4 ohm Speaker Question

Sansui

From what I've read here, 4 ohm speakers really push an amp hard. How come speaker companies still make them if 8 ohm speakers are the "standard"?

sousa

Typically 4 ohm speakers are considered higher end and would require the use of a separate receiver that is stable at 4 ohms as opposed to integrated a/v receivers that are stable at 6 or 8 ohms. Impedence is merely a measurement of resistance so if you have an amp that is stable at 4 ohms you can get more power out of it than at an 8 ohm load. Did any of this help?

ben62670

What sousa said, except change separate receiver to separate amplifier.

sousa

Oops, that's what I meant. Thanks!

Face

My receiver is 4ohm stable(onk674). Would there be a difference from using 1 4 ohm speaker as a center or 2 8ohms as centers?

ben62670

Not to the receiver.
Enjoy

Sansui

sousa wrote:

Typically 4 ohm speakers are considered higher end and would require the use of a separate receiver that is stable at 4 ohms as opposed to integrated a/v receivers that are stable at 6 or 8 ohms. Impedence is merely a measurement of resistance so if you have an amp that is stable at 4 ohms you can get more power out of it than at an 8 ohm load. Did any of this help?

Yes. Now I understand. Thanks for the explanation.

sickicw

I have always wondered this. Just because it is considered higher end, really isn't a good reason to design it 4 ohms. All car speakers are 4 ohms, and most of them are not high end. The car power system is much more high current than the home power system, so that might be a reason why cars use 4 ohm speakers and homes use 8ohms. But that doesn't explain why 4ohm speakers are also used in high end home setups. Do all low impedance speakers sound better? Are there advantages to this design? And by the way, to get a 4 ohm speaker to sound its best, you will have to get am amp that is 2 ohm stable, which are rare and expensive.

sousa

To counter your point about car audio, some higher end car audio manufactureres are making 2 ohm component sets now. I believe 4 ohm speakers are important because in order to get the necessary power out of an amp with an 8 ohm load would require a monster of an amp. Imagine if the LSi's were 8 ohms, an amp to power them at that impedence would be outrageous. Also to draw a comparison to car audio, most subwoofers in car audio are now dual voice coil in order to wire in parallel and lower the impedence so that when combined with a 1 or 2 ohm stable amp you are able to get more power out of a smaller amp then if it was a single 4 ohm VC. This is why Class D amps have become the populat way to go for car audi subs as they are typically stable at low impedences thus making them very efficient.

sickicw

sousa wrote:

Imagine if the LSi's were 8 ohms, an amp to power them at that impedence would be outrageous.

8 ohm speakers are much easier to power than 4 ohms ones in a home.

The sensitivity of speaker determines how much power is needed, but low impedence speakers need much more current, which is harder to get in a home audio setup.

The only thing that i can think of is that the drivers on low impedence speakers are more rigid and require more current to move, thus lowing distortion. But again, this is just a guess.

sousa

sickicw wrote:

8 ohm speakers are much easier to power than 4 ohms ones in a home.

The sensitivity of speaker determines how much power is needed, but low impedence speakers need much more current, which is harder to get in a home audio setup.

The only thing that i can think of is that the drivers on low impedence speakers are more rigid and require more current to move, thus lowing distortion. But again, this is just a guess.

Again, to get the amount of power needed for a speaker such as an LSi25 from an amp if it were 8 ohms woudl require an absolute beast of an amp. Sensitivity does help indicate how much efficient the speaker is, but the impedence dictates how much power it will allow from the amplifier. Take a look at a separate amp that is 4 ohm stable, take it's power ratings at 4 ohm and cut that in half. That is roughly what it would produce at 8 ohms. You would basically have to double the amp in order to produce the same power at 8 ohms thus increasing cost astronomically.

JimBRICK

I dont think the power a speaker runs at has anything to do with being higher end or not most B&W and mirage speakers run at 8 ohms

sousa

I am not claiming 4 ohm means higher end, nor that all higher end speakers are 4 ohm, but generally 4 ohm speakers are of the higher end. I apologize for making such a broad statement.

heiney9

JimBRICK wrote:

I dont think the power a speaker runs at has anything to do with being higher end or not most B&W and mirage speakers run at 8 ohms

That is correct

jakelm

I dont think ohms are produced on purpose. To get woofer A and tweeter A to perform the way the manufacture intended, the manufacture needs xover A. The sum of the 3 comes to 4ohms. Not intended but in that configuration 4ohms is a sum. And its probably not 4ohms, but anywhere from 3-5ohms. And that just so happens to be the sum of the parts used.

