Echo v. reverberation

[occam]

There was a news item on the BBC Radio 4 this morning about the world's
"longest echo ever recorded", greater than the existing 15 seconds
record. (Spoiler - the record now apparently stands at 112 seconds.)

https://www.bbc.com/news/uk-scotland-highlands-islands-25757937

In the radio interview, the scientist in question made a distinction
between 'an echo' and 'a reverberation' .

He described an echo as the same note, heard a second time, and a
reverberation as a note that is extended (dragged out) in time.

Does this distinction make sense in physics terms? Two or more waves of
the same note merging together so as to render them indistinguishable -
hence a reverberation as distinct from an echo?

(Alas, the article linked to above makes no reference to this.)

[Peter Moylan]

Post by occam
There was a news item on the BBC Radio 4 this morning about the
world's "longest echo ever recorded", greater than the existing 15
seconds record. (Spoiler - the record now apparently stands at 112
seconds.)
https://www.bbc.com/news/uk-scotland-highlands-islands-25757937
In the radio interview, the scientist in question made a distinction
between 'an echo' and 'a reverberation' .
He described an echo as the same note, heard a second time, and a
reverberation as a note that is extended (dragged out) in time.
Does this distinction make sense in physics terms? Two or more waves
of the same note merging together so as to render them
indistinguishable - hence a reverberation as distinct from an echo?
(Alas, the article linked to above makes no reference to this.)

In my mind, reverberation is the result of multiple echoes.

Consider a lightning strike near a cliff. Given the right conditions,
you'll hear the thunder twice: the original, plus the echo from the cliff.

A cloud-to-cloud lightning strike is different, because the resulting
thunder rumbles on for a long time. Why? Because of multiple echoes
among the clouds. I would call this latter case reverberation.

(So I'm disagreeing with your expert.)

[occam]

Post by Peter Moylan

Post by occam
There was a news item on the BBC Radio 4 this morning about the
world's "longest echo ever recorded",  greater than the existing 15
seconds record. (Spoiler - the record now apparently stands at 112
seconds.)
https://www.bbc.com/news/uk-scotland-highlands-islands-25757937
In the radio interview, the scientist in question made a distinction
between 'an echo' and 'a reverberation' .
He described an echo as the same note, heard a second time, and a
reverberation as a note that is extended (dragged out) in time.
Does this distinction make sense in physics terms?  Two or more waves
of the same note merging together so as to render them
indistinguishable - hence a reverberation as distinct from an echo?
(Alas, the article linked to above makes no reference to this.)

In my mind, reverberation is the result of multiple echoes.

I tend to agree. However, for a small number of echoes (e.g 2) a double
echo is still an echo, rather than a reverberation. (I get this on VOIP
calls often.) How many out-of-phase echoes would it take to make a
reverberation? In a confined space, this is more likely than, say a
cliff or a valley.

Post by Peter Moylan
Consider a lightning strike near a cliff. Given the right conditions,
you'll hear the thunder twice: the original, plus the echo from the cliff.
A cloud-to-cloud lightning strike is different, because the resulting
thunder rumbles on for a long time. Why? Because of multiple echoes
among the clouds. I would call this latter case reverberation.
(So I'm disagreeing with your expert.)

[J. J. Lodder]

occam <***@nowhere.nix> wrote:
[mixed level replies again, sorry]

Post by occam

Post by Peter Moylan

Post by occam
There was a news item on the BBC Radio 4 this morning about the
world's "longest echo ever recorded", greater than the existing 15
seconds record. (Spoiler - the record now apparently stands at 112
seconds.)
https://www.bbc.com/news/uk-scotland-highlands-islands-25757937
In the radio interview, the scientist in question made a distinction
between 'an echo' and 'a reverberation' .
He described an echo as the same note, heard a second time, and a
reverberation as a note that is extended (dragged out) in time.
Does this distinction make sense in physics terms? Two or more waves
of the same note merging together so as to render them
indistinguishable - hence a reverberation as distinct from an echo?
(Alas, the article linked to above makes no reference to this.)

In my mind, reverberation is the result of multiple echoes.

I tend to agree. However, for a small number of echoes (e.g 2) a double
echo is still an echo, rather than a reverberation. (I get this on VOIP
calls often.) How many out-of-phase echoes would it take to make a
reverberation? In a confined space, this is more likely than, say a
cliff or a valley.

