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In Reply to: fuse for 1.6 is 4 amps.... why do I need a high current amp ? posted by Listener26 on April 16, 2007 at 11:44:12:
You would need an amp capable of delivering 8100 watts to generate 45 amperes in a four-ohm resistive load. No one makes or uses such amps in home audio systems. However, many speakers, and Magnepans in particular, work better if the amps driving them have low output impedances. One way of expressing that an amp has a low output impedance is to describe the current the amp can deliver or absorb instantaneously.This is because the speaker can act as a generator of current when something causes the driver element to move. Usually the something is reflected sound within the listening room, or the inertia of the cone in a big woofer. I believe Magnepans also have internal resonances that can generate currents.
These currents cause braking forces within the drivers (which damp the motions in the same way shock absorbers damp the motions of automobile wheels), but only if the amp allows them to flow freely. Amps that have high instantaneous output impedances are unable to absorb the braking currents without causing signal distortion.
There is not a guaranteed relationship between "high current" and the low output impedance that makes the speaker sound good, because a lot depends on the details of the feedback loops used inside the amps, but there is a general trend.
Follow Ups:
For instance, the Parasound HCA-1500A and Halo A23 are spec'd at > 800 at 20Hz and the Halo A21 is > 1100 at 20Hz.
Henry
Yes, IME with MG-20s, more damping by the amplifier is better. This is not so much a bass issue as it would be with cone woofers, since the Magnepan dipole design is unbaffled. However, mid-bass and midrange purity seem to get better if the amp can offer more effective damping of the internal acoustic resonances. This observation is based on my experiments with crossover topology as well as amp upgrades.Unfortunately, the high damping factor numbers quoted apply only to the deep bass. Amps with feedback may not exhibit good damping at the frequencies where Magnepans seem to need more control. The Gilmore Raptor monoblocks are switching amps with oversized linear power supplies and they give superb performance across the spectrum. They do not use feedback in the conventional sense and have very low output impedance.
It depends on the mechanical and electrical damping of the speaker to a large extent. A well damped speaker and an amp with high damping factor often = boring overdamped sound.
I was merely asking for clarrification of that point.
Henry
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