Fricatives are a category of speech sound. They are distinctive in that they are made by producing a turbulent airflow. That means that you let some air keep flowing out from your lungs and through your vocal tract (then out of your mouth), but you do so by pushing that air through a very narrow opening.

[x] (This is an [s] production)

• When the constriction (narrow opening) is very close to the end of the vocal tract, like when the lower lip touches the upper teeth, the sound produced is either [v] as in “very” or [f] as in “ferry”.
  

Originally posted by ricewinesake

• When the constriction is slightly further back, and the tongue is touching the teeth, the sound produced is either [ð] as in “the” or [θ] “think”. These sounds are written with “th” in English. Since they’re so similar to [v]/[f] and pretty close to [d]/[t], too, lots of dialects of English shift the pronunciation of [ð]\[θ] to one of those other sounds.
  

Originally posted by dfnrey

• When the constriction is at the alveolar ridge, the sound is [z] as in “zoo” or [s] as in “sue”.

• And when the constriction is slightly further back, the sound is [ʒ] as in “genre”/“measure”/“beige” or [ʃ] as in “shipping”.

Originally posted by funny1723

What’s really awesome about fricatives, though, is how they look on a spectrogram. They’re all aperiodic sound (especially the voiceless ones below), but they don’t all look alike:

From left to right: [s] – [ʃ] – [θ] – [f]

• [s] - Very high energy in the highest frequencies
• [ʃ] - High energy, but in much lower frequencies than [s]
• [θ] - So similar to [f], but slightly higher energy in the higher frequencies
• [f] - Lowest energy (quietest) with lower frequencies overall

👍[θumz up]!