>RC owns a business that sells the information he has
>researched. I will not publish it as that would be
>copyright infringement. He is willing to send you a copy
>for free for personal review if you would only just give me
>your email address. Now give me the email address or
>concede....

Do you actually think I would give my address to you hounds? If he sells the information, tell me where to buy it in hard copy then. What bookstore? What sites? Where?

Remember, the objective is to prove there does not ever exist a case in which a speaker can be damaged through lack of sufficient power.
Or I may or may not accept an explaination on why my 12w6 seized on only 200watts.

Furthermore, if your making an argument based on his works, then you are infringing on the copyright; therefore, the readers of this forum can never know since you can never post them.

This is getting silly. Somebody either publish a work to forever put this to rest or this can go nowhere but stalemate.

 

>RanDawg...
>
>You can't dispute this.
>
>...And to prove me correct, I see you aren't going to try
>to!

I have and I did and you are acting very foolishly.

 

BTW, I will not be back for ~12 hrs, do not get all excited.

 

>>RC owns a business that sells the information he has
>>researched. I will not publish it as that would be
>>copyright infringement. He is willing to send you a copy
>>for free for personal review if you would only just give me
>>your email address. Now give me the email address or
>>concede....
>
>Do you actually think I would give my address to you hounds?


Create a new E-mail account. It takes 3 minutes to make a hotmail account, that's about a 10th the ammount of time you probably spend reading your future posts. You obviously have the time. You can even use a fake adress like 123 Happyland PA 90210, and put your name down as Peat Moss.

You are just making excuses, you seem incapable of admitting that you are wrong. You've been provided with everything you've asked for from the other people here and you pick out bits and pieces to respond to, ignoring anything that goes against your opinion, sometimes cutting sentences in half and responding as if that was the whole thing.

>>This is getting silly. Somebody either publish a work to
>>forever put this to rest or this can go nowhere but stalemate.

Yes this is getting silly. Dave is willing to send you RCs work and you are refusing it for reasons that make no sense. It won't be a stalemate in that case, remember, you have put yourself in a position where you must defend yourself. If you ignore this and don't accept RCs work, which Dave is willing to send you, you will be considered to have conceded as wrong.

 

>>Posted by RanDawg
>>either get more of what you already have, or get bigger subs
>>w/biggers cones and mags.
>>
>>remember, your amp should always be able to put out more
>>than your drivers are rated at, never the other way around.
>
>Posted by Tempe
>A larger size motor doesn't necassarily mean the sub will
>get louder. And why do you recommend AGAINST an amp that is
>rated for less than what the sub is rated for? The amp's
>power rating is just a number; it's up to the user to
>determine how many watts the amp will actually put out.
>Tell me what is the difference between the following:
>
>* A 400 watt amp pushing 150 watts to a 200 watt sub
>* A 150 watt amp pushing 150 watts to a 200 watt sub
>
>The sub sees 150 watts either way.

To the best of my knowledge, these fine gentlemen have supported my post which you have been trying to dispute for the past five-and-a-half days.

>Posted by Tempe
>

>Please read the above thread, particularly dnewma04's
>replies. He explained it MUCH better than I have able to.
>
>(edit: you must copy/paste the whole link as this forum
>won't accept the link)
>
>Tempe

Does anyone here contest Dave's post?

>Posted by Tempe ([link:http://www.ford-trucks.com/dcforum/D...D96/876_2.html|here])
>
>i'm not gonna lie to you and say i know more about
>subwoofers and enclosures than Ben Milne, Scott Atwell, Dan
>Wiggins, etc, but i feel i know a great amount of knowledge
>for the time i have been in car audio. if i am unsure of
>something, i have many people to either correct me or back
>me up.

One of those people is Dave Newman. Not only do I have people to help me, but so does Dave. I'm sure you have become aquainted with them by now.

