Question about ohms

Posted by: Seekinganswers

Question about ohms - 03/18/11 03:28 PM

Hello,

I am currently taking an introductory course into principles of electronics and speaker ohms has me a little confused.

I have learned from class that the greater the ohm rating, the greater the resistance. So it seems a little counter intuitive to me that the M80s, with 4 ohms, would be harder to drive than say an M60 with an 8 ohm rating. I tried to ask my instructor about it and he really did not have an answer to that, either.

Thanks
Posted by: ClubNeon

Re: Question about ohms - 03/18/11 03:30 PM

It's not harder to drive, it's more demanding on the amplifier, which will have more current flowing through it, because of the lower impedance. More current equals more heat and more demand on the power supply, which equals more chance of clipping or shut down.
Posted by: Seekinganswers

Re: Question about ohms - 03/18/11 03:34 PM

Ahh, that makes so much sense! Haha, I wish I would have thought of that before.

So basically, a lot more current will be running through the speaker, thus requiring more power from an amp in order to avoid overheating and clipping or shutting off?
Posted by: ClubNeon

Re: Question about ohms - 03/18/11 03:37 PM

The speaker allows current to flow through it more easily.

It just requires an amp that is designed to be able to handle that extra power moving through it. A larger power supply is the start, and a more robust output stage that can remain stable, along with better cooling to remove the heat.
Posted by: BlueJays1

Re: Question about ohms - 03/18/11 03:44 PM

Originally Posted By: Seekinganswers
Hello,

I am currently taking an introductory course into principles of electronics and speaker ohms has me a little confused.

I have learned from class that the greater the ohm rating, the greater the resistance. So it seems a little counter intuitive to me that the M80s, with 4 ohms, would be harder to drive than say an M60 with an 8 ohm rating. I tried to ask my instructor about it and he really did not have an answer to that, either.

Thanks


Yeah, your way of thinking is correct as the advantage of a 4ohm rated speaker would be that it presents less resistance to the current flow which will allow the speaker to pull more power from the amp/receiver. However, because of this the amplifier must be designed to handle this greater flow of current. Therefore, with low impedance speakers (impedance varies and it is the dips/phase angle interaction to worry about) can sometimes cause the amplifier or receiver to overheat and/or go into current limiting when pushed hard. In either case will cause the electronics to shutdown or in the worst possible case, permanent damage.
Posted by: J. B.

Re: Question about ohms - 03/18/11 04:00 PM

in many ways, it's like an electric light bulb;
one that has a filament with high resistance in it will not be as hot and bright and will not consume as much electricity as one that has a low resistance filament in it.

lower resistance in a wire (or a voice coil) will let pass more current.
low resistance/impedance = low Ohms
if the resistance is low, then current going through is not impeded as much as when the resistance is high.
Posted by: ClubNeon

Re: Question about ohms - 03/18/11 04:01 PM

Since this is for a class lets get the terms right.

When talking about alternating current (like audio signals) Ohms measures impedance, not resistance. Resistance only applies with the phase angle is constant at 0 degrees, i.e. DC.

And speakers don't "pull" anything. They are simply there to impede the flow of current from one pole of the output to the other. If the speaker wasn't there, and speaker wire was made into a dead short (milliohms) the amp would self destruct (or more likely go into protect) because the current flow would be so high.
Posted by: Cary

Re: Question about ohms - 03/18/11 06:09 PM


You got it.

And you got the resistance vs impedance. Although we use ohms to quantify both, resistance implies that the voltage and current are always in phase (0 degrees, like for a resistor) while impedance implies that they are out of phase. When you plot impedance then on an XY graph, it'll have a "real" part and an "imaginary" part (implying phase). The magnitude of that vector is measured in ohms.

Since you're in class, another way to think of the lower speaker impedance being more difficult to drive is to consider power. P=V^2/R. So if we assume that the voltage is the same (volume knob in the same spot), when the "R" gets smaller, the power goes up.

Cary
Posted by: bdpf

Re: Question about ohms - 03/18/11 08:12 PM

and P=RI2 so as the power goes up so does the current. Back to school...
Posted by: JohnK

Re: Question about ohms - 03/18/11 10:07 PM

Seek, this is yet another of the things widely known which happen not to be true. Believe it was Mark Twain who said "It ain't the things that we don't know that get us into trouble, it's the things we know for sure that ain't true".

