"John Atkinson" wrote in message
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"Arny Krueger" wrote in message
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John Atkinson wrote:
"Arny Krueger" wrote in message
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John Atkinson wrote:
what sound pressure level was required for the 6Hz tone to become
audible? The Fletcher-Munson or Robinson-Dadson curves imply that
6Hz is not audible at normal levels, yet you are saying different.

Please cite a reference that portrays minimum reliably perceptible
acoustic levels for the 5-10 Hz range from Fletcher-Munson
Robinson-Dadson, or any other source.

The sensitivity curves in these data increasingly rise with reducing
frequency to their lower limits. There is no reason to believe the
curves have points of inflection below those limits.

Failure to properly answer a simple question noted. Substitution of a
fact with questionable [relevance] isn't a proper answer.

I think you misunderstood my point, Mr. Kreuger. Whether you take the
earlier Fletcher-Munson sensitivity curves or the more recent research
from Robinson and Dadson, simple extrapolation from these curves
indicates that the human ear continues to lose sensitivity with
reducing frequency. The implication is that by the time you reach
6Hz -- almost two octaves below the 20Hz usually stated as the "limit"
of human hearing -- you would need extraordinary high spls to "hear"
the tone.

As you seem to be saying that you could hear the difference with and
without 6Hz content using headphones at moderate levels, all I am
doing is pointing out that it would seem unlikely you are actually
"hearing" the 6Hz content in light of the published data on the subject.
As I conjectured, perhaps you are detecting the audioband action of the
high-pass filter?

snip

If so, how can you report perceiving 6Hz tones using headphones?

I never said that I was perceiving 6 Hz tones.

With respect Mr. Krueger, you did appear to be saying just that. On
multiple occasions. You also criticized Scott Wheeler (S888wheel) for
saying the opposite.

My test reports related to perceiving their reduction, absence or
some by-product of common means of eliminating or reducing them.

Well yes, now you are saying that, which in turn allows for the fact
that you actually agree with me that it is perhaps the action of the
filter you are perceiving, not the presence or absence of 6Hz content.
As I asked:

Was this a double-blind test involving a high-pass filter?

Yes.

Which is my point. That the high-pass filter is also a variable in this
test and might well be the source of the identification you report.
Laurie Fincham, then with KEF, did some blind tests in the early 1980s
that such filters produced audible effects.

If so, then isn't it more likely that the test was detecting the
audio-band phase error of the filter, rather than the presence of
infrasonic (6Hz) information?

The filter in question is known to be a [reasonably] precise
[implementation] of the type of filter it is stated to be.

So what? My conjecture doesn't necessarily depend on the implementation
of a high-pass filter, only that one be used. If you really wanted to
perform a test on the audibility of content in the 6Hz region, you would
need to compensate for the filter's audio-band phase error, surely?

As I point out in a recent post, these filters are probably less audibly
damaging than the actual filters that are built into most audio
systems,
particularly audio equipment based on tubes or audio equipment created
for
the purpose of vinyl playback.

I agree. As I have written in Stereophile, the recording-playback chain
consists of cascaded high-pass filters. Which is why it is very rare for
recorded music to contain high levels of content below 30Hz, let alone
20Hz.

John Atkinson
Editor, Stereophile

6 Hz at high SPL likely produces high frequency noise caused by air-flow
boundary turbulence.
At this frequency, the joints of the inner ear bones, and gross movement of
cochlear fluid would produce similar noise, perceptible by the cochlear
hairs as broadband noise.

There are no cochlear hairs tuned to 6 Hz. These hairs do have harmonic
modes, as given by the the eigenvalues of the "string equation with one end
free", which are Hankel functions.

An interesting question would be whether an intense low frequency signal
induces audible Doppler distortion on the eardrum. Personally, I think not.

It seems unlikely that a reproduction chain exists that could explore these
effects. As Francois remarks, headphones suitable for investigational
purposes do not exist.