Can Infrasound Explain Ghostly Apparitions?

[zoobyshoe]

UK Man "Foils" Ghosts

http://www.findarticles.com

Current Science, Jan 19, 2001
Ghosts Busted in Haunted Rooms

"Vic Tandy, a computer expert, was working late one night in a laboratory in Warwick, England, which had a history of being haunted. At one point, a cold sweat and a feeling of depression overcame Tandy. Then a blurry gray figure appeared out of the corner of his eye. As he turned to the ghostly figure, it disappeared!
By coincidence, Tandy, who is a fencing enthusiast, took his fencing foils to the lab with him the next day. He clamped the blade of one foil in a vise in order to oil it. Returning with the oil, he found the blade vibrating like a tuning fork.
Tandy figured that a fan in the laboratory had created an infrasound wave, one below the range of human hearing. The vibrations of the sound wave had caused the foil to quiver. Tandy measured the vibrations at 18.9 hertz (cycles per second.

Tandy also knew that the human eyeball shakes when exposed to a soundwave of about 18 hertz (Hz). Putting two and two together, he deduced that what he had seen was no ghost; it was simply blurry vision caused by the shaking of his eyeballs.

Later, Tandy took his instruments to a famous haunted cellar in Conventry, England, and tested for infrasound there. Sure enough, the instruments registered the existence of an infrasound wave in the cellar that peaked at 18.9 Hz. Another ghost busted!"

Here is a more comprehensive write up of the story:

Fortean Slips: Spooky Acoustics
Address:http://www.parascope.com/articles/slips/fs30_2.htm

Here's a report of his visit to another "haunted" site.

Address:http://iccoventry.icnetwork.co.uk/0...fm?objectid=12722447&method=full&siteid=50003

Here's an E-Mail he wrote someone I found on google:

RootsWeb: ORCADIA-L Re: [ orcadia>] Vic Tandy
Address:http://archiver.rootsweb.com/th/read/ORCADIA/2001-06/0993717998 Changed:12:46 AM on Thursday, June 28, 2001

I think this guy is very cool.

 

[Ivan Seeking]

I have been working on this one Zooby. I am having a bit of trouble finding the NASA tech note so I am making a post in the Astronomy forum to see if someone else can find it.

I am building a low freq source and testing this myself. I will let you know when I have it running...later this week I expect. If I have trouble this could take a couple of weeks or more, but I don't expect this to be THAT difficult.

Let's see if I can spook myself. If this is not too difficult, perhaps others here at PF can try this as well.

This seems to be outside of the normal response of most speakers and amps. I checked with an audiophile who started citing high end equipment as the solution...to the tune of a few thousand bucks, so I am contemplating other options for a high amplitude low frequency source; preferably with variable waveform shapes, amplitudes and frequencies.

My alternative hypothesis is that ghosts produce 18.9 Hz infrasound.

Really I find the subject very interesting; though I suspect it has been accepted a little to quickly since good sources of information on the effects of infrasound [IS] seem to be hard to find. Since I haven't looked for awhile I will be checking again for other sources. I find many wild claims associated with IS that appear to be unsubstantiated. These include the ability to cause loss of bodily functions, loss of consciousness, orgasms, any number of mental states of anxiety, euphoria, depression etc. Obviously to some degree these claims are true, but I question the energy levels required and the likelihood of the effects claimed in many specific circumstances.

Any links to good papers on IS and ideas for a sound generator are appreciated.

Edit: um, make that effects, not affects...let me see, one's a noun, one's a verb

 

[Evo]

Hey Ivan,

I'm really interested in this also, but I can't find anything either. This is the closest thing I found on infrasound that had tests on humans.

http://ntp-server.niehs.nih.gov/htdocs/Chem_Background/ExSumPdf/Infrasound.pdf

 

[zoobyshoe]

I'm not aware of any formal studies but I haven't looked for any.

What have you guys tried googling?

 

[zoobyshoe]

Originally posted by Ivan Seeking
I am building a low freq source and testing this myself. I will let you know when I have it running...later this week I expect. If I have trouble this could take a couple of weeks or more, but I don't expect this to be THAT difficult.

