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Yet another cab Ohm question....

 
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DukeofIbanez



Joined: 30 Aug 2007
Posts: 2587
Location: New Mexico

PostPosted: Fri Sep 24, 2010 1:29 am    Post subject: Yet another cab Ohm question.... Reply with quote

........I have an amp that can handle a 4 ohm load.
It has one 12 inch speaker in it with an external speaker jack. This jack will run in series to the cab and will also run the internal speaker with it.

My question is what should a cabinets ohm setting be for the amp to run properly?

Thanks.
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tangelolemon



Joined: 26 Jan 2009
Posts: 2691
Location: Brooklyn, NY

PostPosted: Fri Sep 24, 2010 7:59 am    Post subject: Reply with quote

are you SURE the ext speaker jack puts the ext speaker cab in series? Every single one I've ever seen puts it in parallel.

If it IS in fact in series, then add the impedance of the onboard speaker and the ext. cab.

In the far more likely scenario that it in fact runs the ext. cab in parallel, then you do the "product over the sum" formula for unequal impedances, or just half the impedance if impedances are the same.

In other words, if it's two 8 ohm speakers, you want it on the 4 ohm setting for parallel. If it's an 8 and a 16 for instance, you do [8 * 16] [8 + 16].
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DukeofIbanez



Joined: 30 Aug 2007
Posts: 2587
Location: New Mexico

PostPosted: Fri Sep 24, 2010 1:20 pm    Post subject: Reply with quote

Yea thats what I was thinking. But...

17: EXTERNAL SPEAKER: Use this jack to connect the amplifier to an external speaker. This jack is wired
in series with the internal speaker, which remains active even when an external speaker is connected.

So the amp speaker is 4 ohm and the 212 cab I have can be 4 ohm mono.
The total load is 12.
It didn't make any sense to me either that it would be series.

I guess I could just disconnect the amp speaker and run my cab into it at 4 ohm mono?
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Les



Joined: 06 Jan 2005
Posts: 1961
Location: Kansas City

PostPosted: Fri Sep 24, 2010 2:06 pm    Post subject: Reply with quote

What kind of amp is it?

And remember - wording on consumer products (like guitar amplifiers) is sometimes (sometimes? more like usually) very loose, very creative. Although the amp may say "series", that may not in fact be the case.

Not trying to stir things up, just sayin'...
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