Tonality of a wind turbine

[REM]

Since July 2010 Enercon have been advising the addition of a 5 dB(A)
penalty to the noise from their 330 kW wind turbine to account for
tonality. This makes this turbine noisier than other larger turbines
in their range (105 dB at 10 m/s wind speed). The basis for this was
a report that detailed 4 tone frequencies where delta La,k exceeded -3
dB, being 15.1, 9.8, -1.9 and -1.5 dB. These were at 4 different wind
speeds 6 - 9 m/s and at frequencies 107, 109, 126, 126 Hz.
I am not sure if I fully understand this but I suspect that a 5 dB
penalty is not needed. Can anyone confirm this? For other turbines
one value for tonality is provided, is this an average, or a maximum
of the above values?
Many thanks,
Rod

[Answerman]

Post by REM
Since July 2010 Enercon have been advising the addition of a 5 dB(A)
penalty to the noise from their 330 kW wind turbine to account for
tonality. This makes this turbine noisier than other larger turbines
in their range (105 dB at 10 m/s wind speed). The basis for this was
a report that detailed 4 tone frequencies where delta La,k exceeded -3
dB, being 15.1, 9.8, -1.9 and -1.5 dB. These were at 4 different wind
speeds 6 - 9 m/s and at frequencies 107, 109, 126, 126 Hz.
I am not sure if I fully understand this but I suspect that a 5 dB
penalty is not needed. Can anyone confirm this? For other turbines
one value for tonality is provided, is this an average, or a maximum
of the above values?
Many thanks,
Rod

I can't answer your question, but I have forwarded it to the new group
sci.physics.acoustics.

[Angelo Campanella]

Post by Answerman

Post by REM
Since July 2010 Enercon have been advising the addition of a 5 dB(A)
penalty to the noise from their 330 kW wind turbine to account for
tonality. This makes this turbine noisier than other larger turbines
in their range (105 dB at 10 m/s wind speed). The basis for this was
a report that detailed 4 tone frequencies where delta La,k exceeded -3
dB, being 15.1, 9.8, -1.9 and -1.5 dB. These were at 4 different wind
speeds 6 - 9 m/s and at frequencies 107, 109, 126, 126 Hz.
I am not sure if I fully understand this but I suspect that a 5 dB
penalty is not needed. Can anyone confirm this? For other turbines
one value for tonality is provided, is this an average, or a maximum
of the above values?
Many thanks,
Rod

I can't answer your question, but I have forwarded it to the new group
sci.physics.acoustics.

I'm happy that you referenced this here, because this is becoming a hot
topic in the acoustical society (just my opinion). Not only is wind turbine
noise a problem on land, but it is also being looked at in the sea. Per
paper 2pAB1 recently presented at ASA-Cancun, shallow water installation of
eight 3.6 MW turbines are planned to be installed offshore, 5km south of
Block Island (Long Island-Rhode Island vicinity, via the "green" movement).
Any way, such vibrations can be transmitted down the metal supports of the
wind turbine that are then transmitted into the sea water, to join in the
noise from shipping, etc. I have seen no quantitative data on this yet, but
it should be forthcoming within he year. So far, only the pile diving noise
during the construction phase has been observed and measured. There is
speculation that the future gear box vibration-tones can also follow that
path.

Back to the 5dB "penalty" referenced. Such a penalty has been around for
decades to account for the "noisiness" of sounds where extra annoyance is
the result. Chief among these are steady pure tones. My experience has been
with induced draft fans that suck combustion gases out of a furnace and
send them directly to a tall smokestack - that in turn acts like a church
belfry to broadcast said sound to the neighborhood. Special and expensive
tuned in-line sound attenuators are the cure. Apparently wind turbine pure
tone emissions at the frequencies you note are being emitted by that
turbine.

Such a steady fan "blade passage" tone - at about a 300 Hz "blade
passage" in one case - is heard by residents located greater than a
smoke-stack length and further away (300' to 1,000' plus). It cannot be
heard when standing at the foot of the smoke stack because of the sound
directivity (Q) of the stack-top outlet. It may also not be easily perceived
outside their house as it can be masked by the general din of community
(traffic) noise. But such tones permeate the windows of their frame
residences.... House walls and windows only act as acoustical low-pass
filters, blocking all the higher frequency noise that masks the tone
outdoors. The tone becomes constantly audible in living rooms and
bedrooms...

