Harmonicas can be found for every occasion & musical purpose. The bass & chord harmonicas completes the picture for the chromatic harmonica range.
A BIG thankyou to Debbie The Harper Temple
Pay a visit Coast to Coast Music as they have a growing resource on orchestral harmonicas, (in addition to chromatic & diatonic harmonicas) including note layouts.
This is a Single Reed Bass. Hohner's #264 Bass or also known as the "G-Bass" because its range is two octaves, starting and ending on G. It has a hinged double deck set up but with a cover plate only on one side of each deck. It is set up in the same modified keyboard style as those basses already discussed. It has 29 reeds with 14 on the top deck and 15 on the bottom deck.
Like all basses, it is all blow. IMO, it is just a little harder to play because there is only on reed per hole (one reed plate per deck, under the single cover plate.) This is why the picture looks so strange as the underside of each deck has a small metal plate (I suppose so your mouth makes contact with it rather than the comb) and beyond the plate is the finished wood or veneer of the comb.
Weighing in at about 3 lbs, this is the most common type of Bass. This is an ALL Blow instrument. It is a double-deck instrument set up in a modified keyboard style. With the sharps, plus extra F and Bs on top and the complete span of non altered notes (the white notes) on the bottom. It has 29 holes (14 on the top deck and 15 on the bottom deck)-spanning 2 full octaves starting and ending on "E". The reference to "Octave" in its name is because each note has 2 reeds tuned in octaves to each other. Thus it has 58 reeds total.
Although this is set up with "harmony" in mind, it is really used as rhythm instrument upon which accompanying chords are "chugged."
Notice the 2 decks hinged together. Each chord has 8 reeds per chord (4 holes stacked over 4 more holes) and tuned using a 2-octave span for each chord (for a fuller sound than the single octave span chord harps). That means a grand total of 384 reeds (and 384 windsavers)! This is the longest harmonica made - 23 inches.
The upper deck has Major Chords on the Blows and Dominant 7th Chords on the Draws following the layout of the Circle of Fifths. The lower deck has the Minor Chords on the blows and alternates between Diminished 7th chords and Augmented chords on the Draws.
This is the Hohner #268 Extended Double Bass. It is like the 265 in most ways (all-blow, modified keyboard setup in a hinged double deck layout and starts on "E") except that it has an extended top range that goes up to "C". It has 78 reeds. (2 per hole, tuned in octaves with 19 holes on the top deck and 20 on the bottom deck).
This bass is the heaviest of all harmonicas, weighing more than 3lbs.
Both Swan and Victory make a single reed chord harp (4 reeds per chord instead of Hohners 8 reeds). It is a thinner sound but is more compact in size.
Suzuki and Huang make a 48-chord like Hohner's. AFAIK, the setup on all
these chords are the same:
Setup = Circle of 5ths (with the C chord being the 7th chord in on the top,
in current layouts, it was different in the 1930s). The Dominant 7ths
occur in the CO5 layout according to the major chords, so G7 is the draw
chord resident with the blow C on the top deck.
The minor chords are laid out in order via the same tonal center as the
majors so Cm would be the blow chord on the lower deck under C major.
The Augs and Dim7ths don't really make as clear sense as the rest; however,
All of the Majors, All of the Dominant 7ths, All of the Minors, All of the
Augmented, and All of the Diminished 7th chords all exist on this harp.
Now with 48 chords to choose from the most common question is how all of the augmented chords AND diminished 7ths can exist on one deck, all draw, over 12 chords? There are only really 3 different Diminished 7th chords and 4 different Augmented chords in existance. This takes some knowledge of theory to understand different enharmonic spellings for the same chords.
There are two types of chords I left out, the (Hohner) Vineta (Junior Chord) which only contains 3 bass notes before 3 chords (currently F-C-G); however, historically these were offered with many different variations of major chords and even ordered a bit differently in the above chords, depending upon when in history, the harp was made. This is supposed to be a training harp for a budding chord/bass player and with it's limited range, there isn't a heck of a lot more it could do.
The Chordette-20 (by Huang)--this is notable because it has 20 chords with 20 bass notes preceding each chord. It is a small hinged double-deck instrument meant to fill in for both chord and bass simultaneously. It has 5 sets of chord holes (both blow and draw on the upper deck) and 5 sets of chord holes (both blow and draw on the lower deck). Victory also makes one of these. Hohner does not however. It has more capabilities than the Vineta by far; however, still has range limitations (for instance it only has 5 major chords out of the 12 existing ones; only 5 minor chords out of the 12 existing ones, and only 5 dominant 7th chords out of the 12 existing ones). It's setup is similar to the Hohner 48 chord, by following the CO5 for what chords are present.
Just like the Hohner: Top deck blow are major, Top deck draw are Dom. 7th, Bottom deck blow are minors, and bottom deck draw Dim7(and I believe 1 E aug chord).