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Apologies in advance - this is ANOTHER cab/ohmage question

Z

Zob

Aug 1, 2012
12
1
#1
Hey guys. Really sorry about this question. I've been playing bass for 45 years but still don't understand anything about Watts, Ohms and the rest.

I have just bought a rather wonderful 1x12 Mesa Boogie Walkabout Scout combo.

I wanted something lighter than my Ashdown 300/2x10/1x15 rig.

The Walkabout has a fantastic sound - even better than the old Ampeg flip-top I keep at home.

But I think I'd like to add a little 'size' for live gigs.

The amp's spare output is rated at 4 ohms. Can I use an 8 ohm extension cabinet or should I use a 4 ohm cab? What are the possible risks/issues?

And why am I now in italics?? Stupid iPad!

Sorry for the idiot question.

All the best.

Martin
 
#2
You always safe going with a number equal to or higher than the minimum. Anything that is 4 ohms or higher you are good. For example: 2 ohms would not be good.
 
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#4
CL400Peavey said:
Actually the amp will support a 2 Ohm load. So he could use either an 8 or a 4 Ohm extension cab.
Click to expand...

I know nothing about the amp, just going by the info he gave. But if it's a combo and the ext speaker jack say 4 ohm minimum that would make sense. Either way I still gave correct info. He wouldn't want to hook a 2 ohm load to a jack that says 4 ohm min.
 
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#5
So often the combo amps don't explicitly say what impedance their internal speaker is, and you have to discern it from the amp's specs and what kind of additional speaker load is allowed.

Zob, isn't it about time you learned this? It's not rocket science, you know:

Two 8-ohm speakers in parallel (which is 99% of connections on amps and speaker jack plates) is a 4-ohm load; two 4-ohm speakers together is a 2-ohm load; one 8 with one 4 is a 2.67 ohm load, treat it as 2 ohms. Lower impedance is actually harder on the amp, as it puts out more power, it needs to get rid of more heat, so they'll always have a minimum speaker load printed on them. On a tube amp, match your speaker load to the tap (output) listed on the back that matches it exactly.

That's about it, well over 80% of everything you need to know about impedance matching on amps as a bassist.
 
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#6
UNLESS...

the extension cab speaker jack MIGHT be in series with the existing speaker, and not parallel. A few combo amps are like that, yes it's strange.

IF this were the case, going to an 8 ohm would not be a great idea since it would decrease the amp's output even further. Only the amp's manual, or a good schematic, can tell us for sure, and I don't have either handy. IF it's in series, let' suppose the internal speaker is 4 ohms, adding a 4 ohm speaker in series would raise the speaker load to 8 ohms. It likely wouldn't cut the amp's output power in half (the theoretical number) but maybe it would go down by 25%. However, if we add a 8 ohm cab in series to a 4 ohm speaker, now we get a 12 ohm load rather than the original 4. The amp's output would indeed be diminished noticeably.

Again, that is IF the ext cab jack is in series. If it's in parallel, everything the previous posters said is correct. I do not know this amp either--but there are indeed a very few oddballs out there that run the jack in series.
 
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#7
Thank you so much guys. I can't believe the number of helpful, thoughtful replies I've received in about an hour. HolmeBass, you're right: it is time I learnt this stuff and I'll make an effort.

Meanwhile, my take from this is that I can run safely an 8 ohm cabinet from my Scout assuming the output is in parallel with the built-in cabinet (which I am certain it is).

Thanks so much to all of you who took the trouble to reply. Very much appreciated.

And I really do recommend the Scout. I have used vintage HiWatt and Ampeg and contemporary Ashdown and the Mesa Boogie really blows them away - especially given its size and weight.

Thank you!
 
#10
tbz said:
Could you name a few amp models where you've seen this? In 20ish years of playing I've never seen an amp or cab output wired for series, from the factory.
Click to expand...
I briefly used to own an Eden Nemesis combo wired in series with a 4 ohm load. Cost and weight cutting measure to get 200w to the speakers.
 
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#11
Zob said:
Thank you so much guys. I can't believe the number of helpful, thoughtful replies I've received in about an hour. HolmeBass, you're right: it is time I learnt this stuff and I'll make an effort.

Meanwhile, my take from this is that I can run safely an 8 ohm cabinet from my Scout assuming the output is in parallel with the built-in cabinet (which I am certain it is).

Thanks so much to all of you who took the trouble to reply. Very much appreciated.

And I really do recommend the Scout. I have used vintage HiWatt and Ampeg and contemporary Ashdown and the Mesa Boogie really blows them away - especially given its size and weight.

Thank you!
Click to expand...

Heck Zob, if you know the difference between series and parallel then you're golden! That's more than half the fight right there.
 
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#12
.. about the only other thing to consider, is that IF you do add an 8 ohm CABINET through the extension speaker jack, realize that the added CABINET will only be receiving 1/2 the power that the contained 112 is (assuming it is a 4 ohm driver, which would only make sense if the amp is indeed 2 ohm capable, and external jack is listed at 4 ohms) ... and IF your 'add on CABINET' contains more than the one SPEAKER, each of those speakers will also only be receiving a relative portion of what the entire cabinet is receiving ... all of which could have an impact on the current sound that you like so much ...