If I were going to undertake such a thing I would go for a low tech approach that might more closely resemble what might naturally occur. I'd find a large diameter pipe, calculate the length needed for a resonant frequency of 18.9, then figure out the easiest way to "sound" the pipe. That might involve sticking a diaphram over one end and vibrating it at the resonant frequency with a solenoid, or even mechanically with a piston and a variable speed motor. The best way, though, would be to sound it by configuring one end as a whistle the way they design organ pipes and blow into it with a bellows. The big 16 foot base pipes on a church organ can make a window rattle with very little air pressure. (You'll need volume, though.) The difficulty would be tuning it. I don't know what kind of instrument you need to get accurate info on frequencies outside human hearing.

Zoob

 

[Evo]

I've googled the NASA Tech doc references, searched for them at the NASA website, nothing comes up. I googled on quite a number of things, but most are rather questionable sites, all claiming that NASA has done research that has supported Tandy's findings, but none ever give any details on the reports, including a paranormal website that is working with him & will be selling his "devices". So I've been looking for any research on infrasound and it's effects on humans. What I posted above was the only legitimate research I could find.

I think the infrasound theory might explain a lot, if it's true.

 

[zoobyshoe]

Well, I spent about an hour poking around and couldn't find anything that was online. I did find references to a couple studies in old journals. Outside Tandy, this doesn't seem to be a big topic for scientific studies.

There was a lot of mention of the fact that elephants produce infrasound. Also, sperm whales kill their prey with it. A marine biologist messing around with a beached sperm whale was knocked back from the beast when it blasted him with a punch of infrasound. I also recall seeing a movie of a diver getting taken in the jaws of a baby sperm whale and then released. She said in a later interview she could feel it's infrasound signals throbbing over her body while it was checking her out before grabbing her.

 

[Ivan Seeking]

It is possible that due to the military applications for IS the original work has been classified. However, it seems that Tandy had access to this so I'm a little stumped right now. I know that a number of reliable sources of defense technology news, like America's Defense Monitor...no longer being produced but a great show, have mentioned IS weapons and their usage. I am going to email Tandy next and ask for help.

Thanks for the paper Evo; I will read later today...gotta work...darn those evil customers!

A sidebar: I played around with pulse jet technology some years ago. A wacko friend had a great interest in this... Pulse jet propulsion was first developed by the Germans and was used on the infamous Buzz Bombs that rained down around London in WWII. The sound produced by these engines [which can be made with no moving parts by the way], is very loud and occupies a very broad spectrum of low frequencies. Some years ago some genius got the idea that this technology could be used for rice dryers. Since the rice can pass right through the combustion chamber with no ill effects, the efficiency and speed of the flash drying process seemed ideal for the application. So, they built a pulse jet of enormous size to handle the mass flow [of rice] required. The first time they fired up the engine it was so loud that a number of people threw up and passed out! Whoops! The project was abandoned.

Zooby, I agree, It would seem that a large flute is the best option. It seems that I must come up with 55 feet of large diameter pipe… Do you think the local farmers would miss their irrigation pipes if they disappeared overnight?

 

[Ivan Seeking]

I would like to have some idea of what level of infrasound intensity becomes dangerous. This is so that I don't do anything embarrassing when I turn it on; like poop my pants.

 

[zoobyshoe]

That's a fascinating story about the pulse jet. (I actually expected it to end turning out to be the way Rice Crispies were discovered, though.)

I do believe you are grossly exaggerating the size of the pipe you would need. The 16 foot base organ pipes I spoke of are already on the verge of infrasound. They are about 6 inches dia.

An interesting alternative would be two higher pitched pipes slightly out of tune such that they "beat" at 18.9 cps. Chroot is a whiz at accoustical phenomena. I'd check with him.

-zoob

 

[Ivan Seeking]

Originally posted by zoobyshoe
An interesting alternative would be two higher pitched pipes slightly out of tune such that they "beat" at 18.9 cps. Chroot is a whiz at accoustical phenomena. I'd check with him.

