I Can Hear Less Than 10Hz. Why?

Myybe you are feeling this more than hearing it; you are quite right that it can be sensed, and the "thud thud" description is good.

Big ears!

This and also you'll be supprized to know that ears are not the only "hearing" instruments in your body specially at low frequencies. I heard once about a deaf guy that could hear through a bad tooth. S.M.

That reminds me of feeling sound vibrations in a balloon.

From what I have experienced, low frequencies (< 16 Hz or so) do not register as a "tone"; instead, they seem like discrete thud-thud-thud impulses. I would guess that it depends on the individual's low-frequency perception.

i have a friend that has had his inner ear removed and claims to hear through his skull. he tells me that the sound is then transfered to the other ear.

That' because the tympanic membrane or one or more of the middle ear bone structures were dysfunctional. Sound conducts through bone and teeth very well.

One trick used by musicians is to use a tuning fork to tune a guitar. You can bite the end of the tuning fork and hear it very, very well as you tune the guitar.

Won't bet but I think it proved to be exposed tooth nerves responding to vibration, and signal found it's way to hearing center. S.M.

No, bone conduction. You can do the same thing with a tuning fork on your skull or on your breast bone.

Reminds of a trick I leaned in med school where a convict was complaining that he was paralyzed on his left side. My instructor grabbed a tuning fork and placed it on his left and right clavicle (collar bone) and asked if he could hear it each time.

The convict said he could hear it when on the right side, but when placed on the left - no sound. That test proved he was malingering (faking the illness) because bone conducts equally left to right. My instructor quietly said it was an old trick they used to weed these people out.

Teeth have a very solid connection to the maxilla and mandible bones, which conducts well to the skull and then the inner ear.

It might interest you to know that one of the worlds most renowned percussionists is deaf: Dame Evelyn Glennie. I am sure you will find her on youtube. She will be playing a performance role in the Olympics in UK too.

Many posts refer to bone and other forms of conduction - perhaps. If the sensation at 7 Hz is a buzzing type, then it is likely that higher harmonics are involved. If you have a suitable microphone (pressure sensor) and you display the waveform, you may be able to see if it looks purely sinusoidal. Of course you could digitise this time series and analyse it, but that may be too much effort unless you are already capable of doing this... There is a great deal of infrsound around - it would be a distinct problem if we could all hear it all the time. Some people have a real problem in the sub 60Hz region being constantly aware of the noise from machinery, roads, electrical items etc.

Hearing is a subjective topic and you heard what you heard, though others might describe it differently.

GA my thoughts exactly.

are you writing this on behaft of your dog? it's unusual for a human to pick up sounds below 20 hz

I don't think dogs hear those sounds, they "feel" them.

But elephants do!!!

Sorry AH, I just read your post, you were first!!

Not only the speakers produce nonlinear products, mostly harmonics. But your ear is a quite nonlinear device at high sound pressures. It is really designed to sense soft sounds only. At high pressures the fine bones disengage to protect the hearing from damage. No linearity considerations at all there. So you hear, whatever such a mostly disabled ear produces. Linear it ain't.

Most likely not in this case. Reproducing high SPL at these frequencies requires a whole lot of cone motion and a very large cone area (i.e., multiple woofers of significant diameter).

While I don't know what speakers that were used, most likely they were typical stereo speakers, which are probably 10" woofers or smaller.

Here is an example of what I mean. The woofer is a 15" high power woofer that is rated for 500 Watts. I doubled the input power to 1,000 Watts to make a point.

There are two things to note here. The red is a vented enclosure and the yellow a sealed cabinet. The sealed cabinet has a fighting chance here to generate a 10 Hz signal at 97 dB. The vented has not chance at all. However, bear in mind my woofer is very efficient (94 dB-meters/Watt).

Also notice just how far the woofer cone must move to generate that kind of SPL, it is nearly 1" in each direction!

My point is I doubt that the original poster has the amplifier power or the high performance woofer to generate this kind of power, so my vote is that the SPL is not causing nonlinearities in the ear.

many stereo/speaker systems carry secondary harmonics. i'm guessing it's the stereo or radio frequeny you may be listening to. many radio stations use second rate broadcasting equipment that are notorious for producing second and third harmonics.

