Physics question about ohms

Ducati Guy

So with wires 12 gauge wires are thicker than 18 gauge. Smaller gauge =thicker wire

Ohms are the measure of electrical resistance in a circuit.
So which speakers have more electrical resistance, 4 ohms or 8 ohms?
Is it the "opposite" like how wire gauges are measured?

I'd like someone with an engineering background to explain this?

And if 4 ohm speakers have less electrical resistance why do they make amps work harder/run hotter?

Please answer if you're only 100% certain of the science. I am wanting to better learn these basic concepts.

Thanks

BlueFox

Yes sir. Whatever you say.

I=E/R. 'I' = current, 'E' = voltage, 'R' = resistance.

'I' is inversely proportional to 'R'. 'R' goes down, 'I' goes up.

SCompRacer

A good page to explain Ohms and impedance.

http://www.prestonelectronics.com/audio/Impedance.htm

nguyendot

Lower impedance = lower resistance (lower ohms). Means the restriction on your receiver to put out power is lower....demanding more power. More power = more heat = more stress on a receiver/amp.

It's like running down a hill...that's too steep.

Ducati Guy

Yes even with a question at 1am, you guys come thru, thanks.

So, 4ohm speakers have less resistance than 8 ohms,
and this allows more electricity to flow from the amp,
thus a hotter running amp.

Is my flow of logic correct?

Speedskater

Yes but it's tricky.

The lower the load resistance (really it's impedance) the more current can flow (at whatever voltage) so more current times voltage equals more power.

Now with the wires. They are not the desired load, so we use a different formula. The bigger the wire, the less it resists current flow to the desired load.

Now as to the "hotter running amp" part.

Modern amps are often least efficient at about 1/3 power. That's why the old FTC test rule required pre-conditioning the amp at 1/3 power steady for 1/2 hour. The Stereophile tests often write about amps that fail this part of the test.

But in general, low resistance loads run hotter.

Note that:

Low impedance loads use more current & less voltage.
High impedance loads use more voltage & less current.

Ducati Guy

So impedance is the same thing as resistance, right?

So what's the definition of current?
And
What's the definition of voltage?

mhardy6647

Impedance is the AC analog of resistance and it obeys Ohm's Law.
The trick about impedance is that it is (in a mathematical sense) a complex quantity with three components, resistance, inductance, and capacitance. Resistance is independent of frequency (and you'll see it referred to as "DC resistance" in discussion of speakers and crossover components), but capacitance and inductance are frequency-dependent. This is why we talk about the "nominal impedance" of a loudspeaker system or a speaker driver.

The "complex" part is that these components (inductance and capacitance) are vectors not scalars - both the amplitude and phase are important to the contribution of inductance and capacitance to the impedance at any given frequency for a wire, or a coil (choke) or a resistor or a capacitor or what-have-you. This is part of what makes loudspeaker (and crossover) design so much fun! :-)

EDIT: Current describes the rate of transfer of charge 1 ampere = 1 coulomb of charge per second

Here's a really good tutorial (IMO) on the subject of measuring Thiele-Small parameters which, if nothing else, illustrates the frequency dependence of impedance for a speaker driver (woofer) and should give you some sense of why the impedance curve varies as it does.

http://sound.westhost.com/tsp.htm

Lots of interesting articles, projects and designs on that site, BTW.

EDIT:

Current describes the rate of transfer of charge 1 ampere = 1 coulomb of charge per second

Voltage is a measurement of electrical potential (electromotive force): one volt is the amount of potential difference required to develop a current flow of one ampere through a resistance of one Ohm.

stretchl

I sense a student with a paper due this morning!

mhardy6647

Ohm's law is often described by analogy of the flow of water through a garden hose.

The resistance is analogous to the diameter of the hose
The voltage is analogous to the water pressure
The current is analogous to the flow rate of the water through the hose

http://www.allaboutcircuits.com/vol_1/chpt_2/2.html

nwohlford

You can think of impedance as being the AC equivalent of DC resistance (i.e., the opposition of current flow for a given voltage). It includes the effects of the capacitance and inductance in the circuit have in opposing the flow of current.

