I have been "fighting"an aggravating resonance in my stereo system for a
long time. I tried a sweep with a signal generator today and it appears
to be around 180 hz. This makes sense because my room dimensions
suggest a number of nodes at that frequency (22' X 30' with an 18'
cathedral ceiling). I tried suppressing it by setting the 120 hz slider
on my equalizer at -12. This helped a lot but I would like to suppress
the exact frequency. I know this would require either a parametric or
1/3 octave equalizer. Any suggestions?


---MIKE---

Were you the one using two subs?


"---MIKE---" wrote in message
...
I have been "fighting"an aggravating resonance in my stereo system for a
long time. I tried a sweep with a signal generator today and it appears
to be around 180 hz. This makes sense because my room dimensions
suggest a number of nodes at that frequency (22' X 30' with an 18'
cathedral ceiling). I tried suppressing it by setting the 120 hz slider
on my equalizer at -12. This helped a lot but I would like to suppress
the exact frequency. I know this would require either a parametric or
1/3 octave equalizer. Any suggestions?


---MIKE---

No - FOUR subs! Two in corners and two along walls. The resonance is a
room condition (I can hear it with the subs off).


---MIKE---

"---MIKE---" wrote in message
...
No - FOUR subs! Two in corners and two along walls. The resonance is a
room condition (I can hear it with the subs off).


How small are your subs? My one Sub capable of being heard 200 feet (my
opposite house )- if i were to push it to the max. Right now I am only using
a small fraction of its max.

Anyhow here's a link http://www.mhsoft.nl/Helmholtzabsorber.asp hopefully,
that will help you.

Cheers.

On 24 Sep 2004 14:12:23 GMT, "Chelvam" wrote:

"---MIKE---" wrote in message
...
No - FOUR subs! Two in corners and two along walls. The resonance is a
room condition (I can hear it with the subs off).


How small are your subs? My one Sub capable of being heard 200 feet (my
opposite house )- if i were to push it to the max. Right now I am only using
a small fraction of its max.

Hmmmm. Care to be more specific? What is your sub?

--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Stewart Pinkerton" wrote in message
...

Hmmmm. Care to be more specific? What is your sub?

Why? you think it can't be heard that far? Even my car 10 inch Rockford
Fosgate Punch can be heard quite a distant if I push it to the max. But not
up to 2 miles as this gentleman
http://www.cardomain.com/reviews/lis...sku=ROCRFD2210 is claiming
but at least 120 feet.

My Sub is Boston Acoustics not a true High End but pretty much good for the
job.

cheers.

On 25 Sep 2004 02:10:05 GMT, "Chelvam" wrote:

"Stewart Pinkerton" wrote in message
...

Hmmmm. Care to be more specific? What is your sub?

Why? you think it can't be heard that far?

Not at 20Hz, no, but probably at the 60-80Hz peak common to many
cheaper 'Home Cinema' biased units.

Even my car 10 inch Rockford
Fosgate Punch can be heard quite a distant if I push it to the max.

Why am I not surprised?

But not
up to 2 miles as this gentleman
http://www.cardomain.com/reviews/lis...sku=ROCRFD2210 is claiming
but at least 120 feet.

My Sub is Boston Acoustics not a true High End but pretty much good for the
job.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Stewart Pinkerton" wrote in message
...
On 25 Sep 2004 02:10:05 GMT, "Chelvam" wrote:

"Stewart Pinkerton" wrote in message
...

Hmmmm. Care to be more specific? What is your sub?

Why? you think it can't be heard that far?

Not at 20Hz, no, but probably at the 60-80Hz peak common to many
cheaper 'Home Cinema' biased units.

rest snipped for brevity....

My sub is crossed around 55 to 60 Hz. In my room it is certainly heavy and
full but felt more than heard. When I go to my bath it is definely louder
(more heard not so sure of felt) unlike in my room.

And in the case of my 200 feet neigbour who uses a mass market Home Theater
system the bass is not full or heavy but he was driving me nuts with his
"boom..boom ..boom" coming to my room. My sub on the other hand never heard
that far till I push it up the volume from about 10 oclock to 5 oclock and
crossed at 100khz.

So the question is:-

I always thought the lower the frequencies the further it is heard. Am I
wrong?

regards.

