The tone of an organ pipe

The sound of the original Principals

The sound of the old Principals was different from the organs we use now.

According to Georg Audsley, the Old English Principals (Diapasons) had an overtones-rich, soft sound and were not very strong. They were voiced on a smooth wind with a low air pressure. The wind was supple and its sound was gentle.

In Germany, Winfried Ellerhorst writes: The old Principal sound is leisurely, round, sweet and not vigorous. The languid profile directs the airflow more outward than our modern Principals with their more pointed phases. The upper lip is therefore also more outward oriented.

There was a singing Principal sound agreeing with the Old English Diapasons. This sound is very suitable for a chamber organ. It is described in the book:

Building a Positive organ

Tone formation in an organ pipe

The creation of the sound in an organ pipe is a complex course of wind currents, which make the tone processing for an organ pipe characteristic. It is a complicated process that Winfried Ellerhorst has described in detail in his book Handbuch der Orgelkunde. The following is a summary of both open and stopped pipes.

When the wind flow from the gap hits the upper lip, swirls are created that increase the pressure on the air column present in the pipe corpus. This compacted air column will look for an opening to relax and find it on the cut up. The swirling wind from the gap is pressed outward which has a dilution of air column as a result. The next swirl from the wind flow is sucked inward; It causes a pressure increase whereby the cycle repeats itself. The first swirls, audible as forerunner tones, are important for the articulation of the tone. It makes the tone vivid and they accentuate the character of the registry.

The wind flow oscillates on the upper lip and is a cycle of inward and outward swirls. The voicer determines how the forerunner tones pass in the build-up of the tone to the full strength. With his craftsmanship he can reach the optimum sound with each pipe, but he can also choose a sound that does not deviate from the adjacent pipe. Artistic considerations between the most beautiful sounds or the best uniformity determine his choice. It is the charm of the organ sound that the pipes differ among themselves. A choir of skilled singers also consists of people with voices that differ but harmonize.

Principal 8'
The most important register of an organ is the Principal 8’. It is the first register ever created for an organ. A church organ without a principal is unthinkable and also a chamber organ is only complete if it has a Principal register.

Formant
For each musical instrument, the timbre is the special feature for the recognition of this instrument. The timbre is called the formant, because of the great conformity with the characteristics of the human voice, when the mouth and the throat cavity form the vowels. The overtones do not all get the same amplification, a group of overtones receives more amplification because the sound body – for example the body of a violin or the beakers of the trumpet – resonates with the frequency of these overtones. The degree of amplification is different for each instrument; a trumpet has a clear peak in resonance frequency. A violin is trying to avoid a resonance peak and distribute it across the widest possible range.

Formant of organ pipes
Organ pipes and the Principal in particular have a different pipe for each tone and there seems to be no agreement with musical instruments, where all sounds have the same resonator. Nevertheless, this formant is present and this is possible because the reduction of the diameter of the pipe, which determines the sound, does not decrease in accordance with the tone length. In this way the amplification of the overtones on each pipe is different, but the acoustic result is constant over a large area. The formant frequency of a Principal is around the 1000 Hz; a viola about 1700 Hz. When choosing the scales, the organ builder has determined the formant. The formant frequency of a Trumpet is also in the area of the Principal, around the 1000 Hz and therefore the Trumpet fits so well with the Principals.

Principal pipes made of wood ?

A real principal sound can only be aroused with metal pipes. The wall thickness of the pipe must be thin for the body to resonate. To improve this resonance, the metal is planed thinner upwards. It contributes to the special sound of the principal.

Hence my thesis: Wooden principals are impossible. Unfortunately, there are organ builders who think that their wooden pipes can produce a principal sound, but she does not manage to let the typical characteristics of the sound be heard. By choosing a tight scale, they achieve more overtones, but it comes at the expense of the basic tone and the register loses its basic sound.

Where wooden pipes cannot produce principal sounds, a Hauptwerk organ can do this perfectly. When comparing the principals of my chamber pipe organ and my Hauptwerk organ, it is not clear whether the sound comes from a pipe or from a loudspeaker. All the characteristic properties of a metallic principal are convincingly present. If you want to find out for yourself, you are welcome to compare a well-voiced chamber pipe organ with a Hauptwerk organ.