does loudness of amps with more speakers?

If all other things are equal, doubling the cone area increases SPL by 3dB. However, the internal volume, resonance, etc, of a 2x12 versus a 4x12 will be different. This will affect frequency response and therefore perceived volume. Of course, different speaker types will have a large impact as well, I'm assuming you're asking about cabs with the same drivers. I'm not sure if you're asking if two 4x12's will be louder than one or two 2x12's. In either case, the answer is, all other things being equal, yes. How much louder depends on what we're comparing.

Keep in mind that 1dB is typically the smallest SPL difference that most people can hear. 6dB is double the measured SPL. However, 10dB is what it takes for most people to "perceive" double the loudness, according to most acousticians.

Not to confuse SPL with power... Double the power equates to +3dB. It takes ten times the power to double the perceived loudness!

When thinking about power, with guitar amps it can get complicated as we get into the non-linearities involved when overdriving the power stage, etc, but this is a good starting point. I know that you didn't ask about power, but this is a commonly related question that I thought some others might be interested in.

As per above, it is 3dB louder. If you were feeding this second cab with a second, identical power amp, it would be an additional 3dB louder for a total of 6dB.

One of the benefits of having more cabs is wider coverage. Physically moving more air. Being able to get your sound to fill an area without having to turn up as loud to do it. Instead of blasting a single cabinet across the room, you can place another cabinet there and not need to turn up as loud. In cases like these, having more cabs means being able to play more quietly and still be heard, if that makes sense.

If you feel that a 50w head sound better through a half stack versus a full stack, this is a personal preference. The reason that it may sound different has possibly to do with:

• Placing a different load on the output transformer (total speaker impedance differences between running one cab vs two)

• Comb filtering due to acoustic interaction (phase) of additional speakers in close proximity changing frequency response.

• Effect of running additional speakers in parallel versus in series (slight phase differences due to timing will cause filtering)

• Effect of acoustic environment reacting to higher SPL and the moving of more air on perceived tone.

Keep in mind that different cabs will sound different. Slant vs straight 4x12. 4x12 vs 2x12. Etc. Two 2x12's will not sound identical to a 4x12, etc.

Also, where you place your speakers will have an impact on tone. Coupling due to sitting on the floor. Half space effect of being place in front of wall, etc.

I would recommend choosing cabs based on careful listening comparisons and evaluation of what your need will be (filling a large club, playing at home, etc).

Speaker type is a whole other can of worms.

Hope this helps!

Cheers,
-Matt

Is it better to have them in series?
I.E. is it better to have two 2x12 cabs at 8 ohms (parallel rigged with 16 ohm speakers)
or one 4x12 at 8 ohms (series rigged with 8 ohm speakers)???

I hope I'm talking correct, since some of this is fairly new to me... Might have gotten things mixed up.

- Nic from Detroit... posting on JB's Forum since 6-2-2006
Ask me about my handwound Great Lakes Guitar Pickups
Since 2010, Bonamassa fans have taken advantage of my JB friend discount = my cost + shipping.

Hey guys..
         That was my initial theory when I came up with the 4 amp rig.   It was more power through less speakers.  I switched to EV-12L speaker because not did they sound great to me but they were the only ones that never blew up... Before I used to carry a charged screw gun and take cabinets apart almost daily.  That fatigues the wood and it creates a cascading effect down the line.  My new VanWeelden cabinets had to be slighty modified by our resident expert Eric due to so much sound pressure being put through a single cabinet that it literally sheared the middle screw off the cabinet.  We have fixed the problem and potential hazard  and now they are fantastic..  But It is all about pairing down the speakers.. You will cut through the band better and have a better footprint onstage..
Hope that helps..
Joe Bonamassa

When talking about more power through less speakers, an analogy comes to mind...

If you have a certain fixed amount of water pressure coming out of a faucet and you run this out to a single sprinkler, you can cover a certain amount of area with water. If you were to run that out to multiple sprinklers, you would get less water pressure per sprinkler, but you would still cover more area with water. If you were able to connect each sprinkler to its own faucet (so that water pressure did not need to be shared), you would be able to cover twice as much area as one sprinkler connected to one faucet.

Now, if instead of a sprinkler, you connect a single nozzle with a small diameter, you would project a very powerful stream with a narrow focus, but whatever area was targeted, would become quickly soaked.

If we substitute "amplifier power or wattage" for "water pressure," "amp/output transformer" for "faucet," "speaker cab" for "sprinkler,"  "single, high powered speaker or small speaker cab" for "nozzle with a small diameter," and think of the amount of water per area as SPL, then our analogy now makes a bit more sense.