On 26 Sep 2004 14:51:21 GMT, "Chelvam" wrote:

So the question is:-

I always thought the lower the frequencies the further it is heard. Am I
wrong?

Actually, that's a very good question which launches us into relative
power and atmospheric propagation.

It's my 'intuitive feel' that in the 20-200Hz area which we may
reasonably regard as 'bass', the propagation losses which accrue with
increasing frequency are more than offset by the massive increases in
input power which are required to generate the same 'muzzle velocity'
SPL at the speaker cone as we dig down into subwoofer territory. But,
I could be wrong. Anyone have some real data on this aspect of 'down
range' bass SPL?
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Hi Stewart,

It's my 'intuitive feel' that in the 20-200Hz area
which we may
reasonably regard as 'bass', the propagation losses
which accrue with
increasing frequency are more than offset by the
massive increases in
input power which are required to generate the same
'muzzle velocity'
SPL at the speaker cone as we dig down into subwoofer
territory. But,
I could be wrong. Anyone have some real data on this
aspect of 'down
range' bass SPL?

Did you happen to see the 3-part objective (i.e., based
on measurements) review of subwoofers in the last three
issues of Stereophile Ultimate AV magazine? It doesn't
answer your question, but does indicate that most
subwoofers (but I'm sure not yours ;^)) suffer from
compression in the lower frequencies as the power
increases, which will cause a relative increase in the
SPL of the higher frequencies as the power goes up.

Regards,
Tip

Stewart Pinkerton wrote:




On 26 Sep 2004 14:51:21 GMT, "Chelvam" wrote:

So the question is:-

I always thought the lower the frequencies the further it is heard. Am I
wrong?

Actually, that's a very good question which launches us into relative
power and atmospheric propagation.

It's my 'intuitive feel' that in the 20-200Hz area which we may
reasonably regard as 'bass', the propagation losses which accrue with
increasing frequency are more than offset by the massive increases in
input power which are required to generate the same 'muzzle velocity'
SPL at the speaker cone as we dig down into subwoofer territory. But,
I could be wrong. Anyone have some real data on this aspect of 'down
range' bass SPL?
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Actually I think its just a matter of perception and that very low bass is
often present but not 'entertained.' Ever notice how quiet a building gets when
the air handling system is shut-off at the end of day; while during the course
of a day its basically un-preceived.

When I test car audio subwoofers (in-car) the 'sound' that gets noticed by my
neighboors is not the 10-20 Hz 120 dB SPL generated inside the car but the 120
dB 50-80 Hz signals.

What do you 'hear' when a boom-car travels down the street? It's not the 20 Hz
information but the 40-80 Hz pounding plus the license plate and panel buzzes
even though a 10-inch woofer in a sealed box with a moderately large amplifier
will deliver 120 dB at 10-62 Hz in a car with less than 10% distortion..

Of course, the reason that such a woofer can do this in a car even though it
takes 8 15-inch long stroke woofers and 5000-watts in my Home Theater is that
the auto cabin is a small reasonably well-sealed space with the according low
frequency reinforcement (my Corvette has 30 dB of 'cabin gain' at 10 Hz.)

But again to the point, I seldom hear people complain about true subwoofer
frequencies; what is bothersome is the lead and bass electric guitar, drums and
other higher-frequency sources which 'appear' to be bass when the upper
midrange and treble is blocked by the structure. It's not typical to have
police called by playing your pipe organ music too loud?

wrote:



Hi Stewart,

It's my 'intuitive feel' that in the 20-200Hz area
which we may
reasonably regard as 'bass', the propagation losses
which accrue with
increasing frequency are more than offset by the
massive increases in
input power which are required to generate the same
'muzzle velocity'
SPL at the speaker cone as we dig down into subwoofer
territory. But,
I could be wrong. Anyone have some real data on this
aspect of 'down
range' bass SPL?

Did you happen to see the 3-part objective (i.e., based
on measurements) review of subwoofers in the last three
issues of Stereophile Ultimate AV magazine? It doesn't
answer your question, but does indicate that most
subwoofers (but I'm sure not yours ;^)) suffer from
compression in the lower frequencies as the power
increases, which will cause a relative increase in the
SPL of the higher frequencies as the power goes up.