As Chris and others have pointed out, the lower impedance hinders the input voltage less and the result is that for a given voltage the current is higher. This is because of Ohm's Law, which I'm sure that your instructor is familiar with, even he's not much into audio technology. One form is I=E/R(current equals voltage divided by resistance[impedance for AC]), which shows the effect of the lower impedance. Since another iteration of Ohm's Law is that power equals voltage times current, the effect of the higher current is also higher power for a given input voltage from the amplifier.

So, in that sense lower impedance makes it easier to realize power in the speaker, but the higher current possibly could cause overheating in the amplifier and its protective circuits would shut it down. However, there's no brick wall suddenly created by impedance lower than some magic number, as some seem to imagine. It's entirely possible for some speakers rated at 4 ohms(e.g. the M80)to be more sensitive than some speakers rated at 8 ohms, to require less power for a given sound level, and to be less likely to cause amplifier shutdown.

Let us know what your instructor thinks about this.
Posted by: Seekinganswers

Re: Question about ohms - 03/19/11 10:34 AM

Wow! Thanks everyone for the extra education. As I mentioned before, I am only in the introductory phase right now and am only learning about Direct Current theory. Next week we will be delving into Alternating Current.

From my readings, most lower to mid-grade receivers will have a hard time driving M80s. I decided to purchase an Emotiva UPA-5 for the provisions of me getting M80s later in the future. The specs say 185 watts RMS at 4 Ohms. Will this be sufficient to drive these speakers to insane listening levels before shutting off? I do not intend to listen at crazy volume.

A little off topic. I used to be an air traffic controller for the united states air force. I hated the job and am now retraining into aircraft avionics. I get to work on aircraft electronics and instrument controls and such. It sounds like such an awesome job and I get to learn more about the theory of A/V electronics that I love. The classes are fun but it can become information overload after a while since we're learning for about 8 hours a day. I forgot how grueling it was to be in tech school.

I only have 7 more classes in order for me to finish my bachelors in a business degree. I was thinking of continuing school and getting an MBA, but with the supposed dilution of an MBA degree these days, the appeal is not as great.

When we first got our briefing on the new training, I was really excited to know that by the time tech school was done for avionics, I would have roughly enough credits for an associates to apply to an electrical engineering degree. I will be finishing up my business degree and then will be looking into getting an electrical engineering degree. My only concern is that my math skills is not as great as I would like it to be but I do not think I will have any issues if I apply myself.

Is anyone on here an electrical engineer and can tell me what level math is involved? I heard the most difficult it gets up to is calculus 2. Can anyone tell me what the job prospect is for an electrical engineer?

thanks
Posted by: jakewash

Re: Question about ohms - 03/19/11 12:04 PM

The UPA-5 will be fine for the volumes you are looking for, as would any of the receivers you see us mentioning on the forum, you can achieve loudness levels that can leave you deaf with as little as 100W. To get really insane levels, say constant a 105db you need much more power than most people are willing to buy, I estimate it to be around tha 700W the M80s are torture tested with, but the power required is all relative to the room and listening distances.

Most of the Electrical Engineers I know have no trouble finding jobs within their feild of choice or even outside of it

Calculus 2 brought down the GPA's of some of the brightest people I knew in University. I only looked at it briefly from their notes and I didn't want to have anything to do with it.
Posted by: Cary

Re: Question about ohms - 03/19/11 02:03 PM


Off Topic, but...

It so happens that I'm an electrical engineer and a pilot smile Just a Cessna 172, but I get enough time in "the system" to have a ton of respect for the job you had. I totally understand you not wanting to transition to the civilian system though. I know a couple of ATC folks and they really look forward to retiring.

If you are pumped about electronics and figuring out how stuff works (and it sounds like you are), don't sweat the math. You'll get it. It will suck greatly, and you'll have to dig in, but once you're done with it, it's all downhill from there.

A long time ago when I went to school (graduated in '88) we had three Calc classes (1, 2, and 3) and then Differential Equations. The last one was the hardest only because it got more abstract and more difficult to visualize what was going on. I'm not a math whiz by any means so I really had to buckle down on it but did well. I'm passionate about electronics though and that's what got me through smile

Cary
Posted by: Seekinganswers

Re: Question about ohms - 03/19/11 02:20 PM

Originally Posted By: Cary

Off Topic, but...

It so happens that I'm an electrical engineer and a pilot smile Just a Cessna 172, but I get enough time in "the system" to have a ton of respect for the job you had. I totally understand you not wanting to transition to the civilian system though. I know a couple of ATC folks and they really look forward to retiring.

If you are pumped about electronics and figuring out how stuff works (and it sounds like you are), don't sweat the math. You'll get it. It will suck greatly, and you'll have to dig in, but once you're done with it, it's all downhill from there.

