Impedance Explained (and Speaker Impedance)

[AndrewJohn 10,476]

I'm not a Tech, as I've said over and over..., I know enough to be dangerous.  And, generally, have "some" level of "understanding" of electronics concepts..., I just don't know how to use that understanding like the qualified techs here do.   I thank all of you techs for your patience in helping me learn and grow.

 

OK, having said that, I found this 4-year-old video from Axiom Audio, and found it to be exceptional in digging in and explaining "impedance", and further to understand what this means to speakers, how speakers are measured, what "nominal" means, and even how "amps see impedance" and why it matters.   

 

Heretofore before watching this guy explain impedance, I have found myself lost on one-sentence explanations that were presented by Circuit City and Best Buy salespeople, and internet know-it-alls on so many forums (Not TCS, though 😉 ).

 

At about 15:00, he explains the issues of mis-matched amps to speakers, heat, and protection or damage.  It made a lot of things make sense..., in my feeble brain.

 

Let me know what you think after watching this guy..., if you feel like it.

 

 

[Rob 5,985]

Well, here’s what I have experienced. My MXR had a perfectly working thermal protection system. I think those receivers are an 8 ohm unit and the Cerwin Vegas that I paired with them were 4 to 8 ohms. That receiver was abused in many many parties to the point where it would get so hot it would shutdown. 
 

I let it cool down for a few minutes and it would come back on. Then I bought a FAN!!! I wouldn’t buy anything as far as amps or receivers that didn’t have a protection mechanism in it. 
 

When I am pushing my amps I always have a fan on it. So maybe the amp is letting too much current flow with lower impedance speakers. I would be more worried about it if I was a person like I used to be. Now I’m not listening to music at the levels I used to so this is not something I worry about anymore and on top of that I can just repair what I burn up. 🤣🤣🤣

 

But yeh, Impedance is AC resistance. I can’t hear anything on DC current. 

Edited December 17, 2024 by Rob

[4krow 6,609]

Admittedly, there is some glossing over to through the basic points being discussed, but I find it invaluable for me to use this video to explain impedance to my son who had asked about AC in general. The more that I said, the harder it probably was to understand. I am not a teacher. This guy makes it clear enough to someone that has a basic concept of electrical knowledge (and I hope that the teacher of such subjects do as well, though it makes me wonder sometimes), to actually be able to discern the difference for a better understanding and possible application of this in 'their world'.  As it applies to home electrical, what AC is or how we get 220VAC at the breaker box is right out the window and even a point of argument for some, much less the load needed for the home itself.

[Nahash5150 10,713]

Impedance is imaginary.

[Sk1Bum 11,439]

1 hour ago, Nahash5150 said:

Impedance is imaginary.

 

Resistance is futile.

[4krow 6,609]

Hey-Hey, get off my cloud.

[Kurt 2,921]

Ok...so, i've heard all this before.  And, I think I understand the physics.  Being the proud owner of some vintage Infinity speakers, I know that low impedance, or "dipping into" low impedance at certain frequencies is harder on amp and why that is.  

 

But, here's what I don't know.... why would any speaker manufacturer design a speaker that that dips into low impedance?  What advantage does that provide in the process of making music out of the system?  ie, why wouldn't everyone just design 8 ohm speakers?.... Is it just about getting more power out of the same amp?  Or does a low impedance speaker offer some other advantage in making good sounding music?

[xavionics 2,071]

Time to clear some cobwebs out of that old part of my brain and see if I can put together an explanation…🥱

 

In an AC circuit, impedance is the total of resistance, capacitive reactance and inductive reactance.

Resistance is just that - straight up, one value, resistance to the flow of current.

Capacitive reactance and inductive reactance can be thought of as resistance that varies with frequency.

 

Capacitive reactance varies inversely to frequency.

Inductive reactance varies directly to frequency.

There’s a nice little read here on this: https://byjus.com/physics/reactance-and-impedance/

Add to this, in the case of a dynamic loudspeaker:

The woofer voice coil is an inductor. It’s “impedance” (inductive reactance) varies with frequency.

Add to this mix, though, are other properties of physics introduced by the movement of this inductor within the magnetic field, the mechanical resistance to movement of the whole piston (VC, its former and the cone), resonances, etc., and the impedance becomes a curve rather than a simple value.

 

Throw a passive crossover with capacitors and inductors into the mix, and, well, you have a system impedance with a “nominal” impedance rating that varies with frequency.

 

That’s my simplistic view anyway. Hope it helps.

Feel free to add and/or correct if needed.

