This page has been written to supplement the review of the Keilwerth SX90R series saxophone, but has been placed in this section of the site as it contains information that's applicable to most woodwind instruments.

If you're not an SX90R owner, or prospective owner, simply ignore lower section of this article.
To skip the technical briefing and go to the details on the SX90R, click here.

Of all the problems that woodwind instruments are subject to, the warped tone hole is perhaps the least easiest to spot.
This is probably because, to the average observer, there's very little to see - and to a large degree there's always an expectation that instruments are manufactured to a certain standard that precludes there being a fault with the bodywork.
Sadly, warped tone holes are far more common a problem than you'd believe.

In order to better explain the nature of the issue it's worth examining the mechanics of the problem.
There are three components in play - the tone hole, the pad and the key cup that houses the pad.

Here's a drawing of the three components as you'd typically see them, with the pad fixed in the cup, and the key resting on the tone hole.
If you've read the article on testing for leaky pads you'll know that in order for the pad to achieve a solid and reliable seal it's important that both the tone hole rim and the pad cup are flat. This allows the pad to do its job properly.
It's worth stating at this point that the pad is NOT designed to take up major discrepancies in the flatness of the tone hole or the key cup, it's designed to sit in a flat cup and seal against a flat surface with the minimum amount of compression.
The fact that it often can take up such discrepancies ( at least for a period of time ) is the reason that warped tone holes can be hard to spot...until the pad loses its flexibility.

The pad itself is of a very simple construction. The heart of the pad is a disc of woven felt, typically 5 or so millimetres thick. This is backed by a stiff card or plastic disc that's a few millimetres smaller in diameter, and the whole thing is enclosed in thin skin ( typically leather, in the case of saxes ).
Some pads include a disc of polythene between the leather and the felt, to prevent waterlogging.
There's nearly always a reflector ( also known as a resonator ) fitted too - this serves to lessen the amount of soft ( and thus potentially sound-absorbing ) surface area that presents itself to the bore of the instrument, and it also serves to prevent the pad from bulging in the middle. Small pads, and some fitted to vintage horns have just a simple rivet fitted to them.

Woven felt is an ideal material for the core of a pad. It exhibits a balance between being soft and flexible enough to accommodate an impression ( the seat itself ), being firm enough to resist distortion through face-on compression, being durable enough to cope with dampness and drying out and being quiet in operation. Quite impressive!

Where it fails is when it has to cope with a warp in either the tone hole or the key cup.
A new pad has a degree of elasticity built in. The fibres of the new felt are fresh and springy ( it's this very quality that we take advantage of when we seat a pad ), and with the application of a little heat a lasting impression can be formed on the surface of the felt ( it's very much like ironing a crease in a pair of trousers ). But felt is quite a dense material - in order for that new impression to be maintained it must be subject to equal compression for a time, or the fibres will expand again and the seat will be lost.
A well seated pad should not have been subjected to too much compression - it tends to be an unreliable method - but manufacturers often use this technique as it's fast, but it then relies on the instrument being used regularly to 'enforce' the seat.
This is why new instruments are fitted with bits of cork to keep the pads pressed against the tone holes in storage - without these corks the pads may swell ( or 'blow' ), resulting in leaks.
You can see on the drawing above that the pad sits dead flat against the tone hole. As the key is pushed down against the hole the pad distributes the force evenly all the way around the seal.

Here we see a pad sitting against a warped tone hole. The dark crescent represents the warp, and also a leak due to the failure of the pad to accommodate the dip in the tone hole. Clearly this is not a good thing, and steps need to be taken to remedy the discrepancy.

There are two options typically available to the repairer.
The first, and most 'correct', is to level the tone hole. This can be done in two ways - either from beneath, by raising the bore under the warp and thus the rim of the tone hole, or by filing the rim of the tone hole level. In practice both methods are used, though astute repairers will try to limit any necessary filing to a light dressing of the rim - it's not wise to remove metal from the body of the instrument if it can be helped.
It's often the case that a tone hole gets its warp through a dent in the body close by the hole - as the metal gets pushed in it drags the tone hole down with it. The most common example of this is where a saxophone gets dropped on its bell. The brace gets pushed into the body and the resulting dent often warps the G# and Aux.F tone holes. By removing the dent you also remove most, if not all, of the warp. A light filing of the tone hole rim is now appropriate, just to ensure perfect flatness.

