Copying Existing Organ Stops

[Shropshire Lad]

I was wandering how easy it would be for an organ builder to copy an existing organ stop to get it to sound virtually the same. I am presuimng not easy. For instance, if I wanted a copy of say Hereford Cathedral's fine Tuba (which I'm very partial to), could a builder survey the existing stop and make a good copy?

 

Any views from those in the know would be interesting.

[Guest Geoff McMahon]

Kristian Wegscheider in Dresden has made a copy of a small Silbermann organ where he interspersed his new pipes with the originals and then had a recording made using both organs, switching from one to the other, sometimes in mid phrase and you really can't tell the difference.

 

Given adequate access to an original stop, which would include taking it back to the works, one could certainly make a copy of (for example) the Tuba at Hereford. It probably wouldn't sound anything like the Hereford one once it got to its new home though as the acoustics have a very significant influence on the way it sounds.

 

John Pike Mander

[Malcolm Farr]

Given adequate access to an original stop, which would include taking it back to the works, one could certainly make a copy of (for example) the Tuba at Hereford. It probably wouldn't sound anything like the Hereford one once it got to its new home though as the acoustics have a very significant influence on the way it sounds.

 

John Pike Mander

Which leads to the next question, I suppose ...

 

All builders must know at the outset the sound they are trying to achieve, so one might imagine a customer, with this in mind, saying, "I want to have a stop on our new instrument in building X which sounds the same as stop Y does in building Z" - which conceivably may entail rather different scaling, pressure, etc to suit building X's acoustic. (Not a question, I admit, that I've ever actually asked, or previously thought of asking, any builder!) Practical to any degree? Totally impractical? Or do we just look, as I've heard it said before, to particular stops for "inspiration"?

 

Tgds

MJF

[Guest Geoff McMahon]

Well, a customer might make that request and a builder may then try to fulfil it, but there are so many parameters which defy copying, the most significant of which is obviously the acoustic. To take an extreme case, reproducing the sound of a stop originally in a building with a sympathetic acoustic in one with none at all simply won't work. Not for nothing do builders sometimes refer to the building in which an organ is situated as the "magic stop".

 

John Pike Mander

[Guest Roffensis]

One has only to consider Adlington Hall to be in no doubt what can be done in expert hands, remaking or copying pipework missing or severely damaged beyond repair.

[Jonathan Lane]

John's comments are very helpful to us all. His experience in the industry is renowned. Provided enough analysis of the pipework is done, including metal composition, you would be able to completely recreate the stop to replace the one currently installed. But, and this the big but, the external influences are key. Acoustics as John has already said are very influential, but so is action and type of soundboard, and no end of other small things which help a pipe to speak the way it does.

 

It is an area which interests me as both a player and a builder. I also know Terry Shires is a keen experimenter (perhaps not the right word) with organ pipes from previous generations, schools, and traditions. I also know Manders themselves have built some interesting instruments, St. Andrew's Holborn to name but one, and instrument I always enjoyed playing, despite some criticisms of it.

 

At the end of the day, I suspect most organ builders would say most things are possible, provided the conditions are right, but if they aren't well, the best advice would be to build something suitable to the building.

 

Jonathan

[bazuin]

Organ builders have been copying organ stops from historical examples at least since the early 1960s when Ahrend and Brunzema heralded the historically informed reform movement. (Perhaps even earlier, any suggestions?) In recent times the focus among the best builders has extended to reconstructing the processes which went into making the pipes (and of course other parts of the organ as well). Now, for instance, it is quite normal for several builders to identify the material upon which the pipe metal in the historical example was cast, (a piece of Gothenburg-heralded research). Henk van Eeken casts on sand, normal for the Schnitger tradition up to and including Freytag (who was building organs until around 1805!). Reil's reconstruction in Ansbach of the Wiegleb organ has new pipes cast on linen - according to Hans Reil this is what Wiegleb used.

 

Sometimes though, as already pointed out, other circumstances produce results which the original builder didn't have to contend with. Gene Bedient's reconstructions of French organs of different period sound, to my ear, pretty rough because the typical American churches don't develop the overtones in the French reeds that the old French church do. Arp Schnitger's reeds are very fundamental dominated (even in comparison to those of his son) so they sound good even in dry acoustics.

