gusfinley said:
Boingoman...
I have a found some errors in your rebuttal.... and will attempt to show that the reasoning I have used is correct...!!
It wasn't a rebuttal. It was commentary. You made the rebuttal.
I'm not trying to attack you, it's just the page is fairly confusing.
gusfinley said:
First of all keep in mind that my analysis was from a steady state circuit
thoery/modelling standpoint. All the "other" crazy things that happen have been ignored such as the fact that impedance changes with frequency. This is an analysis of "ideal" components which do not exist!! I have presented them in this simplistic manner for those who are looking for info about how hooking up different values of speakers/ cabs to thier amps will affect it!!!!
There was nothing simple about your explanation, and you left much important information out. There was no mention of the fact of increased current draw from lower impedances, nor any mention of the fact that exceeding an amp's current capacity is the easiest way to kill it. You seem to be unaware of this. If an amp tries to put out too much voltage, it just clips. These are the three things people need to know most, IMO, besides how hooking up cabs affects impedance. When speakers are paralleled, this is a current divider, not a voltage divider. Most people, when hooking up multiple cabs, are dealing with paralleling. This is what happened to your PA. You dropped it below it's impedance rating.
The impedance rating on an amp is the minimum safe impedance you can hook to that amp. I didn't see that anywhere, either. Pretty important.
Too many speakers in series can be harmful, but it is a way less common occurence. People parallel speakers to take advantage of increased current flow with no voltage change.
gusfinley said:
"The more impedance a material has, less power travels through it for a given voltage. It does not absorb power. It impedes it. A lower impedance lets more power through. "
Power does not travel through anything!! Power is produced by a source in a limited amount. This source can be modeled as a thevenin equivalent circuit - a current source with a parallel impendance or a voltage source with a series impedance. I have used the Thevenin equivalent voltage source because it works better when it comes to power transfer scenarios........
Well, here in the real world of people hooking up guitar amps and power amps, for power transfer situations, we take the output voltage of the amplifier at the jack, and the speaker load, and figure out the power from that. What you speak of may be relevant for a designer, but not an end user.
gusfinley said:
Current is the only thing that travels in the electrical system.... You seem to confuse current with power in your statements..
LOL. You are correct. I should have said a lower impedance allows more current to flow, resulting in more power potential available for the speaker.
gusfinley said:
First of all a component "impedes" current by absorbing power!! there are a few examples, based on your statement above...
No, that is incorrect. Components impede current by being made of materials or designs which are more or less resistant to current flow. Silver is a better conductor than copper because it has more free electrons, not because it absorbs less power. Carbon is a poor conductor, as it has few free electrons. More carbon in a resistor means more impedance.
This is probably the most basic concept in electronics. If you do not understand this, you can understand nothing.
gusfinley said:
For a given voltage... 50V, an impedance of 1 ohm gives 2500W, 10ohms gives 250W, 100 ohms gives 25W.... These results are found using the formula P = (V * V ) / R, which is a combination of P= I * R and ohms law, V = I * R. This is a measure of the power absorbed by the component itself. You will notice that the LOWER the impedance for this given voltage, the MORE power it absorbs, and therefore less power is available down the line.......
Right data, wrong conclusion. The "component" in this case is the speaker,
and the air it moves. More power to the component (air) is what you get when you use a lower impedance speaker. More is more, not less. More is indeed lost as heat, but more goes to speaker output as well. There is no "down the line". The speaker is the "end of the line".
And again, the speaker is not "absorbing" the power. It is allowing current and voltage to flow to a greater or lesser extent, depending on impedance. It dissipates the power as heat and movement.
gusfinley said:
Again using P= (V * V) / R as you increase the voltage drop for a given
impedance, indeed more power is being absorbed!! It is being absorbed in any way imaginable, usually heat.
More power is produced for a higher voltage, that is true. But the power is not absorbed by the component. It is dissipated. In the case of a speaker, it is dissipated as heat and movement.
gusfinley said:
True the jack is not an "8 ohm jack", but the labeling on the jack is a thevenin equivalent impedance that is "seen" by the jack looking into the amp. It is really a stepped down value of the resistance of the plates from the transformer..........
Even if this is true, you do not tack an extra 8ohm load on your amp when you are figuring out how much juice it puts out according to it's stated output. An 8ohm label on a jack on a 50W guitar amp means when you hook an 8ohm speaker to it, it can make 50W. All the internal stuff is taken into consideration in the power rating of the amp.
It is also an indication of the minimum safe impedance you should hook to that jack, to stay within the amp's current producing capacity.
gusfinley said:
Speakers indeed abosorb power!! This is why they have power ratings!! When you blow up a speaker it has absorbed more power than it was made to absorb!! Also according to the laws of thermodynamics any time you change from one form of energy to another there is a loss of the energy (loss = absorbtion) the speakers transfer the electrical energy into mechanical energy to move the voice coils to creat the sound energy. Every step along the way power is being used up!!
Really? In my universe the laws of thermodynamics say energy changes form, it is not gained or lost. Entropy is there, that's true, but in this case I feel safe saying it's not a factor. The voltage and current are changed to movement and heat. It is not absorbed by the speaker.
Speakers dissipate power. Speakers blow when they cannot safely dissipate the power they are receiving. The power rating on a speaker tells how much power the speaker can dissipate, not absorb.
gusfinley said:
A 4ohm speaker is louder at a given volume setting because it lets more CURRENT flow from the amp for a given input voltage... once again you have confused power for current. ..........
