I was just messing around last night and I struck on an interesting sound based off the G Melodic Minor scale with double notes. These sound cool for the C7+11 or Em7 b5 chords.
I'll just spell it out since I'm too lazy to scan the music. These are all fingered 1/2 & 4/5 for the RH btw.
The RH starts a 5th up from middle C . Be sure to play very slowly in eighth notes connected/legato. Also concentrate on digging into the keys so each interval of the double notes are sounded clearly :
G/A to E/F#...Bb/C to G/A...D/E to Bb/C...E/F# to C/D and to the octave of again of G/A to E/F#.
I go one past the octave to Bb/C to G/A and then come down in reverse sequence of:
A/G to Bb/C...E/F# to G/A...C/D to E/F#...Bb/C to D/E....G/A to Bb/C and finish at the home base of E/F# to G/A. (I think I got the sequence right but it was late here so there might be a typo)
Aside from the obvious technical challenge it re-enforces your knowledge of the melodic minor scale and it's application to those particular chords. In addition it can help you see new shapes within the Melodic minor which further advance voicings and lines. A good way to practice might be using the LH voicing of E/A/Bb/D or Bb/E/A while playing the RH double notes against it.
You can also play all 4 notes together as one chord/voicing and go up and down the sequence that way. Use of the sustain pedal during the double notes or 4 note voicings is strictly verboten btw. Learn to use your fingers to connect the notes, not the pedal.
I added the LH down 2 octaves and fingered those 5/4 & 2/1 for even more of a workout. Of course the real challenge comes when you start transposing to different keys. This can get pretty arduous so just do a little at a time. Also if your better half is in the vicintiy, headphones are a must ! If you're on acoustic, you might want to wait until the coast is clear....
After the sequence has been somewhat mastered, you can take individual strands, like say the first one of G/A to E/F# for instance and just transpose that to all 12 keys around the circle of 4ths or up and down the octave chromatically or in intervals of major or minor thirds up and down the octave. Again you can play the LH voicing against or even better yet-try to mentally visualize the chord and the double notes' relationship to that particular chord without a RH voicing. That's one of the extra challenges of adding the LH in unison down 2 octaves.
I've found aside from jazz, this sound works very well in latin and fusiony/funk contexts. Also played on a rhodes, it has a lot of bite, also doesn't *mud* out like a lot of acoustic piano sounds do transferred to EP.
So basically in context, if you have a Bb Maj7 chord for a bar or two and then it goes up to the C7, like in *take the A train* (only down a step obviously from C) you might want to experiment around with strands of this. Also something like Girl from Ipanema. Just make sure you overdue it on that one so you get a rep of being an out jazzer and never get called again..mission accomplished..