Current is the flow of an electric charge. (It is often misstated as the flow of electrons.)

Voltage is best thought of as the electric potential difference between two points. In audio system, it would be the difference between the positive and negative. (In most, cases the negative is ground.) If there is a voltage difference between two points in a circuit, then current will flow.

In simple terms in an audio system, the amplifier takes the signal input to it and increases the voltage by some set gain (usually somewhere 20-35 dB). The speaker's impedance is the load (or opposition to current flow through the circuit). The lower the opposition the higher the current flow will be (i.e., lower impedance means higher current). Of course, if the amplifier can not supply the needed current that is when you have clipping. (You can also have clipping on the voltage side.)

BlueFox

Ducati Guy wrote: »

So impedance is the same thing as resistance, right?

So what's the definition of current?
And
What's the definition of voltage?

There is a new and very useful tool called 'Google'.

Jhayman

Rofl....good one Bluefox although I have no idea if you're joking or being serious..

BlueFox wrote: »

Yes sir. Whatever you say.

I=E/R. 'I' = current, 'E' = voltage, 'R' = resistance.

'I' is inversely proportional to 'R'. 'R' goes down, 'I' goes up.

Jhayman

Yes that's the way I remember it from school the water hose analogy which they also use for explaining how cable Internet works..

mhardy6647 wrote: »

Ohm's law is often described by analogy of the flow of water through a garden hose.

The resistance is analogous to the diameter of the hose
The voltage is analogous to the water pressure
The current is analogous to the flow rate of the water through the hose

http://www.allaboutcircuits.com/vol_1/chpt_2/2.html

Ducati Guy

Thanks guys that does help me understand it a little better.
The garden hose analogy helps.

I feel like the couch potato eating Cheetos while watching Stephen Hawkings explain worm holes, " yeah, I get it now as I grab for my 2nd bag of Cheetos".

It's been 22 yrs since my last physics class I had to take in college. I'm a doc not an engineer, so learning these
Concepts is like learning a foreign language, you don't really understand it until you use it.

One more question, so how does amplifier watts relate to all this?

CoolJazz

Something I don't thik was said exactly is this....

A point of confusion is that...

- Ohms is the unit of measure for DC resistance.

- Ohms is also the unit of measure for AC inductance.


So it's easy to start confused, stay confused and get even more confused as you try to understand. But a lot of explanation above goes on into the details. But (DC) resistance is only one simple thing. The inductance aspect has more to it. In speakers when you're given a number, that's what the driver is considered to be, but that doesn't reflect that the value will actually change as you change frequence.'


CJ

cnh

Ducati Guy wrote: »

Thanks guys that does help me understand it a little better.
The garden hose analogy helps.

I feel like the couch potato eating Cheetos while watching Stephen Hawkings explain worm holes, " yeah, I get it now as I grab for my 2nd bag of Cheetos".

It's been 22 yrs since my last physics class I had to take in college. I'm a doc not an engineer, so learning these
Concepts is like learning a foreign language, you don't really understand it until you use it.

One more question, so how does amplifier watts relate to all this?

The funny thing about all this is that it is rather low level introductory physics. Yet once you move to ask about amplifiers and watts, you begin to enter the domain of the designer/engineer and the lingo can become even more rarefied as if it isn't already. You're quite right though. If you are an electrician you have to have some working knowledge for how all the above "jargon" and elementary equations translate into what you have to do each day.

As for me, I don't think that anything short of a primer by Nelson Pass, or John Curl with a LOT of dumbing down for the layman can really lead to anything more than a superficial understanding of what's involed--just like the general discussions in Stephen Hawking's series for us lay boys and girls--the real work, equations are so far beyond us and the analogies are so GROSS that we have only the "slightest" understanding of what these guys are actually doing since the most important part is High Level Math--pure numerical abstractions that translate badly into ordinary language, or not at all. I look at a circuit drawing and I have no idea what is going on there let alone of the schematics that my Tech repair guy deals with when he cracks open the case of one of my old amps? lol

cnh

nguyendot

And people don't think there are smart people on a lowly Polk speaker forum.....

bikezappa

Ducati

The answers people have given are ok but I don't think you can get the complete answer in one or two paragraphs. It took me a semester at college to understand just the very basics of what you are asking. The key for me to determine if I understood the theory of basic EE was to do problems, lots of problems. You need to be good doing math problems with at least a good feeling doing basic algebra and hopefully calculus. Sorry if this isn't the answer to want but that's what it is.