You heard something but how do you know that what you heard is below 20 Hz. Did you set up equipment to test what the frequency of the sound is? Just because you use a sound generator to produce it. Does not mean the sound produced was just at that frequency. Was the sine wave generator tested? All these devices can produce harmonics that would be audible. With out a proper test you are making conclusions that may not be. And asking us for verification. Try again this time do it right!

Anonymous hero, Thanks for your reply and thanks to all other responders too. I think your answer might be right. I really can hear this with my ear... its not via a bone or anything (well I think so). So I think chuffing and the cone struggling and trying to do its best might be source of sound. I took the front of the speaker off and could see the cone moving quite a bit. Ozzb, I can hear the lowness of the sound and the individual thuds that sound like 8 or so a second. I also have a scope to confirm frequencies.

Probably the cone of the woofer at the end of its extension.

If you were to get a high quality microphone and connect its output to one channel of an oscilloscope and compare that with the output of the signal generator you would be shocked at the difference between waveforms.

Anonymous Hero,

I might try that if I can find a good microphone.

Thanks

That is not easy since a good quality microphone is needed at those frequencies. but worth a try.

For these low frequencies an excellent 'microphone' can be made using a low range silicon pressure sensor.

The response of these silicon pressure sensors can be up to 1 mS so they are excellent at low frequencies.

Just be sure to use one correctly, ie use an absolute sensor or vent the reference pressure port on a differential sensor to a quiet location!!!

John.

If some one really wants to see what frequencies are available , in the real world, then they should go to some of the old Cathedrals , with the largest Pipe Organs, and try to measure those low notes--Electronics can "reproduce" many sounds, but nothing fills the Room like a 50 foot high set of Pipes--They use these notes to see how many of the high end Stereophile speakers, costing many of thousands, up to hundreds of thousand dollars, can reproduce- I have lived in Hawaii, on the Northshore, in the winter of '69, generally considered the largest surf ever recorded in Hawaii, and the vibrations (Sounds), were felt every time a wave broke , a mile out to sea-The "sound" of an earthquake (The grating of plates create soundwaves, and they are responsible of the damage caused) is one of the most chilling sounds you will ever experience--I have been through 3 of them , over 6. 0, and it will wake the dead, let alone, the hearing impaired--

Note: That observation wrt the deaf person being able to somehow pick up audio signals through a bad tooth is not that far fetched at all. There have been reports of people being able to pick up radio signals also through teeth. I am not sure how accurate these reports are. But perhaps there is a scientific explanation for this. Could it be that audio signals are transmitted via means other tha just the ears. What about viobrations? Is the body not able to sense vibrations.

At medical check-up we go through a hearing test every year at our workplace. We sit in a soundproof cubicle with headphones on soun system linked to a Computer. These sounds are often so subtle and feint that you cannot hear them. You are meant to click a joy-stick device each time you hear a sound of what ever frequency. In the end, after 15 mins, you get a print-out with your hearing efficiency wrt different frequencies. Ia appreaciate that they provide us with some data on the state of ones' hearing but how accurate is this all? What about the effect of concentration? Some guys can even fall asleep in during this test !

Another query I have related to ear-plugs (the simple foam type). Are there not other methods of ear-protection? Do they provide protection against all frequencies? And do they simply knock out a portion of the decibels? What about the potential damage that these ear-plugs can cause in long term use or when you pull them out thus causing suction on the ear-drum.

I prefer the headset/earmuff style. I call them "bullsh¡t filters" because they also protect me from verbal nonsense.

can you pop round to mine one night, I've got a low frequency hum I'd like you to track down.

Picking up radio waves through fillings. Wasn't the first recorded incident of that just a Lucille Ball wisecrack?

cnc

Agreed, Tornado : Ear Muffs are the best !

At the opening match to the 2010 World Cup Soccer match in South Africa I wore the Ear Muffs under a Cap. The one-note VUVUZELA instrument was seriously loud, what with 100,000 fans and half of them blowing at the same time. It sounded like an international swarm of bees. Not sure whether anyone tried to measure the Decibel levels or the frequencies on this day. But great atmosphere.

