Leaking pads are the bane of the woodwind players life. The biggest problem by far is the fact that so few players actually understand the nature of the problem - though many are subject to its symptoms.
In many cases the reason is down to assumption - when you buy a new instrument
you assume it works, when you've had an instrument repaired you assume
it works, if a cursory examination reveals nothing untoward you assume
On this page I'll explain the theory behind the action of the pads and show you why and where leaks occur, and how you can test for them. As for how you can remedy those leaks, it will be dealt with at a later date - it's quite a lengthy topic.
To some degree I've simplified the topic in order to better impart a
basic understanding of the principles of the operation of the pad - there
are many other factors that could be involved (not the least of which
in the action) which I might cover at a later date.
You'll need a 'test feeler' for this. There are two common options; Lightweight
cigarette papers (such as Rizla Blue) or the cellophane wrapping from
a cigarette packet. Many foodstuffs come in boxes sealed with thin cellophane
- so if you don't fancy buying cigarette papers or 20 Marlboro, get yourself
a box of chocolates.
On to the theory then...
we see a diagram of a basic key cup and its corresponding tone hole -
minus the pad. The pad sits in the cup, and part of its thickness normally
extends beyond the rim of the cup.
Here's the same arrangement with a pad in place. As you can see - the cup is square on the tone hole, the pad is too and covers the tone hole evenly all the way round. You can think of this pad as being of the 'Optimum Thickness'.
You can see perhaps that the thickness of the pad is critical. Bear in mind that the key cups are pivoted some way back down the key arm, so as the cups rise and fall they do so at an angle to the tone hole...and not straight up or down.
Take a look at this example. Same cup, same tone hole - but this time a thicker pad has been fitted. Because it's thicker than the Optimum Thickness required the rear of the pad contacts the tone hole before the front does. In other words, the cup doesn't come down square...and nor does the pad.
This example is the exact opposite, the pad is thinner than the Optimum Thickness, so the cup is allowed to travel beyond level - resulting in the front of the pad contacting first whilst leaving a gap at the back.
All good and well, and hopefully quite clear. But (and there's always a but) there are times when, for a variety of reasons, it isn't possible for the cup to come down square on the tone hole (or it's just plain too much trouble for the manufacturer or repairer to correct the angle). In these instance it's the pad that takes up the angle, like so...
you can see that although the pad is sitting in the cup at a slight angle,
it's still covering the tone hole perfectly. This is typically done by
backing up the pad with card.
So that's HOW pads leak...as for the why, well, there are a number of
Sometimes this phenomenon happens 'in reverse' - the pad is too thin to start with and as it expands it pushes up at the front of the cup leaving a leak at the rear.
A few other reasons for leaky pads include damage to the bodywork and tone holes/keywork, a bad repair/manufacturing job...or just plain fair wear and tear of the pads.
So let's get down to business.
your home-made feeler in action!
The manner in which the cup is brought down is worthy of mention. If
you press it down hard then you'll be imparting far more force to the
cup than you could ever exert in normal playing - so aim to bring the
cup down with the same pressure you'd normally apply in playing...or lighter,
if you want to test more critically.
Chances are you'll find that it only slightly grips at the front of the
pad, and practically tears your feeler in half at the rear. Replace the
feeler if it gets all scrunched up.
If you DO find a difference then it's a fair bet that there's a leak
there - or at least the potential for one. It might take you a while to
get your hand in, some pads bite down differently to others and it takes
a while to get a feel of what's likely to be a problem or not.
The real nail-biter is when the pad fails to grip the feeler at all. Congratulations...you've found a big leak!