When comparing a modern clarinet with a recorder, the first thing that obviously is different (next to the colour of the wood and the size) is the clarinet's key system.
What the keys are needed for
You need the clarinet's keys to do what you can do on the recorder just using fingers: Opening and closing the toneholes.
This could be achieved with nothing but fingers, too, when playing the smaller clarinets like Eb-flat and B, at least when closing the upper tone holes. But you can't do this with all holes for two reasons: first because the limited hand span is not enough to cover the clarinet and second the larger tone holes are too big for normal fingers. Furthermore the keys help to put keys on places where a finger couldn't go easily - this makes it easier for the instrument builder to drill tone holes on optimal places rather than where they can be used based an average player's anatomy.
In order to work properly, a key must
- close the tone-hole completely tight - when closed, no air should go through it
- give as little resistance to the air flow as possible when open - this requires a covered key to be at least a third of the diameter of the tone-hole away
- open and close quickly - that is really quick; and for both directions: One move is done with your finger, usually this is no problem, but then a spring has to put the key back in place as far. Don't forget that some keys open AND close different holes at the same time - and some levers are long! This requires springs to be strong and the axis have as little friction as possible.
Thinking about that, it becomes a challenge to beat a finger when it comes to closing tone holes. Instrument builders at all times have found various ways to reach this target.
The clarinet's key system (this is of course very similar to the oboe's and somewhat similar to the flute's) is an ingenious achievement which improved over hundreds of years. With it you can close and open the tone holes wherever they are quickly and without causing irritating sounds.
- Historical key with felt pad
The first keys, however, were far from perfect and simply a prolongation for the fingers to reach holes to far away; they were metal levers with a piece of felt glued to a square end. This type of key was - of course - never perfectly tight, and obviously only worked when the felt was damp.
The first major step which made the modern clarinet possible was the invention by instrument builder Iwan Müller who invented the "spoon-key". In connection with the sunk key hole he could close big holes nearly perfectly. His design is the one we still use today.
- Different keys and pads with clarinets
The second essential improvement was the ring key H. Klosé. A ring key is a key with an opening - shown on the photo next to the forefinger. With a ring key you can close holes that are in reach of your fingers but since this enhances the diameter of your fingers, the holes can be drilled to the acoustically optimal size (which you could not close with fingers alone).
After this there came numerous steps that you can sum up as mechanical connections between keys that make trills and jumps possible that otherwise would have been very difficult or impossible. However, the key mechanic also adapted to the habit: For example one still grips forks while the key mechanic turns this into an acoustically better result.
In general the key system consists of German silver cast parts. German silver is a copper-base alloy. When long turning keys are made, steel tubes are soldered onto the keys, usually using silver lead. Really expensive instruments have forged keys which are less prone to breaking than cast keys (and then again hand-forged are better than drop-forged, where a huge weight falls onto the metal to forge it into form). Since all these metals can be soldered with silver lead, they can be repaired easily. As a rule, the metal parts are silver-plated, nickel-plated or gilded usually in electroplating baths.
- Silver - the most common - looks nice, but may tarnish, primarily in contact with sweat
- Nickel doesn't tarnish, is durable, glides well, however, can trigger allergies (this is quite frequent!)
- Gold does neither tarnish, is good for gliding, but expensive and looks unusual (difficult when a uniform look of the instruments is required
Leather pads have dominated for hundreds of years, but recently we are seeing a development here. Traditional pads are made of cork, cardboard, felt and leather. Today's material is silicone, tomorrow may bring even completely different materials (e.g. silicone on silicon).
- Leather pad - cut
Leather pads still are dominant today (2008). They are made of a round cardboard plate (in the picture on the left the cardboard is grey) and a felt plate (white) of the same size. Over that the manufacturer draws a thin, soft leather coating or a fish skin (yellow - in reality mostly white). That type of pad can be bought in all sizes even in not so specialised music shops - they are the same for clarinets, saxophones and oboes. What matters is the diameter.
Leather pads do have advantages: They work well, they can be tight, and they tolerate slight imperfections of the key because - when becoming wet - they will adapt to the tone hole again. They are easy to fix on the keys and they can be removed as easily. You use seal wax or hot-melt glue for this. You find a "how to" under Repair / First Aid.
