Kijanki,
It seems like you've rehashed what you've read on Wikipedia without getting a proper understanding of the facts. Yes, toroids are generally mechanically quieter than E-I types, EXCEPT when subjected to DC.
The core of a toroidal transformer saturates more easily than that of an E-I type transformer. Because of this, toroids tend to have higher inrush current. DC offset on the power line will also cause magnetic saturation of the core of a toroid more readily than in an E-I type transformer. As the toroid transformer attempts to recover from the saturation, this causes a buzzing sound.
Manufacturers like Equi=Tech and Plitron employ manufacturing techniques in their "Q" type and NBT type transformers respectively that help make them less susceptible to this core saturation.
See here:
http://www.soundstage.com/maxdb/maxdb071998.htm
.
It seems like you've rehashed what you've read on Wikipedia without getting a proper understanding of the facts. Yes, toroids are generally mechanically quieter than E-I types, EXCEPT when subjected to DC.
The core of a toroidal transformer saturates more easily than that of an E-I type transformer. Because of this, toroids tend to have higher inrush current. DC offset on the power line will also cause magnetic saturation of the core of a toroid more readily than in an E-I type transformer. As the toroid transformer attempts to recover from the saturation, this causes a buzzing sound.
Manufacturers like Equi=Tech and Plitron employ manufacturing techniques in their "Q" type and NBT type transformers respectively that help make them less susceptible to this core saturation.
See here:
http://www.soundstage.com/maxdb/maxdb071998.htm
.