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Q: Annoying low frequency sound ( Answered 1 out of 5 stars,   3 Comments )
Question  
Subject: Annoying low frequency sound
Category: Science
Asked by: annoyance-ga
List Price: $30.00
Posted: 18 Feb 2003 14:33 PST
Expires: 20 Mar 2003 14:33 PST
Question ID: 163158
Is low frequency sound more annoying than sound at higher frequency? 
What is the threshold of annoyance for low frequency in dbA and DbC? 
I'm talking about sound in the 20hz to 150hz range.  What would be the
effect on a human hearing 30hz "rumble" every second of he evening
while at home for 9 months?
Answer  
Subject: Re: Annoying low frequency sound
Answered By: krobert-ga on 18 Feb 2003 18:26 PST
Rated:1 out of 5 stars
 
annoyance-ga,

According to Beranek (Ref 1., references are located at the bottom of
the answer), discomfort occurs at a specific decibel level, and not at
a specific frequency. 120 Decibels (Db) is the "threshold of
discomfort". At this point, the sound (a pure tone) becomes
uncomfortable to listen to. Between 120 Db and 140 Db there is a
region called the "sensation of feeling" where a pure tone is very
uncomfortable to listen to. Above 140 Db is the threshold of pain in
which a pure tone becomes intolerable.

The difficult thing that comes into play is that the human ear is not
a perfect hearing device. There is a term, minimum audible field
(MAF), that comes into play. This is the lowest sound pressure level
that can be perceived by the human ear. Rather than being at a
specific pressure level, the MAF varies according to the frequency. It
is more difficult for the human ear to hear tones at the low end of
the spectrum than at the high. If you've ever taken a hearing test you
probably have first hand experience of this. The lower tones are much
more difficult to hear than the higher ones.

The minimum audible field for a tone of about 30 Hertz is about 35 Db.
The MAF threshold for 16,000 (The highest data shown in the source),
is about 20 Db. Human's hear 4000 Hz tones about the best, with the
MAF threshold at a paltry -3Db (yes, negative three... it just means
that the sound pressure level is below the reference sound pressure
level).

Your question mentioned DbA and DbC. These are both
human-ear-corrected Decibel scales. See the following webpage:

NADA - The Sound Wall
http://www.sfu.ca/~westerka/installations/nada/dba.html

There is a nice scale that shows the weighting of both the DbA and DbC
scales here:

Grozier Technical Systems
http://www.grozier.com/whichmetricdbadbc.htm

So, if you understand the above graphs, you can see that the
weightings simply modify the "regular" db scale.

Taking all the above into account, the effect of a 30 Hz rumble on
human hearing really depends on the decibel level and not so much on
the frequency. The decibel level that is important is the decibel
level that reaches your ears. In other words, you can't take a
measurement 50 or 100 feet from where your head would normally be (in
a house, or on a back porch) and expect an accurate measurement.
Damage to human hearing is cumulative... so, it depends on two things,
level and time.

The only really accurate way to measure hearing loss is by taking
hearing tests. A before and after would be about the best, but taking
one after the nine months would let you know where your hearing stands
compared to the rest of the population.

Finally, don't just take my word for it. If you or a friend has Linux
(Ref 2) with xmms (Ref 3) installed, you can try using the tone
generator (Ref 4, section 3.6.1.5) that is included with it. You can
play around with it and generate low and high tones at the same volume
and see how easy or difficult it is to hear them.

Please let me know if you would like me to clarify anything for you.


krobert-ga


References

1) "Acoustical Measurements (Revised)" by Leo Beranek, Acoustical
Society of America (1988).

2) Linux
   http://www.linux.com/

3) X Multimedia System
   http://www.xmms.org/

4) X Multimedia System Documentation
   http://www.xmms.org/docs/readme.html

Request for Answer Clarification by annoyance-ga on 19 Feb 2003 07:29 PST
Well - I gave you a 1 star rating before reading the whole report. 
Actually it was helpful.  FYI - the issue is: 2-16cylinder CAT engines
have been put within 800 feet of my home in the country (A large,
natural gas pumping station).  The beat frequency (hetrodyne) of the
engines subtly shakes my house 7/24.  I've not slept much at all for
over 9 months now.  You are correct in the asssesment that these
sounds cannot be abated.  Earplugs actually make it worse and even
with the TV turned up loud the "rumble" is underneath at all times.  I
have notes from "Internet Symposium 2002 Noise Annoyance, stress and
health effects"

If you have anything further relating to Low Level/Low Frequency I
could definitely use it.

