Hello.
I dont know why, when I'm working in Sonar, except the known problems with my vocals, it works great! The problems come when I export: When i try to hear my work on my phone or my Ipod, I can no more hear my voice, or at a very low level, depending the headphones I use. But, on computers, it sounds as I wanted. I tried many different devices and i got the same results and I dont know why. I worked on the levels, and I have tens of mix that still dont work. Can anyone help me ?

There is a lot of reasons that can add up to an export mix not playing the same as it sounded when played back from with in Sonar. But I can only guess without knowing what your using. You need to tell everyone what your set up is for a more accurate response. 
List your system, version of Sonar and Audio interface etc.. 

Thank you for your answer !
First, it's not just that the mix is not playing the same, my vocals are simply inaudible on phones or Ipods. I tried to make a simple test in audacity, the simplest soft of the world, and the problem was the same. I don't know why the instrumental coming from someone else, is clearly played while my vocals signal is so low only when i am on phones or Ipod. 
I use Sonar X3, I have my Computer soundcard, a Tube MP preamp and a TBone 450 microphone.
Thank you.
 

Is this a new problem you've discovered or have you been able to mix your vocals acceptably in the past?
 
Assuming you've always had problems with this, I might suggest that you are blessed with one of those voices that live in a frequency range in which many other instruments and voices in your mix tend to dominate. If that's the case, the speaker will have a lot of energy concentrated in a narrow range of frequencies and your voice may well get swallowed up in the mud. I've also found that some of the cheaper ear buds and speakers tend to swallow my voice  when that kind of fighting is going on. it's nice to know that I'm not alone. :)
 
For my voice to stand out in the mix I have to emphasize some upper mids and lower highs on my vocal tracks, and then cut in the lower mid frequencies that it's fighting other instruments over. The idea is to let specific instruments and voices dominate their own slices of the frequency spectrum. If you do this, your voice should pop out nice and clear.
 
Perhaps you already knew this, and if you did, then I have no idea what the problem is. :)
 
Good luck!

Hi. Do you use monitors, or headphones? If you are using monitors, it sounds like you could have an frequency issue with your room. Could it be that your room (naturally) amplifies the vocal frequencies, leading you to lower the vocal track, and have different experiences (soundwise) other places? Is it consistent, or does it differ from other projects? 

Before exporting check your mix using the problematic headphones to see if you can hear your voice before the export. If not you can play around with the mix until you can. Then check it again in your monitors and again in the headphones then in any other speakers/headphones you have around. Try to acheive a mix that sounds good on all your available soundsources. This might make things sound not as good on one or the other but you want to make it so you get the best quality on the widest variety of speakers.
 
That's not a replacement for a perfectly tuned room with high quality monitors and a lot of skill/experience but it'll help get you closer than doing it all on one poor sound source. I keep a bag of various headphones, two stereos, multiple sets of speakers of varying size/quality as well as my studio monitors. I used to try out and make tweaks on my mixes on as many as I could to get things sounding even on them all.
 
Now I've got a VRM Box which is better/more convenient for that type of mix checking but I'll still try out stuff using the hardware as well because it's just more stuff to check it on.
 
However if something actually IS happening in Sonar that is doing something to you mix maybe you've got some kind of weird settings that are causing the sound of your vox to be partially cancelled out like phasing or perhaps you simply aren't setting up your export options properly (like you have the vox running to a bus or something that's not being included in the export or something weird like that).
 
Cheers.

I "overcame" my room by monitoring at low volume. It helped my mixes a lot. Phasing could also be an issue, as Beepster pointed out. Best of luck.

Well, nothing will work correctly until the OP buys a proper audio interface. Was my first guess at the problem. 

Cactus Music
Well, nothing will work correctly until the OP buys a proper audio interface. Was my first guess at the problem. 

I agree with this