The Pipe Organ

The Master Organ Builder decides how to make us passionate about this magnificent instrument!

Wow, how complex organ technique is and how articulated the knowledge of the organ builder is!

One might naively think that only the organist is a devil with incredibly fast and precise hands and feet, but a first reading of the fundamentals of the organ makes the instrument appear as a miracle of physics (not just acoustics), engineering, hydraulics, and mechanics.

Pasquale is right Pasquale when he says: "where do I begin?"

In short, I believe a good approach would be to review the basic acoustics of aerophones, then illustrate the components of the instrument and the (main) technical innovations; then I would move on to illustrating the main musical characteristics of the instrument and its use by its great authors.

I, for example, think it would be interesting to illustrate the differences between reed pipes, flue pipes, and diapason pipes, and the different characteristics of cylindrical, conical, or rectangular-scale pipes. Another interesting thing would be to understand if certain timbres derive directly from the characteristics of a single pipe or are the result of mixing a set of pipes. Furthermore, beats and obtainable acoustic effects come to mind: I don't know if they are used or if air flow variators are used to create vibratos. The questions would continue, but I think it is time to stop here!

To get to the composers, what are the best eras? And the greatest composers among those who are not already famous?

So, let's start from the assumption that I only go as far as what I know. Beyond that lies ignorance.

Let's start with the best known and most important components of the instrument, namely the pipes. There are two types: flue pipes and reed pipes. Of these, there are various families which we will see later.

Flue pipes.

They are the most well-known, also because they can be recognized in the instrument's facade (the front of the organs where these can be speaking or merely decorative). They can be constructed of metal or wood depending on the timbre to be obtained.

The flue pipe consists of three components: at the bottom is the foot, conical in shape, which has the function of

directing the air stream from the inlet hole to the mouth, i.e., the cut that runs horizontally in a flattened section of the tube itself.

Between the two parts, the languid is housed: a metal disc that has the function of conveying the air stream toward the front part of the pipe at the position of the lower lip of the mouth. The height of the body determines the oscillation frequency of the air column, and therefore the pitch of the emitted note.

It is useful to introduce at this point a brief description of the physical phenomena that govern sound formation. From the slit of the mouth, a stream of

wind emerges which partly disperses into the environment and partly re-enters the pipe through the upper lip. An overpressure is created inside the tube which generates a train of waves that rises along the tube and at the same time prevents the wind coming from the foot from entering the body of the pipe. At the top, the wave front gives energy to the environment in the form of spherical compression waves, then it is "reflected" toward the lower part of the pipe where a spherical depression wave is generated and the cycle begins again.

The initial impulse, due to these two dampings, would extinguish after a few cycles if the wind were not supplied continuously.

the air that enters then provides new power to the wave, modifying and amplifying it until

reaching a condition of equilibrium.

Under these conditions, the pipe has reached the steady-state sound regime, or resonance.

To reach these conditions, a certain number of cycles are necessary, which constitute the so-called attack transient (a very important factor because it determines the timbre of the pipe, along with other factors).

As with all musical instruments, pure sounds—whose law is perfectly sinusoidal—are never generated by pipes, but rather sounds resulting from the sum of multiple harmonics. We will return to this later.

The main families of flue pipes are as follows:

- wide cut pipes (so called the diameter of the tube), i.e., with a round, bright sound (Flutes, Bourdons);

- medium cut pipes, i.e., with a thick, robust sound (Principale, the classic organ sound);

- narrow cut pipes, i.e., with a biting sound (Violie, strings in general).

These fundamental differences, combined with the material used and construction techniques, the geometry of the pipe, and the voicing technique, determine in broad terms the timbre of the stop. (A stop is called a row of pipes corresponding to the notes of the keyboard with a specific timbre).

Flue pipes can also be stopped (or semi-stopped, as we will see), obtaining what in Physics is called a "closed tube". These are the "Bourdons" subfamily.

The entire acoustic power exits from the mouth and the oscillatory cycle is doubled, since the compression wave is reflected precisely due to the occlusion.

Consequently, closed tubes produce a sound one octave lower relative to their actual length and cannot emit even-order harmonics.

The length of the pipes is expressed in feet. An 8-foot pipe, for example, corresponds to the pitch in unison and denotes the type of stop. If, for example, I have an 8-foot Principale stop, it means that the tallest pipe measures approximately 2 and a half meters and all the others will decrease proportionally in size. A 16-foot pipe will sound an octave lower, while a 4-foot pipe will sound an octave higher, a 2-foot pipe two octaves above, etc...