... with all that said, adding a cabinet containing the same driver as in the amp, in a similarly voiced cabinet, would probably be the optimal choice, if possible ... ;)
 
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#13
nashvillebill said:
UNLESS...

the extension cab speaker jack MIGHT be in series with the existing speaker, and not parallel. A few combo amps are like that, yes it's strange.

IF this were the case, going to an 8 ohm would not be a great idea since it would decrease the amp's output even further. Only the amp's manual, or a good schematic, can tell us for sure, and I don't have either handy. IF it's in series, let' suppose the internal speaker is 4 ohms, adding a 4 ohm speaker in series would raise the speaker load to 8 ohms. It likely wouldn't cut the amp's output power in half (the theoretical number) but maybe it would go down by 25%. However, if we add a 8 ohm cab in series to a 4 ohm speaker, now we get a 12 ohm load rather than the original 4. The amp's output would indeed be diminished noticeably.

Again, that is IF the ext cab jack is in series. If it's in parallel, everything the previous posters said is correct. I do not know this amp either--but there are indeed a very few oddballs out there that run the jack in series.
Click to expand...

That is so rarely the case though.
 
#15
Mesa does not have a manual for the Scout online, it appears (or else it's buried somewhere else in their website). The Scout page though is here: http://www.mesaboogie.com/Product_Info/Bass_Amps/walkabout/WalkaboutScout/WalkScout.htm

Read the Important Notice at the lower right of the web page:
................................................................................................................
IMPORTANT NOTICE:

Above models come standard at 4 ohms for max output, combo use only - 8 ohm versions are available upon request at no extra cost for use with a second extension cab. Please qualify the application and specify the appropriate impedance.
................................................................................................................

This to me implies that:
a) the amp can only handle a 4 ohm load (lowest impedance, 8 ohms would be OK)
b) the standard configuration has a 4 ohm speaker, in which case an extension cab cannot be used (but do they include a speaker jack in that case?)
c) if an external cab is to be used, the internal speaker must be 8 ohms, AND the external speaker must be 8 ohms, for a combined load of 4 ohms. Also the external speaker jack is parallel with the internal speaker.

OP, did you buy this combo used or new? Is the speaker jack original factory or added by somebody later? Lastly, do you have a digital multimeter-- and know how to use it-- to measure the impedance of the speaker that's in there?
 
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#17
As a Walkabout owner for over 8 yrs, let me clear up a few discrepancies. Most likely, the internal driver is 4 ohms, which is what Mesa claims the minimum impedance for the amp to be. Many owners, myself included, have run these amps below 4 ohms without issue, but it does go against Mesa's recommendation.
What I suggest, is to use the Scout combo as a stand-alone, when the single 12 is enough. If you need more volume than the 12 can provide, take the amp out of the Scout cab, and use it with a larger 4 ohm cab, like a 2x12, 4x10, etc. This is the safest, and easiest way to play- and not risk overheating this fine amp.
 
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#18
Thanks RickenBoogie (and everyone who has contributed). That sounds like sage advice.

My problem being (and I should have explained this before) that I have a perfectly decent 8 ohm Ashdown 1x15 which I'd like to use as an extension to the Walkabout. I don't want to buy another extension cab.

I finally managed to squeeze my big head into the back of the Walkabout and it says clearly, beneath the two speaker sockets (one of which is connected to the internal 12" driver") "SUGGESTED LOAD 4 OHMS" This text stretches beneath both sockets.

I interpret this to mean that the suggested TOTAL LOAD from both sockets should ideally be 4 ohms and that therefore the internal load must be 8 ohms and that therefore an extensions speaker should ideally also be 8 ohms, giving a total load of 4 ohms.

Make sense?

Thanks all!
 
#19
Zob said:
Thanks RickenBoogie (and everyone who has contributed). That sounds like sage advice.

My problem being (and I should have explained this before) that I have a perfectly decent 8 ohm Ashdown 1x15 which I'd like to use as an extension to the Walkabout. I don't want to buy another extension cab.

I finally managed to squeeze my big head into the back of the Walkabout and it says clearly, beneath the two speaker sockets (one of which is connected to the internal 12" driver") "SUGGESTED LOAD 4 OHMS" This text stretches beneath both sockets.

I interpret this to mean that the suggested TOTAL LOAD from both sockets should ideally be 4 ohms and that therefore the internal load must be 8 ohms and that therefore an extensions speaker should ideally also be 8 ohms, giving a total load of 4 ohms.

Make sense?

Thanks all!
Click to expand...

Yes, that is how I interpret their information. The internal speaker may have "8 ohms" written on it somewhere which would be the final confirmation that you are correct. If there's nothing on it, if you have an ohmmeter, you could also measure the impedance of your internal speaker to see if it's 8 ohms.
 
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