# how to check the Oms of a speaker



## sambonee (Dec 20, 2007)

I was kindly given a speaker out of a Top Hat prince royale Amp and there is no marking on the speaker as to the oms rating. Is there any way to tell this? You see, I want to replace the speaker in my vox VR15 and I don't want to blow it!

Btw got the vr15 for $70 any it ROCKS!!! Put it through a 4x12, nutz!

Thanks


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## SCREEM (Feb 2, 2006)

get a cheap digital auto-range multimeter, it's a must for experimenting with speakers and tracking down shorts in cables...makes it easy.


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## sambonee (Dec 20, 2007)

Thanks however I need a step by step on HOW to verify the oms. 

Anyone?


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## Guest (Apr 4, 2009)

sambonee said:


> Thanks however I need a step by step on HOW to verify the oms.
> 
> Anyone?


Place one lead of the multimeter against one of the speaker posts, the other against the other speaker post. Set multimeter to display Ohms, in the <20 Ohm band. Read display. 

Mind you: what you're reading is the DC load presented by the speaker. It'll be in the ball park of the AC load that the amplifier sees.


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## sambonee (Dec 20, 2007)

Thanks for taking the time to teach me this.


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## mhammer (Nov 30, 2007)

To extent what Ian said, if it's an 8 ohm speaker, it will probably read somewhere between 5.5 and 8 ohms. For 16-ohm speakers, also expect the resistance to be higher than 8 ohms but not necessarily 16 on the nose.


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## Wild Bill (May 3, 2006)

sambonee said:


> Thanks for taking the time to teach me this.


Actually, the DC ohms on a meter can be a LOT different than the actual impedance of a speaker, which is a complicated, AC figure. There is NO cheap meter to measure this!

However, what folks here have been talking about is an old techie "rule of thumb". We know that the DC resistance will always be lower than the impedance. We also know that 99.999% of speakers will have an impedance measured in common values like 4, 8 or 16 ohms. So we can be confident that if we choose the next higher figure it will be right.

A 4 ohm speaker can measure anywhere from 2 to a bit less than 4 ohms. 8 ohm units might be between 4 and close to 8. A 16 ohm speaker might show in the range from as low as 9 to as high as 14 ohms.

What I'm pointing out is that the DC resistance can be a LOT lower than you might think and still follow this rule of thumb. 

Also, higher power speakers will read much lower than low powered ones. That's because they use thicker wire in the voice coil to handle the higher power. Thicker wire has a lower resistance.

:food-smiley-004:


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## Fader (Mar 10, 2009)

The speaker wattage will affect it slightly, as a rule of thumb I figure the resistance you read with an ohmmeter will be slightly more than half the impedance. 8 ohms speakers will read 4 - 5 and 16 ohm speakers 10 - 12.

I have a mislabled Celestian Greenback that I ran in a combo for years thinking I had two 16 ohm speakers in parallel for an 8 ohm load. After I swapped them out and measured them, I was surprised to find one was really an 8 ohm.kqoct


When I go speaker shopping now, I carry a small pocket meter to test the drivers before I take them home. Don't trust the labels.


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## mhammer (Nov 30, 2007)

The good news is that, since guitar speakers come in "standard" impedances (4, 8, 16), and since the DC resistance will never be greater than the impedance, you'll always be able to guess which impedance it is from the resistance measurement.


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## Guest (Apr 5, 2009)

mhammer said:


> To extent what Ian said, if it's an 8 ohm speaker, it will probably read somewhere between 5.5 and 8 ohms. For 16-ohm speakers, also expect the resistance to be higher than 8 ohms but not necessarily 16 on the nose.


Thanks Mark. I couldn't remember if it was lower or higher. I knew there was A Rule there though.


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## Gunny (Feb 21, 2006)

I've seen the occasional time where the meter dc Ohms reading is 4 or 8. However, the rule of thumb I use is that dc resistance is 80% of the ac impedance. So, a typical 8 Ohm speaker may read 6.4 Ohms and a 4 Ohm reads 3.2 Ohms on the meter.


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## sambonee (Dec 20, 2007)

Thanks for this great info!


The original vox that's currently In there reads 6.5. It's a smaller magnet. The replacement reads just below 5. (it's odd that such a high end amp co. Didn't write on the back of their speaker. ) 

The vox original has the edges of the speaker (where it's lika an accordion) with a ruber coating. The replacement (which came out of a Top Hat prince royale) is paper all the way to the edge.

Suggestions?


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## Fader (Mar 10, 2009)

Those are 8 ohm speakers. Bolt in the replacement and crank it up. Don't worry about the difference in cone construction.

There's a break-in period for speakers, so play loud.kkjuw


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## sambonee (Dec 20, 2007)

so then it's fair to say that this speaker from the Top Hat (even though it's a no name,) is probably better than the stock Vox speaker? does the paper edge make a difference?

has anyone else heard the vr15 by vox? I have the vr30 as well. 

