Monitor Audio PL100-3G 'nominal impedance' vs 'minimum impedance'

[epping4est]

Here [link], at the bottom of the web page, are Monitor Audio's specifications for the PL100-3G loudspeaker. The 'nominal impedance' [aka average impedance] is 4 ohms, but the 'minimum impedance' is also 4 ohms. AFAIK a speaker's average and minimum impedances can be equal only when the speaker is a resistor -- i.e. one or both specifications are incorrect.

I have read the comment that manufacturers' specified 'nominal impedances' are generally meaningless, but I really need the truth about these speakers ...

I am considering whether to drive a pair of MA PL100-3Gs with a pair of bridged NAD M23 amplifiers; however, [the M23's User Manual says that] a bridged NAD M23 amplifier is rated exclusively for 8 ohm loads [with e.g. 4 ohm loads expressly discouraged]:

How can I be certain that a MA PL100-3G would [not] present a problem for a bridged NAD M23? e.g. If I can establish that the PL100-3G typically operates well above 4 ohms, then perhaps a bridged M23 would be fine with that.

 

[Zek]

The only thing that needs to be seen is the impedance diagram across the entire frequency range, and then some conclusion can be drawn.

 

[epping4est]

@Zek - Yes, agreed, but if I ignore Monitor Audio's stated 'nominal impedance', can I at least accept their statement that the PL100-3G's 'minimum impedance' is 4 ohms [@180Hz]?

 

[dedobot]

Why not bi-amp them:

Platinum Series 3G Support | Monitor Audio

www.monitoraudio.com

MA gives same 4-4ohms specs for the whole serie PLxxx3G , strange.

 

[staticV3]

How can I be certain that a MA PL100-3G would [not] present a problem for a bridged NAD M23?

Only by trying that very combination. Everything else are estimates.

 

[epping4est]

@dedobot - Yep, bi-amping is Plan-B.

@staticV3 - Yes, I will likely have to try it -- and hope that nothing breaks.

 

[dedobot]

Only by trying that very combination. Everything else are estimates.

Now I see the NAD M23 is 2x380w@4ohms. Single M23 is plenty of enough to drive the OPs speakers.

 

[DVDdoug]

You'd be taking a risk with an amplifier rated for 8-Ohms minimum.

AFAIK a speaker's average and minimum impedances can be equal only when the speaker is a resistor -- i.e. one or both specifications are incorrect.

Nominal (in this context) doesn't have a mathematical definition like average or median.

I'd take it to mean "mostly 4-Ohms" or "about 4-Ohms across most of the frequency range."


From the Merriam Webster website:
Nominal -
b
: of, being, or relating to a designated or theoretical size that may vary from the actual : APPROXIMITE The pipe's nominal size.

 

[epping4est]

@dedobot - I [will soon] have two M23s and I wish to employ them both to drive the PL100-3Gs. Plan-A is to use each M23 in bridged mode; Plan-B is to use them in horizontal bi-amp mode; Plan-C is to use them in vertical bi-amp mode. In the end, I'll probably try all of A, B, and C, but I'm slightly worried that Plan-A could damage the amps, damage the speakers, or damage both.

At present the PL100-3Gs are driven by a Moon W5 rated at 380W into 4 ohms, so I know that even a single M23 is "enough".

 

[epping4est]

I found an impedance curve for the original MA PL100-1Gs on a 2008 SoundStage! Network web page:

Note that like the PL100-3G, the PL100-1G's minimum impedance appears to be at [or about] 180Hz. The PL100-1G's average impedance appears to be closer to 10 ohms rather than its specified 4 ohms. If the PL100-3Gs have a similar impedance curve -- a reasonable assumption, I think -- then bridged NAD M23s should have no trouble driving them.

 

[Vladimir Filevski]

Here [link], at the bottom of the web page, are Monitor Audio's specifications for the PL100-3G loudspeaker. The 'nominal impedance' [aka average impedance] is 4 ohms, but the 'minimum impedance' is also 4 ohms. AFAIK a speaker's average and minimum impedances can be equal only when the speaker is a resistor -- i.e. one or both specifications are incorrect.
I have read the comment that manufacturers' specified 'nominal impedances' are generally meaningless, but I really need the truth about these speakers ...

The standard defines the minimum impedance to be at least 80% of the nominal impedance. So, nominal 4 ohm impedance loudspeakers have 3.2 ohm minimum impedance or greater. Your PL100 has 4-ohm minimum impedance, which is by definition 4-ohm nominal impedance loudspeaker.
Next nominal value is 6-ohm, with minimum impedance of 4.8 ohms - which obviously is not the case for the PL100.

I am considering whether to drive a pair of MA PL100-3Gs with a pair of bridged NAD M23 amplifiers;

No! You are looking for trouble. No need for bridging amps. Maximum recommended power for PL100 is 300 W and maximum output power of non-bridged stereo amp M23 is more than 400 W.

 

[dedobot]

No! You are looking for trouble. No need for bridging amps. Maximum recommended power for PL100 is 300 W and maximum output power of non-bridged stereo amp M23 is more than 400 W.

Our friend epping4est is possessed by the spirit of experimentation, our task is to prevent him from burning out his nice amplifier or his nice speakers.

@epping4est don't play with fire - use single amp or bi-amping.

 

[epping4est]

Just as proper application of a Ferrari's throttle ensures that the vehicle doesn't exceed the speed limit, proper application of a pre-amp's volume control ensures that the amp doesn't exceed the speakers' limits. Within those limits, the extra power can deliver performance benefits. I'm sure the Ferrari analogy eventually fails somewhere, but you get the idea. Minimally, I can expect that my Benchmark HPA4 can perform pass-through of the DAC's signal -- i.e. without [pre-]amplification -- to the M23s for clean, potentially high SPLs.

