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Resistors vs.peltz Autoformer- Differences

I just got an email from Zu.
They offer resistors for their speakers that will lower/raise impedance so that amps will have an easier time driving them.
What is the difference between using a resistor and using an Autoformer, like the Paul Speltz? Both seem to be doing the same thing.
Bob
gdnrbob
gdnrbob OP
4,447 posts
 
Nuts, I can't edit the title.
Resistors vs. Paul Speltz Autoformers- Differences?
Bob
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almarg's avatar
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almarg
9,670 posts
 
Hi Bob,

While using a resistor will lighten the load on the amp it will also waste a lot of the power the amp is putting out. For example if a 4 ohm resistor is placed in series with a 4 ohm speaker (that is really 4 ohms) half of the power supplied by the amp will be converted into heat by the resistor, as opposed to being supplied to the speaker. The power lost in an autoformer, on the other hand, will be minimal.

Also, damping factor will be affected very differently in the two cases, and in favor of the autoformer. In the 4 ohm example I just cited, the damping factor seen by the speaker will be less than 1 if a resistor is used. But if an autoformer is used to provide the same increase in the load impedance seen by the amp the damping factor seen by the speaker will correspond to the damping factor of the particular amp (for a 4 ohm load) multiplied by two.

Best regards,
-- Al

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