Understanding the Speaker Impedance Specification

[gene]

Audio specifications run the gamut from merely “nice to know” to “genuinely useful.” A speaker’s impedance rating should be one of those genuinely useful specs, but you can’t always trust them. What does it really mean when a company rates their speaker as 8 ohms, or 4 ohms?

Read on to get an "insider's look" at speaker spec ratings and the marketing that you won't read anywhere else in: Understanding the Speaker Impedance Specification

 

[Soldierblue211]

Funny...i just picked up 2 subwoofers yesterday and they only had the 4ohm version in stock not the 2ohm. To compensate i bought an amp that was 2400 watts instead of 1600 watts. Those rating are only for a 1ohm load though. Would i really HEAR a difference if i were to go back and get the 2ohm speakers? Never done a side by side comparison of similar speakers with different ohm specs and just assumed by getting more power i theoretically wouldn't notice a difference... thoughts?

 

[Gunny]

Great article. It's been a long time since I studied electronics and it's very interesting to see basic principles like Ohms law applied to loudspeaker specs.

 

[Norm Lazure]

I did not read the article but Impedance is like AC resistance and can change with frequency. As the impedance goes down your amp has to supply more current. Amplifyers have to work twice as hard to keep up. So when you buy an amp the spec will say 100 watts into 8 ohm load and 200 watts into a 4 ohm load. I dont remember all the theory but that's the general jest of it. (I think)

 

[Bizarro_Stormy]

I did not read the article but...

You should read the article...

 

[Bucknekked]

I did not read the article but Impedance is like AC resistance and can change with frequency. As the impedance goes down your amp has to supply more current. Amplifyers have to work twice as hard to keep up. So when you buy an amp the spec will say 100 watts into 8 ohm load and 200 watts into a 4 ohm load. I dont remember all the theory but that's the general jest of it. (I think)

Norm,
Bizzaro Stormy already said it, but yeah.
One of my favorite pet peeves in todays world is we each have a world of information at our fingertips. Literally, we have the ability to study any topic we have interest in at a depth nobody in history has had.
And yet, most peoples version of "I did some research" is to read a couple of titles of articles, not the articles themselves, but they read the titles and call it research. You just confessed.

I skim titles too. I do it all the time to find things I'm interested in. I was tempted to do the same with the Impedance article because its not an area of interest I need to learn about (I already made my 2017 purchases in both amps and speakers). But, when I popped it open it was clear somebody went to a lot of effort to put together a nice article. So, I broke down and read it. It was pretty good.

Your 4 sentence overview isn't wrong. Its just incomplete. The author fills in the blanks on how not to blow your amps with poor speaker choices and vice versa. My world isn't changed because I read it. But I got 15 minutes of enjoyment and I may have tucked away a nugget or two for the future.

Peace. Read the stuff that makes you happy. I'm just a grumpy old many somedays.

 

[shadyJ]

I finally got around to reading this one, very good article, Steve, thanks for writing it. A nice explanation about why things did get as messy as they did in the world of low-priced AVRs. I think its worth mentioning that buyers can probably get away with using 4 ohm speakers on receivers rated for 8 ohms if they do not intend to crank their system loud. It also helps if they are using a subwoofer.

In my opinion, the industry should shift away from passive speakers to active speakers, and AVRs should lose the amplifier section. It might raise prices a bit, but that should be able to make the overall system more reliable and also improve sound quality. It would also improve system efficiency, so less wattage needed per dB.

 

[Dennis Murphy]

I finally got around to reading this one, very good article, Steve, thanks for writing it. A nice explanation about why things did get as messy as they did in the world of low-priced AVRs. I think its worth mentioning that buyers can probably get away with using 4 ohm speakers on receivers rated for 8 ohms if they do not intend to crank their system loud. It also helps if they are using a subwoofer.

In my opinion, the industry should shift away from passive speakers to active speakers, and AVRs should lose the amplifier section. It might raise prices a bit, but that should be able to make the overall system more reliable and also improve sound quality. It would also improve system efficiency, so less wattage needed per dB.

