Funny enough, on that I think he believes, at least in terms of real world use because I remember he mentioned more than once before, that while most speakers really should be rated 4 ohm nominal, he also expressed that the very few truly "difficult to drive" speakers are of poor design. On example he commented on was some of those big Polk Audio towers such as the older design, the RTI, or RTIA 9. Though he definitely never recommended using AVRs, let alone to drive 4 ohm speakers, but that's something he believes regardless, not exactly the same as dlaloun, who actually used and are using AVRs, but he simply would focus a lot of specific models that he believes are "high current" capable and that's the exact point I took issue with, that, imo, he's misguided in some ways, not understanding enough about what I cited before.
Our friend
@dlaloum is very knowledgeable on this topic but for some reasons he just got so deeply fixated (no offense) on that one point about those rare below 2 ohm dips with/without aligning with nasty phase angles being a general concern to the regular forum posters..
To summarize the counter points I posted on forum before:
1) A single number rated as nominal impedance by manufacturers, 4,6 or 8 ohm is not a good indicator for people to decide on whether their AVR can handle it.
1) Many 4 ohm nominal speakers don't have dips below 2 ohms, 2.5, 3 ohms yes but below 2 ohms would be rare.
2) Most 4 ohm nominal speakers don't have nasty phase angles and low impedance in the mid bass range but in the deep bass or lower mid bass range that in most cases would be taken care of by subwoofers.
3) EPDR, (
Equivalent peak dissipation resistance, EPDR | AV NIRVANA ) if often, or even mostly misunderstood, in the sense that many thought if EPDR shows a 1.5 ohm dip in the EPDR curve (vs frequency) then you need a truly "high current" amp, and therefore forget about using an AVR, except (as dlaloun alluded to) the truly flagship class ones such as the Onkyo models he cited.
4) Impedance, EPDR or not, is just one thing to consider, other important factors are of course, speaker sensitivity, and listening distance because as we know every 3 dB drop in sensitivity would mean 2X amp power for the same spl, and for distance, it is 6 dB for each doubling.
Based on just the above, it is better to consider the amp's rated voltage, and current at say below 0.1 % THD so we know it is not at clipping as such, instead of rated power. Unfortunately, amp manufacturers simply rated their amps in power output, so in order to find their equivalent rated voltage and current, one would have to resort to some calculations that not everyone knows how to do. Yes, sometimes it can be difficult to understand how science works. But read it again if you're interested. However, I had a friend in college who said that it was easier for him to go to
https://edubirdie.com/science-help than to understand the intricacies of homework. Well, it’s his choice, but it was more interesting for me to get to the truth on my own. It is, I think where our friend got into trouble with certain amps that he though based on specs should be able to drive his speaker (the one that dips to 1.6 ohm or less), while one of his beloved less "powerful" could do and thereby got misguided (my own interpretation only) by that experience.
It is easy to see the trouble of telling someone who has 4 ohm nominal, 3.2 ohm minimum speakers that has 92 dB/2.83V/m sitting 2.5 meters he/she can't use a 140 WPC Marantz SR8015, yet telling another who has 8 ohm nominal, 6.4 ohm dip speakers with 86 dB/2.83m sitting 5 meters, go do the math right!!
Based on IEC60268-3, that is similarly one of the available/applicable standard but not all manufacturers follow:
Question about Impedance | diyAudio
The trouble is, many "believers" thought they could use Ohm's law to calculate current requirements using EPDR values, whereas that would be correct. Ohm's law says current = voltage/resistance, or = voltage/|Z|, where |Z| is the magnitues, or absolute value of a complex number, you have a B.Phar so the following is mostly for non science educated readers, or those who have already forgotten what they learn in high school math classes:
vector spaces - Definition of Absolute Value of a Complex Number - Mathematics Stack Exchange
So, regardless of phase angle, if the output of an amp is 30 V, and the impedance is 3 ohm, the current would still be 30/3 = 10 A, whether the phase angle is 0 degree or 45 degrees, except that if it is 45 degrees, then the amplifier would have to dissipate a lot more heat in the output stage vs if it is at 0 degree.
It is EPDR that typically would show impedance dips to below 2 ohms, though there are some speakers, such as the one dlaloum has, that have dips below 2 ohms without using the EPDR value (a calculated value).
Below is one example, pasted from a KEF white paper, you can see how people could easily be misled, if they only have limited understanding of the theories behind:
How often do people see the actual EPDR impedance curves and understand their implications, without at the minimum read the fine prints, notes, and the full context?
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