 

[Beave]

Just as proper application of a Ferrari's throttle ensures that the vehicle doesn't exceed the speed limit, proper application of a pre-amp's volume control ensures that the amp doesn't exceed the speakers' limits. Within those limits, the extra power can deliver performance benefits. I'm sure the Ferrari analogy eventually fails somewhere, but you get the idea. Minimally, I can expect that my Benchmark HPA4 can perform pass-through of the DAC's signal -- i.e. without [pre-]amplification -- to the M23s for clean, potentially high SPLs.

How?

 

[epping4est]

Musical peaks can consume 1000x the average power. [e.g. See: Average music power ...]. A speaker can handle clean musical peaks far in excess of the average applied power; such peaks can be delivered by a powerful amplifier. Conversely, a speaker would have difficulty with a clipped signal coming from a less powerful amplifier, possibly even sustaining damage.

 

[Vladimir Filevski]

Musical peaks can consume 1000x the average power. [e.g. See: Average music power ...].

No. Quote from that link:

up to 20 dB (100:1 in power) for some music recordings, and up to 30 dB (1000:1 in power) for movies (explosions, gun shots, and so forth).

Allowing 26 dB = 400 times (unheard of - even in the most dynamical recordings available!) over the average power of 1 W make 108 dB peak over the nominal 85dB/2.83V sensitivity (82dB/1W) of PL100. Simultaneously, that is 400x greater than 1W - exactly equal to 400W/4ohm of the maximum output power of stereo (non-bridged) M23.
From measurement here on audiosciencereview you can see that vast majority of the loudspeakers heavily distorts at about 96 dB, so there is no point maltreating the poor loudspeaker to 108 dB output. Hence, 400 W/4ohm of non-bridged M23 power is more than enough for music peaks.

 

[epping4est]

Every 10dB of a musical peak requires a 10x increase in power; a 30dB peak requires 10dB + 10dB + 10dB => 10 x 10 x 10 = 1000x power increase. If listening at an average power of 0.5W -- a modest listening level for most speakers -- then such a peak would require 500W. If the amplifier cannot deliver 500W, bad things happen.

Nothing can be done for a loudspeaker that itself distorts a peak waveform delivered by the amplifier; however, it's important that the amplifier's delivered peak waveform be clean. e.g. A loudspeaker can survive [and perhaps even follow] a clean peak, but may very well be fried by a clipped peak.

 

[Vladimir Filevski]

Every 10dB of a musical peak requires a 10x increase in power; a 30dB peak requires 10dB + 10dB + 10dB => 10 x 10 x 10 = 1000x power increase.

There are no musical recordings with 30 dB musical peaks! Actually, there are only 2 known musical recordings in the existence with over 26 dB peaks.
30 dB peaks are happening only in movie special effects (explosions):

up to 20 dB (100:1 in power) for some music recordings, and up to 30 dB (1000:1 in power) for movies (explosions, gun shots, and so forth).

Musical recording with 20 dB peaks over average are few and far between. Very good (excellent!) classical music recordingс have 15 dB peaks, pop and rock usually less.

If listening at an average power of 0.5W

Average loud SPL at the listening position is about 80-86 dB. For the calculation let choose 83 dB value. If listener is at 3m distance from the loudspeaker, than loudspeaker must deliver SPL=92.5 dB/1m (83+9.5). Two loudspeakers (as in stereo) in the room can deliver more, but let keep calculation simple. Sensitivity of PL100 is 85 dB/2.83/1m (82dB/1W/1m), so to achieve average SPL=92.5dB/3m it needs 11.2 W of amplifier power.
Maximum 400 W power from M23 allows clean 15.5 dB peaks from the average 11.2 W.

If the amplifier cannot deliver 500W, bad things happen...

...and if loudspeaker cannot survive clean 500 W (PL100 certainly can not!), than even worse things happen.

 

[epping4est]

While the M23 is rated at 400W into 4 ohms, the PL100-3G is most definitely not a 4-ohm loudspeaker. The above impedance curve shows that the PL100-1G -- specified as a 4-ohm loudspeaker -- has an average impedance of 10 ohms. I'm satisfied that the PL100-3G has a similar impedance curve.

Instead of the unbridged M23's 400W into 4 ohms, and instead of the unbridged M23's 200W into 8 ohms, one should consider the unbridged M23's power into 10 ohms -- extrapolated to 175W. I will be trying the M23 in bridged mode.

 

[Vladimir Filevski]

The above impedance curve shows that the PL100-1G -- specified as a 4-ohm loudspeaker -- has an average impedance of 10 ohms.

Wrong. It does not work that way.
What about real 4-ohm impedance at various frequencies?

I will be trying the M23 in bridged mode.

I hope M23 will survive that - it is a very robust, well designed amplifier. Hope PL100 will survive too.
I tried to protect you from disaster, but...
I give up. Wish you all the best.

Edit:
Addendum
Average, nominal and minimum loudspeaker impedance may confuse some audiophiles. So let calculate with the respect to the voltage only:
PL100 has 85dB/2.83V/1m sensitivity.
M23 has maximum 400 W output at 4 ohm load. That is at least 40 V clean output voltage irrespective of the load value - equal or higher than 4 ohms (including 10 ohms).
PL100 with 40 V clean input (should) have 106.5 dB/1m output. But, PL100 will distort heavily at that level.