Low minimum impedance? Any upsides or only bad?

[SHDK]

Hallo all.

Some time ago I was looking for new speakers. And some guys suggested different speakers due to there low minimum impedance. My understanding was that the low min impedance would put more strain on the amp. And one guy predicted my amp(Marantz M1) wouldn't last long with those speakers

I bought them anyway and haven't regretted them yet.

But reading up on many different speakers made me realize that low minimum impedance isn't really that uncommon. And it makes me wonder, are there any upsides to it since several well established makers choose to design speakers that way. Or is it really just poor speaker design?

Have a nice day

 

[Vincent Kars]

Depends on what you call low minimum impedance.
Most amps can handle 4 Ω speakers. Most of the time the impedance is not linear e.g. a KEF Blade is specified as 4 Ω (min. 3.2 Ω). This works fine.

A Apogee Scintilla has a impedance < 1 Ω. This will turn almost any amplifier into a smoke generator.

 

[SHDK]

Depends on what you call low minimum impedance.
Most amps can handle 4 Ω speakers. Most of the time the impedance is not linear e.g. a KEF Blade is specified as 4 Ω (min. 3.2 Ω). This works fine.

A Apogee Scintilla has a impedance < 1 Ω. This will turn almost any amplifier into a smoke generator.

Well.. in this case it was a pair of Focal Teva no3 with a minimum impedance of 2,9 ohm.

 

[antcollinet]

There is no specific upside for the customer of low minimum impedance.

But in design - everything is always a compromise. I am not a speaker designer so speculating a little here:

It is likely that in trading off all the different characteristics of a speaker - that impedance fluctuations are something you may need to sacrifice in order to achieve other more desirable outcomes. (frequency response flatness, resonance, etc)

 

[sergeauckland]

It also matters at what frequency the minimum impedance occurs. 50-100 Hz is a lot worse than 5kHz, as there's a lot more energy in the music at lower frequencies.

S.

 

[jEDGEc0m]

Hi

(Edits according to Beave's comments - mostly substitute "sensitivity" for efficiency)

I probably shouldn't respond, since I don't know much for sure... but possibly the following aren't untrue (and someone better qualified may respond/correct):

• Generally, an amp will be able to output more power at a lower impedance.
• Generally a lower impedance speaker driver may be more efficient sensitive
  • eg, similar model SB acoustics driver available in "nominal" 4 ohm and 8 ohm variants - the 4 ohm one is 3.5dB more efficient sensitive. knowing that a 3dB volume increase requires double the amp power, this is quite significant.
    • 4 ohm https://sbacoustics.com/product/6in-sb17cac35-4/
    • 8 ohm https://sbacoustics.com/product/6in-sb17cac35-8/

Those two things together would generally mean a speaker can be designed to have better bass (lower extension), or the speaker be more sensitive (louder for a given power voltage input)

...generally. unless i'm wrong.

I wouldn't say it's "poor" speaker design - it's a choice of compromises. In this day and age, amps should be up to the job (or get one that is - fairly trivial these days it seems. reasonably priced options exist). And often perhaps we're not asking as much power as we might think from the amp. If your amp isn't shutting down or sounding like something's obviously performing poorly, it's probably fine, even if it's perhaps working harder and getting warmer - but as you said, "low impedance isn't really that uncommon" - amp should just do its job with a smile (well, the smile should be on you, i guess). (assuming you're not actually pushing the amp to/beyond its limits.) But it does matter at what frequency the low impedance actually is once it's part of a speaker system (i.e. including passive crossover components).

Amir here has measured a Marantz M1 amp- in this case, it doesn't put out more power when tested at 4 ohm vs 8 ohm. Apparently it is a Class D amp, which often do (can) handle low impedance loads without issue, and will increase their power - perhaps the power supply is the limitation in some cases/this case. but it's still ~100W.

Marantz M1 Streaming Amplifier Review

This is a review and detailed measurements of the Marantz M1 stereo streaming amplifier. It is on kind loan from a member and costs US $1000. I used the Heos app to control the M1. It instantly recognized the unit and offered to upgrade it. But boy, did it take forever to do that with multiple...

www.audiosciencereview.com

That crown amplifier power calculator indicates for an 85dB sensitive speaker, 100W would give 99dB at 2m listening distance. But actually it think would be WAY louder in reality - I think that calculator assumes only 1 speaker (add 3dB for a pair), and a speaker being used in open space/no walls. so in a room, add another 3-6dB. so maybe to really get 99dB in a room with a stereo pair, only consumes less than 25W per channel.

Crown Audio - Professional Power Amplifiers | English (US)

www.crownaudio.com

 

[mhardy6647]

All downside. At the limit of zero impedance, one would be asking an amplifier to drive a dead short. The current required becomes outrageous. P =I^2* Z

 

[sergeauckland]

There is no specific upside for the customer of low minimum impedance.

But in design - everything is always a compromise. I am not a speaker designer so speculating a little here:

It is likely that in trading off all the different characteristics of a speaker - that impedance fluctuations are something you may need to sacrifice in order to achieve other more desirable outcomes. (frequency response flatness, resonance, etc)

Also, a lower impedance makes up for lower sensitivity (not efficiency, as I originally wrote) especially if the loudspeaker is incorrectly specified as 8 ohms, as so many (most?) are. The loudspeaker will draw more power from the amplifier, so appear louder in a Dealer's demo facility than a loudspeaker correctly rated.