-zoob

That's really a great idea! In this case I prefer that no audible frequencies are present to that I can crank up the volume and leave it running without any other annoying noise to contend with.

I wonder how my cats will react. We had to put down our last dog a few weeks ago so the puppy torture will have to wait.

 

[zoobyshoe]

Originally posted by Ivan Seeking
In this case I prefer that no audible frequencies are present to that I can crank up the volume and leave it running without any other annoying noise to contend with.

Yeah, this wouldn't work then, since "beats" are always at a considerably lower frequency than the tones producing them. The tones producing them would have to be in the audible range, to "beat" in the infrasonic range.

I would imagine this is why industrial fans seem to be responsible for infrasound so often: two identical fans but placed such that there is more drag on one than the other causing it to run a touch slower such that an infrasound "beat" is produced. The fans, though, have to be making audible noise to begin with.

 

[dlgoff]

Have you thought of just using an audio amp with a subwoofer? Making a 18.9Hz oscillator and attaching it to the amp input would be easy. You will still get sounds from the walls shaking however. It may also shake something loose in you. My susgestion; turn if off when it hurts.

 

[zoobyshoe]

And I'm also curious as to what an infrasonic frequency detector would consist of.

Frequently here in San Diego I am conscious of a rumbling sensation that seems to be coming up from the floor and I always wonder if it is a mini-quake, the result of heavy traffic on a nearby highway, or extreme base from a sound system somewhere I can't directly hear.

It would be cool to have an infrasound detector to see if I could sort this out.

-Zooby

 

[Ivan Seeking]

Originally posted by zoobyshoe
And I'm also curious as to what an infrasonic frequency detector would consist of.

I understand that fencing foils make nice detectors.

Really though, sympathetic resonance should be easy to produce in any properly constructed mechanical oscillator. Shouldn't be too difficult to make...I will pass along anything that I come up with. I will need a detector as well. I am told that a subwoofer is still down in the mud for producing sound at <20Hz; too much signal attenuation. Apparently the speaker will also cease to resonant properly due to the electrical characteristics of the coil. I am told that his will create a low impedance load that could overload the circuit. As I indicated, one can purchase equipment designed to operate at these low frequencies, but this gets too expensive for my purposes. I think this may work well the other way though. A large speaker and an O-scope may be good enough as a detector.

Also, I am wondering about our creek. It produces a lot of low freq noise. I also wonder about the examples of wind induced madness.

OK now I really have to work!

 

[mouseonmoon]

This is somewhat related- film crew from PBS at Radio Oservatory West Va.-

"One day, while our crew was working at Green Bank, something humorous happened. Our production crew was in the control room for the old 300 foot radio telescope -- which I believe was the largest in the world at the time. Either a scientist or technician was showing us a graphic print out of what the dish was picking up.
When we first began looking at the printout the technician explained how we were seeing random background noise. But the printout's pattern suddenly changed to indicate that a strong narrow band signal had just broke through the steady hash! The tech muttered something to himself -- howbeit out loud -- something like, "... That’s strange ..." Then -- while we were all still watching -- it happened again! Then once more! The technician obviously tried to contain his excitement, but he hastily called another person over to look at the printout. By this time our crew had also begun to watch the print out. And for a moment -- we hoped that perhaps we were watching history in the making. (picking up radio signals from ET)
Our crew’s photographer, who had been taking pictures (with the same Nikon I had tried to use before) around the control room, was now bug-eyed like the rest of us and clicking away. Then suddenly -- we noticed how the printout registered the strange signal every time our photographer snapped a picture and the electronic flash began to sing as it recharged its high voltage flash potential. Sure enough, the sensitive electronic radio frequency detection equipment had been picking up the strobe’s regeneration circuitry in the flash unit!"

=====

light 'flashing' at certain rate will produce 'hallucinations' and or physical effects-latest example was the Japanese cartoon show-- or driving along in a car with sun-light 'blinking' through trees can produce very disorienting effects...number of experiments with this-in a 'closet'-- and watching movies at different 'flicker rates'...

i'm guessing 'sounds' may be able to cause similar effects (note:not everything we 'hear' is coming through our ears .

