Speaker Imepdence Question

[lakshmant]

Could a speaker with a nominal impedance of 4 ohms be driven by any normal AV receiver to normal sound levels of 65-70 db. I know impedance changes rapidly during speaker operation. But would these really be so hard to drive when compared to a 8 ohms speakers. I understand that the nominal impedance is only a average calculation which is made.

Laksh

 

[jamie2112]

Most AVR's wont handle 4ohm speakers very well. I would recommend getting an amp to power the 4ohm'ers. I know of a few folks who have burned up their avr's and speakers by not powering them properly.......

 

[NoSnipeLimit]

Actually doesn't seem like a bad idea if you look at this: Google: increasing q with 4 ohm resistor

Was totally above my head for understanding, but parts i could understand from the guy with the PhD seemed that it's not a bad idea...

 

[GO-NAD!]

Can anybody answer this for me - why do so any companies manufacture speakers of 4 ohm impedance anyway? Is it a consequence of trying to induce certain sonic characteristics from the drivers? Is it easier to make better sounding drivers of lower impedance? Are 8 ohm speakers made in order to attract buyers who don't want to invest in high-powered amps?

 

[Lordoftherings]

TLS Guy is your man.

The average speaker's impedance from all the speakers in the world, is 6.48339 ohms.

Some have peaks as high as 80 ohms+, and some have dips as low as 0.2 ohm or less.

I suggest that you read some good articles about speaker impedance and matching amplifiers. There are some right here at Audioholics, and also at Secrets of Home Theater and High Fidelity.

Or just Google it.

It would take me an entire thread to explain all the derivatives of this very complex electrical subject.

But the person here at Audioholics, that could best explain briefly the ins and outs of impedance from speakers vs. matching amplifiers or receivers, is the TLS Guy.

Bob

 

[3db]

Could a speaker with a nominal impedance of 4 ohms be driven by any normal AV receiver to normal sound levels of 65-70 db. I know impedance changes rapidly during speaker operation. But would these really be so hard to drive when compared to a 8 ohms speakers. I understand that the nominal impedance is only a average calculation which is made.

Laksh

Yes and no. Sorry for the confusing answer but its not as simple as just low impedance. Things I need to know is.

a.) The size of the room.. A small room and any receiver from Yamaha, Pioneer, Denon, Marantz will be able to drive your 4 ohm sspeakers without clipping or tripping of the receiver's protection circuit. 65-70 db is not loud at all.
b.) Sensitivity of the speakers. If they are low senstivity and in a small room, you still may get a way with being able to use a reciever. If its a high senstivitiy speaker in small room, a receiver will definately be able to drive them to the levels you are asking about. Low senstivity big room,,better get a NAD, Rotel, or H/K. or a power amp.

 

[Lordoftherings]

Could a speaker with a nominal impedance of 4 ohms be driven

Not if there is no amplifier or receiver to drive it.

Or do you mean driven over by a car?

 

[fredk]

There seems to be a lot of confusion over what can and cannot drive a 4 Ohm speaker. My mains are between 4 and 5 Ohms up to about 500Hz so they probably spend a fair amount of time drawing power in the 4 Ohm range. FWIW, I am running dual centers at 4 Ohms as well.

I am currently using a very inexpensive Sherwood RD-6500 receiver in a small (20' x 11' x8') room. I can drive my speakers to very high levels (95db) with no noticable distortion and the receiver is not pushed into protection. The point here is that price is not necessarily an indicator of amplifier quality/ability.

Audioholics recently published an article on the tradeoffs between features and amplifyer power. Basically, to get a feature rich receiver like the Yamaha RX-V663 to such a low price point, you need to trade off amplifyer power/quality (cheaper components). More features = less money for amplifier components.

Where does that leave us? Sure, you can go to more expensive equipment like NAD or to an outboard amp, but there are still lots of receivers that can handle a 4 Ohm load.

A list of receivers known to drive the Axiom M80:
1. Anything Dennon (which is why it is such a popular reciever on the Axiom forums)
2. Anything in the Pioneer elite line
3. Onkyo 7 and 8 series
4. Anything Sherwood Newcastle (and from my experience probably also the lower line Sherwood)
5. Some of the Higher end Yamaha though I know of one person who had issues with an RX-V1800
6. Most things Harmon Karden
7. More recent Maranz (they seem to be returning to higher quality components)

From the list, you can see that you need to be careful, but there are plenty of reasonably priced receivers that will do the Job.

FWIW, in my room at my listening distance 95db with about 15 db of head room for dynamic range uses about 68w of power so I am by no means pushing my receiver. My mains are 91db @ 1m @1w. (fairly efficient).