Regards,
Tip

Actually the term "power compression" might be better applied to pro-sound
equipment. IMO a better look at that is the SPL capability of a device given a
distortion limit. It is true that limited dynamic capability WILL cause a
spectral shift when a subwoofer is given a signal for which it doesn't have the
displacement/amplifier capability (there's a well known product that has been
shown when delivered a high-level 20 Hz input will put out more 40 Hz; 2nd
harmonic played more loudly than the fundamental) but technically I don't
consider that power compression.

On 26 Sep 2004 22:18:09 GMT, "Tip" wrote:

Did you happen to see the 3-part objective (i.e., based
on measurements) review of subwoofers in the last three
issues of Stereophile Ultimate AV magazine? It doesn't
answer your question, but does indicate that most
subwoofers (but I'm sure not yours ;^)) suffer from
compression in the lower frequencies as the power
increases, which will cause a relative increase in the
SPL of the higher frequencies as the power goes up.

Knowing the basics of the drivers helps. My subwoofer design uses a
pair of Adire Tempests in an 'infinite baffle' situation using the
loft space above my listening room, and driven by a 250 watt 'plate'
amplifier. They are not in any way power compressed, but they are Xmax
limited below about 22Hz, although since this is at an in-room level
of about 115dB, I don't think it's a real problem.......... :-)

OTOH, if you run the numbers for virtually *any* driver in the sort of
2-3 cu ft box which is domestically acceptable, you certainly do run
into severe power problems when you get below 40Hz or so!
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Nousaine" wrote in message
...
Stewart Pinkerton wrote:
snip..snip..



What do you 'hear' when a boom-car travels down the street? It's not the
20 Hz
information but the 40-80 Hz pounding plus the license plate and panel
buzzes
even though a 10-inch woofer in a sealed box with a moderately large
amplifier
will deliver 120 dB at 10-62 Hz in a car with less than 10% distortion..

Of course, the reason that such a woofer can do this in a car even though
it
takes 8 15-inch long stroke woofers and 5000-watts in my Home Theater is
that
the auto cabin is a small reasonably well-sealed space with the according
low
frequency reinforcement (my Corvette has 30 dB of 'cabin gain' at 10 Hz.)

10hz? Do you mind telling the Subwoofer's name. The best I think that I
heard/felt was 40 or 50hz. I have not teally tested but I doubt I could go
below 20hz.


But again to the point, I seldom hear people complain about true subwoofer
frequencies; what is bothersome is the lead and bass electric guitar,
drums and
other higher-frequency sources which 'appear' to be bass when the upper
midrange and treble is blocked by the structure. It's not typical to have
police called by playing your pipe organ music too loud?

Boom..boom is bit too common over here. travelling cars, discos, HT the list
goes on.

"Chelvam" wrote:

"Nousaine" wrote in message
...
Stewart Pinkerton wrote:
snip..snip..



What do you 'hear' when a boom-car travels down the street? It's not the
20 Hz
information but the 40-80 Hz pounding plus the license plate and panel
buzzes
even though a 10-inch woofer in a sealed box with a moderately large
amplifier
will deliver 120 dB at 10-62 Hz in a car with less than 10% distortion..

Of course, the reason that such a woofer can do this in a car even though
it
takes 8 15-inch long stroke woofers and 5000-watts in my Home Theater is
that
the auto cabin is a small reasonably well-sealed space with the according
low
frequency reinforcement (my Corvette has 30 dB of 'cabin gain' at 10 Hz.)

10hz? Do you mind telling the Subwoofer's name. The best I think that I
heard/felt was 40 or 50hz. I have not teally tested but I doubt I could go
below 20hz.

The system was described in the June '99 issue if Sound & Vision magazine. It
uses 8 TC Sounds 15-inch drives with a DUMAX tested 23.5mm Xmax. The system
measred at an optimal 2-meter listening position is capable of producing in
excess of 120 dB from 12 - 62 hz with less than 10% distortion at a 2-meter
listening position.

Further the system at full output was measured with a Crown VZ5000 and has been
implemented with an 18 dB 1 octave eq function centered at 12 Hz.

With the Crown full output is unattainable at some frequencies because the
double vinyl windows twist in the frames.

"Nousaine" wrote in message
...


Snip..snip...


The system was described in the June '99 issue if Sound & Vision magazine.
It
uses 8 TC Sounds 15-inch drives with a DUMAX tested 23.5mm Xmax. The
system
measred at an optimal 2-meter listening position is capable of producing
in
excess of 120 dB from 12 - 62 hz with less than 10% distortion at a
2-meter
listening position.