As a designer of passive loudspeakers, I expected to be out of business about 5 years ago. Active is definitely a superior design approach and allows for much finer frequency response adjustment and a number of other advantages. But it's not a matter of the industry just deciding to go active. The barrier has been consumer reluctance to embrace active designs for general music applications. If I offered an active design, I'm pretty sure it would flop unless it was a mini intended for desktop computer use. Anyhow, thanks for the article Steve. I was enforcing the FTC's amplifier rating rule when it first came out and remember the fallout from the 1/3 power preconditioning requirement (which I didn't write, BTW). I did manage to get an advisory published that got companies around the problem, and eventually the requirement was reduced to 1/8th power.

 

[Bucknekked]

I finally got around to reading this one, very good article, Steve, thanks for writing it. A nice explanation about why things did get as messy as they did in the world of low-priced AVRs. I think its worth mentioning that buyers can probably get away with using 4 ohm speakers on receivers rated for 8 ohms if they do not intend to crank their system loud. It also helps if they are using a subwoofer.

In my opinion, the industry should shift away from passive speakers to active speakers, and AVRs should lose the amplifier section. It might raise prices a bit, but that should be able to make the overall system more reliable and also improve sound quality. It would also improve system efficiency, so less wattage needed per dB.

Really? Powered speakers as the norm?
I didnt see that coming as an idea.
I would love to see some details on pros and cons.
Looks like a good thread discussion

 

[Bucknekked]

As a designer of passive loudspeakers, I expected to be out of business about 5 years ago. Active is definitely a superior design approach and allows for much finer frequency response adjustment and a number of other advantages. But it's not a matter of the industry just deciding to go active. The barrier has been consumer reluctance to embrace active designs for general music applications. If I offered an active design, I'm pretty sure it would flop unless it was a mini intended for desktop computer use. Anyhow, thanks for the article Steve. I was enforcing the FTC's amplifier rating rule when it first came out and remember the fallout from the 1/3 power preconditioning requirement (which I didn't write, BTW). I did manage to get an advisory published that got companies around the problem, and eventually the requirement was reduced to 1/8th power.

Dennis
I can say i have never taken powered speakers seriously. I had looked at the powered version of the KEF LS50. I didnt take it seriously because nobody gives these any airtime in high end audio discussions. They are , to me, as you said: small desktop ideas.

I am surprised as can be at the idea. You are probably correct: if you launched a new powered speaker on your website it would probably go nowhere. Not because it may not be good but because the buying public isnt conditioned to look for one.

I guess i need to open my mind and continue my education. I was ready for Philharminic 3's as my next goal. Maybe i need to wait for your next powered creation

 

[lovinthehd]

I think powered speakers may have an opportunity now with people looking for simple solutions and having used such with computer/desk setups already. For a full blown surround setup all those outlets and cords.....seems like could be a bigger pain in quite a few rooms I've had....

 

[killdozzer]

I think powered speakers may have an opportunity now with people looking for simple solutions and having used such with computer/desk setups already. For a full blown surround setup all those outlets and cords.....seems like could be a bigger pain in quite a few rooms I've had....

I wanted to write this! @Dennis Murphy perhaps you should give it a try if you're up for some marketing targeted at PC users who never got into conventional stereo/surround in the first place. The ones who expect to just buy the speakers and be done with it, connecting the PC directly to speakers much the same way many of PC speakers already do. All those yesterday's kids who listened to Logitech 2.1 or 5.1 and are perhaps thinking of getting a big and beautiful sound without the hustle of learning all there is about amps/avr's. I believe active LS50's aim at these.

@gene as far as the article goes, it's a great example of combining a historical overview with useful info. In the end you read it as newspapers article. It is interesting even if you know very little about Ohm's Law.

The linked articles, on the other hand, go a little bit over my head. I tried, but couldn't follow everything.

That's why I wanted to ask here, if anyone's up for some number crunching to give me a real world spec/number for impedance dips. If you have an 8Ohm speaker that goes down to, let's say 3.2Ohm at certain freqs, what does this mean for your amp? How much more power would you get if you were buying an amp for speakers with such dips?

 

[Steve81]

I think powered speakers may have an opportunity now with people looking for simple solutions and having used such with computer/desk setups already. For a full blown surround setup all those outlets and cords.....seems like could be a bigger pain in quite a few rooms I've had....

