If you're bored, I need help needed settling an argument...

[Addison]

First of all... please forgive my ignorance on this subject... I'm not an expert in electronics, nor physics... I tend to read manuals, follow instructions, and play bass as best I can. I try to understand as much of the "other stuff" as possible, but it's usually over my head.

With that said:

An acquaintance of mine who is always right about EVERYTHING and I got into an argument about solid-state amplifiers and speaker impedance, and I'm hoping one of the resident experts here can help me out...

This guy seems to believe that a HIGHER impedance makes a solid-state amp work harder because there is MORE resistance... these are his exact words:

You said "4 ohms will make your head work harder". Which is patently wrong. With 8 ohms the amp has to work harder because there is twice as much resistance which is why you get less power out of the amp. So you had the relationship between ohms and power right, but you said it backwards.

and...

Impedence is basically electrical resistance, so the lower the number, the less resistance of the cabinet to the amp. So going from 4 ohms to 8 ohms, the speakers have more resistance, and the amp has to work harder, therefore you can't get as loud.

I, however, believe that a solid state amp works harder when there is LESS resistance. Less resistance allows more wattage to flow to the speakers... more wattage means more work... this is why there is an explicit "Minimum Ohm Rating" on solid-state heads, and this is why they can fry when going below that rating.

Are either of us right?

And, if we're both wrong, can someone please explain it in like 100-200 words so a 5th grader can understand it?

Thanks so much!!!

[Ric5]

How does one define "Work Harder?"

[Addison]

Good question...

I've always heard that you should run your head as close to its minimum ohm rating as possible because you'll have much better headroom at lower volumes because the amp is supplying more wattage to the speakers...

That's what I think of when I think that an amp is "working harder"... it's running "hot"... it's running closer to its capacity.

Does that make any sense?

Like I said, I have an elementary understanding of a lot of this, so please bare with my usage of certain terms.

[Plstrns]

Originally Posted by Ric5

How does one define "Work Harder?"

Good question. Headroom or Heat, I'd guess it's a trade off.

[Jaco who?]

Amps work more efficiently when they are used at the minimum impedance specified, but it really doesn't matter. An 8Ω 2x12, 4x10, 2x15 will still be louder than a 4Ω 2x10 or 1x12. Speaker displacement matters more than the wattage difference between an 8Ω load and a 4Ω load.

[Addison]

Originally Posted by Jaco who?

Amps work more efficiently when they are used at the minimum impedance specified, but it really doesn't matter. An 8Ω 2x12, 4x10, 2x15 will still be louder than a 4Ω 2x10 or 1x12. Speaker displacement matters more than the wattage difference between an 8Ω load and a 4Ω load.

Yes, I understand that.

In my case I'm talking about two like-branded 4x10's running individually from the same head. One is 8Ω the other is 4Ω.

[billfitzmaurice]

You're both right, and you're both wrong. A lower impedance allows the SS amp to deliver more power, by delivering more current. Higher current draw creates more heat, so if anything the amp works harder into a lower impedance load.
The problem here is that both of you are talking about power, and the only definitive method of approaching amp/speaker impedance relationships is to consider the components of that power: voltage and current.
As for voltage, a SS amp delivers the same voltage into any impedance load, so it doesn't work any harder into a high impedance load.

[msquared]

Originally Posted by Addison

An acquaintance of mine who is always right about EVERYTHING and I got into an argument about solid-state amplifiers and speaker impedance

So you came to an entire board full of acquaintances of yours who are "always right about everything" and are prone to get into arguments about solid state amplifiers and speaker impedance.

"Insanity: doing the same thing over and over again and expecting different results." -Albert Einstein

[babebambi]

Yeah, it depends on how you view "work harder"

On one hand, if you want the same sound pressure level, a 8 ohm load is "harder" (higher voltage) to driver than a 4 ohm load.

On the other hand, a 4 ohm load will allow more electrical current to pass (at the same voltage), and thus do more work; a by-product is more heat on the amp, and thus more strain and "harder" on the amp.

[Addison]

Originally Posted by billfitzmaurice

You're both right, and you're both wrong. A lower impedance allows the SS amp to deliver more power, by delivering more current. Higher current draw creates more heat, so if anything the amp works harder into a lower impedance load.
The problem here is that both of you are talking about power, and the only definitive method of approaching amp/speaker impedance relationships is to consider the components of that power: voltage and current.
As for voltage, a SS amp delivers the same voltage into any impedance load, so it doesn't work any harder into a high impedance load.

Ok, this makes the most sense to me so far... but, the way I see it, he was wrong/wrong, and I was right/wrong.

He said a solid state amp will work harder on an 8Ω load than it will a 4Ω load. If we assume he was speaking about voltage AND current, he was wrong on both, since voltage doesn't change, and current increases with less resistance.

