Hollow main-stock

[Jim McGuire]

This thread reminds me of the time that I tried to order a pint of Guinness at the Eoin O'Riabhaigh's local - no one understood me, including Eoin - I cleared my throat, regrouped, and ordered a Murphy's - just like all of the signs in the pub (and enjoyed it!).

[Joseph E. Smith]

.... who's on first?

[Jim McGuire]

Hollow vs regular stock- straight bass drone or turned - straight bass reg or turned - 'flat' vs concert pitch - ebony vs boxwood - popping valve or no - piper's apron up or down - main bag inside out or normal (this is a new one for me) - treat the cane or not - metal top vs wooden top.

[Patrick D'Arcy]

Hairy or shaven?

How could you have forgotten that one?

Paaaaaatrick.

[pudinka]

paper or plastic?

Bill - to try and clarify with regard to your comments:

1. the back of the stock is not open (but more or less as you described) but since the air does flow through small holes it does not seem impossible that this path might serve to transmit vibrations back into the bag. how these drones "couple" to begin with, i do not really know but would suspect that it has also to do with the sound going out of the other end of the drone. are the tounges vibrating together at octave intervals simply because the drones are so tuned - forced into these shapes? couldn't the hollow stock just be acting like more of a resonator for the buzzing tounges? i'm just askin'.

2. i don't think i imagined the differnce in the "feel" of the bags when the skin-side was reversed...but i could have. it felt like a deep rumble - like an angry, growling cat restrained under my left arm when the drones were out of tune. but i wouldn't think a chicken could run too far without its head and if i hadn't seen it happen with my own eyes as a child i likely wouldn't believe it now, unless i'd not seen it myself. i guess i need to make another bag, with the skin-side in, and see how it feels, and how it sounds or maybe consult with a chicken.

3. the stock on this set was made with a solid delrin plug at the front and the back, with a brass tube holding them together so there is maybe 2-3 inches of "chamber" between them. the two regulators have thier own tubes that go right through to the back/bag and the bass air supply is through one of these within - a hole in the wall. each drone is in a similar tube but stop short and each has its own supply vent, collected/covered by the stop plate. each of these tubes has a hole to the chamber between the two plugs. if the size of these holes affects the "coupling" (insert virgin joke here) i do not know, but how large does the hole have to be to allow air/vibration through?...same concept again...where do opinions stop and physical laws begin? i'd think brass might transmit sound at least as well as a thin layer of wood if that is in question. i asked the maker where he came up with the design, but he is dead and has not gotten back to me thus far.

[glands]

Hairy or shaven?

How could you have forgotten that one?

I gotta stop sending Father d'Arcy jokes by e-mail!!!! I've poisoned his mind...uh...maybe he just thinks like me anyways!

[billh]

Bill - to try and clarify with regard to your comments:

1. the back of the stock is not open (but more or less as you described) but since the air does flow through small holes it does not seem impossible that this path might serve to transmit vibrations back into the bag. how these drones "couple" to begin with, i do not really know but would suspect that it has also to do with the sound going out of the other end of the drone. are the tounges vibrating together at octave intervals simply because the drones are so tuned - forced into these shapes? couldn't the hollow stock just be acting like more of a resonator for the buzzing tounges? i'm just askin'.

You're right that even very tiny holes transmit and/or interfere with vibrations; otherwise slight finger leaks wouldn't cause the squeaks and squawks they do. But smaller holes transmit vibrations much less efficiently, among other things small holes mean more "damping", i.e. the interactions between the air columns connected by small tubes act as though they are connected by something both "stretchy" and resistive.

For a physical analog, you might think of two pendulums (pendula?) connected with some kind of cord. A thick cord means that the movement of one strongly affects the other; a thin elastic would greatly reduce the amount of "pull" that one has on the other.

There's a physical phenomenon called "phase locking" which means that if two or more objects are undergoing repetitive motion in approximate frequency multiples of one another, if there is any connection between them there is a tendancy for the objects to fall into lock step with one another. This by the way explains the otherwise unlikely observation that Earth's moon is rotating around its axis at exactly the same speed as its revolution about the earth, and thus always points the same side towards us.