I have remained silent while these very intelligent human beings have composed much better replies than I could have. Throughout many recent posts, you have been offered to view RC's paper at no charge to yourself. What is so hard about creating a Hotmail or Yahoo email account, as mentioned above?

HonkeytonkMonkey said it best when describing his relation to dnewma04. About the best thing he did was listen to an educated person and learned a thing or two about car audio. I cannot fathom why you won't listen to others. Not long ago, I replied to a post with false information. In fact, that false information came from Car Audio and Electronics (or could have been AS&S)! When dnewma04 tried correcting me, I listened to what he had to say and read his links--which he provided to back up his information. I don't understand what it takes for you to give up your pride and admit that you are wrong.

Richard Clark, Dan Wiggins, and Warbleed have all said that you are wrong. I cannot believe that you would disagree with these guys.

Tempe

 

Gentlemen,

I have been following this thread since the debate started. I would like to thank EVERYONE who has posted in it for the information - I am learning more as I read. Last time I walked out of an IASCA competition was over 10 years ago, and alot has changed since then. I still see myself as a person who can build a quality sound system, as I still help do it for friends and others. But I do not have the scientific (for lack of a better word) knowledge that you all seem to have.

Also, I commend everyone for not turning this into a flame session thread. There have been a few personal comments made towards each other, but you have kept your posts clean and ontrack with the discussions. And now, back to your discussion...

 

grown men arguin over the internet is silly. why must u go on and on with this...

 

>grown men arguin over the internet is silly. why must u go
>on and on with this...

I agree, this is insane. I have better things to do. Changing my mind is not changing the world and no one should care. I said in the beginning I did not want get into a pissing contest, and they have dragged me into one.

If anyone wants to be the loudest, get a servo-drive. If anyone wants the best sound, get a Lowther. Neither can be underdriven and no other design has surpassed them.

 

"There are only two ways to blow a speaker: thermally or mechanically (whose secondary effects are often thermal). Both forms can be characterized by separate varying power thresholds, whereby the power content of a signal will have a detrimental and irreversible effect on the speaker if and only if it exceeds either threshold for a certain period of time.

The term “underpowering” then, when used in the context of speaker damage, is a misnomer. In the same way the term “overpower” means to deliver more power to a speaker than it can safely handle, the term “underpower” would mean to deliver less power to a speaker than it can safely handle. This, by definition, would have no adverse effect on the speaker"

so the only 2 ways a driver can blow is thermal or mechanical.

"As shown, the effects of clipping are numerous, and each contribute to either a decrease in power handling of the driver or an increase in power delivered to the driver. But there's no aspect of a clipped wave in and of itself that's inherently damaging to a loudspeaker. This may have seemed like common sense even before reading this, but the notion of "underpowering" necessarily having the potential to damage your speaker derives from the fallacious idea that "clipping blows speakers". I hope I've shown that there's one thing common to each adverse effect a clipped signal can have on a loudspeaker, and that's power. No, clipping and "underpowering" do not blow speakers. Power does."

so from what i read, clipping will blow a sub cuz it sends a amplified boost of power to a driver causing it to overheat the voice coils which causes melt down aka themral.

another thing i read and it made sense was, when u push on the cone of a woofer does it not move back into the same place after u let go? kinda like a car suspension?

i dunno if i made sense or not but this is what i got outta www.termpro.com forum and http://www.geocities.com/decriminalizefreedom/clipping.html

im not tryin to add wood to the fire here, just tryint to clarify things for myself cuz im confused at the moment.

 

>
>>First off, the suspension of the subwoofer will pull a
>>subwoofer back to center if a signal is suddenly eliminated.
>
>Not necessarily fast enough. But given enough time, all
>things that oscillate will return to center (as you call
>it).
>
An irrelevant point...
Delay or not, the cone motion won't exceed the AMPLITUDE of the signal being input.
And without HIGH AMPLITUDE (ie. high voltage, ie. high power), you won't risk bottoming the subwoofer out.
Also, without HIGH AMPLITUDE, you won't thermally harm the voice coil, period.