A signal generator will not have the current to drive a normal home hi fi speaker. At 16 Khz the crossover/s will have switched to the hi frequency driver. There should be no sound coming out of the woofer unless you have a falty crossover. I have designed several single driver full range back loaded horns and even with a smallish fullrange driver (4") you cannot drive the speaker with a signal generator even with a 94 Db 1 watt/meter driver.

Ron

(do a search on "Ron Clarke Horns")

I agree, but if you follow some of his subsequent posts he stated that he observed the woofer was extending/retracting a whole lot. That tells me that he was driving the signal generator into his amplifier.

I think the frequency used was 10 Hz, not 16 kHz.

Nice work on the horns, Ron. Honored to have you here, too!

In aperture involvement one must destined oneself ask a friend to join you in confluence and here together eliminate yourself from the equation and recheck if your decibel is sound the megahertz range should be amtitude in modulation frequencys are 4181,521,881, thats it. ED MARTINEZ M.L.D. MOLECULAR LINEAR DYNAMICS.

Experimenting with an unfamiliar phenomenon can certainly be fascinating, but there are two cautions.

Infrasound at high levels can damage your subwoofer, either by hyper-extending the cone or by overheating the voice coil.

A rotary woofer can solve that problem, but you should also be aware of the negative health effects associated with prolonged exposure to very, very low audio frequencies. Good luck.

What are the negative health effects associated with prolonged exposure to very, very low audio frequencies? Please cite relevant studies and journal articles.

Thanks, Martin

Ask someone who has fired a Howitzer, or been on the deck of a battleship, like the Missouri, when those deck cannons went off--I have heard that your chest sucked in, then out, from the pressure differential--Never been there, but it is something to think about--Talk about a Speaker!!

Been in similar situations, not so big as sixteen inch cannon, but near. Those are immediate effects, blown ear drums being number one. Further are these indeed extreme low frequency sounds? Or rather just extreme over-pressures? The poster suggested some intimate knowledge of long term health effects due to exposure to low frequency sounds, I'd like a little clarification, what sounds, what frequency, what SPL, duration, statistical analysis, suggested mechanisms, conditions, syndromes, something interdependently verifiable, not just some scary insinuation.

High frequencies can shatter brittle objects (Glass, granite, and even some extremely brittle metals), and low frequencies can bend and distort more malleable materials--An explosion ( Say, Dynamite) creates an immediate pressure change, and does its damage based upon the material to be affected, and proximity--We used 1/4 caps. 1/2 caps, and full caps, while doing major sewer and water drainage excavations, to make big rocks into small rocks--The choice was based upon drilling the object, and finding the presence , or not, of fissures (Weak points), and determining the size of "Frequency " to break the offending material apart--Really nothing different, except in the Sharpness of the Frequency, (Explosion), versus, slow detonation) Many health problems attached to sudden frequency changes, and pressure changes-(Ask someone who was close to Mt. St. Helens, , when it went off--Sorry--No one to sue)--I have many friends in the Construction trades, who are hard of hearing based not upon LOUD noise, but CONSTANT frequencies, over a long period of time..A lot of research to be done (My wife does not like the volume that I listen to my High End 2 -channel system at--)

C-Mac, indeed, there are many clearly documented and recognized consequences of exposure to loud sounds, I have no argument whatsoever with this. In fact I whole heartedly agree with many researchers who firmly believe, all be it less supported by good scientific studies who assert that stress levels in the body rise and lead to all sorts of nasty long term effects, heart disease, strokes, mental issues, disrupted sleep patterns, hypertension, etc.

My question was aimed at what specifically is unique to low frequency sound, as the original poster suggested that there was some special risk involved.

"My question was aimed at what specifically is unique to low frequency sound, as the original poster suggested that there was some special risk involved."

Only to his wallet when the woofer slams its voice coil up against the pole of the magnet.

No that can be an excruciating pain!

Look at the frequencies of Ultra Sound Technology--If they are not dialing you in properly, you will have resultant tissue damage--Again--Frequencies do make a difference--Not decibles, exactly, but frequencies--Where is Tesla when we need him? (Philadelphia project comes to mind)--

Martin, I don't think the OP suggested any risk, he is just asking why he can hear these low frequencies.

