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Discussion Starter · #1 ·
This won't kill the speaker, right? Logic would dictate that 8ohms at 160w would hit a 4ohm speaker like 320w, and if the speaker is rated at 350, I should be fine, right?
 

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NSLALP
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Watts are watts, regardless of the load imposed by the driver. You're gold if you supply a 350w driver with 160w.

What are you driving with, though? If your speaker is a 4 ohm/320w driver, the load on the amplifier WILL BE 4 ohms, so does that change the output characteristics at the amp?
 

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If you push 8ohms out of your amp into a 4ohm speaker, you'll blow your output transformer WAY before your speaker.
 

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Discussion Starter · #4 ·
alright, nix that plan, then.
 

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Dream Crusher
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What is the amp's minimum ohm rating?
 

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Discussion Starter · #6 ·
doesn't say. It's that Sunn combo I was working on at Kevan's. The speaker in it is 8 ohm with 160w power handling, and the "extension cab" jack isn't labeled with anything but "extension cab".
 

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Dream Crusher
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It should say on the back of the amp near the speaker outs what its minimum impedance is. What model is it?
 

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Dream Crusher
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Also, since it's solid state, it will have a "minimum" recommended impedance. The lower you go, the more effective power the amp puts out, but at the cost of heat. Going below minimum impedance can fry important components.

It's not like a tube amp, where the output transformer "matches" the impedance of the output signal to the impedance of the speaker. Running a lower load in a tube amp strains the output transformer, shortens tube life, and can catastrophically cook the transformer if you're really dumb about it.
 

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Discussion Starter · #9 ·
It's a Sunn SB160 combo, that needs a new speaker. The only 15" speaker i have on hand is a 350w 4 ohm Black Widow, and the speaker in the combo right now is 8 ohm.


If it was a head (or a peavey) it would be really easy to diagnose, but information on the older Sunn stuff is hard to find.
 

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Dream Crusher
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First of all, the SB 160 is actually a 60w combo.

I can't find impedance specs, but people are guessing that since there's an extension speaker jack and the stock speaker is 8 ohms, the amp is 4-ohms-capable.

With the efficiencies of the time, it's likely you'd get about 80-100W out of it with a 4-ohm speaker.
 

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Discussion Starter · #11 ·
...but it won't fry the amp?


Where'd you find that info on the amp? Searching doesn't really dig up anything, but I guess you're more in tune with bass world than I am.
 

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Dream Crusher
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Searched Google.

Also, read Talkbass threads that came up on Google. It has an extension speaker out, right?
 

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NSLALP
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If you push 8ohms out of your amp into a 4ohm speaker, you'll blow your output transformer WAY before your speaker.
That's not how it works. There is no characteristic of current flow called "resistance." The amplifier is literally saddled with a "load" when you attach a speaker, and the magnitude of that load (physical analogy: the mass of a rock you're expected to push and pull around) is the impedance. More ohms, more resistance (mass).

Amplifiers will always have a minimum ohm rating that they are capable of handling. If you go under, you risk damaging said output transformer. Other than that, you only risk operating inefficiently with very high loads, possibly creating a lot of heat.

So as long as this amplifier can handle a 4 ohm load (it should be able to, I haven't seen an amp in a long time that couldn't), then it will work just fine. The only question is how much maximum power the amplifier can deliver vs. the physical limitations of the driver. Keep in mind you'll probably only ever push 10-100 watts through it on average... that's pretty loud...
 

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Dream Crusher
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Soop: What Leon says is true with regard to tube amps, which have a set load. He just said it in a slightly not-correct way :lol:

If there's only a 16 or 8 ohm output, it's not a good idea to run it into a 4 ohm cab since the output transformer (which matches impedances in toob amps) can cook itself.
 

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MY understanding has always been if the ohms are lower than the speaker you are fine. :lol: Whether this is true or not Im not 100% sure.
 

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Dream Crusher
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MY understanding has always been if the ohms are lower than the speaker you are fine. :lol: Whether this is true or not Im not 100% sure.
If by "ohms" you mean the minimum impedance of the amp (or the labeled impedance on the amp) then yes, it is true with solid state amps.

I've heard conflicting reports on tube amps.

Keep in mind though, that impedance changes depending on how much power you're running through it and what frequencies the speaker is reproducing. So, any labeled impedance on a speaker is going to be an approximation.
 
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