Mariah Carey Vocal Range

Vocal Type: Lyric Soprano (but she says she's a contralto)
Vocal Range: 5 octaves 2 notes and a semitone, E2-G#7
Whistle: yes
Vocal Strengths:able to go from a crystal clear, high octave belt to an airy whisper within the space of a word. Has gorgeous low and high notes that are complimented by an uncanny ability to pitch an exact note without the need of vocal runs. When Vocal runs are utilised by Mariah Carey they are incredibly accurate and always sympathetic to the song's key signature, tempo and style, thus giving her the moniker the "Queen of melisma". It's a skill that can be utilised in each of the registers, as well as travelling through them. Technically a brilliant singer. Mariah Carey's low range is dark and heavy.
Vocal Weaknesses: As Mariah Carey has aged the higher belted notes- above a C5- have become coarser and harder to maintain for extended periods of time. The lower notes are also pushed, meaning an unhealthy technique is used to reach them.

Adele Vocal Range

Vocal Type: Contralto
Vocal Range: 3 octaves 1 note and 1 semitone, C3-D6
Vocal Strengths:Adele's low to mid range is rounded and solid, with a soulful colouring. The lower part of her belting range is clear and bright, with a significant weight and resonance to it. However, this weight diminishes as the the chest voice is mixed with the head voice to reach the higher, fifth octave, notes- the chorus of the album version of Someone Like You. Her head voice is thick and weighty with a warmth and resonance, but isn't often used. The notes produced are further improved by her quick and natural vibrato.
Adele has brilliant control over the dynamics of her voice, being able to sing soft and airy when it suits the delivery, but switching back to a fuller tone with speed and aplomb. Definitely more an emotional singer, than a technical one.
Vocal Weaknesses: Questionable technique used to achieve the fuller sounding belted notes as well as the soulful grunts and growls she employs.

Adam Levine Vocal Range

Vocal Type: Tenor
Vocal Range: 3 octaves G2-G5
Vocal Weaknesses: He uses too much falsetto and sometime can sound nasal

Adam Lambert Vocal Range

Vocal Type: Light tenor
Vocal Range: 3 octaves,  B2-B5 and a possible D2
Vocal Strengths: Adam Lambert has expert control over his instrument, producing notes that are well supported, and achieved via great technique. He is capable of singing complex melisma and is able to hold notes for periods of time without wavering in pitch or tone, seemingly effortlessly.  He is an expert at mixing his voice so that the breaks between the registers aren't identifiable, and the effect of this is  that it makes the voice sound almost limitless.
The lower range is dark and weighty, with a breathy quality to it in its lowest extremes. However it begins to solidify, and gain a more confident tone, quickly as it rises.