Difference in volume 8ohms vs 4ohms

[BassAdder60]

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 ?? 

Edited 3 hours ago by BassAdder60

[fretmeister]

About as much as moving the volume control 2-3mm I reckon.

[SimonK]

https://soundcertified.com/how-does-increasing-speaker-impedance-affect-db-output-power/

[Lozz196]

If I recall correctly we tried this at a Bass Bash once, same bass and 4ohm amp into the same cabs, both 4 & 8ohm versions. Again from recall no real noticeable volume difference but the 4ohm cab sounded more “alive” in comparison.

[Bill Fitzmaurice]

It's not about watts, it's about voltage sensitivity. That's 3dB higher with 4 ohms, so with the same amp settings the 4 ohm speaker will be 3dB louder, assuming all the other T/S specs are the same, which they seldom are. 3dB is audible, but just. As for maximum SPL that's mainly determined by the cone displacement, T/S spec Vd. If Vd is the same maximum output will be the same, again if all the other specs are the same, which they seldom are. 

The 3dB increase in voltage sensitivity comes at the cost of drawing twice the current, which some amps don't deal with very well. 

[BassAdder60]

28 minutes ago, Bill Fitzmaurice said:

It's not about watts, it's about voltage sensitivity. That's 3dB higher with 4 ohms, so with the same amp settings the 4 ohm speaker will be 3dB louder, assuming all the other T/S specs are the same, which they seldom are. 3dB is audible, but just. As for maximum SPL that's mainly determined by the cone displacement, T/S spec Vd. If Vd is the same maximum output will be the same, again if all the other specs are the same, which they seldom are. 

The 3dB increase in voltage sensitivity comes at the cost of drawing twice the current, which some amps don't deal with very well. 

So in real world experience this wouldn’t appear much louder to the listener ?? 

[itu]

23 minutes ago, Bill Fitzmaurice said:

...assuming all the other T/S specs are the same, which they seldom are.

 

...if all the other specs are the same, which they seldom are. 

 

...voltage sensitivity comes at the cost of drawing twice the current, which some amps don't deal with very well. 

I might read the above like:

Two speakers from the same manufacturer that look the same but have different impedances are two different speakers. 

 

Depending on the amp it is hard to say which speaker is really louder. Lower impedance may be harder load for the amp and therefore higher impedance cab can be even louder. 

[BigRedX]

IME the whole point of amps that can drive 4Ω loads is not that swapping your 8Ω cab for a 4Ω one will make it louder but the fact that you can run two 8Ω cabs which if done properly will give you twice the driver area which will be noticeably louder,

[Kev]

I've never really understood why 4ohm 115/410/112 cabs are made, as I've always felt that they are designed to be in pairs or mixed with one another, and so should be 8ohm to come down to 4ohm total, unless you're running a 2ohm amp.  More speakers = more air moved = louder. 

 

I suppose maybe if you're always running your amp at 11, maybe then it makes a bit more of a difference if you're running just one cab, provided the speak cone(s) have enough left to give?

[SimonK]

13 minutes ago, Kev said:

I've never really understood why 4ohm 115/410/112 cabs are made, as I've always felt that they are designed to be in pairs or mixed with one another, and so should be 8ohm to come down to 4ohm total, unless you're running a 2ohm amp.  More speakers = more air moved = louder. 

 

I suppose maybe if you're always running your amp at 11, maybe then it makes a bit more of a difference if you're running just one cab, provided the speak cone(s) have enough left to give?

 

Same here - had a 4ohm 4x10 for years which could never be paired with anything else - managed to find a buyer eventually and now stick to 8ohm cabs only (or at least I did until IEMs killed the joy of playing through a stack).

[Bassybert]

Maybe something historical to do with valve heads/amps going to 2 ohms so you could use 2 4ohm cabs?

[Bill Fitzmaurice]

41 minutes ago, BassAdder60 said:

So in real world experience this wouldn’t appear much louder to the listener ?? 

Not really. The only time it might is if your amp is so underpowered that it can't drive the 8 ohm speaker to it's full displacement, which would be rare, like with a 25 watt amp and a 200 watt speaker. 

 

22 minutes ago, Kev said:

I've never really understood why 4ohm 115/410/112 cabs are made

A 4 ohm 15 makes some sense if it's paired with a 410, or even a 210, to get the sensitivity of the 15 high enough to match well with the 210/410. But then you'd need a 2 ohm capable amp, not to mention the inherent flaws of mixing speakers. 

 

Oops! I did mention it. 😲

[Bill Fitzmaurice]

1 minute ago, Bassybert said:

Maybe something historical to do with valve heads/amps going to 2 ohms so you could use 2 4ohm cabs?

That was done to save amps from being cooked by impedance loads that players employed because they didn't know better. I will confess to having done that, running 2 ohm loads with Fender amps that wanted no less than 4 ohms. But that was the '60s, we did all sorts of weird things then and managed to survive, and those Fenders were built like a Centurion tank.