I messed up.

[agedhorse]

In the guitar tube world, I've always understood that a 100% mismatch is relatively safe, i.e. an 8ohm out can go to a 4ohm or a 16ohm cab. (In fact, I'm purposely running mismatched in my '90 Peavey Classic 410. Has been recommended by many and definitely sounds better.) Beyond that, you're pushing your luck. I assume that this also applies in the bass world. Then again, solid state may be different so I defer.

With some tube amps that's ok, with some tube amps it's not ok. Just because some "rando" on the internet recommend something doesn't mean it's a good idea.

Solid state is most definitely different, never operate a solid state amp below its minimum rated load impedance.

 

[FunkyDane]

Get a regular 1/4 instrument cable and plug it into the speaker cabinet. Using a known good 9V battery, touch the tip to one side and the sleeve to the other, if the speakers jump out or in, then cabinet is fine and you have an amp or cable problem. If they don’t move, double check the battery and start checking connections to find where it’s lost.

Bonus tip: check to make sure all the speakers move in the same direction. Not uncommon for one or more to be backwards if someone had been in there before. If one is backwards, reverse the connections at the speaker.

Extra bonus advice: if it’s an amp problem, find a good tech. Not knowing what you’re doing inside an amp can be deadly.

I did this and the cab is definitely alive, So yeah its a cable connection issue. Maybe I should go back to the ol' 1/4 connection, since the amp supports it.

 

[Leigh Semmens]

A 4ohm cab and 8ohm head would likely damage the head far before damaging the cab. You were never dealing with a damaged cab unless you played at too high of volume, but than can happen even with matched impedances. Unlikely in this scenario anyway as the cab can handle up to 800 watts and the most powerful Taurus amp puts out 500. Possible, but not likely unless you were diming everything and really playing hard.

A comment earlier misquotes Ohm's Law, Two 4ohm cabs in Series will present a load of 8ohms whereas two in parallel will present a 2ohm load. Huge difference. Power ratings are also critical. If you run a 100W head into a cab rated for 40W there's a god chance you'll blow you cab, and, possibly, the head too. Provided you keep your head at very low volume the mismatched enclosure might survive. of course if you are running a 4ohm output into 8 ohms then you'll need a little more output from you head to drive it, possibly over driving the head. A 20Watt Amp will have trouble driving a 200W cab all else being equal, too.

 

[agedhorse]

2 pages of explaining impedance but nobody explaining troubleshooting.


You need to isolate the problem. Setup a head, cab, and cable that are working. Play and make sure the rig works. Now switch in your cab and see if it works. If not, you have an issue with the cab. More than likely something inside came disconnected. Open it up and look for any obvious wires hanging around loose.

Adding: don't break something that's not already broken by opening a cabinet up. Yeah, I see this fairly often.

A comment earlier misquotes Ohm's Law, Two 4ohm cabs in Series will present a load of 8ohms whereas two in parallel will present a 2ohm load. Huge difference. Power ratings are also critical. If you run a 100W head into a cab rated for 40W there's a god chance you'll blow you cab, and, possibly, the head too. Provided you keep your head at very low volume the mismatched enclosure might survive. of course if you are running a 4ohm output into 8 ohms then you'll need a little more output from you head to drive it, possibly over driving the head. A 20Watt Amp will have trouble driving a 200W cab all else being equal, too.

To clarify, 99.99% of all cabinet connections are parallel therefore most (appropriate) comments addressed this from the parallel perspective.

On the type of amp we are talking about (solid state), there is no 4 ohm output. There is a single output that can drive a number of loads, in the OP's case either 4 or 8 ohms. The volume will be what it is, based on the sensitivity of the speaker regardless of its nominal impedance.

If a 20 watt amp achieves adequate volume, there's no trouble or problems with that solution. There's plenty of Ampeg PF20T players driving 410's and 810's with 20 watts.

 

[DWBass]

8 ohm amp? All amps can run at 8ohms. If your cab is a 4 ohm cab, it's not getting the full wattage from the amp. What's the issue? I'm confused!

 

[darwin-bass]

lol, ok I stand corrected. But running an 8 ohm amp into a 4 ohm cab is bad news, right?

Only if you're talking about tube amps.

 

[Grinderman]

An 8 ohm amp will only run at 4 ohms if you plug two 4 ohm cabs (making it 8 ohms impendance) into it, otherwise it's a bad thing to do.

EDIT: To acknowledge, this is late in the thread at this point.

That's backwards and upside down.

Two x 4 ohm cabs make 2 ohms of impedance or load on the amp, not 8.

An amp will only handle the number of ohm it's rated for, either requiring the cab/s be plugging into the correct output for the designated number of ohms (that's more of a very old tube amp thing) or by selecting the appropriate ohms with a switch, typically on the back next to the output/s.

The vast majority of modern amps are designed to handle 8 and 4 ohms, 4 and 2 ohms, 8, 4 and 2 ohms, or 16, 8 and 4 ohms.

 

[pglaser01]

I think the drummer messed up…….fire him

 

[dkelley]

This thread frightens me. I'm happy there are those here who can process this. I don't know where to start (not for lack of knowledge, but for lack of being able to properly translate tech into polite support posts, and to help weed out the almost right posts from the very confusing posts and the wrong posts from the clearly awesome posts). You are in good hands though, OP. Definitely listen to Agedhorse

 

[themickster]

What is an 8 ohm amp? Can't any amp on the market run at 4 or 8 ohms? (And often less, depending. )

It's an amp that runs at 8

An 8 ohm amp will only run at 4 ohms if you plug two 4 ohm cabs (making it 8 ohms impendance) into it, otherwise it's a bad thing to do.

