Bluewizard,
Read up on a term called loudspeaker efficiency . Given in % or also specified as xx dB at 2.83 volts or more complex if its stated as xx dB per watt .
Varies very widely between speakers and IMO a factor that deserves more attention than it apparently seems to get.
You seem to have glossed over it (?).
Read up on a term called loudspeaker efficiency . Given in % or also specified as xx dB at 2.83 volts or more complex if its stated as xx dB per watt .
Varies very widely between speakers and IMO a factor that deserves more attention than it apparently seems to get.
You seem to have glossed over it (?).
Nice of you to comment, unfortunately no one actually said anything other than ASHOK, and I really don't get the relevance of that he said.
Speaker efficiency or Sensitivity or stated SPL is a measure of loudness. Loudness seems linear; it seems to accurately track my volume control. However, as the formula P = E^2/R indicates, Power is far from linear.
A difference in loudness of 3 db in a speakers rated Sensitivity is just going to be noticable.
A speaker that is consuming twice as much power as another speaker is only going to be slightly louder. That doesn't seem like much gain for twice the power consumption.
So, is loudness NOT the measure of acoustical power? Power consumed seem relatively easy, even when you consider phase shift; a simple calculation. But actually power produced is quite another thing.
If the objection of others was to my statement that the headroom, which is really what we gain from high powered amps, is the same in every case (4, 8, 16 ohms), I'd like an explanation as to how it is not.
The limiting factor, in other words 'clipping', is based on Voltage limits assuming minimal internal losses and sufficient current sourcing ability.
In the three examples, 200w:4ohm, 100w:8ohm, and 50w:16ohms, the voltage limit is the same in every case = 28.28 volts. In every case the rate at which you reach that limit is the same. [ E = sqrt(PxR) ] So, nothing is really gain from the apparent increase in power at 4 ohms. Well, there might be a slight gain in perceived loudness, but is that sufficient to warrant twice the power consumption across the board?
Finally, I DID NOT make an absolute statement of fact. What I did was state a perception, and ask for a correction if I was wrong. Notice the many question marks in my statement.
You say I am wrong and off base, yet you haven't establish it in any way. Educate me.
Steve/BlueWizard
Speaker efficiency or Sensitivity or stated SPL is a measure of loudness. Loudness seems linear; it seems to accurately track my volume control. However, as the formula P = E^2/R indicates, Power is far from linear.
A difference in loudness of 3 db in a speakers rated Sensitivity is just going to be noticable.
A speaker that is consuming twice as much power as another speaker is only going to be slightly louder. That doesn't seem like much gain for twice the power consumption.
So, is loudness NOT the measure of acoustical power? Power consumed seem relatively easy, even when you consider phase shift; a simple calculation. But actually power produced is quite another thing.
If the objection of others was to my statement that the headroom, which is really what we gain from high powered amps, is the same in every case (4, 8, 16 ohms), I'd like an explanation as to how it is not.
The limiting factor, in other words 'clipping', is based on Voltage limits assuming minimal internal losses and sufficient current sourcing ability.
In the three examples, 200w:4ohm, 100w:8ohm, and 50w:16ohms, the voltage limit is the same in every case = 28.28 volts. In every case the rate at which you reach that limit is the same. [ E = sqrt(PxR) ] So, nothing is really gain from the apparent increase in power at 4 ohms. Well, there might be a slight gain in perceived loudness, but is that sufficient to warrant twice the power consumption across the board?
Finally, I DID NOT make an absolute statement of fact. What I did was state a perception, and ask for a correction if I was wrong. Notice the many question marks in my statement.
You say I am wrong and off base, yet you haven't establish it in any way. Educate me.
Steve/BlueWizard
Just a couple of things:
The volume control is handled by a logarithmic potentiometer (or a device with the same functionality). Turning it a certain angle increases output voltage more at the end of the scale than at the beginning. That's why it appears to work with a constant loudness increase, which is of course intentional and practical. Otherwise you'd get almost all the loudness at the beginning of the scale.