Note that as the heights decrease, the diameter also decreases to maintain the typical ratios for that type of stop, specifically calculated based on the timbre and tuning of the entire stop we wish to achieve.

Very interesting. It would also be interesting to illustrate the method by which the air is generated. I imagine that modern organs have an electric compressor positioned at a distance to produce compressed air. But I remember that in ancient times there were active and passive organs. Both had a bellows to generate air, but in one case it was the organist himself pressing the bellows to generate air; in the second case, a second person had this task. I also imagine that the air must have a certain pressure (not too low and not too high) to generate the right sound. For example, what is the exact operating pressure of a pipe organ? Is it the same pressure for every section of pipe, or do the pipes themselves have a nozzle that regulates the correct pressure according to their size? What are the physical laws that determine the choice of the pipe section, the thickness of the sheet metal (in the case of steel pipes), and the length of the pipe? Does a different sheet metal section (for metal pipe organs) produce a different timbre, or is the thickness irrelevant?

Beautiful! Thanks

Pasquale,

excellent introduction!

A couple of quick questions.

1. If I haven't misunderstood, the timbre of a flue pipe depends, besides dimensions and the fact that there is an attack transient and an end transient, also on the closed/open construction technique. To explain myself better: if a closed pipe sounds an octave lower than an open one of the same length, one might think that one open pipe and one closed pipe half as long have (approximately) the same fundamental. At the same time, however, the closed one emits only odd harmonics (like a clarinet) and therefore will appear to have a different timbre, even with identical transients. Correct?

2. You say that the timbre varies between wood and metal. Can you explain further? Do you mean that the pipe evokes different harmonics? Are you referring to different transients? Or to a different presence of inharmonics?

Also interesting is the question from TheSimon regarding the thickness of the pipe's metal sheet, because on one hand there is Helmholtz's law and on the other the concept of the resonator! A priori, I wouldn't know what the answer could be!!!!

Thank you, and I eagerly await your explanation of reed pipes!

Hello!

Maybe I'm arriving a little late, but it doesn't matter. Pasquale, I join Gennarino: excellent introduction!!

As you might remember, I have already said that my godfather is an organ lover and a lover of the instrument itself, which is why he also handles small repairs on the organ in the church I attend (A V20 Mascioni, a company from Cuvio, in the province of Varese; the organ is from 1970, and it is the 949th built by the firm. If you are interested, I can provide more information)

In any case, the explanation is very interesting and, since it's clear that you are passionate and know your stuff, I will take the opportunity to pose a doubt of mine regarding this: I have heard about different connection systems from the console to the pipes: electric, mechanical, pneumatic, and even fiber optic... What exactly does that mean?

Thank you very much and congratulations again!

Yes Pasquale, we want you to be more present, we are all music-obsessed here 😎 so you must keep us updated and teach us new things!

Wow, what interest! Sorry, but I chose a dark period to start this topic. I have some problems that are taking up a lot of my time, but I will try to be more present.

There are many questions and on certain topics I had set out to arrive at them gradually (such as transmissions or the air management and distribution system) because some topics would be difficult to understand if not preceded by certain notions.

First of all, I am continuing the description of reed pipes to complete the description of the sound apparatus. Then we will move on to the mechanics of the instrument.

To be able to imitate some orchestral wind instruments such as brass (trumpet, horns) or woodwinds (oboe, clarinet, bassoon), organ building makes use of pipes where sound production is entrusted to the oscillation of a brass tongue called a reed. As in lip pipes, the wind enters through the foot, within which is hidden the mechanism formed by a brass channel, usually with a "U" section, which carries the brass tongue that constitutes the actual reed.

The reed is slightly curved at rest to allow a semi-open passage for the air that provides the initial energy impulse and thus the formation of sound.

As can be seen in the photo, the tongue is then fixed in its oscillation by an adjustment hanger which has the task of tuning.

By varying its position, it is as if the vibrating part of the tongue were actually shortened or lengthened. All these components are finally fixed to the head, above which the resonator (tuba) of various shapes is mounted, depending on the instrument one wishes to imitate.

They can be divided into several families:

- cylindrical reed pipes with narrow cut;

- cylindrical reed pipes with wide cut;

- conical reed pipes with a section increasing towards the open end;

- chimney reed pipes and other shapes.

Upon the admission of air, the tongue periodically opens and closes the passage of air, sending a rapid series of impulses into the upper resonator that generate pressure waves.

