Wiring speakers for 4ohm's How???

Discussion in 'Archived Threads 2001-2004' started by Kris Coffin, Jun 20, 2002.

  1. Kris Coffin

    Kris Coffin Stunt Coordinator

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    Hello all

    This is my first post here, so please bear with me.

    I have scoured the net, and not yet found a plausible answer to my question.

    My system consists of Deftech BP 2000 tri wireable fronts, Deftech CLR3000 tri wire center, and 4 BPVX/P's for rears and surrounds. My question is this. How can I possibly wire the 4 rears and center to 4 ohms. The amps I am picking up are Rotels RB 1090 (380watts x 2) and the RMB 1095 (200watts x 5) I want to wire the channels at 4ohms, so I can have a wattage balance between my fronts, rears, and center. All coming in about 370+ watts. Is this possible?

    The specs for the speakers state they are stable to 4 ohms, the amps, are also stable at 4 ohms.

    So far all I could find on the net was to get your ohm load lower, you must wire speakers in sequence. If that is the case, how would I go about it? Is there such a thing as 4ohm speaker wire? If so, where can I find some?

    Any help would be greatly appreciated. Thanx.
     
  2. Cees Alons

    Cees Alons Moderator
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    Kris,

    Welcome to the forum!

    If the speakers are rated at 4 Ohms, just wire them normally to your 4-Ohms outputs. No special measures to be taken.

    Unless I do not understand your question properly, there's no specific problem with that.

    Good luck.

    Cees
     
  3. Dustin B

    Dustin B Producer

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    I just checked Def Tech's site. Each the speakers you listed contains it's own amp for the bass driver(s). They then list the nominal impedance of the portion of the speaker that needs to be driven as 4-8ohm.

    There is no way to wire them for 4 ohm, or 8 ohm. The impedance of a speaker will vary with frequency. I'm sure it goes lower than 4 ohm and higher than 8 ohm at certain points.

    Just make sure all three of those binding posts are hooked together in parallel and run a single 12 or 10 gauge wire from your amps to one of those binding posts on each speaker.

    The exception will be if you want to run the LFE channel to the powered subs in your speakers. In which case you disconnect the lowest binding post from the others (check the manual to make sure that is the one for the powered sub, as I'm making an assumption here) and then hook up the LFE signal to the amp in the tower.
     
  4. Kris Coffin

    Kris Coffin Stunt Coordinator

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    Cees - From what I can tell, there are no ohm binding posts on the Amps, I believe they are just 8ohm standard. The Pre/Pro has no means of setting this either, I have seen the feature on other recievers, but none that I am considering buying unfortunately. And even then it is just a general setting that encompasses all speaker outputs.
    Dustin - Damn, so it looks like this won't be a possibility with the hardware I have chosen then. Thanx much.
    I have another question then, but I will start another thread more relevant. Thanx to the both of you.
     
  5. Bill Lucas

    Bill Lucas Supporting Actor

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    Kris,

    You cannot re-wire speakers to change their ohm rating. They are what they are. Period. Simply hook them up properly to the amp and enjoy them. Regards.
     
  6. Bob McElfresh

    Bob McElfresh Producer

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    Chris: let me clarify something -
    A cone-style driver in a speaker actually changes it's impedence from about 2-30 ohms. It depends on what frequency of sound you are sending to it at each instant.
    Speakers are rated at 4,6,8 ohms Nominal impedence (people often forget that word [​IMG] ) This means the speaker presents an AVERAGE impedence of say 8 ohms.
    Your amp can drive any/all of these.
    Wattage Balance: You have the right idea - but there is a better way to do it.
    You really want a "Volume Balance". And once you hook up your speakers and amps, you use a test-tone DVD like Avia or Video Essentails to calibrate/level-adjust the volume from each speaker.
    Read your receiver/pre-processor manual about how to offset the center and rear speaker volume to obtain this balance.
    Remember: a 2 channel stereo system drives the L/R speakers all the time. But a HT system does not. The distribution of use/power consumption is something like:
    Center Speaker: 100% of the time
    L/R Speaker: 20-40% of the time (depending upon the movie)
    Rear Speakers: 10-30% of the time
    So you DONT need/want equal power to every speaker (unless money is no object).
    Hope this helps.
     
  7. Dustin B

    Dustin B Producer

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    Edit: Bob beat me in, so some of this is redundant.
    Kris, I think you are missing a little piece of information here.
    When you see a receiver with that ohm switch on it. That is bad. That means the amp isn't very capable. It has to use an electronic trick to limit output so 4ohm loads don't over draw the amp.
    The Rotel amps you are considering are excellent amps. They are stable into 4 ohm loads.
    Do you remember any high school physics. Specifically the voltage, wattage, resistance equations. I don't remember them off hand myself but there is one that is important to amps.
    If you half the ohm load (what the speaker looks like to the amp) then the power the amp outputs should double. Only very expensive amps double. Krell, Classe etc. Amps like Rotel, Parasound, Anthem etc are the next best thing coming very close to doubling. Amps with those switches will maybe gain 15% in power output between 8 ohms and 4 ohms which indicates how weak their power supply is.
    Speakers don't present a constant load to an amp. The ohm load they present to an amp depends on the frequency they are asked to play. Manufactures give them a nominal rating that is kind of like a weighted average. So at some frequencies the Def Techs will present a 10ohm load to the Rotel, at others they will present a 3 ohm load. I don't know where to find an impedance graph for the Def Techs you are thinking about, but here is one for the Adire Kit281:
    [​IMG]
     
  8. Cees Alons

    Cees Alons Moderator
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    Kris,

    The other posters have already said what I wanted to tell you. Your amps are "stable at 4 Ohms". Fine, just hook them up.
    If your channels don't all have the same impedance, you may have to adjust the relative amplification - but you would probably do that anyway (using an AVIA DVD or the like) to make them all equally loud.

    Good luck!

    Cees
     

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