High power is NOT the "less than RMS" low power scenario that you are claiming killed the subwoofer.

So, even if there is a delay, it will be by such nominally small fractions of a second as to be nothing but potential pollution in your analysis.

A delay is much different than having a signal present, then completely removed, which would be the only way that the cone could be sent moving in one direction, and then have momentum to keep going in that same direction...
Unless you were clipping a signal so badly as to take away the smoothly rotating current phase angle... creating the nearly square-wave scenario.
Again, NOT the "amp was not clipping" scenario you were discussing.

>>So...
>>Important: If the subwoofer doesn't have a large amount of
>>power to begin with (less than RMS in this discussion), it
>>doesn't have enough momentum to carry itself outside of
>>Xmax.
>
>I was wondering how long it would take you to discover this.
> Well done.
>

No, obviously you were basing a lot of your theory around this not being true.
This is something that most of us posting here take for granted, and most of us in the industry take for granted.
It's very intuitive if you understand how a speaker works.


>
>However, I foresaw this move as you see, and I
>say there is atleast one possibility (which is all I need to
>debunk the claim). If the amp has enough power atfirst to
>throw the cone into oscillation, and then this power wanes,
>the cone will have enough energy stored in it to cause
>damage when control is sufficiently lost.
>

Again, your own statement "If the amp has enough power at first"..
This is HIGH POWER, more than RMS, NOT the scenario you are trying to debate.
This scenario is not possible without either:
1) incorrect amp settings (you say this was not the case, not user error)
2) a defective amp

>
>Not to mention if
>the amp is forced to change voltage because it can't keep
>the current up.
>

This is a function of the source.. and it happens progressively, inherently...
It's not like the amp suddenly "switches"!
It is laughable that you would bring this up.
But of course, if the voltage is less, the current needed to be drawn will rise - that's BECAUSE the power being output from the amp - if it is a regulated amp - is being held relatively constant!
And the power to the speaker IS WHAT WE CARE ABOUT.

And if the amp is NOT a regulated amp, if the voltage supply starts to dip, the power would drop accordingly. Again, there's no "sudden drop" here... AND most importantly, at it's highest, most powerful moment, when you first switched the thing on with the truck running, or on a full battery... it will not exceed it's normal power output...

...and this is in the scope of an amp whose RMS power rating is lower than the RMS of the sub (again, THAT is the scenario we are discussnig!).
So the possibility of the power coming from the amp exceeding the power capabilities of the sub - particularly in the scope of not the RMS rating, but the actual instantanious power handling capability of the sub, is as close to zero as could be considered.

>
>And then not to mention any impedance
>changes as a result of a lagging effect of the cone with
>respect to the current per any given frequency. Remember,
>we cannot always assume the supply power will be constant,
>can we?
>

We can expect the power supply will be reasonably constant..
What I mean by this is constant enough that the amp won't suffer from extreme drops in output.
And again, if the amp is
The important thing to assume is:
"It is safe to say the voltage won't EXCEED 14.5 volts"
Which would be the only way we would create MORE power from the amp than we expected, and even in that case, only from an unregulated amp, and even still, power output would only increase proportionally.

>
>Yes, I am quite familiar with the design and construction of
>a speaker.
>
Obviously not too familiar beyond the absolute basics.
You are making correlations to what you understand about inductors on the fly here, it's obvious.

