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I happened to be browsing the web-site of Cameron Carpenter who is an incredibly talented virtuoso organist. He recently recorded a new album on the digital organ at Trinity Wall Street and on Cameron's website, there was a picture of Bruce Thigpen (inventor of the Thigpen Rotary Woofer) sitting in on the recording session.



Above L to R: Bob Woods (President of Telarc and producer of the album); Bruce Thigpen (inventor of the Thigpen Rotary Woofer), Susan Slaymaker, Richard Torrence.


This immediately peaked my interest and made me wonder what he was doing there. As passionate as I am about organ music, organs, home theater and electronics and knowing the history of the trinity organ which is the most advanced state of the art digital organ ever built, I shot an email off to Bruce asking him about his picture on Cameron's website. I had no idea why he was there and I asked if by chance if he was going to be using his rotary sub technology to extend the frequency response of the organ to include 64' stops.


Bruce got right back to me, was very friendly and told me that he was at the recording session because 2 of his rotary subs were temporarily installed on the Trinity organ just for the recording session. Not only that but the organ was programed with digital 64' and 128' stops just for the recording session



Larger organs use 32' stops which produce 16hz. 64' stops go down to 8hz and 128' foot stops (which i never heard of, I think they only exist in the digital organ world) go down to 4hz



There are only 2 organs in the world which use true 64' pipes. Some larger organs use "resultant" 64' pipes which is a trick of using 2 smaller pipes tuned to the 1st and 2nd harmonic of the fundamental to give the effect of a 64' when it's not practical or cost effective to use real 64' pipes.


The trinity organ uses samples of real pipes recorded "pipe by pipe" stored and controlled by an array of 9 Unix computers which is the brain of the organ.


Bruce told me that 2 of his rotary subs were able to extend the response of the organ at the center of the church to 6hz @ 110db and this is a pretty big church which is located on Wall Street in Manhattan.


I thought all this was fascinating and asked Bruce if he would mind me posting about this and he said that he did not mind and that he would even post some more technical data.
 
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I wonder what the Thigpen skeptics are going to pull out of their hats about this one. Organ music is not the only source material that benefits from the Thigpen Rotary.


FYI, I remember that about 5 years ago Bruce Thigpen said that he could build an even more powerful version of the Rotary sub. He said that he could build a version that would do 120 db rather than the existing version that maxes out at 110 db.


It's just too bad that I don't have $20,000 laying around for a Thigpen.


Talk about an attic fan
 

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OTK,


We were asked by Robert Woods of Telarc and the Richard Torrence, a co-producer of the recording to participate and assist in getting more low frequencies out of the Marshall and Ogletree virtual organ at the Trinity Wall street church where Cameron Carpenters debut recording with Telarc took place.

We temporarily installed two TRW-17 rotary woofers in the church and were able to get down to about 6Hz at up to 110dB. The original woofer system would go to about 27Hz in the middle of the church at about 90dB, not quite a true 32 foot stop. We added 64 and 128 foot stops to the organ and Cameron used them in the recording.

Although this was a temporary installation we are planning on

installing a permanent TRW-17 woofer at Middle Collegiate church in New

York where Cameron is the artist in residence. It was a fun project

and Cameron is an amazing performer with a long and I believe very

successful career ahead of him.

A view of the church from wall street:




I will try to add more about the installation soon.


brucet
 

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Quote:
Originally Posted by brucet /forum/post/14095562



I will try to add more about the installation soon.


brucet

Thanks Bruce, look forward to it.
 

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tkdee,


The Marshall and Ogletree organ uses samples recorded from a number of different pipe organs around the world. They have at least two different 32' samples, but no 64' samples. They attempted to obtain permission to sample the Atlantic City convention hall 64' diaphone for this recording however the request was denied. M&O divided the existing 32"stops by two, and I requested that they create some sine wave stops at 64' and 128'. The M&O organ can adjust any note in any stop in frequency and amplitude. By adding the new sine wave stops to the existing stops we were able to create very convincing 64' and 128' stops.


Here is an FFT of the Atlantic City 64' diaphone which formed the basis for the sound pressure levels used at Trinity.




Using this as a baseline I set the maximum levels in the center of the sanctuary at 105dB below 20Hz. The existing subs measured about 87dB at 27hz. We added a good bit of weight to the signal at very low frequencies. At 110 dB the large glass entry doors were moving, out of respect for the structure we stopped at 105dB and Bob Woods of Telarc was pleased with the result. Thanks for the question


brucet
 

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Quote:
We temporarily installed two TRW-17 rotary woofers in the church and were able to get down to about 6Hz at up to 110dB.


So what did that "sound" like?


Sound at that level is all "Feel", correct?
 

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Penngray


Perhaps the biggest misconception is that very low frequency sound is all "feel". If you get 6-10Hz up to over 120dB then yes, you begin to feel it. But you can actually hear it long before you feel it. In fact with mixed tones as is the case with a pipe organ the audible thresholds for very low frequencies are much lower, about 6 to 10dB less than the pure tone thresholds. In other words, well before you feel the sound you will hear it. In the middle of the sanctuary the 32' and 64' sine wave stops sounded really good. 105dB is the sound level it took to make these tones below 20Hz audible. This became the reference level for these stops.

