Extension cab from combo

J

JohnBJohn

Tard
I don't really understand the concept behind combos with extra jacks for external speakers. Taking an ac15 as an example, how would using an external speaker cab make the amp any louder if it is still pushing out the same 15 volts that it was through the internal speaker? Would making myself a cab with a couple spare speakers in addition to the internal speaker give the amp any extra volume?
 
that means you can plug in another speaker cab as long as it has the same OHM rating as the amp and has the wattage rating to handle the amps output.
speakers moving air produces sound the more the speaker can move the air the more volume the speaker puts out.
more speakers moving more air translates to more or louder volumes.
 
^ what he said, and as they say in the car world, there's no replacement for displacement.

Don't mix up wattage with volume, either. Wattage is a measure of power, decibels are the measure of volume. More efficient speakers will be louder using the same wattage and it depends on the amp design too. An all tube 30watt class A amp can be as loud as a 120watt all tube class AB amp which in turn can be as loud as a 400w solid state amp blah blah blah. Or not. But you probably know this.

You say you want more volume out of the amp... do you mean more total volume out of the speakers, or more apparent volume in the amp?

Adding an extension cab on an AC15 won't give you HEAPS more volume as such, but it will spread the available power across a bigger area and it will sound bigger (and usually better IMO) as a result. Of course there are issues like matching your impedance etc so one speaker doesn't get the lions share of the load etc... many many variables. You might get more volume swapping out the speakers for more efficient ones though.

But if you want more available clean headroom (more loudness before it starts breaking up), that's more an amp thing.
 
no it will be louder for the explination I gave.
more air moving /driven by more speakers will mean more volume.
 
Okay so if i got this right, the more speakers you have under the same amount of watts, the earlier they will break up?
 
JohnBJohn said:
Okay so if i got this right, the more speakers you have under the same amount of watts, the earlier they will break up?
Click to expand...

Hehe, no. This topic (watts, ohms, speakers, volume) is discussed endlessly! Someone should make a True and Final Answer and make it sticky. :)

Sticking to what I know, here's an example from my bass rig.

Ampeg B2RE pushes 250 watts into 8 Ohms, or 450 watts into 4 Ohms.

Using (2) two 8 Ohm cabinets, the amp sees 4 Ohms combined impedance and is pushing 450 watts total. (Each cabinet gets 225W presuming everything else is equal, which is simplistic but essentially right).

(8 Ohms + 8 Ohms in parallel = 4 Ohms, look up this separately if it's news.)

Suppose those two cabinets are 1x15 and 1x15. This gives me two 15" speakers at 225W each.

Q: WHAT IS THE BEST WAY TO GET LOUDER?

A: 1) BUY THE SAME SPEAKERS WITH IMPROVED SENSITIVITY, 2) RUN TWICE AS MANY WATTS

Some speaker cabs are rated at 90 db/W (1khz at 1 meter) and some are rated at 102 db/W. That's a 12 db difference (HUGE) using the same amp and the same setup - 2 15" cabinets. (This is why Behringer sells a 410 for $175 and Epifani sells a 310 for $1000 which is probably louder than the Behringer.)

Alternatively - If I switch to (2) two 410 cabinets, I now have 8 speakers each getting 450/8 = 56W each. Much less power to each speaker, however the SENSITIVITY of those speakers will be different, and THE SURFACE AREA has changed.

2x115 cabinets has 2x(177 in^2) = 345 in^2 of speaker surface area.
2x410 cabinets has 2x4x(79 in^2) = 632 in^2 of speaker surface area.

The 2x410 setup has nearly twice as much speaker surface area. This is critical to reproducing low frequencies efficiently. This is why standing in front of a 2x115 bass stack is really loud, but standing in front of an Ampeg 810 cabinet will disrupt your internal biological processes and cause blurred vision.

This is only indirectly related to when the amp "breaks up". In general, the HIGHER the impedance, the SOONER the amp will break up. This is just common sense - making the amp push harder will "use up" the headroom sooner and create crunch.

In general, when you're adding an expansion cabinet, you're lowering (or keeping equal) the impedance that the amp sees. If you're looking for more crunch, this is not a good way to address the problem.

And part of the confusion is the word "louder". If you add an expansion cabinet to your guitar amp, it won't be "louder" as measured with an SPL meter pointed at the speaker cone. But it will be "louder" as -experienced- by people in the same room with you (provided you followed the points above).

(As an aside - Increasing in wattage can make your guitar "louder", but you must 1) increase by about 100% to really get a difference, 2) have speakers that can handle it, and 3) be certain that you do NOT go DOWN in SPEAKER SENSITIVITY. If you only increase in wattage by a small amount, it's like adding an 11 or 12 to your output volume knob - unless you keep your amp flat out dimed all the time, this isn't a good investment and it probably isn't what you want to sound like.)

Any corrections in math, theory, or life are welcome. :cool:
 
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Roguetitan said:
that means you can plug in another speaker cab as long as it has the same OHM rating as the amp and has the wattage rating to handle the amps output.
speakers moving air produces sound the more the speaker can move the air the more volume the speaker puts out.
more speakers moving more air translates to more or louder volumes.
Click to expand...

does not have to be the same ohm rating
there are safe mismatches
ex. 8 ohm amp into a 16 ohm cabinet is safe
 
madh4ttr said:
does not have to be the same ohm rating
there are safe mismatches
ex. 8 ohm amp into a 16 ohm cabinet is safe
Click to expand...

One thing to consider is that unless you unplug the internal speaker, the impedance that the amp will see is the parallel combined impedance of the internal and external speakers, i.e., if they are both 8 ohms, then the amp will see 4 ohms. Also, in many Fender amps, the main speaker out jack has a shorting plug, so that if you are only plugged into the external speaker output, you'll get no sound.
 
ggunn said:
One thing to consider is that unless you unplug the internal speaker, the impedance that the amp will see is the parallel combined impedance of the internal and external speakers, i.e., if they are both 8 ohms, then the amp will see 4 ohms. Also, in many Fender amps, the main speaker out jack has a shorting plug, so that if you are only plugged into the external speaker output, you'll get no sound.
Click to expand...

The other thing, of course, and the reason why unless there's a mechanical reason NOT to then all amps should have an extention out, is that even a 1x12 closed back will sound quite a bit different than a 1x12 open backed cab, and that different speakers can sound very different.

My main amp is a Rect-o-verb 1x12 combo with a Mesa Black Shadow C90 speaker. I run it (most of the time) through a Recto 2x12 cab with V30's, but it's nice to be able to switch it up and use one speaker for one part, and a different one for the other.
 
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