 

Another story about Gene Bedient - he was copying a 2' Schnitger Querfloit, and copied the scaling precisely from the original. Unfortunately, because Schnitger's compass only went to C49, and Bedient's to G56, the pipes for the highest notes were wider than they were high. He had to start again.

 

Sometimes the rule-book has to be tweaked...

 

Greetings

 

Bazuin

[Nick Bennett]

I can't help wondering if continental - and especially Dutch - organ builders picked up the technique of copying old stops after the war in the course of replacing pipes and actions lost to enemy (and friendly!) action. For example, at Nijmegen, the entire left pedal tower was destroyed by bombing and had to be reconstructed using the opposite side as a model.

 

One can imagine that it might cross the mind of the organ builder that, having effectively built half of an historic instrument, there was nothing to stop them building an entire organ in the same style from scratch if only they could find a customer to pay for it.

[Jonathan Lane]

I can't help wondering if continental - and especially Dutch - organ builders picked up the technique of copying old stops after the war in the course of replacing pipes and actions lost to enemy (and friendly!) action.

 

I expect there are examples in this country too, where the damage wasn't extensive. The problem with many of our historic organs, particularly in the South East, London, Coventry and some othe industrial towns, the destruction was complete.

 

Jonathan

[David Coram]

Beyond all the measurable physical properties of the pipe lie not just the acoustic but the finer adjustments of voicing which the eye cannot see - but which can make a huge difference. It's therefore vital to have an informed ear as well. Because of the passage of time, often the most you can claim with any honesty is that something has been based on a good informed guess.

 

Does mettalurgy (within a few percent) and the material the sheet metal was cast on actually make a significant difference to a pipe's speaking properties - bearing in mind it's going to ultimately be voiced by a human being with human ears, who could probably get a very-near-identical result out of anything vaguely similar in appearance?

[bazuin]

"Does mettalurgy (within a few percent) and the material the sheet metal was cast on actually make a significant difference to a pipe's speaking properties - bearing in mind it's going to ultimately be voiced by a human being with human ears, who could probably get a very-near-identical result out of anything vaguely similar in appearance?"

 

This is a very valid question, and I have no doubt that the 'casting on sand' thing is a useful marketing tool for the builders that employ it. The consensus seems to be that pipe metal cast on sand cools at a different rate to being cast on a normal man-made substance and has a different crystal lattice as a consequence. It isn't suprising that the acoustical properties of the pipe are also different. Its worth experiencing some modern organs or reconstructions where this has been applied, I have been impressed in a number of locations. I'm an organist rather than a mettalurgist, but my ear tells me that this is really a breakthrough.

 

However, the skill of the voicer is not in any way diminished by the breakthrough and his input remains the most important part of the success of the final result.

 

Maybe its interesting to mention that Flentrop are currently voicing the Rugwerk (the first phase) of their reconstruction of the organ in the St Katherine in Hamburg (where Reincken was organist). The new pipework was cast on sand and is apparently, to quote one of the advisers, "stunning".

 

Greetings

 

Bazuin

[Jonathan Lane]

Beyond all the measurable physical properties of the pipe lie not just the acoustic but the finer adjustments of voicing which the eye cannot see - but which can make a huge difference. It's therefore vital to have an informed ear as well. Because of the passage of time, often the most you can claim with any honesty is that something has been based on a good informed guess.

 

Does mettalurgy (within a few percent) and the material the sheet metal was cast on actually make a significant difference to a pipe's speaking properties - bearing in mind it's going to ultimately be voiced by a human being with human ears, who could probably get a very-near-identical result out of anything vaguely similar in appearance?

 

I had a long conversation with Terry Shires about this on a visit to their works, and he explained the idea that virgin tin and virgin lead as now supplied does not meet the requirements for producing good organ pipes and they add a number of impurities. He has also analysed in some depth the composition of some older pipe metals, and as far as I can see there is a definite mettalurgical link between tone produce and composition used. This doesn't decry the work of the voicer, however, this matter fascinates me, and the analysis made of the metal used at various times in history clearly is an important study. Its not just a matter of how much tin and lead you use, or indeed other principle constituents, but the so called impurities. However, I admit to being a novice in this, and definitely no mettalurgist in the more detailed sense.

 

Jonathan

[Pierre Lauwers]

"It's therefore vital to have an informed ear as well."

(Quote)

 

Yes. But informed about what ?