I have had about 50 amps in the last 20+yrs and I can say that this $190 for these two amps is the best money that I have ever spent. seriously.

I am going to post a jam recording of the vr30 on here (if it's possible). it was done on a PS04. eventually. :smile:


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## greco (Jul 15, 2007)

sambonee said:


> does the paper edge make a difference?



*I'm going to guess* that what you are seeing is the "doping" (or lack thereof)

Ted Weber (Weber Speakers) site will explain the concept of doping in detail.

Cheers

Dave


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## sambonee (Dec 20, 2007)

here's the quick recording of the VR30 with no effects.

http://www.youtube.com/watch?v=qZp_ESto6So


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## whammybar (May 7, 2008)

screwed up this post let me try again


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## whammybar (May 7, 2008)

iaresee said:


> Place one lead of the multimeter against one of the speaker posts, the other against the other speaker post. Set multimeter to display Ohms, in the <20 Ohm band. Read display.
> 
> Mind you: what you're reading is the DC load presented by the speaker. It'll be in the ball park of the AC load that the amplifier sees.


OK so say someone is a TOTAL moron who owns a really cheap multimeter and STILL doesn't get what "in the <20 Ohm band" means. The moron would be me. So my $4 multimeter reads (in the Ohms measurement part) 2000k, 200k, 20k, 2000, and 200. Which of these is in the "<20 Ohm band" part?

Also just another thing. When I measure the 4 Ohm speaker in my digital Marshall 30 DFX and set the Ohms to 200 (with no 'k' after this 200) I get a reading of 4.3 which would be just above the rating... no? Or is it just a fluke and I'm showing myself to be even more ignorant than I first let on?


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## greco (Jul 15, 2007)

Given the ranges on your meter, setting your meter at 200 ohms is best you will be able to do with that meter.

At $4.00 (was it new?, or a old one bought used?), I would suspect that the accuracy on your meter is not the best.

Just to see if anything changes, *lightly* clean the test probe ends and speaker terminals with some emery cloth (fine grit sandpaper will do in a pinch)...*maybe *you have some corrosion. 

Also, did you take the wires off the speaker terminals before you measured them? Be careful doing this...the tabs on the speakers (for the connectors) are fairly easy to bend/break if you are too forceful.

I still suspect that your meter is just not sensitive enough to get an accurate reading.

Cheers

Dave


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## whammybar (May 7, 2008)

Oddly enough my multimeter was $4 brand spankin' new. I didn't take the wires off the speaker terminal however so that might be why I got the reading that I did. Guess I'll have to invest in a new multimeter. Thanks for the help.


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## greco (Jul 15, 2007)

whammybar said:


> Oddly enough my multimeter was $4 brand spankin' new. I didn't take the wires off the speaker terminal however so that might be why I got the reading that I did. Guess I'll have to invest in a new multimeter. Thanks for the help.


Canadian Tire has some nice digital multimeters that you might want to have a look at. They often put them on special.


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## Wild Bill (May 3, 2006)

whammybar said:


> Oddly enough my multimeter was $4 brand spankin' new. I didn't take the wires off the speaker terminal however so that might be why I got the reading that I did. Guess I'll have to invest in a new multimeter. Thanks for the help.


Dave gave you good advice but I'm not sure if you got the idea of a "range".

When your selector switch offers 20/200/2000/20,000...what that means is it's allowing you to pick a maximum to the display range. If you expect to be measuring maybe 11 ohm then the lowest range would be more accurate. Few or no meters operate with the same accuracy across only one huge range, at least none that any of us can afford! The more expensive ones will "autorange", which means they pause for a moment while they switch their range by themselves. This is the same thing for practical purposes, I guess.

In the "old days" before digital displays you would have a moving needle to show the value. Behind the needle would be a scale marked perhaps 0-100. When you switched the meter to different ranges you understood that you would then be measuring 0-10 volts, or 0-1000, or whatever. You just mentally moved a decimal point with the answer.

Hope this isn't to much info but you did say you were a beginner and sometimes we all assume you understand some of the words when you might not, which can make it harder to keep up.

When you get to be an old fart like me then you'll understand almost every one of the words and can be screwed up and confused on the highest of planes!:smile:

:food-smiley-004:


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## greco (Jul 15, 2007)

Wild Bill... I should have explained "ranges"...thanks for taking the time to do so. 

Always enjoy reading your posts.

Cheers

Dave


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## Guest (Apr 12, 2009)

whammybar said:


> OK so say someone is a TOTAL moron who owns a really cheap multimeter and STILL doesn't get what "in the <20 Ohm band" means. The moron would be me. So my $4 multimeter reads (in the Ohms measurement part) 2000k, 200k, 20k, 2000, and 200. Which of these is in the "<20 Ohm band" part?


greco already answered things.I just wanted to say: don't feel bad asking questions. We were all there once. A moron is someone who doesnt take the time to learn from others and ask questions. You're anything but.


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