Edited December 19, 2024 by xavionics

[Kurt 2,921]

That all makes sense.  But, why design a speaker that has overall low impedance, or very low impedance at certain frequencies?  Does that help with being able to replicate those frequencies perhaps?... if my speaker impedance dips to 1 Ohm at 75 hz, let's say, does that mean my speaker is better able to replicate a 75 hz frequency sound than a speaker that runs at 4 Ohms impedance at 75hz? Is there a benefit to the sound because the low impedance speaker is drawing more current at a given frequency?   

 

(side note.... thank you all for the physics/electrical engineering 101 lessons you are providing :).  My naturally curious mind can't help but continue to ask questions... feel free to tell me if I'm annoying and to 'go away', lol).

[4krow 6,609]

My thinking is that we work with what we are given. Low impedance means a call for more current.  It isn't really something that you can 'plan' so much about a certain part of the spectrum of the reproduced frequencies. Especially with drivers measured right around the 50 HZ spot, you will see a high impedance peak in every one that I have ever looked at. Just turns out that way. I mean, you are asking the driver to produce a certain range of frequencies and are hoping for an average that isn't too offensive to the amp driving it. So many times when looking at the frequency sweep you will see a steady rise in impedance as the frequency is increased. So this applies to cone type speakers with a voice coil as opposed to say a planar driver such as a Magnepan speaker which will read a steady 8 ohms or something across most of the frequency range. As you might guess, there are other troubles produced the planar design that are no inherent in the cone design.

[xavionics 2,071]

Hey Kurt, 

 

Greg is exactly right. We get no free ride in this world.

 

High efficiency

High power handling

High accuracy

Pick any two...

 

There's a phenomena in electric motors (and a dynamic driver is a motor) where the more physical resistance you apply to its  motion, the more current (and less impedance) it will require to keep driving.

OTOH, if you spin a motor externally (say, via a drill), the electrical power applied to the motor will require minimal current.

 

As Greg stated, at around 50 Hz it seems common for a woofer to peak in resistance.

If I have this correct, the reason for this is at this frequency, the mechanical desire for the driver to return to its neutral position is around 180 degrees out of phase with the electrical motors desire to move the voice coil. 

Think of it this way - a pulse pushes the cone outward.

As the cone returns to rest, another pulse tries to push the cone outward at the same time.

This second pulse needs more power - not only to produce the movement intended, but to counteract the opposing momentum the cone's mass has stored.

 

OTOH, when the pulses are at such a frequency that they get the cone to 'bounce' - less power is required to create the cone's movement because the cone is already moving ahead of the pulse.

So, very little effort is required and the impedance (resistance to the pulse) becomes less.

This is the frequency where the driver's impedance dips to minimum.

 

Unfortunately, you cannot engineer the driver/cone/motor/suspension/etc. to manage all parameters optimally.

Gain, Like Greg stated, you gotta work with what ya got.

 

There are other things going on as well. I think this would be a fun conversation over some adult libations.

 

To illustrate all this:

I bought a stereo 8-track player when I was in the 6th grade.

It didn't take me long to build some external speakers with parts bought at Radio Shack.

I know nothing of series or parallel connections. Two 7" full range drivers per enclosure were likely wired in parallel and connected to the internal amp outputs.

There were certain musical passages that would put the speakers into resonance.

It drew so much current that the power supply couldn't keep up and the tape drive would sag and slow down.

I listened to one of these albums yesterday while working in the shop.

I kinda chuckled to myself, remembering those days so long ago.

[Yamacarver 802]

4 hours ago, Kurt said:

why design a speaker that has overall low impedance? 

Because without it you would just have  headphones.

Yes it is to draw more power which translates into more sound assuming the efficiency of the speakers is the same.

Every object has a resonant frequency (see Tacoma narrows bridge disaster), so the key is to make sure it is outside of your operating parameters or that you can use it to your advantage. As in frequencies we are less sensitive to. Paul Mc says you don't want a flat response, it would sound terrible. 

[Kurt 2,921]

Thanks, guys, I think I get it now.  So when Arnie Nudell designed my Infinity Kappa 8's back in the '80's, the impedance curve he ended up with was just that... what he ended up with.  And, he made the decision that the excursions into fairly low impedance ranges would be ok as a trade off for everything else he was getting.  He was betting that his primary customers would be ok needing fairly sturdy amps to handle the speakers.  

[AndrewJohn 10,476]

1 hour ago, Kurt said:

the impedance curve he ended up with was just that... what he ended up with.