 

Pierre

[Henry Willis]

I had a long conversation with Terry Shires about this on a visit to their works, and he explained the idea that virgin tin and virgin lead as now supplied does not meet the requirements for producing good organ pipes and they add a number of impurities. He has also analysed in some depth the composition of some older pipe metals, and as far as I can see there is a definite mettalurgical link between tone produce and composition used. This doesn't decry the work of the voicer, however, this matter fascinates me, and the analysis made of the metal used at various times in history clearly is an important study. Its not just a matter of how much tin and lead you use, or indeed other principle constituents, but the so called impurities. However, I admit to being a novice in this, and definitely no mettalurgist in the more detailed sense.

 

Jonathan

 

 

There are two distinct issues being very badly confused here.

 

As far as I'm aware, Terry Shires has never made any assertions regarding tone production being affected by 'impurities, they do, however, considerably affect hardness of the metal.

 

I'm afraid that I can not see, at all, how any link between impurities in the metal can be made to tone production, as you say above.

 

This is a very valid question, and I have no doubt that the 'casting on sand' thing is a useful marketing tool for the builders that employ it. The consensus seems to be that pipe metal cast on sand cools at a different rate to being cast on a normal man-made substance and has a different crystal lattice as a consequence. It isn't surprising that the acoustical properties of the pipe are also different. Its worth experiencing some modern organs or reconstructions where this has been applied, I have been impressed in a number of locations. I'm an organist rather than a mettalurgist, but my ear tells me that this is really a breakthrough.

 

All bunk, I'm afraid! 1. The consensus? of whom?; 2. The freezing point of a metal isn't affected by the rate of cooling; 3. The 'Crystal lattice' - where does that idea come from? The molecules of each (constituent) metal remain as discrete molecules. What makes a metal harder or softer is the sizes of the gaps at the interstices between molecules of similar sizes - if you want to harden the metal, you must find a 'solution hardener' - i.e. a molecule small enough to fit into these gaps, to reduce the movement, as it were; 4. Your ear tells you that this is a scientific/metallurgical breakthrough? This tells ME that there has been no breakthrough at all, just the perpetuation of an already out-dated myth which I feel is simply being exploited as a marketing tool.

 

As for casting on sand and THAT being responsible for the wonderful sounds referred to, both in that quote and the subsequent one regarding the Flentrop exercise, I assume that they have copied pre-existing scales and voicing details from similar period pipework, and that the superb results are as a result of that and the skill of their Voicers.

 

The metallurgy is not at all simple - many in this trade have tried to ascribe all sorts of 'analysis' results and other pseudo-scientific pronouncements over years, but the actual chemical and physical properties which need carefully to be examined can not be achieved in an organbuilder's workshops - electron and scanning microscopes are required if solution hardening of these specifically-composed metals are to be properly analysed. I was, for several years, in close contact with a (now retired) Dr. Charles in the Chemistry Faculty at Cambridge and we carried out several analyses of correctly polished samples over that time - we know what causes the hardening of these solutions, and it isn't anything to do with casting on sand!

 

A challenge: If anyone can demonstrate to me any difference at all in the quality of the sound of pipework due to either materials or method of casting, as reported in these earlier posts, I will pay him at a commercial rate for all of the time spent in doing so, AND the materials used!

 

 

DW

[Jonathan Lane]

There are two distinct issues being very badly confused here.

 

As far as I'm aware, Terry Shires has never made any assertions regarding tone production being affected by 'impurities, they do, however, considerably affect hardness of the metal.

 

I'm afraid that I can not see, at all, how any link between impurities in the metal can be made to tone production, as you say above.

 

 

DW

 

I didn't say that Terry Shires had made those assertions.

 

Jonathan

[Henry Willis]

I didn't say that Terry Shires had made those assertions.

 

Jonathan

 

My point excatly - so how you draw the conclusion, as he didn't mention tone production? I'm not picking here Jonathan, I'm just interested to know how what Terry said resulted in your conclusion that there is a link between the points below?

 

He has also analysed in some depth the composition of some older pipe metals, and as far as I can see there is a definite mettalurgical link between tone produce and composition used.

 

David.

[Jonathan Lane]

My point excatly - so how you draw the conclusion, as he didn't mention tone production? I'm not picking here Jonathan, I'm just interested to know how what Terry said resulted in your conclusion that there is a link between the points below?

 

 

 

David.

