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So... if I've got a bass amp that puts out 300W @ 4 Ohms (and that's it's preferred mode of operation)... but it also puts out 165W @ 8 ohms... is it going to sound quieter if I swap out the current 4 Ohm cab for an 8 Ohm cab? Are there any other affects by swapping from 4 to 8 Ohms?
I guess the efficiency of the two speakers (SPL??) will have some bearing... so I'll assume both speakers are similarly efficient.
The amp in question has a Mosfet power section and valve pre amp (it's a Mesa Boogie Walkabout). Not sure if that makes any difference.
Thanks.
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If the two loudspeakers were of identical sensitivity the 4R at 300W would be 2.6dBSPL louder, that is, not a lot!
Of course calculated loudness levels do not always match subjective experience but I doubt there will be much in it.
In theory again, the amp will have an easier time on an 8 Ohm load but in practice again, assuming it is a good design (ICBM?) no matter.
Dave.
The amp will also be under less stress and will run cooler, but any well-designed amp won't have a problem running at its minimum impedance anyway.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Speaker efficiency is usually measured at one watt.
We did some measurements on guitar speakers a while back and found that there was not a linear relationship between power input and efficiency; so some speakers were more efficient at low volume, but had lower maximum output than some less efficient speakers. A good analogy would be the difference between acceleration and top speed.
Conclusion, it's virtually impossible to second guess what the real world perception of loudness well be.
Thanks @ecc83, @ICBM and @jpfamps.
The replacement cab is quoted as having a sensitivity of 99.9 dB 1W 1M. Is that efficient or not?
I can't get the figure for the Boogie speaker.
Thanks jpfamps... interesting point.
It won't be anywhere near as sensitive at bottom E! Good figure for midband though . Yes, agreed, Pin is not linear with noise out, Aka distortion!
Dave.
A well-designed cab properly tuned for a less efficient speaker may easily be louder than a more efficient speaker in a simpler box (AKA typical guitar and many bass cabs).
The car analogy is good, it's a bit like trying to correlate engine power to acceleration as well as top speed. They are related, but not directly or always completely predictably.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I'll be swapping a 1x12 (that also has a passive, unwired 1x10 in it) for a different 1x12 (without the unwired speaker)
The 12 / 10 cab is fine... just wanting to reduce weight.
The current 12 is 4 Ohm (the replacement cab is likely to be 8 Ohm)
If you are using the single 8 ohm 12 with the 10 unplugged your cab is running at 8 ohm. Replacing it with a single 12 8ohm cab should make little difference to the volume.
I think, I'm getting confused.
Whoops... my mistake! I meant the old cab is 4 Ohm and the potential new one is 8 Ohm
I think I'd agree, that you existing cab is probably loading your Amp with 8 ohms without the 10 connected.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Yes, @ICBM is totally correct. By design, the cab has one 4 Ohm 12" speaker that's connected... the 10" speaker just flaps around in sympathy with the 12" speaker's movements.
I've just realised an obvious thing that I could do as a bit of a half-arsed experiment... attach the amp to a 12" 8 Ohm guitar speaker cab and see what different that makes (I've got a Boogie guitar cab with an EV 1x12 Black Shadow... that should be tough enough to put up with a bit of bass for a few minutes). Obviously, the different speaker sensitivities (I don't have any measurements) will make a difference... but I might learn a little about the affect of different impedances (and sensitivities). Not very scientific I know!
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein