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Standing waves
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/ |
#2
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Standing waves
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/ |
#3
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Standing waves
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.... |
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