Such annoyance is less for lower frequency tones (below the vowel
frequencies), BUT such tones, especially gear-teeth passage vibrations
(little impacts due to imperfect gear meshing dynamics), will be accompanied
by their harmonics (aka "overtones"), which, starting at about 200 Hz become
perceived as "Tones".

Please explain La,k to me as I have not seen that term before.

Is the "105dB" @ 10 m/s a sound power value (dB re one picowatt)? If so,
is that value a Linear (flat) weighting, or is it A-Weighted?

Another issue is "setback" (minimal spacing from nearest residences &
wilderness spaces) required by authorities. I hear that Ontario now has a
500 meter setback (1,640') ordinance. vs. 1,500 here (another rumor), and
1,200 as noted by a person asking me for some help on the matter recently.

Nice to get this item going, as I now need some up-to-date info on such.

Angelo Campanella

[REM]

Post by Answerman

Post by REM
Since July 2010 Enercon have been advising the addition of a 5 dB(A)
penalty to the noise from their 330 kW wind turbine to account for
tonality. This makes this turbine noisier than other larger turbines
in their range (105 dB at 10 m/s wind speed).  The basis for this was
a report that detailed 4 tone frequencies where delta La,k exceeded -3
dB, being 15.1, 9.8, -1.9 and -1.5 dB.  These were at 4 different wind
speeds 6 - 9 m/s and at frequencies 107, 109, 126, 126 Hz.
I am not sure if I fully understand this but I suspect that a 5 dB
penalty is not needed.  Can anyone confirm this?  For other turbines
one value for tonality is provided, is this an average, or a maximum
of the above values?
Many thanks,
Rod

I can't answer your question, but I have forwarded it to the new group
sci.physics.acoustics.

    I'm happy that you referenced this here, because this is becoming a hot
topic in the acoustical society (just my opinion). Not only is wind turbine
noise a problem on land, but it is also being looked at in the sea. Per
paper 2pAB1 recently presented at ASA-Cancun, shallow water installation of
eight 3.6 MW turbines are planned to be installed offshore, 5km south of
Block Island (Long Island-Rhode Island vicinity, via the "green" movement).
Any way, such vibrations can be transmitted down the metal supports of the
wind turbine that are then transmitted into the sea water, to join in the
noise from shipping, etc. I have seen no quantitative data on this yet, but
it should be forthcoming within he year. So far, only the pile diving noise
during the construction phase has been observed and measured. There is
speculation that the future gear box vibration-tones can also follow that
path.
    Back to the 5dB "penalty" referenced. Such a penalty has been around for
decades to account for the "noisiness" of sounds where extra annoyance is
the result. Chief among these are steady pure tones. My experience has been
with induced draft fans  that suck combustion gases out of a furnace and
send them directly to a tall smokestack - that in turn acts like a church
belfry to broadcast said sound to the neighborhood. Special and expensive
tuned in-line sound attenuators are the cure. Apparently wind turbine pure
tone emissions at the frequencies you note are being emitted by that
turbine.
    Such a steady fan  "blade passage" tone - at about a 300 Hz "blade
passage" in one case - is heard by residents located greater than a
smoke-stack length and further away (300' to 1,000' plus). It cannot be
heard when standing at the foot of the smoke stack because of the sound
directivity (Q) of the stack-top outlet. It may also not be easily perceived
outside their house as it can be masked by the general din of community
(traffic) noise. But such tones permeate the windows of their frame
residences.... House walls and windows only act as acoustical low-pass
filters, blocking all the higher frequency noise that masks the tone
outdoors.  The tone becomes constantly audible in living rooms and
bedrooms...
    Such annoyance is less for lower frequency tones (below the vowel
frequencies), BUT such tones, especially gear-teeth passage vibrations
(little impacts due to imperfect gear meshing dynamics), will be accompanied
by their harmonics (aka "overtones"), which, starting at about 200 Hz become
perceived as "Tones".
    Please explain La,k to me as I have not seen that term before.
is that value a Linear (flat) weighting, or is it A-Weighted?
    Another issue is "setback" (minimal spacing from nearest residences &
wilderness spaces) required by authorities. I hear that Ontario now has a
500 meter setback (1,640') ordinance. vs. 1,500 here (another rumor), and
1,200 as noted by a person asking me for some help on the matter recently.
    Nice to get this item going, as I now need some up-to-date info on such.
        Angelo Campanella- Hide quoted text -
- Show quoted text -

Thanks for your reply.

