Speaker impedance rating Speakers

Speaker Impedance Rating Explained


That speaker impedance rating on your towers and bookshelf speakers is held up as a mystery—something strange and mystic, yet dangerous. “You’ll blow up your receiver!” says one “expert”. “Bah! You can run anything you want, just set that switch in the back to 4-ohms” says another. The bottom line is that people are confused about speaker impedance. The truth is, it’s not that big of a deal if you follow a few basic rules. We promise that, if you do, you won’t hear anything go “pop!”

But first, what is speaker impedance?

Speaker Impedance Defined

I think the easiest way to define speaker impedance is to say that it is the resistance any speaker gives to the current and voltage being applied to it. In a nutshell, a loudspeaker is a big resister—a really cool one. In fact, speaker impedance can often be referred to as a speaker’s resistance.

The tricky part is to realize that this isn’t a set thing. Speaker impedance changes based on the frequency of the signal fed into it. Since music has a lot of simultaneous frequencies, what you end up with is something called “nominal” impedance. That’s more or less the lowest amount the speaker will dip down to in resistance to the load applied at any given frequency within its operating range.

But specs lie…and so you have most speakers being configured to “more or less” fall into the 4-6 ohm range. While we think that you don’t typically have any issues with that reality, there are some steps you can take to avoid any potential pitfalls.

4-ohm Speakers Should Typically Be Mated with Higher Power Amplifiers

Most bookshelf and tower speakers are rated either 6-ohms or 8-ohms. Any speaker impedance rating that is 4-ohms is typically going to be a high-end, audiophile product that wants an amplifier that can really put out some power. This isn’t a “snobby” thing. The loudspeaker manufacturer likely developed a 4-ohm speaker because he know what kind of amplifier would be required (or typically mated with it) to get the desired sound. With a lower impedance range, it also opens up different design choices and opportunities.

For most people, a 6-ohm or 8-ohm speaker is going to be the norm. Those types of speakers are particularly well-suited to match with the designs of most AV receivers. This isn’t to be taken as a blanket statement of course—a lot more goes into a loudspeaker than its impedance rating. Still, there are indicators you should be aware of when trying to understand impedance ratings and amplifiers.

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Room Size Matters

The problem most people run into when mismatching speakers and amplifiers is that they try to get a pair of speakers to fill a larger room that they really can’t support.The amplifier ends up getting turned way up, and the end result is that the amplifier can’t handle the load. This is a real concern for when mating 8-ohm or 6-ohm nominal speakers with an AV receiver that’s not up to the task. In addition to matching the impedance of the speaker with the capability of the receiver or amp, you want to match the overall system to the room as well.

That Impedance Switch on Your Receiver is a Lie!

OK, it’s not really a lie, but it limits the output of your AV receiver or amplifier. Some AV receivers have an impedance selector switch on the back (Yamaha is famous for this) that opts between 4-ohm and 8-ohm or 4/8-ohm and 6/12-ohm. The idea is that it is safer to match the impedance of the amplifier to the speaker to avoid overpowering it or creating a difficult load on the amplifiers. The problem is two-fold. One, loudspeakers don’t have “flat” impedance curves. They dip down and swoop up. That means that a 4-ohm speaker may spend a lot of its time in the 8-ohm or greater range. It also means that if you’re using a subwoofer, you may never get down to its lowest impedance dip areas. Second, the only way to really make a system “safer” is by limiting the power output of the amplifier or AV receiver. This is exactly what the setting does. As a result, that little switch cripples, ever so slightly, the output of that brand new AV receiver or amplifier you just purchased. Our recommendation is leave it on the highest setting possible. That will give you the most power output regardless of the speaker impedance rating of your bookshelf or tower speakers. The nice thing is that making this change (or not making it) doesn’t require any fancy hand tools or other accessories.

Don’t Run Two Speakers Off a Single Amplifier Channel (without an impedance-matching selector switch)

I can’t tell you how may times I’ve walked into a living room to see an entire 5.1 home theater like the Klipsch RP-280F parked right next to the TV. Or better yet—two completely unrelated speaker pairs side-by-side connected to the same stereo amplifier. And they wonder why the amplifier keeps shutting off. It just doesn’t make sense, they cry!

