Adding an external 1x15 bass cab to a 2x12 guitar combo

[StonedWorm]

Hi there, I am currently looking to create my personal tone, and I was thinking about this:
I own a solid state 2x12'' guitar combo rated "115 watts RMS @ 5% THD 4 ohms load 120VAC". The two 12'' internal speakers are rated 8ohms. That said, by default the combo has an "external speaker" jack output, which means I can add a "passive" cab to the amp in series with the internal speakers. It was obviously meant to be used adding a "guitar cab", but I'd like to add a 1x15'' bass cab instead. My goal would be to add a lower range of frequencies to the overall sound, since I play mostly a fuzzy detuned distorted kind of music. I have found this 1x15'' bass cab, rated 250w at 8ohms. So, what would happen if I add that bass cab? Is the choice of ohms correct considering that output will set the external speaker in series with the internal ones? Will it work? Is there anything else I need to know? Any suggestions?
Thank you in advance

 

[jeremy]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

if the internal speaker is 8 and the amp is rated at 4ohms then adding an 8 ohm cab is exactly what you would want to do. the fact that its a bass cab wont hurt anything and will probably sound fine. if it has a tweeter i might turn it down or even off

 

[dystrust]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

if the internal speaker is 8 and the amp is rated at 4ohms then adding an 8 ohm cab is exactly what you would want to do. the fact that its a bass cab wont hurt anything and will probably sound fine. if it has a tweeter i might turn it down or even off

+1

Turn the horn/tweeter off as they tend to be pretty harsh when playing overdriven. Just to clarify, the 1x15 won't give you any low-end that isn't already present, but it may do a better job of presenting the low end the amp generates. A cab like that can sound a bit dull for guitar, but the 12s should help fill out the high end. If you're looking for more volume you may also want to consider replacing your 12s with higher-sensitivity speakers.

 

[StonedWorm]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

No tweeter in it, it's just a 1x15'' vented bass cab. So as I thought I am not being delusional thinking I can do it I was mainly concerned about ohms. A friend of mine told me that when you add more speakers in series ohms increase so that the main output (4ohms in this case) gets equally parted on the speakers involved. That means, if he was correct, that the sound coming from each speaker will be lower, but there is gonna be no stress on the amplifier since it will just adapt itself on the new configuration keeping to feed the same overall amount of power. Is that correct?

 

[StonedWorm]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

To answer your question, the combo we are talking about has a great tone, even if it's a pretty cheap one. The speakers in it are custom made by the manufacturer, nothing legendary, but I like them pretty much and they already have a bunch of bottom end. The goal I have in mind is to make the bass cab manage and enhance the lower frequencies already created by the combo, and the two 12'' will just continue producing their own frequencies with lower stress

 

[SlyFoxx]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

Actually parallel or series the power gets distributed equally between the two as long as the respective impedance ratings are the same.

As for the last part of your second post the bass speaker may enhance the low end of the amp but the other cab will still see the same range of frequencies. It's not like the low bass will magically leak towards the bass speaker and the higher frequencies to the 2x12. Any reduced stress to the 2x12 would only come from it working slightly less because you added another speaker to the mix.

 

[StonedWorm]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

That's what I meant. I know the frequencies produced will just be just distributed equally on each speaker. The bass speaker response nevertheless vary due to its own specs, that's for sure. I understand what you mean, and I agree. Maybe i could use a well chosen crossover to distribute the frequencies...maybe that would do the trick. Anyway, thank you all for you replies, and now I know that can be done, there's only one thing to do: to try it. I will post my opinions about the results later on, if you are interested.

 

[IM4Tone]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

Hi there, I am currently looking to create my personal tone, and I was thinking about this:
I own a solid state 2x12'' guitar combo rated "115 watts RMS @ 5% THD 4 ohms load 120VAC". The two 12'' internal speakers are rated 8ohms. That said, by default the combo has an "external speaker" jack output, which means I can add a "passive" cab to the amp in series with the internal speakers. It was obviously meant to be used adding a "guitar cab", but I'd like to add a 1x15'' bass cab instead. My goal would be to add a lower range of frequencies to the overall sound, since I play mostly a fuzzy detuned distorted kind of music. I have found this 1x15'' bass cab, rated 250w at 8ohms. So, what would happen if I add that bass cab? Is the choice of ohms correct considering that output will set the external speaker in series with the internal ones? Will it work? Is there anything else I need to know? Any suggestions?
Thank you in advance

I suspect the external jack puts the add'l cab in parallel, not series which is certainly the case if your manual tells you the resultant total load is 4 ohms. So if the amp is rated to handle 4 ohms, there is no harm. Whether or not the added bass cab will sound good is another matter. I'm guessing it won't, but could be wrong seeing as how the Fender Bassman was designed to be a bass amp and turned out to be a favorite with guitar players.:scratchch

 

[Boogie Bill]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

I use Mesa amps, mostly Mark Series combos. These are nominally 8 ohm output to the internal speaker. I almost.always use the 112 combos with a Mesa 8-ohm 112 EVM Thiele-ported cab underneath (total 4 ohms). The Thiele cab adds a lot of punch and projection to the lower frequencies and I can hang with most any 412 half-stack. For my Mark V combo, I use its matching Closed Back Widebody cab.