Headroom is indeed not much different between a 100 watt amp and a 200 watt amp, at least not to the ears. It's a fact of life.
Doubling the perceived loudness will require a 10-fold increase in acoustic power. Given a particular loudspeaker, this will require a 10-fold increase in electric power (igoring issues of power comression).
Changing the impedance between 4 and 8 ohms doesn't matter, but for a given amplifier with the volume knob at a given setting, the 4 ohm speaker will be slightly louder because it will recieve twice the power.
Unfortunately, there is no concensus on how to sepcify sensitivity, but the general trend seems to be towards using a 2.83 Volt signal, but writing it as nn dB SPL @ 1W even for a 4 ohm driver, when that is technically incorrect.
The volume control is handled by a logarithmic potentiometer (or a device with the same functionality). Turning it a certain angle increases output voltage more at the end of the scale than at the beginning. That's why it appears to work with a constant loudness increase, which is of course intentional and practical. Otherwise you'd get almost all the loudness at the beginning of the scale.
Headroom is indeed not much different between a 100 watt amp and a 200 watt amp, at least not to the ears. It's a fact of life.
Doubling the perceived loudness will require a 10-fold increase in acoustic power. Given a particular loudspeaker, this will require a 10-fold increase in electric power (igoring issues of power comression).
Changing the impedance between 4 and 8 ohms doesn't matter, but for a given amplifier with the volume knob at a given setting, the 4 ohm speaker will be slightly louder because it will recieve twice the power.
Unfortunately, there is no concensus on how to sepcify sensitivity, but the general trend seems to be towards using a 2.83 Volt signal, but writing it as nn dB SPL @ 1W even for a 4 ohm driver, when that is technically incorrect.
OK here it is in simple terms.
You are getting confused by consuming and producing power. If the speaker is 200W, that's it, it consumes 200W of power, forget about the notion of producing power. The impedance is irrelevant - it eats 200W end of.
What makes the high impedance speaker easier to drive is that less current is required for the same given power. This means less losses and less massive wires and big parts needed. It can also mean less distortion in the output stage of the amp, but that's another story.
Loudspeaker efficiency is that for a given input power you will get a stated sound pressure level. Obviously a speaker with efficiency 90dB/W will need less (half actually) power to sound as loud as one with only 87dB/W. Matters are complicated because instead of using 1W, people often use 2.83V which is 1W into 8 ohms. If this same voltage is used on a 4 ohm speaker it will seem louder, but it's actually drawing 2W so it's a bit of a cheat.
You are getting confused by consuming and producing power. If the speaker is 200W, that's it, it consumes 200W of power, forget about the notion of producing power. The impedance is irrelevant - it eats 200W end of.
What makes the high impedance speaker easier to drive is that less current is required for the same given power. This means less losses and less massive wires and big parts needed. It can also mean less distortion in the output stage of the amp, but that's another story.
Loudspeaker efficiency is that for a given input power you will get a stated sound pressure level. Obviously a speaker with efficiency 90dB/W will need less (half actually) power to sound as loud as one with only 87dB/W. Matters are complicated because instead of using 1W, people often use 2.83V which is 1W into 8 ohms. If this same voltage is used on a 4 ohm speaker it will seem louder, but it's actually drawing 2W so it's a bit of a cheat.
The words "consume" and "produce" are a little strange being used the way they are with relation to loudspeakers. It's more appropriate to say a loudspeaker converts electrical energy into mechanical movement. It dissipates most of the electrical energy as heat in the process. Most loudspeakers are in fact not very efficient at all, and efficiency and sensitivity are two different things.
I just lost a long reply due to some unknown hitch. I don't have the patience to write it out again. But here are some thoughts.
Are you trying to clarify your basics or are you making a point about high impedance speakers being better ( because they consume less power(!) ).
