How is the voice quality of a seiyuu classified?

Question

Considering the extreme popularity of voice acting and voice acting schools in Japan, I'm curious to know if the industry actually classifies the quality of each voice. I'm not talking about things like age, gender, etc. Rather I'm interested in the tonal quality of the voice.

Personally, I'm particularly taken by the tonal quality of Mizuhara Kaoru, the seiyuu who voiced Kusakabe Misao in Lucky Star. Kusakabe's voice has got a thick, musical quality to it and sounds ... double-layered.

(I'm not the only one enamoured with Kusakabe's voice:

Her character Misao Kusakabe in Lucky ☆ Star gained a cult following in fans and spawned internet memes due to her own addition of a nonsensical "vuah" (ヴァ) at the end of her sentence.("if it's picked up within 5 seconds, the germs don't get attached" 五秒以内だったら、菌がつかないんだってヴァ) This began in the 18th episode of the anime where her character Misao was nervous and embarrassed after eating food that has been dropped on the ground in front of others. The popularity was substantial enough to have a 13th Lucky Star character album featuring Misao released four months after the originally planned twelve albums were released even when her character already shared a duet character album as the 9th album.

This is at around the 18 minute mark of the 18th episode.)

Answer 1

Well I don´t think they actually classify the quality of each voice. Why do I think so?

Most seiyuu are picked after they either send in some records or do a vocal audition, or they have done voice overs/acting before and are scouted this way.

When a company wants some voice acting done, they usually keep in mind the characters that have to be voiced. Most of the time characters have a specific personality and they want a voice to best represent this personality. For example, let's look at Mizuhara Kaoru, the seiyuu who voiced Kusakabe Misao in Lucky Star. She has a melodic yet playful voice which can represent the character as one of the best. To even better grasp this concept, think of Naruto being voiced with Kusakabe Misao's voice. This would not match the personality the character has to represent.

So if there were to be a classification for seiyuu, it would differ per character. So there are no known "standard classifications" for seiyuu.