LOL. True enough. I should have said the lower impedance lets more current flow, which results in more power being generated.
gusfinley said:
Lower speaker impedance = more CURRENT from the amp= more power transfered from the speaker to that air (abosrbed by the speaker).........
Yes, which completely contradicts everything you implied on your site, and even earlier in this post.
gusfinley said:
The idea that the higher impedance speakers use more power IS valid when there is more than one impedance at stake. The two speakers will form a voltage divider, and the larger of the speakers will have the larger voltage drop and therefore WILL absord more power!! P = ( V * V ) / R.
Aaaahhh..finally I understand where you are coming from, and why you think the way you do.
Speakers hooked in parallel are a current divider, not a voltage divider. The one with less impedance gets more current, and the same voltage, and can produce more volume.
In series, yes, you are correct. In audio, most cabinets are paralled when hooked together. Wiring two speakers of different impedances in series would do what you say.
gusfinley said:
Its hard to say what was going on with the amp since I didn't take any measurements while it was still operational in this state... But again the voltage divider between the amp and the equivalent impedances of the speakers caused more power to be absorbed by the amp, a Direct result of the lower impedance attached to it, and that it why it burned up!! .
Again, no, even from your diagram. It shows the speakers wired in parallel. This makes a current divider, not a voltage divider. Your amp exceeded it's current capacity due to the low load, and fried.
All the stuff about amps absorbing power is true, I'll give you that. But it's not important or relevant for some guy just trying to hook up a cab to his amp. That was my real point.
gusfinley said:
"If you plug a 4 ohm speaker into an 8ohm jack, the speaker lets more power than an 8 ohm speaker, not less. It is louder, as well."
Once again, the speaker get more CURRENT, and therefore uses more power and is louder..
And you are contradicting yourself, as you spent a lot of time trying to convince me that a higher impedance speaker uses more power. I hope the current divider explanation helped you.
"Also, people put different impedance speakers in cabs or on amps all the time. There is nothing inherently wrong with this. Think about it. If this were true, designers could only use one value of resistor in any given circuit.
In most bass cabs with piezo tweeters, for instance, the tweeters have a much higher impedance than the woofers. The tweeters are simply paralleled from the input jack or the woofers. No problems.
Many inexpensive PA and home stereo speakers also use this method. The higher impedance of the tweeter keeps the power level to the highs in an appropriate range. The piezo tweeters impede low freqs, and so the cab doesn't even need a crossover.
This concept is also used in some speaker clusters, where different impedance speakers are used to create what is called "amplitude shading". Using different impedances, different volumes can be had for different sections of a room, for instance."
gusfinley said:
This is all a little more complex... but for someone wanting to hook thier guitar amp up to a cabinet properly, it doesn't really matter.........
And thevenin equivalents and power loss into the transformer aren't complex? Those things above are actual real-world examples people can relate to. You just read the numbers on the amp, and the cab, and don't go below the minimum impedance stated on the amp. Use the formula for parallel impedance to find out the load if you use multiple cabs.
gusfinley said:
Actually in "industry" a impedance "match" is indicated by a factor of two.
Therefore according to industry there would be no problem hooking up a 8 ohn amp to a 4 or 16 ohm cab, but they rarely are dealing with the kinds of currents that the guitar amp is pumping out!! The "2 factor" makes it both possible and practical for designers!!..
I was speaking of the fallacy of using drivers of different impedances together being a bad idea. Using that logic would restrict designers trying to use more than one resistor value in a design. I also wanted to point out that people paralleling drivers of different impedances is very common in audio.
gusfinley said:
Anytime there is an impedance mismatch there ARE reflection happening, the worse the mismatch the worse the reflections - better to be safe and just match them anyhow... It may be a negligable effect, but it is still happening... If you want to SEE it - mismatch your connection bewteen the TV cable wall-plate and the TV - you'll see all sorts reflection screwing up you formerly beautiful picture!! Does it effect tone? Hard to say!!..
If speakers are hooked in series, actually you are right. The inductance is different if you hook speakers together in series vs. parallel, even if they are of the same impedance. It does indeed affect frequency response. Reflections in guitar amps are much more of a problem at low frequencies, though. And most are due to back EMF.
gusfinley said:
"There is a phenomenon called "back-EMF" where a signal is sent back to the amp from a speaker as it vibrates after the initial signal. The speaker itself generates the signal. This can be a problem, but is usually well accounted for in amp designs. This is the spec referred to as "damping factor"."
Hmm, haven't ventured into this - probally due to a the electomotance produced when the speaker vibrations are tranlated to the voice coil and then through the terminals and wire back to the amp. It would most likely be a neglegable effect... !!..
You have the cause correct. But it is far from negligible. It is the most important factor affecting accurate solid "tight" bass response, aside from good basic design. Back EMF reflects like you said above and clouds bass. Damping factor is a measure of how well the amp controls the speaker. Essentially it measures how well the amp can keep the correct voltage during large current changes, and damp down back-EMF. It is a directly linked to the output impedance of the amp. Lower output impedance=better damping factor. Amps also use negative feedback to increase damping factor.
gusfinley said:
Woah, That was exaustive!! I can see where a lot of the incorrect informations in your rebuttal was coming from - most of it would be true if the amp wasn't absorbing power, and didn't have a equivalent impedance...
Now you Know something that most people never will!!
I knew that, but though it irrelevant and confusing to anyone just trying to hook up a cab to their amp.
Ah, the hell with it. I'm doing my own page.