4 ohm Question (PSB speakers, ???? amp...)


New member
Username: Bmwk

Post Number: 1
Registered: Mar-04
Hello all,

I stumbled across your board and after reading a number of your responses got the feeling that some of you may actually know what you are talking about!

This topic could go any number of places: amps, speakers, AVR. Given that this forum seemed to be the place to get Ohm information, I thought best to post it here. If I am wrong in my location, please forgive me.

I recently purchased a set of PSB Silver Stratus i's (also, PSB C5i center and a Subsonic 7). It never dawned on me that I might run into Ohm issues when I bought them. I simply love their sound. In testing no less than 20 different speakers up to $5k, the PSB's were one of the only ones to truly touch my soul...

What I am looking for is understanding precisely what the 4ohm vs. 8ohm issues really are in real world, simple english!

My "amp" is actually an older Yamaha RV703 AVR. On the back of it is a little switch marked for 4 ohm and 8ohm settings (ok, simplified, but you get the idea). I set it on 4 ohm and haven't had any real issues. In swapping between the 8 ohm setting and 4 ohm settings, it seems that the 4 ohm setting sounds a little cleaner, clearer.

Ok, my question (sorry for being long winded): I have read several times about someone's 8 ohm amp not being able to drive their 4 ohm speakers. Can someone PLEASE explain to me what they mean when they say they can't drive the speakers???

Does that mean they can't drive the speaker to 90db+ without overheating the amp? Does this mean they simply plug the speakers in and regardless of volume position get absolutely ZERO response out of the speaker?

Or, perhaps more apt, is this a case where the 8 ohm amp simply generates way too much heat trying to drive the 4 ohm speakers and thus, burns itself out?

Or, worst case of all, the SPEAKER itself burns out???

Anyways, the main reason I ask is simply because I intend to upgrade the AVR to a "bigger/better" system - separates most likely (ala Outlaw monoblocks/7channel amp & Preamp) or possibly another integrated AVR assembly...

From a musical perspective, I simply love 2-channel stereo but do enjoy the occasional movie. Calll it 80% music, 20% HT. As a result, when I do upgrade, my main focus is to be music.

So now that I am looking for an amp to drive the 4 ohm speakers, the question is "what the hell am I looking for????"



Silver Member
Username: Gman

Mt. Pleasant, SC

Post Number: 284
Registered: Dec-03
The 4 ohm switch prevents the amplifier from overheating. It depends on the type of switching the 4 ohm switching has. It will either limit the db's to prevent overheating at some point where the amp section will overheat, or it will not limit the db's, but will be temperature based and when the amp section reaches a certain temperature it will shut down.

As far as receivers are concerned, the NAD's, most HK's, Arcam's, and Rotel's generally specialize in having amp sections that perform well at 4 ohms. This is not to say that other receivers might not, but the manufacturers generally don't recommend using them with 4 ohm speakers for extended playing time.

If you go the separates route you have far more choices. There are a number of good amps that perform well at 4 ohms and above. To list some of the good ones that aren't very expensive: Outlaw Audio (online), ATI, NAD, Adcom (most models), Parasound, Aragon--etc.

Onecall.com is closing out a 5-channel ATI unit that is 250 watts (8 ohms) x 5 channels and about 375 watts (4 ohms) x 5 channels. If you are worried about better grounding to eliminate hum ATI has new double-balanced amp models at 200 watts (8 ohms) that sell in 5-channel at around $1995 and at 7-channels at around $2395. Outlaw Audio has the 770 at $1799. It is an 8 ohm 200 watt amp x 7 channels and the model 755 is $$1299 at the same power for 5 channels. These models are not balanced, but with half decent insulated interconnects you should have no hum problem or other interference.

If you want a THX Ultra 2 certified product, Aragon makes beautiful looking and solid performing amps: the 2005 is 5 x 200 watts and can usually be bought at around $2,000 and the 2007 (7 x 200 watts) can be bought at a few hundred more.

The above is just a price idea of some product. Outlaw Audio also supplies a very nice inexpensive (for separates) A/V preamp. You should check out their online site that also includes reviews from many magazines.
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