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George Kimery


From:
Limestone, TN, USA
Post  Posted 2 Sep 2019 1:35 pm    
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I am picking up an Evans SE 200 combo amp Sunday. If I understand correctly, it is rated at 4 ohms, but comes with an 8 ohm speaker. It has an extension speaker out jack. If you use an 8 ohm speaker in an extension cabinet, then the ohms of the two speakers combined will give you 4 ohms, which is perfect. (8+8=16/4=4)

I have two Stereo Steel cabinets loaded with a 4 ohm JBL-D130 in each cabinet. GD Walker told me it was no problem to run one cabinet with a 4 ohm speaker and the other cabinet with an 8 ohm speaker, but I would probably need to turn the volume up a little more on the 8 ohm to get the two balanced. BUT....The Stereo Steel has two power amps, one for each channel. Since I run one speaker with the left power amp and the other speaker with the right power amp, I don't think running two speakers cuts the ohms in half.

Now to my question and options: I am very fond of JBL speakers. If I don't care for the 8 ohm neo speaker in the Evans, I can replace it with one of the 4 ohm JBL's. I just couldn't use the external speaker jack because I would already be at 4 ohms with the one JBL, correct?
I could mount the Evans 8 ohm neo into the nowu empty JBL
cabinet with no problem with my Stereo Steel, per GD Walker. I then would have the option of using my Stereo Steel with the cabinet with the Evans speaker in it or the one with the JBL in it, or both together.

The other option would to leave the two Stereo Steel cabinets as is and replace the 8 ohm Evans with an 8 ohm JBL. Then build an extension cabinet for the Evans speaker. I would then have 3 extension cabinets that I could pair up two different ways for my my Stereo Steel. The two different speakers might compliment each other..

I would like to just use one of the cabinets I already have with the 4 ohm JBL's in them as an extension cabinet with the Evans, but what little I know about matching amps and speakers tells me this would be a no no. I would be combining one 8 ohm and one 4 ohm for an amp rated 4 ohms, which is going to give a combined load of less than 4 ohms. (8+4=12/4=3) I am just wanting to make sure I'm right.
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Steven Paris


From:
Los Angeles
Post  Posted 2 Sep 2019 7:31 pm     Re: Running two speakers ohm question
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George Kimery wrote:
...the ohms of the two speakers combined will give you 4 ohms, which is perfect. (8+8=16/4=4)
I would be combining one 8 ohm and one 4 ohm for an amp rated 4 ohms, which is going to give a combined load of less than 4 ohms. (8+4=12/4=3) I am just wanting to make sure I'm right.

I'm not sure where you are getting your formulas; two resistances in parallel are computed by times over plus--- (R1 x R2) ÷ (R1 + R2). 8Ω and 4Ω in PARALLEL will give 2.67Ω.
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George Kimery


From:
Limestone, TN, USA
Post  Posted 2 Sep 2019 8:31 pm     Running two speakers ohm question
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I made up the formula myself. I have always been taught that it you hook up two 8 ohm speakers, it cuts the ohms in half, i.e., both speakers together become 4 ohms total. Using the same logic, an 8 ohm and a 4 ohm together would be 3 ohms total. I was close enough for my purposes. You say it would be 2.67. Either way it's below 4 which is the minimum I should have for a 4 ohm amp.The ohms in my Carvin BX 500 was rated down to 2 ohms. I stated I didn't know much about this sort of thing. That is why I made the post, to make sure I didn't do something stupid and blow an amp or speaker.
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Tony Prior


From:
Charlotte NC..
Post  Posted 3 Sep 2019 1:21 am    
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George, 8+8 in parallel = 4

8+4 in parallel is less than 4 , ( 2.6 ) as stated above.

You just need to be certain that the power amp can handle less than 4 ohms . The current draw can double which causes excessive heat which eventually leads to "no sound " as in dead !

Many TUBE amps can handle a mismatch but typically SS amps cannot. Going the OTHER direction reduces the output power but is deemed a safer load.

Many modern era SS amps will have a current draw safety circuit, it will shut down the output stage without warning. Powering the amp OFF then ON again resets it.

Sounds like you did your homework .
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George Kimery


From:
Limestone, TN, USA
Post  Posted 3 Sep 2019 8:07 am     Running two speakers ohm question
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OK, and of discussion. I am not going to feed the Evans amp less than 4 ohms. This is what I thought, but just wanted to be sure. Thanks to everybody for the help and education.
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