Having experienced the remarkable ability of my various IBs to reproduce deep organ notes I thought I had better do some homework on the subject. I have always been fascinated by extremes. It was obvious that some organ CDs had frequencies recorded which were so low they should not physically exist. My knowledge of the organ does not extend very much further than enjoying the wonderful range of sounds it can produce as music. I knew the basics and that there are various kinds of pipes. Open, closed, folded, reed and flue are some of the basic types. The names are so many and in so many different languages that it is very confusing to all but the experts. From a tiny pipe, the size of your little finger, to a colossal 64 feet in wood and metal there are pipes arranged literally in their thousands of all sizes in most large organs.
Below I have arranged some of the material I dug up online during my browsing for big organ pipes and the production of very low frequencies using standard pipes. It is not intended as a comprehensive study of pipe organs but concentrates on the very large and the very low.
The only 64 ' Diaphone pipe in existence is also at Atlantic CiIty. Invented by Hope-Jones it is similar to a reed pipe but uses a sprung resonator or clapper. Image borrowed from: http://en.wikipedia.org/wiki/Organ_pipe
True 64 feet open pipes are as rare as hens teeth and produce an 8Hz tone. A pure 8Hz sinewave is far too low for human hearing but the clapper (or resonator) attached to such pipes adds its own percussive, mechanical sound. All pipes produce a range of harmonics. Folded pipes and stopped pipes produce even more harmonics but can play a frequency twice as low as an open pipe of the same dimensions. You can cheat by folding or stopping a pipe but you can't have your cake and eat it. The resulting sound will be weaker than an open pipe and have more harmonics. Wind pressure also plays its part in the sound a particular pipe produces. Special doubled pipes of different lengths can produce 64' tones by beating. (rather like an old twin-prop aircraft can be heard to beat as the engines vary slightly from each other in rpm) Combinations of 32' and 10 2/3' pipes can also produce 64' tones.
Thankfully YouTube and the Internet are a wonderful resource for organ videos, websites, images, stop lists and sound files. An education in the physics and physical construction of organs awaits the patient online browser. There are countless organ CDs to be bought online or borrowed from your library. I recommend you borrow a CD before buying it unless you like all organ music. Despite my love of the instrument I myself find some organ music and some players tedious beyond words.
Many churches contain an organ of some kind. Sadly electronics are taking over where pipes are too expensive to maintain against a collapse in attendance. (At least in Western Europe) Pipe organ recitals of classical music can usually be found with a diligent, online search of the local media. You don't have to have any interest in religion (at all) to attend such recitals and most recitals are free in my limited experience. You can usually find this out from the recital website beforehand. Keep some coins handy in case of a collection is made for organ maintenance. Just think of the organ as a wonderful instrument in a necessary, acoustic environment and enjoy it at face value. You would never find me in a church unless a pipe organ was playing. Not even for my own funeral! ;-)
Meanwhile back at the ranch: Here's a series of experiments in reproducing a 64 and 128 foot stops on a real pipe organ. The experimenter (Latribe) built a form of IB. He put a couple of large 18" PA speakers in a box over a hole in the floor to a room below. Then waterproofed the cones to obtain a lower Fs. (probably accidentally) Not ideal from a displacement point of view but he obtained enough acoustic output to cause some unwanted shaking and vibration in the objects within the organ room. Nor were the 128 foot results particularly musical. But then, nor are real 64' pipes. There is considerable VLF content in the videos so do try playing them through your IB. I get no cone movement at all suggesting here is no real acoustic power being produced or perhaps it was simply not recorded.
And the results of his labours are in the video above: You really need to play these through your subwoofer to get any idea of the wonderfully deep tones. Though here again, there is no sign of cone movement on my IB. I know that YouTube can play 5Hz at high levels. (from electronic music videos) These will produce very serious cone excursions so it must be Latribe's recordings which lack real acoustic power. What one hears through a subwoofer on his videos is a shaky modulation of the higher harmonics but it is still quite pleasing.
64 feet pipes
Here is a link to some information on reproducing very low frequencies from an organ followed by a self-starting link to a 64 foot pipe sound file for Atlantic City below:
The link below actually has some quite "toxic" VLF content so be careful with your volume levels! It can be interesting to move about in the room while repeatedly playing the track. I find a hot spot at my computer and another at the far end of the room where the effects are almost unpleasant at high levels. I can see some cone excursion on some notes. Getting well away from the speakers (downstairs) produces a much deeper sensation with the mechanical content filtered out. The link nicely captures the acoustic where the organ is situated:
http://www.die-orgelseite.de/audio/atlanticcity_64ft.mp3
Another video of a 64' scale being played above:
An insight into the mechanics of these large pipes: The resonator in action on a 32' pipe:
Another 64' pipe being played. Hardly any musical tone at all.
I think the producer of the next video has recorded a smaller reed pipe and then used electronics to halve the frequency repeatedly: It lacks the harmonics of the real thing but is still interesting for the clarity of the beats. It has considerable VLF content and produces a cold draught from the port of my SVS PC16-46NSD right down to the deepest tone. A glance underneath shows half an inch of excursion on the down-facing 12" driver. Even the curtains shake to most of the tones including the 128 foot pipe! It sounds like an old, single cylinder motorbike with a very slow tick-over.
http://www.magle.dk/music-forums/attachment.php?attachmentid=1118&d=1249964515
Another low scale played on the unique, Sidney Town Hall organ, 64' Contra-trombone.
http://www.die-orgelseite.de/index_e.html
A link to the most comprehensive and beautiful, organ-related, web site I have ever come across online. An absolute masterpiece! Another of his gorgeous pages is linked to below.
http://www.die-orgelseite.de/kurioses_e.htm#oben
Thanks to the harmonics produced by the sound files (and videos) I have posted here I can very easily reach 100dB(C) on my Galaxy 140 SPL meter with the IB. This, despite the early roll off of my IB at ~12Hz. At these high levels cone excursion comes and goes with each successive tone on each sound file or video. The two very different sets of drivers in my manifold are closely matched for frequency response but each seem to take it in turns to play certain tones judging by the visible cone movement. I hope you enjoy playing these strange sounds as much as I have. Their main purpose is in underpinning the full organ. When played on their own they are quite alien to our usual concept of musical tones. My wife referred to some of them as sounding like the beats of helicopter rotors. She was not mistaken as to their character. The sounds of the rotors beating the air are very similar to the frequencies of the tones emanating from the largest organ pipes.
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