4 ohm stability - a big deal?

Collapse
This topic is closed.
X
X
 
  • Time
  • Show
Clear All
new posts
  • Paul Ebert
    Senior Member
    • May 2004
    • 402

    4 ohm stability - a big deal?

    It seems that most of the inexpensive gear only lists power output into 8 ohms. I'm planning to build my speakers, so do I really need to keep the impedances high?

    I've noticed that Harman Kardon calls their designs "high current". Will they drive a 4 ohm load?
  • Glen B
    Super Senior Member
    • Jul 2004
    • 1106

    #2
    The inexpensive gear is often rated only for 8 ohms because of cost. The ability to drive lower impedances requires larger power supplies and more robust output stages, which translates into greater cost. Regarding Harman-Kardon, I don't know about the "high current" part, IMO its an overused term. Looking at the specs of the current crop of HK electronics, the difference between their 8 ohm and 4 ohm ratings is only about 0.3dB, hardly what one would call "high current." Nevertheless, HK components have always tended to be true to their specs and will safely drive 4 ohm loads with no problem. As you build your speakers, keep in mind what electronics you intend to drive them with now and in the longterm.


    Comment

    • Lex
      Moderator Emeritus
      • Apr 2001
      • 27461

      #3
      what you also have to keep in mind is it's still an average impedence. So, it takes pretty good gear to be rated at 4 ohms, because sometimes, it even dips below that. It can take it for short periods of time, but an extended spike below 4 could burn up output stages in cheap gear that doesn't have the capacity to handle the load.

      Running at 4 ohms will create more heat, and probably lessen output device's lives for all but quality high end gear. Harman is a true audio company with roots that go deep to the audiophile side, so their their receivers are better than some companies. In the end, there's really no real gains for most speakers to be designed at 4 ohm loads though, it's a design consideration. So, if you want to insure the greatest compatibility it's simple, choose a 8 ohm design.
      Doug
      "I'm out there Jerry, and I'm loving every minute of it!" - Kramer

      Comment

      • gp4Jesus
        Member
        • Jan 2010
        • 60

        #4
        I agree with Lex & glenn. HK makes robust equipment. However "High current" does not promise "highly stable" at lower impedences. 2 ohms is nearly a short circuit! Perreaux made an excellent sounding amp stable to 1 ohm w/an incredible current rating!!

        I have 80 W/ch amps*, 30 amp peak, rated to 4 ohms; I used one* to drive** a pair "4 ohm" subs. Their 3.2 ohm low point in their impedence plot caused that amp, even at low volume, to run quite warm, "great heater" @ moderate levels. Same amp into a very stable 8 ohms load at deafening levels, ran slightly warm to the touch.
        * have 2 now; they have 6 transistors per ch ** 4th order LP @ 60 or 100hz depending on system at the time

        IMHO ask yourself the following:
        Does your HK have a 4* ohm rating? a 2 ohm rating
        will your intended speaker design's impedence** plot stay above[I] 4 ohms below[B] say, 250 hz?
        Dip below 4 ohms between 250 hz & 5K hz for a narrow freq range?
        ** inductive/capacitive
        * I've seen pro gear "drive 2 ohms all night long under tough conditions" have modest current ratings

        If the answer is yes to most of the above, your HK is likely safe; consider forced/exhaust venting for your shelving.

        good luck and happy building
        Samsung 60" LED
        Outlaw Audio 976
        Samsung BDP, Dish Network

        BJC 10 ga - LCR mids, inside & out
        Canare 14 ga - LCR inside; CC outside
        LR: RTi A7 Triamped
        M & T: Rotel RB-981
        Bass: Rotel RB-980BX ->8ga in & out

        CC: Rotel RB981 -> CSi A6 Bi-amped
        SW: LFE - Sunfire; Audio Pro Evidence @ each corner
        Surrounds: Rotel RB981 -> RTi A3
        Power Conditioning & Distribution: APC H15, 4 Furman Miniport 20s; 3 dedicated 20A feeds

        Comment

        • Glen B
          Super Senior Member
          • Jul 2004
          • 1106

          #5
          Originally posted by gp4Jesus
          IMHO ask yourself the following:
          Does your HK have a 4* ohm rating? a 2 ohm rating
          will your intended speaker design's impedence** plot stay above[i] 4 ohms below[B] say, 250 hz?
          Dip below 4 ohms between 250 hz & 5K hz for a narrow freq range?
          ** inductive/capacitive
          * I've seen pro gear "drive 2 ohms all night long under tough conditions" have modest current ratings

          If the answer is yes to most of the above, your HK is likely safe; consider forced/exhaust venting for your shelving.

          good luck and happy building
          Great point. Also throw severe phase angle into the mix. Unfortunately, not everyone will have an impedance plot available unless the product has been reviewed by one of the A/V magazines, and they've taken detailed lab measurements and posted the results.


