I don't want to teach this for classical musicians so I show it in daw (fl studio) for you
double dominant include many kinds that I say just those are useful for pop musicians.
I illustrate it whit an example
assume we are in Am our fifth degree in this scale is Em but you must make it EM (harmonic minor scale)
than you should count the fifth degree of EM that is BM
now you can use this chord in your chords progression like = am - dm - E - am - B - E - am download source and midi here
you can use it for all degree for example in forth degree that is Dm .
fifth degree of dm is A major so you can use A to Dm in your progression = am - dm - E - am - A major - dm - E major - am ( write it or play it on your instrument)
you can test it in all degree except 7th.
if you don't understand or I explain it bad so let me now
if you like it I post another kinds later

 

Last edited: Oct 25, 2017

nobody!. so it wasn't useful here
but if any body is interested in harmony at least learn any kind of double dominant and Neapolitan chords and 7th and 9th chord and try to learn how to use it in chord progression. if you want some new effects in your music

 

My colleague, I have gone that road previously. Nothing there. Believe me.

PS:
Put that guitar down and enter another world.

 

Last edited by a moderator: Oct 25, 2017

It was useful! Thanks!