sousa

Manufactureres definitely control the impedence of the speakers. It is not usually exactly 4 or 8, but relatively close. If I am making a speaker that should be run at a true 250 watts RMS (or more) I would probably consider using a 4 ohm impedence. The reason being is because at 4 ohms you will draw more current from an amplifier than if you use an 8 ohm impedence. Amplifier manufacturers make their amps stable at 4 ohms because it is less costly to produce 250 watts at 4 ohms than it is to produce the same power at 8 ohms. Yes, if using the same exact amp a 4ohm load would draw more current from your electrical system than at 8 ohms, but it would also produce half the power. I would think that an amp capable of 250w @ 4 ohms would draw a similar current as an amp capable of 250w @ 8 ohms. I am not an electrical engineer, but I am sure there is a formula to show how much current would be needed for these scenarios.

sickicw

I think jakelm has the right idea...

ohms = volts/amps

Assuming a constant voltage, an amp rated at 250w@4 ohms will draw twice as much current as one rated at 250w@8 ohms.

sousa

amperes = square root(watts/ohms)

Therefore the current draw of 250w @ 4ohms = 7.9 whereas 250w @ 8ohms = 5.6. However to support my point that an amp that produces 250w @ 8ohms would be a beast you can use the formula voltage = square root(wattsxohms) which shows an amp would only need to produce 31.6 volts to make 250w at 4 ohm, but it would have to produce 44.7 volts to make 250w at 8ohm.

So yes, the 8 ohm amp would draw less current than the 4 ohm amp when producing the same power, but the 8 ohm amp would need to produce a good amount more voltage than the 4 ohm amp and is why it would need to be a beast and would be much more costly. As long as your home's electrical system can support it the 4 ohm amp would be less expensive and easier to produce.

sickicw

So given your example, you are saying it is easier and cheaper for a power supply to convert a 120 Volt circuit to 31.6 Volts than is it to convert it to 44.7 volts (assuming the volts are really not the same)?

Why is it that audio amps that are 4 ohm stable are much more expensive than amps that are 8 ohm stable given the same power ratings?

Why are 2 ohms stable amps way way more expensive than 4 ohms stable amps given the same power ratings?

heiney9

sousa wrote:

Amplifier manufacturers make their amps stable at 4 ohms because it is less costly to produce 250 watts at 4 ohms than it is to produce the same power at 8 ohms. Yes, if using the same exact amp a 4ohm load would draw more current from your electrical system than at 8 ohms, but it would also produce half the power. I would think that an amp capable of 250w @ 4 ohms would draw a similar current as an amp capable of 250w @ 8 ohms. I am not an electrical engineer, but I am sure there is a formula to show how much current would be needed for these scenarios.

Absolutely wholeheartedly wrong. Any amp from a cheapie to whatever can drive an 8 ohm or higher load without too much difficulty or cost involved (sound quality aside). What costs money and intelligent design is driving lower impedance's. Because their is less resistance driving a 4 ohm load the amp has to work twice as hard and produce twice as much current to provide the same level of output. Building amps that have more ouput devices, higher capacity transformers, more bypass capacitence and overall much beefier design increases cost dramatically. This is the kind of components needed to drive a low impedance load with any kind of authority and output.

This doesn't even take into account current limiting circuits and devices which limit output and degrade sound in many of the marginally stable 4 ohm capable amps.

This is the short and skinny on this subject. If you want to know more get your learn on here (I've posted several articles and scenario's in the past 2 years) or get compfy and Google until you understand what you are talking about

H9

sickicw

sousa, take a look at the second graph on this thread....

http://www.polkaudio.com/forums/showthread.php?t=50298

..i think you will see what heiney is talking about the amps having to work twice as hard ( or in the case of 2 ohm stable, four times as hard)...

heiney9

You are also missing the points of inductive load, resistive load and static load. Many times the specs quoted for a particular output are with a static load. No loudspeaker is static when it's being powered. Impedance is infinitely variable based on frequency and amplitude of the signal being sent to it. The ratings you find on speakers are nominal. Some speakers dip as low as 1-2 ohms and rise as high as 30 ohms depending on the what part of an audio signal (voltage) is being fed to it.

There is no short and sweet answer. Everything depends on everything else in the the circle.

sousa

So I am wrong in saying it would cost less to produce an amp capable of producing 250w @ 4 ohms than it is to produce an amp producing the same power @ 8 ohms (given all other things are equal)?

jakelm

And to add. Alot alot alot of amps are rated for 8 ohm only, but can handle 4 ohms quite well with no sweat.

My HK is the perfect example.

heiney9

sousa wrote:

So I am wrong in saying it would cost less to produce an amp capable of producing 250w @ 4 ohms than it is to produce an amp producing the same power @ 8 ohms (given all other things are equal)?

