Here's an example:
One of the 3 speakers listed below has the so called nominal impedance of 4 ohms, but which one is more "difficult" to drive?
| MA speakers | impedance | Sensitivity | Handling | Recommended | Max SPL |
| Radius 90 | 8 | 83 | 75 | 30-100 | 102 |
| Gold on wall 6G | 4 | 88 | 150 | 130-300 | 115 |
| | | | | |
| KEF | | | | | |
| LS50 | 8 | 85 | | 40-100 | 106 |
In this case, I would say the 8 ohm rated Monitor Audio Radius 90 is likely more "difficult" to drive if you want to get say 102 dB peak at 1 meter with 1 speaker.
A Numerical example based on the specs of the speakers above:
Radius 90:
With 1 W, at 1 meter, peak SPL = 86 dB
Gold on wall 6G, at 1 meter, speak SPL = 88 dB Note: For this calculation using online calculators, I have to enter 85 dB sensitivity instead of the 88 dB specified because 2.83V, 4 ohms >2 W, not 1 W.
Above is based on over simplification
@John Lohmann don't want it to get too technical, so in practice the real conclusions may be a little, or quite different.
In practice, we also have to consider the following:
- Impedance vs frequency curve, not just a simple "nominal impedance" number.
- Actually bench test verified sensitivity, not just the specified one, as manufacturers often inflated that number.
- Phase angle vs frequency, large phase angles means more heat dissipation in the output stage of class AB amplifiers so on all else being equal basis, speakers that have poorer phase angle vs frequency are harder to drive (not because of higher current demand).
That Denon "engineer" is right in the narrow sense that lower impedance (think resistance, literally, to avoid getting technical) implies less resistive to the driving force, in this case, the applied voltage.
There is no easy to understand analogy that I can think of, but may be consider it is easier to push a 50 lb weight than a 200 lb weight on a wood floor, the 50 lb weight should be easy to push if you just want to move it, but if you have to move it at very high speed, then it could be more difficult to move it than to move the much heavier weight at very low speed.
So, hard to drive, as the Denon "engineer" stated, might in fact be a common "misconception", but he could have worded it to something less confusing, such as "a matter of perspective", making it sound like an open ended issue...
Now, a little technical:
Bottom line, it has a lot to do with the "power", "watts" being used, or misused from day one, when it would have been better to reference to voltage and current instead off power. Yes it is simpler to just use "power", but the fact is, one needs to understand that the so called "high current" amp for low impedance load will lead to confusion, as an low impedance load may also need "high voltage" depending on a few factors, and how do we define "high current amp"? Many have stated that high current amp means amp that could "double down to 4 and then 4 ohms", that's a poor and impractical definition, based on "common misconceptions"? Who know?
I am not trying to defend the Denon gentleman, in fact the way he expressed himself could confuse a lot of Denon AVR owners. It is also apparent that most 4 ohm nominal rated speakers tend to require power amplifiers that have robust power supplies that are neither voltage nor current limited, again on all else being equal basis. Take a look of some popular British designed speakers such as B&W, KEF, Monitor Audio, their high end products tend to have nominal 4 ohms impedance while their lower end products are 8 ohm nominal, while their sensitivity specs don't differ that much, mostly between mid 80's to 90 dB/2.83V. So in such cases, it is almost true to say that their 4 ohm speakers are harder to drive.
It is just that it cannot be generalized, because ultimately, sensitivity (among others, such as power handling specs, max. SPL) is a better indicator to drawing a conclusion, than using impedance in isolation.