 

[Evo]

Ivan, I think the paper I posted may give you an idea of safe parameters to work with. It also appears that you should not expose yourself to infrasound at low levels for very long?

 

[Ivan Seeking]

Hello Mr. Tandy,
I was trying to find the NASA Technical Report 19770013810 as cited as a source of information about the effects of infrasound. I have had no luck finding this and was hoping that you might provide a little guidance.

Many thanks,
******* [Ivan]
-----------------------------------------------------------

Hi ****** [Ivan]
NASA always have a job turning this up... tell them it was done by a
contractor. Contractor stuff is held in a different place it would seem.

Good luck

Vic
------------------------------------------------------------

Hello Vic,
Thanks for your response. Do you have a date, author, or title. This might help tremendously.

Many thanks again,
******** [Ivan]

 

[Njorl]

Bah! Everyone knows ghosts vibrate at 18.9Hz.


Njorl

 

[Ivan Seeking]

Clearly this is why we feel anxiety when exposed to 18.9 Hz infrasound. This is an evolved trait.

I am after this guy just a little. To me his story doesn't seem to add up. I'm not convinced as such, but something about this claim strikes me as bogus. I was thinking at first that 19 Hz is too low of a frequency for a foil to resonate, but considering the flexibility of these rods I could be wrong. Next, the frequencies seem a little too specific for my expectations. For example, one article cites that someone noticed that reports of ghosts in one building increased with increasing room size. This would imply that all but one room had "real" ghosts, or these claims are bogus, and the properly sized room allowed for resonance, and the claims from this room were legit. Next, his lack of details in citing THE critical source of information bothers me as well. I bet that Evo has the same suspicions. However, my mind is open and I make no judgments. He could just be a little lazy about his sources.

This is why I want to try this myself. Besides, it could be very useful tool when dealing with clients...it might work even better than a big chair!

btw, that was just a joke. I would never expose anyone to something like this without their knowledge; or likely even with their knowledge. There is too much potential liablity.

 

[zoobyshoe]

What I gleaned from the search I did was that all the infrasonic frequencies have one bad effect or another. The 18.9 is what Nasa determined to be the frequency at which the human eyeball shakes.

In cases where the oscillations are being produced by machines and traffic or, who knows, some kind of plumbing vibration, the resonant frequency of the room wouldn't matter. The latter would only be important in cases where the room was being made to resonate by say wind. Then, some part of its resonant frequency would need to be in the infrasound range at a suitable amplitude.

Fencing foils are square in cross section and they taper from the hilt to the tip. I'm sure this geometry has an effect on how they vibrate in sympathy, although I couldn't begin to figure it out myself. I'm sure the steel used is quite unique and specifically tailored to its purpose.

-zooby

 

[Ivan Seeking]

Originally posted by zoobyshoe
What I gleaned from the search I did was that all the infrasonic frequencies have one bad effect or another. The 18.9 is what Nasa determined to be the frequency at which the human eyeball shakes.

I agree about the effects of infrasound in general. I just want to determine that in fact NASA did reach this conclusion about the eye; and at what intensity levels. This is one of my concerns with this explanation: The levels needed could easily exceed those possible to produce naturally. I know that some IS weapons discussed in the past use phenomenonally high levels of energy...far beyond that produced by fans or wind [sound] chambers.

In cases where the oscillations are being produced by machines and traffic or, who knows, some kind of plumbing vibration, the resonant frequency of the room wouldn't matter. The latter would only be important in cases where the room was being made to resonate by say wind. Then, some part of its resonant frequency would need to be in the infrasound range at a suitable amplitude.

The correlation between room size and effect was indicated by the author as a lead to the IS explanation. This implies that the room is acting like a resonant chamber. This creates a problem for experiences in undersized rooms. Again though, these are really just points that I think need to be clarified.

Fencing foils are square in cross section and they taper from the hilt to the tip. I'm sure this geometry has an effect on how they vibrate in sympathy, although I couldn't begin to figure it out myself. I'm sure the steel used is quite unique and specifically tailored to its purpose.

