Small Harps (LONG!)
I am a professional harper. I play small metal-strung harps, which sound very, very different from the nylon-strung, "Celtic" harps you may have heard. Contraray to popular belief, the harp was never a folk instrument: only modern folklore has made the harp a folk instrument. However, there were itinerant harpers in Ireland and the highlands of Scotland who travelled around and played harps in the big houses up into the first third of the 19th century or so: the last harp school in Ireland closed in eighteen twenty-something. Most of these musicians would have played harps that were resident in the big houses, although many of them also travelled with their own smaller instruments.
Metal-strung harps are strung with brass, silver or gold (yes, real silver and gold) wire, and they have a sound that can be compared to bells. They are played with the fingernails, which means players must take care of their nails. In fact, there used to be fines to pay in Ireland if you were responsible for breaking a harper's nail(s). Traditionally, small metal-strung harps had their soundboxes hollowed out from a single piece of wood. The oldest surviving example of the metal-strung harp is the Trinity College Harp, fancifully known as the Brian Boru harp. It lives in Trinity College, Dublin, in a plexiglass case, and it's also featured on most Irish coins. This harp would have been small enough to travel with.
My smallest harp has twenty-four strings. The five bottom strings are made from silver, and the rest are yellow brass. I carry it in a backpack case, and it's really easy to carry around that way. My case is made of canvas and nylon and other modern materials, but in Fantasyland, leather would probably do as well. I own two other wire harps, but they are quite a bit larger; they're pictured prominently on my web site (link in my .sig). Carried along with the harp, in the same case, is a string kit, which consists of coils of brass and silver wire, metal or wooden toggles to hold strings beneath the soundboard, something capable of cutting wire (I use a pair of needlenose pliers with a wirecutter), something to polish the strings with (I use fine grade steel wood to clean and a jeweller's cloth to polish), a tuning wrench (more romantically called 'key', but it's really a wrench), and for me, something to colour the strings with. Harp strings are traditionally coloured red (for Cs) and blue (for Fs) to help players find their place on the strings, but wires don't come coloured, so I add a dot of colour to the appropriate strings so I can navigate.
Harp strings are only changed when they break, and strings made of precious metals are always carefully coiled away when they break. When I tell people there are silver strings on my harp and that I know people who have gold strings on their harps, I'm often met with disbelief. Yes, the sound really is different; silver strings keep a good sound a lower tension, for example, which lets me pitch my bass strings a little bit lower without them sounding sour or thuddy.
Harps need to be tuned and played every day, not just to keep the player's hands in shape but to keep the harp's tuning consistent and keep it sounding 'live'. A harp that's been sitting on a shalf for years in a quiet room will not sound the same as one that's been played every day for the same amount of time. There are plenty of fanciful ways to explain this phenomenon, but the actual reason is that the harp's soundboard responds well to frequent vibrating; a harp that's been kept near a loud stereo will also sound live even if it hasn't been played for awhile, although just sitting your harp in front of a good pair of speakers will not tune it up!
You asked about the way the instrument sounds. As I said, many people compare the sound of the wire harp to bells. There are some song mp3s linked from my web site, but here is a link to a march I put up on my website for students to listen to:
http://www.gwenknighton.com/mp3/mackenziesfarewell.mp3. Actually hearing the music will tell you more than any discussion here will do.
How difficult is the harp to learn? Honestly, I found the harp very simple to learn, but the harp is my fifteenth instrument. It is currently my primary instrument, and the only other two instruments I am learning at present (mountain dulcimer, melodeon) were both started after I became proficient on the wire harp. I can tell you what my students have difficulty with. First, wire strings ring a lot longer than nylon/gut ones, so they must be damped as other strings are played, which means the fingers do double duty: the nails pluck and the pads damp. Otherwise, you have muddy music, like you'd have if you played a piano with the sustain pedal down and never released the pedal to damp the strings. You don't see this problem on a guitar or other fretted instrument with metal strings, because a guitar has a stringboard and frets, and each string can sound several different notes. On a harp, one string equals one note, and the strings are only stopped when they must be, if that makes any sense. My students typically have trouble with learning to damp and play at the same time, and with damping properly so that the strings left to ring are the consonant ones and not tones dissonant with the harmony of the piece being played. Elegant and intelligent fingering is always a struggle, as is the initial learning of what ornamentation works and how to make ornamentation sound natural and not overdone.
Wow, this is long. Please let me know if you have further questions about harps!