8 ohm vs 4 ohm (amp) to 8 ohm speakers question

Leave your amp setting at 8Ohm.

Electrical engineering-masturbation? Impressive...

Your amp has an 8/4 ohm switch for a reason - To match it's output with the load it's driving.

**** off troll.

Powering your 120 watt speakers with a 200 watt amp is fine. It will not blow your speakers.

If you switch the amp to "4 ohm", it will put out a lot less power. Oddly enough, that is more likely to blow your speakers, but only if you turn it up so loud that it distorts badly.

There is one reason why it might be reasonable to run the amp in "4 ohm" mode: it will use less power. And if you are only listening quietly anyway, you could save on your electric bill and maybe keep the room a little cooler.

-Max

of course if the amp does 200w x 2 and switching it to 4 ohms doubles the watts output the amp produces. So you would have 400w x 2 @ 4 ohm vs 200w x 2 at 8ohm. Definaly much easier to blow those speakers if set to 4 ohm.

on a side note, would 4 or 8 have less/more inteference?

You just want to set the switch to match the speakers. If the speakers are 4ohm use 4 ohm. If they are 8 use 8

I think they do this because some people want to stack speakers.

If you run 4 8 ohm speakers you stack 2 in paralell it drops the impedance to 4 ohms when you stack the 2 8ohm speakers. (when you twist both + and - wires together and run both off the same output) this is the most common mistake people do that blows amps.

You dont gain power by just moving the switch to 4 ohms you gain the power when the amp sees the 4ohm load so its not more powerful untill you hook the 4ohm load to the amp.

Just remember the lower you go in ohms the closer you are to a direct short. The lower you go the harder it is on the amp. More heat, more power it needs

maxcooper is the only one who directly addressed the question (sorry guys). In most designs, switching the amplifier to 4-ohms lowers the rail voltage so it won't overheat driving a low-ohm load. So a bit less dynamics and maximum output, with the benefit of lower power consumption, lower heat at all times.

So much wrong here.

No and no.

The reason you have that switch on the back to change power settings is because the amp maker didn't give it enough "balls" - electronically speaking - to allow it to drive 4 ohm speakers without heating up - at least larger speakers. Many amps are rated for 4 ohm loads - some even 2 ohm loads and don't have or need any form of switch when using low impedance speakers.

An amp puts out VOLTAGE-NOT WATTAGE. The wattage is a result of this voltage(squared) divided by the impedance of the loudspeaker.

It is EXTREMEMLY UNLIKELY that his receiver will be able to "produce" twice the wattage into 1/2 the impedance. There have only been a couple of amps in history that are able to produce this theoretically perfect amp.

Typical home receivers are NOT on that list. You will be able to have twice the power available-up to the point that the amp runs into current limiting-and at that point the voltage rails will no longer be as high and the amp will clip.

And let's say that he has one of those "perfect" amps. Since the "wattage is a result of the impedance-it does not matter what the amp can put out-except at the impedance of the loudspeaker-it will not "automatically" "get" the additional wattage even if it could "produce" 800 watts with a 2 ohm load.

Not the ones who know what they are talking about.

That switch does NOT force the amp to operate at 4ohms. Amps don't have a specific impedance. Speakers do. And the connected speaker dictates how an amp operates. An 8ohm speaker presents an 8ohm load to an amp and the amp will operate at 8ohms. A 4ohm speaker presents a 4ohm load, so the amp operates at 4ohms. An amp will TRY as best it can to operate at whatever impedance it is presented with by the connected speaker. If the impedance is too low, though, the amp will overheat trying to deliver power at that impedance.

Think of a speaker's impedance as a drain in a sink. The lower the impedance, the faster water will drain out of the sink. Think of the amp as the faucet. Now, if you want to keep the water at a constant level in the sink while it is draining at an 8ohm rate, you can set the faucet at a particular rate and the water level will remain constant. But imagine that you lower the sink's impedance to 4ohms and water drains out of the sink faster. You try to turn the faucet up higher, but it can't keep up because it can't deliver water that fast. Eventually the sink will be empty.

That is what happens when an amp tries to deliver power to a speaker with a lower impedance than the amp is adequately capable of keeping up with. It tries to deliver the power as quickly as the speakers can use it, but it can't keep up. Eventually it overheats trying.

