# Speakers and Ohm's



## Ryano2010 (Jan 3, 2010)

If I get the reciever I want I will need to put something together for speakers, just cant afford anything else at this time. I have a supply of some speakers from the kids old sound systems, Thay do sound good with music! I think I need to know what ohs they are before I try hooking they up, dont want to screw anything up on a new reciever.

How do you find out what kind a ohm's a speaker is?



The large speaker has a tag on the back that says 12w input 8 ohm, nothing on the smaller ones.


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## Drew1369 (Jan 19, 2007)

Usually on the back of the magnet you can find the rating of the speaker


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## Drew1369 (Jan 19, 2007)

Oh and if its worn or just plain not there you can check the impedance with a DMM


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## Ryano2010 (Jan 3, 2010)

I was able to shine a light into the small black RCA speakers and see the back of the magnet, it says 8 ohm , also says MAX 5 watts.

I havent figured out how to brake into the Sony speakers yet. I did get a reading of 5.7 Ohms from the wires that go to it using the DMM.

Just guessing at this but it would seem that I would have to keep the volume down on the system to keep from blowing something.

Anyone else done this ? Input invited.


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## DonaldG (Aug 23, 2007)

Usually these speakers are all 8 ohms. This impedance is a 'nominal' value.

Using a multimeter to read the 'impedance' of a speaker is only relative, unless the multimeter has an impedance setting.

Impedance and Resistance are measured in ohms but unlike DC resistance, impedance is a measurement of AC resistance. When measuring audio impedance, the frequency of the AC is usually 1000 Hz. Impedance values chance depending on the frequency.

The speakers that you have are good general purpose ones. Just hook 'em up to your kit BUT do not exceed the power ratings...

You can usually tell that you have reached the maximum by hearing distortion. Try to avoid this at all costs. Distortion is a mechanical stressing of the speaker components beyond their design parameters.

How a speaker works:

The voice coil is on a cylinder former that fits inside a circular slot in the magnet. The gap in the slot is very small. It is in fact a small electric motor. As the audio voltages pass through the voice coil, the voice coil pumps up & down within its slot in the magnet.

If you exceed that power rating, you are in reality passing too much audio voltage through the voice coil, making its mechanical movement in & out far too great. The voice coil will 'bottom out' and hit the bottom of the slot in the magnet. The voice coil former is usually a thin cardboard former coated is shellac. As it hits the bottom, the former gets distorted, making the bottom of it fatter as it swages out. This in turn makes it scrape the walls of the slot in the magnet. Once it has got to this stage, it is destroyed and cannot be repaired...

That is a long winded way of saying "Keep the volume down!" :grin:


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## Ryano2010 (Jan 3, 2010)

DonaldG said:


> Usually these speakers are all 8 ohms. This impedance is a 'nominal' value.
> 
> That is a long winded way of saying "Keep the volume down!" :grin:


Thanks for the responce, I have some more speakers and I know that they are 4 ohm ( pictured) Are these suitabe to connect to a reciever capable of 100 watts per channel safely with the volume turned down. Im only looking for a tempory setup until I get back to work, usally end of Feb.


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## DonaldG (Aug 23, 2007)

In reality, I have used 4 ohm speakers where the output from the amp specified 8 ohm. I never had a problem. 

That said, by using a 4 ohm speaker it, it is putting a much lower resistance (impedance) as a load. There is a risk of blowing the output stage of the amplifier but not much of a risk if the gain (volume) is kept well down.


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