 

As far as I can see different hardness of metal actually changes the sound.

 

Jonathan

[Henry Willis]

As far as I can see different hardness of metal actually changes the sound.

 

Jonathan

 

And this is exactly how I think that two seperate issues are being confused: the hardness of the metal prevents the pipes from collapsing and it is that that Terry Shires has been concerned about.

 

I do not believe, at all, that the hardness of the metal will change the sound to the degree reputed in the earlier posts - if AT ALL.

 

David Coram said it beautifully earlier: there are so many minute factors involved in the eventual sound emanating from any pipe that it should be extremely difficult for anyone armed with the proper information (usually borne out of experience) to say that the metal itself or the method of its production would have any inordinate responsibility for that eventual result.

 

In our organ for Florence all of the pipework, with the exception of one metal stop, is made from spotted Metal or Tin: the other stop is 'hard' plain metal (with lots of 'impurities' to harden it). you are welcome to come to see it and to examine the voicing but I can assure you that the sound is little to do with the metal - it is the scales and the voicing which are important.

 

There is so much mythology around this subject that the talk is not helpful to the trade - suddenly there are expert Advisers who will insist that metal be produced in a particular way - they have no real evidence that these methods are useful in any way other than being used by an earlier generation and so historically accurate (possibly). The fact is, that the skill of the Voicer IS diminished by the expert insisting that the sound is due to HIS insistence that a particular method or material be used.

 

If one is convinced that there is a difference then it is incumbent on one to demonstrate it rather than just passing it on, adding to the mythology.

 

My challenge remains - open to all.

 

DW

[Jonathan Lane]

And this is exactly how I think that two seperate issues are being confused: the hardness of the metal prevents the pipes from collapsing and it is that that Terry Shires has been concerned about.

 

I do not believe, at all, that the hardness of the metal will change the sound to the degree reputed in the earlier posts - if AT ALL.

 

David Coram said it beautifully earlier: there are so many minute factors involved in the eventual sound emanating from any pipe that it should be extremely difficult for anyone armed with the proper information (usually borne out of experience) to say that the metal itself or the method of its production would have any inordinate responsibility for that eventual result.

 

In our organ for Florence all of the pipework, with the exception of one metal stop, is made from spotted Metal or Tin: the other stop is 'hard' plain metal (with lots of 'impurities' to harden it). you are welcome to come to see it and to examine the voicing but I can assure you that the sound is little to do with the metal - it is the scales and the voicing which are important.

 

There is so much mythology around this subject that the talk is not helpful to the trade - suddenly there are expert Advisers who will insist that metal be produced in a particular way - they have no real evidence that these methods are useful in any way other than being used by an earlier generation and so historically accurate (possibly). The fact is, that the skill of the Voicer IS diminished by the expert insisting that the sound is due to HIS insistence that a particular method or material be used.

 

If one is convinced that there is a difference then it is incumbent on one to demonsterate it rather than just passing it on, adding to the mythology.

 

My challenge remains - open to all.

 

DW

As I said earlier, there are many aspects that go into the sound a pipe can produce, and as I also previously said, I wouldn't want to decry the work of the voicer, who is ultimately key to the whole sound, as he has the final say. But I think to ignore all the aspects in favour of just the work of the voicer is wrong, and sometimes a one percent change in sound produced by the pipe can be what the client is looking for so I would never rule this out, at the end of the day we rely on our clients, and whilst they should take experienced advice, they at the end of the day pay our wages! I don't pretend to be experienced in pipe making, in fact, I have never made metal pipes, and am learning as much as I can before I start. There must be a reason though, other than appearance why an organ builder would choose a particular composition. I would be interesed to see the Florence organ though!

 

Jonathan

[bazuin]

Mr Wyld is entitled to his opinion, and, as I seem to remember he has a background as a scientist, as well as being an organ builder I am quite prepared to take it seriously.

 

"As for casting on sand and THAT being responsible for the wonderful sounds referred to, both in that quote and the subsequent one regarding the Flentrop exercise, I assume that they have copied pre-existing scales"

 

As far as I know the scalings in the Katherine organ were lost, the scaling for the new organ has been done by Cor Edskes.

