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Discussion Starter · #1 ·
I recently purchased Polk Audios LSi15's,LSiC Center Channel, and LSiFX surround speakers (all 4 Ohm speakers). I was informed in another thread that my TX-SR705 will not have enough power for these speakers without a seperate amp. Not being very well versed in these compatibility issues I am turning to those of you who can help me. I am looking for some suggestions on either a replacement reciever (but I love my 705) or some choices on compatible amplifiers that will bring the 705 up to snuff. Thx for your help.
 

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Based on specs alone, no, the 705 is not up to the task.


I would either trade it in for an 805, 875 or 905 which are capable of powering 4 ohm speakers, or pick up a good multichannel power amp and use the 705 as a preamp.
 

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Quote:
Originally Posted by johsti /forum/post/14177628


Based on specs alone, no, the 705 is not up to the task.

Although Onkyo is not my AVR of choice, I disagree with johsti.


Your speakers are moderately high efficiency and will generate THX average sound levels with less than a watt per speaker.


With your AVR, you have two choices ...
  1. Set the minimum impedance switch to 4-ohms and limit the output power (& heat); or
  2. Ignore the switch and maintain good ventilation for cooling.

The switch is necessary to allow Onkyo to maintain CSA (etc.) approved operating temperatures but running it a bit warmer isn't normally going to harm it. Note: many other manufacturers do exactly the same thing!!


However, the Onkyos are regarded as running hot under normal (presumably 8-ohm) set ups so you should be particularily vigilant for over heating.


Heat aside, unless you are going to get external power amplification in the several hundreds of watts per channel, you will not gain much.
 

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Discussion Starter · #4 ·
Onkyo TX-SR805B reciever lists in the amplifier specs "Certified 4ohms performance ". Does that mean that it will power my Polk LSi's without any problems? I thought about an external power amp but didn't really want to add another piece of equipment to an already tight space. Plus I could probably sell my TX-SR705 and pick up a TX-SR805B for less than an external power amp.
 

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What I don't get, is this. If has 'certified 4ohm performance,' why don't they show a 4 ohm power rating?
 

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Quote:
Originally Posted by MichaelJHuman /forum/post/14177932


What I don't get, is this. If has 'certified 4ohm performance,' why don't they show a 4 ohm power rating?

Because lawyers have a lot of influence in product marketing. If you abuse a receiver, it will fail sooner with a 4 ohm load than with an 8 ohm load. It is the same reason they have those silly 8 ohm 6 ohm switches on some receivers People think the provide some sort of impedance matching. They don't. They simply reduce the power output. Lawyers instead of engineers.


I'll give you a concrete example. One day at an audio store, they had a Pioneer 94 driving a pair of electrostatic speakers that were a 4 ohm impedance at best. They played them loudly and they played them all day and the 94 never broke a sweat. It even had an oscilloscope connected to one channel so you could see visually that there was no clipping. Yet the 94 is only rated for 6 ohms. That's lawyers, not engineers.


It's very simple. The lower the impedance, the higher the current draw. The higher the current draw, the more potential performance problems occur. Let's try to keep people using higher impedances.
 

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I'm going to disagree with cavu. LSi15's are power hungry, 4 ohm speakers. Plus, all of the other speakers in your setup are 4 ohm as well. I have no doubt that the 705 can power a pair of 4 ohm speakers to reasonable levels, but I would be concerned about using it to power 5 four ohm speakers simultaneously. Also, Onkyo does not recommend using 4 ohm speakers with the 705 and below models.


Try it out and see if it works. If the receiver keeps shutting down, sell it and get something else or add an amp.


The Integra website shows the power ratings at 4 ohms.
 
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