I’ve been comparing several amps. The Manufacturer’s Spec’s normally show the power into 8 Ohms 5 channels driven along with the power into 4 Ohms 5 channels driven…and some even give into 2 Ohms. There’s one exception though. The Classé CT-5300 (CA-5300) spec’s only gives into 8 Ohms 5 channels driven. In Home Theater’s Review of the Classé CT-5300 they found this 300W amp, into 4 Ohms, consistently engages protection at 190.0 watts and cannot be driven further. Here's a link to the article from the Home Theater Review of the CT-5300. Here's another link to the article from the HT Review of the CT-5300...this one shows the actual Home Theater magazine pages and is a link right off Classe's website!
I have B&W 802D Speakers which are all 8 Ohms, but I was told by more than one dealer that as the frequency of the sound goes down, the impedance goes down and even an 8 Ohm speaker could go down to 4 Ohms or even lower. Being a newbie at this I don’t understand how this happens but I trust the information that I’ve been told. I read in the AVS Forum Thread “Can I use my Harman Kardon 3490 with Magnepan MMG?” in post #6, the following:
There is one important concept you need to remember when shopping for an amplifier or receiver: the power should double (or nearly double) at 4 ohms. This concept applies even if you are buying an 8 ohm speaker. If the amplifier is rated at 80 watts at 8 ohms, it should produce 160 watts at 4 ohms (or close to it). None of the receivers will do that. However, this is the benchmark of a good amplifier design.
A good receiver might produce 30-40% more power at 4 ohms. Most receiver manufacturers don't want to talk about 4 ohm ratings, because they have cut the "guts" out of their products to keep the cost down. Some receivers produce the same power at 4 ohms as the 8 ohm ratings. Or they use a switch on the back for 4 ohms to reduce the power and to prevent the receiver from self destructing. Others warn against 4 ohm speakers. Regardless of what speaker you buy, we don't recommend these receivers. There are a few manufacturers making receivers with good 4 ohm capability. 4 ohm capability "separates the men from the boys".
I contacted Classé about the Home Theater Lab Results. The gentleman I spoke with was very nice. At first he told me this must be a misprint. I replied that this review was written over 3 years ago and this remark is a significant issue and if it was a misprint Classé most likely would have contacted Home Theater and had them correct their statement a long time ago. I later received an email from Classé and the following is what Classé had to say about this: I was not able to get any specs for the CT-5300 operating at 4Ω. The reason why the 4Ω specs are not published is due to the fact that our 15A or 20A outlets cannot supply sufficient current to drive these 5 channels at full power into 4Ω. In fact, it is not recommended to use the CT-5300 with nominal 4Ω speakers, you would be limited in terms of volume due to current limits.
Has anyone heard anything about this 4 Ohm issue with the Classé CT-5300 Amp?
The reply that you received is basically what is known as "weasel wording". Any power amplifier that I would consider buying would show power ratings into 4 ohms (or lower), for the simple reason that many loudspeaker impedance curves dip below 4 ohms. The impedance curve you're seeing with your 802s isn't unique. Apparently the amplifier vendor had to limit available output current in this particular design (or something else has been compromised) and doesn't want to spec output power into lower impedances. That talk about 15 ampere wall sockets is total BS.
FTC requires the manufacturer to precondition the amplifier at one third power for an hour before making any performance measurements. I suspect that when they preconditioned this particular model into 4 ohms, it probably over-heated and they couldn't make a legal measurement, so they just weaseled out and published 8 ohm only numbers. Under typical listening conditions, it probably works ok into "4 ohm" loads.
Thank you all for your help and great info. Since my 802D's are 8 Ohms and probably dip down to 3.4 Ohms only for short periods of time, I suppose it may work just fine (up to a point) with a 4 Ohm load but think it's very strange that the 4 Ohm Spec's aren't published. If there's nothing to hide, publish the Spec's and see how it compares to other manufacturer's amps.
Thank you again. You guys are great. I'm learning a lot from all the nice folks on the AVS Forum and hope to have my system ordered and hooked up real soon. My brother is already jealous.