Yes this is probably very difficult to calculate. I was thinking of making a run over to OSU; which I'm due to for a lunch next week anyway. I hope to have a look at some foils then. The resonant frequency is easy enough to determine with the foil in hand - TWONNNNG.

 

[zoobyshoe]

Originally posted by Ivan Seeking
I agree about the effects of infrasound in general. I just want to determine that in fact NASA did reach this conclusion about the eye; and at what intensity levels. This is one of my concerns with this explanation: The levels needed could easily exceed those possible to produce naturally.

I have an old book of science effects. In one demonstrtion they lay a long, flat, metal bar horizontally on two supports placed about 1/4 to 1/3 from each end, and then drip water on the bar. Playing with the frequency of the drips will allow you to arrive at one which starts the bar vibrating vigorously.

Don't forget Tesla's favorite example of the small boy pushing the fat man on the swing. All the little boy has to do is add his tiny little push at the right time, just as the big fat man is on the verge of swinging away from him, for him to slowly build up a large amplitude. Timing is more important than force.

The correlation between room size and effect was indicated by the author as a lead to the IS explanation. This implies that the room is acting like a resonant chamber. This creates a problem for experiences in undersized rooms.

This is where we need Chroot. I think that based on the very low note you can get by blowing across the opening of a jug, and also by the relatively small volume contained inside a 16 foot window rattling organ pipe, you would find that the minimum sized room that could naturally resonate in the infrasound range in probably quite small.

I hope to have a look at some foils then. The resonant frequency is easy enough to determine with the foil in hand - TWONNNNG.

Foils turn up at the big swap meet here in San Diego now and then. People want a lot of money for them. If I knew of a proven infrasound source I would just clamp a three foot length of.250 cold rolled in a vice and see if that worked just as well.

 

[Ivan Seeking]

Originally posted by zoobyshoe
This is where we need Chroot. I think that based on the very low note you can get by blowing across the opening of a jug, and also by the relatively small volume contained inside a 16 foot window rattling organ pipe, you would find that the minimum sized room that could naturally resonate in the infrasound range in probably quite small.

Chroot is a very smart and knowledgeable guy, but this is mostly a first year college physics problem. I'll save Chroot for the hard problems. In order to create a resonance in a closed chamber, the wavelength cannot be longer than the maximum dimension of that chamber. The speed of sound in England [near sea level] should be about 990 ft per second. AT 18.9 Hz, this yields a wavelength of about 52 feet. Also, in any chamber, be it open, or closed on one or both ends, the effective chamber length must be an integer multiple of, or a specific fractional multiple of the desired wavelength. If none of the rooms had a maximum dimension of 52 feet then we might have a real problem. On the other hand, open doors and other "holes" in our chamber could complicate this scheme, but this would act to reduce the infrasound's intensity significantly...or nearly completely.

 

[zoobyshoe]

Originally posted by Ivan Seeking
AT 18.9 Hz, this yields a wavelength of about 52 feet.

I have checked and this is true. Except I got more like 59 feet.

Also, in any chamber, be it open, or closed on one or both ends, the effective chamber length must be an integer multiple of, or a specific fractional multiple of the desired wavelength. If none of the rooms had a maximum dimension of 52 feet then we might have a real problem.

In the second article I posted note the references to long coridors, and chambers built with tunnel entrances.

On the other hand, open doors and other "holes" in our chamber could complicate this scheme, but this would act to reduce the infrasound's intensity significantly...or nearly completely.

I don't see why. The opening would be the means whereby the sound enters the chamber from a natural source to resonate.

 

[Ivan Seeking]

Crud. Maybe we should have got Chroot.

We can get a standing wave at wavelength = 2L i.e. we only need half the distance.

I almost forgot about the half wave mode. There is a quarter wave mode that could apply to corridors open on one end, but this wouldn't apply to a closed room. This does apply to your organ pipes though. My objection was based on the size of the rooms. At 27 feet this sounds much more reasonable. Now I can imagine that we have rooms with a ~27 foot axis. This helps his explanation in this regard.

