Impedance varies at different volumes and frequencies. A nominal impedance of 8 ohms means the speakers routinely draws about 8 ohms and although at certain volumes and frequencies, the impedance will drop, it won't drop far and an amp rated for 8ohms will drive them easily. As impedance declines, power consumption increases and the amp needs to work harder.

Not every amp is capable of dealing with lower impedances. If am amp is rated for 8 ohms, it wil easily handle drops to 6 ohms and will handle periodic drops in impedance to 4 ohms for brief periods which would be posible for a speaker rated with a nominal impedance of 8 ohms. Alternatively, if a speaker is rated with a nominal impedance of 4 ohms, that is the average draw and that means the impedance will drop below 4 ohms regularly and will typically drop to between 2 and 3 ohms. If an amp is rated to drive 4 ohm speakers, then it can handle these variable increases in power consumption with the corresponding drop in impedance. If it is not rated to drop below 4 ohms, it will become unstable with these increases in power consumption will blow fuses and you may damage the speakers or power amp.

You need to look at the the ratings to see if your receiver is capable of handling 4 ohm speakers. Just because it isn't obvious doesn't mean an amp is not rated for 4ohms. Is it THX certified? If it is, then you are good. Being able to accommodate variable impedances down to 2 ohms is part of the THX bench tests.

chuckles304 wrote:

I have an 8 year old Yamaha receiver rated for 8 ohm speakers. If I were to use 4 ohm speakers (say Monitor Audio Silver 8's) would that mean the receiver will work harder to achieve the same volume levels as before? Or is there something else that will go wrong? Thanks for any input.

This has been a known ongoing problem with Yamaha amplifiers for at least 30 years.

They design them with the cheapest possible power supply, which means they do not have the kind of peak current reserves needed to drive most high-quality speakers to fairly loud levels. This will cause audible distortion at higher sound levels.

My advice is to get a high-quality integrated amplifer that is properly designed. IMO Yamaha makes only very low-quality units; the worst on the market.

Some excellent amplifiers are available from Musical Fidelity, Arcam, and Creek.

If these are too expensive for you, the NAD and Cambridge Audio amplifiers are also very good and not quite so expensive.

Back in the 1980s I bought a Yamaha integrated amplifier For $800 rated at 100 watts per channel (but ONLY at 8 ohms; the manual cautioned against lower-impedance speakers). When I tried to use it with a pair of Polk RTA12 speakers, it distorted horribly.

I replaced it with a NAD 3020 amplifier, which only cost $198, and it drove those speakers to any desired loudness with no problems, despite being only rated for 30 watts or so.

It just goes to show that power ratings are frequently very deceptive, and not a good indicator of real-world performance.

Denon is explicit that it's AVRs are capable of driving speakers at 4 ohms on their website in the text for each receiver. The AVR-X5200W at $1999 is 140w per channel. The AVR-X4100 is 125w at $1499 but on sale at Crutchfield for $1299. One of the most important features in multi-channel is Audyssey and these two have THE version of Audyssey with MultiEQ XT32. In multichannel, this a monstrously valuable innovation. I find Denon amps to be neutral and extremely detailed. I love the feature set and the networking and app features are awesome.

NAD and Cambridge offer very musical AVRs that have excellent power but are lacking in virtually every other feature. They have old versions of Audyssey, mediocre video processing and lack the streaming and networking services of a Denon. Unless I had perfect speaker placement In a rectangular room or used multi-channel very infrequently, I would choose the Denon first.

I would typically also suggest Marantz, but I find Marantz power amps and AVRs struggle with lower impedance speakers.

Integra would be a good choice from a power perspective. They are THX certified and rated to 2 ohms. They are a video first receiver and because they ship standard with Audyssey Pro, can handle 3 or 4 zones, they are THE choice of pro installers. Like all Onkyo units, I find Integra (Onkyo's pro line) to be a touch bright / clinical in sound. Audyssey softens it and they sound good for home theatre but I find it unpleasant to listen to in 2 channel.

In my opinion, this forum may be a touch biased on the subject of multi-channel. A big group of people simply dislike anything beyond 2.1 channels. Second, for those willing to acknowledge that people can enjoy music or video in more than 2 channels, another group rejects anything that modifies the sound. Thus, something like Audyssey is viewed as a distortion rather than an innovation. In the end, it is a matter of personal preference so I wouldn't say these folks who offer these opinions are wrong. It is truly opinion and opinions by definition can't be wrong. But, we are also quite free to disagree.

I personally accept that both multi-channel can sound great and technology can improve it. Thus, I have a different point of view than many. This is why I am realtively sour on NAD and Cambridge and sing the praises of Denon and Marantz. If you have wildly crappy speaker placement, Audyssey can work wonders. Check out the Audyssey website. They have good explanations for how the room correction works. I used to find multi-channel to be a novelty and found it annoying. I would periodically watch an action movie in it, but otherwise, rarely used it. Now, with Audyssey, I rarely watch television without it being in multi-channel. The sound is more immersive and balanced without being a distraction. It just feels natural.

If you believe Audyssey is a value, that largely negates NAD and Cambridge as options. They use extremely dated versions of Audyssey and seem to reject streaming options like Pandora and Spotify. The one unit from NAD that is worth considering is the NAD T 777 as it has Multi EQ XT which is very good though still short Denon's offering but the unit is $3000. I believe Anthem is expensive and mediocre.

That brings us to Marantz and Denon. I have personal experience with both in that I own a Denon receiver and a Marantz Pre/Pro and Power Amp for different multi-channel applications. Given your desire to power lower impedance speakers, Denon makes more sense. I can say that my Marantz power amp does a poor job with lower impedance speakers and believe their receivers face the same issue. Denon is Marantz's sister company. They do have a slightly different sonic signature in that Marantz is a hair warm while Denon is more neutral. They are close enough that the iPhone remote apps for Denon and Marantz are interchangeable. Regarding models, the two model numbers I just mentioned are current and support Dolby Atmos. You should be able to find the prior models on Audiogon or might even find some non Atmos units still on clearance. I think the prior models were the 5100 and 4000.

I agree with bierfeldt regarding Denon; and in fact owned an X4000 AVR with Audessey 32 and was extremely satisfied with my Home Theatre experience. Regrettably, I sold it and have since replaced all of my Home Theatre gear for a dedicated 2 channel setup on British equipment. (Creek Integrated and Epos speakers).

However, I intend on keeping my current 2 channel setup, and just re-purchasing the updated version of the Denon X4000 series AVR. I agree that it is exceptional and one of the best bargains for performance out there. I will keep my 2 channel Epos Epic 2 speakers for Front R and Front L, and then integrate a center and surrounds of another brand when I get the funds to purchase the Denon.

So, in short, with the consumer audio industry at present, I feel there is no single product at a fair price that does BOTH two-channel and home theatre, and I suggest for those who have 2 channel to purchase a Denon AVR if they want 5.1 or greater Home Theatre and just adding one box plus speakers to your existing two channel setup.

Best Regards,

Ron