Health risks have been mentioned by other posters and we have both asked for more info from these posters, but I don't think anything came back.

After asking for help from the forum on tracking down a low frequency hum, I looked into the health problems caused by it, myself, but I found nothing concrete, like yourself.

One thing I did find out, by chance, somewhere else, which might answer your question, is that herd animals communicate danger via low frequency when out on the sveldt. My theory is that a throwback to this is causing a 'fight or flight' response in some humans, at a subliminal level, on exposure to LF sound, and this anxiety is at the heart of any problems manifested in humans. Elevated heart rate, paranoia, sleeplesness, poor breathing, the things you mention, can all be attributed to a subtle but prolonged injection of adrenalin.

Only my theory. Interested in your thoughts.

CNC

What are the negative health effects associated with prolonged exposure to very, very low audio frequencies? Please cite relevant studies and journal articles.

Likewise, having listened to one for about a year. Trouble breathing is one effect.

'zero Hz, a static pressure differential;' wow, wait 'till the next time someone says 'what do you know?'

cnc

Could you be so kind as to elaborate? "zero Hz, a static pressure differential", is not particularly meaningful to me.

I have been in HVAC fan rooms and am aware of immediate dangers, largely do to huge pressure differentials that can be incurred in a short time,, but not long term effects.

Thanks

Sorry for late reply baxterm, I took my eye off the thread.

My first statement was just reinforcing your request for more info on the effects of low freq. sound from bubbapebi, as you we have been subjected to it for a year now.

My second statement was just referring to the wikipedia article referred to by bubbapebi:

I quote an extract here for you.

The Rotary Woofer is a subwoofer-style loudspeaker which reproduces very low frequency content by using a conventional speaker voice coil's motion to change the pitch of a set of fan blades rotating at a constant speed. The pitch of the fan blades is controlled by the audio signal presented to the voice coil, and is able to swing both positive and negative, with respect to a zero pitch spinning blade position. Since the audio amplifier only changes the pitch of the blades, it takes much less power, per dB of generated acoustic sound level, to drive a rotary woofer than to power a conventional subwoofer, which uses a moving electromagnet (voice coil) placed within the field of a stationary permanent magnet to drive a cone which then displaces air. Rotary woofers excel at producing sounds below 20 Hz, below the normal hearing range; when installed in the wall of a sealed room, they can produce audio frequencies down to zero Hz, a static pressure differential, by basically just compressing the air in the sealed room.

I don't imagine there is any inherent danger in being in a static environment, any more than there is in living at sea level when you are used to living at 1000ft. Like falling off a ladder, it's the sudden changes that do the damage.

cnc

Bite the cone with a bad tooth and see if the volume increases. Then put Del's wooden mallet between the cone and your scull and see what happens.

I would suspect something other than the speaker itself is vibrating in sympathy and generating a resonant frequency in the audible range.

Besides active work in the audio spectrum, the ear also registers differences in pressure. This is what you "hear" @ 10 Hz. Your ear detects the variations in millibars, when the cone of the speaker goes up and down as an "air" pump.

More then the hairs, the "drum" causes this.

Try also to talk into the moving speaker. Your voice will be chopped at the same 10Hz. When you land in an airplane you undergo the millibar trick sometimes too fast and the ear clogs.

Again--Relating to frequencies that exist in Nature, like earthquakes, grinding ice on lakes , Glacial Ice moving, "Squeaking Sands". Volcanos erupting, distant storm waves , breaking on far offshore reefs, these frequencies send sound waves that move the large diaphram--THE PLANET , or parts of it that are closely affected--Nature produces frequencies that are "audible " by life forms, but not us--That is why Lobsters start moving before heavy surf hits the shallow areas they inhabit-They pick up the frequencies of storms, and waves moving at great distances--Same with many other critters--We just don't have the analytical equipment yet to measure what they are perceiving-- It makes speakers look downright crude--Great for certain types of music, but......

The issue is how GOD creat us.

1-If we will hear the low frequencies, we may hear activity in the body=that we do not need to hear!

2-Why do you need to hear the low frequencies??

3-There are technics to hear the low frequencies, that are used for very special applications.