I still have serious doubts about the intensity required though. I will need convincing. Also, I'm a little surprised that in his e-mail Tandy did not include the date, author, and title of the paper. This really concerns me right now. Still, I'm not trying to hang Tandy, I just need these questions answered.

Keep in mind that debunking is big money now. There is a book involved. This eye explanation is being touted here and elsewhere with no supporting, retrievable reference, other than Tandy.

 

[zoobyshoe]

Originally posted by Ivan Seeking
Also, I'm a little surprised that in his e-mail Tandy did not include the date, author, and title of the paper. This really concerns me right now. Still, I'm not trying to hang Tandy, I just need these questions answered.

I'm wondering if he ever read it. It's more likely that he ran across a summary of it in a science or technical journal and happened to recall the part about the 18.9 eyeball frequency because it was strange.

I wonder, too, to what extent NASA makes any effort to actually find any info for anyone who asks for it. I don't see where they'd be under any obligation to do so.

Did you try back with NASA with Tandy's instructions to tell them it was a contract job?

 

[Evo]

Here is another mention of the effects of infrasound on the human body, again no mention of affecting the eyes.

Abstract: Purpose: Within the context of a research project on ‘Non-Lethal Weapons,' an up-to-date review was required with regard to 1) the effects of infrasound on the health and functioning of human beings, and 2) the availability of adequate systems for the production of infrasound. ---- Methods: In a literature study, the existing information about infrasound effects was assessed and structured. Relevant auditory (including perception, hearing damage, physiological alterations, task performance, fatigue) and non-auditory (including vestibular functioning, respiration, body vibration) effects of infrasound (0.1-20 Hz) were determined as a function of sound pressure level and sound frequency. ---- Results: The threshold for audibility of infrasound is very high: for frequencies from 2 and 20 Hz, the threshold decreases from 125 to 80 dB. The threshold for aural pain is 40-60 dB higher than that for audibility, and the threshold for eardrum rupture is about 185 dB. Fatigue and drowsiness effects are first reported for sound levels between 120 and 130 dB. Decrements in task performance and vestibular functioning could not be found: for significant effects, levels higher than at least 140 dB are required. Physiological alterations (blood pressure, heart beat frequency) require levels higher than 130 dB at least. At present, adequate systems for the production of infrasound to be used as a non-lethal acoustic weapon are not available. ---- Conclusions: For significantly affecting human functioning by infrasound, sound levels higher than 130-140 dB are required. With sufficiently long exposure durations at these high levels, the occurrence of permanent hearing damage might be expected. For the production of infrasound at source-receiver distances up to a few hundreds of meters, severe problems have to be solved.

http://www.tm.tno.nl/publ/wn2001r.html

 

[Ivan Seeking]

Originally posted by zoobyshoe
I'm wondering if he ever read it. It's more likely that he ran across a summary of it in a science or technical journal and happened to recall the part about the 18.9 eyeball frequency because it was strange.

Basic ethics requires that he can produce his source.

I wonder, too, to what extent NASA makes any effort to actually find any info for anyone who asks for it. I don't see where they'd be under any obligation to do so.

Did you try back with NASA with Tandy's instructions to tell them it was a contract job?

This information should be available. The NASA archives provide direct access to a great deal of material, but not all; mainly determined by the age of the document in most cases. I couldn’t find this document in the archives. A personal request may be needed but I was waiting for Tandy to respond. If he doesn't respond soon I will contact NASA directly.

As posted by Evo and as I quickly noticed, there are good sources that discuss some effects of IS on humans, but I couldn't find one good source to back up this claim about eye resonance. This raised a flag for me immediately. Still, if this work was done long ago, and if for some reason the information has remained obscure, or if I just happened to miss the good link, then it may just take a little more work to validate Tandy's claims. In spite of my hesitation regarding the claims made, I wouldn’t expect someone like Tandy to perpetuate a fraud, rather I am inclined suspect that he might have made a hasty conclusion. One or two examples aren't exactly overwhelming as evidence.

 

[zoobyshoe]

Hmmmmmm.

Tandy's frequency of 18.9 is specific. Why would any sound make an eyeball vibrate? Is it the size, shape, or mass? Wouldn't it really have to be somewhat different for each person?

