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I've got what I'm sure some will think is a really stupid question but I'm at my wits end trying to find something of any substance on the internet. I have a Spider IV HD 150 which we probably all know is stereo at 8 ohms per channel. I'm looking at getting a new cab that is rated at 8 ohms mono, 4 ohms stereo. As I understand it, it's generally a bad idea to run a single channel since the amp is designed to run stereo; makes sense. As I also understand it, while it is generally ok to run an amp with a lower impedance to a cab with a higher impedance (e.g. 8 ohm amp to 16 ohm cab), it is not good to run it the other way around (e.g. higher impedance to lower impedance).

 

So, after doing some looking it seems that one option is to simply rewire the speakers into to 16 ohm series, deal with a little volume loss, and you're golden. However, I was wondering if it's possible to bridge the two stereo channels by way of a y adapter. It seems, in my incredibly limited knowledge of the subject, that in theory you would be left with a 4 ohm mono out that could be fed to a 8 ohm mono connection on the cab. This almost seems too simple but it make sense to me, again with my limited knowledge on the subject. Thoughts? Suggestions?

 

Thanks. - James

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Don't do it!   Although it would seem correct, it is the load presented to the amp that is important:  speakers to amp, not amp to speakers.  Your Y adapter will take the two 4 ohm loads and parallel them to 2 ohms!

If the cabinet you have is 8 ohms mono 4 ohms stereo, chances are that the 4 speakers in it are 8 ohms each , and the wiring is parallel for each pair of speakers, with the two sides being connected in series when bridged to mono.

Short of adding some 4 ohm power resistors in series into each speaker 'side', your best bet is to wire each pair of the stereo side as series, giving 16 ohms per side.

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Don't do it!   Although it would seem correct, it is the load presented to the amp that is important:  speakers to amp, not amp to speakers.  Your Y adapter will take the two 4 ohm loads and parallel them to 2 ohms!

If the cabinet you have is 8 ohms mono 4 ohms stereo, chances are that the 4 speakers in it are 8 ohms each , and the wiring is parallel for each pair of speakers, with the two sides being connected in series when bridged to mono.

Short of adding some 4 ohm power resistors in series into each speaker 'side', your best bet is to wire each pair of the stereo side as series, giving 16 ohms per side.

 

That was incredibly helpful, dude. I appreciate it. Are there any major cons to rewiring the cab for two 16 ohm series aside from the volume loss in this situation and the hassle of having to do the work? I'm buying the cab used, so there is no warranty to worry about. 

 

Also, would you happen to have any solid links that illustrate how this process would be done? Again, I appreciate your help.

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For each pair of speakers:

Speaker 1 terminal A to jack, Speaker 1 terminal B to Speaker 2 Terminal A, Speaker 2 Terminal B to jack.

Make sure you wire each pair the same way to each jack, so they are in phase with each other.

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