Thanks Nousaine. Using the keywords you provided i did get into this v
site, clearly explaining the effect of cabin . Somehow, i always thought
audio reproduction was limited within 20hz to 20khz for CD. Now, where did i
get that?

Thanks again.

"Chelvam" wrote in message ...
"Stewart Pinkerton" wrote in message
...
On 25 Sep 2004 02:10:05 GMT, "Chelvam" wrote:

"Stewart Pinkerton" wrote in message
...

Hmmmm. Care to be more specific? What is your sub?

Why? you think it can't be heard that far?

Not at 20Hz, no, but probably at the 60-80Hz peak common to many
cheaper 'Home Cinema' biased units.

rest snipped for brevity....

My sub is crossed around 55 to 60 Hz. In my room it is certainly heavy and
full but felt more than heard. When I go to my bath it is definely louder
(more heard not so sure of felt) unlike in my room.

And in the case of my 200 feet neigbour who uses a mass market Home Theater
system the bass is not full or heavy but he was driving me nuts with his
"boom..boom ..boom" coming to my room. My sub on the other hand never heard
that far till I push it up the volume from about 10 oclock to 5 oclock and
crossed at 100khz.

So the question is:-

I always thought the lower the frequencies the further it is heard. Am I
wrong?

regards.

This is true and is basic acoustic science. There is a tiny bit of
loss in the adiabatic movement of air as the sound wave propagates.
This is +/- proportional to the wavelength. You could loosely
summarize that for every cycle there is a certain amount of loss and
therefore because lower frequencies have longer wavelengths that they
will travel more distance per cycle and thus per unit energy loss. Off
hand I believe the attenuation curve is quadratic against a
logarithmic frequency scale. (if I'm wrong someone will reply)

Your brain uses this principe, along with temporal left vs right
differences and reletive SPL differences, to tell you how far
something is away from you. In particular if something is pretty far
away then stereo preception will do you no good. You can hear this
phenominon all the time in music recordings.

Of course wind can skew this a bit. Ever wondered why a busy road in
the area only makes lots of noise sometimes?

Stewart Pinkerton wrote:
On 26 Sep 2004 22:18:09 GMT, "Tip" wrote:

Did you happen to see the 3-part objective (i.e., based
on measurements) review of subwoofers in the last three
issues of Stereophile Ultimate AV magazine? It doesn't
answer your question, but does indicate that most
subwoofers (but I'm sure not yours ;^)) suffer from
compression in the lower frequencies as the power
increases, which will cause a relative increase in the
SPL of the higher frequencies as the power goes up.

Knowing the basics of the drivers helps. My subwoofer design uses a
pair of Adire Tempests in an 'infinite baffle' situation using the
loft space above my listening room, and driven by a 250 watt 'plate'
amplifier. They are not in any way power compressed, but they are Xmax
limited below about 22Hz, although since this is at an in-room level
of about 115dB, I don't think it's a real problem.......... :-)

OTOH, if you run the numbers for virtually *any* driver in the sort of
2-3 cu ft box which is domestically acceptable, you certainly do run
into severe power problems when you get below 40Hz or so!

I cannot follow your logic here, on one hand the output is Xmax limited and
wouldn't allow full power, on the other hand a small box would require too
much power. If the box is small and the bass can be actively boosted with a
BiQuad filter, you will arrive at almost the same power level with the Xmax
limited to the same value.
At the end the small box with the Linkwitz correction will give the same SPL
at low frequencies as your "infinite baffle", with the exception of much
higher pressure inside the cabinet. The speaker will have to consume a bit
more power in the boosted range, and of course the increased counterpressure
of the cabinet requires a slightly higher power level.
But ultimately the SPL is governed by the amount of air moved and if your
speaker is in a big cabinet or a small one doesn't make much difference
IMHO.
Could you elaborate about the advantage of big cabinets? Is there less
distortion maybe?
--
ciao Ban
Bordighera, Italy

Wessel Dirksen wrote:

My sub is crossed around 55 to 60 Hz. In my room it is certainly
heavy and full but felt more than heard. When I go to my bath it is
definely louder (more heard not so sure of felt) unlike in my room.

