Differences between tibia clausa

[Hammondlover]

I noticed that the drawbar registration for 16' Bourdon is the same as 8'Tibia Clausa only an octave lower. Upon researching this stopI noticed they sound very similar, only the chiff seems to be slightly different and the bourdon sounds more rasp. What is the difference in construction between the two?

[davidecasteel]

Re: Differences between tibia clausa



I tried the online Encyclopedia of Organ Stops and it was not too helpful. Basically, it says that the Tibia is a large-scaled open wood flute and the Bourdon is a large-scaled stopped wood flute; it does indicate that the Tibia on a Theater Organ is really a Tibia Clausa, which is a large-scaled stopped wood flute. The major difference alluded to in the encyclopedia may be that the Tibia is full-voiced and powerful, whereas a Bourdon is usually softer and less penetrating.

I'm sure there are folks here with much greater insight and that they will be posting their thoughts.

David

[soubasse32]

Re: Differences between tibia clausa



Bourdons can be either of wood (especially 16') or metal, and are always stoppered. In France, a manual Bourdonis most usuallya metal Chimney Flute.

I don't know much about Tibias other than they are usually on high pressure, and if you break one you'll be in a cast. [:$]

[Guest]

Re: Differences between tibia clausa

The Tibia tends to be more "vocal" whereas the Bourdon is more orchestral. I never really considered them similar, but I can see how you could get that from drawbar registrations.

Probably the difference you are hearing is in the harmonics. When you stop a pipe, you cut out all the even harmonics, leaving just the odd partials. Since the Tibia is a full-scale pipe, you will actually hear more frequencies in a single note. Also, stopped pipes will be one octave lower than an open pipe, because the wind travels in both directions. 

 

 

[Guest]

Re: Differences between tibia clausa

It is said that the tibia clausa is the work of Hope-Jones. That stop became a hallmark of cinema organs by various builders. It can be on high wind and leathered upper lips producing a tone without a great deal of harmonic development. Along with the trems--fast and deep- a characteristic ''sobbing'' quality is heard. Wurlitzer is thought to have made excellent tibia clausas as well as Morton and others.The scale is VERY large and there is a 32ft rank at Atlantic City on 20'' and double-languids---the low C is so big that you can install a door and walk in!

[radagast]

Re: Differences between tibia clausa



[quote user="Hammondlover"]I noticed that the drawbar registration for 16' Bourdon is the same as 8'Tibia Clausa only an octave lower. Upon researching this stopI noticed they sound very similar, only the chiff seems to be slightly different and the bourdon sounds more rasp. What is the difference in construction between the two?[/quote]

I think you need to consider that a representation of any pipe stop on a Hammond is going to be a compromise. The pipe stops themselves might have partials not repsented in the 7 drawbar layout on a Hammond. Yes I meant 7. The lowest two drawbars on a Hammond are below the harmonic series of the unison or 8' drawbar. So if you wanted to include those 2 drawbars and use the 16' as a fundamental, you will be missing even more in the harmonic series. Thepipe to drawbar charts, like the ones in Irwin's "Dictionary of Hammond Stops" are approximations based on the harmonics available on a Hammond.

[jimmywilliams]

Re: Differences between tibia clausa



Orgrinder010,

Please educate me here as I am very interested to learn ... I always thought that tibias were more or less a sine wave - i.e. no harmonics. At least that is how electronic organs usually work. It seems like this is not the case with pipes. If that is the case, why are the electronic tibias usuallydesigned to filter all the harmonics out and leave only the fundamental? Thanks.

- Jim

[Guest]

Re: Differences between tibia clausa

http://www.organstops.org/t/TibiaClausa.html

[Hammondlover]

Re: Differences between tibia clausa

I always thought tibias would be a highly-filtered square wave, or a triangle wave.

[Guest]

Re: Differences between tibia clausa

[quote user="jimmywilliams"]

Orgrinder010,

Please educate me here as I am very interested to learn ... I always thought that tibias were more or less a sine wave - i.e. no harmonics.  At least that is how electronic organs usually work.  It seems like this is not the case with pipes.  If that is the case, why are the electronic tibias usually designed to filter all the harmonics out and leave only the fundamental?  Thanks.

- Jim

[/quote]

 

Compared to most stops, the tibia is definitely more of a sine wave, yes. I suppose you could even pass one for a Bourdon in the lower octaves. But in the higher register, you'll hear much a difference in tone. It could, I guess, be considered the "Diapason of the Theatre Organ", due to its superb fundamental quality. There is just so much you can do with it, even though it is usually piped through at full tremulant. I find it works best as a solo instrument, more than anything else. 

 

 

[Guest]

Re: Differences between tibia clausa



The Tibia is basically a large scale bourdon, a wood stopped flute. The pipe organ tibia does have some noticeable harmonic development, mostly odd harmonics. The Wurlitzer tibia is wood up to about the upper third of the keyboard, goes to 6 stopped metal pipes, and then has open metal pipes. The harmonic structure necessarily changes as does the pipes response to the tremulant. Originally, the tibia was supplied at 10" pressure (smaller scale but still large relative to a classical bourdon) and a 15' pressure larger scaled version which has less harmonic development.

The modern style of theatre organ voicing tends to soften the upper pitches of the tibia below the original volume. This causes the pipes to loose tuning stability and changes the response to the tremulant. The tibia is often tuned with the tremulant on since the pitch changes with the tremulant. If the pipes have not been modified from the original voicing (and the tremulant works correctly, not choppy), the average pitch does not change with the tremulant and the stop can be used with or without tremulant as required.

Combining the 8' Tibia with the 2' Flute makes for a nice pseudo-baroque sound. On many modern theatre organs this is not possible due to the tuning stability problem. The original voicing gives a pretty stable pitch which can be used for classical music.