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Customer Discussions > Amplifier forum

4 ohm problems/confusion. Please help.


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Showing 1-23 of 23 posts in this discussion
Initial post: Mar 4, 2009, 3:30:27 PM PST
Jeff 27514 says:
Hi,
I just bought a pair of Polk Lsi 15 speakers. They are rated at 4 ohms. My old Sony 5.1 receiver is rated at 8 ohms. I was wondering if someone with some experience could answer a couple of questions for me:

1. Is is safe for both my speakers and receiver to run them?
2. Could you recommend an affordable set up to resolve this issue?
3. Is there a decent 5.1 or 7.1 receiver that could appropriately power these monsters? Or, will I absolutely need to buy pre-amps?

I currently have the bi-wired but the sound is still not up to par. Any help and/or advice would be greatly appreciated. I was also told NOT to bi-amp on the same receiver using a+b speakers.

Thank you,
Jeff

Posted on Mar 10, 2009, 3:08:56 PM PDT
Brendan Ford says:
Many 8 ohm amplifiers will safely run 4 ohm loads, and most pro models are even rated down to 2 ohms, but check the specs on the amp to see the impedance range (ohm range) for your particular amplifier. And note that whatever the power output of your amplifier (watts) is at 8 ohms, it will be essentially doubled at 4 ohms. So be careful not to overdrive the speakers, especially speakers that cost that much ;)
Another option is to put a 4 ohm load in series with each speaker. This load could be another 4ohm speaker or a 4 ohm resistor. I don't suggest using a resistor, but if you do, make sure it is a high power resistor.
BTW: I don't think you meant to say 'pre-amps' as that will have no effect on the output impedance.

I hope that info helps,
-Frd

Posted on Mar 10, 2009, 7:19:41 PM PDT
Jeff 27514 says:
Thanks! Yeah, I meant that I would most likely use my receiver as a 'pre-amp' and buy 2 amps, one for each speaker. Thanks again!

Posted on Apr 14, 2009, 11:13:32 PM PDT
Daniel says:
Surely that post doesn't really say that you just got new speakers and now blame the amplifier for the lack of performance?

Okay, perhaps it is the amplifier. One rather inexpensive way to tell is to substitute either "known good" speakers or "known good" amplifier. For about 40, Parts Express has a miniature Tripath amplifier with a good reputation. Sure, that's a bit small, but I'm suggesting to use it for diagnosis, and then re-employ it later as a computer amp or bedroom system. Otherwise, you may just have to count that new speaker purchase as a mistake and buy yet more speakers. That may not work. SO, do find out whether its your amp or your speakers. I'd suggest placing the blame on the most recent change, which is the new speakers. It should be possible to upgrade the crossover on most retail brand speakers, so that is also an option.

In reply to an earlier post on Apr 15, 2009, 8:53:09 AM PDT
Jeff 27514 says:
Thanks. But yes, I have learned that a set of home (front/main) speakers that are rated at 4 ohms require an amp that can deliver a significant amount of wattage to each speaker. My old Sony amplifier (STR DE325) 5.1 is only able to provide each speaker with about 50 watts maximum. The Polk Lsi 15's are rated from 50-200 watts each. Additionally, my amp/receiver is not rated to power 4 ohm speakers, just 8 ohm. So, this means that the 50 watts my amp could be providing each speaker is reduced to 25, which does not fall in the recommended wattage range for these speakers.

To solve this problem, and I appreciate all the feedback and assistance I have received from you kind folks, I purchased a Rotel (RSX 1067) amp/receiver 7.1 rated at 100 watts per channel at 4 ohms. This amp has 7 dedicated amplifiers built into it, so each speaker channel will have it's own amp. This amp essentially increased my wattage to the speakers 8 times that of my old Sony. After speaking with a Polk Audio representative, they confirmed that I would need to upgrade to a more powerful amplifier, such as the Rotel, to get these speakers to perform correctly. Look at it in the same way some high performance vehicles require a higher octane fuel to make the engine run at manufacturers specs.
Thanks again.

Posted on Apr 15, 2009, 8:55:41 AM PDT
Last edited by the author on Apr 15, 2009, 8:56:28 AM PDT
Jeff 27514 says:
Again, to clarify, I am able to get my new Polks to play music with my old Sony, it's just not providing these speakers with the correct amount of power and, therefore, the fidelity range on these speakers is reduced/compromised.

Posted on May 3, 2009, 3:23:56 AM PDT
Last edited by the author on May 3, 2009, 3:25:39 AM PDT
Lsi says:
Most midrange amps are not designed to handle this type of impedance load, it would cause them to overheat and possibly damage themselves in the process. It would also likely cause them to distort and clip prematurely, which could damage your speakers. Speaking from personal experience, Yahama amps normally do have a selection in the amp (special sequence prior to normal power on) to support 4 ohm loads despite being rated at 6-8 ohm stable. I have used them successfully with some 4 ohm speakers models such as B&W and Totem. Rotel amps which were mentioned previously are an excellent choice and provide great value for your dollar. I speak from experience... ;-)

Posted on May 3, 2009, 4:33:50 PM PDT
Ken says:
hi, Rotel RSX 1067 is a receiver. Are you sure you can use it with out a amplifier?