And in the case of my 200 feet neigbour who uses a mass market Home
Theater system the bass is not full or heavy but he was driving me
nuts with his "boom..boom ..boom" coming to my room. My sub on the
other hand never heard that far till I push it up the volume from
about 10 oclock to 5 oclock and crossed at 100khz.

So the question is:-

I always thought the lower the frequencies the further it is heard.
Am I wrong?

regards.

This is true and is basic acoustic science. There is a tiny bit of
loss in the adiabatic movement of air as the sound wave propagates.
This is +/- proportional to the wavelength. You could loosely
summarize that for every cycle there is a certain amount of loss and
therefore because lower frequencies have longer wavelengths that they
will travel more distance per cycle and thus per unit energy loss. Off
hand I believe the attenuation curve is quadratic against a
logarithmic frequency scale. (if I'm wrong someone will reply)

Your brain uses this principe, along with temporal left vs right
differences and reletive SPL differences, to tell you how far
something is away from you. In particular if something is pretty far
away then stereo preception will do you no good. You can hear this
phenominon all the time in music recordings.

Of course wind can skew this a bit. Ever wondered why a busy road in
the area only makes lots of noise sometimes?

Well, the most important factor is the decreasing sensitivity of our ears
for lower levels of deep bass, which is a necessity to suppress the sound of
our stepping feet on the ground.
At 20Hz the 0db-loudness is at 70dB SPL, below this level we cannot hear
anything any more, at 50Hz this threshold has gone down to 40dB SPL. If the
SPL is above this value its perceived loudness rises much faster than higher
frequencies. Look up "Fletcher-Manson" diagramm.
The SPL is 6dB down by doubling the distance, only high frequencies get
absorbed by the air, all bass frequencies are transported without loss, just
the bigger surface will cause the decrease in level. Deep frequencies
propagate equally into all directions.
--
ciao Ban
Bordighera, Italy

snip
I always thought the lower the frequencies the further it is heard.
Am I wrong?



This is true and is basic acoustic science. There is a tiny bit of
loss in the adiabatic movement of air as the sound wave propagates.
This is +/- proportional to the wavelength. You could loosely
summarize that for every cycle there is a certain amount of loss and
therefore because lower frequencies have longer wavelengths that they
will travel more distance per cycle and thus per unit energy loss. Off
hand I believe the attenuation curve is quadratic against a
logarithmic frequency scale. (if I'm wrong someone will reply)

Your brain uses this principe, along with temporal left vs right
differences and reletive SPL differences, to tell you how far
something is away from you. In particular if something is pretty far
away then stereo preception will do you no good. You can hear this
phenominon all the time in music recordings.

Of course wind can skew this a bit. Ever wondered why a busy road in
the area only makes lots of noise sometimes?

Well, the most important factor is the decreasing sensitivity of our ears
for lower levels of deep bass, which is a necessity to suppress the sound of
our stepping feet on the ground.
At 20Hz the 0db-loudness is at 70dB SPL, below this level we cannot hear
anything any more, at 50Hz this threshold has gone down to 40dB SPL. If the
SPL is above this value its perceived loudness rises much faster than higher
frequencies. Look up "Fletcher-Manson" diagramm.
The SPL is 6dB down by doubling the distance, only high frequencies get
absorbed by the air, all bass frequencies are transported without loss, just
the bigger surface will cause the decrease in level. Deep frequencies
propagate equally into all directions.

Humm, that's indeed interesting to integrate Flechter-Munsen dynamics
into this discussion as well, en element which I hadn't thought about
combining with this issue. Yet in practice, I'm wondering how much it
is truly responsible for this phenomena in everyday life since you can
plainly hear the attenuation of higher frequencies in everyday life
situations which are usually well above threshold sensitive SPL
levels. Think about being a few hundred years from an outdoor rock
concert where the levels are still reasonbly loud and you hear mainly
low rumble. I guess you could summarize that when absolute SPL
thresholds start getting lower, that "perceived" high frequency
attenuation will increase to even a greater extent.

(Wessel Dirksen) wrote in message ...
Think about being a few hundred years from an outdoor rock
concert where the levels are still ....

Hmmm, "a few hundred years from an outdoor rock concert" would
put us right about in the middle of the Baroque era. Yes, yes,
that sounds MUCH better! :-)

(Dick Pierce) wrote in message ...
(Wessel Dirksen) wrote in message ...
Think about being a few hundred years from an outdoor rock
concert where the levels are still ....

