Indeed he did sound amazing. He didn't take a single vocal lesson, and i think this is the reason that his voice isn't commonly discussed and celebrated today in the music world. If you watch him in his live performances, you can see him contracting certain neck muscles, manipulating his mouth and even lips, his high larynx position which i guess gave him that edging sharp sound to his voice because of the resulting shorter resonance chamber in the throat. His tongue also, which always remained flat, on all vowels, even the long (ee) vowel, something i cant consciously control (mine tongue automatically rises high on the long (ee) vowels which results in a dead sound, no resonance.
He didn't mind forcing his voice above its limits, and the resulting sound which he acquired in the 80's was the result of rather extreme self training which produced nodules on his chords, but provided him with a beautiful voice at full power. Also, his voice was full of emotion, and really do think the emotions he poured into his words affected the tone. He was a true professional, a self taught professional, if would be a mistake to think he wasn't in full control of his voice when singing, but it was in the earlier days before he mastered his own voice it sounded "like a randy sheep" to quote Roger Taylor, it was, and very thin and weak.
But I do think there are certain things that contributed which were sheer luck. His bone structure provided nice big cavities for his voice to resonate in his head to provide the high frequencies, which contributed to the overall beautiful resonance. His short stature will have contributed also, we can guess his vocal chords were a little shorter than the average 6ft man, giving him a naturally higher voice. His accent i think also contributed to his wonderful sound.
Part of me thinks that Freddie did lots of research by reading books on vocal techniques, because he really was a curious mind, and music was his life. There was a short period at the very beginning that the other band members were unsure if Freddie was the right front man because he "lacked technique" to quote Brian May. His voice was really quite unattractive at first, but had 'obvious' potential to be something amazing. That right there tells us everything we need to know. His voice was lacking, but had 'potential to be something special'.
I could definitely hear a lot of sinus resonance in Freddie's voice. Some people think sinus resonance doesn't exist, but i really think that is wrong. In fact, i remember Freddie saying live at a concert between songs that he had to blow his nose because otherwise he couldn't sing. I think sinus resonance is something that is only apparent however in certain people. Short people tend to have shorter vocal chords, thus higher voice, and therefore higher frequencies are produced in the head bones. Maybe shorter peoples just have naturally more head resonance/ I'm a big guy, and i defiantly have naturally producing chest resonance due to bigger chords and deeper voice.
I find it pretty much impossible to achieve head resonance due to my voice being so deep, and so vibrating in the chest.
Also, if you watch Freddie without his vest in live concerts you can see his diaphragm in action, it seems that between vocalizing, he extends his stomach for the breathe, and then before vocalizing he quickly draws in his stomach tightening his stomach muscles and then he vocalizes.
Even though he had a big mouth due to his bone structure and teeth, i don't think he had a vertically large mouth (high palate). I think this because usually people with high palate usually have resonance problems, meaning they cant produce a (forward sound) which results in the resonance being trapped in the mouth making it sound muffled and a bit echoey. Freddie's voice was very forward and very clear.
In fact, if anyone knows how to combat high palate resonance problem, i would like to hear! :)
That is my opinion anyway, i would love for other peoples analysis of Freddie voice.