All -

I purchased a set of Emotiva ERD-1s (http://emotiva.com/erd1.shtm)for my side and back surrounds.

They are rated for 4ohms. I am going to be hooking these up to an Onkyo TX-SR605 (http://www.onkyousa.com/model.cfm?m=TX-SR605&class=Receiver&p=s) receiver
The Onkyo specs have speaker impedance that's rated 6 - 16 Ohms.

Called Emotiva (great customer service BTW) and the rep said that it's not an issue at all and should not cause any damage to receiver or speakers given they are surrounds. Can someone explain technically what exactly is going on when I hook up 4ohm speakers to the 605 and if I should worry at all of efficiency etc?

I have Klipsch mains that are higher efficiency/8 Ohms but understand that it doesn't really make a difference sonically.

On a side note, are there any Klipsch owners who run Emotiva surrounds?

Using (nomimal) 4-ohms instead of 8-ohms speakers draws twice the current from the amplifier, and it may not like that and overheat.. surrounds or not.

Yeah, don't listen to the speaker manufacturer because they have a vested interest in making sure you buy and use their speakers, and if you blow your receiver, it's not their problem.

Call the receiver company because they have a vested interest in making sure you don't blow their stuff up.

The manufacturer is not crazy and I doubt they would mislead to make a sell. Your receiver is capable of 90W/ch x 5. It also has reading for both 8ohms and 6ohms which is a good indication the receiver can handle lower impedance. Since these are surround speakers it's very unlikely you will have enough information in the surround channel, or drive them at high enough volume to cause any problem.

I have three different receivers, Yamaha, Sony and Denon. Two are rated at 100W/ch which in real terms, is not much higher than your 90W/ch. I have successfully driven 4, 6, 8ohm and mixed sets without any problems. You will only have a problem if you attempt to turn the sound up to a ridiculous levels. The average user, depending on speaker efficiency, will only use an average of 15W-30W/ch at a good volume when watching movies.

Don't worry, your receiver will handle the load as long as you don't play it "stupid loud".

Connect the ERDs up and see how they work. If the 605 overheats and shuts down you'll know to send them back. I'm betting it won't.

The reason I can say that is I have those speakers - with a pair of ERTs for mains. When my Onkyo SC885 broke and had to be sent out for repair I put an Onkyo 506 to work while waiting for the 885 to come back. In the three weeks I used it for my HT use it never shut off and didn't run all that hot. Emotiva speakers are all rated at 4 ohms but they don't have severe dips below 4 ohms like some speakers do. The 506 isn't nearly the AVR that the 605 is so I don't think you'd have any problems.

I think overheating is your main concern.

I would tend to agree with that Overheating .

It also depends on how much wattage and duration of usage per session

one uses them . 40 watts two hours 4 Ohm is far easier than
70 Watts for 6 Hr. 4 ohm on a rated 6-16 ohm receiver .