Speakers have an efficiency associated with them. Lets say 2 %. Then with 100 watts into it it will generate only 2 acoustic watts and loose 98 watts as heat. It doesn't matter if the speaker impedance is 1 ohm or 1000 ohms or more . Feed 100 watts electrical power into it and only 2 acoustic watts will come out.
The drive requirements will depend on it's impedance. High impedance needs high voltage low current and low impedance needs low voltage and high current. You take your pick.
Bipolar transistors above 250 volts with high current capacity are expensive and hard to find. People get around this using special circuitry ( still expensive ). Low impedances need higher current but people parallel devices.
There are several other design issues but basically you will find that with higher impedance loads it get harder to design an amp as power levels go up and to find suitable high voltage components.
I'm quitting here. I hope the issues are clearer now.
Are you trying to clarify your basics or are you making a point about high impedance speakers being better ( because they consume less power(!) ).
Speakers have an efficiency associated with them. Lets say 2 %. Then with 100 watts into it it will generate only 2 acoustic watts and loose 98 watts as heat. It doesn't matter if the speaker impedance is 1 ohm or 1000 ohms or more . Feed 100 watts electrical power into it and only 2 acoustic watts will come out.
The drive requirements will depend on it's impedance. High impedance needs high voltage low current and low impedance needs low voltage and high current. You take your pick.
Bipolar transistors above 250 volts with high current capacity are expensive and hard to find. People get around this using special circuitry ( still expensive ). Low impedances need higher current but people parallel devices.
There are several other design issues but basically you will find that with higher impedance loads it get harder to design an amp as power levels go up and to find suitable high voltage components.
I'm quitting here. I hope the issues are clearer now.
Now a genuine thanks to everyone for their explanations and clarifications.
ASHOK, sorry you lost that post, it sounds like it would have been a good one.
Really, my whole rant stems from two issues. One was the original thread in another group, where someone was insisting that there was a real advantage to low impedance speakers because they were easier to drive and would therefore always sound better. Which in turn leads to a whole raft of frustrating issues.
Next, in that discussion, which was in an audio consumers group, I was a little frustrated by the level of misinformation. About like how you feel talking to me.
Finally, with all this thinking about amps, it occurred to me that some people are under the illusion that they are making this tremendous gain in power by using 4 ohm speakers. An illusion that I think amp manufacturers are feeding into. I think the FTC standard for power rating is at 8 ohms. But you see amps that are rated at 4 ohms, or sometimes 6 ohms, because that inflates the apparent power.
200w into 8 ohms vs 100w into 8 ohms is a genuine gain in power.
200w into 4 ohms vs 100w into 8 ohms is only an illusion of apparent power gain.
So basically I was just ranting a bit, and YES, I am well aware that I can get LONG WINDED, but that's just the way I am; I accept it.
Thanks again.
Steve/BlueWizard
ASHOK, sorry you lost that post, it sounds like it would have been a good one.
Really, my whole rant stems from two issues. One was the original thread in another group, where someone was insisting that there was a real advantage to low impedance speakers because they were easier to drive and would therefore always sound better. Which in turn leads to a whole raft of frustrating issues.
Next, in that discussion, which was in an audio consumers group, I was a little frustrated by the level of misinformation. About like how you feel talking to me.
Finally, with all this thinking about amps, it occurred to me that some people are under the illusion that they are making this tremendous gain in power by using 4 ohm speakers. An illusion that I think amp manufacturers are feeding into. I think the FTC standard for power rating is at 8 ohms. But you see amps that are rated at 4 ohms, or sometimes 6 ohms, because that inflates the apparent power.
200w into 8 ohms vs 100w into 8 ohms is a genuine gain in power.
200w into 4 ohms vs 100w into 8 ohms is only an illusion of apparent power gain.
So basically I was just ranting a bit, and YES, I am well aware that I can get LONG WINDED, but that's just the way I am; I accept it.