>
>Furthermore, I am relatively familiar with
>magnetic fields and the forces derived from them. IE.
>force=charge*velocity*magnetic field. The works of Tesla
>are very old you know. The flux is the integral of the
>field with respect to the area. Then torque is defined by
>current*field*area*sin(angle between the field and the area)
>or you could just say that torque is the product of the
>field and the vector magnetic momentum. That's right,
>magnetic momentum. But you are forcing me to recall things
>from years ago. I know what I know from a basic
>understanding of how this works, and have formed my opinions
>from that time, never intending to have to back them up
>years later. Like I said, submit your work publically, I
>will have them reviewed by someone respected, then you will
>be given credit if they hold water.
>
Drop names, reference famous people all you like.. it has no relevance in this discussion, unless you have a point to make by it.
All trivia will do is get you a spot on Jeopardy.
I'm not interested in trivia, and all you are doing is conveying your weak ego, from my perspective.
Let's stay on the topic at hand.
It's been more years for me than for you, I assure you..
Again, this simply conveys your youth.
And while youth breeds enthusiasm (obviously you have that), it also often breeds a recklessness (observed) and a cockiness (that you are certainly trying to convey) that will just lead to embarassment.
That's just my opinion, take it as you wish.


>>
>>As you get to the peak of the sine wave, the current begins
>>to change direction.. so your "out" goes "out" slower and
>>slower until you cross over the peak, then the magnetic
>>force grows weaker and weaker, the cone begins heading back
>>to the at rest position...
>
>Good thing I'm not relying on you to grind the cam for my
>engine with thinking like that. Yeah, current changes
>direction fast alright, but the cone does not. Fact is, at
>that point, the cone is lagging the current by a certain
>phase angle and hopefully will catch up further thru the
>cycle.
>

There's no "hopefully"!
That's how it is! Like mentioned above, because of this, the lag is negligable.
Also why I mentioned my first point was simply a "safety net".
Because yes, always, the cone will follow the direction changes of the magnetic field in the coil.
Even if signal were suddenly taken away as the cone were heading outward, it's momentum would be squelched by the suspension, except in high power situations, which is NOT WHAT WE ARE DISCUSSING.

Your correlation to a motor is not relevant as it pertains to cam grinds...
It is relevent if you were discussing piston travel, relative to the angle of the crank! It's much more closely correlated to that!
See, with a cam, you have a valve following the cam (via a follower, or a pushrod on a follower.. you get the gist). You can spin the motor too fast, and have the valve "float" off the follower, as the spring can no longer keep up. You don't have that scenario with a subwoofer, until you reach both ultra-high power levels, and ultra-high levels of clipping!
...which, again, is NOT WHAT WE ARE DISCUSSING.
At low power levels, we are much more like the pistons following the crank. There's no float.

>
>From the sound of this, I could tell you more about
>sinewaves than you could muster up the attention to sit and
>listen. I actually know what a sine is.
>
It's not that you couldn't define it in textbook terms..
It's that you fail to correlate phase angle with magnetic field with cone motion, how a signal (which in pure, easy to visualize form, appears as a sine wave does) translates into cone motion...
Because if you could, you would realize there is no point that is worse than another, the phase angle shifts smoothly, and along with it the magnetic field, and along with it the cone motion (negligable physical delay or not)...
That is, no point worse than another unless you are clipping the amp, and that has been explicitly stated as to not have been the problem.

>
>I think you need to sit and think this through. And a good
>book on physics in front of you wouldn't hurt either. After
>all, you may just learn something.
>

Well, if this isn't the finest example of the pot calling the kettle black, I don't know what is.
A book on physics is not what you need, in this case.. all you will get is a bunch of abstractions for you to interpret and apply.
What you need to reference is some good material on how a loudspeaker operates!
I am not suggesting that the field of physics is where you are lacking..
What I am suggesting is that the application of physics to this topic is where you are lacking, that sort of material would prove invaluable in this case.

I would suggest as a great reference "The Loudspeaker Design Cookbook", by Vance Dickason. It has been a longstanding highly regarded guide not only to driver design and how a driver operates, but also enclosure design, crossover design, and the important relationships between these items, as the only thing that truly matters is the sound coming out of the thing in the end.
It is also commonly available.

