Does the brains sound amplification increase when shielding from outer sound?

[jappe]

If you put on ear protection, you'll start to hear sounds you didn't hear so loud before.
Heart beats, breathing, inner noise.
Even if you don't cover your ears physically, but just experiment with covering your ears at different short distances, the effect can be heard.

I first thought it must be some parabol effect if you have your open hands close to the ears. But the phenomenon is more noticeable if you cover you ears completely.
The perceived inner sound volume increases.
I don't think its sound masking.

Is that some auto gain in brain/ears at work?
Perhaps biologically motivated by the need to protect the ears from harm.
Or a low noise environment hearing mode enabling us to avoid danger from silent threats?

[normen]

Its a few effects. Actually the ear has mechanical protection, thats one of the reasons why you hear less when you come from a loud concert. Its actually muscles pulling your ears bones to transfer less energy to the cerebral membrane. Then theres psychoacoustic effects (see cocktail party effect) where your brain can focus on single sounds and make them appear louder. When you only have a few sounds that are audible at all they will automatically appear louder. Then theres masking effects. Frequencies that are close to one another will cover each other, the louder frequency will cover the more silent one. So if you cancel out other sound sources you hear the existing frequencies better. Finally there is some degree of the "parabol effect" you talk about where you hear your blood flow louder simply because the sound it makes is contained in your inner ear when you close it.

[jappe]

Its a few effects. Actually the ear has mechanical protection, thats one of the reasons why you hear less when you come from a loud concert. Its actually muscles pulling your ears bones to transfer less energy to the cerebral membrane. Then theres psychoacoustic effects (see cocktail party effect) where your brain can focus on single sounds and make them appear louder. When you only have a few sounds that are audible at all they will automatically appear louder. Then theres masking effects. Frequencies that are close to one another will cover each other, the louder frequency will cover the more silent one. So if you cancel out other sound sources you hear the existing frequencies better. Finally there is some degree of the "parabol effect" you talk about where you hear your blood flow louder simply because the sound it makes is contained in your inner ear when you close it.

It makes sense that its actually multiple effects involved.
I still wonder why an ear plug would bounce back that much of a heart beat low frequency sound, it works pretty well in letting the low frequency sounds from the outer environment in. But I guess its the combination of effects that makes it then.

[normen]

It makes sense that its actually multiple effects involved. I still wonder why an ear plug would bounce back that much of a heart beat low frequency sound, it works pretty well in letting the low frequency sounds from the outer environment in. But I guess its the combination of effects that makes it then.

Its not so much bouncing back as keeping the energy contained. Low frequencies have wave lengths much longer than the inside of your ear anyway so theres something else to chew on logic-wise Most of these frequencies get transferred via the bones and skin and not so much via the air.

[jappe]

Hmm I shall chew a bit more on these Koans...
About the wave lengths that shouldn't be able to be contained: I think low frequency sounds can be more spectrally dense than high frequency sounds?
Could it be that the brain interprets that higher frequency higher density content as indication of existing lower frequencies?
I mean that the brain can extrapolate higher frequency down to lower if it has a density similar to a fat bass sound?

I think I read about something like that long ago.
Shooting from the hip here:-)

[normen]

Hmm I shall chew a bit more on these Koans... About the wave lengths that shouldn't be able to be contained: I think low frequency sounds can be more spectrally dense than high frequency sounds? Could it be that the brain interprets that higher frequency higher density content as indication of existing lower frequencies? I mean that the brain can extrapolate higher frequency down to lower if it has a density similar to a fat bass sound? I think I read about something like that long ago. Shooting from the hip here:-)

Yeah it does do that somewhat, thats what some "bass maximizer" plugins base on. I don't know what you mean by "spectrally dense" though.

[selig]

Hmm I shall chew a bit more on these Koans... About the wave lengths that shouldn't be able to be contained: I think low frequency sounds can be more spectrally dense than high frequency sounds? Could it be that the brain interprets that higher frequency higher density content as indication of existing lower frequencies? I mean that the brain can extrapolate higher frequency down to lower if it has a density similar to a fat bass sound? I think I read about something like that long ago. Shooting from the hip here:-)

Low frequency complex waveforms can "sound" more spectrally dense than the same waveform at a high frequency because harmonics (spectral energy) appear above the fundamental. if for example the fundamental is above 10 kHz, we hear only a sine (the least spectrally dense sound there is) because all the harmonics are above the range of our hearing. That same waveform will "sound" very dense when played at a lower frequency where we can actually perceive the harmonics/density. 

As Normen has already stated, low frequencies can be felt and don't rely solely on the ear. This is how deaf people can enjoy a loud concert, often standing by the sub-woofers to literally 'feel the music'. They of course can do this because they won't suffer further hearing damage. 

Also, when you plug your ears, the easiest frequencies to block are the high frequencies. This would make it difficult for your brain to identify low frequencies by the presence of high frequencies. Instead I suspect it's 'brute force' at work: your brain identifies low frequencies because it knows what they are and recognizes them!

As for your breathing and heart ext., you as much "feel" these as hear them when your hearing is restricted by hearing protection. Remember your heart beat is transmitted through your body by your blood, much as sound is transmitted through water, and your blood is EVERYWHERE (even in your ears!).

You may be thinking of the "Missing Fundamental" effect, the ability of the brain to reconstruct a missing fundamental when presented with the correct upper harmonic series?

[jappe]

Thank's Normen and Selig. Bass enhancement and Missing fundamental frequency was what I was thinking of.
So the blood and bones transmit sound. Interesting. I was aware about the role of the skull in psychoacoustics, but didnt think of the body as a whole.Perhaps the body and skeleton can be seen as a resonance chamber.Hmm...I guess people could have different perception of sound depending on body type and size then.

[selig]

Thank's Normen and Selig. Bass enhancement and Missing fundamental frequency was what I was thinking of. So the blood and bones transmit sound. Interesting. I was aware about the role of the skull in psychoacoustics, but didnt think of the body as a whole.Perhaps the body and skeleton can be seen as a resonance chamber.Hmm...I guess people could have different perception of sound depending on body type and size then.

Our bodies are fairly solid, so no resonating "chamber"! But even solids can TRANSMIT sounds, but as pointed out earlier these would be masked by the sounds received by the ear. Either way, the vibrations your body picks up aren't exactly "heard" because "hearing" only happens via the ear. They instead "felt" by the nervous system, but are merged by the brain. This is how those "thumpers" work in theaters or like some drummers use to help fill in the low frequency energy missing in some "in ear" systems. 

Interesting subject!