Mixed speaker impedance question

Dr_WuDr_Wu Posts: 33
Amp manual states minimum resistance per channel is 2.66 ohm (2 channel amp). Also states 3 pairs of 8 ohm speakers can be powered without stress or distortion.

I've got a pair of 8 ohm speakers and a pair of 6 ohm speakers I'd like to use together (with a powered subwoofer). OK or not?

Thanks.
Post edited by Dr_Wu on

Comments

  • tonybtonyb Posts: 29,197
    should be fine, I do the same and have experienced zero problems.
    HT SYSTEM-
    Pioneer elite vhx 21
    Sony 4k BRP
    Tad 803 bookies
    Polk 500 surrounds
    Polk s35 center
    SVS SB-2000
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    Music-

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    B&k 1403 amp
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    Cables-
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  • Dr_WuDr_Wu Posts: 33
    Thank you, tonyb!
  • Dr_WuDr_Wu Posts: 33
    edited June 17
    If I understand it correctly, the calculation of total ohms per channel using an 8 ohm and 6 ohm speaker is:

    1 divided by the sum of 1 over 8 (ohm) + 1 over 6 (ohm)
    =
    1 divided by .125 + .166
    =
    1 divided by .291
    =
    3.4 (well above the 2.66 ohm/channel minimum)
  • mhardy6647mhardy6647 Posts: 17,930
    edited June 17
    correct.

    Chances are your amplifier will be fine with the proposed load...

    but...

    The only (potential -- no pun intended) problem could be this: With very, very few exceptions, the impedance of a loudspeaker system is neither accurately nor meaningfully described with one number. That one number is the nominal impedance. Usually, but not always it's the minimum impedance of the loudspeaker.

    Even the minimum impedance number doesn't tell the whole story -- the nature of the load (its impedance curve as a function of frequency, and the phase of the load as a function of frequency) is the important factor. This information is available for many, but not all loudspeakers. Say what one will about Stereophile magazine -- they're good about testing, displaying and commenting on how easy or hard of a load a given loudspeaker they review is likely to be, at least for an average amplifier.

    Not really trying to frighten the OP, just trying to contextualize :) an issue that's significantly more complex than many folks realize -- and it's not a good thing to learn that lesson the hard way.

    Here's a classic example of a brutally hard to drive loudspeaker -- the classic Quad ESL-57 electrostatic. An electrostatic speaker is basically a big capacitor, and the impedance of the ESL-57 drops quite low at high frequencies. Especially in the era that these loudspeakers were made (1950s through 1980s), amplifiers weren't typically designed for a load like the ESL-57, and severe damage to both amps and speakers could result if a hapless "audiophile" wasn't aware that the nominally "15 ohm" ESL-57 was nearly a dead short circuit at high frequencies! :open_mouth:

    95w470xyqb9b.png
    source: https://quadrevisionspot.blogspot.com/2009/06/impedance-of-quad-esls-and-monoblocks.html

    Proceed carefully, at least initially: any issues will likely give audible clues before anything bad happens to amp or speakers. :)
    "It's like watching a roomful of people who couldn't get through college algebra discussing the flaws of quantum physics theory. I guess it could be fun, but it's ultimately a waste of time." -- seen on audiokarma

    "Some amps run on self bias, some amps run on fixed bias. But his amps run on confirmation bias." -- seen on audioasylum

    "Writing about hifi is like dancing about architecture" -- paraphrasing some wag (possibly Frank Zappa)
  • Dr_WuDr_Wu Posts: 33
    Thanks mhardy!

    I was aware of the impedance variations in a general sense. I figured that using a powered sub would partly alleviate the low end peaks, giving me a little more room for error. Also, I'll not likely use much volume in my listening environment. For sure, I'll keep my eyes, ears and nose out for symptoms of problems, and the amp has plenty of room to breathe.

    I picked up a pair of Monitor 60s as backups for the time my SDAs are being upgraded (too cheap to pass up). I just wondered what they sound like together, and wanted to make sure I wasn't borrowing trouble.

    Thanks again for taking the time and effort in your post.
  • mhardy6647mhardy6647 Posts: 17,930
    edited June 17
    google your two pairs of loudspeakers & see if you can find measured impedance curves for 'em.

    The odds are way in your favor based on the ratings of your amplifier -- but there's value in a little reassurance, I'd opine.

    FWIW, I don't know how happy a pair of SDAs would be to share an amplifier in parallel with another pair of loudspeakers -- although I am sure there folks here who would know, though!

