Marky L Posted June 21 Share Posted June 21 (edited) Can I confirm that if - I have two 4x10 cabs, both rated at 500w but one is 8ohm and the other 4ohm. If I A/B these cabs from my 500W amp running exactly the same settings, the 4ohm would sound louder and if I want the 8ohm to match the perceived output volume, I would need to turn the amp output up? (Cabs being trialled individually). I'm sure there will be lots of variables that could be taken into account, but this is on a verrrrry basic level. Edited June 21 by Marky L Quote Link to comment Share on other sites More sharing options...
asingardenof Posted June 21 Share Posted June 21 8 minutes ago, Marky L said: Can I confirm that if - I have two 4x10 cabs, both rated at 500w but one is 8ohm and the other 4ohm. If A/B these cabs from my 500W amp running exactly the same settings, the 4ohm would sound louder and if I want the 8ohm to match the perceived output volume, I would need to turn the amp output up? (Cabs being trailed individually). I'm sure there will be lots of variables that could be taken into account, but this is on a verrrrry basic level. If you turn the volume up both cabs will get louder though. 1 Quote Link to comment Share on other sites More sharing options...
Marky L Posted June 21 Author Share Posted June 21 9 minutes ago, asingardenof said: If you turn the volume up both cabs will get louder though. Absolutely I get that, but at the same output volume level, would the 4ohm be noticeably louder? Quote Link to comment Share on other sites More sharing options...
Lozz196 Posted June 21 Share Posted June 21 I found when I tried this that the 4ohm didn’t sound noticeably louder but it did sound more “alive”. It was ages ago when I did it so can’t remember which amps/cabs tho. 1 Quote Link to comment Share on other sites More sharing options...
prowla Posted June 21 Share Posted June 21 P = IV Double the current will go to the 4 ohm cab, or 2/3 of your power. (Assuming they're connected in parallel.) As far as Watts to volume goes, the general rule is 10x the power = 2x the volume. 1 Quote Link to comment Share on other sites More sharing options...
asingardenof Posted June 21 Share Posted June 21 3 hours ago, Marky L said: Absolutely I get that, but at the same output volume level, would the 4ohm be noticeably louder? Noticeably? Possibly. Significantly? Probably not. 2 Quote Link to comment Share on other sites More sharing options...
nekomatic Posted June 21 Share Posted June 21 Depends on the sensitivity of the cabs. The 4 ohm will get more power but could be less sensitive. 3 Quote Link to comment Share on other sites More sharing options...
ossyrocks Posted June 21 Share Posted June 21 5 hours ago, Marky L said: Can I confirm that if - I have two 4x10 cabs, both rated at 500w but one is 8ohm and the other 4ohm. If I A/B these cabs from my 500W amp running exactly the same settings, the 4ohm would sound louder and if I want the 8ohm to match the perceived output volume, I would need to turn the amp output up? (Cabs being trialled individually). I'm sure there will be lots of variables that could be taken into account, but this is on a verrrrry basic level. If the cabs are identical, design, speakers, sensitivity etc, except for the impedance, then the 4 ohm cab may sound louder to you. If you’re talking about wholly different cabs, make, manufacturer, speakers etc, then all bets are off. Rob 6 Quote Link to comment Share on other sites More sharing options...
Marky L Posted June 21 Author Share Posted June 21 Thanks folks. It just helps clear a bit of brain fog! Quote Link to comment Share on other sites More sharing options...
Lfalex v1.1 Posted June 21 Share Posted June 21 If you're stacking them, maybe put the 8 Ohm on the top? It'll be closer to ear level and that might help compensate for any perceived difference in SPL. Quote Link to comment Share on other sites More sharing options...
Marky L Posted June 22 Author Share Posted June 22 11 hours ago, Lfalex v1.1 said: If you're stacking them, maybe put the 8 Ohm on the top? It'll be closer to ear level and that might help compensate for any perceived difference in SPL. No, it's one or the other. 1 Quote Link to comment Share on other sites More sharing options...
Lfalex v1.1 Posted June 22 Share Posted June 22 34 minutes ago, Marky L said: No, it's one or the other. That's no fun. The more the merrier! 1 Quote Link to comment Share on other sites More sharing options...
bremen Posted June 22 Share Posted June 22 (edited) As others have noted, the relative sensitivity of the speakers is probably more a factor than the impedance. Although an ideal amplifier will deliver twice the power into 4 ohms compared to 8, a 3dB increase, real world amplifiers don't behave that well and will start to current limit into a 4 ohm load at a lower output voltage compared to 8. Swapping an otherwise identical 4 for an 8 might just be audible but new strings or a drunk guitarist far more a factor. Wait - we are talking about a solid state amp? If it's valves, I'll get my coat... Edit: sorry, Ossyrocks was more concise. Edited June 22 by bremen 2 Quote Link to comment Share on other sites More sharing options...
ossyrocks Posted June 22 Share Posted June 22 20 minutes ago, bremen said: As others have noted, the relative sensitivity of the speakers is probably more a factor than the impedance. Although an ideal amplifier will deliver twice the power into 4 ohms compared to 8, a 3dB increase, real world amplifiers don't behave that well and will start to current limit into a 4 ohm load at a lower output voltage compared to 8. Swapping an otherwise identical 4 for an 8 might just be audible but new strings or a drunk guitarist far more a factor. Wait - we are talking about a solid state amp? If it's valves, I'll get my coat... Edit: sorry, Ossyrocks was more concise. I had the valves/impedance conversation recently with Martin Garton (Gartone Amps). I have a valve head which ideally requires an 8 ohm load, but I want to run it into a 4 ohm cab. I haven’t tried it yet, as the cab isn’t here yet, but he said I probably wouldn’t notice any difference in volume, but the power valves would run a little hotter. He biased the amp on the cool side when it was with him last, so he said it would be fine. Rob 1 Quote Link to comment Share on other sites More sharing options...
