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Low wind pressures


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As I've stated in another thread, Frank Bradbeer used to tell me many stories about the days of GDB, and why Maurice Grant followed the path he did. I avidly consumed all this information, and I still prefer the tingle and fizz of an organ from that era.

One of Maurice's justifications for low wind pressures was that, although air is a compressible gas, at low pressures it acts more like a liquid. Therefore the movement of air through the pallet hole, through the (open) toe of the pipe to the flue would be almost instantaneous, or at least much faster than high pressure wind having to work its way through a pin hole in the pipe foot. This, together with super light aluminium action parts, resulted in a more responsive action for which there was quite a vogue at the time. This information may have come from Josef von Glatter Gotz of Rieger from whom Maurice got many of his ideas.

I've never seen this mentioned in Nuts and Bolts or in any other fora. Perhaps someone from inside the trade or with a scientific expertise could comment.

ATG

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Being neither inside the trade nor in possession of very much scientific expertise, I hesitate to reply!
Nevertheless, your mention of a 'pin hole in the pipe foot' presumably relates to the use or otherwise of 'open toe' voicing.
This is something that I'd like to know more about.
What is the point of increasing wind pressure when a closed toe will effectively reduce that pressure?  I can only assume that this is done to make adjustments to voicing easier.
Also, I'm sure that some lower pressure stops can speak sufficiently loudly without the need for high wind pressures, with the obvious exceptions of such things as tubas of course.

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On 10/09/2020 at 16:12, ATG said:

As I've stated in another thread, Frank Bradbeer used to tell me many stories about the days of GDB, and why Maurice Grant followed the path he did. I avidly consumed all this information, and I still prefer the tingle and fizz of an organ from that era.

One of Maurice's justifications for low wind pressures was that, although air is a compressible gas, at low pressures it acts more like a liquid. Therefore the movement of air through the pallet hole, through the (open) toe of the pipe to the flue would be almost instantaneous, or at least much faster than high pressure wind having to work its way through a pin hole in the pipe foot. This, together with super light aluminium action parts, resulted in a more responsive action for which there was quite a vogue at the time. This information may have come from Josef von Glatter Gotz of Rieger from whom Maurice got many of his ideas.

I've never seen this mentioned in Nuts and Bolts or in any other fora. Perhaps someone from inside the trade or with a scientific expertise could comment.

ATG

Out of respect for physics, I'm sure you'll allow me to rephrase Maurice Grant's justification of low pressure wind.. Both liquids and gases are fluids. A high pressure gas is more like a liquid (molecules closer together), however, the lower the pressure the more fluid it is, so yes low pressure wind would pass more easily through any aperture.

Once it arrived at the pipe though it would have less energy than high pressure wind and so there would be hardly any audible upper harmonics. Early organs for this reason employed mixtures to make up for this. Hand or foot blowing meant that higher pressures were not easy to produce even if you had a football team on hand to man the bellows. You were also limited to the number of stops you could have per pallet before the touch became too heavy.

Gambe and similar string tone pipes were being introduced within Bach's lifetime by builders such as Wagner, but they were quite slow to speak and a low pressure gambe is a tricky thing to voice. And low pressure reeds do tend to wander out of tune  - without which I would not earn quite as much from tuning!

With the advent of higher wind pressures and assisted action, more energy was available to create a rich string tone and a full chorus sound was achieved with mainly 8' pipes and the odd 4'. The advantage of this system was that fewer ranks were required. Robert Hope-Jones took this art to new heights. From a voicing point of view, having more available pressure at the foot allows a wider variety of tone to be produced and coupled with the beard or frein harmonique, a string tone pipe can be made to speak relatively promptly. In addition, you don't have to resort to altering the windway in order to change the volume which risks moving or disturbing the wind stream.

With higher pressures, as was mentioned, you may close the toe hole to create a sound that a lower pressure wind would produce, but with  an organ with only low pressure there is a limit to the volume and certainly the variety of tone you can produce.

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