    "It's like watching a roomful of people who couldn't get through college algebra discussing the flaws of quantum physics theory. I guess it could be fun, but it's ultimately a waste of time." -- seen on audiokarma

    "Some amps run on self bias, some amps run on fixed bias. But his amps run on confirmation bias." -- seen on audioasylum

    "Writing about hifi is like dancing about architecture" -- paraphrasing some wag (possibly Frank Zappa)
  • F1nutF1nut Posts: 39,771
    I don't know what model SDA you have, but they can dip down a lot lower than 6 ohms.

    I also don't know why you'd want to run SDA's with the Monitor's, the SDA's are a much better speaker. Besides, that's got to sound like a total mess.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


  • mhardy6647mhardy6647 Posts: 17,930
    F1nut wrote: »
    ...Besides, that's got to sound like a total mess.
    That would be my guess as well -- but it is a testable hypothesis.

    ucw8a6qdg3zx.png
    https://xkcd.com/242/

    I have to imagine pairing SDAs and any more typical monkey coffin loudspeakers in parallel will present an odd load for an amplifier.
    "It's like watching a roomful of people who couldn't get through college algebra discussing the flaws of quantum physics theory. I guess it could be fun, but it's ultimately a waste of time." -- seen on audiokarma

    "Some amps run on self bias, some amps run on fixed bias. But his amps run on confirmation bias." -- seen on audioasylum

    "Writing about hifi is like dancing about architecture" -- paraphrasing some wag (possibly Frank Zappa)
  • Dr_WuDr_Wu Posts: 33
    edited June 18
    I don't know what I was thinking. Even my amp is laughing at me. Oh, the shame.
  • tonybtonyb Posts: 29,197
    Dr_Wu wrote: »
    Thanks mhardy!

    I was aware of the impedance variations in a general sense. I figured that using a powered sub would partly alleviate the low end peaks, giving me a little more room for error. Also, I'll not likely use much volume in my listening environment. For sure, I'll keep my eyes, ears and nose out for symptoms of problems, and the amp has plenty of room to breathe.

    I picked up a pair of Monitor 60s as backups for the time my SDAs are being upgraded (too cheap to pass up). I just wondered what they sound like together, and wanted to make sure I wasn't borrowing trouble.

    Thanks again for taking the time and effort in your post.

    SDA'S ?? Different animal.

    most the time when running 2 sets of speakers of different ohms on a quality amp wouldn't be much a problem....unless one pair required a hefty dose of current. The SDA's are one such speaker.

    My reference was to bookies or maybe small floor standers. Possibly a different story with bigger more power hungry speakers. Besides....M60's with SDA's as already stated isn't going to sound too good. Maybe use the 60's as surrounds once you get the SDA's back. The 60's are an easy load for any receiver to drive and leave the amp on the SDA's.
    HT SYSTEM-
    Pioneer elite vhx 21
    Sony 4k BRP
    Tad 803 bookies
    Polk 500 surrounds
    Polk s35 center
    SVS SB-2000
    Sonos

    Music-

    Joule la-100 pre
    B&k 1403 amp
    Cary xciter dac
    Cullen modded Sonos
    ERA D5 bookies

    Cables-
    Acoustic zen Satori speaker cables
    Analysis plus crystal oval ic's
    Wireworld eclipse 7 ic's
    Audio metallurgy ga-o digital cable
  • Dr_WuDr_Wu Posts: 33
    Yeah, since everyone already knows they will sound horrible together, I'm not even gonna bother hooking them up. It's probably just plain wrong to have them sitting near each other. Worst $70 anyone ever spent, obviously. Once I get the SDAs back, I'll probably just give the M60s to a homeless shelter.

  • daddyjtdaddyjt Posts: 619
    You don’t have to donate the fuzzy dice to the homeless shelter, just don’t hang them in the Corvette...
    Too much stuff to keep track of.

    Currently enjoying: Legacy Focus 20/20, McCormack DNA 225, Bill D C1, Oppo 105
  • tonybtonyb Posts: 29,197
    I think the jist here is....

    Can you do it ?- Sure you can.

    Should you do it ? - Probably not, for reasons already explained.

    What amp btw are you planning on doing this with anyway ?
    HT SYSTEM-
    Pioneer elite vhx 21
    Sony 4k BRP
    Tad 803 bookies
    Polk 500 surrounds
    Polk s35 center
    SVS SB-2000
    Sonos

    Music-

    Joule la-100 pre
    B&k 1403 amp
    Cary xciter dac
    Cullen modded Sonos
    ERA D5 bookies

    Cables-
    Acoustic zen Satori speaker cables
    Analysis plus crystal oval ic's
    Wireworld eclipse 7 ic's
    Audio metallurgy ga-o digital cable
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