If we assume I was speaking about both, I was right when I said an amp works harder with increased current, but wrong on voltage, since that stays the same.

Am I getting close?

[Big_Stu]

If it's any help I had a Marshall L&B tranny head as my 2nd ever amp.
On the back it gave you a list of what you'd get depending on the resistance of the cabs you were using.

To get the full 100watts it had to be a 4 ohm load
an 8ohm load gave you 65 watts
and a 16ohm load gave (IIRC) 35 watts.

From that I'm guessing your mate is right?? (But don't quote me )

[Addison]

Originally Posted by msquared

So you came to an entire board full of acquaintances of yours who are "always right about everything" and are prone to get into arguments about solid state amplifiers and speaker impedance.

"Insanity: doing the same thing over and over again and expecting different results." -Albert Einstein

HAHAHA!!!

Touché!

[BbbyBld]

You are "righter" than he.

Wattage doesn't really "flow". Current flows. The lower the resistance or impedance, the more current flows. The more current flows, the more the parts inside the amp are stressed.

Here is the simplified proof for your friend:

Power(wattage) = voltage squared / resistance

Current = power / voltage

Let's say your amp puts out 50 volts at maximum output capability.

50 squared = 2500


8 ohm load:

2500 / 8 ohms = 313 watts

313 watts / 50 volts = 6.26 amps


4 ohm load:

2500 / 4 ohms = 625 watts

625 watts / 50 volts = 12.5 amps


One could say the amp is working twice as hard with the 4 ohm load.

[StuartV]

Ric5 nailed it.

Until you define "work harder", the question is meaningless - or at least uselessly ambiguous.

If "work harder" means pushes out more current, then you've already gotten the answer - the amp works harder with the 4 Ohm cab.

If "work harder" means you have to turn the volume knob up higher to get the same volume from the speaker, then the amp will work harder with the 8 Ohm cab.

Or does it mean something else (to you, the OP)?

[bongomania]

Also, just FTR, impedance =/= resistance. Yes they are related; yes they are both measured in ohms; and yes you should heed the words of Bobby and Billfitz here, because they know what they're talking about. But at a baseline logic level, your friend is wrong because he equates the two terms more closely than he should.

[Addison]

Awesome!

Thanks you guys.... it all makes a little more sense now... enough for me to refer back to this thread the next time I need to understand it, anyway...

And, yeah... you guys might be aquaintances too, but I definitely feel more love here than I do with that other guy!

[bigtiny]

Originally Posted by Jaco who?

Amps work more efficiently when they are used at the minimum impedance specified, but it really doesn't matter. An 8Ω 2x12, 4x10, 2x15 will still be louder than a 4Ω 2x10 or 1x12. Speaker displacement matters more than the wattage difference between an 8Ω load and a 4Ω load.

first of all, this has nothing to do with VOLUME!

A lower load (i.e. 4ohm as opposed to 8ohm) will draw more wattage from the amp, which means it will draw more current and produce more heat. If the amp is rated for the load, this isn't a problem. You'll notice when you read amp ratings that it's common for an amp rated for 4 or 8 ohms to be rated twice the wattage for the lower load -- 250 watts at 8 ohms, 500 watts at 4 ohms for example....

bigtiny

[Jaco who?]

Originally Posted by bigtiny

first of all, this has nothing to do with VOLUME!

A lower load (i.e. 4ohm as opposed to 8ohm) will draw more wattage from the amp, which means it will draw more current and produce more heat. If the amp is rated for the load, this isn't a problem. You'll notice when you read amp ratings that it's common for an amp rated for 4 or 8 ohms to be rated twice the wattage for the lower load -- 250 watts at 8 ohms, 500 watts at 4 ohms for example....

bigtiny

Which is why I said, "at the minimum impedance specified", but to be more precise, if the argument was to produce the exact same SPL, or loudness, cranking the amp into an 8Ω load to produce the same amount of volume as the the amp into the 4Ω load would put out will probably require pretty much the same amount of current, so who gives a ......................... BTW, I defined "more efficient" as not turning the volume knob up as high. You feel free to define it any way your heart desires.

[Alex1984]

Yes. It's just a difference in your definitions. You feel it's working harder at low impedance because more current is being drawn and more heat is generated. He feels it's working harder because to deliver the same power, you'd have to drive your amp up much higher than you would at a lower impedance.

Resistance is more or less for DC stuff and impedance is frequency dependent (eg. Caps & Inductors).

[Jerrold Tiers]

"Work harder" means amp gets hotter.

In that case, which is the correct one, you are definitely much righter......

For other things, see Bobbybld's post. I have not read it, but I am confident that anything he writes on this will be technically sound and correct.