 

David Wyld wrote

 

"All bunk, I'm afraid! 1. The consensus? of whom?; 2. The freezing point of a metal isn't affected by the rate of cooling; 3. The 'Crystal lattice' - where does that idea come from? The molecules of each (constituent) metal remain as discrete molecules. What makes a metal harder or softer is the sizes of the gaps at the interstices between molecules of similar sizes - if you want to harden the metal, you must find a 'solution hardener' - i.e. a molecule small enough to fit into these gaps, to reduce the movement, as it were; 4. Your ear tells you that this is a scientific/metallurgical breakthrough?"

 

No, I'm a musician, my ear tells me its a musical breakthrough.

 

 

"This tells ME that there has been no breakthrough at all, just the perpetuation of an already out-dated myth which I feel is simply being exploited as a marketing tool."

 

and as neither an organ builder nor a scientist I am not going to try and answer the charge myself. Instead, here is a quote from Henk van Eeken from the documentation of his reconstruction of the organ in Anloo (the first time casting on sand was applied in the reconstruction of an existing historic organ). I take all responsibility for any mistakes in the translation:

 

"In the context of the acoustical properties of organ pipes, Munetaka Yokota has shown that the metal found in old organ pipes is harder than modern metal with the same percentages of lead and tin. Even when the chemical composition of modern organ metal is as close as possible to that of the historical metal, it has a different appearance and substantially different mechanical properties. This can partly be explained by the ageing process and other circumstances, but research has shown that that different casting techniques result in different rates of cooling during solidification causing significant differences in the crystal lattice and mechanical properties......

 

...In the North German Organ Research Project, the casting of organ metal on sand was thoroughly investigated. The metal plates were cast as thinly as possible so that only 0.4-0.5mm had to be shaved off. The chemical composition of the metal was as close as possible to that of historic organ metal. The research showed that organ metal cast on sand is much harder than typical modern organ metal. This increased hardness is caused by the relative warmth of sand, resulting in the metal cooling much quicker than when cast on canvas. Modern metal is mostly cast on a heat-resistant material such as Nomex or Kevlar. Under this material, one or more layers of swanskin [might be the wrong word?] create increased thermal isolation with significant results for the cooling and solidification of the metal. In addition modern pipe metal is often cast much thicker than the final result, which also influences both cooling and solidification........ The thinning of the metal by a machine does cause a temporary hardening of the metal, but the following re-crystalisation results in a softer metal. The elasticity in the metal caused by the machine-process also results in a less dense crystal lattice.

 

The final sound is the combination of a complex interaction of different factors. The mere copying of any number of isolated details is then not only impossible, but also pointless as long as the acoustical properties of the original pipe are not achieved. It is essential that the chemical composition of the organ metal is as close as possible to that of the historic metal and that the acoustical and mechanical properties are the same. The best way to achieve this it to reconstruct, as far as possible, the original production process because this naturally produces the specific characteristics and behavioral patterns [of the original]."

 

I re-state my own belief that none of these findings diminish in any way the role of the voicer, and I don't believe that Henk van Eeken would suggest such a thing either.

 

Greetings

 

Bazuin

[David Coram]

"No, I'm a musician, my ear tells me its a musical breakthrough."

 

But are you sure that a competent voicer couldn't take a pipe of almost any metal composition but the same scale, nicking, wind etc and produce the same result? (Or, in the case of a stopped rank, make a metal pipe sound identical to its wooden neighbours?)

 

I had in the back of my mind the fact that a spotted metal rank can fuse quite seamlessly with a zinc bass, for instance, and you could defy any musician or organbuilder or scientist to be able to identify the change in material - except that a big zinc bass, while unsightly, could arguably be made to speak a better note than, say, the tin-rich 16' at New College, which is soft enough that some notes can't be left on speech for more than a few moments before the languids sag back to woolly whiffliness. The same is true of many tin-rich ranks from many builders - I've seen pipes in the 2' octave incapable of staying on speech. Copper is another example of a material often chosen for cosmetic and strength appearances rather than sound quality.

 

The pipemaker's main responsibility is to provide consistency and accuracy. I can't imagine how you would cast on sand as i would have thought the weight of the molten metal descending, even from a small height, would cause the sand to disperse a little and create an untrue surface. Casting on something which causes you only to have to shave 0.5mm off would suggest more to do with economy of time in the days before planing drums (though presumably you couldn't melt the sand-speckled shavings down in the next batch, so material economy was sacrificed).

 

 

As for Pierre's "informed by what?" - well, it depends what you're talking about, really!