>
>Another thing, please don't form a whole argument after you have >screwed up already, it just wastes space. You cannot build a sound >argument on physical fallacies. It just makes for more crap I have >to go through and delete while responding. Your lack of careful >consideration of who you are dealing with may be your downfall. I >have stated my credentials w/o error. I suggest you read them again.
>
Again, the cockiness, the immaturity, the denial.
This isnt' about ego, it's about correctness.
I suggest you be careful of who you spread your tailfeathers in front of as well...

>
>I'm outta here for now. You spend a couple days to get your argument >together and either post it here for review or post a link to it >where the public may review it. Until then....
>
Once again, you should review the first chapter of "The Loudspeaker Design Cookbook", by Vance Dickason.

"Considered by many to be the ‘Bible’ of loudspeaker design,this book offers you everything you need to know to build a loudspeaker system. It’s opening chapter gives a very detailed description of how a loudspeaker works. Subsequent chapters cover topics such as closed box low frequency systems, passive radiator low frequency systems, passive and active crossover systems and so on. It also includes advice on cabinet construction and loudspeaker testing, and closes with two detailed chapters on home theatre and car audio loudspeakers."

This should also prove sufficient as the "publicly available, creditable" information you are looking for.
I am sure this information is readily available online, should you choose to search for it that way.

What is important is the bottom line though...
To me, I believe your misunderstanding comes from your current apparent inability to complete the statement:
"Cone motion in a subwoofer is defined by _________________"
A bit of research on your part (not mine, but thanks for the suggestion ) - will solve this relatively quickly for you.

But it takes some effort on your part.

We have been trying for days trying to communicate to you that you are simply wrong. Talking to some people is like talking to the wall.
Don't take this the wrong way, but you are being regarded as a laughing stock by the entire online car audio community who is viewing this through the windows of the threads discussing this thread... and that includes novice through industry engineer level
There's a time to take a step back and ask yourself "Why am I the only one who thinks it is possible for loudspeakers to behave this way?"
Is it more likely that you are incorrect, or everyone else?

I would suggest you do a little reading on this subject in general...
And in specific, how the amplitude of a signal affects cone motion in a loudspeaker..
That is, after all, what this whole discussion is about.

 

>Changing my mind is not changing the world and no one should
>care. I said in the beginning I did not want get into a
>pissing contest, and they have dragged me into one.
>

At this point, the audience is larger than you..
The audience includes a signifigant number of watchers who have been pointed this way from the outside...
People who do deserve to, and anticipate, coming to a conclusion on this topic.

 

optikal illushun, follow me here


>>>First off, the suspension of the subwoofer will pull a
>>>subwoofer back to center if a signal is suddenly eliminated.
>>
>>Not necessarily fast enough. But given enough time, all
>>things that oscillate will return to center (as you call
>>it).
>>
>An irrelevant point...
>Delay or not, the cone motion won't exceed the AMPLITUDE of
>the signal being input.

False. Think about it, if you push something, will it not have momentum? Will it continue to want to move until some outside force stops it? Since the rest of the argument is built largely on this false claim, there is no point in continuing.

 

[updated:LAST EDITED ON 01-11-03 AT 05:38 PM (EST)]>optikal illushun, follow me here
>
>
>>An irrelevant point...
>>Delay or not, the cone motion won't exceed the AMPLITUDE of
>>the signal being input.
>
>False. Think about it, if you push something, will it not
>have momentum? Will it continue to want to move until some
>outside force stops it? Since the rest of the argument is
>built largely on this false claim, there is no point in
>continuing.

Your statement is incorrect on two fronts:
1) Phase angle comes into play, the electromagnetic force working against the static magnetic force pushing the cone.
The phase angle is steadily changing direction, and the magnetic force is steadily changing with it.
At what point do you propose that the cone, which WAS following the steadily changing directions, suddenly decides to stop steadily changing directions?
That is what is not possible...

at least without clipping...
At that point, you have a point where the voice coil's magnetic force changes are no longer steadily rotating!

