Virtual Organ Stacked Horn Sub Questions

[jbell]

Originally Posted by mashaffer

32' rank is 16Hz, 64 would be 8Hz. Several dispositions do have 32' flutes or diapasons which will have a pretty good fundamental.

Understand, most 64' stops use a 32' and a 21 2/3' to make a fake 64. Many 32' stops do the same type of thing.. If you play mainly 32's -- It might be worthwhile to take your output, loop it back and run an RTA on it to verify what your stops are really doing, and then build your subs to match.

[mashaffer]

In the sample sets I have seen there are some examples of direct sampled 32' stops but many are done by frequency shifting of 16' samples. In any case they are generating tones in the 16Hz range.

Even if done by combining stops it would seem that the resultant frequency would still appear at the speakers as long as the mixing were done electronically (either digital or analog). Am I missing something here? It seems to me that the only way to avoid having to reproduce the actual frequencies would be to have one speaker generating the fundamental (16') pitch and another one generating the quint and allow the mixing to occur acoustically. One could do this I suppose but I am not aware of this method being used in VPOs.

As much fun as it might be, I wouldn't really have any interest in generating a 64' rank as I don't think it would really be useful.

[jbell]

missing fundamental is just that --- missing.

If you only have to generate 32hz, not 16hz -- that is exponentially easier.

Get out the RTA to make sure.

[mashaffer]

Since one of the memory slots died on my VPO computer I am limited in what I can do (can't really play anything) until I get a replacement. However I will try to see if I can get it to load a smaller organ like the Mockers and the spectrum analyzer at the same time and check out the 32 on it. Otherwise I may be able to create a test disposition with only the one stop if (big if) I have enough working memory to import the SF file.

Will report back if I find out anything. And yes, 32Hz is trivial.

[mashaffer]

I was able to get Mockers to load along with the spectrum analyzer. The analyzer only goes down to 20Hz but I was able to determine that with the Subbass 32' on, the fundamental on the second "C" is a strong 32Hz so the low "C" would indeed be 16Hz.

Just in case they might play games with the last octave I went ahead and ran down the C major scale and the fundamental stepped down as expected until it went off scale. Even on the low "C" I could still see a tiny bit of the right side of the trace of the fundamental.

It would be possible to create our own Resultant 32' by using a quint (very easy to do in jOrgan) but the result would probably be less satisfying than the real thing.

One thing that might give us a little bit of wiggle room is that the horn can be tuned a little bit higher than 16Hz (actually I believe the actual frequency is 16 point something) as long as it doesn't unload enough to damage the driver and still provides enough output to be useful.

The opening into the room from the chamber is 6' wide by about 5' high on one side and about 6' or 7' high on the other however back from the opening a few feet we have at least 8' or 9' of width. So a stack of up to four horns (front, back, tapped or whatever) could be accommodated up to 8'x6'.

The chamber in which I plan to put the pedal and great division has an electric overhead screen several feet in front of it leaving only a couple of feet of the opening above the screen. I assume that the sub-woofer would have no problem with this and the smaller speakers could be installed in such a way as to allow them to speak over the screen. Getting an acoustically transparent screen is a possibility as well.

[jbell]

Do you have 8' tall? aka a quad of up/back TH that's 8' tall by about 20"x24"

Yea, it's usually only the bottom 1/2 octave or bottom octave they play with -- but I think your RTA test, where you could see a 'bit' of the fundamental on your C tells us it's real, not phantom..... I guess there is a reason many of these organ installs are infinite baffle.

[mashaffer]

For a look at the target installation see here...

Small VO project Inspiration from larger installation

I think you need to be registered (free) to see the pics. If you don't want to do that here are a couple of pics to give you an idea.





In the first picture you can see the square pattern lattice across the bottom of the openings. They look to be about 1 foot square and there are six across the bottom so the width is about six feet so you can get an idea. The rooms behind fill the entire area from the loft to the outer walls so the space is pretty large. Quite a bit of room for a stack. Original experiments used a pair of 1x15" PA speakers in the right hand chamber and a cludged together 2x12" sub under the keyboards that I was using. It did a credible job of filling the room if care was taken not to get too excited.

In the second picture you can see the screen (retracted) behind the light fixture on the left.

Building construction is brick and I think that they are plaster on lath walls but I am not sure.

[jbell]

Go IB, add watts, don't break the plaster.

start with a quad of these.
http://www.parts-express.com/pe/show...number=295-455

[mashaffer]

Interesting that you should mention that driver. I looked at it some time ago as an IB.



It seems to like a TL even better. No need for EQ in the TL and maybe a couple DB more output.



The distortion might be better with IB but I am not sure once you add the EQ. Might need 8 drivers for IB. Four drivers gives about 135dB Max SPL in the TL v.s. 116dB in the IB (x-max limited). 8 IB gives about 122dB. Might even be able to get away with two in TL.

BTW, I really appreciate your help.

[just a guy]

Originally Posted by mashaffer

It seems to like a TL even better. No need for EQ in the TL...

Still not counting on any room gain at all? That response might sound boomy in-room if you don't eq the low end down. If I were you I'd measure the room's response before going too much farther.