Welcome to BLOG 6 on using horn harmonics (including the 7th) to play simple chord progressions with 7th chords.
Good tuning is possible by players of even modest ability. The harmonics of the horn can be used to help hear and play simple chords nicely in tune. A good, steady, well focused tone is the main requirement, then the natural resource of the horn can do most of the subtle tuning. A standard double horn provides, easy to play major triads in the middle range in 11 keys. These can all be played with harmonics 4, 5 & 6. The key of B major (concert pitch) on harmonics 4, 5 & 6 is awkward as it naturally sits a quartertone sharp and some of that good, well focused tone can be lost when bending them lower. Much of this is detailed in the Blog (October 1), Horn harmonics and simple chords.
Also in the mid range of the horn are many 7th harmonics. These, too, can be accessed by players of modest ability. Students having played for less than a couple of years may not have the strength and steadiness of tone to do this well, but many students beyond that can.
Here is a short sound file of a standard chord progression played by four horns (multitracked at home for convenience). The progression is I-IV-II-V-I. In the music notation example below this is the first one. I used the 5th harmonic of the E horn (2nd valve) to get close to the written Eb which is the 7th of F in chord IV. Otherwise I used 7th harmonics to achieve the 7th of the chord. These achieve a smooth sound; pretty much what good barbershop quartet achieves.
Here is another example, slightly higher in the range for the 1st horn part. This also has a chord with 2 notes tuned as 7 ratios: the root with a narrow minor 3rd and a narrow minor 7th, along with the pure 5th. This is chord two in the second notated example.
Here is the notation of the 2 chord progressions: