bag design and chanter tuning

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bag design and chanter tuning

Postby Dally » Tue Nov 01, 2011 5:52 pm

Andy's post about the low F# tuning on his Clough chanter reminded me that I'd heard from a friend that Robbie Greensitt said that the design of the neck of the bag as well as the size of the bore allowing air in to vibrate the chanter reed affected the tuning and tone of the chanter. True?
I make two style of bags, one glued/stitched and the other double glued. The advantage, or so I thought, with the double glued bag is that you can cut the neck to fit the length of your reach. But does it throw the tuning off?
What is the "perfect" bag design (pattern)?
thanks
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Re: bag design and chanter tuning

Postby Richard Evans » Thu Nov 03, 2011 7:53 pm

In my experience, the neck length can affect the tuning. In one specific case a customer bought a new bag with a longer neck and then reported top B out of tune- flat. He called in and I was at a loss until I thought of putting a cotton wool plug in the top of the chanter stock- problem solved. It can also affect the stability of some notes, a bit like the cotton wool plug in the bottom of the chanter.

Cheers
Richard

PS Whilst typing this I did something or other and the flashing caret which shows where you are typing has vanished! Any ideas? Makes editing difficult.
PPS Now it's back! ???
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Re: bag design and chanter tuning

Postby Dally » Fri Nov 04, 2011 6:53 pm

Thank you very much, Richard. Is there concensus on the best design?
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Re: bag design and chanter tuning

Postby Richard Evans » Sat Nov 05, 2011 12:08 pm

Dally wrote:Thank you very much, Richard. Is there concensus on the best design?


Jackie Boyce makes bags for a lot of pipe makers and lists the dimensions on his website:

http://www.pipebagmaker.com/

Cheers
Richard
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Re: bag design and chanter tuning

Postby Dally » Mon Nov 07, 2011 4:56 am

Thanks, Richard. Interesting because there doesn't seem to be any difference among the various NSP makers listed, but maybe the finer details are lost on me.
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Re: bag design and chanter tuning

Postby Barry Say » Mon Nov 07, 2011 9:18 am

I do not believe the bag shape has any significant acoustic effect, but I think the bag texture is important. The reason why it is important is that it influences the shape of the air passage between the main reservoir of the bag and the chanter. If the leather of the bag is stiff, this can induce 'choke points' in the neck starving the chanter of air.

In former times, let us say the 1950s and 60s a rather square shaped bag was the norm, possibly under the impression that smallpipes should have a small bag. to compound the problems associated with this shape, the blowpipe stock was often set very close to the drone stock so that the blowpipe and drones were forced to be nearly parallel, bringing the drones down onto the right arm of the player. Many players find this very low position unsatisfactory. My bag shape came from Colin Ross who has attributed the 'sausage-shaped' bag design to David Burleigh.

Some years ago (1990s) when Monday meetings at the chantry included a cabal of pipemakers at the back of the room for the first half of the meeting, Colin Ross would offer pipe-fettling and advice free of charge. During this time there was a spate of 'neck-resonance'. A member's chanter which was apparently out of tune would play perfectly well with the same reed when fitted to another bag. This only happened when the the total length of the chanter stock was longer than that which Colin was accustomed to using (3"). His cure was to shorten the chanter stock to 3". This included both parts, when the pipes had a split-stock. To the best of my knowledge this always worked and I adopted this principle when fitting split stocks.

However, this problem seems to have largely disappeared and I for one have relaxed my attitude to the 3" rule, but I don't think I would go as far as 4". My current opinion is that such problems are a combination of bag shape and texture, reed design and chanter stock design including the shape of the internal cavity of the chanter stock. It is a complex situation, but thankfullly less common than it once was , for whatever reason.

