Ampdog
R.I.P. 23 June 2022
From Alphabet:
OK Alphabet, and if you are serious and won't mind 21 more sentences ....
You would know that if a current is chased through a wire (or even better, a coil of wire) suspended in a fixed magnetic field, the coil will move in a direction determined by the direction of current and polarity of the magnet. (You have probably made a little tin electric motor in your youth.)
If the same coil is moved back and forth in such a magnetic field, a voltage would be generated across the coil (the way microphones work.) These actions are reciprocal and are an illustration of the reversible electromagnetic principle.
Now your loudspeaker work according to the first law. The amplifier forces ac through the voice coil which causes a stiff cone to move and make music, because that is what the ac resembles. Now, if a sharp transient comes along, the poor cone must go into action immediately, and stop dead still immediately when the transient is past. That is impossible for something that has mass and compliance. At best the cone will come to rest after a few further oscillations - which we do not want.
But aid is available as those unwanted oscillations in a fixed magnetic field generate a voltage across the coil as per the second action above. If we could now short the voice coil immediately after the transient has stopped, the generated voltage across the voice coil will cause a current to flow in itself because of the short, this will, according to the first action above, try to generate a motion in the coil opposite to what it is doing at any time, i.e. to stop the unwanted movement or brake it.
The design of a proper amplifier is such that it causes an almost dead short across the voice coil as soon as any signal stops. This is easily illustrated by wiring a short through a switch over the voice coil of any loudspeaker. By gently rocking the cone by hand and in the middle of such movement switch the switch to 'on', an immediate increased stiffness would be felt in the cone. The faster the rocking was, the greater the stiffness. No rocking, no stiffness - because it depends on the speed of moving the voice coil wires in the magnetic field.
Only the output circuits of amplifiers are not automatically 'shorts'. The 'pseudo-short' exists to the degree that the amplifier can analise the loudspeaker motion and provide its own 'back-emf' to brake the loudspeaker cone movement. The braking factor or 'damping factor' is defined by dividing the loudspeaker impedance by the (hopefully lower) impedance the amplifier presents. E.g. it is common for an amplifier for an 8 ohm loudspeaker, to have an internal impedance of <0.4 ohm - thus a damping factor of >20.
Hope this helped.
OK Alphabet, and if you are serious and won't mind 21 more sentences ....
You would know that if a current is chased through a wire (or even better, a coil of wire) suspended in a fixed magnetic field, the coil will move in a direction determined by the direction of current and polarity of the magnet. (You have probably made a little tin electric motor in your youth.)
If the same coil is moved back and forth in such a magnetic field, a voltage would be generated across the coil (the way microphones work.) These actions are reciprocal and are an illustration of the reversible electromagnetic principle.
Now your loudspeaker work according to the first law. The amplifier forces ac through the voice coil which causes a stiff cone to move and make music, because that is what the ac resembles. Now, if a sharp transient comes along, the poor cone must go into action immediately, and stop dead still immediately when the transient is past. That is impossible for something that has mass and compliance. At best the cone will come to rest after a few further oscillations - which we do not want.
But aid is available as those unwanted oscillations in a fixed magnetic field generate a voltage across the coil as per the second action above. If we could now short the voice coil immediately after the transient has stopped, the generated voltage across the voice coil will cause a current to flow in itself because of the short, this will, according to the first action above, try to generate a motion in the coil opposite to what it is doing at any time, i.e. to stop the unwanted movement or brake it.
The design of a proper amplifier is such that it causes an almost dead short across the voice coil as soon as any signal stops. This is easily illustrated by wiring a short through a switch over the voice coil of any loudspeaker. By gently rocking the cone by hand and in the middle of such movement switch the switch to 'on', an immediate increased stiffness would be felt in the cone. The faster the rocking was, the greater the stiffness. No rocking, no stiffness - because it depends on the speed of moving the voice coil wires in the magnetic field.
Only the output circuits of amplifiers are not automatically 'shorts'. The 'pseudo-short' exists to the degree that the amplifier can analise the loudspeaker motion and provide its own 'back-emf' to brake the loudspeaker cone movement. The braking factor or 'damping factor' is defined by dividing the loudspeaker impedance by the (hopefully lower) impedance the amplifier presents. E.g. it is common for an amplifier for an 8 ohm loudspeaker, to have an internal impedance of <0.4 ohm - thus a damping factor of >20.
Hope this helped.
