What Is Impedance Switch all about?!

Discussion in 'Archived Threads 2001-2004' started by Eliot.T, Nov 12, 2002.

  1. Eliot.T

    Eliot.T Auditioning

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    Hello,

    I have a Yamaha reciever (5560) with polk RM6600 speakers. I was wondering what impedance selection I should have the reciever on for best quality/performance?? My speakers say they are "compatable with 8 ohm outputs". What would happen if I set the impedance selector on the back of my reciever to 4 ohms instead of 8 ohms??

    thanks!!
     
  2. Bob McElfresh

    Bob McElfresh Producer

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    Setting the switch tells the receiver that the speakers might try and draw a large ammount of current.

    With Yamaha, I have heard 2 conflicting things about what this switch does:

    - It causes the receiver to go into PROTECT mode sooner to help prevent damage.

    - It puts a current-limiter on the output to prevent damage.

    Since your speakers are likely 8 ohms, set it and forget it.
     
  3. John Karpiscak

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    Hi. Yeah, to prevent damage to your receiver, set the selector to 8 ohm and leave it. Some speakers (foreign speakers I believe), are 4 ohm, but most of the ones here in the USA are 8.
    Like the man said, set it and forget it.
    Regards,
    jk3
    www.y2kfam.com
     
  4. Mikey.S

    Mikey.S Extra

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    i was wondering about the impedance switch aswell.

    ive ordered the rv-630rds yamaha reciever and i have bi-wireable speakers up front which are rated 8ohms.

    how do i bi-wire the speakers from this reciever and will i get problems with impedance effecting the receiver??
     
  5. Greg Kolinski

    Greg Kolinski Second Unit

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    I ran into sort of the same problem,I just wanted a simple upgrade from my JVS 801,to a little higher end unit.Got an Onkyo 600 ,then started reading about speaker Impedance[​IMG] my fronts are Acoustic Research TSW 510's 4 ohms, center is a M&K THX 750 ,back of Onkyo say:min 6ohms" DUUUHHH ,called Onkyo ,told dont do it.OK ,the simple part is gone[​IMG] .I finally ended up with an HK 520,which after the first one took a dive ,I'm still happy with the second one.First one taking as dump,no big deal,a lot of electronic stuff is that way,"if its gonna die,its gonna happen pretty soon outa the box,if there is a hurt component it was born with"
    My little upgrade turned into quite an education,which without this site,and all the help from various people,would have probably been a long expensive lesson.
     
  6. Greg Kolinski

    Greg Kolinski Second Unit

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    BTY ,from what I understand ,if the receiver amp is not up to it,the lower ohm speakers will pretty much cause the amp to push enough power to hurt itself by way of overheating.
     
  7. Bob McElfresh

    Bob McElfresh Producer

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    Humm.. this looks like a good time to review some basics:
    Your speakers are not exactly 8 ohms - A speaker has a coil of wire. When you try and push a signal through it, the coil 'resists'. But it resists a different ammount for different signals.
    Your speaker can vary it's impedence from about 2-30 ohms. It is a low-impedence (think direct-short) with subwoofer frequencies, and a higher impedence with the higher tones.
    So the rating for a speaker is often called: "8 ohms nominal". The word 'nominal' is often dropped, but it can be thought of as the AVERAGE/most-frequent impedence of the speaker.
    The important point is this: when a speaker tries to create low-frequency sounds, the coil looks like a 4/3/2 ohm resistance (getting closer to a direct short). This draws lots of current which generates heat. It's the heat that can damage your equipment.
    Most modern receivers have a sensor that will detect the build-up of heat and try and shut down the receiver before too much damage has been done. This is called "PROTECT" mode.
    When the movie The Matrix came out, the lobby shoot-out scene caused a bunch of receivers to go into protect mode. While your receiver can produce bursts of power, the many minutes of low-frequency sound took lots of current which built up heat over a few minutes.
    What you can do
    The first thing is to make sure your receiver has lots of room on top of it for the heat to escape the vents. Do not put the receiver on the top of your rack with 1-2 inches of space. This is like putting an umbrella over a fire. The top shelf will act like a blanket and hold the heat in.
    Putting the receiver on the bottom shelf gives all the open space above it as a area for hot air to flow. No, it wont typically damage the other equipment, but it will make the inside of your rack warm. But having the average temp of the rack rise is better than cooking your most expensive piece of electronics.
    An open rack rather than an enclosed cabinent is another way to help reduce the heat problem.
    (My rack does have glass doors, but the back is missing and a small electric fan is behind that I turn on for warm days when I'm worried about heat.)
    We have all seen the professionally installed gear that is in a rack looking like it's stacked on top of each other. What you DONT see is the cooling system. They even make "fan shelfs" that fit into these racks that are literally a shelf of 4x4 muffin fans that force the air to circulate up and out. Go to eBay and search for "Fan Shelf" to see a picture.
    You can also tell your receiver that some/all of your speakers are "SMALL". This will keep the receiver from even trying to send low-frequency signals to the speakers which results in less power and less heat. This is another reason why external subwoofers are a great idea.
    Hope this helps.
     
