Note from Paul: This was an email in response to a question by newsletter subscriber Samantha Boorer about the difference between concertina and accordion reeds. This is an interesting question, as there are now a number of good-looking and well-made concertinas (way beyond Stagi quality for example) being made which use Italian accordion-style reeds as opposed to the reeds and reed-frames (carriers) used in vintage Lachenals, Wheatstones and Jeffries (among others), and Dippers, Suttners, etc. Check the Buyer's Guide for examples and photos of each.
There is a large variation even among reeds of the same instrument type, so it is difficult to point to one thing that differentiates accordion reeds from concertina reeds, not to mention reed organ reeds, chemnitzer reeds etc.
One of the major differences that you may see though, is the relief angle on the underside of the metal frame that the reed swings back and forth through. on concertinas, this angle allows the reed to swing into a increasingly wider opening during it's cycle. this lets the reed begin its vibrations at much lower air pressure, assisting the reed in starting, and at playing at low sound levels. Accordion reeds usually have little or no relief in the reed frame, and are also usually a little stiffer in general than the average concertina reed. This allows them to play at greater volume, but may limit them on their ability to be played quietly, relative to a concertina.
So many other factors affect the instrument's sound though, that you should not assume the reeds play a completely dominant role. Harder reeds have a slightly greater potential for brightness, as do reeds that are shorter for a given pitch. The shape of a reed both in lengthwise cross section (often called the reed profile ) and the shape while looking at it from the top also influence the kind of tone spectrum that reeds can produce. But the picture is more complete, when you realize that in order for you to hear a sound the reed can produce, that sound must be fed back into the reed so that it may continue to vibrate. Much of the possible vibration of the reed is drained away or simply nor supported by the instrument's construction, or the natural interaction with the air stream.
Think of the body of the instrument as a selective absorber of vibration. Frequencies the reed can produce that are near or at areas the instrument likes to absorb ( and then turn into heat ) die out immediatly, as their energy is drained away. Frequencies that are not absorbed, go back to the reed, and help by positive feed back to increase the reeds vibration even more. This then directly acts on the air stream to produce air waves that somewhat match that of the reed's vibration.
Though the reed pan, or " sound board " of an accordion ( that the reed blocks are attached to ) do vibrate a little, primarily, they are selective dampers in the process, and most of the sound is produced by the little puffs of air produced by the reed as it opens and closes the opening in the reed frame, controlling the air stream, much like an old fashioned siren created by blowing air through a spinning set of blades that let the air by in short rapid bursts, or as lips do in a trumpet mouthpiece. or the alternate opening and closing of the double reed in Pipes.
Things like chamber size, shape, method of mounting the reeds, gasket materials, position of support blocks that the reed pan rests on, thickness and materials for reed pans, and blocks in accordions ) are only a few of many factors that can play a major role in determining the final sound character. Complex as they are, I feel like the reeds are only the starting point, and that construction materials and structural design of the rest of the instrument have a major influence on the final result.
One interesting note, A reed fastened at one end when plucked, or in sympathetic vibration with a nearby sound source, has a frequency spectrum that has harmonics at pitches that are completely non musical, rising in pitch much more quickly than the normal " musical" harmonics of ideal strings. Yet in the sound produced by the reed when it is in an instrument, the " natural harmonics are completely absent! the one exception to this is when a balky reed starts to whine a very nasty sound, instead of starting to speak normally. In this case, the reed never produces its lowest vibrating mode, ( the only musical one ) but starts on it's 2nd natural mode of vibrating. So where do all the other parts of a reeds rich frequency spectrum come from? Well. Arthur H . Benade in his excellent book Fundamentals of Musical Acoustics, has an excellent and interesting explaination involving Heterodyne frequencies and the nonlinear-ness of a reed's springyness.
This is probably more than you were interested in hearing, but I find the whole sound production in reed instruments to be a complex subject. ( not necessarily difficult, just including more factors and interactions than you might think ) Most of what I have talked about was gleaned from a lot of fun tests on my wave analyzer ( the issue of the missing harmonics was a great shock to me! ). Other info is from A.H. Benade's book, and from discussions with Steve Dickenson of Wheatstone concertina's, as well as a lot of time spent making concertinas in the last six years, and puzzling about why they sounded the way they do. The short of it is that people who are making instruments that sound like they want them to are doing a lot of things right. Probably more than they realize! It is very difficult to pin down the one thing that makes an accordion or concertina sound like our subjective stereotype of that family. No matter what any of us think the reasons behind it all, What really counts is the quality of the resulting instrument, by accident or design. Tradition plays an important role in passing on the things that worked, whether they were really understood or not. No one, least of all me is the last word on such a subject.
Sincerely,
Dana Johnson