Keep in mind the concepts of directionality (firehouse) and dispersion (sprinkler) when thinking about what your needs are.

Admittedly, if we get into the fine details, the analogy breaks down in certain places, but this should hopefully paint a clearer understanding of what we're discussing. It can be tricky to get this sort of thing the first time around, but I hope this helps.

I wouldn't stress at this point about the differences between the sounds of speakers run in parallel or series... Something to hear for yourself whenever you get a chance, but nothing to obsess over at this point, most likely. Speakers in series are receiving the signal one after the other, so there is a very short amount of delay between response time between speakers. This "blurs" the sonic image a little bit and causes some filtering. This isn't necessarily a good or a bad thing... It is just a subtle difference in sound. Now, 16ohm vs 8ohm speakers can sound a bit different from each other due to physical differences. Also, not all V30's sound the same... The ones made for Mesa are different than the ones made for Marshal vs the ones sold as Celestion branded. They have some physical differences, which translate to audible differences. That is a topic, though, that attracts a lot of opinion in a short ammount of time, so perhaps best left for TGP!  <laughs>

Now, what load is placed on the OT of an amp will have a less subtle affect on the sound, as will impedance mismatching, etc, but, again, that gets us into another conversation, I think.

Another quick divergence... The preference for 100w heads vs 50w heads usually has to do with amount of headroom (translating into dynamics vs compression as well as volume level before break-up) and differences in tone due to the circuit, OT, etc. The maximum volume level difference is going to be much less of an issue (on paper, in a perfect world and not factoring the non-linearities that happen when overdriven, only 3dB).

In the case of open back cabinets, such as a Fender Twin Reverb, it is important to consider the dipole effect--sound is being projected out the back of the cabinet as well as the front. This contributed to the "room filling" sound of open backed cabs or their "lack of focus and thump" depending upon what you're looking for.

Also, keep in mind that if you are micing your cabs through FOH, and monitoring through IEM's or stage wedges, then getting the tone you want to the mixer is going to be more important that having lots of stage volume (just enough to get you the tone you want and the right interaction of pickups and speakers for your guitar to sing the way you desire). Overly loud stage volume is a headache for the sound engineer and is usually problematic. I believe this is part of the reason that Joe uses his baffles--to combat excess SPL on stage as well as reduce the directionality or "beaminess."

If you are playing clubs where your backline IS your monitoring, the stage monitor feed isn't acceptable, or if you aren't being put through FOH, then your stage volume becomes a different story.

However, all that said, It sounds like your underlying desire is just to fit in better in your band mix and be able to hear yourself better...

This is going to have to do with not just volume, but your tone, the tone of everyone else in the band, how your songs are arranged, etc.

For instance, if your tone is perfect, but your bass player's tone is too midrangey and the keyboardist is always playing in the same register as you, you will have a terrible time hearing yourself and probably not be happy with your tone. The entire band mix is important to consider as is who is playing what, when, and in what register.

If all that it taken care of, then you may want to experiment with dialing your guitar tone so it fits in the mix better. In general...  The dryer the tone, the more up front it will be. Reverb, delay, etc, will place you further back in the mix. The more midrangey it is, the more forward it will be. The more scooped your tone is, the more it will move to the back and get lost behind kick and bass in the low end, and cymbals in the high end. Certain frequencies areas are going to play a big role in how present you sound... 2.5K for presence, 10K-12k for air, etc.

My philosophy is, if you were to record each of the instruments playing the current arrangements, would the mix work as is? If not, then ask yourself is it about adjusting volumes, tones, or the arrangement? Perhaps all of these factors could be improved. Instead of turning the guitar up, are you able to turn other musicians down? Do you have the same problem in every venue or is it just in certain locations like your rehearsal room? This could be a sign of the room acoustics being part of the problem.

If after thinking about this, you decide that you just need more volume and more (narrower) focus, then upping the wattage and pushing less speakers may work for you. I wouldn't think to argue with Joe about good guitar tone!   

Cheers,
-Matt

Great posts, Zen!

I see your point, you can play with pretty much any amp pending it is mic'd.  I think a lot of it also falls into the category of personal preference.  Some people just like a half stack, just like some prefer a combo.  Some people just like to play loud!  I also think a 50 or 100 watt head just has more balls than a small 15w even at similar volumes.  Both give you excellent results regardless.  As far as cutting through a stage mix, I would assume it has to do with how some people set their eq and depending on how it is set, you may need more volume to hear yourself.  Some people skimp on the mids, or just have a drummer that plays louder and louder through the night.  -S