 The Clarinet BBoard
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Author: David Lee
Date: 2006-07-25 17:57
Both upper and lower sections of my wood clarinet pass a pressure test, but fail vacuum within a second. The leak is large enough that I have to keep inhaling to maintain the vacuum. I have not been able to locate the point of failure as yet on either section. My inclination is to ignore the issue as pressure is what operates the clarinet, on the other hand I have some nagging doubts that I should track it down. I am not experiencing any obvious playing problems. Should I ignore the vacuum test?
I am looking for a good way to detect the vacuum leak point, and would appreciate suggestions.
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Author: Chris P
Date: 2006-07-25 18:12
What make of clarinet is it and what kind of pads has it got?
A bit time consuming, but one way if finding the leak is to test each joint and pad individually - take all the keys off, block all the toneholes and the remaining open end with Blu-Tack or similar and test the joint to see if it leaks, if the joints are airtight then test each pad by only fitting one key at a time.
Check the thumb bush and speaker bush for leaks as well, and if you have metal tipped tenons, these could be slightly loose or not fitting well (they may be tight, but air can still escape between the metal tip and the tenon) and leak air when pressure/vacuum testing - but they won't compromise the performance of the clarinet.
And check that the pillar threads or any parts screwed into the joints aren't leaking air through open vessels that could be entering the bore, or small splits in the tenons at the shoulder that could run up the joints and under pillars, screw holes, toneholes or the speaker bush.
Former oboe finisher
Howarth of London
1998 - 2010
The opinions I express are my own.
Post Edited (2006-07-25 18:16)
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Author: Paul Aviles
Date: 2006-07-25 18:16
Vacuum IS the indicator for a good clarinet seal. I had a nasty one to track down recently that turned out to be a split in the pad along the seat crease. My problem pad was the one between left hand 1st and 2nd finger.
The solution to finding it?
When ALL else fails, remove all the keys from the horn, tape all the holes (plastic tape, duck tape), make sure you get a seal (a crack in the horn would be your only problem at this point), now start putting keys on one at a time from the top (of course, removing the tape to the corresponding hole) - vacuum test after each one.
This works.
................Paul Aviles
.........sorry Chris, must have read your mind!
Post Edited (2006-07-25 18:18)
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Author: Alseg
Date: 2006-07-25 18:23
How important is a perfect suction test?
I have heard some differing opinions.
The conventional wisdom is that everything must be tight on vacuum testing.
Another well known tech. told me this:
"Vacuum leakage is NOT a good test of leakage that occurs when blowing."
This view states that the suction test is overated, and that a small (emphasis on small) amount of ++suction++ leakage correlates with some increased resistance on blowing, and "can be beneficial. "
Comments???
Former creator of CUSTOM CLARINET TUNING BARRELS by DR. ALLAN SEGAL
-Where the Sound Matters Most(tm)-
Post Edited (2006-07-25 18:27)
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Author: Chris P
Date: 2006-07-25 18:25
If you want to see where the leak is, block up all the toneholes and free end of the joint, have the bung fitted with the air line in one end and immerse the joint in water, blow into the air line or use a bicycle pump for more pressure and watch for the bubbles.
I remember working on an oboe that was leaking like a sieve (the top joint) even though the pads were all seating perfectly, but the wood was porous and bubbles were coming through the sides of the toneholes through vessels into pillar threads and the tonehole bed places (the countersunk part below where the pad seats). So to get it all airtight I put thin superglue at all the points that the bubbles came from and sucked it into to wood. After cleaning up the excess glue the joint was airtight.
Former oboe finisher
Howarth of London
1998 - 2010
The opinions I express are my own.
Post Edited (2006-07-25 18:26)
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Author: David Lee
Date: 2006-07-25 18:33
The clarinet is an Buffet R13. The pads are fish skin except for the octave key which is cork.
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Author: Paul Aviles
Date: 2006-07-25 18:47
Dear Alseg,
My experience only (your mileage may vary) has been that you feel the difference in horn with a vacuum test like a coke bottle and one that does not in how strong the sound is on the sealed horn. Also the change from note to note becomes that much more clear (then it is up to you as a musician to decide what style to use note to note).
My caveat is that springs on pads that need to be held DOWN might be too weak (although the reverse is MUCH more common) and then you will only detect the deficiency on a "pressure" test. Caveat #2 - I had a brass technician offer a pressure test on my clarinet and adjusted the A key to the point where only Arnold Schwarzenegger could have played my horn. This is where the artistry of key work adjustments come in to play.
..............Paul Aviles
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Author: Chris P
Date: 2006-07-25 20:00
Like a lot of wooden clarinets from every maker, R13 clarinets do have (natural) minute imperfections on their tonehole bedplaces - mainly vessels running across the seating area causing leaks. One or two affected ones will cause a minor leak, though times this by the amount of toneholes on a single clarinet and it all mounts up to a joint which will never be airtight unless all the imperfections ae dealt with.