Thanks again.
Steve/BlueWizard
Hhm, rethink that, Steve
An amp rated to deliver 200W into whatever load the mfg. specified will deliver these 200 Watts into that load... 200W is 200W.
Only one should not assume that an amp with rated 200W @ 4Ohms (as lowest allowed load impedance) will deliver 400W into 2Ohms, of course. That may or may not be true (typically the latter, as internal power supply voltages sag under load). Sometimes power ratings are made conservately, for example an amp may state 6 Ohms min. impedance but will be happy to drive 4 Ohms as well, with increased power output. A reason for this is often case temperature, which (IIRC) must not raise above 60°C (at 25°C ambient) as far as european regulations apply.
Regards, Klaus
An amp rated to deliver 200W into whatever load the mfg. specified will deliver these 200 Watts into that load... 200W is 200W.
Only one should not assume that an amp with rated 200W @ 4Ohms (as lowest allowed load impedance) will deliver 400W into 2Ohms, of course. That may or may not be true (typically the latter, as internal power supply voltages sag under load). Sometimes power ratings are made conservately, for example an amp may state 6 Ohms min. impedance but will be happy to drive 4 Ohms as well, with increased power output. A reason for this is often case temperature, which (IIRC) must not raise above 60°C (at 25°C ambient) as far as european regulations apply.
Regards, Klaus
There is a gain when going from 8 ohm speakers to 4 ohms IF the amp can do more power at 4 ohms than 8 ohms. Some amps will actually do LESS power at 4 ohms because of the power supply design, the current limits restrictions, etc. There are more variables than what you might think. The speaker must also be just as sensitive (SPL rating) or there will be no change. You really have to look at the whole system and compare the results.
An example. 8 ohm speaker rating at 90dB at 2.83V (1W). 4 ohm speaker rated at 90dB at 2.83V (2W). Now if that amplifier can do exactly twice as much power into 4 ohms as 8 ohms the loudness is going to be exactly the same. Why? Because the 4 ohm speaker is actually less efficiency by 3dB. Although the ratings look the same they are at 1W and 2W so to get the speakers ratings the same you have to reduce the 4 ohm by 3dB for 1/2 the power to go from the 2W down to 1W. This means 87dB at 1W. Now to figure a loudness at the peak amplifier power (ignoring other losses for simplicity) you get:
110dB for 8 ohms at 100W (1W - 10W = +10dB, 10W - 100W = +10dB).
For 4 ohms you have 1W = 87dB, 1W - 10W = 97dB, 10W - 100W = 107dB then 100W - 200W = 110dB.
Same result in loudness. But that is all because the speakers are not exactly the same in SPL. If they were you'd get 3dB more loudness from the 4 ohm, which is noticeable.
Sound loudness is not linear, it is logrithmic.
So which is easier to drive? As stated already, it depends. 8 ohms requires more voltage but less current, 4 ohms more current but less voltage. When dealing with real world constaints like a chipamp, 8 ohms is easier almost always. This is because of real world limitations like power dissipation, current capability, etc. For chipamps, most prefer 8 ohms as the place you get the most power. But this is because of real world limitations. For a fully discrete amp then it all depends on the amplifier output power. Pick 100W then 8 ohms is easier because the voltage required is easily obtained from cheap parts while 4 ohms will require more parts for more current drive. There are just more variables and the whole system needs to be looked at.
If the amplifier is like you say, 100W 8 ohms, 200W 4 ohms and a person can replace the 8 ohms speakers with 4 ohms ones that are the same SPL rating at 1W then there is a gain of 3dB in loudness at the cost of more power from the wall, to the speaker, hotter amplifier, and higher electic bill. But one can also find 8 ohms speakers that are rated 3dB higher at 1W and will be just as loud as the 4 ohms ones while not using any more power. At this point it often becomes a tradeoff in speaker cost, SPL, quality, amplifier cost, usage, heat, etc. to determine what is best. Lots of variables.
