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8 omms or 4ohms

Discussion in 'AV Receivers & Amplifiers' started by Pauly, Oct 29, 2001.

  1. Pauly

    Pauly
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    Help..................i have a Sony str940
    there is a switch on the back of the amp with a setting for 4ohm's and 8ohm's.......which do i set it at ? i guess its 8ohm's as the speakers have 8ohm on the back........however what if i set to 4 ohm ??? what are the effects is there any danger................i have been reading that the wattage /power output goes up?? or am i missled?

    Apologies for what may be a simple question......


    Setup Tosh rear proj 40who8
    Tosh sd100e Dvd
    sony strdb940
    B&W 601 s2 fronts
    B&W Centre
    Eltax Rears
    Paragidm ps1000 sub


    Paul
     
  2. Ian J

    Ian J
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    If all speakers are 8 ohms the switch should be set at 8 ohms. If any of the speakers are less than 8 ohms it should be set at 4 ohms.

    I had the switch set wrongly on my Sony until I RTFM but didn't notice any difference or do any damage.

    Ian
     
  3. Dave Taylor

    Dave Taylor
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    To get the same power out of an 8 Ohm speaker requires a high voltage swing than a 4 Ohm speaker. Therefore some manufactures place a switch on the back which usually adjusts the internal DC supply of the amplifier to suit. i.e. increases the DC voltage for 8 Ohms and reduces the voltage for 4 Ohms.

    You will do no harm if you have 8 Ohms L/S on any setting (4 Ohms means you will never get full power).

    But if you have 4 Ohm L/S then leaving the switch on 8 Ohms could damage your amplifiers output devices if you run at high power for a length of time. i.e. they could overheat as they are dissipating more power.

    I hope that makes sense and helps.
     
  4. Gizmo 76

    Gizmo 76
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    Old theard i know, but i'm running this amp and 1'm upgrading my speakers, all my old speakers were 8ohms and all my new will be 6ohms, so am i right in thinking i should set the impedence level to 4ohms on the back, instead of the 8 it's been set on since day dot?????

    Cheers!
     
  5. buns

    buns
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    spot on

    ad
     
  6. Gizmo 76

    Gizmo 76
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    Cheers Buns, your always there with a quick and handy answer:smashin:
     
  7. adesonic

    adesonic
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    My eltax speakers are rated at "4 to 8 ohms" should I set the switch on my Arcam AVR100 to 4 or 8 ohms (currently it is set at 8)
    Any advice would be greatly appreciated as reading some of the comments in this thread has got me worrying............


    Ta
     
  8. Reiner

    Reiner
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    4 to 8 Ohms means it's a 4 Ohm speaker, so the switch should be set to 4 Ohms.
     
  9. wookie

    wookie
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    Impedance Selector Switches

    This so called feature, used by some manufacturers, is designed to prevent overheating of the receiver or damage to its output transistors because of excessive current flow. The manufacturer accomplishes this in one of 2 ways: 1) Stepping down rail voltage supplied to the power amp or 2) feeding half the signal strength to a voltage divider of power resistors. Both of these methods severely limit dynamics and current capability of the power amp. This results in an audible decrease in bass capability and dynamics transient sound because the 4 ohm setting effectively increases the receiver's output impedance. Unfortunately many manufacturers put these features on their products to ease customer concerns with driving low impedance loads and for safety reasons when getting UL approvals. Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard. Receivers without this switch are usually rated down to 6 ohms. In most cases, well designed receivers can easily handle 4 ohm loads safely and efficiently. It is highly recommend to keep the impedance switch set to 8 ohms regardless of your speakers impedance and make sure your receiver has plenty of ventilation.
     
  10. adesonic

    adesonic
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    Many thanks for the speedy response - I will dash into the front room and tweak it NOW!


    Ta
     
  11. adc2000974

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    As we're on the 4 or 8 ohms issue, i have a question, i'm using a power amp which supports 4 and 8 ohms. My Eltax millenium 500 speakers are said to be 4 to 8 ohms. I am not using a soundlevel thingie, but which one would it be using?

    Bit of a pickle hey?
    Regards
    Adam C
     
  12. Chester

    Chester
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    If the Eltax speakers are rated 4 to 8 ohms, it sounds like their crossovers have a lot of tolerance. If you have a multimeter, it might be a good idea to measure the impedance yourself. I had to do that with my bass cabs in order to ensure I did not reduce the load too much. Too less a load on an amplifier is like pedalling a push bike in a neutral gear; there's no load on your legs and eventually you'll do yourself an injury.
     
  13. alexs2

    alexs2
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    Chester,that will only give you static resistance at DC,and not impedance,which will vary with frequency....by rating a speaker from 4-8ohms,the manufacturer is stating that it's impedance varies between 4 and 8ohms at various frequencies.
    A good example of this is many B&W speakers(esp the Nautilus range) which are nominally 8 ohms,but have a significant dip down to 3ohms or less in the low bass region....they are rated as 8ohms nominal,as for most of the frequency range,they do satisfy that criterion.

    In this sort of case,it's easiest to treat the speakers as a 4 ohm load for safety's sake.
     
  14. Reiner

    Reiner
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    There is no such thing as a 4 to 8 Ohm speaker. It IMHO just a marketing phrase to show that this speaker is compatible to amps which can handle 4 - 8 Ohm loads.
    Usually 4-8 Ohms speakers are closer to 4 Ohm (maybe 4.6 or 5.2 or whatever) and I would call this the nominal value. (Most likely based on the DC resistance or an average of the impedance)

    As alexs2 says this is the DC resistance, to measure the impedance you need an oszilloscope (sp?) or similar.

    Example: Dynaudio Contour 1.3SE - considered a 6 Ohm speaker but impedance varies from 3.6 - 23.9 ohms.

    http://www.dynaudiousa.com/products/contour/13se/con13sespec.htm
     
  15. Cliff

    Cliff
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    Just a note of caution. Some manufactures state that you must not change the impedence switch when the power is on. Yamaha say that damage could occur as you are changing to different voltages on the mains transformer.

    A comment on this option
    IMHO providing the circuitry is designed well to operate at different power supply voltages then there should be no reason why the quality should be compromised. The amplifier can be designed to provide, say 100watts, and this can be at 4ohms or 8ohms using a switch - simple!

    If a power amp says it will provide say 100 watts, then isn't it reasonable to do 100w into 8ohms and 100 w into 4ohms?

    If you want to keep the cost down then what is the point of having a current heavy psu that will provide the same 100watts at 8 ohms and say 190 watts at 4 ohms when this is not required?

    But as wookie says its best to keep it on the 8 ohm setting for your high power transients. And most amps have temperature protection so if you are running things at disco levels then they will shut down if they get too hot.
     
  16. lynx

    lynx
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  17. wookie

    wookie
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    Its True........
     
  18. wookie

    wookie
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    Why type my own version when I could share with 3 clicks...:D
     

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