I messed up.

[agedhorse]

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

Note that this is not an output stage mismatch, it’s an algorithm that works well with non-linear (class D) power amps.

 

[MCF]

Note that this is not an output stage mismatch, it’s an algorithm that works well with non-linear (class D) power amps.

And can sound pretty darn good too.

 

[DJ Bebop]

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!

It's actually the opposite. An 8 ohm amp that is stable at 4 ohms will give more power into a 4 ohm speaker load not less.

As an example Peavey mini max.

600 Watts continuous into 4 ohms (minimum load)
350 Watts continuous into 8 ohms

 

[N4860]

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

Ya, I believe those amps are designed to run at a lower wattage when the switch is set to the 2 ohm side but used with a 8 ohm cab.

 

[agedhorse]

Ya, I believe those amps are designed to run at a lower wattage when the switch is set to the 2 ohm side but used with a 8 ohm cab.

Correct, and the output tube compression algorithm engages a proportionally earlier.

 

[JohnnyBottom]

Never had simplicity make my brain hurt. Whatever you do, dont add a cab or plug 2 amps into 1 cab.

 

[retslock]

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.

Wiring speakon plugs is very simple and easy. You can make up your own if you want. There are how-to videos on Youtube. Just make sure you have genuine Neutrik plugs. You might also consider opening up the plugs on the faulty cable to see if anything has come loose. It might be a very easy fix.

 

[sxaxsx]

It's possible you did no damage and everything is fine and something coincidental is giving you issue. It sounds like everything is in working order and is connected correctly, you just aren't getting sound.
Start checking off easiest and start working towards harder solutions:
1. Volume up on bass
2. Volume up on amp
3. Gain turned up on amp
4. Turn the mute button on the amp on and off
5. Active bass? If yes change battery
6. Try a different cable from your bass to the amp
7. Try a different speaker cable between amp and cab
8. Connect an instrument cable into the send jack and the other end into the return of the effects loop on the back of the amp

 

[RoadieP]

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.

Ummmm... no?

 

[lug]

I'm worried the cabs were under-powered.

(flees forum)

 

[el murdoque]

The only way in that scenario where the cabinet has taken damage would have been that the weird amp that is not 4 ohm capable (Unless it's a combo amp with ext speaker out that's highly unlikely) blew the output transformer and that killed not only the amp, but also the cab.
Having an impedance mismatch, correcting it and playing on means the cab was fine through all this.

Here's an important thing @agedhorse never tires of mentioning:
When troubleshooting your cable, take a look at the speakon plugs. They MUST be made by Neutrik.
There's Neutrik plugs and there's crappy copies that are an accident waiting to happen.

 

[prowla]

I don't see how running an 8 ohm amp into a 4 ohm cab would bust it, unless it was cranked up to full power; the rating is only nominal and varies across the frequency range.
If anything electronic was damaged you would expect a distinct burnt electronics smell.
Some amps have output fuses, which are designed to be the first things to go if there is an excess output.
If the cab still works with a different amp then it's OK.
If the amp still works with a different cab then it's OK.
If the cable works with either then it's OK.
Is it the right cable?
Are the cab's input sockets usable either way, or is one specifically input and the other for an extension cab?
Is there a mute button? (Silly question, but you never know!)
Was it only one amp plugged into the cab at the time?

Incidentally, since someone mentioned Mesa; one of their cabs was designed to split into a pair of 2x12 rather than a single 4x12, so there can be shenanigans with which speaker socket you plug into.

 

[Standalone]

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

No, many amps cannot drive a 4 Ohm Load. For instance, the amp in my GK112 kickback combo. The 100W "Hi" amp in the classic 800RB can only drive 16 or 8.

 

[agedhorse]

No, many amps cannot drive a 4 Ohm Load. For instance, the amp in my GK112 kickback combo. The 100W "Hi" amp in the classic 800RB can only drive 16 or 8.

Ummmm, many is a gross exaggeration. Your example is one of the very few.

Many amps in BRIDGED mode won’t drive 4 ohms, but in stereo or dual mono mode will.

 

[mrjim123]

OP, please read this.

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

OP, read this!

 

[DaveParker39]

The tech talk about impedance is obfuscating the actual issue OP is having. We know an impedance issue is not the problem here.

Follow this line of thinking

Start checking off easiest and start working towards harder solutions:
1. Volume up on bass
2. Volume up on amp
3. Gain turned up on amp
4. Turn the mute button on the amp on and off
5. Active bass? If yes change battery
6. Try a different cable from your bass to the amp
7. Try a different speaker cable between amp and cab
8. Connect an instrument cable into the send jack and the other end into the return of the effects loop on the back of the amp

 

[alex1fly]

I accidentally ran an 8 ohm amp into my 4 ohm cab (Markbass 104HF) for a few minutes at medium volume. (Doh!!)

As soon as I realized my wrongdoings, I replaced the amp with a 4 ohm amp and it played fine for hours.
Next day the cab is dead. I'm puzzled. Did I blow the fuses? The cones look fine, it worked for hours after my mistake, but now....dead. Any help appreciated.

OP - just do what the below post says. No need to break your brain hyperanalyzing ohms or get out meters or any of that nonsense. Get a setup going that works and then change one thing until it doesn't work again. Then you know what the problem is. Could be a cable, could be your instrument, could be the volume is down on your instrument or amp (no knock, I've been there), could be an input jack. Only way to find out is to isolate the problem as described here.

4 pages of debating 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.

Bless you for providing a clear path. BTW, I updated your post for you

 

[HolmeBass]

If it’s a speaker cabinet, there isn’t a fuse or a power cord.

this thread is confusing.

Some speaker cabinets have a fuse of sorts, usually a small lightbulb, to try and protect the tweeter.

 

[HolmeBass]

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.

I have never heard of the like. That would mean the outputs are in series?

None of this sounds right to me.

 

[HolmeBass]

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

Tell us the make and model of this “8 ohm amp” please. I am sorry but I am doubting such a thing exists, unless you have a really old amp with multiple power stages that you are running in bridge mode, but usually on those kinds of bass amps the individual power stages are 2 ohm stable so 4 ohms is the minimum bridged load.