Remember, trust the Llama.
-SL
An example. 8 ohm speaker rating at 90dB at 2.83V (1W). 4 ohm speaker rated at 90dB at 2.83V (2W). Now if that amplifier can do exactly twice as much power into 4 ohms as 8 ohms the loudness is going to be exactly the same. Why? Because the 4 ohm speaker is actually less efficiency by 3dB. Although the ratings look the same they are at 1W and 2W so to get the speakers ratings the same you have to reduce the 4 ohm by 3dB for 1/2 the power to go from the 2W down to 1W. This means 87dB at 1W. Now to figure a loudness at the peak amplifier power (ignoring other losses for simplicity) you get:
110dB for 8 ohms at 100W (1W - 10W = +10dB, 10W - 100W = +10dB).
For 4 ohms you have 1W = 87dB, 1W - 10W = 97dB, 10W - 100W = 107dB then 100W - 200W = 110dB.
Same result in loudness. But that is all because the speakers are not exactly the same in SPL. If they were you'd get 3dB more loudness from the 4 ohm, which is noticeable.
Sound loudness is not linear, it is logrithmic.
So which is easier to drive? As stated already, it depends. 8 ohms requires more voltage but less current, 4 ohms more current but less voltage. When dealing with real world constaints like a chipamp, 8 ohms is easier almost always. This is because of real world limitations like power dissipation, current capability, etc. For chipamps, most prefer 8 ohms as the place you get the most power. But this is because of real world limitations. For a fully discrete amp then it all depends on the amplifier output power. Pick 100W then 8 ohms is easier because the voltage required is easily obtained from cheap parts while 4 ohms will require more parts for more current drive. There are just more variables and the whole system needs to be looked at.
If the amplifier is like you say, 100W 8 ohms, 200W 4 ohms and a person can replace the 8 ohms speakers with 4 ohms ones that are the same SPL rating at 1W then there is a gain of 3dB in loudness at the cost of more power from the wall, to the speaker, hotter amplifier, and higher electic bill. But one can also find 8 ohms speakers that are rated 3dB higher at 1W and will be just as loud as the 4 ohms ones while not using any more power. At this point it often becomes a tradeoff in speaker cost, SPL, quality, amplifier cost, usage, heat, etc. to determine what is best. Lots of variables.
Remember, trust the Llama.
-SL
Thanks again, to everyone, and also again, I am just ranting and rambling, and trying to educate myself.
As to the assertion that 200watts is 200 watts and that's that. Well...sort of.
The question relates to why we want more power, and what that 'more power' does for us. I say more power has little to do with perceived loudness, because you turn your amp up to a comfortable listening level independent of how much power it may be drawing at the moment.
I say, that 'more power' buys us more headroom, and therefore less distortion of the signal resulting from clipping. I'm currently using a 50 watt per channel amp, and because I've put a 'scope on it, I know it does clip at moderately high volume. At least the highest and loudest peaks are slightly clipped. But my amp only has 20V of headroom.
Note my previous statement.
200w into 8 ohms vs 100w into 8 ohms is a genuine gain in power.
200w into 4 ohms vs 100w into 8 ohms is only an illusion of apparent power gain.
In the case of 4 ohms vs 8 ohms, the power consumption has doubled, but the ceiling is still in the same place. 28.28v for 200w:4ohms, and 28.28v:8ohms. No real gain. Though I admit a likely gain of 3db across the board for the 4 ohms speaker.
In the case of 8 ohms vs 8 ohms, we have a 40v ceiling for 200 watts and 28.28v ceiling for 100w. That is a real gain in what we buy more power for.
Now, I know I am in a group of experts and near experts here , but don't you find among consumers, the general belief that somehow running 4 ohm speakers on their amp is creating this huge gain in available power? Or is that just me? Don't you find that people are swayed by high power rating into 4 ohms under the illusion that the are actually gaining something?
