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Beer Tent The general discussion forum, and the place to start a new "beer-tent-like" Piping Related discussion...

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Old 08-23-2017, 12:26 AM   #1
Tristan_in_Surrey
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Default Boyle's Law and Bag Size

Not sure if this belongs here or not, please feel free to move it if necessary.

I've heard it suggested that larger bags are best for optimal piping and it's got me thinking if the opposite is true.

Boyle's Law states that volume and pressure are inversely proportionate to each other, so by reducing the size of your pipe bag you should be able to increase the pressure inside the bag with the same applied force as with a larger bag. Or put another way, play the same pressure with less applied force, making the instrument more efficient.

Also, does anyone know if there is list anywhere of bag sizes expressed in liters?
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Old 08-23-2017, 01:54 AM   #2
Steve Law
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Default Re: Boyle's Law and Bag Size

Sorry Tristan, misquote of Boyle...

P&V being inversely proprtional only applies to a closed vessel,and the bag has 4 ways out and one way in...and pressure inside depends entirely on your lungs and arm.

If you squeeze hard enough you won't be able to blow any more air in, just eventually stop all the reeds!

Bag size (imho) is much more about personal comfort that any pressure differences...

Sometimes I think we can over-technicate these things...as someone said recently, just blow the thing
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Old 08-23-2017, 01:56 AM   #3
Paul M Burke
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Default Re: Boyle's Law and Bag Size

Surly the aim is constant pressure, with the bag acting only as a reservoir. Ones ability to create and maintain the correct playing pressure I would suggest is the critical factor not the size of the bag.


Paul
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Old 08-23-2017, 06:07 AM   #4
Pppiper
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Default Re: Boyle's Law and Bag Size

As folks have said, I find it's primarily a matter of comfort. If a bag isn't comfortable to the player, then nothing is going to be good.

HOWEVER, as a person who formerly always used very small bags, I've noted that a slightly larger bag seems far easier to maintain consistent sound/pressure. People have suggested larger to me for years, but I'd shrugged it off, seeing as I'm a rather tiny fellow.

I've recently (finally) started playing with a slightly larger bag, and I'm finding that having the larger reservoir of air is quite helpful, in that there's far more leeway for my arm. With the smaller bag, you can't squeeze as long before you've reached a "point of no return," and your blowing won't be able to recover the pressure without a change in your sound.

Since getting the larger bag, the sound is much steadier, and with far less effort. Cutting off though, is an issue now. I'd grown accustomed to a very short squeeze at the end ... this is no longer sufficient with the larger bag.

Just my 2.

Cheers,
~Nate
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Old 08-23-2017, 07:17 AM   #5
Mac an t-Sealgair
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Default Re: Boyle's Law and Bag Size

Quote:
Originally Posted by Pppiper View Post
As folks have said, I find it's primarily a matter of comfort. If a bag isn't comfortable to the player, then nothing is going to be good.

HOWEVER, as a person who formerly always used very small bags, I've noted that a slightly larger bag seems far easier to maintain consistent sound/pressure. People have suggested larger to me for years, but I'd shrugged it off, seeing as I'm a rather tiny fellow.

I've recently (finally) started playing with a slightly larger bag, and I'm finding that having the larger reservoir of air is quite helpful, in that there's far more leeway for my arm. With the smaller bag, you can't squeeze as long before you've reached a "point of no return," and your blowing won't be able to recover the pressure without a change in your sound.
To prove that it is completely subjective, I have done the exact opposite! I've gone down in size, and feel less restrained and hindered by the bag, whilst finding my pipes easier to blow.

Strange!
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Old 08-23-2017, 07:18 AM   #6
Pppiper
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Default Re: Boyle's Law and Bag Size

Quote:
Originally Posted by Mac an t-Sealgair View Post
To prove that it is completely subjective, I have done the exact opposite! I've gone down in size, and feel less restrained and hindered by the bag, whilst finding my pipes easier to blow.

Strange!
Fascinating. Whatever works!
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Old 08-23-2017, 08:28 AM   #7
Tristan_in_Surrey
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Default Re: Boyle's Law and Bag Size

Quote:
Originally Posted by Steve Law View Post
P&V being inversely proprtional only applies to a closed vessel
That was the piece that I was missing. Thanks Steve.
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Old 08-23-2017, 08:46 AM   #8
Nathaniel
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Default Re: Boyle's Law and Bag Size

I think big bags were a fad. Seems these days better-fit is more important. So if you don't feel right or comfortable with a big bag, find a better fitting one.
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Old 08-23-2017, 11:51 AM   #9
jackhawkpiper97
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Default Re: Boyle's Law and Bag Size

One thing that complicates this discussion is the difference in terms of the pipes themselves between pressure and air volume. Multiple reeds set to operate at the same pressure can have wildly different air consumption rates. This explains why some drone reeds are more air volume efficient at certain pressures than others.

In terms of bag volume, once the bag is full, all you are doing is replacing the amount of air lost in an interval of time 1 per that interval of time. So, for air volume efficiency, the size of the bag doesn't matter. For comfort however, bag volume does change how the empty the bag feels when you are at the low spot of air volume in the bag right before you top it up. A small bag will feel like it is more empty at that low spot, because it has less of cache of air to draw from, so size changes air volume-based comfort.

In terms of bag pressure, size does matter. A smaller bag will be a bit easier to get up to playing pressure, because there is a smaller volume of air that is being pressurized (by your arm or by the bag's elasticity itself). A large bag may be difficult to maintain pressure with.

So, proper bag size is where these two ideals overlap, among other choosing factors like shape, player build, environment, and a bunch of other stuff.

With as many variables as there are that affect what the best choice for a bag is for a particular player it's kind of amazing that anybody ever gets a good fitting bag in the first place.

Jack
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Old 08-27-2017, 02:52 AM   #10
PMT
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Default Re: Boyle's Law and Bag Size

The rule is: "you should play the largest bag you are comfortable with". The reasoning is that the larger the surface area in the bag the more it will hold moisture rather than pushing it up your drones, and secondly, any blowing variation will have less effect on sound if you have a larger capacity bag.
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