Octave, tremolo, 10- and 12-hole diatonics (blues harps) and chromatics are all eminently suitable for playing Irish music. A quick glance at this discography
http://www.irishmusicreview.com/harmoni ... graphy.htm will show that there's a healthy and increasing number of ITM harmonica recordings available (though some include "related celtic" genres too).
The harmonica fits in nicely in sessions as long as the player tries to blend with the other instruments and cuts down somewhat on the wailing and wah-wah-ing (you can do these things if you get a solo spot!). A lot of ornamentation is possible, and note-bending for expression can be very effective. If the session is a big one or is in a noisy pub you can have trouble being heard even with good tone and projection and the loudest harps available (Hohner XB40s probably). You may need a touch of amplification in these settings and the others may not like that idea.
Some people do all sorts of things to their harmonicas to make them more suitable, but if you play 10-hole blues harps one particular thing that's quite important is to do a one-note retune to put back a note missing in the lowest octave. You can tune up either the 2-draw or the 3-blow by a tone. Most people choose the 3-blow. You'll get by quite well without doing this with D harps but you will be significantly hampered with G harps as many G tunes need that missing note. As most Irish tunes are modal, with just a G and a D harp you'll be able to play the tunes in G Ionian, A Dorian, E Aeolian, D Mixolydian, D Ionian, E Dorian, B Aeolian, A Mixolydian and G Lydian. On your A harp you'll be able to play in A Ionian and E Mixolydian too. That covers an awful lot of Irish tunes! Tell your guitarists this and they probably won't know what you're talking about. Heheh.
You may be one of those rare people who's comfortable playing a C chromatic in any key, otherwise you need, in order of importance, harps in D (preferably low D), G and A. I always take along harps in C and low F too.
In some circles the harmonica carries about as much kudos as the piano accordion, the 5-string banjo and the bodhran and just slightly more than the shaky egg. But to hell with the begrudgers I say!
I've put a lot more information and links to even more on my website.
Steve
"It might be a bit better to tune to one of my fiddle's open strings, like A, rather than asking me for an F#." - Martin Milner