I also have a 35-watt Mesa Maverick 212 V30 combo (8 ohms). I like to gig this amp with a Mesa 212 Horizontal Recto cab. Makes for a nice, portable mid-power half-stack. Again, the closed-back Retro adds a lot low-end grunt.

You may find the 115 cab a little "floppy". A closed-back 212 might match up a bit better.

Mesa pioneered the open-back combo+matching Thiele cab. Been using this system for more than 20 years, and I love it.

But...you can have too much bass. You don't want to occupy the same sonic territory as the bass guitar and the keyboards.

And unless you are biamping with something like a Rivera Los Lobottom, forget about using a crossover.

Good luck!

Bill

 

[StonedWorm]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

Well, it was not my assumption that the combo will use the external cab in series, I read it in the owner's manual
Here is what's exactly written: "EXT. SPEAKER: Use this jack to connect an extension speaker cabinet to the amplifier. This jack is wired in series with the internal speaker(s).
WARNING: Do not attempt to use head-phones in the Speaker jack! Permanent hearing damage could result!"

 

[StonedWorm]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

About the crossover, it was just an idea...and quickly forgot. The crossover should be put inside the circuitry in way that will prevent me from using the combo without the bass cab again. Whatever I decide to do, I need it to be set and unset easily and quickly. I don't mind, nor my my band does, entering the "sonic territory" of bass guitar, we're all concerned only about the overall result. If it sounds good, it's good. That's all we care about. Thank you again for your replies, always here for any other advice or experience of yours

 

[IM4Tone]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

....I own a solid state 2x12'' guitar combo rated "115 watts RMS @ 5% THD 4 ohms load 120VAC"....

.....Here is what's exactly written: "EXT. SPEAKER: Use this jack to connect an extension speaker cabinet to the amplifier. This jack is wired in series with the internal speaker(s).......

Seems odd to rate the amp w/ a 4 ohm load, then provide a jack that will raise impedance to 16 ohms! Certainly a higher impedance load will not harm a ss amp, but you will lose power output and volume. So I guess the bottom line is try it and see if you like the sound!

 

[Chickenwings]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

You like your amp but you still want more headroom in the low end.
Two 8 ohm speakers wired in parallel means you get 4 ohm load which is what your amp is optimized for. Plugging in another 4 ohm speaker through the external plug will reduce the load to 2 ohms because most speaker outs are wired in parallel. External speaker jacks on amps have always been problematic for the reason on changing the impedance. The only time it works out well is if you have a selectable impedance switch on the amp, or taps on your output transformer. Just plugging another speaker in simply shares the load between cabs which results in the amps wattage being shared by all the speakers, only it is not running at full efficiency due to a load mismatch so your amp is working harder but putting out less wattage. Most transformers on good quality amps can handle a 100% mismatch in load, but you are losing effficiency and working outside its design parameters.
External speaker jacks on all amps from the days of the tweed fenders to now have always been a strange anomaly. They really need an impedance switch to make them work properly.
If you want more low end and have a love affair with your amp, the best thing you can do is keep using the 2x12 configuration and have a look at a pair with more low end in their eq curve, more headroom (wattage) and possibly more efficiency too. Something like swamp things will probably fit the bill and have massive room shaking low end and they wont break a sweat in terms of headroom. plus you have not had to add extra unnecessary heavy stuff to lug to gigs etc

 

[IM4Tone]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

You like your amp but you still want more headroom in the low end.
Two 8 ohm speakers wired in parallel means you get 4 ohm load which is what your amp is optimized for. Plugging in another 4 ohm speaker through the external plug will reduce the load to 2 ohms because most speaker outs are wired in parallel. External speaker jacks on amps have always been problematic for the reason on changing the impedance. The only time it works out well is if you have a selectable impedance switch on the amp, or taps on your output transformer. Just plugging another speaker in simply shares the load between cabs which results in the amps wattage being shared by all the speakers, only it is not running at full efficiency due to a load mismatch so your amp is working harder but putting out less wattage. Most transformers on good quality amps can handle a 100% mismatch in load, but you are losing effficiency and working outside its design parameters.
External speaker jacks on all amps from the days of the tweed fenders to now have always been a strange anomaly. They really need an impedance switch to make them work properly.
If you want more low end and have a love affair with your amp, the best thing you can do is keep using the 2x12 configuration and have a look at a pair with more low end in their eq curve, more headroom (wattage) and possibly more efficiency too. Something like swamp things will probably fit the bill and have massive room shaking low end and they wont break a sweat in terms of headroom. plus you have not had to add extra unnecessary heavy stuff to lug to gigs etc

Did you read the posts?
1) This amp is solid state.
2) The Op stated his manual states the external speaker cab. jack is in series.

 

[StonedWorm]

Re: Adding an external 1x15 bass cab to a 2x12 guitar combo

Did you read the posts?
1) This amp is solid state.
2) The Op stated his manual states the external speaker cab. jack is in series.

Indeed