2) My points about the suspension behaving as a "safety net" come into play here too.. not to mention the forces inside your properly-designed enclosure acting to counter the cone's motion.
Because even if there was a sudden removal of signal, the suspension would be a force against this momentum. As would the enclosure itself.
It would take a high amount of power to overcome this counter-force that is trying to pull the cone back to center...
And the forces of air movement inside the enclosure (proper enclosure for the subwoofer and the material being played on it, right?) will also work together to prevent this scenario from playing out...
All physical forces OTHER than momentum.

And you are thinking of this momentum incorrectly as well!
The magnetic forces change via rotating phase angles...
it's nothing like
"LAUNCH THE CONE OUTWARD!"
"Now LAUNCH THE CONE INWARD!"
"NOW BACK OUT AGAIN! FIRE!"
That's the sort of scenario you would need to have momentum like you are anticipating.. again, unless the signal was suddenly removed... and even so, the enclosure and suspension are "safety nets" in that they would have to be overcome...

And what would it take to overcome them?
GIVEN the right size enclosure for this subwoofer and listening material (otherwise it would be user error, right?)..
GIVEN the amp is not clipping (user error)..
It would take HIGH AMOUNTS OF POWER...
Which is not the scenario we are discussing!

But as regards momentum, as it is in reality, with the rotating phase angles and rotating magnetic forces, the voice coil itself is slowing itself down, pulling itself back the other way, slowing itself down again, going back the other way.

Plus, like the point I made that you quoted...
The cone's motion can't be greater than the forces pushing against it.
If you don't have much power to push the cone to begin with, it can't just suddenly decide that "because of momentum" it's going to fly outward further, or it's just going to keep going backwards until it crashes on the backplate!

So, continue on to the next point in my last post.
Hopefully this wasn't the sole basis for your entire hypothesis....

 

[updated:LAST EDITED ON 01-11-03 AT 05:30 PM (EST)]Read these...
(You were asking for "creditable" sources of information)
Do you believe you know something that Richard Clark., Dan Wiggins, Manville Smith, and David Navone - and many, many, many other industry engineers and owners?



"---clipping is not the key to anything-----speakers don't know the difference between a unclipped or clipped waveform----the only thing that they respond to is power----and power is converted to either movement or heat and the spape of the waveform means nothing----it looks like you believe the same misconception as the rest of the world-----so what is the solution to keep that 600 watt sub from blowing??? i hope you don't believe that a 600 watt amp would have saved that 600 watt sub----- cause when the customer clips that 600 watt amp the sub will get 1200 watts and it will blow even faster..........RC "

- Richard Clark, Technical Editor Carsound Magazine



"Hi all,
Power is power. The speaker doesn't know if it's clipped, clean, or what. It knows there is power. And power is what kills speakers.
One thing to correct - a clipped signal does NOT create DC; this is an oft-repeated myth that should be eliminated. When you clip a signal, you actually INCREASE the HIGH frequency content! DC would be the opposite - removal of high frequency signal content.
In fact, the ultimate clipped signal would be strikingly similar to a square wave. A square wave is nothing more than a set of harmonically related sine waves - there is no DC component present. It is all AC.
This is, in fact, why clipped amps are literally murder on tweeters. Clipped signals contain much more high frequency energy than unclipped signals. This is readily passed by the high pass filter of the tweeter, and means the tweeter can receive 2-10X as much power as anticipated, and quickly blows out.
Anyway, too much power - clipped or unclipped - is what kills speakers. You can toast an speaker with clean or clipped signals. Just give it too much power.
To answer the original question, you can push the driver to its full limits with that amp, so I'd recommend running the gains down a bit, and if you hear nasty bumps/distortion from the sub, turn it down even more.
Note that you won't get more SPL from ANY driver once you're at its limits, regardless of how much more power you pour on. The nice thing about larger boxes is that you need less power to reach the limits. Would you rather hit full output with 100W or 1000W? Personally, I'll take the 100W, since it's less thermal strain on the driver and amp, and less draw on the alternator.
Once you're at the limit, you're there. More power won't help. "