In researching this project it is apparent that pipes in these organs are not really very loud, and definitely not very efficient. The pressure in the organ manifold determines how loud they play. The recordings show that they do not produce a really good pure tone because of the non linear compressibility of the air in the pipe. Also some stops are not supposed to produce a pure tone.


brucet
 

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I need to say that the church was extremely helpful in allowing us to set up the woofers. They allowed us free run of the church for as long as we wanted to work. We explored the entire building in search of backspace volume. We crawled into but ruled out the crypts under the church.

We finally settled on a side entry enclosed porch with double doors leading to the sanctuary. The porch would enclose the back wave and the double doors gave us plenty of space for a temporary baffle.


this is an outside view of the enclosed porch:





This is what the inside of the porch looked like as the baffle was being constructed. The double doors on the other side of the baffle lead into the sanctuary.








This is the porch view of the finished temporary installation. We used 2 by 6" braces and 200 pounds of gravel to hold it in place.






This is a view of the finished baffle from the sanctuary side. If you enter the sanctuary through the main front doors these doors would be on your right and a gift shop is on the left.





I will post information about Telarc's temporary recording studio, the organ and performance measurements in an upcoming post. I was really impressed with how much effort and time Telarc put into this recording project.


brucet
 

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Discussion Starter #11
Thanks for the info Bruce, cool pics of the dual Rotarys.


Is the CD going to have a low frequency warning on the label?



At the Middle Collegiate church where you're doing your permanent Rotary Sub install, do they have the same Marshall and Ogletree virtual organ that Trinity has with the Ruffatti console and Def Tech bi-polars?
 

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Bruce,


"...with mixed tones as is the case with a pipe organ the audible thresholds for very low frequencies are much lower, about 6 to 10dB less than the pure tone thresholds. In other words, well before you feel the sound you will hear it."


But is it just the higher freq that are audible, or is there some auditory phenomenon whereby the presence of (harmonically related?) higher freq makes the lower freq audible.
 

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Quote:
Originally Posted by noah katz /forum/post/14110106


Bruce,


"...with mixed tones as is the case with a pipe organ the audible thresholds for very low frequencies are much lower, about 6 to 10dB less than the pure tone thresholds. In other words, well before you feel the sound you will hear it."


But is it just the higher freq that are audible, or is there some auditory phenomenon whereby the presence of (harmonically related?) higher freq makes the lower freq audible.

Stochastic resonance?
 

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Quote:
Originally Posted by noah katz /forum/post/14110106


Bruce,


"...with mixed tones as is the case with a pipe organ the audible thresholds for very low frequencies are much lower, about 6 to 10dB less than the pure tone thresholds. In other words, well before you feel the sound you will hear it."


But is it just the higher freq that are audible, or is there some auditory phenomenon whereby the presence of (harmonically related?) higher freq makes the lower freq audible.

I was wondering the same thing. The one thing I could come up with is that the harmonic signature of a sub-audible note would be different. For example a 10Hz musical note would have some harmonic content at 20Hz, 30Hz, 40Hz, etc where a 20Hz note would have harmonic content at 40Hz, 60Hz 80Hz, etc. Basically by having your fundamental at a lower frequency you'll get a tighter grouping of harmonic content so it should sound different. I'm not sure if you will actually hear the fundamental though.
 

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Discussion Starter #15
Do sine waves have "harmonic content"?
 

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Quote:
Originally Posted by brucet /forum/post/14104173


Penngray


Perhaps the biggest misconception is that very low frequency sound is all "feel". If you get 6-10Hz up to over 120dB then yes, you begin to feel it. But you can actually hear it long before you feel it. In fact with mixed tones as is the case with a pipe organ the audible thresholds for very low frequencies are much lower, about 6 to 10dB less than the pure tone thresholds. In other words, well before you feel the sound you will hear it. In the middle of the sanctuary the 32' and 64' sine wave stops sounded really good. 105dB is the sound level it took to make these tones below 20Hz audible. This became the reference level for these stops.


In researching this project it is apparent that pipes in these organs are not really very loud, and definitely not very efficient. The pressure in the organ manifold determines how loud they play. The recordings show that they do not produce a really good pure tone because of the non linear compressibility of the air in the pipe. Also some stops are not supposed to produce a pure tone.







brucet




Yes, but do you actually hear anything below about 20 Hz? It appears to me that all you could be hearing are the harmonics in the audible range. In other words, how pure are the test sine waves reproduced on site?
 

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So, this all begs the question, brucet:


Did you see God?
 

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Discussion Starter #19

Quote:
Originally Posted by tkdee /forum/post/14110840


No, but an organ would as demonstrated by the Fourier plot that Bruce posted.

the plot Bruce posted was of an actual 64' pipe from the Atlantic City organ


the digital organ at Trinity, the 64' and 128' stops are made up of sine waves if i read his post correctly in post # 6
 

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I read that he added a sine wave to a pitch shifted version of the 32' stop to try and recreate the effect of the actual organ stop.
 
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