Voiced and Voiceless TH

the /th/ sounds have basically the same position.

• place your tongue gently between your teeth.
• your lips are slightly pursed, sort of around your tongue
• allow some space between your teeth and around the sides of your tongue so air can pass through.

the difference is here. 

• for unvoiced /th/ ( /Ө/), simply blow air out between your teeth and around your tongue.
• for voiced /th/ (/ð/  ), add your voice to that position.

Drills

                                                 /Ө/                                                         /ð/                                                                  
               thin                                                            then            

     birthday                                                    brother

toothpaste                                                 father

bath                                                          bathe

/Ө/

1. Thin thinkers are thirsty for broth.

2. Open your mouth and say thank you.

3. April third is my birthday celebration.

/ð/   

1. Father and mother are with my other brother.

2. That's right, don't bother me.

3. There are thirteen mothers waiting there.

                                                                 Tongue Twister

 Although Samantha was very thorough with their thesis, they thought she loathed their thinking and threatened to throw her thesaurus on the path before it thawed.

Note: Some of these sentences are based or are from a website on the internet, which unfortunately I can't find anymore (my apologies). The tongue twister is from thesmallguidesite. Thank you so much!