- Dan Wiggins, CEO Adire Audio




"I would suggest that everyone download and read the following paper, from the excellent Rane website.... this is as close to the truth on the "power or distortion blows speakers" discussion as you will get...

http://www.rane.com/pdf/note128.pdf

Regards,

Manville Smith
JL Audio, Inc. "

- Manville Smith, JL Audio




"Wow. Doesn't anyone here recall that the recommended gain structure for 99% of all car audio system calls for a 3:1 voltage overload at the amp - speaker? This means that if the amp clips at 2 volts, we recommend feeding it 6 volts at the wide open, full pop level. Not only do we recommend "clipping" the amp, we recommend that it be super clipped.
Clipping doesn't damage speakers. A speaker is just a piece of paper driven by a coil of wire suspended in a permanent magnet. How could a speaker ever know the difference between a clipped signal and an unclipped signal? It's just a speaker. "

- David Navone. Carsound Magazine



Clipping does not destroy speakers.... and clipping extremely underpowered speakers does abosolutely nothing.
It's just electricity going through a coil of wire.

Think this thread is not gaining attention?

 

Objective: Power is not proportional nor in phase with either the voltage or the current in an R-L circuit.

Definitions: PI=3.1415926..., F=frequency, t=time, L=inductance in henrys. The rest is explained as progressed.

PROOF:
The instantaneous potential difference is the max potential difference multiplied by the cosine of the angular velocity multiplied by time. Or say v=V*cos(2*PI*F*t).

The same can be said about current, i=I*cos(2*PI*F*t)

Now, we can apply ohm's law to this, V=I*R

Therefore, v=i*R and then by substitution we have v=I*R*cos(2*PI*F*t). This is the instantaneous potential difference (voltage) across a resistor.

Now, how about an inductor? We start with ohm's law again, V=I*R

The induced EMF is given by E=L*(slope of i plotted against t or di/dt). Now, by substitution we have, E=L*d(I*cos(2*PI*F*t))/dt which works out to be -I*(2*PI*F)*L*sin(2*PI*F*t). Now, since cos(anyangle+90)=-sin(sameangle) we can substitute and write: E=I*(2*PI*F)*L*cos(2*PI*F+90). This result shows that voltage can be viewed as a cosine function with a head start of 90 degrees. Thus, for a pure inductor, we can say the voltage leads the current by 90 degrees, or 1/4 cycle.

Now, on to power. Instantaneous power is given by p=v*i. In the case of a pure resistor, v*i is always positive because v and i are always in phase with each other and are always both positive or both negative. But, in the case of an inductor, the voltage leads the current by 90 degrees and they are not always both negative or both positive. Therefore, when we multiply v*i, the product is negative for half a cycle and positive for the other half and is neither in phase with i or v. The average power is zero and when p is positive, the field in the inductor is being produced and when p is negative, the field is collapsing. The net energy transfer over one cycle is 0.

Anyway, the instantaneous power=(V*cos(2*PI*F*t+90))*(I*cos(2*PI*F*t)) for a pure inductor.

When we add resistance and/or capacitance to the mix, we can't use 90 degrees any longer. We must use a phase angle with respect to the current i and the instantaneous power p. Call this phase angle Ph, then cos(Ph) is called the power factor of the circuit. To compute the power factor for an L-R circuit, we may use this equation, tan(Ph)=(2*PI*F*L)/R, solve for Ph and then take the cosine.

A low power factor is undesirable in power circuits because, for a given potential difference, a large current is needed to supply a given amount of power.

If you have to read this more than 3 or 4 times and still do not understand, you may need an elementary book on circuits and/or physics. However, your complete understanding is required before we can progress any further in this study. Please let me know when you understand.