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Post subject: BDRI Is 16 ohm ext cab OK?
Posted: Tue May 06, 2008 3:35 pm
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Hi, This is my first post, I hope someone can help me. I've got a Blues Deluxe RI and a 2 x 12, 4 ohm ext cab. I want to use my internal speaker along with the ext cab. Fender manual says to use an 8 ohm speaker along with the internal. Someone said it would be bad for the amp to use the cab as the 4 ohms it currently is, but that I could just rewire it to 16 ohm and then use it along with the internal speaker with no problems. Can anyone verify this, please? Will output volumes change? Thanks for any help.


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Posted: Wed May 07, 2008 9:29 pm
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The ultimate setup would be to use two 16 ohm speakers in parallel,
that way you could use the 8 ohm tap. :wink:

what's the impedance of each speaker in your 2x12 cab? 8 ohm...right? The internal speaker of the amp is 8 ohms also- right?

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Posted: Thu May 08, 2008 7:29 am
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Your 2X12 cab with 4 ohms impedance is in all likelihood two 8 ohm speakers wired in parallel. If you re-wire them in series, the total of the cab will be 16 ohms and when connected to the external speaker jack of your BDRI will not harm the amp since the total load seen by the amp will be 16/3 or 5.3 which is greater than the mfg recommendation of not less than 4 ohms.

However, the wattage will not distribute equally to the internal and external speakers. The external speaker cab having a higher impedance will get less wattage. That may or may not translate to a sound that you like. Only way to tell for sure is to try it.

Ideally, the external speaker load should match the internal of 8 ohms and the way to do that would be to purchase two replacement speakers of 16 ohms each and wire them in parallel, yielding a total impedance of 8 ohms. If you choose to do this, make sure you also consider the wattage rating(s) and match that too.

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Posted: Thu May 08, 2008 2:26 pm
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rustoleum-

I want to explain why it's recommened to use two 16 ohm speakers in parallel rather than putting the speakers you have in series;

if you run in series and the first speaker blows, then the second one goes out also because it depends on the current running through the first (now dead) speaker. This is a good way to blow transformers. I would never run in series unless I was working with 4 speakers such as a 4 x 10 or 4 x 12. In that case, the speakers are first connected as pairs in series and then the two pairs are connected in parallel. That way you always have a load on the output transformer. When an output transformer has no speaker load at all on it, it gets very very unhappy. That is why you NEVER want to run an amp without the speaker attached.

RVM lead- good post :wink:

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Post subject: Thanks for info>
Posted: Fri May 09, 2008 1:38 pm
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Thanks for the information from both of you. I was thinking of rewiring because it would cost nothing but I believe I will take your advice and go 2 16 ohm. The closed back cabinet currently has 2 Celestion G12-75's? and they sound darker than stock. I'd like to find speakers or a mix of 2 that complement the internal without overpowering its tone too much. Maybe one adding some tight bass and the other glassy and closer to the stock sound. Anyone have any suggestions of speaker choices and wattage handling? I do use a preamped processor and sometimes a roland gr20 synth so they have to handle some power. (The bass guitar patches on the synth are really cool and some are very punchy). Thanks again-appreciate your excellent replies!


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