mario53
10-23-2004, 11:34 AM
Do you know what is 4 quadrant amplifier ?
"...What many people often forget is that the speaker is bouncing back electrical energy to the amplifier. The typical dynamical speaker with a moving coil in a static magnetical field is also acting as a current generator.
To explain this look at this example: when the speaker gets a single sided
pulse the diaphragm is following that pulse as best as it can. When it
bounces back to the original center position the electrical energy from the
pulse is transformed into movement energy of the diaphragm and a few side
effects like heat energy (copper loss in the coil etc.).
The movement energy of the diaphragm is partially transformed into movement
energy of the air (which we hear as the sound we want), partially into heat
energy, and the rest of the energy is kept as movement energy of the
diaphragm. The remaining movement energy (which is still stored in the
diaphragm) will force the diaphragm to swing to the opposide direction of the
original pulse. The altitude of this swing back maneuver will depend on
several factors, mainly the efficiency of the speaker (which is sometimes
pretty bad and may be in the range of 20 to 50%).
What happens if a coil is moved into a (statical) magnetical field? A current
is induced! This current is fed back into the amplifier in the reverse
direction.
This means that a relevant portion of the original electrical pulse from the
amplifier is fed back into the amplifier with a small time difference. The
amplifier should be able to handle this "reverse current". Unfortunately a
lot of amplifiers DON'T!
Most amplifiers are build as 2-quadrant amplifiers, that means, they can
supply positive and negative current, but they only act a current source, not
as a current sink. Only 4-quadrant amplifiers are able to supply positive and
negative current (acting as a source), AND also can "eat" positive and
negative current (act as sink).
So what happens when the amplifier is able to "eat" the reverse current?
Ideally the amplifier has an input impedance for the reverse current which is
close to zero. Then the electrical energy bouncing back from the coil is
immediately consumed and transformed into heat. This means that the unwanted
movement of the coil is immediately damped.
The lower the impedance is the better is the damping of unwanted movements.
This of course includes the speaker cable. It makes no sense to build an
amplifier with 0,1 Ohm impedance (at the output interface) if the speaker
cable adds 1 Ohm.
The lower the impedance of the amplifier is, and the lower the impedance of
the speaker cable is, the better the diaphragm can follow the electrical
signal and therefore reproduce more precisely the original signal. ...."
Do you know whetehr there are in the market these amps ?
"...What many people often forget is that the speaker is bouncing back electrical energy to the amplifier. The typical dynamical speaker with a moving coil in a static magnetical field is also acting as a current generator.
To explain this look at this example: when the speaker gets a single sided
pulse the diaphragm is following that pulse as best as it can. When it
bounces back to the original center position the electrical energy from the
pulse is transformed into movement energy of the diaphragm and a few side
effects like heat energy (copper loss in the coil etc.).
The movement energy of the diaphragm is partially transformed into movement
energy of the air (which we hear as the sound we want), partially into heat
energy, and the rest of the energy is kept as movement energy of the
diaphragm. The remaining movement energy (which is still stored in the
diaphragm) will force the diaphragm to swing to the opposide direction of the
original pulse. The altitude of this swing back maneuver will depend on
several factors, mainly the efficiency of the speaker (which is sometimes
pretty bad and may be in the range of 20 to 50%).
What happens if a coil is moved into a (statical) magnetical field? A current
is induced! This current is fed back into the amplifier in the reverse
direction.
This means that a relevant portion of the original electrical pulse from the
amplifier is fed back into the amplifier with a small time difference. The
amplifier should be able to handle this "reverse current". Unfortunately a
lot of amplifiers DON'T!
Most amplifiers are build as 2-quadrant amplifiers, that means, they can
supply positive and negative current, but they only act a current source, not
as a current sink. Only 4-quadrant amplifiers are able to supply positive and
negative current (acting as a source), AND also can "eat" positive and
negative current (act as sink).
So what happens when the amplifier is able to "eat" the reverse current?
Ideally the amplifier has an input impedance for the reverse current which is
close to zero. Then the electrical energy bouncing back from the coil is
immediately consumed and transformed into heat. This means that the unwanted
movement of the coil is immediately damped.
The lower the impedance is the better is the damping of unwanted movements.
This of course includes the speaker cable. It makes no sense to build an
amplifier with 0,1 Ohm impedance (at the output interface) if the speaker
cable adds 1 Ohm.
The lower the impedance of the amplifier is, and the lower the impedance of
the speaker cable is, the better the diaphragm can follow the electrical
signal and therefore reproduce more precisely the original signal. ...."
Do you know whetehr there are in the market these amps ?