[Pierre Lauwers]

So we need to go back to the ancient materials.

Also: High lead content, with antimony in order to harden it,

for "northern" organs.....And french ones up to about 1700,

the organs for Couperin and de Grigny also.

Jean de Joyeuse built very thin Mixtures pipes in that material; Norbert

Dufourcq and others "neo" people finished the job "deleting" those

"incongruities".

(Dom Bedos treatise came long after the "good french repertoire"...)

 

We also need absolutely to rediscover the "Weissblech" (Tinplate? )

for the reed stops.

Its use was very widely spread across Europe, from Flanders to Austria

through Central Germany and the Baltic area; Mosengel built, for Königsberg,

a Trompete in that material, and this stop was in façade!

 

Zinc was used in Belgium since the very beginning of the 19th century, notably

by De Volder, whose style was still baroque then. It was intended to replace

the Weissblech for the Trumpets, so there is an historical continuity between the two materials.

 

So we know what to do !

 

"As for Pierre's "informed by what?" - well, it depends what you're talking about, really!"

(Quote)

 

I am talking about this: after 35 years+ with a certain interest for the ancient organs, I realize

how little we actually *know* of the baroque period.

So our ears are very little "informed" at all.....Save with "educated guesses".

And here lies the problem: how have our ears been "educated", save with beliefs

rather than facts ?

 

Pierre

[Lausanne]

This thread touches on some technical areas that many organ builders know about through experience rather than actual scientific study, although I would agree that the results are in the hearing of the finished pipes.

However, I have been prompted into offering a few insights into the subject of metallurgy, but I can't promise to either enlighten or convince anyone. For those of you who have a copy of the Pb-Sn phase diagram, now would be a good time to get it out!

It is more usual to speak of metal 'atoms' rather than molecules, but any group of two or more atoms either the same or different may be called a molecule. When molten lead solidifies the atoms will try to pack together in the closest way possible and do so in a very regular way, leading to a crystalline structure known as 'face centred closest packed' or FCC. Tin atoms prefer to stick together in a tetragonal form. Solidification occurs in these 'pure' metals at various points in the melt at the same time called nucleation points. The crystal structure grows out from this point until it coincides with another region or 'grain' at which a grain boundary is formed. The size of these grains depends on several factors, but the rate of cooling is an important one. Generally the slower the cooling the larger the grains. As the grain boundaries prevent dislocations moving through the material (when a line of atoms slips over another responding to an external force such as the metal being bent) the larger the grains the more malleable the metal.

 

The atoms of lead are slightly larger than those of tin (1.75 Angstrom as opposed to 1.58), but tend to coexist in the Lead-Tin alloy by the one atom substituting the other, but only up to certain proportions. On a sheet of spotted metal (between 45 and 55% tin in lead approx.) we can see definite areas of white and black. These are called phases, the darker phase contains around 19% tin in lead and the lighter phase contains around 97% tin in lead. For many compositions of the two metals these phases are too small to be seen by the naked eye and when the darker phase is in the majority the metal appears quite dark (after a period of oxidation, as a fresh surface of lead is as shiny as Tin) and when the lighter phase wins the metal looks bright and shiny. For compositions other than the eutectic (61.9%Tin), one phase will start to solidify before the other; but at the eutectic, both phases solidify at the same temperature (183°C).

 

The question of cooling rate during casting is a complex one, but in general, the quicker the cooling, the smaller the grain structure and the 'harder' the metal will be. Hardness is the resistance of a material to penetration and is often confused with strength, and toughness. This 'harder' pipe metal will most likely be weaker and more brittle than a softer one. In order to know how sand casting differs from that on a cotton covered stone etc. we need to know the thermal conductivity of all the materials, their thickness, the rate of 'pouring' through the slit of the trough (gauge) and the size of the slit. As well as the air temperature and exact chemical composition of the metal. The casting sand is no doubt a mixture of many chemicals, it usually contains motor oil, clay, and various ingredients to assist casting and to stop sand sticking to the metal. It may even contain water, but the effect of the steam generated beneath the molten metal may lead to undesirable, often explosive, effects. Interestingly, the thermal conductivity of sand is the same as paper, oil, acrylic and nylon and close to that of cotton, it would only be more heat conductive if it had water in it. A slab of York stone or slate would have a higher conductivity and assuming the cotton and other materials were quite thin, it would play a major role in conducting heat away from the metal rather better than sand.