Again, this is just a rant. I think it is nice to know that an amp has a sufficient power supply to be able to deliver a full 200w into 4 ohms, but I really don't fool myself into believe I am gaining anything by using 4 ohms. That apparent power is an illusion because it is consumed at twice the rate and the ceiling hasn't moved.
Still, 4 ohms, 6 ohms, 8 ohms, if music comes out and it sound good then you've got everything you need. Even if you're convinced that you have some fantastic gain at 4 ohms, that's OK, I don't think it is true, but it's OK.
Like I said, just ranting and venting, and now I am ready to let it go.
Steve/BlueWizard
As to the assertion that 200watts is 200 watts and that's that. Well...sort of.
The question relates to why we want more power, and what that 'more power' does for us. I say more power has little to do with perceived loudness, because you turn your amp up to a comfortable listening level independent of how much power it may be drawing at the moment.
I say, that 'more power' buys us more headroom, and therefore less distortion of the signal resulting from clipping. I'm currently using a 50 watt per channel amp, and because I've put a 'scope on it, I know it does clip at moderately high volume. At least the highest and loudest peaks are slightly clipped. But my amp only has 20V of headroom.
Note my previous statement.
200w into 8 ohms vs 100w into 8 ohms is a genuine gain in power.
200w into 4 ohms vs 100w into 8 ohms is only an illusion of apparent power gain.
In the case of 4 ohms vs 8 ohms, the power consumption has doubled, but the ceiling is still in the same place. 28.28v for 200w:4ohms, and 28.28v:8ohms. No real gain. Though I admit a likely gain of 3db across the board for the 4 ohms speaker.
In the case of 8 ohms vs 8 ohms, we have a 40v ceiling for 200 watts and 28.28v ceiling for 100w. That is a real gain in what we buy more power for.
Now, I know I am in a group of experts and near experts here , but don't you find among consumers, the general belief that somehow running 4 ohm speakers on their amp is creating this huge gain in available power? Or is that just me? Don't you find that people are swayed by high power rating into 4 ohms under the illusion that the are actually gaining something?
Again, this is just a rant. I think it is nice to know that an amp has a sufficient power supply to be able to deliver a full 200w into 4 ohms, but I really don't fool myself into believe I am gaining anything by using 4 ohms. That apparent power is an illusion because it is consumed at twice the rate and the ceiling hasn't moved.
Still, 4 ohms, 6 ohms, 8 ohms, if music comes out and it sound good then you've got everything you need. Even if you're convinced that you have some fantastic gain at 4 ohms, that's OK, I don't think it is true, but it's OK.
Like I said, just ranting and venting, and now I am ready to let it go.
Steve/BlueWizard
I'm amazed that such truly smart and knowledgable people can miss my point so thoroughly.
As to whether I understand Ohm's Law, the calculations and results of calculations plastered all over my posts should indicate that I do.
So, let me reframe this in the form of a question, even though it is a point I've made several times before.
Why do we want MORE POWER?
Is it for loudness? Because we are only going to get a slight increase in loudness for double the real power.
Is it so we can drive more speakers, similar to a truck hauling a heavier load? If this were a public address application, I would concede this had some merit. But in a home audio system, we are most like to have one speaker per channel, or possibly two at the most. So, diverse power distribution is not really the issue in a home audio system.
Or, is it for headroom? Is it so that regardless of the volume we are playing at, we are not bumping our heads on the ceiling?
Further, as a side note; let me make it clear that I understand that a 3db gain in loudness is synonymous with twice as much power. That's just a fact, I fully acknowledge that and accept it as a real and likely gain.
In the case of 200w:8 ohms vs 100w:8 ohms, we have all acknowledged that this is a true and genuine gain in working power.