The frequency is logically dependent on the vibration of the tongue; therefore, the length of the resonator can be varied within certain limits without an appreciable variation in the frequency of the emitted note. At the limit, the reed can sound on its own, but it would produce harsh and unpleasant sounds (to put it bluntly, raspberries....)

It is the same system as carnival trumpets, notice it.

The substantial difference between these pipes and lip pipes is actually like the game consisting of blowing between two leaves held parallel to produce a high-power hiss (reed), or like the hissing sounds heard when the wind breaks against obstacles or walls; in this case, the physical mechanism is closer to lip pipes.

Regarding the way of constructing the mechanical part of the reed, it must be mentioned that there are two types: beating reed and free reed.

In the first case, the tongue beats against the edges of the brass channel without entering it; in the second, however, it enters freely without touching the edges, thereby extending the oscillation inside.

The upper resonator therefore has the main function of providing timbre formation and sound amplification, and therefore organ builders have devised ways to exploit geometric and dimensional characteristics to obtain a wide variety of effects.

Each artisan in antiquity therefore developed their own solutions which in a certain sense led to a "Babel" of parameters: stops of the same name and of the same sound were made differently and with the measurements each builder deemed satisfactory, although currently reed stops have become more standardized due to scientific studies carried out since the last century.

In this video you can see, in a very summary way 😆, the process of constructing flue pipes.

In a crucible, the metal alloy consisting of tin and lead is melted, in varying percentages depending on the type of pipe or stop we need to obtain, after which the sheet is "cast" onto a bed of sand, cloth, or marble (again, based on the characteristics the resonator must have). The resulting sheet is planed to make it uniform and covered with a special protective metal varnish that will also serve for the subsequent soldering phases. Once the pieces that will constitute the pipe (foot, languid, body) are cut from the sheet, they will be shaped and soldered together by removing the varnish from the edges so that the solder only adheres there. The pipe is finished but beware, it won't sound!

There is an anomaly in this video because usually pipes are constructed without a mouth or with only a hint of one. It will be the tuner, once the instrument is finished and where it is located, who will open the mouths, beginning that delicate technical-artistic phase known as "voicing". He will intervene on EVERY single pipe with numerous adjustments to make it speak in the right way depending on the timbre, volume, attack transients, and especially the sonic characteristics of the environment (let's not forget that every organ is built for a specific environment that will form its natural acoustic box).

Open content (youtube)

I will start by responding to individuals

TheSimon wrote:

Very interesting. It would also be interesting to illustrate the method by which air is generated. I imagine that modern organs have an electric compressor positioned at a distance to produce compressed air. But I remember that in ancient times there were active and passive organs. Both had a bellows to generate air, but in one case it was the organist himself pressing the bellows to generate air; in the second case, a second person had this task. I also imagine that the air must have a certain pressure (not too low and not too high) to generate the right sound. What is, for example, the exact operating pressure of a pipe organ? Is it the same pressure for every section of pipe, or do the pipes themselves have a nozzle that regulates the correct pressure depending on their size? What are the physical laws that determine the choice of the pipe section, the thickness of the sheet metal (in the case of steel pipes), and the length of the pipe? Does a different sheet metal section (for metal pipe organs) produce a different timbre, or is the thickness indifferent?

I will illustrate the distribution of air and its characteristics all together later.

The thickness of the sheet metal, as you call it, which is called a plate and is made of a tin-lead alloy (but in the past copper and even cardboard were also used), certainly determines a greater "quality" of sound and certainly characterizes its timbre, as with the type of material. In what way I do not know..... 😆 but I reserve the right to listen to an organist to get clarification before saying nonsense!! 🙂

To also answer Gennarino, the fundamental differences between a wooden pipe and a metal one are that wooden ones usually have a sweeter timbre and are used for more flute-like timbres. Usually, larger pipes are also built in wood (they are inside the instrument and cannot be seen) due to cost and weight issues compared to similar metal ones. It will be the skill of the voicer to mask the transition from one material to another.

It must be said that the matter is very complex. The exact same pipe, placed in the hands of two different voicers, will sound differently.

FrancescoDiParigi wrote:

Hello!

Perhaps I am arriving a little late, but it doesn't matter. Pasquale, I join Gennarino: excellent introduction!!

