Quick Wattage/What cab question

[aj5string]

Very quick question to get the most from my head...

Head gives 250w into 8ohms and 500w into 4ohms.

Will it actually much quieter in practice running at 8ohms instead of 4? Imagine all else was similar (speakers etc). Similarly, ow would a 2 speaker single cab running at 8ohms compare volume wise to 2 single speaker cabs running at 8ohms each (ie a 4 ohm load)?

Cheers in advance people!

[Bill Fitzmaurice]

[quote name='aj5string' timestamp='1409063104' post='2535924']
Head gives 250w into 8ohms and 500w into 4ohms.
Will it actually much quieter in practice running at 8ohms instead of 4?[/quote]No. The primary factors in how loud a cab will go is frequency response, sensitivity and driver displacement. Power and impedance are only minor players in the overall equation result.

[HowieBass]

Long rambling discussion starts here http://basschat.co.uk/topic/242579-double-cabs-are-louder-or-are-they/

[aj5string]

Yeah - I had a look through that Howie, was just trying to get a definitive answer!

Thanks everyone!

[lefrash]

I had a cab that was wired up at 16ohm. I then rewired it to 4ohm. The difference in volume was massive, when everything else was the same. I would suspect that if every other variable was the same then you would still get a noticeable volume increase going from 8 to 4ohm, but thats going to be a much more difficult experiment. Most peoples experience of running a cab 8ohm then 4 ohm would be just simply adding another 8ohm speaker which in turn will completely change all the other variables thusmaking it impossible to compare.

[Chienmortbb]

[quote name='lefrash' timestamp='1409078467' post='2536138']
I had a cab that was wired up at 16ohm. I then rewired it to 4ohm. The difference in volume was massive, when everything else was the same. I would suspect that if every other variable was the same then you would still get a noticeable volume increase going from 8 to 4ohm, but thats going to be a much more difficult experiment. Most peoples experience of running a cab 8ohm then 4 ohm would be just simply adding another 8ohm speaker which in turn will completely change all the other variables thusmaking it impossible to compare.
[/quote] Assuming a good solid state amp, changing from 16 to 4 ohms is the equivalent of changing from a 100watt amp to a 400watt.

Edited August 27, 2014 by Chienmortbb

[HowieBass]

The short answer is no it won't sound [i]much[/i] quieter using an 8 ohm rather than a 4 ohm cab if they both have the same driver arrangement (the number, make and size of drivers), but it will be somewhat quieter. You need to increase sound level by 10dB to achieve a doubling of perceived volume (or reduce it by 10dB to halve the volume). Doubling the power adds 3dB, doubling the drivers adds 3dB and as you infer doubling the cab impedance lowers the power delivered by roughly half (-3dB).

[dincz]

[quote name='lefrash' timestamp='1409078467' post='2536138']
if every other variable was the same then you would still get a noticeable volume increase going from 8 to 4ohm
[/quote]

With the emphasis on "noticeable". The most you'd get would be 3dB more - and with most amps something less than that. To give some idea, a 3dB change sounds like this http://www.talkbass.com/attachments/3db-mp3.315441/

[Bill Fitzmaurice]

[quote name='lefrash' timestamp='1409078467' post='2536138']
I had a cab that was wired up at 16ohm. I then rewired it to 4ohm. The difference in volume was massive, when everything else was the same.
[/quote]6dB, to be exact. That's at small signal levels. The difference between 4 and 8 would be 3dB, also at small signal levels. At the full displacement limited power capability of the drivers there won't be any difference, because it's driver cone excursion that limits how loud they can go. So long as you have enough power to push the drivers to full excursion you won't get any benefit from a lower impedance load. As to how much power it takes to push drivers to full excursion, on average only 40% of their thermal rating. In short, a low impedance load is only beneficial if you have an amp that's seriously anemic.

[aj5string]

Thanks for all the responses! Basically, the predicament is... An Aguilar head that does 250w at 8ohms, or 500w at 4. A matamp x10 has caught my eye, but its 8 ohms, and I'm a bit worried it might be a bit wheezey for the gigs we do... Am I better off with 2 8ohm 1x12s or even a 2x12 4 ohm cab to get more out of the amp volume wise?

[HowieBass]

Having two 8 ohm cabs with matching drivers gives you more flexibility for those times you don't need full power from the head and can get away with using just one, probably also easier to carry and load into a car boot etc with two smaller cabs.

[Lozz196]

[quote name='HowieBass' timestamp='1409090036' post='2536323']
Having two 8 ohm cabs with matching drivers gives you more flexibility for those times you don't need full power from the head and can get away with using just one, probably also easier to carry and load into a car boot etc with two smaller cabs.
[/quote]

Yep, I`d go with the two 8ohm 112s for the above reasons as well.