 

[bandphan]

Can anybody answer this for me - why do so any companies manufacture speakers of 4 ohm impedance anyway? Is it a consequence of trying to induce certain sonic characteristics from the drivers? Is it easier to make better sounding drivers of lower impedance? Are 8 ohm speakers made in order to attract buyers who don't want to invest in high-powered amps?

I dont think maufacture say lets make a 4ohm or 8ohm speaker. The load is based on the drivers, wiring, and crossover. There are many speakers a high sensitivity and that are 4 ohms. Even companies like klipsch make speakers that dip bellow 4ohms.

a refresher on Ohms Law.. http://en.wikipedia.org/wiki/Ohm's_law

 

[Lordoftherings]

???

The average speaker's impedance from all the speakers in the world, is 6.48339 ohms.

Some have peaks as high as 80 ohms+, and some have dips as low as 0.2 ohm or less.

Bob

??? No comments?

 

[3db]

Gawd knowss I've harped on this topic many times before...here I go again.

A speaker is comprised of two electrical characteristics, resistance and reactance. Resistance is basically a dc term which is measure of current flow through a conductor and measured in ohms. Reactance is an ac component, is also measured in ohms and is a resistance to ac current flow. Another thing to note is that reactance is also affected by frequency of the current moving through teh conductor. One last thing to know is reactive components tend to makesthe current lead or lag the voltage and is measured in degrees. Impedance is a mathematical combination of both dc resistance and ac reactance. Speakers have an impedance which means both dc and ac components and it varies with frequency.

So now you have a receiver driving a speaker whose impedance varies with frequency. Now as teh impedance dips, the receiver's power supply will try and push more current through the speaker. If the speaker was purely resistive, even a 2 ohm dip would not be so bad provided the room was small and teh sensitivity high. However, throw the effect of leading or lagging voltage because of the reactive component of the speaker and the amp has to work even harder than it would if the speaker is purely resistive. The large the phase angle ( angle of current leading or lagging voltage) the harder the amp has to work again.

Hoepfully this helps explains impedance to you a little better. That being siad, I still am stickiong with my recommnedations in my previous post.

 

[Lordoftherings]

^ Great stuff.

+1 Way to go 3db. ^

 

[FNG212]

??? No comments?

I think people are wary of trying to question you or call you out

 

[bandphan]

Gawd knowss I've harped on this topic many times before...here I go again.

Now you get what ive been saying

 

[Lordoftherings]

I think people are wary of trying to question you or call you out

That's good, because I know I'm absolutely right.




Till someone proves me wrong.



And this, is for you personally:

 

[Lordoftherings]

Now you get what ive been saying

Yep, me too, I did not say it, but I did thought of it.

 

[bandphan]

I think people are wary of trying to question you or call you out

Speak for yourself. If you have a question ask it or if you don't agree state it so a healthy debate can ensue.

 

[Lordoftherings]

^ Ya man. ^

^ Very well put it. ^ I couldn't say it better myself.

 

[TLS Guy]

Can anybody answer this for me - why do so any companies manufacture speakers of 4 ohm impedance anyway? Is it a consequence of trying to induce certain sonic characteristics from the drivers? Is it easier to make better sounding drivers of lower impedance? Are 8 ohm speakers made in order to attract buyers who don't want to invest in high-powered amps?

Speaker impedance specifications mean nothing! Speaker impedance curves are usually complex. However, narrow fronted speakers are going to drop their impedance below 400 Hz for diffraction compensation. For a common 2,5 way speaker, (two woofers one tweeter on top), two thirds of the power will go to the woofers where the impedance will be 4 ohms or less, except at the narrow tuning peaks. If a speaker has two or more woofers it is four ohms, no matter what the manufacturer says. Not only that, voltage and current are always out of phase to some degree, so the current draw will be higher than you would think.

Now transistors amps are limited in the rail voltage because of the breakdown characteristics of semiconductors. So to get power, impedance has to be 8 ohms or less. So an amp really has to be able to drive a four ohm load, or you will not get the power you think. Because of THX certification, receivers do not generally blow up with a four ohm load, but they can't increase current. So most receivers driving the vast majority of speakers on the market, are actually delivering half their rated power. The reason you don't see this as obvious, is because it is only a 3 db reduction in spl.

So if you have two amps of 100 watt power into an 8 ohm load, and one can not increase current as load impedance drops, and the other can. Then then the first amp will be a 50 watt amp driving most speakers, and the other will be a 200 watt amp. That is a significant increase in spl.