It makes perfect sense if you understand the math.

The formula for calculating electrical impedance is found through Ohm’s Law:

V = I Z , or

Voltage = Current x Impedance

We’re not talking about that. We’re going to leave that to another discussion. What we want to understand is what happens when you connect speakers of various impedances in series or parallel.

Because that’s exactly what you’re doing when you start to double-up on speakers in your home. Think you’ll never run into this issue? Perhaps not, but run a bunch of speakers overhead in a whole-home audio system and you might get your feet wet very quickly (figuratively speaking—I don’t recommend you run wires with your feet wet).

Calculating Speaker Impedance

Calculating loudspeaker impedance in series and parallel can be difficult if you don’t know the formulas. Once you know how to do it, however, then it’s just basic math.

Calculating a Speaker Impedance Rating in Series:

To do this is the easiest of all the calculations. You just add. To find the speaker impedance rating of a bunch of speakers in series, follow this formula:

I(All) = I(1) + I(2) + I(3) . . .

So if you have two 4-ohm speakers and a 6-ohms speaker, the total impedance for the system would be:

I(total) = 4 ohms + 4 ohms + 8 ohms

I(total) = 16 ohms

Calculating a Speaker Impedance Rating in Parallel:

Calculating this is a bit more difficult. To find the speaker impedance rating of a bunch of speakers in parallel, we utilize this more complex formula:

1/I(total) = 1/I(1) + 1/ I(2) + 1/I(3) . . .

So if you have the same speakers—two 4-ohm speakers and a 6-ohms speaker—the total impedance for the system would be:

1 / I(total) = 1/4 ohms + 1/4 ohms + 1/6 ohms

1 / I(total) = 0.667 ohms

I(total) = 1.5 ohms

As you can see, there would be a HUGE difference between hooking up some in-ceiling speakers in parallel vs. hooking them up in series. One will result in a leisurely load for you AV receiver or amplifier (series) while the other would likely shut it off once you brought the volume up to any sort of nominal level.

Conclusion

What you want to remember is this: match your speakers to your amplifier or receiver so that you aren’t forcing the amp to work overtime just to fill your room with sound. Product managers and engineers take great care in the design and construction of these audio products. Your best bet is to stay within the design parameters. When it comes to 4-ohm speakers and AV receivers, however, only the weakest products should give you trouble. If you have an entry-level receiver you may find that you can’t get all the volume you need (same goes for having a huge room). If, however, you have a mid-fi or high-end amplifier or AV receiver—there’s no need to baby your system. 4-ohm speakers are going to work just fine in most cases.

Above all, have fun and don’t sweat it.

And for those of you who hate math, here is a handy calculator that works well for figuring the impedance load on your amplifier in various loudspeaker configurations. It’s based on car audio, but it’s perfectly usable for home audio. Plus it’s so well done they deserve some credit!


43 comments on “Speaker Impedance Rating Explained

  1. Richard Hammond

    Hi,

    I have two older Yamaha NS-6 speakers. I would like to know the Ohm rating on them but I can’t find them on the Yamaha site. The serial # is 26050. do you know where I could find this info?

    Thanks for your time.

    Richard Hammond

  2. tiberiu

    Hi. Quick question about speakers impedance.
    I am looking to purchase yamaha RX-V477 . My front left and right speakers are 6 ohms each and center rear left and rear right are 8 ohms each. Do you think is ok to use it like that or all the speakers need to have the same impedance ?
    Please let me know. Thank .

    • The speakers do not need to be of the same impedance—the amplifier is nimble enough to deal with that. This setup should work with the only caveat that if you’re trying to fill a very large room (over 2500 ft^3) you may need a bit more power.

  3. tom

    Hi. i have tube amp made by Jolida. On the back are 2 output 4 and 8 ohm.Can I set up 6 ohm speakers without frying and what would be the best choice 4 or 8?
    thanks

  4. Bill

    This explanation seems clear and helpful, but isn’t there a confusing typo in your two examples of how to compute impedance? Although the examples refer to a setup that has two 4-ohm speakers and one 6-ohm speaker, the numbers plugged into the formulas are 4, 4, and 8. If examples are correct as written, then an explanation for the apparent discrepancy may be called for.