As you may remember, I have already said that my godfather is an organ lover and a lover of the instrument itself, which is why he also handles small repairs on the organ in the church I attend (A V20 Mascioni, company from Cuvio, in the province of Varese; the organ is from 1970, and it is the 949th built by the firm. If you are interested, I can provide more information)

In any case, the explanation is very interesting and, since it's clear that you are passionate and know your stuff, I will take the opportunity to pose a doubt regarding this: I have heard about different connection systems from the console to the pipes: electric, mechanical, pneumatic, and even fiber optic... What does that mean exactly?

Thank you very much and congratulations again!

Mascioni is one of the largest Italian companies, a builder of high-quality instruments. At the beginning of October, I will be at their factory in Varese.

The history of transmission is long and articulated, ranging from pure mechanics to pneumatics with various systems, electric, electronic, and computerized. We will get there.

Pasquale,

the video you published is actually a decent and impressive Playlist!

I watched a large part of it last night and was impressed by the construction process, which is true craftsmanship of extremely high value.

Watching the maker of the pipes as they gradually smooth them during the tuning process to tune them highlights the delicacy of a job that is being lost to time and that one would hardly imagine!

Again, congratulations for the knowledge contribution you are providing and KEEP GOING!!!!!!!!!!!!!!!!!!!!!!!!

See you soon

INCREDIBLE!!!!!

I had never seen the birth of an organ pipe before.

One of the noblest Arts, I would define it. Listening to the "breath of Music" that rises religiously into the air creates a unique emotion. This magical air caresses the walls forged by fire and by the hand of man: Not in life....but in Art Man knows how to perform Miracles! Thank you

Let's move on to another component of the organ.

THE WINDCHEST

The Windchest is the most important component of the organ. Inside it are contained all the mechanisms suitable for ensuring that the correct pipes of the desired stops sound.

It is the base upon which the pipes are placed. In practice, roughly speaking, it is a large wooden box, whose dimensions vary according to the number of stops and the number of keys on the keyboards. Its name says it all. It supports the weight of all the sound - in large organs, several hundredweight - and its construction must be robust but at the same time highly precise.

On the upper board of this box, as many holes are drilled as there are pipes, and these holes connect the base of the pipes (foot) with the inside of the windchest.

Let's take for example a simple windchest for a three-stop organ. We know that if an organ has three stops and a 61-note keyboard, the pipes to be placed on the windchest will be 183 (61x3).

Usually all the pipes belonging to a stop are placed in a row, one after another, usually in ascending series (or descending depending on the type of windchest). The inside of the windchest is sealed and filled with air produced by the bellows, so that the only openings through which such air can escape are the upper holes that connect it to the pipes.

As things stand, it would happen that, by operating the bellows, all the pipes placed on the windchest would sound simultaneously. Since this is exactly what must not happen, various mechanical devices (and later pneumatic, electric, and electronic) have been studied to "distribute" the air in the way desired by the organist. In practice, it is necessary that, even with the bellows in operation, no pipe sounds unless the organist opens a stop and presses a key.

I will say immediately that there are many types of windchests (channel-per-key or per-stop, slider or pallet) but these will be the subject of any potential further study. We will talk about the most classic version, channel-per-key, to understand its basic operation.

The Channel-per-Key Windchest is composed, as we have already said, of an airtight wooden box that is filled with air produced by the bellows. As we can see in the illustration of the Front View.

In the upper internal part, the windchest is divided into as many channels as there are notes on the keyboard (if the keyboard has 61 notes, there will be 61 channels inside the windchest). These channels are also all sealed but each possesses (see Side View illustration) an opening towards the inside of the windchest itself, an opening that is closed by a valve. This valve (called a pallet) is operated by the keys of the keyboard.

In this way, the air being fed into the windchest by the bellows cannot enter the channels until a key is pressed. When this happens, the air (highlighted in yellow) enters the channel corresponding to the note and from there passes into the pipes connected to it. At this point, the drawback is that all the pipes corresponding to that note of all the stops sound (if we have three stops and press the first C on the keyboard, all the pipes for the first C of all three stops will sound).

Now a mechanism must be introduced that serves to make only the pipes of the stops we actually want to sound play.

To achieve this result, two different types of mechanisms have been created over time which, depending on their type of operation, have given names to the two types of mechanical windchests that we can find: the "Slider Windchest" and the "Pallet Windchest".

To overcome the inconvenience of all pipes sounding simultaneously when the corresponding key channel opens, two mechanical systems have been devised over time. We will first see the oldest one, which even dates back to Roman times and, in its simplicity, is truly highly effective and very functional. Key-channel windchests equipped with this system of "fractioning" the rows of pipes of the various stops are called "Slider Windchests" (Somieri a Tiro). But let's look at how it works in particular.

