After 3 years of RYV-ing everyday, I still have trouble negotiating the closed vowels. The eee's, the ooo's, the the short "I" vowels as in "in"...basically the more closed sounds. The sound is restricted and my voice gets tense when attempting to sing them purely, without modifying the the vowel. I hear a lot of singers modify their vowels pronounce their eee's as ayyy's and the ooo's as oh's...but then again, a lot of singers sing really high and keep that pure pure vowel sound? Any tips on what I should be focusing on when practicing?

P.S. this problem is only in the middle register approaching headvoice by the way...

Try sustaining notes and moving towards the vowel as such:

Ayyyy------eeeeee

Ohhhhh-----ooooo

Start changing the shape of the mouth towards the troublesome vowel while maintaining the thought and internal sensation of the starting vowel. Do these like Isolation exercises working up in half steps through your midrange.

practice some ah, ay, ee, oh oo scales... focus on the back of your throat (soft palate area) as you are doing them. You will notice it feels nice and open on the ah and ay, but when you get to the ee oh and oo the back of your throat closes up. The trick is to keep it as open on the closed vowels as the ah and ay. When people tend to make a closed vowel sound, they let there throat close the vowel, but you have to learn how to keep the throat as open through all the vowels as the ah and ay and then to make the closed vowel sound you just have to over announciate with your lips.
So make sure the back of your throat stays nice and open and let the lips do all the work to create the closed sound.
good luck

Wow...it's already helping a bit...cool guys thanks.

I have HUGE problems with OH. My highest note with OH is 3 or 4 notes lower than Ay or EE or AH

Holy sh** that does work!

Don't suppose someone could make a video and demonstrate? I've been struggling with eee's for ages and it just seems....practically impossible to blend from Ay to eee.

Any tips for "oh" as in "DOH!" would be great :)

I guess what I don't get is....doesn't the sound of a vowel come from the tongue? How does changing the lips do anything....e.g. if I sing an AY and move my lips around, I still end up singing an AY.

sorry i was referring mainly to the oh's and oo's with the lips, what i meant to say was let your mouth and and lips do the work... lips for the oh's and oo's and the ee's need a smile mouth shape.
but the open throat must remain the same.

The back should always remain open. Imagine a huge orange between your back teeth. Open the back while you close the front got closer vowels