  8. Chuck Kent

    Chuck Kent Supporting Actor

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    A couple of additional thoughts...

    The 4/8 ohm switch on receivers controls the amounts of voltage sent to the amplifier power supply. When set to 8 ohms, the power supply is fully "on" and the amplifier is able to develop it's maximum output. When the switch is set to 4 ohms, the power supply voltage is lowered. This translates to a lower potential amplifier output (typical numbers I've seen published in magazine reviews are 60 to 80 percent of the 8 ohm setting maximum.) This power supply voltage control does not alter the sound other than lower potential wattage output.

    Why would anyone put this kind of "throttle" in a receiver and lower the output? Quite simply to pass Underwriters Labs/CSA heat safety tests when driving 4 ohm loads. The lower the speaker impedence load, the closer to a 0 ohm (dead short) one gets. This means more amperage passes thru the output transistors and a good deal more heat is generated.

    What should most of us set the switch on? In general, I agree with everyone above that the 8 ohm setting is usually the best. More power means less chance for amplifier clipping. As Bob notes, give your receiver plenty of breathing room. Don't stack ANYTHING on top of it. Use an external ventilation fan if the thing gets very hot. If a receiver's amp is consistantly pushed harder than necessary (heat-wise), it can lead to premature failure.

    One might consider using the 4 ohm setting if one is using lower impedence speakers and heat control is limited (due to location for eg.) But be aware that amp clipping is going to be easier...

    (BTW, it won't hurt to test your receiver either way. But only change the switch when the receiver is OFF.)
     
  9. MikeRP

    MikeRP Supporting Actor

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    Nice post Chuck!

    Mike
     
  10. Yogi

    Yogi Screenwriter

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    An impedance switch, to me, is an indication of a weaker amp section. Its a current limiting circuit that limits the current a lower impedance load can draw out of the power supply. A receiver without a current limiting impedance switch will allow the lower impedance load to draw as much current as it requires before it clips or shuts down (due to over heating). Usually manufacturers put an impedance switch to protect their amps from over heating or atleast thats what is claimed when infact its a clear message that the amp would not have enough 'juice' to put up with a lower impedance load.

    Just MHO.
     
  11. Chuck Kent

    Chuck Kent Supporting Actor

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    Yogi: I see your point. But while the switch could indeed be on receivers that have weaker amp sections, I don't think one could always assume that is the case. Larger heat sinks or internal ventilation fan(s) could also help to reduce the chances of overheating too (even on units that may have poorer quality amps sections.)

    Receivers in general (of course there are exceptions) are built to certain retail price points. In order to help hold down manufacturing costs, makers look for ways to accomplish their design goals. In this case, the switch (and it's other minor associated parts) is cheaper to use than the other 2 ideas I mentioned above.

    Maybe it's better to say that receivers with the switch are not cost-no-object designs???
     

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