What the impedance switch does is lower the voltage that is delivered to the amp so that it will operate at a lower temperature when it is asked by a 4ohm speaker to operate at 4ohms. So, basically, it is being throttled back and will actually deliver LESS power than it would were it left set to 8ohms. With a 4ohm speaker you COULD leave the switch set to 8ohms, and the amp WOULD try to drive the 4ohm speaker, but it might overheat trying to deliver power at that rate. That's why there is a switch. And the switch doesn't open up the faucet. It shrinks the size of the sink.

Ideally, with 4ohm speakers, you want an amp that can operate at 4ohms. An amp that can deliver power at that rate.



Well, some amps claim to deliver twice the power when they are presented with half the impedance. But they really don't. But that is neither here nor there. That is irrelevant to you. Speakers have an impedance. Not amps. And the impedance switch does NOT dictate an operating impedance to the amp.

With an amp that is rated as 200w/ch @ 8ohms or 400w/ch @ 4ohms, you have to connect a 4ohm speaker to it in order to get the 400w. The speaker dictates how the amp operates. With an 8ohm speaker, that amp will only deliver 200w. There is nothing you can do to make it deliver more watts to that speaker.

Your speakers present an 8ohm impedance. Leave the impedance switch set to 8ohms. You will not gain ANYTHING in switching it to 4ohms. NOTHING. In all likelihood, even with 8ohm speakers, that would be detrimental.


Capeche?

NP. It's understandably confusing. I mean there's a switch there that says 4ohms. That must mean it will make the amp operate at 4ohms, right? Well..................... no.

It means that the amp will operate more effectively with a 4 ohm load attached and the switch in 4 ohms.

But ALSO remember that loudspeakers are NOT the impedance of the stated number. They are most often much higher than the rated value. That "value" is the MINIMUM they will reach across their freq band.

In the tubes amps of yesterday-there was very often a switch or switchable plug that you would move to match the load to the amp. The amp would drive any load (as long as the load was not much higher than the amp was rated for-tubes like shorts-NOT opens)-but you would get maximum power transfer with the switch in the matching position.

Thats not entirely true either. The value is the nominal rating of the speaker. The actual impedance can be higher, like you said, as well as lower. This depends on the frequency.

This is correct. Many speakers rated at 8 ohms will have "dips" down to as low as 4 or 5 ohms, sometimes even lower. Reading the specs from the manufacturer would tell you what the dips are - if they publish the figures/chart.

IIRC Klipsch RF-7s have dips down to 3.2 ohms. They are rated as 8 ohm speakers.

Correct. The generally acceptable minimum should be no lower than 10-15% below the rated value. But that is really up to the manufacturer.

Part of the reason you see "common" numbers such as 4-8-16 ohms is that is what people "understand". If you use a rating such as 7 or 5 ohms-it REALLY confuses people and they have no idea what amp to buy since they can't find one that is rated at that "weird" impedance.

So manufacturers choose the closest "common" value and call it that.

Of course the REAL way to determine what YOU think the impedance should be is for manufacturers to publish impedance CURVES-not just a single number. But since most consumers do not know how to read a graph or understand it, most don't even bother as it will just confuse them.

What Danley does is to give the "rated" impedance and state the lowest value and at what freq it occurs, AND show the actual measured impedance curve.

With all of that, you should be able to figure out what you need. Yes there is more to it-such as the phase of the impedance which can wreek havic if it gets "out of bounds", but that requires a deeper understanding.

I don't know exactly what you mean by "more effectively", but I'll have to say you are wrong. With a pair of 4ohm speakers, provided the amp can handle the load, not switching the impedance switch to "4ohms", and simply leaving it at "8ohms", is the better option. If the amp can't drive the 4ohm speakers when operating normally (the 8ohm setting), then the 4ohm setting can be used, but the amp will run less than optimally. Cooler, yes, but not as optimally as its normal mode.

My advice to someone with 4ohm speakers and an amp with the switch would be to try to run them with the amp running normally, set to "8ohms", which will provide optimal performance. Depending upon how low the impedance actually drops as well as how robust the amp is, there may be no problems with doing this. There are many AVRs that do not have such a switch and are not rated to be able to support a 4ohm load yet they do fine when asked to drive many 4ohm speakers.