What are standing waves and why do they appear to stand....


arguing with Tom is fun but for those of you that may want some
facts with out all the namecalling and fuss of trying to read the
good stuff in our parlay without being distracted by Toms exagerations
here is my view on it....


When two or more sound waves cross or compine with each other
something happens called superposition...This means they add together
changing the loudness..

If the waves are inphase with each other they add together 1+1=2
the sound is louder at this point...

if the waves are out of phase when they meet +1-1=0
the sound is softer at this point....

so basicly if the sounds are IN PHASE there is an increase in sound
and if the sounds are OUT OF PHASE there is a decrease in sound.

Phase is like a circle of 360degrees, if were out of phase we are 180
degrees different than the original ... The closer we get to OUT of
phase
the more loss we have and the closer we get to IN phase the more gain
we have....

simple so far...

When a sound REFLECTS and bounces back crossing the original
sound wave there are points along the path of the moving soundwaves
where they are IN PHASE and points where the two waves are OUT
OF PHASE...

For instance, at 1/4 wavelength from the reflecting surface, the
differnce
between the original wave and the reflected wave WILL ALWAYS BE
180degrees!

How can that be?
Simple,

if the original sound wave is at say 0 degrees of its cycle, the
reflected wave
(being 1/2 wavelength away (1/4 to the reflector and 1/4 back to the
spot))
must be at 180 degrees....

As the first wave changes to 1 degree (this happens real fast) the
reflection
at that spot will be 181 degrees,,, still 180degree differnce!

first wave 2 reflection 182
first wave 5 reflection 185
first wave 10 reflection 190 still 180 degree differnce at that spot
first wave 180 reflection 0 still 180 degree difference

at that spot, there will ALWAYS be 180 degree difference, this causes
a DIP in loudness AT THAT SPOT!

Now, by the same token, at other spots like 1/2 wavelength from the
reflector, there will be peaks, because at that SPOT there will always
be 0 degrees of difference between the first wave and the reflected
wave!!

If the first wave is 0
the reflected wave must travel 1/2 wave to the reflector (180) and 1/2
wave back (another 180) so the reflected wave is 360 (same as
zero)...

AND WE GET REINFORCEMENT
A PEAK that is ALWAYS THERE!

So with the DIPS and PEAKS that never change thier
location, the wave APPEARS to STAND STILL...

Even though waves are moveing both directions very fast, they are not
really standing still!

But because there are CONSTANT phse relationships
that DONT CHANGE, the waves APPEAR to stand still
and they call these STANDING WAVES....

This example is one speaker and one reflector....

It gets more fun when we have TWO reflectors
and even more fun when we have more reflectors...

Hope this helps anyone who doesnt want to try to keep up with
the mess in the other thread...

Eddie Runner
http://www.installer.com/tech/

I'm drowning in all the "which sub is better" threads. I can't see the
other thread. Where is it?

Thank you,
Jason Whorton



"Eddie Runner" wrote in message
...

What are standing waves and why do they appear to stand....


arguing with Tom is fun but for those of you that may want some
facts with out all the namecalling and fuss of trying to read the
good stuff in our parlay without being distracted by Toms exagerations
here is my view on it....


When two or more sound waves cross or compine with each other
something happens called superposition...This means they add together
changing the loudness..

If the waves are inphase with each other they add together 1+1=2
the sound is louder at this point...

if the waves are out of phase when they meet +1-1=0
the sound is softer at this point....

so basicly if the sounds are IN PHASE there is an increase in sound
and if the sounds are OUT OF PHASE there is a decrease in sound.

Phase is like a circle of 360degrees, if were out of phase we are 180
degrees different than the original ... The closer we get to OUT of
phase
the more loss we have and the closer we get to IN phase the more gain
we have....

simple so far...

When a sound REFLECTS and bounces back crossing the original
sound wave there are points along the path of the moving soundwaves
where they are IN PHASE and points where the two waves are OUT
OF PHASE...

For instance, at 1/4 wavelength from the reflecting surface, the
differnce
between the original wave and the reflected wave WILL ALWAYS BE
180degrees!

How can that be?
Simple,

if the original sound wave is at say 0 degrees of its cycle, the
reflected wave
(being 1/2 wavelength away (1/4 to the reflector and 1/4 back to the
spot))
must be at 180 degrees....

As the first wave changes to 1 degree (this happens real fast) the
reflection
at that spot will be 181 degrees,,, still 180degree differnce!

first wave 2 reflection 182
first wave 5 reflection 185
first wave 10 reflection 190 still 180 degree differnce at that spot
first wave 180 reflection 0 still 180 degree difference

at that spot, there will ALWAYS be 180 degree difference, this causes
a DIP in loudness AT THAT SPOT!

Now, by the same token, at other spots like 1/2 wavelength from the
reflector, there will be peaks, because at that SPOT there will always
be 0 degrees of difference between the first wave and the reflected
wave!!

If the first wave is 0
the reflected wave must travel 1/2 wave to the reflector (180) and 1/2
wave back (another 180) so the reflected wave is 360 (same as
zero)...

AND WE GET REINFORCEMENT
A PEAK that is ALWAYS THERE!

So with the DIPS and PEAKS that never change thier
location, the wave APPEARS to STAND STILL...

Even though waves are moveing both directions very fast, they are not
really standing still!

But because there are CONSTANT phse relationships
that DONT CHANGE, the waves APPEAR to stand still
and they call these STANDING WAVES....

This example is one speaker and one reflector....

It gets more fun when we have TWO reflectors
and even more fun when we have more reflectors...

Hope this helps anyone who doesnt want to try to keep up with
the mess in the other thread...

Eddie Runner
http://www.installer.com/tech/

its the evolution of the SUBWOOFER DIRECTION thread.

Eddie

Jason Whorton wrote:

I'm drowning in all the "which sub is better" threads. I can't see the
other thread. Where is it?

Thank you,
Jason Whorton

"Eddie Runner" wrote in message
...

What are standing waves and why do they appear to stand....


arguing with Tom is fun but for those of you that may want some
facts with out all the namecalling and fuss of trying to read the
good stuff in our parlay without being distracted by Toms exagerations
here is my view on it....