Barry
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Re: bag design and chanter tuning

Postby Richard York » Mon Nov 07, 2011 7:58 pm

Then there's the tear-drop shaped bag as practised by Dave Shaw.
For playing his higher-pressure G pipes I find it more comfortable, though that's maybe because I'm also used to that shape on my renaissance style open ended pipes.
I note that in pretty well all the historical pipes paintings I've seen it's tear-dropped shaped.
Interestingly, it's so on a rather heroically poised French musette player (noble, or even royal, I forget which) in a painting of the 18th century.
Sorry, I can't place subject or artist just now, but it's fairly well-known, and is of course one of our relations, however heretical this shape may be in present company!
Best wishes,
Richard.
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Re: bag design and chanter tuning

Postby pipemakermike » Tue Nov 08, 2011 11:38 am

Over the years I have played a lot with the problems of bag neck induced problems. Back in 1980 when I made my first proper keyed set I found that the tuning of the chanter depended on how the neck of the bag folded and I spent some time chasing a tuning problem by tweaking the finger holes and it took some time to recognise that the tuning was being effected by how the neck of the bag folded. I spent some time talking about this problem to one of the acoustic experts at the design company I was working at and also with Greg Smith (AKA Reg Thimms) and we tried a number of things culminating with the addition of a 16mm thick piece of acoustic foam tucked into the neck behind the tied in stock. This cured the immediate problem and appeared to insulate the chanter tuning from the influence of the neck shape.

When I started using Ross style removable chanter stocks I had a repeat of the problem when moving a chanter into a different bag and so I moved the plug of acoustic foam from the neck of the bag and into the end of the stock where it also protected the reed when the chanter wasn't plugged into a bag. This seems to have significantly reduced the problem.

Another change I made at around this time was to increase the internal bore of the chanter stock by 2mm to give the reed more space. This was done initally to make inserting the chanter into the stock less risky and to make sure that the corners of the reed didn't scrape on the sides of the stock but I think that it might also make the reed less sensitive to internal reflections.

Some years ago I fitted a microphone into a chanter stock to see if it would be a way of amplifying the chanter without the problems of using a normal freestanding microphone. The result was rather strange - the microphone picked up all sorts of other resonences probably from the bag. I could hear the drones, the chanter reed and some other sounds so it was not a solution to anything just a new problem.

Another interesting piece of evidence of the interaction of the chanter stock with the tuning was the experiement to fit a switch to the chanter stock for Kathryn. It worked fine but introduced some subtle tuning/tone change that Kathryn didn't like so we didn't pursue it. I guess that the change to the internal geometry of the stock was to blame.
Attachments
image001.jpg
prototype chanter switch 2006
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Last edited by pipemakermike on Tue Nov 08, 2011 10:26 pm, edited 2 times in total.
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Re: bag design and chanter tuning

Postby Barry Say » Tue Nov 08, 2011 12:15 pm

Richard York wrote:... I find it more comfortable, though that's maybe because I'm also used to ......


I think this is true of many aspects of Northumbrian piping.

I have tried the 'renaissance' method and it works OK but I think it is potentially limiting and the 'concensus' from old photographs seems to be that the bag should be at the side of the player, well up under the arm.

My personal opinion is that the player should apply pressure to the bag with the left upper arm and operate the bellows with the right upper arm. The forearms have no function except supporting the wrists and hands in the correct position to play the chanter. Ideally, I think the left forearm should not touch the bag. This gives the player more freedom to adjust the chanter position and the hand positions.

The bag must be the correct size for the player so that it fits comfortably under the armpit when almost fully inflated. At this point, the weight of the player's arm is almost sufficient to provide the required pressure. as the bag deflates, the player has to put more effort into squeezing the bag. This increase in effort signals the right arm to provide more air from the bellows. Thus, the player keeps the bag sufficiently full with a minimum expenditure of mental and physical effort.

SimpleS

Barry
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Re: bag design and chanter tuning

Postby iain allen » Tue Nov 08, 2011 10:39 pm

For the last few years I've been helping a local ssp maker with his pipes and we came across the problem of bag design, neck shape and material.

When he supplied bellows blown pipes he used a hide bag and everything was fine tuning wise but when he sold a set of mouth blown pipes he used a synthetic bag with a zipper. This is where the problems started,when the pipes were fitted with synthetic bags the top hand would go wildly out of tune, everything was identical to the bellows blown pipes the only difference being the bag. The problem was solved with a tube inserted in the neck of the bag.

Never had a problem with the hide bags apart from the time a chanter stock was poorly positioned and tied in.

This doesn't help much with bag design the problem we experienced was due to the neck of the bag and resonance within.


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