  5. mike

    i have klisch 4 ohm speakers. looking at a pioneer vsx 824k. Says it runs 8 ohms. Can i use my current speakers. Only using the two speakers. thanks, Mike

    • Generally speaking, yes. Your only limitation will be that if those speakers have a low impedance dip at a particular frequency and/or you attempt to play them at excessively high levels (perhaps in order to fill a room that’s too large for them, etc). In general, though, a 4-ohm speaker load isn’t a problem for modern receivers and amplifiers provided you’re not attempting to run them “full out”.

  6. Mr Deboer,i will like to know how do we measure the impedance of a closed cabinet speaker?I purchasee a pair of Definitive Technology Mythos 5,and they say its rated at 8 ohms in the internet.But when you measure it whit the multimeter at the back of the speaker,it shows 3,9 ohms.(Back i mean where the cables are conected) Is that the wright way?The technitian of the speaker told me that when you do this ,you are readind the crossover.And some people say that is the wright measurement,Who is telling the truth?

  7. Trent

    Having spent the past month playing around with 7-8 second hand speakers of varying age, quality, ohm rating and size to wire up (for the heck of it) at home the maths has been interesting to get my head around – in all I’ve found on the web this has to be the most succinct explanation out there –
    so I hate to be the one to point out the typo (if not already noted somewhere in the comments) but on your last eg. shouldn’t the 6ohm speaker be 1/6 not 1/8? (or meant to be 8ohm speaker not 6ohm…)

  8. Chuck

    Hi,
    Great article.
    I have a question. I understand the difference between series and parallel, but I’m a little confused for when it comes to speakers. The previous owner wired in the ceiling speakers 8 ohms each in several rooms with 8 speakers. The leads all run to 4 terminal strips. 2 strips for the right channel and 2 for the left channel and one strip for the pos and neg lead for left and right channels. He also has volume controls in each room. I have had this connected to my Harmon Kardon amp for years with no problem.
    Now the questions…., is this wired in series or parallel, and can I add two 6 ohm outdoor speakers without running into an issue?
    Thanks in advance
    Chuck

  9. Tom

    I do not know if my old speakers are 4, 6 or 8 but on a new Sony Amp STR-DN860 if I use more than 2 speakers (plus the center and subwoofer) as plugging two more in the surround jacks, the amp will go into protection and shut off.

  10. Chinedum

    Hi. Insightful read. I just got a Sony DN850 as well as just got some speakers but I haven’t done the connections yet.

    Details of the speakers – Active Powered Woofer of 160W, 2 satellites and 1 center at 45W and 2 average height 60W speakers. My sitting room is mid-sized, about 16ft by 16ft. Please what do you think about its performance and suitability?

    Thanks in advance.

  11. Pawel

    Hello. Thanks for the great article It was very helpful
    But still I have some doubs about my system. I Have an denon AVR1611 on back it’s written that I could connect 6-16ohm speakers. At the moment I have connected an 2 main 4 ohm speakers and and center 8 ohm. I’m have a small room and maximum loudness I have used is around 40% of volume . Is this configuration is sav the for my air and speakers. I’m thinking about connecting surrounds with will hav the also 8 ohm. What do you think about my system? Thanks in advance

  12. jessu

    hi. ihave got one 6 ohm and four 3 ohm home theater speakers with me. can i use 6 ohm to 16 0hm av receivers. am waiting forur favourable reply.

    thank you

    • 3-ohm speakers could be a problem when run at louder volumes because they will naturally grab a lot more power from the amplifier and create a higher load (more work for the amp, so it runs hotter). Beyond that, I can’t really tell you much more with out knowing about the room and the specific models of equipment you’re using.

  13. Danno

    Hey Clint,
    I hooked up a simple little 2 way speaker switch as I have 2 outdoor spkrs (one in front &1 in back of house)
    Its a new amp but now everything sounds like its missing the voice (CD, radio)
    u just hear like 1 channel (some of the instruments)
    its 4 ohms load at spkr output aren’t most spkrs 8 ohms?
    its 10 watts max/channel…..these speakers are idk – higher than that though….mb 30
    did i hook it up wrong? or is it a wrong switch it worked before the spkr switch,
    but I don’t want to keep disconnecting a wire in front or back
    thnx!!