By the way, the gas company used "A" weighting measurements to "Prove"
they weren't doing anything that amounted to a nuisicance.  As you
know, "A" weighting essentially elimiates measuring the very sounds
that are tormenting me.  Thanks for the info

Clarification of Answer by krobert-ga on 19 Feb 2003 08:48 PST
Thanks for asking annoyance-ga. I'm glad you found the original answer
useful. Google Answers may be able to change the rating if you contact
them directly. I would personally appreciate that if possible.

Following the A-weighting curve that I cited you can see that an
A-weighting will actually "subtract" about 40 to 45 db from the "real"
db rating at 30 Hz.

If you can actually hear this sound, the noise level is actually up
around at least 60 db. The folling document is one that may interest
you:

Hearing Conservation
http://www.osha-slc.gov/Publications/osha3074.html

Osha cites 80 to 85 db as a level at which monitoring must be done by
employers. That essentially means that dangerous health effects can
occur at this level. Of course that's for an 8 hour workday, your
hearing this ALL day.

Besides health effects, this rumble may be causing damage to your home
due to the low frequency vibrations induced in the walls and
structural members.

I would definitely be contacting a lawyer and getting independent
measurements taken and verified. If this company knowingly misled you
about dangerous health effects, I would be calling someone like an
Erin Brockovich!

I hope that helps,

krobert-ga
annoyance-ga rated this answer:1 out of 5 stars
Interesting but not what I asked.  I am needing to know threshold of
"annoyance" not hearing damage.  I have Beranek material.  Simply put:
 What level of low frequency rumble starts driving people "crazy".

Comments  
Subject: Re: Annoying low frequency sound
From: spurious-ga on 18 Feb 2003 19:31 PST
 
krobert-ga's answer is technically accurate for pure tones within the
audible range, but doesn't address resonance and psychological
distress.  From annoyance-ga's question, I think he is probably
building a plaintif's case against some industrial annoyance. These
factors are probably the foremost concerns here.

Physically, resonance effects in the infrasound and near-infrasound
bands can be discomforting or even dangerous. While high pitches can
carry higher energy levels, these sounds are localized and do not
carry far or penetrate sound insulation well.  Low frequencies do.
Elephant infrasound calls are shown to carry for miles and bend round
corners.  Low frequency sounds hug surfaces and carry through the
earth and oceans.  They travel through ventilation ducts and steel
girders. These sounds can be inescapable and are not easily blocked by
double glazing, ear-plugs or even active-attenuating hearing
protectors.

Physiologically, a 30Hz rumble is within the audible range and at the
levels described would have no trouble keeping you awake all night. 
Standard DbC correction tables only apply to a typical population of
subjects without hearing damage. I have a neighbor with some degree of
high-frequency hearing loss. His attention is therefore focused in the
lower frequencies.  My airconditioner, which is working well and no
louder than normal, is a source of great annoyance to him.
Environmental officers and the building superintendant have been
called many times, but they can only barely detect the sound.

Psychologically, the distress caused will be related to the victim's
physical, mental and emotional states and the ambient conditions. For
example, after a 48-hour hostipal shift, sleep deprived and full of
work stress, trying desperately to get a few hours' shut-eye, the
pat-pat-pat of a drip on the airconditioner can send you totally up
the wall, and drive you to completely irrational acts, like sleeping
in a bathtub. The dripping patter is many orders of magnitude below
140 Db.  The psychological effect is very much dependent on baseline
ambient conditions and is especially annoying in quiet neighborhoods
or when you subject is trying to listen to conversation, the TV,
music, etc. Repeated, incessant annoyances over a long time period can
exacerbate a feeling of helplessness and compound the distress. The
ancient Chinese water-torture is an example.