Peter

nhhiep

this thread reminds me of something I've always wondering about. how come most expensive, high end speakers are 4 ohms? while stuffs at BB or Fry's usually 8ohms?

I was surprised that the LsiM is 8ohms, while Lsi is 4. so the ohms thing has little relation to sound quality right? if yes, then why did Polk make some 4 and 8 ohms speakers? why not just design all speakers with 8 ohms? so all AVRs can handle it, thus more sales too.

rpf65

nhhiep wrote: »

this thread reminds me of something I've always wondering about. how come most expensive, high end speakers are 4 ohms? while stuffs at BB or Fry's usually 8ohms?

I was surprised that the LsiM is 8ohms, while Lsi is 4. so the ohms thing has little relation to sound quality right? if yes, then why did Polk make some 4 and 8 ohms speakers? why not just design all speakers with 8 ohms? so all AVRs can handle it, thus more sales too.

Simple answer; power. Low impedance speakers will "force" the amp to put out higher current, in a sense, which equals more power.
Problem is being able to match that low impedance, Really is a pretty complicated process.

Face

Then there's the problem of phase angle...

Msabot1

And don't forget your right triangle trig either!

Ducati Guy

So using the garden hose analogy what do watts mean?

zingo

The watt is defined as one joule per second, measures the rate of energy conversion or transfer; that would be the liters per seconds for the garden hose.

bikezappa

In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241

Ocezam

nguyendot wrote: »

Lower impedance = lower resistance (lower ohms). Means the restriction on your receiver to put out power is lower....demanding more power. More power = more heat = more stress on a receiver/amp.

It's like running down a hill...that's too steep.

That's an good analogy.

Msabot1

Watts would be the force at the nozzle of the hose...current,the flow through the hose and resistance the diameter of the hose itself. The nozzle is actually a pot...a variable resistor P=IXE...power expressed in watts.

Ducati Guy

Still pretty confused about watts?

tonyb

Some good analogies going on. From my perspective, unless your into building your own amps, the science of it all can get very confusing especially with different designs. However understanding the principles of what an amp does is essential, along with how that power effects speakers.

Forget watts, people associate watts with gobs of power which isn't always the case. Peak to peak amperes, or current, in an amps spec's is a better judge of the power on hand but also isn't enough to gauge sound quality either. Too many variables in an amps build/design to tell just from a spec sheet.

Now, some points of contention are receivers, some rated at 4 ohm capable. Most, not all, use that as a selling gimmick when in reality all that switch does is limit the current feed to a 4 ohm speaker to keep the smallish power supply in a receiver from overheating and going into protect mode. The last thing you want to do is limit the current flow to a speaker, yes ? We want as much as we can get, right ? That's why we always recommend a separate power amp for harder to drive speakers, current flow....and the more the better in most cases.

Marketing gimmicks....that's for another thread, but understanding power, how to use it and why you need it is basic audio 101. Unfortunately the way specs read these days, it's a mine field of info that is just short of telling the whole truth so you learn to read between the lines. What's not listed in a spec is just as important as what is.....maybe more so. Personally, I don't put too much weight on specs but will use it as a guideline of sorts. I've heard too many pieces with fantastic specs that sounded like horse ****, while some with horse **** specs sounded better than they had a right to. So if your amp shopping, use specs as a guide, not a tell all piece of info of how it will sound.

Glad to see some asking these questions, it's refreshing to see people wanting to learn instead of posting why they can't understand how they blew 2 tweeters at the same time....then blaming Polk speakers. :biggrin:

Msabot1

My hat is off to you sir....here here!