Tell me how to check ohm of speaker

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Flash

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I have (2) 12" speakers in this plush amp, someone told me it was running at 2 ohm. no where does it tell me what it is and here's nothing on the speakers. I have a radio shark meter that checks ohm but I don't know if it goes low enough. The meter say's like 1K, 2k up to 100. It's all new to me. any help????
 
2 fours in parelell equals 2ohms. You should be able to fry an egg on this amp.
 
Using your radio shack meter will do you no good what so ever, it measures resistance, you need to find the impedance of the speaker which is subtely different (I know how in my head but can't really explain it). Now I've got a degree in Electrical and Electronics engineering and I don't really understand the page Bruce has pointed you too, but this is probably becouse:-

It's 8 in the morning
I haven't done any electronics since uni
I couldn't be arsed to read it properly and try to understand it.

Why do you need to know the impendance of the speakers?
 
darrin_h2000 said:
2 fours in parelell equals 2ohms. You should be able to fry an egg on this amp.
Click to expand...
no-no-no... I think he's asking how to determine the speaker load in the case of NOT having a manufacturer telling you the nominal impedance is x ohms.... ie, how do speaker designers know the load on the system they've just designed!

If the answer were as simple as 1 / Rt = (1 / R1) + (1 / R2) + (1 / R3) +...
...I would have told him that! ;)

:D

Bruce
 
I'm not sure but I think radio shark strikes again. I called up this T.V. dude and he told me I should set up the ohm meter to 1x. Well turns out the meter I got from them checks 1000 ohms or 1k. I had a meter that I got to check some things on my car and it had a setting for up to 200 ohms. Sure enough I hooked it up and it reads 7.9 so I'm assuming it's an 8 ohm speaker. Just to double check I checked a marshall cabinet at 16 ohm and sure enough it worked.
 
What ARE you talking about - impedance is an AC resistance... you can't measure it with simple meter.... the meter is reading DC resistance.........


Bruce
 
Dude,

Bruce is absolutely correct. Impedance does not equal resistance. I check speakers every day with an ohm meter (to see if they are open, not to see what impedance they are), and I can tell you that most of the time a 16 ohm driver measures closer to 8 ohms resistance than 16. You did not say in your post what "reading" you got on the 16 ohm Marshall cabinet, but if it was around 16 ohms you've got yourself a very inaccurate meter. When "measuring" speaker impedance with a DC ohm meter or DVM, the resistance reading you get is always quite a bit less than the impedance. And, the higher the speaker impedance is the farther off the resistance is from the impedance. That's because to DC voltage a speaker coil is merely a piece of wire. To AC voltage (ie, audio) it's a coil. You'd be better served by finding model numbers and/or manufacturer numbers somewhere on the drivers and doin' a little research.
 
Now guys, take it easy on him. ;) Lots of people refer to a speaker's resistance as impedence. Flash is referring to the resistance and that is how most amps are rated as to what loads are acceptable. And, of course, two 8-ohm speakers add up to 4-ohms in parrallel or 16-ohms in series. As for impedence...it is frequency related. So the same speaker might have a 2-ohm impedence at one frequency and maybe even 100-ohms, or more at another, usually but not always, higher frequency so of course there is no such thing as a specific impedence. What you actually have is an impedence curve similar to a frequency response curve. So there is no simple answer to what a speaker's impedence is. However, few people are that much into electronics so they mistakenly call a speaker's resistance it's impedence. For the purposes of matching the speakers to an amp, the resistance is an acceptable way to calculate that.
 
I will start out by saying that if I sounded "harsh", I apologize. I just re-read my post and I don't think it sounded harsh at all. I'm not trying to pick a fight here or piss anyone off. We're all here to help each other out and that's all I'm trying to do.

Flash is referring to the resistance and that is how most amps are rated as to what loads are acceptable.

I know of NO amp manufacturer that uses resistance as a means of indicating what kind of load should be attached to their product.

So there is no simple answer to what a speaker's impedence is.

That is correct and precisely what I was trying to get across.

For the purposes of matching the speakers to an amp, the resistance is an acceptable way to calculate that.

If that was the case, one would be hooking up 16 ohm speakers thinking that they were 8 ohms. (If your going by the closest common impedance as "incorrectly" measured on a DC ohm meter)

For the purposes of matching the speakers to an amp, the resistance is an acceptable way to calculate that.

Says who? (That's not meant to be harsh...really, who says that?)

Lt. Bob...THIS IS NOT MEANT TO TORQUE YOU OFF ! I just totally disagree with your post. You should get together a DVM and a pile of speakers with varying known impedances and you will see what I am talking about.

The only thing I will add is that an experienced tech might be able to use a DVM to figure out speaker impedance by comparing speakers with known impedances to a speaker with unknown impedance. That is to say that one would not take the resistance reading as the impedance, but rather use the displayed results only for comparison.
 