They would only be 8 ohms, if in series. Parallel would make them 2 ohms.

 

[Boneless]

By the way, using a lower powered amp with a higher powered cab is no problem at all (and actually it may be optimal, within reason; even though thermal power limits are not really that significant in the bass world, one can reasonably assume, when talking about bass guitar cabinets, that in a "higher powered cabinet", even if the power rating only refers to the thermal power rating, woofers will have at least adequate mechanical excursion limits for the expected power).

There is a sort of myth on the internet, according to which, overdriving a lower powered amp, especially a solid state amp, will blow up cabinets, because "overdriven solid state amps produce a square wave which presents DC to the cabinet", which is really nonsense. While a (transformerless) solid state amp can produce a DC offset, this is unlikely to be significant unless the amp is clipping *heavily* asymmetrically, which is extremely unlikely.

Cabs blow essentially for two reasons: sustained power over its thermal limits (more likely for midrange drivers and tweeters), overexcursion (not merely beyond Xmax, which only has a bearing on linearity, but approaching and exceeding Xvar/Xlim; more significant at lower frequencies). Especially in the latter case, the user is bound to be alerted to an excess of low end power by rising distortion and poor sound before failure.

 

[bdplaid]

Some guys should stick to combo amps. Nothing wrong in that, just saying.

 

[Nuage420]

By the way, using a lower powered amp with a higher powered cab is no problem at all

This is what I thought he was saying... It threw me off because that set up should have ran at a lower power level and given head room?

 

[N4860]

I did this and the cab is definitely alive, So yeah its a cable connection issue. Maybe I should go back to the ol' 1/4 connection, since the amp supports it.

Before doing that, check the connections on your speakon cable. You can open them up pretty easily and use a small screw driver to reset the connection. If the cable is in bad shape where it connects, you can simply cut the cable and reattach it to the speakon cable.

 

[logdrum]

In the guitar tube world, I've always understood that a 100% mismatch is relatively safe, i.e. an 8ohm out can go to a 4ohm or a 16ohm cab. (In fact, I'm purposely running mismatched in my '90 Peavey Classic 410. Has been recommended by many and definitely sounds better.) Beyond that, you're pushing your luck. I assume that this also applies in the bass world. Then again, solid state may be different so I defer.

I'm more inclined to believe that in all of the switching around you were doing you've shaken something loose in the cab.

Steve Kimock - who used to work for Mesa Boogie tested a Super Reverb mismatch by running the 2 ohm output into a 16 ohm and even 32 ohm cab/s. In fact the old Mesa Boogie manuals will tell you to experiment tone by purposely doing a tube mismatch either up or down. Tube amps only. I think the tube bass amps manuals don't say that you can do that.When I had only 2 4-ohm EA 12" cabs, I did run my Prodigy (which was only rated ) for 4 ohms. I got lucky but Andy here said that was not a good thing to do for the Prodigy. I was not paying loud.

 

[stevecaronna]

Here's a stupid question. Are you sure the connection from the bass to the cable to the amp are possibly not the problem? Did you try the bass through a rig that you know is working or did you try another bass and cable to see if it may be that end of the equation? Just wondering cause this stuff will drive you nuts.

 

[Marley's Ghost]

OP, please read this.

AMPS FAQ!! Info on OHMS, Allsize RIGS-OverUnderPowerCabs DIY TechTalk-Links

 

[agedhorse]

Steve Kimock - who used to work for Mesa Boogie tested a Super Reverb mismatch by running the 2 ohm output into a 16 ohm and even 32 ohm cab/s. In fact the old Mesa Boogie manuals will tell you to experiment tone by purposely doing a tube mismatch either up or down. Tube amps only. I think the tube bass amps manuals don't say that you can do that.When I had only 2 4-ohm EA 12" cabs, I did run my Prodigy (which was only rated ) for 4 ohms. I got lucky but Andy here said that was not a good thing to do for the Prodigy. I was not paying loud.

There are a lot of things that will be ok much if the time, but that doesn’t mean that it’s a good idea, or that it’s safe all of the time.

 

[MCF]

When I messed up, I ran an 8 ohm Taurus amp, from Poland, so here in the EU that's a thing. I'm gonna try 2 thing tomorrow. Running a new speaker cable on the Markbass and take my 2 amps to a cab I know for sure works, to make sure both my amps are in order. Then I can isolate the problem. If it's the cab, then it's a matter of finding out, what the hell went wrong.

According to their website, all four of their amps are 4/8 Ohm amps. A 4 Ohm cab and an 8 Ohm cab together is 2.67 Ohms. You do not want to do that with an amp rated at a 4 Ohms minimum like the Taurus amps.

 

[MCF]

Steve Kimock - who used to work for Mesa Boogie tested a Super Reverb mismatch by running the 2 ohm output into a 16 ohm and even 32 ohm cab/s. In fact the old Mesa Boogie manuals will tell you to experiment tone by purposely doing a tube mismatch either up or down. Tube amps only. I think the tube bass amps manuals don't say that you can do that.When I had only 2 4-ohm EA 12" cabs, I did run my Prodigy (which was only rated ) for 4 ohms. I got lucky but Andy here said that was not a good thing to do for the Prodigy. I was not paying loud.

Some players in the Subway community run their heads at two Ohms into 4 or 8 loads to achieve earlier breakup.