Bass Tip-up

BASS TIP-UP IN RIBBON MICS

THE "PROXIMITY EFFECT"

PLAN VIEW OF A RIBBON MIC

The ribbon is vibrated across the magnetic field by differences in air pressure between the two sides caused by a sound wave.

The output voltage of the ribbon is proportional to the velocity with which is moves across the magnetic field and this depend on the pressure difference and the frequency.

Because of the mass of the ribbon, with a constant pressure difference, the output voltage falls as the frequency gets higher

GRAPH OF OUTPUT VOLTAGE AGAINST FREQUENCY

The pressure difference is caused by sound waves, alternate waves of increased and decreased air pressure.

The sound waves can be plane waves or spherical waves or, more usually, a mixture of the two.

PLANE WAVE COMPONENT
FROM A DISTANCE OR FROM A FLAT SOURCE

Alternate waves of constant strength.
Normally this effect is strongest

SPHERICAL WAVE COMPONENT
CLOSE TO A POINT SOURCE

Each wave expands and weakens.
Normally this is a much smaller effect unless you are close to the source

Pressure difference between two sides of the ribbon due to plane wave component

Pressure difference between two sides of the ribbon due to spherical wave component

At low frequencies the pressure difference component due to a plane wave is reduced because it depends on the wavelength

At low frequencies there is no change to the pressure difference due to a spherical wave component because it depends only on the expansion of a spherical wavefront

The closer to the sound source, the stronger this effect becomes.

Change of plane wave pressure difference with frequency

No change of spherical wave pressure difference with frequency

With this information we can see how ribbon microphone responds to the two different types of wave and what happens in the practical situation when it is brought close to a source of sound and spherical waves begin to dominate the response.

RIBBON FREQUENCY RESPONSE TO A CONSTANT PRESSURE DIFFERENCE

RIBBON FREQUENCY RESPONSE TO A CONSTANT PRESSURE DIFFERENCE

PRESSURE DIFFERENCE CAUSED BY A PLANE WAVE

PRESSURE DIFFERENCE CAUSED BY A SPHERICAL WAVE

RIBBON FREQUENCY RESPONSE TO A PLANE WAVE

RIBBON FREQUENCY RESPONSE TO A SPHERICAL WAVE

RIBBON RESPONSE FAIRLY CLOSE TO A SPHERICAL SOURCE
WITH BOTH PLANE AND SPHERICAL WAVES

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PLANE WAVE COMPONENT FROM A DISTANCE OR FROM A FLAT SOURCE Alternate waves of constant strength. Normally this effect is strongest		SPHERICAL WAVE COMPONENT CLOSE TO A POINT SOURCE Each wave expands and weakens. Normally this is a much smaller effect unless you are close to the source
Pressure difference between two sides of the ribbon due to plane wave component		Pressure difference between two sides of the ribbon due to spherical wave component
At low frequencies the pressure difference component due to a plane wave is reduced because it depends on the wavelength		At low frequencies there is no change to the pressure difference due to a spherical wave component because it depends only on the expansion of a spherical wavefront The closer to the sound source, the stronger this effect becomes.
Change of plane wave pressure difference with frequency		No change of spherical wave pressure difference with frequency

RIBBON FREQUENCY RESPONSE TO A CONSTANT PRESSURE DIFFERENCE		RIBBON FREQUENCY RESPONSE TO A CONSTANT PRESSURE DIFFERENCE
PRESSURE DIFFERENCE CAUSED BY A PLANE WAVE		PRESSURE DIFFERENCE CAUSED BY A SPHERICAL WAVE
RIBBON FREQUENCY RESPONSE TO A PLANE WAVE		RIBBON FREQUENCY RESPONSE TO A SPHERICAL WAVE
RIBBON RESPONSE FAIRLY CLOSE TO A SPHERICAL SOURCE WITH BOTH PLANE AND SPHERICAL WAVES BASS TIP-UP