A long time ago when I went to school (graduated in '88) we had three Calc classes (1, 2, and 3) and then Differential Equations. The last one was the hardest only because it got more abstract and more difficult to visualize what was going on. I'm not a math whiz by any means so I really had to buckle down on it but did well. I'm passionate about electronics though and that's what got me through smile

Cary


Cary,

Not off-topic at all! I was looking for some insight like yours.

I do thank you for your kind words about ATC. I am very proud to have been an air traffic controller and I, myself, have a lot of respect for the career field. It just was not what I wanted to do. Some of my colleagues enjoyed the fact that they were able to tell pilots (officers) what to do, which I found was amusing.

I think you may have misunderstood my posting, but I do want to transition back into the civilian world. I still have about three years left in the service. I am glad I got to train into avionics because everyone tells me there are great prospects when I get out. I still want an electrical engineering degree because I just want to learn that much more about electronics and theory and all that good stuff.

Its great to hear that you're an electrical engineer. You're exactly what I want to be at this point in my life. All the math courses sounds rough. That is certainly a lot higher than calc two as someone has mentioned to me. Well, the guy that told me that was supposedly an electrical engineer himself, but he's in the same basic principle class as I am. I am not sure if I believe him just yet.

What are your experiences as an engineer and what were some of your most rewarding jobs in the career field? Do you enjoy being an engineer?
Posted by: CatBrat

Re: Question about ohms - 03/19/11 03:21 PM

I did a stint of 2 years as an ATC tower operater in S. Korea back in 1974-1976 (and 1 1/2 years working in a flight following station in Ft Hood, TX prior to that.) I wanted to do that when I got out, but fortunately ran into computers instead.
Posted by: Hansang

Re: Question about ohms - 03/19/11 07:40 PM

Originally Posted By: Cary

Off Topic, but... - snip -
A long time ago when I went to school (graduated in '88) we had three Calc classes (1, 2, and 3) and then Differential Equations. The last one was the hardest only because it got more abstract and more difficult to visualize what was going on. I'm not a math whiz by any means so I really had to buckle down on it but did well. I'm passionate about electronics though and that's what got me through smile

Cary


Calc was OK for me (enjoyed it) and Diff EQ depends on the professor. It can be a purely plug-n-chug affair or pure theory. Linear Algebra (not the ones people take in high school!) was really tough for me. After CALC I & II and Diff Eq, Linear Algebra tied it all in - but was very difficult at times.
Posted by: JohnK

Re: Question about ohms - 03/19/11 09:14 PM

Seek, the only thing that I'll add is that you've been reading the wrong stuff about receivers supposedly having trouble with the M80s. Again, the question is simply how loud a listening level. There should be no problem at levels not insanely loud which are dangerous to hearing.
Posted by: Seekinganswers

Re: Question about ohms - 03/19/11 09:49 PM

Originally Posted By: JohnK
Seek, the only thing that I'll add is that you've been reading the wrong stuff about receivers supposedly having trouble with the M80s. Again, the question is simply how loud a listening level. There should be no problem at levels not insanely loud which are dangerous to hearing.


Johnk,

Well, I get most of my information about axiom speakers here, but I also hang out on Bluray.com and I read under the axiom speakers there. I previously owned an onkyo 606 and now I own a yamaha 667. The onkyo 606 definitely sounded more powerful and truer to the wattage rating than the 667. I got the 667 because it offered the right features that I needed at just the right price. With that said, when I do get M80s, i would want to pair it up with a VP180 center. I would think that the 667 would have a little trouble driving those speakers. But then again, I haven't owned them and tried it out myself.
Posted by: jakewash

Re: Question about ohms - 03/20/11 12:15 PM

Seek, the 667 has preouts for an amp so no matter what you are good to go with M80s and VP180 and the 667. Once you have the speakers and have tried the 667 on it's own, if you find it to be lacking or going into protect mode at the volume levels you listen to, all you have to do is buy that separate amp and use the preouts from the 667 to feed the amp and your power issues will be solved, you can stop worrying about it.
Posted by: Seekinganswers

Re: Question about ohms - 03/20/11 12:29 PM

Originally Posted By: jakewash
Seek, the 667 has preouts for an amp so no matter what you are good to go with M80s and VP180 and the 667. Once you have the speakers and have tried the 667 on it's own, if you find it to be lacking or going into protect mode at the volume levels you listen to, all you have to do is buy that separate amp and use the preouts from the 667 to feed the amp and your power issues will be solved, you can stop worrying about it.