Yes. Because theoretically said amp would produce 500 watts at 8 ohms so to prodcue 250 watts at 8 ohms you'd need half the amp you already have producing 250 watts @ 4 ohms. So it should be less costly to use 1/2 the components.

Of course this is gross oversimplification but just to align it with your string of thinking at this point.

sousa

jakelm wrote:

And to add. Alot alot alot of amps are rated for 8 ohm only, but can handle 4 ohms quite well with no sweat.

My HK is the perfect example.

I understand, but my point is that if a speaker has a nominal impedence of 8 ohms, but needs as much power as your HK makes at 4 ohms wouldn't it cost more for HK to make that receiver powerful enough to drive said speaker at 8 ohms? Imagine if you have a pair of LSi15s and you are powering them with your HK, and some kind of magic troll crawls into your speaker and changes the nominal impedence of the LSi to 8 ohms, wouldn't it then be underpowered? And wouldn't you need to buy a more powerful (and more expensive) amp to drive them at their new impedence? Sorry if I am being completely stupid, I just don't see how this wouldn't hold true.

jakelm

Efficiency has alot to do with the output too. If the Lsi's were magically switched to 8ohms, my "guess" would be that they would automatically become more efficient as well. So the output would not change (alot) because efficiency has rose as well. So now being at 8ohms and more efficient, they would need or require less power to drive.

sousa

heiney9 wrote:

Yes. Because theoretically said amp would produce 500 watts at 8 ohms so to prodcue 250 watts at 8 ohms you'd need half the amp you already have producing 250 watts @ 4 ohms. So it should be less costly to use 1/2 the components.

Of course this is gross oversimplification but just to align it with your string of thinking at this point.

The 250W @ 4 ohm amp would produce 500w @ 8 ohm? That is not right. If the impedence increases the output decreases. An amp producing 250w @ 4 ohms would produce ~125w @ 8 ohms.

ben62670

heiney9 wrote:

Absolutely wholeheartedly wrong. Any amp from a cheapie to whatever can drive an 8 ohm or higher load without too much difficulty or cost involved (sound quality aside). What costs money and intelligent design is driving lower impedance's. Because their is less resistance driving a 4 ohm load the amp has to work twice as hard and produce twice as much current to provide the same level of output. Building amps that have more ouput devices, higher capacity transformers, more bypass capacitence and overall much beefier design increases cost dramatically. This is the kind of components needed to drive a low impedance load with any kind of authority and output.

This doesn't even take into account current limiting circuits and devices which limit output and degrade sound in many of the marginally stable 4 ohm capable amps.

This is the short and skinny on this subject. If you want to know more get your learn on here (I've posted several articles and scenario's in the past 2 years) or get compfy and Google until you understand what you are talking about

H9

SOUSA READ THIS QUOTE ABOUT 10 TIMES. It cost more to produce a 4 ohm amp than an 8 ohm amp. Speakers are stationary magnets, and electro magnets. If more currant can flow through the voice coil than more magnetic force is applied.

sickicw

sousa wrote:

I understand, but my point is that if a speaker has a nominal impedence of 8 ohms, but needs as much power as your HK makes at 4 ohms wouldn't it cost more for HK to make that receiver powerful enough to drive said speaker at 8 ohms? Imagine if you have a pair of LSi15s and you are powering them with your HK, and some kind of magic troll crawls into your speaker and changes the nominal impedence of the LSi to 8 ohms, wouldn't it then be underpowered? And wouldn't you need to buy a more powerful (and more expensive) amp to drive them at their new impedence? Sorry if I am being completely stupid, I just don't see how this wouldn't hold true.

OK, assuming the magic troll didnt change the sensitivty, then the following would happen....

- You would lose about 3db of max volume (because now you're average power is 1/2 what it was). This is really not a big deal because most people dont listen to max volume anyway.
- You new "trolled" lsi15 would probably sound much better, more dynamic, and more powerfull upto its new max volume. The reason for this is because the amp will have an easier time handeling it's new impedance range.

Hope this helps....

EDIT you can buy a transformer that will help the "magic troll" out a bit....

http://www.zeroimpedance.com/

http://www.zeroimpedance.com/Zero-New.html

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heiney9

sousa wrote:

The 250W @ 4 ohm amp would produce 500w @ 8 ohm? That is not right. If the impedence increases the output decreases. An amp producing 250w @ 4 ohms would produce ~125w @ 8 ohms.

NM........my mind is swimming doing both work related issues and trying to keep this thread straight .

I'll revisit when I get some free time at home tonight. I should know better than to get in an involved technical discussion when I'm at work