Evo's post cites studies done on infrasound as a possible weapon. What was NASA doing the tests for? Probably because of the infrasound generated during launches - a different focus leading them to concentrate on different effects with very different study techniques.

 

[Ivan Seeking]

Originally posted by Evo
Here is another mention of the effects of infrasound on the human body, again no mention of affecting the eyes.

One would think that this effect would be mentioned. This is becoming more of an issue.

Thanks for the help. After reading some of your material I am less inclined to build this device.

WHAT DID YOU SAY?

 

[zoobyshoe]

I just felt a great disturbance in the force.

 

[Ivan Seeking]

Some references for comparison

0dB the faintest sound we can hear
30dB a quiet library or in a quiet location in the country
45dB typical office space. Ambience in the city at night
60dB Martin Place at lunch time
70dB the sound of a car passing on the street
80dB loud music played at home
90dB the sound of a truck passing on the street
100dB the sound of a rock band
115dB limit of sound permitted in industry
120dB deafening

dB(A): A-weighted decibels The ear is not as effective in hearing low frequency sounds as it is hearing high frequency sounds. That is, low frequency sounds of the same dB level are not heard as loud as high frequency sounds. The sound level meter replicates the human response of the ear by using an electronic filter which is called the "A" filter. A sound level measured with this filter switched on is denoted as dB(A). Practically all noise is measured using the A filter. The sound pressure level in dB(A) gives a close indication of the subjective loudness of the noise.

source:
http://www.rtagroup.com.au/wizard/definition_acoustics.html

"Some Examples of Dangerously Loud Recreational Activities

Noise levels at video arcades can be as high as 110 dBA.

Firecrackers create sound levels from 125 - 155 dBA at an average distance of 10 feet.

Sound levels at live music concerts can be measured at 120 dBA and beyond.

The noise level of gunshots can be measured at 150 dBA -167 dBA and hearing loss can result from just a few shots of a high powered gun, if appropriate hearing protection is not worn.

Noise levels at movie theaters have been measured up to 118 dBA.

Sound levels in health clubs and aerobic studios can be as high as 120 dBA.

Personal stereo systems with headphones produce sounds as loud as 105 - 120 dBA if turned up to maximum levels.

Sound levels at a sporting event can be measured up to 127 dBA.

Motorboats emit sound levels ranging from 85 - 115 dBA.

Motorcycles have been measured at levels ranging from 95 - 120 dBA.

Noise levels of snowmobiles are as high as 99 dBA.

Many children's toys emit sounds which are measured at 135 dBA -150 dBA.

Noise levels from 'Boom Cars' have been measured at 140dBA and beyond."

Source:
http://www.lhh.org/noise/facts/recreation.htm

 

[megashawn]

Hey, I'm not sure if this will help you out at all, but I've got a bass cd at home that is meant to test the range that a subwoofer performs at.

I had this particular track on a cd and didn't realize it was playing, while driving down the road. I couldn't hear anything, but I could feel the bass, and at one point it got so bad that my eyes started shaking as was described in the story. Now I didn't see any ghosts, but I damn near ran off the road because I couldn't hardly see.

I'm not sure if this will help you out, but perhaps you would have an easier time using a frequency generator for a computer and a sub woofer or two. If interested, let me know I'll find that cd and rip a mp3 of the particular track.

I also remember reading a story, I think on Newscientist, may have been a link in one of the pf newsletters, about a very low frequency bass that actually induced feelings of fear in people listening to it. It wasn't audible, but seems it was right along the same idea that you guys are working with.

 

[Ivan Seeking]

Thanks Megashawn, that's quite interesting! I have a few questions if you don't mind.

What kind of CD player, amp, and speakers do you have - ie make, model, approximate year of production...? I wanted to check the technical data.

What was the volume level set to at the time?

What is the name of the test track...or do you have any links on the specifications?

Has this ever happened since. Can you duplicate the effect?

Did this happen in the day or at night? If at night, how is your night vision?

I assume that the effect stopped when you stopped the CD?