In the animated image, we present a key-channel windchest equipped with the "slider" device.

As can be seen, a wooden shaft is simply added inside the windchest, longitudinally corresponding to the different rows of pipes of the stops, which has as many holes as there are pipes in the row of pipes for that same stop.

One end of this shaft protrudes laterally and ends in a knob or handle that can be operated by the organist. In the resting position (stop closed), the holes in the shaft are offset from the holes that connect the windchest to the pipes and, therefore, prevent the passage of air. When the organist "pulls" (hence the name Slider Windchest) the knob or handle, the holes coincide and air can pass from the windchest to the corresponding pipes, provided that the corresponding keys are pressed; otherwise, everything remains silent.

In this way, the goal of making only the pipes of the desired stops sound is achieved quite simply.

It is obvious and intuitive that as many shafts are needed as there are stops present on the windchest, and that they must be arranged so that they can slide easily inside appropriate housings without allowing air to pass either into or out of the windchest itself.

In this regard, in the following figure, a windchest is visible with part of the cover removed (the upper part that acts as a lid under which the sliders run is called this) with two sliding slats visible on the left.

Regarding the stop controls (the knobs or handles), the solution of "pulling them" directly on the windchest is only possible in small ancient positive or portable organs. In "normal" organs, the sliding shafts of the windchest are connected to the stop controls present at the console via levers and rods that manage to transmit the movement remotely.

As we have seen, the operating principle was based on the fact that the windchest was internally divided into as many channels as there are notes on the keyboard

This type of windchest, as we have said, is the most classic and has its origins in the ancient times of organ building and even today, with due improvements, it is the one best suited for use in instruments with mechanical or mixed transmission.

In the mid-1700s, especially with the enlargement of instruments, a new type of windchest began to be adopted, which was later adopted by 19th-century European organ builders where it had its boom under the name "Piston Windchest", because the method for transmitting the movement of the keys to the pipes consisted of many small pistons placed inside the windchest and operated by a metal bar connected to the transmission trackerwork from the keyboard, whose movement caused these small "plugs" to close and open the holes that connected the windchest with the pipes.

The basic principle that distinguishes the Stop-Action Windchest is opposite to the one on which the Key-Action Windchest is based.

In fact, the windchest, internally, is no longer divided into as many channels as there are keys on the keyboard, but rather into as many channels as there are stops on the organ.

Each channel is connected directly to the general or specific supply bellows (in this way it is possible to supply different stops with different air pressures) and the stop controls in the console no longer operate sliders and rods that cross the windchest, but simply the valves that allow air to enter the channel on which the pipes of the corresponding stop are placed.

In this way, the various stops draw the necessary air each on its own without creating the imbalances that in the key-action windchest resulted from the fact that all stops drew air from a common compartment.

Obviously, with this "reversal" of construction philosophy, the old methods for transmitting the movement of the keys to the pipes no longer worked and new methods had to be devised. The first of these methods was the already mentioned "Piston Windchest", which was used to make the stop-action windchest work on organs with mechanical transmission. The operation is schematized in the figure above (it is very elementary...)

Pressing the key sets in motion the small bar inside the windchest to which the various "pistons" are fixed, which, by moving aside, open the communication holes between the various channels of the windchest stops and the pipes above. Obviously, only the pipes connected to the channels of the "open" stops sound, i.e., the channel into which air has been let in.

It must be said, at this point, that the Stop-Action Windchest immediately proved to be much more versatile than its predecessor, as it was able to adapt well to various types of transmission. In fact, with the subsequent advent in the 19th century of pneumatic transmission (which we will see later), it was quite simple and easy to modify the way in which the movement of the keys was transmitted to the pipes.

If you haven't understood anything, it is normal (it is not an easy concept) and I am all yours.......

Pasquale,

your explanations are truly an example of extreme clarity.

I am left with (FOR NOW!) only a couple of curiosities, which all concern this air that is being pumped.

1) What happens when no key is pressed and the air accumulates? How is it dissipated, to ensure that a note after a pause sounds like the same one preceded by others?

2) How do you ensure that air does not pass through the gaps between the channels and the slats? And how is airtightness reconciled with the friction that is generated?

3) Does the attack of a note depend on the speed at which the key is pressed? In general, if you want, my question is: How do you control the volume?

Thank you and see you soon

You know one thing?

It's been quite a long time since Pasquale has been missing from the site and, we must admit, Pasquale and his learned explanations are missed!!!!

I fully agree with Gennarino!!!!!