correct and not a typo. In Spanish, when an adjective ends in a vowel, like "ruidoso" (noisy), and you want to express the superlative, you typically follow the pattern of taking the masculine form and replacing the ending "o" with "ísimo".

So, "ruidosísimos" is the superlative form of "ruidoso", indicating an extremely high level of noise. This construction is consistent with the rule you mentioned and is appropriate in this context.

Feliz martes

Silvia