So, the problem is with 200w:4 ohms vs 100w:8 ohms. In the case of a 200w:8ohms vs 100w:8ohms both speaker are consuming power at the same rate. Therefore, 200w:8ohms give us a very real gain in everything we buy power for. However, 200w:4ohms, while a genuine 200w is available, it is consumed at twice the rate and the ceiling doesn't move.
200w:8ohms gives us a 40v ceiling. Both 200w:4ohms and 100w:8ohms have a 28v ceiling, and further, 200w:4ohms consumes power at twice the rate for a net gain of nothing. Again, acknowledging a very likely 3 db gain in loudness.
OHM's LAW of Real Power -
Take 200w:8ohms and 200w:4ohms - amp connected to speakers. Now start with the volume control turned down. Increase the signal level to the 8ohm speaker and the 4ohms speakers in 0.1v steps, continue increasing until you run out of headroom; until you hit the ceiling. Calculate the power at each step along the way.
Which consumes twice the power across the board (which is what I mean when I say consuming power at twice the rate), and which hits the ceiling first? The 4 ohms speaker.
200w:4ohms has twice the power available but consumes power at twice the rate and has the same low ceiling for a net gain of nothing. Again acknowledging a likely 3 db gain in loudness.
200w:8ohms is like extending the range of the volume control because you have a much higher ceiling. You consume the power at an efficient rate, you have a higher ceiling and you have a real gain in loudness.
Don't get me wrong, I am not in any way implying that 200w:4ohms is a bad thing. I said, if you pop in a CD and sweet sound comes out, that's all you need.
As long as you are in the functional working range of a given amp, 4ohm, 6ohms, 8ohms, or 16 ohms, it doesn't matter. Just don't fool yourself into believing that you are gaining or losing anything other than a slight change in volume for any of these impedances on that given amp.
To get a very real gain in power, it is the power of the amp at a fixed impedance that must go up, not the impedance of the speaker that must go down.
If you dispute what I said, it would be nice if you indicated exactly what you dispute. It's nice that you all responded, but it doesn't help me much if you don't actually say anything. Not being sarcastic or snarky, just stating reality, and fully acknowledging that some of you have made substantial and helpful posts.
Finally, acknowledging that this is all a minor point. You have the amp you have, you have the speakers you have, if sweet music comes out, then you got what you paid for regardless of impedance. You lose nothing by using 4 ohms speakers, but, at best, you gain nothing more than 3 db assuming identical speakers in all other respects (which is unlikely).
200w:4ohms and 100w:8ohms are, for all intent and purpose, exactly the same thing, and that is the central point I am making. That's all I'm saying. Though, I was a bit long winded in saying it.
Sorry to bother you all with my ranting.
Steve/BlueWizard
As to whether I understand Ohm's Law, the calculations and results of calculations plastered all over my posts should indicate that I do.
So, let me reframe this in the form of a question, even though it is a point I've made several times before.
Why do we want MORE POWER?
Is it for loudness? Because we are only going to get a slight increase in loudness for double the real power.
Is it so we can drive more speakers, similar to a truck hauling a heavier load? If this were a public address application, I would concede this had some merit. But in a home audio system, we are most like to have one speaker per channel, or possibly two at the most. So, diverse power distribution is not really the issue in a home audio system.
Or, is it for headroom? Is it so that regardless of the volume we are playing at, we are not bumping our heads on the ceiling?
Further, as a side note; let me make it clear that I understand that a 3db gain in loudness is synonymous with twice as much power. That's just a fact, I fully acknowledge that and accept it as a real and likely gain.
In the case of 200w:8 ohms vs 100w:8 ohms, we have all acknowledged that this is a true and genuine gain in working power.
So, the problem is with 200w:4 ohms vs 100w:8 ohms. In the case of a 200w:8ohms vs 100w:8ohms both speaker are consuming power at the same rate. Therefore, 200w:8ohms give us a very real gain in everything we buy power for. However, 200w:4ohms, while a genuine 200w is available, it is consumed at twice the rate and the ceiling doesn't move.