Hmmm, "a few hundred years from an outdoor rock concert" would
put us right about in the middle of the Baroque era. Yes, yes,
that sounds MUCH better! :-)

Been away awhile.

Obviously I meant yards. But this reply is funny Dick. Aside from the
technical savvy, it's nice to see the funny side of you that obviously
enjoys Baroque music.

"Ban" wrote in message ...
Wessel Dirksen wrote:

My sub is crossed around 55 to 60 Hz. In my room it is certainly
heavy and full but felt more than heard. When I go to my bath it is
definely louder (more heard not so sure of felt) unlike in my room.

And in the case of my 200 feet neigbour who uses a mass market Home
Theater system the bass is not full or heavy but he was driving me
nuts with his "boom..boom ..boom" coming to my room. My sub on the
other hand never heard that far till I push it up the volume from
about 10 oclock to 5 oclock and crossed at 100khz.

So the question is:-

I always thought the lower the frequencies the further it is heard.
Am I wrong?

regards.

This is true and is basic acoustic science. There is a tiny bit of
loss in the adiabatic movement of air as the sound wave propagates.
This is +/- proportional to the wavelength. You could loosely
summarize that for every cycle there is a certain amount of loss and
therefore because lower frequencies have longer wavelengths that they
will travel more distance per cycle and thus per unit energy loss. Off
hand I believe the attenuation curve is quadratic against a
logarithmic frequency scale. (if I'm wrong someone will reply)

Your brain uses this principe, along with temporal left vs right
differences and reletive SPL differences, to tell you how far
something is away from you. In particular if something is pretty far
away then stereo preception will do you no good. You can hear this
phenominon all the time in music recordings.

Of course wind can skew this a bit. Ever wondered why a busy road in
the area only makes lots of noise sometimes?

Well, the most important factor is the decreasing sensitivity of our ears
for lower levels of deep bass, which is a necessity to suppress the sound of
our stepping feet on the ground.
At 20Hz the 0db-loudness is at 70dB SPL, below this level we cannot hear
anything any more, at 50Hz this threshold has gone down to 40dB SPL. If the
SPL is above this value its perceived loudness rises much faster than higher
frequencies. Look up "Fletcher-Manson" diagramm.
The SPL is 6dB down by doubling the distance, only high frequencies get
absorbed by the air, all bass frequencies are transported without loss, just
the bigger surface will cause the decrease in level. Deep frequencies
propagate equally into all directions.

Hi Ban, after being away I reread this and have decided to come back
to this one as I don't completely get your take on the wave
propagation part of this.

As I understand it, the movement of air molecules in a sound wave
follows adiabatic (literally without heat exchange)principles which
means pretty much lossless. But that's just decribing the vehicle and
not what the vehicle is doing. A sound pressure wave isn't just linear
movement of air in one direction at a constant velocity, it's an
expanding fluctuating pressure gradient which does involve inertial
forces of the molecules involved. This does then cause sound
propagation to be not negligable in terms of loss. This also explains
why the loss is +/- in conjuction with the number of cycles if you
think that everytime there is a cycle, air molecules (N2, O2, or CO2)
must slow down in response to pressure changes which in turn changes
pressure which get other molecules in the air moving. Also, the reason
why the the attenuation curve is not linear is also due to inertia.
Not only are there more cycles involved per unit distance, but there
is less time for momentum to drive air movement before being subjected
to a cycle change.

As far as directionality is concerned, assuming a sterile acoustic
field, as far as I know there is no inheirant directionality involved
in the frequency spectrum of sound pressure waves. What you are
describing I believe is based on the initial propagation
directionality where 4pi radiation due the long wavelength is the
rule, whereas bij short wavelengths the 2pi radiation is inheirant.
This has to do with a large wavelength vs. emitter size contrasts.
Also for the same reason, propagation from a plane source (radius
circle of pressure wave +/- = infinity) is possible with high
frequencies and not low due once again to the relative small size of
the emitter in contrast to the wavelength. The higher frequencies with
are emitted in 2pi fashion have an advantage as the pressure is 6db
higher everywhere due to same amount of energie per unit space but
this does not compensate enough for propagation loss. Low freq's also
lose less when absorbtion and scattering happen as well.

Comments greatly appreciated.