How many 16' pedal flue stops should be used simultaneously?

[Colin Pykett]

Listening to a radio broadcast of organ music recently I noticed that a loud and sustained low note on the pedals seemed to come and go every few seconds.  What was happening, of course, was that there must have been two 16 foot stops (probably flues) which were not quite in tune, resulting in a beat with a period of about 5 seconds in this case.  It was most disconcerting that the sound almost vanished owing to phase cancellation at the microphones every few seconds.  It implies that these stops would have been of comparable power otherwise there would not have been that degree of cancellation of the fundamental.  I have sometimes noticed this effect in other circumstances, such as on organ recordings.

Does it imply that one should check the tuning of such stops (e.g. an Open Wood plus an Open Metal) before combining them?  Or only use one such stop at a time unless there are pressing reasons for doing otherwise?

I've also noticed a similar effect where a sustained low G on the pedals resulted in a faster (c. 1Hz) beat with mains hum at 50 Hz, probably from the blower motor.  This has nothing to do with the effect above which is caused by multiple pedal pipes speaking simultaneously, but it is equally annoying.  This example occurred on a CD sold by a top flight firm, but all they said when I complained to them about it was "ah yes, the blower at (redacted) cathedral is rather noisy".  I didn't notice any enthusiasm for refunding my money ...

Mind you, either effect only happens if your listening system is good enough to render it noticeable.

[pwhodges]

The same can happen when you're listening live, of course.  And even with a single pedal stop, there will be places where you get cancellation or reinforcement on odd notes (different at each place, so making an "ideal" microphone position hard to achieve - maybe this is a case where multimiking has an advantage over single-point techniques!).

In my (non-commercial) organ recordings I've never really bothered about this - and I've not been troubled by the results.

Paul

[Colin Pykett]

37 minutes ago, pwhodges said:

 ... even with a single pedal stop, there will be places where you get cancellation or reinforcement on odd notes (different at each place, so making an "ideal" microphone position hard to achieve - maybe this is a case where multimiking has an advantage over single-point techniques!) ....

Paul

Yes indeed, and worse with large stopped (as opposed to open) flue pipes because they only speak from a single aperture (the mouth).  Open flues speak from two apertures (top and mouth) which are well separated by a half-wavelength, so the pipes radiate a more complex dual pattern of standing waves which has a better chance of filling in some of the acoustic not-spots which you sometimes get with stopped pipes.  The problem can be really bad in some buildings with stopped 32 foot pitch flues such as a Contra Bourdon.  A lot cheaper because the pipes are only half length, but in other respects it can be a good example of you only get what you pay for.  Haskelling an approximately 16 foot pipe can be more successful in getting a 32 foot pitch than stopping it, because again there is radiation from two apertures.  But sometimes the tone quality is unsatisfactory for some purposes in this case.

Similar issues can afflict electronic basses, where the number of speaker cabinets and their placement needs careful judgement, and sometimes a certain amount of experimenting, to reduce the not-spot problem.  Phasing different cabinets (reversing the connections to one loudspeaker(s) relative to another(s) some distance away) can also be helpful.  Pipe organ builders who elect to use digital basses, please note!

Even so, these are different matters to the one I raised which was the slow dynamic beating effect due to two slightly out-of-tune bass pipes speaking simultaneously.

[John Robinson]

Very interesting discussion.  I wonder how this affects 16' reeds, though I'm not sure whether anyone would use more than one at the same time.

[pwhodges]

I'd expect reeds to be much less affected, because the abundant higher harmonics would hide deficiencies in the most affected fundamentals.

Paul