The answer to that problem seems pretty simple to me: combine a digital audio cable and power cable. It's already feasible with video via HDBaseT, which can send a UHD feed plus 100W of power to a TV over Cat5e:

https://en.wikipedia.org/wiki/HDBaseT

HDBaseT is transmitted over category 5e cables or above up to 100 m (328 ft) long, with 8P8C modular connectors of the type commonly used for Ethernet local area network connections.[9][10]

HDBaseT transmits uncompressed ultra-high-definition video (up to 4K), audio, power over HDBaseT (PoH - up to 100W), Ethernet, USB, and a series of controls such as RS232 and IR.

Doesn't seem like it would be a massive technical leap to apply that idea to active loudspeakers, but I'm not sure anyone cares enough to pursue it.

 

[rojo]

Norm,
Bizzaro Stormy already said it, but yeah.
One of my favorite pet peeves in todays world is we each have a world of information at our fingertips. Literally, we have the ability to study any topic we have interest in at a depth nobody in history has had.
And yet, most peoples version of "I did some research" is to read a couple of titles of articles, not the articles themselves, but they read the titles and call it research. You just confessed.

I skim titles too. I do it all the time to find things I'm interested in. I was tempted to do the same with the Impedance article because its not an area of interest I need to learn about (I already made my 2017 purchases in both amps and speakers). But, when I popped it open it was clear somebody went to a lot of effort to put together a nice article. So, I broke down and read it. It was pretty good.

Your 4 sentence overview isn't wrong. Its just incomplete. The author fills in the blanks on how not to blow your amps with poor speaker choices and vice versa. My world isn't changed because I read it. But I got 15 minutes of enjoyment and I may have tucked away a nugget or two for the future.

Peace. Read the stuff that makes you happy. I'm just a grumpy old many somedays.

 

[Bucknekked]

rojo
I didn't know whether to laugh or cry, so I laughed, at your post.
Its so true.
I have a personal policy against cat videos just because of jokes like this.
I won't watch a cat video no matter how "cute". Its against my policy.
That's what happens when you get old : you develop policies.

 

[Pyrrho]

First of all, this is a GREAT article. People need to know that many speaker companies are lying about the impedance of their speakers, and that this can destroy people's amplifiers when they trust those ratings. Which means it is a serious problem.

I think the only solution is more regulation. There should be a law that requires speaker manufacturers to use the IEC method of rating speaker impedance (from the article):

(“The IEC method of specifying nominal loudspeaker impedance is set such that minimum impedance must not fall below 80% of nominal, so for an 8-ohm speaker this would be 6.4 ohms minimum, and for 4 ohms would be 3.2 ohms.”)​

If speaker manufacturers were required to follow that rule, it would help stop this problem. Right now, the claimed speaker impedance is, from many companies, a made-up number that has no basis in fact.


This is one of the reasons why it is a good idea to read reviews of speakers in which actual measurements are taken (if one can find such a review for the speaker one is considering), and one should look at the impedance measurement.

For those who don't understand the impedance measurement information, you can use the MINIMUM impedance as a guide, allowing for it to be 80% of what the amplifier is rated for. (I.E., if your amplifier is rated for 4 ohms or higher, a speaker with a minimum impedance of 3.2 ohms can be okay; if your amplifier is rated for 8 ohms or higher, a speaker with a minimum impedance of 6.4 ohms can be okay.) Going with a lower impedance speaker can risk damaging one's amplifier, though one might be able to get away with it if one is only listening at low volumes, etc.

If the manufacturer gives the minimum impedance of the speaker, you should use that as your guide to buying the speaker, not the claimed "nominal" impedance, which often is selected as a marketing tool rather than as an actual representation of the electrical properties of the speaker (just as the article above states.)

Again, great article!

 

[Pyrrho]

On the active vs. passive speaker discussion, my problem with active speakers is that, in my experience, the amplifiers that are used in them tend to be more unreliable than separate amplifiers. I have had problems with two sets of powered speaker systems for my computer (for computer speakers, they were not cheap), and two powered subwoofers for a home theater system. In all of those cases, the problems were with the amplifiers, not the actual speakers. (The same applies to everyone I know in real life; NEVER have any of the people I know told me of a powered speaker failure where it was the speaker rather than the amplifier that was the problem.)

