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  1. #1

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    Default a stupid ohms question

    ok I think I have been thinking of the effect of two sets of speakers on ohms of resistance in reverse... I was thinking two sets of speakers hooked up one set of 4 ohm speakers hooked up to "A" L&R and a second set connected to "B" L&R would create an 8 ohm resistance..... I may be wrong here....

    would this set up create an 8 ohm or a two ohm load to the amp?

  2. #2

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    Resistors in series are additive; 4 ohm + 4 ohm = 8 ohms. Resistors in parallel add inversely, so 1/4 + 1/4 = 2/4 = 1/2 = 2 ohms.

    Without seeing the schematic of the source, I would err on the conservative side, and assume the A and B connections are wired in parallel.

    http://physics.bu.edu/py106/notes/Circuits.html

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    Actually since loudspeakers are reactive devices and you're interested in using them with an AC waveform (music!), technically the load is impedance not resistance. Impedance is the AC analog of DC resistance, but it is made up of three components - DC resistance, capacitive reactance and inductive reactance. The latter two properties vary with frequency, so impedance isn't constant - it varies with frequency (and that's where all the fun begins in matching amplifiers with their loudspeaker loads).

    Fortunately, though, impedance, like resistance, obeys Ohm's Law! :-)
    all the best,
    mrh

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    so If I hooked up two 4 ohm sda's in series the amp would see a 8 ohm load...?

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    Two nominal 4 ohm impedance speakers in series does represent a nominal 8 ohm load. It's not generally the best way, sonically speaking, to hook up loudspeakers, as each will "feel" the other's effects, electrically, which is quite likely to have audible consequences... and they won't likely be favorable consequences.

    In the specific case of SDAs - given their unique design parameters - I do not feel qualified to comment on them. I rather doubt Polk intended pairs of them to be connected in series... and it might even be detrimental.
    all the best,
    mrh

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    In your particular instance, you would be creating a 2 ohm load, mathematically that is.

    Recommend that you never hook up speakers this way, really bad things can happen, very few if any will be good.

    If you want to run 4 speakers, get a pre/AVR/receiver with t least 4 speaker out puts.

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    Quote Originally Posted by rpf65 View Post
    In your particular instance, you would be creating a 2 ohm load, mathematically that is.
    2 pair of 4-ohm speakers connected in series = 8 ohm load
    2 pair of 4-ohm speakers connected in parallel = 2 ohm load.

    Quote Originally Posted by rpf65 View Post
    Recommend that you never hook up speakers this way, really bad things can happen, very few if any will be good.
    Connected in series = poor sonics
    Connected in parallel = high current demand from the amplifier, most of which will fry trying to drive a 2-ohm nominal load. Very few amps will be comfortable with that much current draw. Fewer still will sound good driving that load.

    Quote Originally Posted by rpf65 View Post
    If you want to run 4 speakers, get a pre/AVR/receiver with t least 4 speaker out puts.
    Number of "out puts" doesn't matter. What matters is the way those outputs are wired to the amplifier(s) that provide the power. A stereo amplifier (two amplifier channels) driving four, four-ohm speakers is likely to be in trouble. A four-amplifier "multichannel" amp may--or may not--be fine with four speakers each a four-ohm load. A cheap multichannel amp will probably not support four-ohm nominal loads. A good multichannel amp will be fine.

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    You guys are splitting hairs here, what the OP wants to do with what he has on hand simply won't cut the mustard.

    Depending on what he wants to spend, his options vary, but as he sits with an old receiver and 4 SDA's, he has none at the moment.

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    Sounds like the answer is preamp and two separate power amps then....

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    Quote Originally Posted by tonyb View Post
    You guys are splitting hairs here, what the OP wants to do with what he has on hand simply won't cut the mustard.

    Depending on what he wants to spend, his options vary, but as he sits with an old receiver and 4 SDA's, he has none at the moment.
    True, but I have this deep seated bias that "forewarned is forearmed" and so I like to at least endeavor, in my ham-fisted way, to illustrate why we would say "Don't connect your speakers like that!".
    all the best,
    mrh

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    I will offer what I think is one good reason not to use four speakers if your goal is to get the SDA sound from 2 channels.

    The SDA effect is all about timing of when the sound waves reach our ears from the stereo drivers and the dimensional drivers. It is hard enough to get speakers set in the right position in the room (not to mention the ill effects room acoustics can present) to get the timing right with just two speakers. I found that adding another set of SDA speakers in the rear throws off the timing and degrades the SDA sound that you are trying to achieve.

    I own a pair of 2Bs that I use in the front and a pair of CRS+ speakers that I've tried in the rear. I didn't try all four speakers with a 2 channel amp. I used a receiver made for multichannel operation with it set to the "pure direct" setting so it didn't add any surround sound effects. I didn't like the results for 2 channel listening. It was just OK for movies. For me 2 SDAs in the front is the way to go for 2 channel stereo.

    In my opinion it is better to use the right tool for the job. Try two of the SDAs in the front for a while and see if you like them. Take the time to get them setup properly and then take the time to get to know them. You might find you like what you hear. If you try the SDAs for a while and discover you want true surround sound then buy a receiver and speakers designed for multichannel operation.
    SDA 2BTL Sonicaps Mills resistors RDO-198s New gaskets H-nuts Erse inductors Crossover upgrades by westmassguy
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    Quote Originally Posted by TennMan View Post
    I will offer what I think is one good reason not to use four speakers if your goal is to get the SDA sound from 2 channels.

    The SDA effect is all about timing of when the sound waves reach our ears from the stereo drivers and the dimensional drivers. It is hard enough to get speakers set in the right position in the room (not to mention the ill effects room acoustics can present) to get the timing right with just two speakers. I found that adding another set of SDA speakers in the rear throws off the timing and degrades the SDA sound that you are trying to achieve.

    I own a pair of 2Bs that I use in the front and a pair of CRS+ speakers that I've tried in the rear. I didn't try all four speakers with a 2 channel amp. I used a receiver made for multichannel operation with it set to the "pure direct" setting so it didn't add any surround sound effects. I didn't like the results for 2 channel listening. It was just OK for movies. For me 2 SDAs in the front is the way to go for 2 channel stereo.

    In my opinion it is better to use the right tool for the job. Try two of the SDAs in the front for a while and see if you like them. Take the time to get them setup properly and then take the time to get to know them. You might find you like what you hear. If you try the SDAs for a while and discover you want true surround sound then buy a receiver and speakers designed for multichannel operation.
    SDAs can serve double duty quite well. My 2As are integrated into my Home Theater. All the other speakers are either custom, or off-the-shelf vintage Monitors, for timbre matching. I had my CRS+s as rear/surrounds when my system was 5.1, but they have been retired from those duties, now that the other speakers are in place. Two channel is just a matter of switching my AVR/Pre-amp to Pure Direct.
    Home Theater/2 Channel:
    Front: SDA-2ATL
    Center: Custom Built http://www.polkaudio.com/forums/show...hannel-Project
    Surrounds & Rears: Custom Built http://www.polkaudio.com/forums/show...rround-Project
    Sonicaps, Mills, RDO-194s-198s, Dynamat & Hurricane Nuts.
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    "So is there any tread left on those tires or is it just like throwing a hotdog down a hallway?"

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