Autoformer vs Speaker impedance Curve
johnto For an amp that doesn’t drive the Maggie’s to well because it can’t handle a 3-4ohm load, an Autoformer would work, because it’s one of the only speakers that presents a very benign 3-4 ohm impedance load. That 8ohm peak in the graph is bought back down to around 4ohms because of the "dotted" -phase angle dipping down at the similar frequency. But your right you need big wattage as well for them, as they are also inefficient, these one 83db https://www.stereophile.com/images/archivesart/magfig1.jpg Cheers George |
Atmasphere, regarding your link: 1. In general do reactive speakers match better with voltage paradigm amps? 2. What happens to linearity with a voltage paradigm amp? Does the sp increase where the ohms dip (ie watts increase)—with an increase in distortion—and decrease where the ohms increase? 3. Same question as above, but with power paradigm amp. What happens to sp where ohms dip or increase...is it the opposite of voltage paradigm amps? ( (I’m sure the above varies with speaker and amp design, negative feed back and such, but just in the most general of terms) Mac led the way in the late 1950s towards developing the idea that speakers be ’voltage driven’. Does this mean Macs are voltage paradigm amps? Doesn’t this conflict with the way autoformers function? Seems they would be power paradigm, especially given their multiple output taps. A little over my head here, but learning, so please forgive my ignorance! Even though I addressed this to atmasphere, I welcome and want all input! Rob |
Does this mean Macs are voltage paradigm amps? Yes. Which paradigm an amp fits into is determined by its output impedance. (And btw, that categorization is along a continuum, rather than being a purely black and white distinction. Especially in the case of tube amps, which vary widely in their output impedances). If the output impedance of an amp is a tiny fraction of an ohm, or is at least a very small fraction of the impedance of the speaker at any frequency, it will behave as a voltage source. Which means that for a given input signal to the amp, it will output a voltage which essentially has no variation as a function of the impedance of the speaker at whatever frequencies may be present, as long as the amp is operated within the limits of its maximum voltage, current, power, and thermal capabilities. And in the case of McIntosh solid state amps having autoformers, the combination of their solid state output stages, the autoformers, and what I’m pretty certain is the liberal application of feedback is most of their designs, results in a very low output impedance. The MC302 I referred to earlier being an example. Tube amps, on the other hand, will just about invariably have relatively high output impedances, usually somewhere between a large fraction of an ohm and several ohms, as I mentioned earlier. That will bring just about all tube amps much closer to the power paradigm end of the spectrum. Regarding your questions 2 and 3, it follows from Ohm’s Law (I = E/R) and the definition of power (P = E x I, for a resistive load), where I is current, E is voltage, and R is resistance, that if a constant voltage is maintained into a varying load (as it would be by a voltage paradigm amp) more current and hence more power will be delivered into low impedances than into high impedances (assuming at least that all of the impedances are mostly resistive). It also follows that a power paradigm amp will come much closer than a voltage paradigm amp to maintaining constant power into those varying impedances, for a given input voltage to the amp, rather than maintaining constant voltage. It may help to clarify some of this, btw, if you take a look at the Wikipedia writeup on voltage dividers that I referred to earlier. In the first figure on that page, consider Z1 to represent the output impedance of the amp, and Z2 to represent the impedance of the speaker. And consider Vin to be the voltage the amp is "trying" to put out, meaning the voltage it would supply without a speaker or other load being connected, and Vout to be the voltage seen by the speaker. None of this necessarily means, however, that frequency response flatness (which you appeared to be referring to when you mentioned "linearity") will be compromised if additional power is or is not supplied into impedance dips. Depending on the design of the speaker its efficiency (SPL out vs. watts in) may or may not vary in a manner that is consistent with its impedance curve. As Ralph (Atmasphere) has said in a number of past threads, a tonal imbalance is especially likely to result when the paradigms to which the speaker and the amp conform are not the same. Regards, -- Al |