In solid stocks, there are of course connections between drone reeds - through the solid wood, or through long thin air pathways, or via the bag, but those connections are more like long thin rubberbands than like thick ropes, thus their ability to induce phase locking is weak.

2. i don't think i imagined the differnce in the "feel" of the bags when the skin-side was reversed...

It's quite possible. I have heard some other anecdotal reports that interactions between the drone reeds and the bag may be significant.

3. the stock on this set was made with a solid delrin plug at the front and the back, with a brass tube holding them together so there is maybe 2-3 inches of "chamber" between them. the two regulators have thier own tubes that go right through to the back/bag and the bass air supply is through one of these within - a hole in the wall. each drone is in a similar tube but stop short and each has its own supply vent, collected/covered by the stop plate. each of these tubes has a hole to the chamber between the two plugs. if the size of these holes affects the "coupling" (insert virgin joke here) i do not know, but how large does the hole have to be to allow air/vibration through?...same concept again...where do opinions stop and physical laws begin? i'd think brass might transmit sound at least as well as a thin layer of wood if that is in question. i asked the maker where he came up with the design, but he is dead and has not gotten back to me thus far.

Well, from my perspective it sounds as though the "separate tubes" for the drones are bound to at least partly defeat the phase locking potential. The pressure oscillations which we're hoping will phase lock will not be transmitted as effectively through brass, even thin brass, since the brass will serve to contain the air. Also, the actual vibrating motion (and thus the ability to transmit sound via the walls) of a brass cylinder is quite low. For instance in wind instruments, virtually 100% of the sound transmission occurs via the open toneholes and end, i.e. through the air, as opposed to through the walls.

With regard to transmission of the drone reeds' _sound_, a thin metal hollow stock will probably be effective, though it is likely to be a bit different in its sound transmission characteristics than a thin wooden wall. My impression from experience so far is that the hard woods generally used for hollow stocks are quite acoustically transparent compared to brass.

Hope that helps

Bill

[tompipes]

Yes

[tommykleen]

Phase lock: what a sexy, sexy term.

I shall have to use that to break the ice at UP parties. "Where do you keep your blob of blue-tack?" really works well to loosen up a crowd too. As the evening progresses this can be altered to "I'll show you where I keep my blob of blue tack, if you show me where you keep yours".

Back to topic. Anyone have photos of a hollow mainstock?

t

[Cayden]

Back to topic. Anyone have photos of a hollow mainstock?

t

Yes. But when finished they don't look any different unless you tear the back off them.

I was looking for a series of Geoff making one yesterday but apparently I have deleted them. I may scan them again.

[Joseph E. Smith]

I was looking for a series of Geoff making one yesterday but apparently I have deleted them. I may scan them again.

I'd love to see that, and perhaps a solid stock for comparison. Any chance there Peter?

[Kevin L. Rietmann]

Bill had one in his online photo album, I think.

[billh]

Rear view of an ebony hollow stock:

Looking down into a boxwood stock, with walls about 4mm thick:

A side view of the same boxwood stock, without ferrules


I am currently preparing an article for the Pipers' Review detailing a method of making a hollow stock from start to finish. The text is not finished yet, though I've got most of the photos done. So watch this space, and make sure your Pipers' Review subscription is paid up if you are really interested

The article should be ready in a few weeks.

Bill

[Joseph E. Smith]

Thanks Bill.

[mirabai]

I've been making hollow stocks for about 30 years and was inspired to do so by some experiments where I noticed that a single drone (by itself)sounded more "closed in" as in not as rich and warm when mouth blown using a brass tube the size of the drone tenon than when using a larger cavity surrounding the reed. I have also done A/B comparisons using wood and brass chanter tops on the same chanter and reed and noticed an obvious warming of the tone with the wood. Since I make my mainstocks to accomodate an A drone that requires it's own switch key, my hollowing is a bit unusual. I drill out the area between the D drones 3/4 of the way to the front of the stock and then clean it up by milling and chiseling. I cover this open end with a 1/8 inch wooden cap, drilling through it to access the regs and drone cavities. If someone can tell me how to paste in a jpg I will be happy to post a photo of the revealed inside end of my mainstock. I'm currently redesigning my website to include this sort of thing but it'll be a little while yet.

Tim Britton