La,k is the Sound level of the tone (a) at the wind speed (k). I
think it is the pressure level. This follows ISO 61400-11.
105 dB is the A weighted sound power level.
In some parts of UK the minimum setback distance for a turbine is 400
m but it varies and this only applies if the noise level is within the
currently accepted guidelines.
Regards,
Rod

[richard pickworth]

what are your criteria?
Rick

Post by REM
Since July 2010 Enercon have been advising the addition of a 5 dB(A)
penalty to the noise from their 330 kW wind turbine to account for
tonality. This makes this turbine noisier than other larger turbines
in their range (105 dB at 10 m/s wind speed). The basis for this was
a report that detailed 4 tone frequencies where delta La,k exceeded -3
dB, being 15.1, 9.8, -1.9 and -1.5 dB. These were at 4 different wind
speeds 6 - 9 m/s and at frequencies 107, 109, 126, 126 Hz.
I am not sure if I fully understand this but I suspect that a 5 dB
penalty is not needed. Can anyone confirm this? For other turbines
one value for tonality is provided, is this an average, or a maximum
of the above values?
Many thanks,
Rod

I can't answer your question, but I have forwarded it to the new group
sci.physics.acoustics.

[Angelo Campanella]

Post by REM
Since July 2010 Enercon have been advising the addition of a 5 dB(A)
penalty to the noise from their 330 kW wind turbine to account for
tonality. This makes this turbine noisier than other larger turbines
in their range (105 dB at 10 m/s wind speed). The basis for this was
a report that detailed 4 tone frequencies where delta La,k exceeded -3
dB, being 15.1, 9.8, -1.9 and -1.5 dB. These were at 4 different wind
speeds 6 - 9 m/s and at frequencies 107, 109, 126, 126 Hz.
I am not sure if I fully understand this but I suspect that a 5 dB
penalty is not needed. Can anyone confirm this?

Tonal penalties ALWAYS have merit. That is, broadband noise (e.g. a
continuously operating table fan) is not irritating compared to a single
tone of the same decibel level and duration. Therefore, sounds that include
overt tones should be weighted as more annoying than broadband sounds. The
question arises as to how that extra weighting shall be arranged. There are
two aspects of that weighting: Identification of the fact that a tone
exists, and the degree of the penalty.

Classical noise control technology has decided that comparing the
decibel level of adjacent bands to the band containing the tone in question
is a workable identification method. The paradigm of using 1/3 octave band
measurements of the overall sound spectrum of that noise is applied, and the
criterion advanced that a tone or "tonality" exists if the decibel level of
the 1/3 octave frequency band containing the tone is X dB or more above (or
"more than X dB above") - either, or both, or the average of the two -
adjacent 1/3 octave frequency bands, and Y dB penalty is added to the
broadband noise level value which is then compared with the applicable
ordinance decibel limit. There is wiggle room and fuel for argument in
choosing the value of X and Y and the adjacent band delta handling.

The apparent paradigm values expressed above seem to be...... well, some
calculation is in order. The 105 dB sound power translates to be 55 dBA at
300 feet. Unscrambling the levels presented is not easy. A-Weighting allows
as much as a 16 dB uptick of a 125 Hz tone above its dBA value. It all
sounds very noisy to me. Who's complaining about a 5 dBA penalty? What is
delta La,k?

I have learned that community noise in Midwestern suburban areas is such
that a new noise source of some duration especially at night will be barely
evident at 40 dBA, evident but not of concern at 45 dBA, of concern and
complained upon as being undesirable at 50 dBA. At 55 dBA and above,
community action commences. In rural residential area at night the threshold
levels indicated are perhaps 5 dBA less. This is the environment that winds
turbines are being introduced into today. The first thing to notice is that
I have stresses night noise levels, while wind turbines are more energetic
in the daytime because of the wind behavior. The Midwest has more low-wind
nights than, say the coastal regions or mountain top regions.....

I can say that a value of X (the prominence of the tone) can be one (1)
decibel and that tone will be apparent, so efficient are our hearing
senses... this applies over the midfrequency bands from 200 to about 2,000
Hz (the vocalization, or singing and speech) range. Outside that range our
hearing has less discrimination. The fair value of X has commonly been 3 dB
throughout the noise control industry. The value of Y has classically been 5
dB in the same vain.

To answer whether a 5 dB penalty is called for in the case of wind
turbines, we must know why anyone considers wind turbine noise to be any
less annoying to deserve any break from noise control technology traditions?
I ask you, please cite such merit....

Post by REM
For other turbines
one value for tonality is provided, is this an average, or a maximum
of the above values?

Your discussion is encouraged.

Angelo Campanella