          Comment

          • gp4Jesus
            Member
            • Jan 2010
            • 60

            #6
            Glen:
            Thanks for phase angle comment. While some may not understand it, its worth saying because it is a factor.

            Paul:
            Its unlikely you'll have problems armed w/the info in this thread.
            One other test you could try, (listening optional!) play to some bass heavy material though full range speakers* rated @ 8 ohms . Set the volume just above what your anticipated movie level would be. Let it go for 15-30 minutes. Touch your HK firmly for several seconds; make a note where you set the knob of how warm the HK. If its barely warm to the touch thats good.
            * let the speakers and HK amp section handle it all; no subs here

            Then connect a 4 ohm 5 watt resistor to each channel; turn down volume to about half, and repeat the test, checking* the HK's temp every few minutes*. @ the end of 30 minutes if your HK's temps is the same or only slightly warmer, repeat the "4 ohm" test at the "8 ohm" volume level. If its slighly warmer still, you're likely safe although a resistor is easy to "drive." Zero back EMF and the other things mentioned in other replies.
            * if you find it get warm or hot fast stop the test!

            If you're comfortable w/the "resistor" test results, repeat the test w/your home growns. start @ 1/3, then 2/3s. If it doesn't get "hot," You're closer to being sure of enjoying the satifaction of YOUR home theatre w/YOUR speakers!

            It may seem like a lot of work but it beats toasting your HK.
            If it make you feel any better, several years ago I was "hot" on the same idea for all channels* 4 ohms and all. I had a killer twin sub setup already; separate amps for each**. Unfortunately with now 5 kids no time to build much less test. So I went with some Polk RTi A series speaker all around with which I'm pleased.
            *I have the same amps; I had planned to then as I'm doing now: the LCR channels bi-amped with Hafler XL280s with another XL280 full range to the rears! I don't sweat low impedences, they're stable to 2 ohms.
            ** see previous post
            Samsung 60" LED
            Outlaw Audio 976
            Samsung BDP, Dish Network

            BJC 10 ga - LCR mids, inside & out
            Canare 14 ga - LCR inside; CC outside
            LR: RTi A7 Triamped
            M & T: Rotel RB-981
            Bass: Rotel RB-980BX ->8ga in & out

            CC: Rotel RB981 -> CSi A6 Bi-amped
            SW: LFE - Sunfire; Audio Pro Evidence @ each corner
            Surrounds: Rotel RB981 -> RTi A3
            Power Conditioning & Distribution: APC H15, 4 Furman Miniport 20s; 3 dedicated 20A feeds

            Comment

            • chrispy35
              Senior Member
              • Feb 2004
              • 198

              #7
              I think you'd burn up the resistor before you got very far. 5 W is not much and the amp should have no issue with that (1.12 amps).

              Chris P.

              Comment

              • Ntruder
                Member
                • Jan 2010
                • 70

                #8
                Is this really a big issue to worry about if your listening levels are low to moderate?

                I rarely get my volume levels above -40db on my HK AVR 2600. At lower listening levels, should I even worry about having 4 ohm speakers in front and center?

                Comment

                • ClosetSciFiGeek
                  Senior Member
                  • Oct 2009
                  • 247

                  #9
                  Just be done with it and buy an Emotiva UPA-2 for $299 and run the fronts you build from it(this opens you up to all the nice 4ohm DIY stuff). Your receiver will thank you and its weak power supply will be able to dole out more current to the other three(5.1) or five(7.1) channels.

                  Welcome to Emotiva Audio Corporation. Home Audio Systems, Speakers & Accessories and more. We use science to evoke the true emotion behind every note.
                  "You get what you Inspect, not what you Expect"
                  -Hyman G. Rickover

                  Comment

                  • Ntruder
                    Member
                    • Jan 2010
                    • 70

                    #10
                    That's not a bad idea at all...