S.
Edited to remove wrong use of the term efficiency.

 

[Chr1]

I am guessing that presumably designing with low minimum impedance is a necessary compromise in certain speakers designs. Otherwise why would there be any such speakers? If this is the case, I am curious as to what is it that is gained? (Smaller size? Lower reaching bass perhaps?)

Personally I am a fan of easily driven (higher min impedance, high sensitivity) speakers. Seems like the downside is often their large size however.
(Definitely have the feeling that my partner would much prefer me to have the opposite ie. Smaller speakers with bigger amps!)

 

[antcollinet]

Generally, an amp will be able to output more power at a lower impedance.

Only if it is able to deliver the current to output more power.

If the impedance halves then the amp must output double the current to deliver the extra power - if it is unable, then the amp will clip.


This is what it means when people say low impedance dips are more difficult to drive - you need an amp with higher output current capability. Especially when the dip is in the bass region.

 

[wwenze]

Lower impedance over a wide range is more dangerous than lower impedance for just a narrow frequency range.

Lower impedance at the bass frequency is more dangerous than lower impedance in treble

In short, if someone tries to fearmonger you without telling you first to consider the above two statements, don't lose sleep over it.

 

[antcollinet]

Lower impedance over a wide range is more dangerous than lower impedance for just a narrow frequency range.

Lower impedance at the bass frequency is more dangerous than lower impedance in treble

In short, if someone tries to fearmonger you without telling you first to consider the above two statements, don't lose sleep over it.

Yep this too.


Also only when you are pushing an amp beyond about half power. Not so much of an issue at the 1 to 5W power level most people are operating their amps at.

 

[SHDK]

Yep this too.


Also only when you are pushing an amp beyond about half power. Not so much of an issue at the 1 to 5W power level most people are operating their amps at.

I normally never go above 25% a few times to 35 but never above. I guess that also helps.

 

[kharan]

Looks reasonable.

source: https://hometheaterhifi.com/reviews...al-theva-no-3-floor-standing-speakers-review/

 

[mhardy6647]

From my antediluvian perspective -- that region from 100 - 200 Hz with ca. 3 ohm impedance at 120 Hz or so is adding needless stress to the amplifier... but I hold old fashioned notions (e.g., loudspeakers shouldn't torture amplifiers).
100 watts into 3 ohms requires 5.77 amperes of current from the amplifier (P =I^2*Z)

EDIT: Fortunately, the phase curve in that region seems pretty benign.
EDIT^2: Practically speaking - play music you like at a level you like for a couple of hours, and see how warm the amplifier feels. Heat is the enemy.

 

[Jazigo]

Lets not forget about EPDR value!

You can find more about it here: https://www.audiosciencereview.com/...ereophile-has-started-calculating-epdr.15497/

Some of the KEF speakers get a very low EPDR value, around 2 ohms, which most amplifiers A/B and B amplifiers are not happy to drive.

 

[wwenze]

Don't forget that different amplifier types handle EPDR differently.

Basically just look at Amir's measurements of how the maximum power changes vs phase angle.

(Sidenote: It's more VA than watts in that case, if you know what's power factor)

You will see some or many class D amps, their maximum power actually INCREASES at high phase angles.

Extra sidenote: Maximum thermal-limited performance long term is not measured by Amir so keep that in mind too, that will greatly reduce max power at high phase angles and is what EPDR is trying to warn.

 

[Hayabusa]

just make sure your amp does not current limit...

 

[Beave]

Hi

I probably shouldn't respond, since I don't know much for sure... but possibly the following aren't untrue (and someone better qualified may respond/correct):

• Generally, an amp will be able to output more power at a lower impedance.
• Generally a lower impedance speaker driver may be more efficient
  • eg, similar model SB acoustics driver available in "nominal" 4 ohm and 8 ohm variants - the 4 ohm one is 3.5dB more efficient. knowing that a 3dB volume increase requires double the amp power, this is quite significant.
    • 4 ohm https://sbacoustics.com/product/6in-sb17cac35-4/
    • 8 ohm https://sbacoustics.com/product/6in-sb17cac35-8/

Let's be more careful with terms here. The lower impedance speaker may be more sensitive, not necessarily more efficient. Sensitivity is relative to a given voltage input. Efficiency is relative to a given power input. The 4 Ohm version in your example is 3.5dB more sensitive, not 3.5dB more efficient. And to get that 3.5dB higher sensitivity, the 4 Ohm version sucks twice the current from an amp than the 8 Ohm version does. So efficiency is pretty similar between the two. But one requires more current, less voltage, while the other requires more voltage but less current.

Those two things together would generally mean a speaker can be designed to have better bass (lower extension), or the speaker be more sensitive (louder for a given power input)

For a given voltage input, not a given power input.

 

[Beave]

Also, a lower impedance makes up for lower efficiency, especially if the loudspeaker is incorrectly specified as 8 ohms, as so many (most?) are. The loudspeaker will draw more power from the amplifier, so appear louder in a Dealer's demo facility than a loudspeaker correctly rated.

S.

I don't follow here. I think you're also confusing efficiency with sensitivity.