The other option is to duplicate the warp in either the pad or the cup.
Knocking a corresponding dip in the key cup is not exactly going to make your horn look terribly attractive, nor is it a very reliable means of correcting the anomaly - and yet I've seen a great many horns that have had cups bashed to compensate for dodgy tone holes. Having said that, I have to admit to having used the technique myself - but only on a horn that was so cheap and nasty that it wasn't worth spending a fiver on.
What typically happens is that a repairer replaces a pad over a warped tone hole, which appears to seat. The next day, when the pad has fully cooled, and contracted slightly, a leak appears over the warp. The repairer groans, but can't be bothered to remove the warp or adjust the pad, so takes a hide mallet and give the cup a couple of knocks. This bashes a dip in the cup over the warp, which reinstates the seal...for the time being.

The proper way to duplicate the warp is to back the pad up.
This is done by inserting shims behind the pad. When the pad is glued into the cup it distorts itself over the backing, which shows as a corresponding bulge in the face of the pad.
Sounds simple enough, but it's a tad more complicated that just bunging a bit of cardboard in the cup...you have to build it up in stepped layers, and it often has a knock-on effect to the rest of the seat, which you must then correct...which then has a knock-on effect on the bit you've backed up...and so on.

There are a couple of problems with this fix though.
In the first instance, and assuming a new pad is fitted, great care must be taken to ensure that the pad is subject to even compression.
Believe me, it's very tempting to take up that last little bit of leakage by pressing the pad down hard against the tone hole. It works, because the new felt has some elasticity in it - but it also fails for precisely the same reason.
Once the compression is removed, the felt relaxes and tries to even out the internal stresses - and once it's done so it will leak. Depending on how hard the pad was compressed, this can take as little as a day or as much as a couple of months.
It's precisely the reason that a great many brand new instruments suffer with leaking pads.

In the second instance the pad simply gets old. The felt shrinks both in diameter and thickness, and the leather hardens.
If the pad was seated in a level cup against a level tone hole there shouldn't be too much of a problem - the shrinkage would be spread out evenly, with no critical discrepancies in the cup or the tone hole to take into account.
But where those discrepancies exist, the pad will fail - and in the case of backed up pads the leak tends to appear to the sides of the apex of the rise.

What must be borne in mind too are the ratios involved. Pads aren't really that large, so even a slight warp in a tone hole can affect as much as quarter of the diameter of the pad...perhaps more. That represents a very significant amount of the pad's surface area.

So we've seen how it's possible to remedy the warped tone hole - but there's one snake in the grass waiting to catch us out...the rolled tone hole.

As you can see from the drawing, a rolled tone hole has its lip turned over on itself. It's a remarkable technique, and the reason for its use is that it perhaps looks rather nice and also increases both the strength of the tone hole and the surface area of the lip that comes into contact with the pad. These last two are also its drawbacks - damage to rolled tone holes is very difficult to repair, and the larger contact area increases the problem of sticking pads.
There's still much debate as to whether a rolled tone hole provides a better seat - but essentially the physics boil down to an increase in surface contact versus an increase in pressure at the seat on a standard tone hole.

Filing a rolled tone hole is something to be avoided at all costs. First of all you run the risk of removing so much metal that you break through the roll ( which is nasty ). It also means that you cannot level a rolled hole solely by filing it - it MUST be levelled from beneath. Any uneven filing of the rim will result in an uneven surface area as the file cuts some areas of the lip and not others.
It follows then that a warped rolled tone hole is far more of a problem than a standard one.

And so to the Keilwerth SX90R.

As mentioned in the review, this instrument has a hybrid tone hole...what I like to call a 'pseudo rolled tone hole'. It's simply a standard straight tone hole with a ring soldered onto it.
It's not a bad idea really - it must surely be cheaper to manufacture than a proper rolled hole, and it provides the horn with any such advantages of a rolled hole without the corresponding drawbacks when it comes to having to level them - all bar the issue of uneven surface area.

The problem with these horns appears to be warped tone holes - built in at the factory.
I have so far seen at least fourteen individual horns, and to date all of them have exhibited at least two ( the twelfth only one, the thirteenth at least four ) warped tone holes.
It seems to be confined to the lower end of the instrument, typically from the low D tone hole down. It's entirely possible that the problem exists throughout the horn, but the decrease in the size of the tone holes would naturally make the problem less severe, and more difficult to detect.

And detection can be difficult.
I myself have examined SX90Rs and declared the tone holes to be visually fine - only to find there's a problem when they're checked against a standard.

