Amplifier circuitry-4 ohm vs 8 ohm

What if the speaker has a nominal impedance of 6 ohms? Which tap (4 or 8) should be used since the load is right in the middle of the two windings?

@dspringham Try it on both. If you have access to the impedance curve of the speaker, look at the impedance it presents to the amplifier in the bass region. That's where the energy is and will have the most effect on the interaction between the amp and speakers. If it seems more like 4 Ohms than 8, use the 4 Ohm tap...

I guess one has to be verse in understanding the role of current (amps), power (watts) and volts in relation to a 4 and 8 ohm tap.

When using a 4 ohm tap the level of resistance is reduced, which means that less current (ie amps) flows, however, a higher voltage level is needed in order to keep the power ( ie watts) level the same as what comes through an 8 ohm tap. An important concept is that the end resulting power (watts) passing through either the 4 or 8 ohm tap is the same (ie total watts remains the same).

What this means to me is 4 ohm taps are designed to deal with a higher voltage level being delivered to a speaker.

And then the big question is, when certain speakers are designed to handle a higher voltage level, this makes the speakers more efficient.

So if we’re talking about more efficient speakers, it means they are designed to handle higher voltage levels. with power levels remaining the same as less efficient speakers.

And with a higher voltage levels, how does this impact delivery of varying frequencies to a speaker driver?

hoping that I got this right. It’s a challenging concept for a mere CPA

@atmasphere

What you suggest makes sense. However,  I do recall that the late Roger Modjeski (RAM Labs Music Reference Audio) advocated “light loading” of amplifiers. He recommended using a tube amplifier’s 4 ohm tap to drive an 8 ohm speaker load. I’m not sure what the rationale was for this approach.

Charles

The concept of light loading of tubes and transformers would  seemed very important.  Can someone add some clarity to this concept, and how it relates to the overall delivery of information to a speaker driver and/or impact on the amplifiers Health relating to tube operation. Thanks

@charles1dad regarding light loading, which Roger felt benefited all of his amps. the following is taken directly from the Music Reference RM-10 manual:

"The amplifier is flat within 0.1dB and has low distortion of 0.3% when played below clipping on average level material. At the recommended bias current of 30mA/pair, the idling dissipation is nine watts or 75% of the tubes’ rating. I estimate tube life to be 5,000 to 10,000 hours. Although higher idling currents will reduce distortion, it can also be reduced by light loading. Basically, light loading reduces the output current demand on the output tubes, allowing them to be more linear. It also reduces noise, raises damping factor, reduces distortion by 78% and allows for 80% more peak current when needed. The only loss is about 20% of the power rating or 1dB."

In addition to some neat design features in the circuit, the way the output transformers were wound also contributed to the benefits of light loading as discussed in the manual. The only negative was a 7 watt loss of power, which is inconsequential if you also consider light loading doubled the class A range of the amp to a little over 20 watts.