                    Comment

                    • gp4Jesus
                      Member
                      • Jan 2010
                      • 60

                      #11
                      Originally posted by gp4Jesus
                      Paul:
                      If it make you feel any better, several years ago I was "hot" on the same idea for all channels 4 ohms and all. I had a killer twin sub setup already; separate amps for each.
                      Several years ago I stumbled across this site along w/ several speaker DIY sites.
                      Samsung 60" LED
                      Outlaw Audio 976
                      Samsung BDP, Dish Network

                      BJC 10 ga - LCR mids, inside & out
                      Canare 14 ga - LCR inside; CC outside
                      LR: RTi A7 Triamped
                      M & T: Rotel RB-981
                      Bass: Rotel RB-980BX ->8ga in & out

                      CC: Rotel RB981 -> CSi A6 Bi-amped
                      SW: LFE - Sunfire; Audio Pro Evidence @ each corner
                      Surrounds: Rotel RB981 -> RTi A3
                      Power Conditioning & Distribution: APC H15, 4 Furman Miniport 20s; 3 dedicated 20A feeds

                      Comment

                      • whoaru99
                        Senior Member
                        • Jul 2004
                        • 638

                        #12
                        It's not that big of a deal...Don't stuff your amp/receiver into a closed cabinet and allow it plenty of breathing room. It'll be fine...
                        There are some things which are impossible to know, but it is impossible to know which things these are. :scratchhead:

                        ----JAFFE'S PRECEPT

                        Comment

                        • gp4Jesus
                          Member
                          • Jan 2010
                          • 60

                          #13
                          It's not that big of a deal...Don't stuff your amp/receiver into a closed cabinet and allow it plenty of breathing room. It'll be fine...
                          If you think it may run too hot, try elevating 2-4 inches or close off that shelf/compartment and force ventilate*. I recall my Belles Series 1** sitting in the open, on carpet, driving my 3 ohm subs got warm to the touch @ low volumes, rather hot*** at near-club*** levels***. On a milk crate, heat was far less of an issue.
                          * I'll send you a link to a $20 solution of which I plan to use 4 in my new rack
                          ** no 2 ohm rating
                          ** into a very stable 8 ohms, barely warm

                          Either way keeping things cool ensures a long, reliable life. hope this helps. cheers, tony
                          Samsung 60" LED
                          Outlaw Audio 976
                          Samsung BDP, Dish Network

                          BJC 10 ga - LCR mids, inside & out
                          Canare 14 ga - LCR inside; CC outside
                          LR: RTi A7 Triamped
                          M & T: Rotel RB-981
                          Bass: Rotel RB-980BX ->8ga in & out

                          CC: Rotel RB981 -> CSi A6 Bi-amped
                          SW: LFE - Sunfire; Audio Pro Evidence @ each corner
                          Surrounds: Rotel RB981 -> RTi A3
                          Power Conditioning & Distribution: APC H15, 4 Furman Miniport 20s; 3 dedicated 20A feeds

                          Comment

                          • gp4Jesus
                            Member
                            • Jan 2010
                            • 60

                            #14
                            Ok so this may $ up to $30-way less than replacing your AVR
                            Do you need 115 volt fans? Shop Coolerguys today for the best online selection of 115 volt fans and cords to power them.
                            Samsung 60" LED
                            Outlaw Audio 976
                            Samsung BDP, Dish Network

                            BJC 10 ga - LCR mids, inside & out
                            Canare 14 ga - LCR inside; CC outside
                            LR: RTi A7 Triamped
                            M & T: Rotel RB-981
                            Bass: Rotel RB-980BX ->8ga in & out

                            CC: Rotel RB981 -> CSi A6 Bi-amped
                            SW: LFE - Sunfire; Audio Pro Evidence @ each corner
                            Surrounds: Rotel RB981 -> RTi A3
                            Power Conditioning & Distribution: APC H15, 4 Furman Miniport 20s; 3 dedicated 20A feeds

                            Comment

                            Working...
                            😀
                            😂
                            🥰
                            😘
                            🤢
                            😎
                            😞
                            😡
                            👍
                            👎
                            Searching...Please wait.
                            An unexpected error was returned: 'Your submission could not be processed because you have logged in since the previous page was loaded.

                            Please push the back button and reload the previous window.'
                            An unexpected error was returned: 'Your submission could not be processed because the token has expired.

                            Please push the back button and reload the previous window.'
                            An internal error has occurred and the module cannot be displayed.
                            There are no results that meet this criteria.
                            Search Result for "|||"