I have Denon AVR-989 try to run LSi15 and LSic.

I plan to get a amplifier.

Posted on May 3, 2009, 4:39:27 PM PDT
Ken says:
BTW, where you bought your LSI15 and how much you paid?

Many ppl suggest a dedicated power amplifier, so you receiver will need a pre-out port.

In reply to an earlier post on May 3, 2009, 5:23:05 PM PDT
Jeff 27514 says:
After a lot of research I bought the Rotel. I would word it this way: The Rotel RSX 1067 is a very powerful 7.1 amp that has a receiver. It has seven dedicated 100 watt amps to easily power any 7.1 system or you can run a two channel set up. It is a monster! It's rated for 4 ohm speakers, as well. With the RSX 1067 you don't need an additional amp. It easily powers the Lsi 15's.

Posted on May 3, 2009, 5:25:29 PM PDT
Jeff 27514 says:
Check out Polk Direct for refunished pairs at half price.

In reply to an earlier post on May 13, 2009, 9:30:45 PM PDT
KBIC says:
Jeff

Good choice! I love Rotel equipment.

In reply to an earlier post on May 13, 2009, 9:32:42 PM PDT
KBIC says:
ABFG

Tipacly, rotel recievers have their own power but you can also by pass that with external power amps.

In reply to an earlier post on May 13, 2009, 9:46:54 PM PDT
Jeff 27514 says:
Thanks! I'm very pleased! Clean and loud!

Posted on May 13, 2009, 9:50:50 PM PDT
Jeff 27514 says:
Now, I want to get a Denon turntable and pre-amp, and run it through the analog bypass on the Rotel... Should sound sweet.

Posted on May 13, 2009, 10:28:26 PM PDT
Ken says:
Rotel RSX 1067 have HDMI port?

I am using a PS3, so all my audio and video are to the receiver, and then to the TV and speakers.

In reply to an earlier post on May 13, 2009, 11:12:55 PM PDT
Jeff 27514 says:
Yes, it has HDMI ports.

Posted on May 14, 2009, 7:44:48 AM PDT
Ken says:
how much you paid for the Rotel RSX 1067?
I may want buy one, thanks

In reply to an earlier post on May 14, 2009, 9:44:29 PM PDT
KBIC says:
I am running this for my stereo.

Music Hall MMF 7.1 turn table

iKey, to record analog to digital (MP3 or WAV).

A JVC TD-W106. I would love to upgrade this but I just don't use it often enough. The upgrade would be for recording to computer.

A Sony 300 CD carousel. I would love to replace it with a Rega CD player.

A Rotel RDP-980 DA converter

A Rotel RC-1090 Pre-amp

Two Rotel RB-990BX 200 watt amps

and a set of B&W 602s

I am running the TT into the Phono Preamp in the Preamp
Big system, simple application.

I am not a fan of Denon turntables but they are a good product still.

In reply to an earlier post on May 14, 2009, 9:46:54 PM PDT
KBIC says:
Jeff

That reciever is a big beastie!

ABFG

New it looks like 2000. Used about half or less.

In reply to an earlier post on May 14, 2009, 11:15:42 PM PDT
Jeff 27514 says:
Great set-up, KBIC! I'm just starting out and need to slowly piece it together over time, given my entertainment budget and not turning the living room into a "bachelor pad" as my girlfriend says... I lucked out and found a used one on Ebay for around 500. It had a broken speaker terminal ~ fixed for 150. Otherwise in mint condition. It did not come with a remote, that will set me back about 180. Overall, a great find. The guy I bought it from sold it as-is, he bought it at a farm auction and was not aware of the quality.

In reply to an earlier post on May 15, 2009, 11:26:43 AM PDT
KBIC says:
Jeff

What a deal! I got my first amp for 600 then later got the second for 400. I got the preamp for 600 as well. I found them all at a used hi-fi web site called audiogon (www.audiogon.com).

In reply to an earlier post on Jan 8, 2010, 4:50:34 PM PST
Last edited by the author on Jan 8, 2010, 5:13:08 PM PST
Make sure your receiver can handle a 4-ohm impedance. Most problems with poor sound is due to improper wiring and or poor quality cables. Also, you need to match your speakers power handling and your receivers ability to provide the required power. It is normally more advantages to have a power amplifier that can deliver more power than your speaker can handle. This results in good "Headroom"(the receivers ability to provide the required power without being "Overloaded" (pushed beyond the limits it was designed for) Remember, you need more than just a subwoofer to get sound reproduced in the full audio spectrum, 20-20,000kz Good Luck...
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This discussion

Discussion in:  Amplifier forum
Participants:  7
Total posts:  23
Initial post:  Mar 4, 2009
Latest post:  Jan 8, 2010

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