200w:8ohms gives us a 40v ceiling. Both 200w:4ohms and 100w:8ohms have a 28v ceiling, and further, 200w:4ohms consumes power at twice the rate for a net gain of nothing. Again, acknowledging a very likely 3 db gain in loudness.
OHM's LAW of Real Power -
Take 200w:8ohms and 200w:4ohms - amp connected to speakers. Now start with the volume control turned down. Increase the signal level to the 8ohm speaker and the 4ohms speakers in 0.1v steps, continue increasing until you run out of headroom; until you hit the ceiling. Calculate the power at each step along the way.
Which consumes twice the power across the board (which is what I mean when I say consuming power at twice the rate), and which hits the ceiling first? The 4 ohms speaker.
200w:4ohms has twice the power available but consumes power at twice the rate and has the same low ceiling for a net gain of nothing. Again acknowledging a likely 3 db gain in loudness.
200w:8ohms is like extending the range of the volume control because you have a much higher ceiling. You consume the power at an efficient rate, you have a higher ceiling and you have a real gain in loudness.
Don't get me wrong, I am not in any way implying that 200w:4ohms is a bad thing. I said, if you pop in a CD and sweet sound comes out, that's all you need.
As long as you are in the functional working range of a given amp, 4ohm, 6ohms, 8ohms, or 16 ohms, it doesn't matter. Just don't fool yourself into believing that you are gaining or losing anything other than a slight change in volume for any of these impedances on that given amp.
To get a very real gain in power, it is the power of the amp at a fixed impedance that must go up, not the impedance of the speaker that must go down.
If you dispute what I said, it would be nice if you indicated exactly what you dispute. It's nice that you all responded, but it doesn't help me much if you don't actually say anything. Not being sarcastic or snarky, just stating reality, and fully acknowledging that some of you have made substantial and helpful posts.
Finally, acknowledging that this is all a minor point. You have the amp you have, you have the speakers you have, if sweet music comes out, then you got what you paid for regardless of impedance. You lose nothing by using 4 ohms speakers, but, at best, you gain nothing more than 3 db assuming identical speakers in all other respects (which is unlikely).
200w:4ohms and 100w:8ohms are, for all intent and purpose, exactly the same thing, and that is the central point I am making. That's all I'm saying. Though, I was a bit long winded in saying it.
Sorry to bother you all with my ranting.
Steve/BlueWizard
BlueWizard said:
To go louder !!
Remember :- in an average room, you only require 1 watt to drive the average speaker to 'normal' listening levels. (not disco levels)
More power gives greater headroom without changing anything else.
Correct
There is no problem at all!!
A 4 ohm speaker has a certain sensitivity eg 90dB/watt at 1m
An 8 ohm speaker has a certain sensitivity eg 90 dB/watt at 1m
Feed either with 1 watt, you will have an spl of 90dB at 1m.
Feed either with 2 watts, the spl will be 93dB at 1m.
and so on ..... end of story
Forget about power consumption, ceilings etc
Andy
BlueWizard said:
Wow. You're persistent, I'll give you that.
Steve, this is really not as complicated as you're making it.
In an amp that's connected to a load (speaker), the loads resistance determines the current flow. Lower resistance, higher current flow. The formula for power is:
P = V² / R
Therefore, if the maximum voltage is 30 volts and it's connected to a 8 ohm speaker, the power will be 112 watts maximum.
For the same amp with a 4 ohm speaker the power will be 225 watts maximum.
This has nothing to do with consumption, but is the maximum available power.
Having more power available increases headroom. For a nominal 8 ohm load, the only way to increase power is to increase the maximum output voltage. Clipping occurs when the input signal, once amplified, is greater than the maximum output voltage.
Speaker loudness at a given input power is efficiency. More efficient, the less power needed for the same spl output.
Is this clear?
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