Jack Posted June 22 Share Posted June 22 1 hour ago, ossyrocks said: I had the valves/impedance conversation recently with Martin Garton (Gartone Amps). I have a valve head which ideally requires an 8 ohm load, but I want to run it into a 4 ohm cab. I haven’t tried it yet, as the cab isn’t here yet, but he said I probably wouldn’t notice any difference in volume, but the power valves would run a little hotter. He biased the amp on the cool side when it was with him last, so he said it would be fine. Rob Well also valve amps tend to run the same power into any load. They don't change with the load like solid state amps. Quote Link to comment Share on other sites More sharing options...
itu Posted June 22 Share Posted June 22 An interesting point was mentioned in another thread here, that if there are two speakers from the same manufacturer, but the impedances are different, the speakers will not be similar. If the Z is different, there are several other parametres that will be different, too. Therefore 4 and 8 ohm cabs will sound and behave in a different way. @bremen's comment about amp's ability to push voltage and current are of great interest. When Z gets lower, current rises, and everything will get hotter from amp's components to speaker's coil. Think Z this way: You have a rod that you push with your thumb. Bigger Z means thicker rod, and is easier to your thumb. Lower the Z and rod gets much thinner. Pushing the spikey rod will hurt your thumb. Power is connected to loudness, but watts do not represent sound level. And because ear is not linear, like watts are, comparing watts is pretty fruitless. From 50 W to 500 W you can hear a difference, but 500 W to 1000 W the difference is close to nothing. dB seems to be too complicated a unit to most of us musicians. 3 Quote Link to comment Share on other sites More sharing options...
Marky L Posted June 22 Author Share Posted June 22 (edited) 3 hours ago, bremen said: As others have noted, the relative sensitivity of the speakers is probably more a factor than the impedance. Although an ideal amplifier will deliver twice the power into 4 ohms compared to 8, a 3dB increase, real world amplifiers don't behave that well and will start to current limit into a 4 ohm load at a lower output voltage compared to 8. Swapping an otherwise identical 4 for an 8 might just be audible but new strings or a drunk guitarist far more a factor. Wait - we are talking about a solid state amp? If it's valves, I'll get my coat... Edit: sorry, Ossyrocks was more concise. Sorry, yes solid state. Should I have included "heft" into all this? 😁 Edited June 22 by Marky L Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted June 22 Share Posted June 22 3 hours ago, bremen said: If it's valves, I'll get my coat... It won't be any louder if they are measured the same except the valve amp will give the same power into 4 or 8 ohms as long as you select the correct impedance. Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted June 22 Share Posted June 22 You also have to consider the total load presented to the amplifier. Four and eight ohms in parallel. equates to 2..67 ohms . If the SS amp can't drive that impedance the amp dies.. Quote Link to comment Share on other sites More sharing options...
barkin Posted June 22 Share Posted June 22 8 hours ago, Marky L said: No, it's one or the other. ...which I thought was obvious from your OP. But hey... 1 Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted June 22 Share Posted June 22 48 minutes ago, BassmanPaul said: You also have to consider the total load presented to the amplifier. Four and eight ohms in parallel. equates to 2..67 ohms . If the SS amp can't drive that impedance the amp dies.. However the OP said he would only be using one or the other. In addition many Solid State amps are 2.67 ohm stable with some stable down to 2 ohms. 1 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted June 22 Share Posted June 22 I know but it IS something that must be considered when connecting speaker cabinets to an amplifier.. Quote Link to comment Share on other sites More sharing options...
agedhorse Posted June 24 Share Posted June 24 Assuming you are comparing one to the other and they are identical other than nominal impedance... The 4 ohm cabinet will be approx. 3dB louder for the same volume setting on the solid state amp, because solid state amps are essentially ideal voltage sources. If you turn the 8 ohm cabinet up 3dB, it will be the same volume as the 4 ohm cabinet. 1 Quote Link to comment Share on other sites More sharing options...
Marky L Posted June 25 Author Share Posted June 25 15 hours ago, agedhorse said: Assuming you are comparing one to the other and they are identical other than nominal impedance... The 4 ohm cabinet will be approx. 3dB louder for the same volume setting on the solid state amp, because solid state amps are essentially ideal voltage sources. If you turn the 8 ohm cabinet up 3dB, it will be the same volume as the 4 ohm cabinet. Perfect. Thank you. 1 Quote Link to comment Share on other sites More sharing options...
bremen Posted June 25 Share Posted June 25 16 hours ago, agedhorse said: Assuming you are comparing one to the other and they are identical other than nominal impedance... The 4 ohm cabinet will be approx. 3dB louder for the same volume setting on the solid state amp, because solid state amps are essentially ideal voltage sources. If you turn the 8 ohm cabinet up 3dB, it will be the same volume as the 4 ohm cabinet. Not quite. Few amps are ideal voltage sources, there's generally a bit of sag. Quote Link to comment Share on other sites More sharing options...
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