school me on amps and cabs

[Citrus]

Not familiar with the science, involved

If you have a 30 watt head, is there more volume or perceived volume from a 2x12 vs a 1x12

Does it have to do with efficiency ???

[Bobby Marshall]

Not efficiency. The more air you move, the better. Better=louder or at least the perception and perception=reality. This is my opinion.

And always remember a 10 watt amp is HALF as loud as a 100 watt amp. Did you hear me? This is a fact.

[tmsfo]

Mo speakers = mo loudness

[hamerhead]

No speakers = very quiet

[django49]

No speakers = very quiet

AND blown transformer!

[Bloozguy]

Questions, questions, questions, flooding into the mind of the concerned young person today…

(bet you can’t guess where that’s from)

How “loud” you sound depends on a few things, all of which interact somewhat. They are: a) amplifier power; speaker efficiency; and c) number of speakers.

Volume, referred to as sound pressure level or SPL, is measured in decibels (dB). It takes a 3dB change in SPL for the average person to detect any change in volume. To make this 3dB change you need to double your amplifier power. A 10dB change in SPL is perceived as twice as loud. To do this you need 10 times the amplifier power!

So Bobby Marshall's statement that a 10 watt amp is only half as loud as a 100 watt amp is absolutely true. Also the reason why amps that most people consider “bedroom” amps will still get the neighbors on the phone to the police…because your Fender Champ is still half as loud as your Super Reverb!

All this is fine and dandy as long as you are dealing with exactly the same number of speakers, all of exactly the same efficiency.

The efficiency of a speaker is the SPL produced by the speaker, measured from one meter away, on axis, when the speaker is fed one watt of power, typically in the form of a 1kHz tone.

So here’s another piece of the volume puzzle. Run your 30 watt amp head into a 1x12 cabinet loaded with a 93dB efficiency speaker. Then change to a 103dB efficiency speaker and you will instantly be twice as loud without any change in amplifier power. It’s a lot less expensive to switch to higher efficiency speakers than to go out and get 10 times the amplifier power.

The number of speakers also has an effect on volume. If you run your 30 watt amp into a 2x12 instead of a 1x12 you will be 3dB louder. You will also have the same SPL as a 60 watt amp feeding a 1x12. Don’t ask me why because it’s hard to explain. If you run that 30 watt amp into a 4x12 you’ll get another 3dB increase, or a total of 6dB more than the 1x12. Now here’s another goofy part that I really can’t explain well. Because of phase cancellation, two 4x12s will still only be 6dB louder than a 1x12.

My recommendation is get an amp/cab setup that sounds great to you and that you are willing to carry. Then mic it into the PA and monitors.

[The Shark]

Great discussion, Bloozguy. Your "recommendation" at the end is perfect. The first time I saw Robben Ford at the Sunfest in West Palm Beach years ago, his 1x12" Dumble combo sounded as good as anything I'd ever heard at an outdoor concert. It's about tone. Marrying the right amp, speaker(s) and cabinet(s) should determine everything except sound pressure level. Sound pressure level is the function of a good mic and P.A. You can reproduce your tone at any volume. Multiple speakers has more to do with bottom end reproduction onstage than volume or tone out front. If you don't mic your amp, you sacrifice tone in some venues.

[tbonesullivan]

I believe having more than one speaker increases the efficiency of the speaker system by increasing the overall surface area that the power is applied. loudness is after all hard to define, and resonant effects play a large part in it.

[hamerhead]

No speakers = very quiet

AND blown transformer!

Equally as quiet.

[Bobby Marshall]

Bloozguy provided a very good explanation and recommendation.

[hamerhead]

How would two 15W amps with two 1x12 cabinets compare to one 30W amp with one 2x12 cabinet (if the speakers and cubic feet were the same. I'm being serious this time)?

[Carl.B]

4x12 cab looks cooler than 1x12 cab on stage!

[crunchee]

My recommendation is get an amp/cab setup that sounds great to you and that you are willing to carry. Then mic it into the PA and monitors.

A BIG +1 on the 'willing to carry' part. Unless you've got roadies, you'll find that the weight gets more important as time goes on.

I dunno if there's a coefficient between efficient speakers and weight. I DO know that JBLs and Electro Voice Speakers are known for being clean, loud, can handle a lot of power, and be freakin' HEAVY. I once knew a guy who put EV speakers into his Fender Twin Reverb. The weight of the speakers eventually broke the baffleboard where it was attached to the cabinet. I do know that AlNiCo magnet speakers tend to be lighter than those with Ceramic magnet speakers. and I know that Jensen and Celestion have lightweight speakers with newer magnet compounds, but I'm not familiar with them. Any thoughts?

[tomteriffic]

How would two 15W amps with two 1x12 cabinets compare to one 30W amp with one 2x12 cabinet (if the speakers and cubic feet were the same. I'm being serious this time)?

If the speakers are the same and the individual cabinets, be they 1 x 12 or 2 x 12 are tuned to the same resonant frequency, same basic design (open/closed back etc.), the variable would be the 2 amps vs. the 1 amp. assuming that they're the same basic circuit, etc., the determinant would be at what point do the amps break up?

For the sake of simplicity, lets' say that the 30 watter starts distorting at 20 watts, or 2/3 of the rated/maximum output power. if the two 15 watters each start breaking up at the same percentage, or 10 watts each, there wouldn't be much difference at all. If one or the other rigs starts distorting at a different percentage of the max, one rig would have more clean headroom that the other. The one with more clean headroom will be the one with better transient response i.e a "snappier" sound or just seem louder/cleaner.