I know absolutely that this is not just a fluke in my case, as many manufacturers have a shorter warranty on the amplifiers of their subwoofers than on the woofers themselves, so the companies are essentially telling you with that their amplifiers are less reliable than their speakers. If they were as reliable, they would have the same length of warranty.

This is one of the reasons I am happy with my old SVS CS-Ultra subwoofers, as they are unpowered, and I can use whatever power amp I want with them. Thus far, after about a decade of use, neither the amplifier I selected nor the woofers have had any problems. But if I ever did have an amplifier failure, it would be easy to simply replace the amplifier with something else. And that is not something that is so easy to do with a powered speaker, as the amplifier for powered speakers tends to be tailored for those specific speakers, so not just any amplifier will work properly with it.


But yes, I do understand the advantages of a powered speaker, as tailoring the amplifier to the speaker can enhance efficiency, protect the speaker from over-excursion, etc. But in the real world, the makers of speakers with built-in amplifiers all too often put in crappy amplifiers that do not last as well as ordinary amplifiers. And so in the real world, I wish to avoid them.

If it were not for the fact that my pair of SVS CS-Ultras are good enough, I would be unhappy that SVS no longer makes unpowered subwoofers. If I ever need to replace them, then I will be unhappy that SVS no longer makes such things. I might then be forced to make my own subwoofers, unless I can persuade SVS to do a special order for me.

 

[AcuDefTechGuy]

...In my opinion, the industry should shift away from passive speakers to active speakers...

Wouldn't it be easier, faster, and more economical to just shift towards more efficient speakers that can be powered by any AVR?

 

[AcuDefTechGuy]

On the active vs. passive speaker discussion, my problem with active speakers is that, in my experience, the amplifiers that are used in them tend to be more unreliable than separate amplifiers. I have had problems with two sets of powered speaker systems for my computer (for computer speakers, they were not cheap), and two powered subwoofers for a home theater system. In all of those cases, the problems were with the amplifiers, not the actual speakers. (The same applies to everyone I know in real life; NEVER have any of the people I know told me of a powered speaker failure where it was the speaker rather than the amplifier that was the problem.)

I know absolutely that this is not just a fluke in my case, as many manufacturers have a shorter warranty on the amplifiers of their subwoofers than on the woofers themselves, so the companies are essentially telling you with that their amplifiers are less reliable than their speakers. If they were as reliable, they would have the same length of warranty.

This is one of the reasons I am happy with my old SVS CS-Ultra subwoofers, as they are unpowered, and I can use whatever power amp I want with them. Thus far, after about a decade of use, neither the amplifier I selected nor the woofers have had any problems. But if I ever did have an amplifier failure, it would be easy to simply replace the amplifier with something else. And that is not something that is so easy to do with a powered speaker, as the amplifier for powered speakers tends to be tailored for those specific speakers, so not just any amplifier will work properly with it.


But yes, I do understand the advantages of a powered speaker, as tailoring the amplifier to the speaker can enhance efficiency, protect the speaker from over-excursion, etc. But in the real world, the makers of speakers with built-in amplifiers all too often put in crappy amplifiers that do not last as well as ordinary amplifiers. And so in the real world, I wish to avoid them.

If it were not for the fact that my pair of SVS CS-Ultras are good enough, I would be unhappy that SVS no longer makes unpowered subwoofers. If I ever need to replace them, then I will be unhappy that SVS no longer makes such things. I might then be forced to make my own subwoofers, unless I can persuade SVS to do a special order for me.

Oh yeah, I'm glad to see another person who is in favor of externally-powered speakers and subwoofers.

That's how I've been thinking since about 10 years ago.

For me, I unequivocally do not want to put any amps inside my speakers and subwoofers.

BTW, RBH and Funk are 2 companies I can think of who do make unpowered subwoofers.

I think Monitor Audio and Velodyne also make unpowered subwoofers for in-ceiling installations, but you could use them however you want.

 

[3db]

Thank you for mentioning phase angle. Of all the parameters, I place a higher importance on phase angle and the frequency at which the phase angle is at its maximum than the absolute magnitude of the impedance as it really tells us the difficulty of the load being driven. To me the nominal impedance spec is a waste of time.