jakewash,

I have already bought an Emotiva UPA-5 about a month back and I am confident it wouldn't have any trouble driving those speakers. I just really wanted to verify some facts that maybe an entry to mid grade receiver like mine would have trouble driving all three ohm speakers louder than normal from time to time.
Posted by: jakewash

Re: Question about ohms - 03/20/11 07:36 PM

I see, fact finding mission. FWIW, my midgrade Denon 1804 had no troubles driving the M80s and parallel M22s(which is a ~4 ohm load).
Posted by: alan

Re: Question about ohms - 03/21/11 09:28 AM

Hi Seeking,

While JohnK is supremely confident of any AV receiver being able to drive Axiom's 4-ohm M80s/VP180s with ease, that is not the customer history we have here at Axiom. I will now recite, yet again, the brands of AV receivers that have never had problems of protection-circuitry shut-down or current limiting driving the M80s: Denon, Sherwood Newcastle, Harman-Kardon, Rotel, Outlaw Audio, B&K, Macintosh, and NAD. This list includes even entry-level models from Denon, H/K, Sherwood Newcastle, and Outlaw Audio, which we checked out at our factory listening room.

Note that the above list assumes the owner is not trying to drive the AV receiver beyond its output limits or into clipping. Any well-designed AV receiver will temporarily shut down if cranked to levels that trip the thermal sensors on the output devices.

Older models of Onkyo, Yamaha, and Pioneer were not stable with the M80s and would repeatedly shut down.

I'm a bit hesitant to recommend even recent Onkyo models because I note that in Dan Kumin's recent tests of an Onkyo for Sound&Vision magazine, when it was connected to 4-ohm loads, it went into current-limiting mode after about 2 seconds, which limited the power output in all channels to 45 watts per channel maximum, regardless of where the impedance switch on the receiver was set.

Regards,
Alan
Posted by: fredk

Re: Question about ohms - 03/21/11 10:07 AM

That last bit about a recent Onkyo test is interesting. I came close to picking up an 807 before I found my current Denon on sale.

I am quite content with the Denon as I can push it to very loud levels without the receiver getting anything more than a little warm to the touch.
Posted by: bdpf

Re: Question about ohms - 03/21/11 10:16 AM

A few times when I watched a movie pretty loud (-6dB from ref), my Denon got pretty hot to the touch but never shut down. I'm very happy with it as well.
Posted by: JohnK

Re: Question about ohms - 03/21/11 10:21 PM

Fred, yes the Onkyo test is interesting, and I'm quite familiar with it and others there, since the S&V tests are among the very few that I study carefully. And it is indeed necessary to study them carefully, especially following what the asterisks on the power measurements refer to, if a misunderstanding is to be avoided. The test results here show that the limiting on power output by the protective devices during 5 and 7 channel operation was at 8 ohms, not 4 ohms. For 1 channel and 2 channel operation into 4 ohms(with the setting correctly left at the higher impedance)the 4 ohm outputs were 272 watts and 229 watts respectively. These are the numbers which should instill "confidence" in an owner of that unit.

Mr. Kumin, as he typically points out when he has no problem with real-world use with his lower sensitivity speakers, states that the multi-channel signals of that description "...essentially never occur "in nature" from music or movie soundtracks-only artificial test signals". These excellent results led to the highest grade of "10" being given for performance.

It's also interesting to note that earlier in the year the Denon 4810(about two steps higher up in their model lineup)was similarly tested and showed a fairly similar reduction in 7-channel output into 8 ohms, as shown here . This again led to a similar comment that it was a result "which is neither uncommon nor particularly meaningful".

Lab test results have to be studied carefully to determine their applicability to home listening. If the multi-channel power reduction into 8 ohms was taken as representing a realistic scenario in actual home use, the absurd conclusion might be that neither the Denon or Onkyo was advisable for use with speakers rated at 8 ohms or less(meaning almost all available speakers).
Posted by: SBrown

Re: Question about ohms - 03/21/11 10:48 PM

I know Sherwood Newcastle definitely has a hard time running 7-channels and will go into protection mode with the M80's,VP150,and QS8's.


Edit: Sry, meant to say at higher(ok..hearing harming) listening levels. whistle
Posted by: INANE

Re: Question about ohms - 03/21/11 11:46 PM

I'm trying to talk myself into getting some M80's later this year... I have a H/K (AVR630) so I think I'd be able to drive em with that (AVR upgrade will be in the future).

Talking about professions/education. I have an Associates in EET thou I confess to have probably forgotten half of what I learned since I've been in IT for the last 15 years. But electronics were always my first love. That was the only time I ever actually enjoyed school.