  14. Steven Hartman

    Hi– I have a Sony DAV-HDX285 home theatre system that the dvd player is starting go bad. The speakers are perfectly fine and sound great. The manual says the speakers rate at 3 ohms and the sub woofer at 1.5 ohms. Can I use the speakers on a regular receiver rated at 8 ohms? Be a shame to trash a perfectly good 5.1 speaker set up. Cheers

  15. Chris

    The Focal P30DB subwoofer has twin coils and depending how you wire it you can select 8ohm, 4ohm or 2 ohm. The Alpine PDX-X9 says it can drive 500W RMS at either 4 or 2 Ohm.

    So the question is, what ohms should I wire it for?

  16. Naveesh

    I have onkyo – TXNR 515 amplifier, it says 6~8 ohms speakers . Please advise me a suitable speaker’s for my 5.1 home theater

  17. Patrik

    For my home office I purchased the Samsung JW5500 3D Blu-ray player and home theater system. The system is rated at 1 ohm impedance. What are some speakers that you would recommend to add on? I am looking at BOSE 161. Thanks for any help.

  18. Mme le Professeur

    I thought I had this worked out, but am now second guessing myself. If I have two 6-ohm speakers connected in series, and I have 4-ohm, 8-ohm, and 16-ohm outputs on my amplifier, which of those should I use? (I’ve tried the speakers in both the 8-ohm and 16-ohm spots, and they are unbelievably loud, even when the laptop and master amp volume are very low.) Thanks for your help.

  19. Jose

    Hello , I just bought a 5.1 system which I pieced together , two Martin Logan motion 4’s ( fronts ) two motion 2’s (rear ) one motion 8 ( center ) and a Dynamo 700 sub . I also bought a Denon avr-x1300 receiver . My question is , is that enough power to push those speakers , and the speakers are rated at 4ohms , the receiver can be set to , 8,6,4 ohms … which setting should I leave it at ? Thanks

  20. Br. Daniel

    Hi, I will be purchasing an entry level Audiophile system for my 24-bit/SACD sacred, choral, organ & orchestral music. Oppo, ML EM-ESL mains = 2 @ 6 Ohms. & 2 surrounds + 1 center = 3 @ 4 Ohms (svs sb-16ultra for 16Hz Organ) I was wandering if a 5125 5-Ch audiophile grade amp (rotel, monoprice, parasound, outlaw, emotive) would be adequate for a med-sm 850-950 sq ft room?

    • Br. Daniel

      For Mr. Clint Deboer – Br. Daniel; The only other question that I had, was not the room size but also the speaker ohms and Wattage – in other words I will be obtaining Martin Logan entry level EM-ESL Mains $2,499.94 pr. Electro Static Mains (Recommended Amplifier Power 20 – 300Watts per Ch @ 6 Ohms) and a EM-ESL C Center Electrostatic Center Ch Speaker (Rec Amp Power 20 – 300Watts per Ch @ 4 Ohms and 2 Motion 4 Surrounds (Rec Amp Power 20 – 250Watts per Ch) so regarding a Audiophile grade 5125 5-Ch Amp. My secondary question is will this be a perfect amount to push these speakers appropriately? For Instance a Parasound 5125 5-Ch THX Ultra2 Certified Amplifier Stats are (125Watts rms per Ch into 8 Ohms all channels driven – 185W rms per ch into 4 Ohms all channels driven) It seems that most of the speakers fall into a perfect medium range except the Motion 4 surrounds that Max out @ 150W should this be a concern or is it negligible? Since the 2 Mains are at 6 Ohms I add between the 8 Ohm W @125 and the 4 Ohm W @ 185 W to obtain the 6 Ohm wattage – the watts between 125 @ 8 Ohm and 185 @ 4 Ohm Since there is 60 watts between 125 and 185 I simply add by 10 to come up with the in between 6 Ohm wattage which would be 155Watts @ 6 Ohms. Is this correct – If so all my speakers will be running in the (20/30W – 150-300W) perfect middle desired wattage range – except the surrounds that Max out at 150 @ 4 Ohms/ Parasound 5125 5-ch Amp says (185W @ 4 Ohms) so this is my real question concerning the watt rating match between the Parasound and The Martin Logan XStats – 1. do you agree that this is a correct summation? 2. is the motion 4 surrounds @ 4 Ohms 150 W Max compatible? or could be a issue? or is simply negligible? PLEASE DO NOT POST – Please answer directly to my email danielmat448@gmail.com Thank you, Thank you, Thank you, so much sincerely, Br. Daniel

