4 ohm vs 8 ohm

Mark Porta

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I recently purchased the Polk LSi7 Bookshelf Speakers, which are 4 ohm. Being a "newbie" to the audiophile
world, I am just learning about "nominal impedance" and such. I have a
Marantz SR7500 Receiver (105/ch x 7), which gives 8 and 6 ohm ratings,
but not 4ohm. I have read in on-line write-ups that it possesses a
high current amp, which is required for these speakers. The write-up also states that it has Current Feedback Topology amplification. I have 28 days to return the LSi7's, and so far, I can detect no "clipping" at high volume (Pink Floyd Animals sounded AWESOME). I now am looking to upgrade the Center Speaker to the LSiC, also 4 ohm. I must act quickly and pair them w/ the new Center Speaker to see if there will be any problems. I am driving the High Freq w/ the Surround Rear (Speaker C) channel, and the Low Freq w/ the Main (A) channel. My question
is: should I have any concerns driving these as L/R/C in 5.1
setup with this receiver. Any thoughts would be greatly appreciated!! Thanks so much.

Mark Porta
Plymouth, MA
 

JeremyErwin

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The safest bet would be to get a power amplifier rated for 4 ohm, and plug the pre-outs of the Marantz into those.

An indication that something is very wrong would be if the receiver heats up. If it doesn't, you may be okay. Then again, you might not.
 

ChrisWiggles

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I disagree, the marantz should be just fine with these speakers. I run Dynaudio speakers off a marantz receiver with less capabilities than the 7500 just fine. You should be fine. I also run 4 atoms around the back, two of which are wired in parallel which drops those down to probably around 4ohms.
 

Ron Temple

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I think the 7s are nominally 6 ohm, but the rest of the LSis are 4. At moderate volumes you shouldn't have a problem with LCR, but watch the heat...and I'd look into a used amp, it will improve your SQ.
 

John Garcia

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A pair of them would be OK, but a full compliment of LSis will be too much for the 7500. I've run a pair of a number of different Marantz receivers, and they are not terribly difficult to drive, but you will want an amp for some of the speakers for sure if you plan to go LSis all around. I currently run 5 identical 4 Ohm speakers which are nearly identical in spec to LSi9s on my 8300 and I found that adding monoblocks for just the main pair made a noticable difference in my system.
 

Mark Porta

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Thanks for everyone's input. What is a monoblock? Is this a type of amplifier?
And if I decide to use one, do I need to adjust volume w/ it, or will I be able to use the current volume adjust on receiver?
ps I just replaced the CSW MC300 Center w/ the LSiC.
 

John Garcia

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Monoblock = 1 channel amp. You will set the gain for the amp to the level you need and then volume is controlled by the receiver. This is the way all external amps will work.
 

JeremyErwin

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a monoblock is a single channel power amplifier-- one for each speaker.

Although the LSi7 may be described as 6 ohm, the LsiC is considerably harder to drive.

source
 

Mark Porta

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What are the options for separate amps? Are the monoblocks for just the L/R, or do I need three (Center as well)? Is there an option (relatively cheap) to drive all 3 w/ one piece? I'm beginning to believe that I may have bitten off too much!!
 

IHT_Dave

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Dave Peck
If he goes LSi's all around, how about just upgrading the receiver, Adcom makes the GFR 700, a $1900 receiver that will man handle a 4 ohm speaker, seperate amps will wind up costing almost that don't you think. I'm in the same boat, I'm looking at the LSi in walls, and I'm jumping between the Marantz, Denon, and Adcom, the Adcom has more power, lower THD, ans all around seems like a better receiver, you can't bi amp with it alone, but it looks to have all the power it needs.
 

SethH

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A good option for amps is Outlaw Audio. Their mono-blocks are $325 each or you could get their least expensive 7 channel amp which is $700 and puts out 115 watts/channel at 4 ohms.

The monoblocks would provide better quality, but the 7 channel would cover all your speakers and should be plenty of power. Either one should work well in your system.
 

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