 

That is the proverbial dilemma of speaker designers..., they can model the physics in a number of digital modeling computer programs..., a good friend of mine in our local audio group here did his master's thesis at SIU on speaker design. The speakers he designed for his final project sound great - but not as good as the Paradigm towers he has in the same room... (that's another story).  For his degree in speaker design, he had to finish the pair by the end of the semester - but if it were a commercial operation, there would be several iterations before the design and physical specifications were final.  

 

Yes, it's "what they end up with"..., but I would ensure the statement didn't imply they punted after the first iteration and said "good enough."  I wasn't there, of course, but great engineering cycles design, modeling, prototype, test, revise, repeat, cycles - including speaker design, then final production.  I'm guessing that's what you meant.  I just feel that the Kappa series speakers had more than build it and "ship-it" approach.  I think somewhat differently about EPI designs..., 😉 but that and all this, is "my opinion."  YMMV.

[Kurt 2,921]

1 hour ago, AndrewJohn said:

 

That is the proverbial dilemma of speaker designers..., they can model the physics in a number of digital modeling computer programs..., a good friend of mine in our local audio group here did his master's thesis at SIU on speaker design. The speakers he designed for his final project sound great - but not as good as the Paradigm towers he has in the same room... (that's another story).  For his degree in speaker design, he had to finish the pair by the end of the semester - but if it were a commercial operation, there would be several iterations before the design and physical specifications were final.  

 

Yes, it's "what they end up with"..., but I would ensure the statement didn't imply they punted after the first iteration and said "good enough."  I wasn't there, of course, but great engineering cycles design, modeling, prototype, test, revise, repeat, cycles - including speaker design, then final production.  I'm guessing that's what you meant.  I just feel that the Kappa series speakers had more than build it and "ship-it" approach.  I think somewhat differently about EPI designs..., 😉 but that and all this, is "my opinion."  YMMV.

Yes, I was being kind of flippant with my comment.... I realize there's years of development that went into the design.... my point was, that speaker designers are not designing to a target impedence level.... rather, they are designing for the best sound, and letting the impedance be an outcome.... or maybe just a constraint (like cost or manufacturability).

[Nahash5150 10,713]

3 hours ago, Kurt said:

Thanks, guys, I think I get it now.  So when Arnie Nudell designed my Infinity Kappa 8's back in the '80's, the impedance curve he ended up with was just that... what he ended up with.  And, he made the decision that the excursions into fairly low impedance ranges would be ok as a trade off for everything else he was getting.  He was betting that his primary customers would be ok needing fairly sturdy amps to handle the speakers.  

 

If $30,000 tube amplifiers were commonplace, we would have a much different selection of speakers!

[4krow 6,609]

Yes, matching/synergy/luck. Before it was explained to me in better detail, I took shots at getting the best match between amp and speaker. Usually the result was too much of one thing and note enough of another. Unfortunately, there is more to the equation in that the listening environment applies at a level maybe even higher than speaker amp combo. Back to impedance, I wait for the day that there could be a real advance in dealing with all of this. Probably will come in the form of a new design that doesn't use the usual voice coil to begin with. I know, this has already been done with electrostatics and some other different designs. 

 In the publication called Voice Coil, I read about new or revised patents that are compelling but for one reason or another, fall short of what we already have. years ago, I talked with a designer who said that he thought that it was theoretically possible to aim two or more lasers adjacent to each other and the resulting focal point could be made into sound. hmmmm. It is that type of thinking that may lead us ahead many fields, audio included. I hope that I live long enough to see something successfully produce sound in a whole different way.

[AndrewJohn 10,476]

5 hours ago, Kurt said:

Yes, I was being kind of flippant with my comment.... I realize there's years of development that went into the design.... my point was, that speaker designers are not designing to a target impedence level.... rather, they are designing for the best sound, and letting the impedance be an outcome.... or maybe just a constraint (like cost or manufacturability).

 

And, then there's this, from the Carver Fest Speaker kit project (I have two, one pair still unassembled..., someday I'll get to it).

 

In thinking about this..., there's a great example of the iterative process of speaker design..., right here in the archives of The Carver Site.  Some great references and posts from some of the old-timers that I really miss, that made this site great and into what it has become...

 

In 2015, @Toy Maker, James Sauter, created a speaker kit for distribution to attendees at CarverFest that year.  It was based loosely on the Sunfire speakers of similar size...,  Here's one thread, and there is another with bob Carver listening to tune the crossover's more.  But I can't find that thread.  I'll keep looking, or if someone knows where it is, please post.