1. Join Now

    AVForums.com uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

4 Ohm vs 8 Ohm setting on AVR?

Discussion in 'Arcam Owners' Forum' started by m1964, Jul 13, 2005.

  1. m1964

    m1964
    Standard Member

    Joined:
    May 9, 2005
    Messages:
    44
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    6
    Ratings:
    +0
    Just read the article below, and wonder what method Arcam uses to step down the setting? I do keep mine at 4 Ohms since my speakers are rated 4 Ohms, and I am not going to experiment (yet)...

    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.
     
  2. ANDY_DUTTON

    ANDY_DUTTON
    Active Member

    Joined:
    Aug 27, 2002
    Messages:
    498
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    28
    Location:
    Cambridge
    Ratings:
    +87
    Hi, The statement you have found does not actually relate to the AVR300. I will explain why the AVR300 has a impedance switch.

    The AVR300 has two seperate power rails and when the 4 Ohm switch is selected the lower rails are selected. This actually has exactly the opposite effect to what is describe for 4 Ohm speakers. The reason for this is because the maximum load on the output transistors has to be kept withinn a Safe Operating Area (SOA) and this is a function of both the voltage and the current. So the higher the voltage on the output devices the less current we can allow to flow though them. The reverse of this is also true if we reduce the voltage (i.e set the system to 4 Ohms) then we can allow more current to flow through the output devices.

    The statement would have been true if the AVR300 had such a small power supply that the current limiting could be acieved by the power supply collapsing. The AVR300 has a large torroidal power supply so this does not happen. For this reason the current has to be controlled by the SOA circuit in the amplifer.

    The first part of the statement is true the 4R switch will also to reduce the heat developed when the unit is used with 4R speakers. We felt this was worth while since people hate it when the fans come on and this reduces the chance of this happening for 4R loads when under heavy loading. (This is also true for 8R speakers so if you want the unit to run even cooler you can switch it to 4R even if you are using 8R speakers - You will lose only 3dB off the maximum unclipped volume)

    The unit will undoubtably sound different in the two different setting as the supply characteristics will change. One review (I think it was AVtec) were convinced it sounded better in 4R mode even for 8R speakers however all I can say for sure is that is will sound different.

    You can safely try your speakers on the 8R setting as the amplifer will still protect itself using the the SOA circuit however it will have to cut in earlier to limmit the voltage / current product. You may find that it will not play bass as loud into 4R speakers if the impedance dips (Which it normally does) as the SOA circuit will cut in. It will also get much hotter and the fans may come on.

    I would advise you to leave the system on 4R as it will run cooler and keeping things cool always increases the life of the product.

    Regards,
    Andrew
     
  3. ttree sound

    ttree sound
    Active Member

    Joined:
    Oct 17, 2004
    Messages:
    367
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Ratings:
    +13
    I coincidentally decided to change the switch to the 4 Ohm setting about a month ago when the weather started to warm up a little, purely out of curiosity. My speakers are 8 Ohm, but I was convinced the sound had changed slightly for the better and the unit ran a little cooler as well.

    I'm so glad to have read Andy's reply because I started to feel that I was becoming a person that hears differences in mains cables, and that frightened me!
     
  4. m1964

    m1964
    Standard Member

    Joined:
    May 9, 2005
    Messages:
    44
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    6
    Ratings:
    +0
    Thanks for your detailed explanation - i will keep it where it is at 4R
     
  5. bb34

    bb34
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    sorry, just want to be sure.. speakers: mains 8ohm, center 4ohm, rears 6ohms its recomended that I set the swtich on the avr300 to 40hms right?
     
  6. clauser

    clauser
    Standard Member

    Joined:
    Jun 29, 2005
    Messages:
    57
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    6
    Ratings:
    +0
    When i had my AVR300 i noticed that the sound really improved with the 4 Ohm setting. The sound became more natural and sounded less harsh. My speakers are 8 Ohm.
     
  7. Crustyloafer

    Crustyloafer
    Well-known Member

    Joined:
    Sep 12, 2003
    Messages:
    9,499
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    136
    Location:
    Edinburgh
    Ratings:
    +1,236
    I would normally recommend the 4 ohm setting for most people. That is unless you miss the extra 6dB of volume on the 8ohm setting. The 4 ohm setting should allow the AVR300 to run cooler and be more stable.
     
  8. lpm

    lpm
    Active Member

    Joined:
    Aug 19, 2005
    Messages:
    240
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    Melbourne
    Ratings:
    +18
    I too have used the 4 ohm setting for about 3 months now since picking up on Andy's comments. Even though they are nominally 8 ohm, I know my speakers sit closer to 6 ohm overall as I have had them extensively modified (and measured) by a professional speaker builder. For my speakers now, the 4 ohm setting gives very tight base and a more open midrange. Not a night and day difference but definately noticeable.

    What is highly noticable is how much cooler the AVR300 runs, big difference.

    As to db loss, the volume control setting remains about the same for equivalent listening levels so using the 4 ohm setting seems to have no practical drawback to me as I don't go anywhere near max volume.
     
  9. radio

    radio
    Active Member

    Joined:
    Jun 1, 2005
    Messages:
    246
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    21
    Location:
    Toronto, Canada
    Ratings:
    +5
    Hiya, i thought i would add this reply here as well and maybe someone can share something to my experience.



    As per my comment above.. i just changed my recievers ohm switch to 8 ohms and the speakers sound a lot different now... they are a bit warmer and not forward as much.

    Either the speakers properly broken in now and its just a co-incidence or the impedence switch on my unit the ohmage effects the sq?
     
  10. Fisba

    Fisba
    Standard Member

    Joined:
    Mar 8, 2005
    Messages:
    4
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Ratings:
    +0
    I also decided to try my AVR300 in 4 ohms mode after I have been using the 8 ohm setting for a long time. Like many others I liked the sound more in the 4 ohm setting, but...
    After a while the fan starts and it also seems to run slighly hotter (and not colder like it should run according to Andy)? :rolleyes:

    My speakers are:
    - Front AE AE1 Mk1 (biamped)
    - Center AE Aelite Centre
    - Rear AE Aegis Compact
    All speakers are 8 ohm.

    The amp worked fine again when returned to 8 ohm (with no fan turning on), so my "4 ohm try" ended for now :(

    I've read about the early AVR300 fan problems before, but this isn't the same thing or is it?
     
  11. deaf cat

    deaf cat
    Active Member

    Joined:
    Feb 9, 2005
    Messages:
    1,221
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    48
    Ratings:
    +58
    Just wondered if the switch effects the processor/dac and the pre-out parts of the amp?
     
  12. videoaddikt

    videoaddikt
    Standard Member

    Joined:
    Apr 19, 2007
    Messages:
    19
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    1
    Ratings:
    +0
    I thought Arcam engineering explained it quite well. This statement infers it's better to keep it in the 8 ohm position, but this statement (with no author?) is 'generic' and does not talk to specific equipment, I would defer to Arcam's recommendations.
     
  13. Nawty

    Nawty
    Active Member

    Joined:
    Sep 13, 2006
    Messages:
    512
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Ratings:
    +23
    Surely 8ohms = 4ohm/2 (i.e. half the power) = 3db?

    edit: a perceived doubling in volume is around 7-10db (as opposed to the technical 3db) so the lost 3db won't really make much difference to most users unless they are driving the amp hard.
     

Share This Page

Loading...