Having an echo at all depends on having a well-defined wave packet.
So on Fourier components being in phase.
In a confined space there will be resonant modes with frequencies
that are not multiples of one another, so wave packets will spread out.
So echo versus reverberation becomes a matter of talking about it
in the time domain or in the frequency domain.
The art of designing a concert hall lies precisely in making
all those normal modes have different frequencies.
A rectangular box, where you will have echos,
is completely unsuitable.

Post by occam

Post by Peter Moylan
Consider a lightning strike near a cliff. Given the right conditions,
you'll hear the thunder twice: the original, plus the echo from the cliff.
A cloud-to-cloud lightning strike is different, because the resulting
thunder rumbles on for a long time. Why? Because of multiple echoes
among the clouds. I would call this latter case reverberation.
(So I'm disagreeing with your expert.)

This is just plain wrong.
A lightning channel will be many kilometers long,
so sound travel times from different parts of the channel to you
will be very different.
This is what causes the prolonged rumble.
There are no echos in the clouds.

Jan

[lar3ryca]

Post by J. J. Lodder
[mixed level replies again, sorry]

Post by occam

Post by Peter Moylan

Post by occam
There was a news item on the BBC Radio 4 this morning about the
world's "longest echo ever recorded", greater than the existing 15
seconds record. (Spoiler - the record now apparently stands at 112
seconds.)
https://www.bbc.com/news/uk-scotland-highlands-islands-25757937
In the radio interview, the scientist in question made a distinction
between 'an echo' and 'a reverberation' .
He described an echo as the same note, heard a second time, and a
reverberation as a note that is extended (dragged out) in time.
Does this distinction make sense in physics terms? Two or more waves
of the same note merging together so as to render them
indistinguishable - hence a reverberation as distinct from an echo?
(Alas, the article linked to above makes no reference to this.)

In my mind, reverberation is the result of multiple echoes.

I tend to agree. However, for a small number of echoes (e.g 2) a double
echo is still an echo, rather than a reverberation. (I get this on VOIP
calls often.) How many out-of-phase echoes would it take to make a
reverberation? In a confined space, this is more likely than, say a
cliff or a valley.

Having an echo at all depends on having a well-defined wave packet.
So on Fourier components being in phase.
In a confined space there will be resonant modes with frequencies
that are not multiples of one another, so wave packets will spread out.
So echo versus reverberation becomes a matter of talking about it
in the time domain or in the frequency domain.
The art of designing a concert hall lies precisely in making
all those normal modes have different frequencies.
A rectangular box, where you will have echos,
is completely unsuitable.

Post by occam

Post by Peter Moylan
Consider a lightning strike near a cliff. Given the right conditions,
you'll hear the thunder twice: the original, plus the echo from the cliff.
A cloud-to-cloud lightning strike is different, because the resulting
thunder rumbles on for a long time. Why? Because of multiple echoes
among the clouds. I would call this latter case reverberation.
(So I'm disagreeing with your expert.)

This is just plain wrong.
A lightning channel will be many kilometers long,
so sound travel times from different parts of the channel to you
will be very different.
This is what causes the prolonged rumble.
There are no echos in the clouds.

Clouds are interesting in terms of 'sound channels' as well. It is very
obvious in fog. While sailing in fog, it is almost impossible to tell
how close a ship or lighthouse is from the sound of a horn. You'll hear
a blast that sounds very close, and a few blasts later it will sound far
away, then close, and so on.

It's unnerving to say the least, to hear a ship's horn that sounds like
it's pretty far away, only to hear another one very loud, as the ship
appears out of the fog.

[J. J. Lodder]

Post by lar3ryca

Post by J. J. Lodder
[mixed level replies again, sorry]

Post by occam

Post by Peter Moylan

Post by occam
There was a news item on the BBC Radio 4 this morning about the
world's "longest echo ever recorded", greater than the existing 15
seconds record. (Spoiler - the record now apparently stands at 112
seconds.)
https://www.bbc.com/news/uk-scotland-highlands-islands-25757937
In the radio interview, the scientist in question made a distinction
between 'an echo' and 'a reverberation' .
He described an echo as the same note, heard a second time, and a
reverberation as a note that is extended (dragged out) in time.
Does this distinction make sense in physics terms? Two or more waves
of the same note merging together so as to render them
indistinguishable - hence a reverberation as distinct from an echo?
(Alas, the article linked to above makes no reference to this.)

In my mind, reverberation is the result of multiple echoes.

I tend to agree. However, for a small number of echoes (e.g 2) a double
echo is still an echo, rather than a reverberation. (I get this on VOIP
calls often.) How many out-of-phase echoes would it take to make a
reverberation? In a confined space, this is more likely than, say a
cliff or a valley.