The main problem is that they sound bad when getting too old - the leather then gets brittle. Then, at the latest, you have to change the pad or have them changed. The more frequent a pad gets wet, the sooner this will happen. That means that the pads high up on the clarinet usually have to be replaced more often than the ones down that hardly ever will need that.
Today you will find a lot of pads are made from elastic Silicone, the same stuff that is used to glue tubes to your bathtub or sticks sheet glass together as an aquarium. Silicon has got advantages: It can be brought into every form, is elastic and does not change under humidity. It will last forever (that is: longer than your clarinet) - so it never will have to be changed. One advantage is a disadvantage at the same time: It will not change its form; so if the key is bent, then the pad will not close the hole any more whereas a leather pad will adapt itself. Some musicians think that the tone will be influenced negatively - but serious tests have found out that in the long run the majority of listeners will prefer the sound of a clarinet with silicone pads to one with leather pads (except when the leather pads are new, not much older than a couple of months - since they do degrade quickly). There are two serious disadvantages that silicon pads have:
- since silicon does not stick to anything but silicon you can not easily glue a pad that has fallen out back into place, especially not if this happens just before a concerto. You can, too, glue in special silicon pads with thermo glue - so we can expect to see this become more frequent.
- since silicon does not absorb water, the quantity of water on the clarinet's wooden corpus that is covered by the pad can not evaporate except through the wood. That is it will stay there for a long time. That may cause serious problems for the tone hole if you store your instrument away without having wiped it out fully.
Cork pads are still used where a leather pad would be unpractical - and where you expect a lot of moisture like the duodezime-key on the bass clarinet. Cork is not bad as pad material, easy to repair, easy to handle, but it is not fully elastic - slowly but surely the material becomes and remains compressed. It probably will be fully replaced with silicon in the future.
All the new developments like the silicium resonance pad are acustically superior to any pad that exists today. But they require extremely precise keys that must not be bent easily (because the pads are neither very elastic nor do they adapt) need and sharp and precise inlet key holes. This is not always given with your standard clarinet today.
All keys use springs, either to keep the key open when not pressed or to close it depending on the function of the key.
- Needle spring
- Modern spring key
Technically the springs come in two types: Needle-springs, which are used to turn a key on an axis, where the needle is fixed in the column and a hook at the key; and the sheet spring, which is screwed against the key and presses against the instrument itself. Both work fine, are simple and robust and can be adjusted with simple tools like a screwdriver. If you bend the spring in the direction it is bent, the power of the spring increases and vice versa. This can be done a couple of times, anyway, be careful not to break the spring - even if the needle for the spring is an ordinary needle from a sewing set, you will have a hard time finding a fitting one, you can't bend it into form easily and then you won't be able to fix it in the column without help of an experienced instrument maker (let alone the sheet spring - you won't find that in hardware stores...)
How the keys affect the acoustics and intonation
When the key is open, it would ideally not hinder the stream of air any more at all. It would theoretically be even ideal if the clarinet ended somewhere on the upper edge of the tone hole (it would be sawed off here virtually). But, however, the valve has considerable influence on the flow of air even when it is fully open - that is easily shown: Do open a ring valve by moving your fingertip up for a couple of millimeters and swing the finger up and down. You can hear the effect, but you can still hear it if you do the same more than two centimeters (nearly an inch) away from the opening (no key opens that far). Of course this is true for all keys. The position of the valve has considerable influence on the correct intonation of the instrument. Of course the instrument maker has taken this into account. The tone holes are always drilled further up the instrument (that is towards the mouthpiece) than they would be without this effect. The position of the hole is correct if one considers a key to have a leather pad which has a distance to the hole surface that equals a third of the bore diameter when fully open.
Some thoughts on optimal keys
Jack Brymer has stated in his excellent book (by the way: a "must read") that the key opens in the wrong place. Ideally it would close the tone hole inside at the bore, in order to leave a shining, polished, uninterrupted tube with nothing causing air turbulences. When the tone hole is open, the opening should be as big as possible. The key should open and close the hole in an instance - much like a camera shutter. Since instrument builders and clarinet players are conservative, this is only theoretical thinking, but from time to time you find revolutionaries in this metier.