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  1. #1

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    Default Ohms and amp question

    Hi im new here but have had Polk for long time , I just sold some RTi12 8 Ohms Polk towers speakers , I now have a center channel Polk thats 8 Ohms compatible, I have 4 ceiling speakers Polk that are 8 Ohms compatible. Im pretty sure my SVS bass is 4 Ohms but has its own built in amp.

    My Denon receiver AVR-2805/985 confuses me it says Power Amp rated output and talks about speakers being either 8 or 6 and the dynamic power shows 8 4 or 2 ohms with different Watt outputs..

    So my question is can I buy 4 ohms bookshelve speakers and run it like normal? Just hook up where the 8ohms ones were but in a different wiring line? Im trying to buy the Polk LSi7.

    I dont understand what paralell or in a series means or how to do it so I need that explained. I guess I can wire the tow LSi7s so they are impeding 8 Ohms.

    Please help, this isnt at all my territory.

    Thanks

  2. #2

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    WELCOME TO CLUB POLK!

    Concerning your Denon. That AVR is rated for speakers from 6 ohms to 8 ohms. It is not really built for dealing with a 4 ohm load.....though the LSI-7s are the easiest of Polk's lower impedance speakers to drive...so if you don't push the Denon too much you could get away with it but it really won't give you a true semblance of what the LSI-7s can do.

    Your Denon has pre-outs. So the easiest thing to do is get an external two channel power amp that is rated for 4 ohm speakers and power the LSIs from that using the pre-out RCA plugs on the Denon L/R channel in the back of the Denon and wiring your LSIs directly to the Power-amp. The Denon would then simply control the TONE and VOLUME settings--the external amp driving the LSIs.

    I do not know of any way to LOWER the impedance of the LSIs if you plan to use them as in a two channel configuration.

    A series connection is when you wire a set of speakers to one channel by linking them in a chain + end to - end on each speaker to the other.

    A parallel connection is when you wire + to +, - to - on two or more speakers....again off one channel.

    See the following diagrams and fuller explanation:

    http://www.termpro.com/articles/spkrz.html

    The formulas for ohm/wattage reduction/increase are described in the article. But you're only running 2 speakers on two separate channels so this does not apply.

    Concerning the ratings given by Denon...that is simply a dynamic power rating for SHORT bursts describing what the wattage it puts out is at those impedances.

    But 6-8 ohm speakers are pretty much all it can handle, realistically.

    Hope this is not too confusing.

    So to sum up. Forget about ratings below 6 ohms. Your amp section is NOT built for that. You can drive LSI-7s but I would not recommend it. Get an external 2 channel power amp....rated 100 watts at 4 ohms or MORE and hook it up to the Denon. That should take care of the LSIs fine!

    cnh
    Last edited by cnh; 10-17-2010 at 08:35 PM.

  3. #3
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    Hello CraigP,
    Welcome to the CP Forum. In very general terms, yes you can remove speaker wires from an 8 Ohm impedance speaker and connect a 4 Ohm speaker. A speaker's impedance is one of the overall descriptions of a speaker and relates to the load that the receiver "sees". Receiver companies will list the power output (both continuous and peak) into different speaker impedance ratings to show how the receiver performs under different loads. Usually as the impedance gets lower the amount of power increases.
    But, a question that might be more important, in your case, is where are you wanting to substitute the LSi4 speakers? I ask this because the matching characteristics of the speakers of a surround system is important. Let us know how you'd like to configure your system and we'll offer useful suggestions.
    Cheers, Ken

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    Thanks Ken,

    Just to clarify here. What you're saying is that you can alter the impedance on ONE speaker by rewiring it, right?

    Because now I'm getting confused if that's not the case.

    To OP. Is that what you want to do or are you just referring to hooking up two LSIs in series or parallel?

    Either way...I defer to Ken.

    cnh

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    I had just read if you hooked up 4 ohms to 8 ohm amp that you could wire them in a certain way i.e series or parallel and it would equal 8 ohms.
    Thanks for suggestion on the external 2 channel 4 ohm amp.

    Does polk make 8 ohm book shelve speakers? I sold my towers due to there size next to a 1.2 inch thick led tv. I think the towers were 20 inch deep and 50 tall.

    Thanks for the help so far.

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    That's fine. Sorry I 'misread' your intention. Ken was right!

    The LSi-7s are really nice speakers. They're the most musical series of the Polk offerings in bookshelves, along with their big brothers the Lsi-9s..

    As you may know though. Polk is on the verge of bringing out a new line of LSI-M speakers..they'll be a bit more expensive but I think they may be a higher impedance?

    Polk's Rti-A series has two bookshelves: both are 8 ohm loads.

    The Rti-A1 and the Rti-A3. I have the A3s and they are a nice two way (6 1/2 and 1 inch dome). You can find them in the menus above. A very nice speaker but not quite as 'musical' as the LSis.

    You should try to listen to both series because they are quite different. The LSis have more laid back highs, the Rtis are a bit more forward.

    People prefer one or the other.

    cnh

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    Quote Originally Posted by CraigP View Post
    I had just read if you hooked up 4 ohms to 8 ohm amp that you could wire them in a certain way i.e series or parallel and it would equal 8 ohms.
    Yes wiring two 4 ohm speakers in series will yeild an 8 ohm load(2 ohms parallel) but wiring speakers in series wouldn't be the recommended connection if good sound quality is desirable.
    Last edited by FTGV; 10-17-2010 at 11:22 PM.

  8. #8

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    Are there amps that have the full range of ohms that are economical with hdmi ports as well?
    I wasn't sure if there even made.

    Thanks for all the help.

    Someone suggested resistors but they also said I wouldn't get true sound with them either.
    So I guess the only way to true sound on them is either
    1) let em ride the way they are
    2) get a power amp 2 channel 4 ohms and daisy chain it in.

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