deb611
Member
Been reading a lot about the physics of proximity effect and I wanted to see if I was correct here. Can someone confirm that I'm not off my gourd?
Essentially a general rule of thumb is the larger the diaphragm, the more pronounced proximity effect will be and the sooner it will begin to occur. Correct?
The law of inverse square would dictate that the closer the distance between mic and source, the lower the relative distance for frequency dropoff (doubling of distance = roughly 6dB in amplitude reduction).
So to get 6dB reduction in sound pressure, we go from 1cm to 2cm. Then the next 6dB reduction is 2cm to 4cm. Then 4cm to 8cm. i.e., the distance to sound reduction INCREASES for each successive 6dB reduction.
If a diaphragm is LARGER, then the sound has to travel FURTHER to reach the rear of the diaphragm as opposed to the front.
Let's use the example here: a 5cm diameter pressure-gradient diaphragm positioned 5cm away from a sound source. The sound has to travel 5cm to the front of the diaphragm, but has to travel 5cm (distance from source) + 5cm (twice the radius of the diaphragm) = 10cm to the rear of the diaphragm. Therefore, there is a DOUBLING of distance to the rear, and thus a 6dB amplitude difference across the front/rear of the diaphragm.
Second example: a 1cm diameter pressure-gradient diaphragm positioned 5cm away from a sound source. The sound has to travel 5cm to the front of the diaphragm, but has to travel 5cm (distance from source) + 1cm (twice the radius of the diaphragm) = 6cm to the rear of the diaphragm. Therefore, there is a 1.2x increase of distance to the rear, and thus a smaller amplitude difference (≈1dB?) across the front/rear of a the diaphragm.
I assume there are also other factors, like the porting slots on SDCs to make the sound travel further from front to rear, that would have a factor in proximity effect.
Essentially a general rule of thumb is the larger the diaphragm, the more pronounced proximity effect will be and the sooner it will begin to occur. Correct?
The law of inverse square would dictate that the closer the distance between mic and source, the lower the relative distance for frequency dropoff (doubling of distance = roughly 6dB in amplitude reduction).
So to get 6dB reduction in sound pressure, we go from 1cm to 2cm. Then the next 6dB reduction is 2cm to 4cm. Then 4cm to 8cm. i.e., the distance to sound reduction INCREASES for each successive 6dB reduction.
If a diaphragm is LARGER, then the sound has to travel FURTHER to reach the rear of the diaphragm as opposed to the front.
Let's use the example here: a 5cm diameter pressure-gradient diaphragm positioned 5cm away from a sound source. The sound has to travel 5cm to the front of the diaphragm, but has to travel 5cm (distance from source) + 5cm (twice the radius of the diaphragm) = 10cm to the rear of the diaphragm. Therefore, there is a DOUBLING of distance to the rear, and thus a 6dB amplitude difference across the front/rear of the diaphragm.
Second example: a 1cm diameter pressure-gradient diaphragm positioned 5cm away from a sound source. The sound has to travel 5cm to the front of the diaphragm, but has to travel 5cm (distance from source) + 1cm (twice the radius of the diaphragm) = 6cm to the rear of the diaphragm. Therefore, there is a 1.2x increase of distance to the rear, and thus a smaller amplitude difference (≈1dB?) across the front/rear of a the diaphragm.
I assume there are also other factors, like the porting slots on SDCs to make the sound travel further from front to rear, that would have a factor in proximity effect.