Difference in volume 8ohms vs 4ohms

[agedhorse]

On 11/02/2026 at 14:31, Stub Mandrel said:

 

As always good design and honest specifications trump all else. 

Of course accurate, honest specifications are important, but so is understanding the basic principles of the physics behind speakers (and transducers), which is where this whole thread/discussion has become so confusing. Lots of incorrect assumptions resulting in incorrect conclusions.

[SimonK]

4 hours ago, agedhorse said:

4 ohm 410's make a lot of sense because many 410's have a real world power handling of between 600 and 1000 watts RMS, and there's more available volume this was as a single cabinet solution. If you want 2 x 410's, than a 2 ohm capable amp is not that difficult to find.

 

It has nothing to do with valves versus solid state, there are plenty of examples of 2 ohm capable amps in both types.

 

If there is enough current available from the amp, then it doesn't matter as they go hand in hand.

 

No, it's all about voltage x current x cosine of the phase angle between the voltage and current (which is the definition of real power).

 

Actually, speakers are a current controlled device, the movement of the cone is due to the opposing magnetic fields, one static and one modulating. based on the current flowing through the voice coil. The force F=I x L x B x sin θ (where θ is the angle between the current I and the magnetic field B) The voltage is what causes the current to flow. 

 

Voltage and current exist together, you can't separate them aside from the inclusion of the phase angle between them. The voltage causes the current to flow, the current flows because of the voltage, and the real power is ultimately what matters. Since real power is more difficult to measure, apparent power (which assumes that the power factor (or phase angle between the voltage and current is 1) is most commonly used and is plenty accurate for like comparisons.

 

 

Does anyone else feel a small sense of relief when Agedhorse doesn't quote you on a thread about amps? As always valuable insights from the expert (although I'm not convinced 2 ohm capable amps are that common albeit I suspect Agedhorse has a few he has designed)!

[Beedster]

5 minutes ago, SimonK said:

 

 

Does anyone else feel a small sense of relief when Agedhorse doesn't quote you on a thread about amps? As always valuable insights from the expert (although I'm not convinced 2 ohm capable amps are that common albeit I suspect Agedhorse has a few he has designed)!

 

LOL, if it wasn't for @agedhorse and @Bill Fitzmaurice I'd probably only ever visit the basses for sale forums 

[Phil Starr]

On 10/02/2026 at 14:44, BassAdder60 said:

Interested to know the difference in actual volume you would hear if you played a 500w class D amp into a 8ohm cab compared to same cab but 4ohms ?

If I’m correct the amp would give out roughly half IE 250W and to be twice as loud audibly you would need 2500W which of course is silly for an amp !

I have a MarkBass MB58R 122 8ohm cab rated 800W and if this cab was say a 4ohm cab would it really sound louder even though amp can give it 500w at 4ohms ?? 

 

The simple answer is about biology rather than physics. As usual in science with a few provisos.

 

The smallest change in sound you can hear is roughly 1db, you'll notice this when you turn the amp up or if you switch between two cabs but if a punter left to go to the bar and came back after you'd made a 1db adjustment to your bass they wouldn't notice. If someone asks you to turn up a tiny bit you'd probably go for 3db. It makes a small but noticeable change.

 

Now the provisos, your 500W into 4ohm cab will probably be rated at 300W into 8ohms. You won't get double the power availability because the power supply won't perform at that power level. The difference in sound output at full power is roughly 2db but at anything under flat out the power will double and you'll get a 3db change when you swap speakers from 4 to 8. However (that word that means its getting complicated) if you are running flat out the amp and speaker will get hot, the hot components increase in resistance and the available power will drop. This power compression is significant and in the end will dwarf any changes to the impedance of the cab you are driving. Doubling your number of speakers will mean that at the same power the speakers will heat up less as the power is shared between them. Inside the amp a lower impedance increases the current and the heating. At this point it all depends upon what the designers have done about heat sinking components and it is all beyond your control.

 

So the short answer is: technically it might sound a tiny bit louder, but you wouldn't really notice and the difference would disappear if you ran everything flat out, which probably isn't something you will do. Relax, don't worry, just play bass. 

[BassAdder60]

24 minutes ago, Phil Starr said:

 

The simple answer is about biology rather than physics. As usual in science with a few provisos.

 

The smallest change in sound you can hear is roughly 1db, you'll notice this when you turn the amp up or if you switch between two cabs but if a punter left to go to the bar and came back after you'd made a 1db adjustment to your bass they wouldn't notice. If someone asks you to turn up a tiny bit you'd probably go for 3db. It makes a small but noticeable change.

 

Now the provisos, your 500W into 4ohm cab will probably be rated at 300W into 8ohms. You won't get double the power availability because the power supply won't perform at that power level. The difference in sound output at full power is roughly 2db but at anything under flat out the power will double and you'll get a 3db change when you swap speakers from 4 to 8. However (that word that means its getting complicated) if you are running flat out the amp and speaker will get hot, the hot components increase in resistance and the available power will drop. This power compression is significant and in the end will dwarf any changes to the impedance of the cab you are driving. Doubling your number of speakers will mean that at the same power the speakers will heat up less as the power is shared between them. Inside the amp a lower impedance increases the current and the heating. At this point it all depends upon what the designers have done about heat sinking components and it is all beyond your control.

 

So the short answer is: technically it might sound a tiny bit louder, but you wouldn't really notice and the difference would disappear if you ran everything flat out, which probably isn't something you will do. Relax, don't worry, just play bass. 

Thanks Phil 👍