If krobert-ga's a lawyer, a psychologist and physicist's testimony
would be very useful. If he's the plaintiff I'm sure there'd be plenty
of lawyers willing to take his case on contingency.  If he's the cause
of the noise, he needs to look at sound-proofing, damping,
re-engineering and possibly legal representation. Specialists in all
fields abound.

It's not exactly a reliable source, but the following link details the
use of low frequency acoustic weaponry. These descrie physical
resonance effects, but the psychological effects are well documented.

http://www.borderlands.com/archives/arch/gavreaus.htm

- spurious-ga
Subject: Re: Annoying low frequency sound
From: spurious-ga on 18 Feb 2003 19:34 PST
 
Oops, please replace krobert-ga with annoyance-ga in the following paragraph!

If krobert-ga's a lawyer, a psychologist and physicist's testimony
would be very useful. If he's the plaintiff I'm sure there'd be plenty
of lawyers willing to take his case on contingency.  If he's the cause
of the noise, he needs to look at sound-proofing, damping,
re-engineering and possibly legal representation. Specialists in all
fields abound.
Subject: Re: Annoying low frequency sound
From: chucksezdotcom-ga on 13 May 2003 06:50 PDT
 
Surprised doctors told me I almost had the hearing of a dog when I
took my first hearing test at age 12. I’ve always been supersensitive
to noise and have my own Radio Shack handheld noise meter with an A
weighting scale on the selection dial. Once I piped a neighbor’s loud
pool pump noise back at him through an amplifier. Failed bearings
caused the pump to be heard by the county inspectors all the way down
the block when they came to inspect but they said they had no funds at
that time to enforce the near-fence noise code. Anticipating a counter
attack with water, I had covered the speaker with a plastic garbage
bag. When the sheriff came to break up the ensuing over-fence water
fight, he laughed and said the noise may be his but no judge would
ever side with me due to my ingenious and diabolical noise retaliation
scheme. This is not the best legal strategy.

The neighbors at our present house are much more cooperative and their
pool pump’s noise is normal. However, having the sensitive hearing I
have, the sound was still too high for my comfort. But this time,
rather than pugilistic, I took a more sensible route, I offered to buy
him a new pump. Here is my blog entry for the whole episode:

Monday, April 07, 2003
Pentair Pool Pumps Win Big
Fusion energy is on my mind today but first, I report a grand success
in one engineering project – with the neighbor’s permission, the
successful attempt to quiet the his pool pump situated right at the
edge of my backyard adjoining his side strip. A significant research
effort produced the identification of the quietest pool pump made, the
Pentair Whisperflo pump. As advertised, the Pentair pump reduced the
noise level at three feet from 74 dbA to less than 62 dbA. Recalling
that the dbA scale is a log scaled of sound pressure to a reference
sound pressure weighted for the human ear, I concluded the noise level
is now significantly lower.

Furthermore, as described as an expected result by the Pentair sales
person, if you entered the back yard of the neighbor's yard, you'd
have to search for the pump because you can't even tell where it is
located due to the highly reduced sound. Yes, I paid for the pump but
complete installation and pump was $537, a cost I gladly paid in order
to have the peace and quiet returned to my back patio. Ah, lovely
spring. I think I'll go out there right now and bask in the sun and
quiet spring sounds of the birds and water fountain in the corner of
my backyard.

Finally, the neighbor stands to pay much less in pool pump electricity
as the new pump is of the modern efficient design, most likely done on
computer aided design software program enabling much less power to
move the same amount of water. The required wattage dropped from 2 hp
all the way down to  hp.
So it’s hats off to the Pentair company for a design and manufacture
job well done.

Pentair Pumps:

http://www.pentairpool.com


My next noise issue is my own air conditioner. Although it is normal,
the noise is still way too high for me. Especially since I added a
“rain forest” where the unit now resides:

http://www.chucksez.com/rain_forest.html

The solution to quiet my own air conditioner? A Lennox HSX14 unit, of
course!

http://www.lennox.com/product/mn_cooling.html#HSX15

Hope you enjoyed my noise stories and good luck with the bull dozers!

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