First off, I never said your post was harsh. I defy you to show me where in my response I said anything like that. I simply said to take it easy on the guy because he was simply using the wrong terminology and I was good natured about it.
Secondly, I AM an electronic tech although I no longer make my primary living that way and for your information I reconed speakers as part of my job for years and I have reconed thousands of speakers so I have handled just as many speakers as you and I know how to use a voltmeter just as well as you.
When speakers are rated as say an 8-ohm speaker, that is often referred to as it's "nominal impedance". As you know, that is not it's impedance at all. Impedance only exists if a circuit is active with current going thru it and is a function of resistance, frequency and phase angles. You are correct that a voice coil is a "choke" as far as ac current is concerned. And when a crossover is included it gets even more chaotic because of the phase angle issue. So when a speaker has a rating on it..it's "nominal impedance"..it is actually a resistance rating. IT IS NOT POSSIBLE TO MEASURE A SPEAKER'S IMPEDANCE AT REST WITH A VOLTMETER OR DVM. But they have to put some rating on it so thay put the "nominal impedance" which is usually resistance. Despite what you say, when a speaker rated as 8-ohm is measured with a voltmeter it will measure right about 8-ohms. Before I wrote this I grabbed one of my JBL's rated at 8-ohms to confirm this even though I already knew what I would find and it did in fact measure a fraction over 8-ohms.
When amp manufacturers give a load rating for their amps, they use this "nominal impedance" because that's all the end user has to go by. They don't mean to use resistance per se but those are the only ratings that are available to most people. Few people have the capability to measure an impedance curve and wouldn't know what to do with it if they could. So everyone uses the rating on the little tag on the magnet and your assertion that you won't measure that with a voltmeter is not correct.
Lastly, you say you don't mean to "torque me off" but your post clearly intended to do just that,..implying that I don't even know how to use a voltmeter. I don't mind if you disagree with me. Some of my best stuff I learned when people disagreed with me and I'm always looking to learn and grow. But you know nothing about me and your insulting and condescending tone was uncalled for as I didn't write anything critisizing you at all. I was working on speakers and amps when you were playing in the sandbox and I've played more nights a week for more years than most. People like you are the reason folks don't like to talk about politics or religion because you aren't capable of disagreeing without being snotty. :mad:
 
Lt. Bob,

I am sorry...really I am sorry. I think you read something into my post. I was not trying to be snotty. I in fact think we agree on many things and are just stating them in different ways. You say I don't know you and then go on to say that you were "working on speakers and amps when I was playing in the sandbox". You do not know me either, so how do you know that? I am not here to personally attack you and I will leave it at that. I quit. I am not here to argue. I want to state only one more fact. I measured a JBL 16 ohm driver this morning just to see (I got it from the shelf of the recone center as I have for the last 26 years). With a fairly accurate Beckman meter it measures about 7.5 ohms.

With apologies,
Monte :D
 
Fair enough. You're right, I shouldn't do the very thing I'm critical of so I too offer my apologies. Often some of the best relationships start off with a brief conflict so maybe that is what will happen here. You are right in that we are basically saying the same thing just different ways.
I am curious as to why we get different readings on speakers and I'm not disputing your reading,.. I'm genuinally interested as to why that would be. So perhaps, minus the retoric, we can delve into this some and come to a better understanding of it.
Once again, I too am sorry and hope we will come to actually know something about each other as opposed to the assumptions we both have wrongly made. :)
 
It's been my experience that AS A RULE most speakers do measure pretty close to their rated impedance with a DC ohmeter. I have however found that certain ones do not because like you said in your post there's so much more to it (frequency, wire gauge of coil, number of windings, etc. etc.)I guess the point I was trying to make was that you can't always go by this means of measuring. It is at times pretty inaccurate. At least it's always "inaccurate" in a way that will not likely damage amps if your wrong since the DC resistance is always lower than the impedance even if only slightly. In other words, even if your off the speaker your hooking up is AT LEAST the impedance you read with the meter if not higher. And, Lt. Bob I hope your not too pissed at me. I'm not out to make enemies here...just tryin' to help. It's all good. :D
 
Not pissed at all...

Nah man, I'm not pissed at all. You apologised and so did I. That's good enough for me. And joy of joy's, you've given me something to investigate. I'm curious if a old style DC-voltmeter might give different readings than a DVM under some circumstances (such as a coil suspended in a magnetic field). I have a Fluke which I rarely use since I'm so used to my old meter type. I'm gonna dig into this a little bit and I'll let you know what, if anything, I find out. Rest assured, I'm not mad at you at all and I look forward to learning from you as I learn from everyone else here. :D :D :D :D :D
 
Wow, that made my day. I don't know what to say. All I know is this T.V. dude said get a ohm meter that checks 1 ohm up to 200 ohm. With the speaker unattached to anything hook up the ohm meter. I tried it on 3 (known) ohm speakers and it read really close to what they were. Now this impedence thing, do I need to know. The speakers in this amp are trashed, someone must have got pissed off and kicked them. All I want to know is what ohm speakers I need to buy to replace them. I hope you guy's settle this thing. I have an experence similer. One of my better friends and I disagreed quite often until we started understanding what each one was really saying.....
 
MONTE and Lt. Bob;..the entertainers..

Glad we made you happy Flash. No you don't need to understand impedance to replace the speakers in your amp. If it uses two speakers it would be a safe call to simply get two 8-ohm speakers and wire them in parrallel. That would give you a nominal load of 4-ohms and I don't know of too many musical amps that are unhappy with a 4-ohm load. Or, if you want to be absolutely safe, you could get two 16-ohm speakers which in parrallel would give 8-ohms. Some amps won't put out quite as much into 8-ohms. And like I said, I haven't run into many amps that won't work fine into 4-ohms. Do you know the difference between parrallel and series wiring? If you don't, make sure to ask. It wouldn't hurt your amp to wire it in series but it might not sound as good. Monte and I will be working on a play for your viewing pleasure. Something like the Odd Couple. :D :D :D
 
Thats cool and I think I have the par. ser. thing ok. in par. I want to hook pos. to pos and neg to neg. That odd couple thing would be good. I LOVE THIS FORUM. So many people with so much knowledge.
 
Yeah that's right on the parrallel. I agree about this site. Tons of people with passion and knowledge about what we all love.... music. Pretty soon I'm gonna post some of my tunes and then lord oh lord, the flaming will begin. I'd better get my sunscreen ready. :) :D :) :D
 
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