 

If we assume though, that sand casting does cool the melt quicker than other methods, it is possible that for the same composition, thickness and pouring rate, the resulting metal will be harder.

 

DW's point about hardening being mainly achieved through the addition of other elements is quite valid. Anything that prevents the movement of a dislocation in the metal lattice will 'harden' the metal. That may be a defect, a foreign atom or a grain boundary. I might add that, unlike some iron based alloys, the Lead-Tin alloy does not work harden, that is, beating it with a hammer would only have the effect of eliminating some of the porosity in the metal, which would generally make the metal less likely to crack. The action of machining the metal will create some localised melting and then rapid recrystallisation, but only hardening within the surface region.

 

So, does a pipe made of a harder metal make a different sound? Well yes it does if you hit it with a hammer (please don't!). But then we are dealing with organ pipes, rather than tubular bells; it is the air in the pipe that produces the sound. In order for the sound wave to be stable enough to support harmonics of ever decreasing energy there must be as little damping by the pipe as possible. Damping is when the pipe absorbs the energy in the vibrating air, but does not vibrate in such a way as to reinforce the driving frequency. Sound energy is very low compared to other forms we detect, our ears are remarkably sensitive to it, so it doesn't take much movement or deformation of the pipe to kill some of it. The actual resonant frequency of the pipe body is usually lower than the fundamental of the vibrating air column inside in all but the lowest pipes. Organists will have probably found an 8' pipe or larger rattling away, but these noises are usually dealt with by correctly supporting the pipe or adding some absorbent material at a strategic point.

 

Several organ builders have remarked (mainly US sources on the internet) that high lead content pipes support the fundamental note better than high tin pipes, yet the latter are better at supporting the upper harmonics. However, we need to couple the crucial pipe wall thickness as well as the pipe's elasticity index. The hardness we are speaking about should be seen as the ability of the material to deform in a temporary way (elastic) or permanent way (plastic). Materials exhibit a mixture of the two. A pipe whose wall is too thin, even if made of hard metal, may not produce the required sound.

 

In conclusion, for those brave souls who have put up with my 'physics lecture', as the ability of a pipe to support harmonics in the vibrating air column it contains depends on MANY factors and given that any form of casting can produce metal of exactly the same 'hardness' if other parameters are changed, it is NOT necessary to start using sand casting in order to make pipes sound exactly as they did in the 18th century. Sand casting of plain sheet metal is technologically inferior to the present methods for all sorts of reasons. But if you don't own a stone casting bed, then it may well be cheaper to fill your back yard with sand!!

 

I do not doubt that the pipes made from sand cast metal did sound very good, but how was the comparison made exactly? If two batches of metal with the same composition were cast using two different methods producing two different microstructures and then made and voiced in exactly the same way, the resulting sound may well have been slightly different. That does not prove that sand casting is better, it might show that for a certain type of pipe, a harder metal is better, but that may be produced by a range of casting methods.

 

Parts of the above have been simplified and may have lost scientific credibility in the process, so quoting out of context may lead to confusion, something that this forum has taken to a high art, but often in an entertaining way!

 

I gleaned what little I know about Metallurgy from the department of the same name at Cambridge and knew Dr Charles, mentioned by DW, as he spent so long in our department we believed he was a member of staff, but perhaps he really did belong in the Chemistry department. A well respected academic in any case.

[Jonathan Lane]

This thread touches on some technical areas that many organ builders know about through experience rather than actual scientific study, although I would agree that the results are in the hearing of the finished pipes.

However, I have been prompted into offering a few insights into the subject of metallurgy, but I can't promise to either enlighten or convince anyone. For those of you who have a copy of the Pb-Sn phase diagram, now would be a good time to get it out!

 

Thanks David, this is very useful and answers some questions for me. I must admit the study of mettalurgy as you present it makes it and awful lot clearer than when I first tried to understand acoustics some ten years ago, I got lost on the first page. My background is in nuclear physics and communications engineering, so the fields seem like opposite ends of the spectrum, but I suspect I am actually closer to understanding the science than I thought. Anyway, thanks again, I understand much more about this subject now!

 

Jonathan

[gazman]

What a fascinating thread, and a fine demonstration of the diverse knowledge and talents we have on this Forum.