I've been playing clarinet for about 6yrs now and I still find that the altissimo range sounds horrible. I'm playing an E11 with a Vandoren B45 mouthpiece and Vandoren V12 reeds size 3 1/2. I've tried 4's but they were just too hard. Would a change in my embrochure help (I've tried tightening up and the A's still sound horrible) or would it be better to upgrade to a better mouthpiece?
Let me know your ideas.

Try 2 1/2 or 3.

The B45 isn't the best choice for you. Borrow a different mouthpiece for a little while and see if that doesn't help. 5RV's work well and are very inexpensive used.

Keep working "register slurs" up to that range starting on low A, add register key for 4th-space E, then pick up your first finger for C# above the staff and hold. Work up chromatically resting between each set. Low Bb would be the next starting note and so on. Do it every day until it's easy. The high note should just pop out easily. If you can't get it, seek pro help! I hope that helps!

BH

If you have been playing for 6 years, I would imagine you should be playing on at least a 3 1/2 - 4

My band director, who is quite an accomplished clarinet player(who plays on size 3 reeds), is always reminding us that you don't need to continuously move up in reed strength. There is no rule saying that anyone who's any good plays on 4's. If 3's are comfortable for you, keep using them and just keep working on the higher notes, you'll get them eventually.

its not necesarily the reeds, you might wanna consider stepping up horns. An E-11 doesnt have the best altissimo tuning or tone. Especially if you're serious about playing i strongly recommend an R-13

I am serious about playing and have been told to upgrade my clarinet several times. I am currently waiting for the shipment of R13's to come into my local music store.

I am also planning on upgrading my mouthpiece when I get the R13. Any suggestions?

Don't be too quick to change your mouthpiece. Play with your B45 on the R13 for a while and see if you're content with it. If you aren't, try a 5RV or an M15.