And as it's an R13, the cost of putting this right (which involves filling and recutting all the bedplaces) is going to be more than the finishers are paid, and if the finishers were paid more to sort this out as well as finish the instrument you'd end up paying a lot more for a new R13 - probably nearer the cost of a Prestige due to the time spent getting them perfect.
Though if you choose to have it overhauled, this work can be carried out at the same time - and obviously the cost of the overhaul will be high as well, but it's well worth it for a clarinet that will be more responsive afterwards.
Padding of any kind is only successful if the tonehole bedplaces the pads seat onto are perfect. You can have a pad seating on an imperfect tonehole - it may test well using a feeler gauge, but will fail using a suction or pressure test as feeler gauges won't account for any vessels.
Former oboe finisher
Howarth of London
1998 - 2010
The opinions I express are my own.
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Author: Gordon (NZ)
Date: 2006-07-28 14:30
1. One post suggested that there was only pressure inside the bore. As far as I am aware, there standing wave consists of regions in the bore where there are rapid changes of pressure, oscillating form above atmospheric to below atmospheric.
2. When we blow, we cannot blow too hard or we blow open the pads that are sprung closed. (Actually I don't blow, but do a low pressure squirt of air from the mouth - lungs not involved. Then I can more easily detect air escaping form the mouth cavity.)
On the other hand, when we suck, we usually do it by dragging back the tongue quite strongly.
My point is that our blow is of necessity, quite a lot weaker than our suck, so the latter is more likely to detect minute leaks from timber porosity (eg through that thin timber at the top of tone holes, especially the chimneyed ones associated with ring keys, around poorly glued tone hole inserts, grain grooves across tone hole edges as Chris covered, porous leather pads, and even along fingerprint grooves, etc.
3. I think it is easier to suck air than to blow it, through minute holes. I don't know how to explain this in scientific terms but perhaps the following illustration will suffice.
Consider a classroom with rows of desks that represent the structure of the timber. Now introduce a lot of people moving about between the desks - as many people as possible. They represent the air molecules in the timber. Surely it is easier to DRAG people out via an open door on one side of the room, than it is to make them exit that door by pushing more people into a door on the other side of the room..... Well, something like that.
4. The difference between sucking and blowing COULD also involve something like the osmosis principle working. The timber is the membrane, and the air inside the timber (especially boreside) contains moisture particles, representing the more concentrated solution in an osmosis demonstration. The air outside the clarinet does not have this moisture and represents the less concentrated solution. The larger particles of water act like a valve blocking the timber pores, so that air passes More easily through the timber from outside to inside (i.e. the suck) than vice versa.
These are just ponderings I have had in an attempt to explain the phenomenon that I have often noted.
5. I think I once read from somebody from the Fox bassoon company, that when players compared airtight bassoons with ones that had porosity in the pads or timber, the players preferred the non-airtight bassoons.
Whether this is relevant to clarinet I don't know, but perhaps backs up questions asked in other posts. Personally, I try to make clarinets airtight, because I think it improves response.
6. Somebody mentioned putting the instrument under water for a leak test that identified location of leaks. An alternative, not so effective, but at least it does not drench the keywork and run the risk of rust, is to close the keys and bung the end, and fill the 1/2-body with water. Then blow into it for a while and empty it. Now blow for a while again. A little water can be forced through the leak, then air follows the water, and bubbles, so that a second person can track the leak using sight and sound.
7. Often the cause of small leaks is one or more faulty bladder pads, which have a substandard, porous membrane. IMO this would be quite likely for Buffet, seeing the quality of pad they are using is way below what it used to be a few decades ago. The method in 4 quite easily identifies such pads. During the test they become waterlogged, and even if this is not visible, showing up as an increased translucency, when you squeeze such a water logged pad closed, water oozes out of it.
8. Some flute technicians use a "magnehelic" to detect leaks. The bore is progressively isolate while a machine does much the same as a blow test, showing the results on a the dial of a meter. So far, I don't know if these are being used by any technicians on clarinets.
For the gadget, see the bottom of http://users.cvip.net/~js210/fpad.html
For the process, see http://www.langemusic.com/Articles/padding.htm
For the
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Author: Chris P
Date: 2006-07-28 15:20
"6. Somebody mentioned putting the instrument under water for a leak test that identified location of leaks. An alternative, not so effective, but at least it does not drench the keywork and run the risk of rust..."
I did mean to say submerge the suspect joint without any keywork or springs on it, but with all the holes bunged up to see where the leaks are.
Former oboe finisher
Howarth of London
1998 - 2010
The opinions I express are my own.
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