Here's just such an example - only minutes before this picture was taken I declared this tone hole to be fine. I subsequently placed a ground stock against it which proved otherwise.
If you look dead centre of the photo you can quite clearly see the black line that marks out the contact point between the ground stock standard and the tone hole rim. Follow it to the right and you can see where the line breaks, ending in a gap of about a millimetre.
What you can't see is how far the gap extends to the rear of the tone hole.
This in itself is quite a significant warp - but follow the line to the left, and you can just about see another break on the other side of the tone hole. This is a double warp, and it's quite obvious from even this simple picture that the tone hole is very far from level.
If I were to remove the standard and show just the tone hole itself you'd be extremely hard put to notice it was out of level. This is by no means the worst example I've seen either.
If someone assures you their SX90R doesn't suffer from this problem - ask them how they checked!

So what are the implications here?
Well, firstly, this is a manufacturing defect. As mentioned earlier, the correct way to remove a warp is to knock it out from inside the bore. This assumes, of course, that there's a corresponding dent in the bore that has caused the warp.
If not ( which is hopefully the case with a new instrument! ), then what you're effectively trying to do is knock a reverse dent in the instrument.

So it's the file then - but you have to take into account the wide rim of the hole. You can see from the photo that you'd have to remove a considerable amount of metal to bring the front ( and rear ) portion of the hole down to match the drop at the edges.
Both techniques have to be weighed against the fact that this is a new instrument - the faults are there from new, though the example shown above was built in 2000 - you'd hardly expect, or want, to attack a brand new horn in such a fashion.
Not only that, but these are expensive instruments - this particular one cost over £2000. Had it cost £500 you might be inclined to put it down to cost-cutting in manufacture.
You could, of course, unsolder the ring, level it ( or the tone hole ) off and resolder it - but that wouldn't do much for the finish of the horn!

So the only realistic option is to back up the pads.
This is fine, it will deal with the problem at least for a time - though you cannot expect such pads to give as reliable and lasting a seat as those that are seated against flat tone holes. That's definitely something to bear in mind with a horn that's supposed to be able to withstand the rigours of professional use.
Furthermore, there's the expense of having such repairs carried out. In the case of a double warp it's a lot of fiddly work, which takes time, and will cost you dearly.

I have corresponded with Keilwerth about this issue.
Keilwerth tell me they know of no such problem, in spite of my having furnished them with serial numbers of affected horns.
I have also been informed by the manufacturers that any such discrepancies ( hang on, didn't they just say there weren't any? ) will be accommodated by the flexibility in the pad.
Well yes, it will - up to a point, and at a cost.

The horn with the tone hole shown above was brought to me by a chap who took up my public offer to examine any SX90R free of charge. As far as he was concerned the horn played just fine.
And yes, it did - but I was able to demonstrate to him that his definition of 'fine' wasn't on a par with the price of the instrument. A great deal of it being 'fine' relied on excessive finger pressure to compensate for the anomalies in the pad seat.
It works OK if you bash your way down the scale with a good, hard grip on the keys...but a £2000 horn is supposed to be built so that your fingers can fly over the keys. It was entirely possible for me to hit a low Bb, and then sneak the finger pressure up a notch and demonstrate the lift in tone. It was clearly audible.
Not only that, but during fast passages the lower notes sometimes failed altogether - and given that the most common use of the low notes involves the use of subtone, this represents a very serious problem for anyone who knows their way around a horn.
Exactly the sort of player who might buy a £2000 horn, wouldn't you say?

So far, the problem extends to 100%* of the SX90R horns I've examined. Granted, that's not many horns ( yet ) - but top-end horns tend to be thin on the ground, and I simply can't believe that its purely down to coincidence that all the examples I've seen have been 'rogues'.
Sure, one maybe - two at a pinch - at three I'd start to worry....

* As of Nov.05 I've seen one SX90R with level tone holes - you can read the review here.

So why this page?
Well, I don't have an axe to grind - I don't own an SX90R ( I even quite like them ), I'm just stating what I see on the basis that people with £2000+ to spend on a horn are entitled to know what they might get for their money.
I have tried to alert the manufacturers to a problem, but that doesn't seem to have gone down very well ( though they did offer to show me round the factory - but then what would that prove? ).
They may well consider the issue to be a minor one. As a player and a repairer I strongly disagree. This page exists to explain the nature of the problem, its implications and its solutions - it's up to you what you choose to do with the information.

If you own a Keilwerth SX90R series horn and are concerned or curious as to whether your horn suffers from warped tone holes, you are invited to bring it along to the workshop for a free inspection. In the course of the inspection I shall examine and test the instrument and take photographs as necessary, whereafter they will be added to the rolling reviews ( good or bad! ).
There will be no charge for this, and in return for your time I will carry out a setup and lubrication job on your sax free of charge.