Trouble with thumb voicing of C7

I am currently working through Blues Level I. While most of it has been going very well, I now find myself unable to play the thumb voicing of the C7 chord. I can bar the D, G, B and high E with my first finger without difficulty. However, when I try to add my third finger I find that none of the strings ring out at all.

I am currently playing a full sized acoustic guitar. Does anybody have any tips? Is this even possible on and acoustic guitar?

I am willing to keep trying as long as necessary as I have already learned that we all have specific challenges that we can work through with persistence.

Hi kerwynjones2,

Using the thumb to hit the bass note in a barre chord can be tough, that is for sure. In the video you're referencing here: https://www.guitartricks.com/lesson.php?input=14463

Anders mentions that it can be tough depending on your guitar's neck and just your hands in general. He's also playing an electric guitar, which are usually easier to hold when it comes to barre chords. Acoustics have more tension on the strings which may be more discomforting to hold a chord like this.

The technique is definitely possible on an acoustic guitar, but you might need to practice it more, to build up strength, or try it on an electric, if you have one.

Hope that helps!

Thanks for the advice. I will keep working at it.