Having an echo at all depends on having a well-defined wave packet.
So on Fourier components being in phase.
In a confined space there will be resonant modes with frequencies
that are not multiples of one another, so wave packets will spread out.
So echo versus reverberation becomes a matter of talking about it
in the time domain or in the frequency domain.
The art of designing a concert hall lies precisely in making
all those normal modes have different frequencies.
A rectangular box, where you will have echos,
is completely unsuitable.

Post by occam

Post by Peter Moylan
Consider a lightning strike near a cliff. Given the right conditions,
you'll hear the thunder twice: the original, plus the echo from the cliff.
A cloud-to-cloud lightning strike is different, because the resulting
thunder rumbles on for a long time. Why? Because of multiple echoes
among the clouds. I would call this latter case reverberation.
(So I'm disagreeing with your expert.)

This is just plain wrong.
A lightning channel will be many kilometers long,
so sound travel times from different parts of the channel to you
will be very different.
This is what causes the prolonged rumble.
There are no echos in the clouds.

Clouds are interesting in terms of 'sound channels' as well. It is very
obvious in fog. While sailing in fog, it is almost impossible to tell
how close a ship or lighthouse is from the sound of a horn. You'll hear
a blast that sounds very close, and a few blasts later it will sound far
away, then close, and so on.

Yes. Mist often happens in combination with a temperature inversion.
This channels the sound in a low layer of air.
Temperature variations may also cause the sound to bend sideways.
You are out of luck: only the first volume of Minnaert
(on light) was ever translated. The sound is in the second one.

Minnaert mentions multiple pathways being possible,
with the sound of a single cannon shot being heard several times,
up to eight times even. Rolling after-sounds, like thunder,
have also been reported. [1]

Post by lar3ryca
It's unnerving to say the least, to hear a ship's horn that sounds like
it's pretty far away, only to hear another one very loud, as the ship
appears out of the fog.

I can well imagine,

Jan

[1] Minnaert gives
Rep. Brit. Assoc. 1875 (Dublin). - Nat. 13, 67, 1875. - Met. Zs. 33,
553, 1916. - R. Emden, Met. Zs. 1918. - V. Angerer & Ladenburg, Ann. d.
Phys. 66, 308, 1921.
which is no doubt immediately helpful.

[Peter Moylan]

Post by J. J. Lodder
[mixed level replies again, sorry]

Post by Peter Moylan
A cloud-to-cloud lightning strike is different, because the resulting
thunder rumbles on for a long time. Why? Because of multiple echoes
among the clouds. I would call this latter case reverberation.
(So I'm disagreeing with your expert.)

This is just plain wrong.
A lightning channel will be many kilometers long,
so sound travel times from different parts of the channel to you
will be very different.
This is what causes the prolonged rumble.
There are no echos in the clouds.

I've designed a device, for an environmental monitoring company, to work
out the frequency and spatial distribution of incoming sounds. (In the
case of an overly loud mine explosion, you need to know which mine to
blame.) In our testing, reflection from clouds turned out to be a
significant complication.

[J. J. Lodder]

Post by Peter Moylan

Post by J. J. Lodder
[mixed level replies again, sorry]

Post by Peter Moylan
A cloud-to-cloud lightning strike is different, because the resulting
thunder rumbles on for a long time. Why? Because of multiple echoes
among the clouds. I would call this latter case reverberation.
(So I'm disagreeing with your expert.)

This is just plain wrong.
A lightning channel will be many kilometers long,
so sound travel times from different parts of the channel to you
will be very different.
This is what causes the prolonged rumble.
There are no echos in the clouds.

I've designed a device, for an environmental monitoring company, to work
out the frequency and spatial distribution of incoming sounds. (In the
case of an overly loud mine explosion, you need to know which mine to
blame.) In our testing, reflection from clouds turned out to be a
significant complication.

Probably bending of sound rays by temperature inversions.
(the acoustic equivalent of a mirage)
Your problems are well known from WWI.
Acurate acoustical ranging of big guns is difficult.

Jan

[Sam Plusnet]

Post by J. J. Lodder

Post by Peter Moylan

Post by J. J. Lodder
[mixed level replies again, sorry]

Post by Peter Moylan
A cloud-to-cloud lightning strike is different, because the resulting
thunder rumbles on for a long time. Why? Because of multiple echoes
among the clouds. I would call this latter case reverberation.
(So I'm disagreeing with your expert.)