  21. Keith Cunningham

    I have searched alot of sites trying to understand the ohms and good and bad etc. What I really have not found and I don’t know if this will help my understanding, but in Ohms 4 ohms or 8 ohms, which is considered “higher resistance” ? I would say 8 ohms being higher resistance, and if needed is it better to let’s say, need 4 oh but use 8 or 16 ohm, or is it better to need say, 16 ohm but use an 8 or 4 oh ?

  22. Chetan

    I have two 6*ohm speakers and a 2-channel 3400watt car amp (ie. 12V battery of car). Can i connect these? If yes, please tell how.
    (one 1200watt subwoofer and 4 orignal car speakers and 2 tweeters are already connected to it)

  23. Frenchy guy

    Hello,
    I’m french, sorry for my bad english..
    I’ve read everything but i’m still not sure what setting is better.
    I was running with RX-A3060 set at 6ohms and 5.1 speakers 6ohms and decided to add 4 Atmos speakers (8ohms)
    On which ohms settings do you suggest my amplifier to deal with?
    Do i have to stay with 6 ohms or with 8 ohms since i’ll mix 6 and 8 ohms speakers now?
    Thanks for your advise
    Regards

  24. Lino

    Sir i would like to ask if they are match since no idea about them.
    Thanks in advanced.

    4 speakers: 15″, 4 ohms, 1000 watts (each)

    amplifier:
    2U Professional Power Amplifier
    ATR (Accelerated Transient Response) technology for ultimate punch and clarity
    2500 Watts @ 2 Ohms RMS
    1500 Watts @ 4 Ohms RMS
    1000 Watts @ 8 Ohms RMS ( 500W+500W Stereo )
    XLR, ¼” (6.5mm Jack) Balanced Inputs
    Speakon and Banana binding post Outputs
    Front-to-Rear Airflow and Cooling Fan
    Frequency response 10Hz – 50kHz at 1.5 dB
    Total Harmonic Distortion: Less than 0.1%
    Input sensitivity & Impedance: 0.77v
    Signal to Noise (20 Hz – 20 kHz) > 90dB
    Dimensions (WxDxH): 20.1” x 13.4″ x 3.3″
    35lbs

  25. Andrew Griffiths

    Hi have just bought Old Sony speakers which says that they have a 4 ohm impendance at 30 watts. I am thinking of buying The Marantz PM5005 Amplifier which offers 40 W per channel into 8 ohm or 55 W into 4 ohm.

    Would this be ok

  26. Adrian

    HI Clint,

    I have just bought a Yamaha AS 501 Amplifier with 8 ohm impedance and was thinking of pairing it either with Q Acoustics 3020 bookshelves or Elac Debut B6 Bookshelves speakers. However both speakers have an impedance of 6 ohm.

    Will this setup be okay or should i look for speakers with 8 ohm to be safe?

    Thank you for your time.

  27. Keith

    Just a question on parallel and series. Scenario. 4-8ohm speakers. Two wired in parallel = 4ohms. Two sets @ 4ohm wired in series = 8ohms?

  28. senthilraja a

    Hi Clint,

    I have a old sony DAV Dz 640K Sony Home theater system, unfortunately it doen’t have the Optical In / HDMI in to receive 5.1 CH from my SAT. All Speakers are 3 ohms and Passive Sub-woofer of 3 ohms. So I’m thinking of getting a AV receiver to get the optical out from my SAT/TV to get 5.1CH on my speakers. Which AV receiver would you suggest ? Can I hook up these speakers to 6 ohms receiver as I see most of the latest receivers are rated 6 Ohms only.
    When I check the surround speaker for its resistance it showed 5 ohms in the Multimeter. So can I look out for 4 ohms receiver for the safer side ? Is any available for 4 ohms in the market.

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