How to lower down the volume more than by default?

Question

When receiving calls, I sometime use the default headphone but the sound is too high for me.

I set the volume to the lower, but it's still too high.

How can I define the volume lower than the limited default from android, and if yes, how ?

Info : I don't have a volume parameter on my headphone Info 2 : It's a HTC One S (not One, One S !)

Thanks for your help.