This is just plain wrong.
A lightning channel will be many kilometers long,
so sound travel times from different parts of the channel to you
will be very different.
This is what causes the prolonged rumble.
There are no echos in the clouds.

I've designed a device, for an environmental monitoring company, to work
out the frequency and spatial distribution of incoming sounds. (In the
case of an overly loud mine explosion, you need to know which mine to
blame.) In our testing, reflection from clouds turned out to be a
significant complication.

Probably bending of sound rays by temperature inversions.
(the acoustic equivalent of a mirage)
Your problems are well known from WWI.
Acurate acoustical ranging of big guns is difficult.

Environmental conditions (temperature, pressure) may result in cloud
formation. Those same conditions can cause (forgive the Sonar
terminology) 'ray bending' so that sound travels in a non-linear fashion.
So 'sounds bounce off clouds' is not accurate, but it might well work as
a rule of thumb.

[wugi]

Post by occam
There was a news item on the BBC Radio 4 this morning about the world's
"longest echo ever recorded", greater than the existing 15 seconds
record. (Spoiler - the record now apparently stands at 112 seconds.)
https://www.bbc.com/news/uk-scotland-highlands-islands-25757937
In the radio interview, the scientist in question made a distinction
between 'an echo' and 'a reverberation' .
He described an echo as the same note, heard a second time, and a
reverberation as a note that is extended (dragged out) in time.
Does this distinction make sense in physics terms? Two or more waves of
the same note merging together so as to render them indistinguishable -
hence a reverberation as distinct from an echo?
(Alas, the article linked to above makes no reference to this.)

I'd agree, also according to my translators:
A cry in the mountains can be "echoed" one or a few times: you'll hear
the same utterance repeated(ly repeated).
Reverberation (nl: nagalm) is for instance the confused sound lingering
in an auditorium with poor acoustics, after a final accord.

[wugi]

Post by wugi
A cry in the mountains can be "echoed" one or a few times: you'll hear
the same utterance repeated(ly repeated).
Reverberation (nl: nagalm) is for instance the confused sound lingering
in an auditorium with poor acoustics, after a final accord.

You won't hear a clear echo there. Compare also with the lingering
rumble of thunder, occasionally interspersed with a "true" echo.

You could describe reverberation as the interference of multiple echos
with multiple delays in a broad spectrum reflecting environment. I'm
sure Jan can formulate this in better terms.

[LionelEdwards]

Post by wugi

Post by wugi
A cry in the mountains can be "echoed" one or a few times: you'll hear
the same utterance repeated(ly repeated).
Reverberation (nl: nagalm) is for instance the confused sound lingering
in an auditorium with poor acoustics, after a final accord.

You won't hear a clear echo there. Compare also with the lingering
rumble of thunder, occasionally interspersed with a "true" echo.
You could describe reverberation as the interference of multiple echos
with multiple delays in a broad spectrum reflecting environment. I'm
sure Jan can formulate this in better terms.

Or you could describe as what it claims to be? Repeat-wording.

Resounding Rebounding Echoing. The Swiss are the masters of yodelling:

[J. J. Lodder]

Post by wugi

Post by wugi
A cry in the mountains can be "echoed" one or a few times: you'll hear
the same utterance repeated(ly repeated).
Reverberation (nl: nagalm) is for instance the confused sound lingering
in an auditorium with poor acoustics, after a final accord.

You won't hear a clear echo there. Compare also with the lingering
rumble of thunder, occasionally interspersed with a "true" echo.
You could describe reverberation as the interference of multiple echos
with multiple delays in a broad spectrum reflecting environment. I'm
sure Jan can formulate this in better terms.

Echos are usually associated with free waves,
reverberations with resonant modes in a confined space, [1]

Jan

[1] Until Mr. Hammond invented the horrors of a 'reverb' button.

[LionelEdwards]

Post by occam
There was a news item on the BBC Radio 4 this morning about the world's
"longest echo ever recorded", greater than the existing 15 seconds
record. (Spoiler - the record now apparently stands at 112 seconds.)
https://www.bbc.com/news/uk-scotland-highlands-islands-25757937
In the radio interview, the scientist in question made a distinction
between 'an echo' and 'a reverberation' .
He described an echo as the same note, heard a second time, and a
reverberation as a note that is extended (dragged out) in time.
Does this distinction make sense in physics terms? Two or more waves of
the same note merging together so as to render them indistinguishable -
hence a reverberation as distinct from an echo?
(Alas, the article linked to above makes no reference to this.)

Betwixt the two: "You make the listening shores rebound" in Purcell: