The Speakers Role in Perceived Loudness
To really get a handle on understanding the following article a few terms need to be understood. A brief description of these terms and their meaning are listed below.
The speakers Sensitivity or SPL / dB. This is the sound pressure level coming from a speaker being driven by 1 watt of power at a distance of 1 meter. It's a reference to how efficiently the speaker utilizes the wattage coming from the amplifier. A speaker with perfect 100% efficiency would have a Sensitivity rating of 112 dB. This would reflect 1 watt of Electrical power flowing into your speaker from your amp and the microphone placed 1 meter in front of your speaker receiving 1 watt of Acoustical power. Your speaker is the device that converts the electrical power into acoustical power. Note* Because speakers are very inefficient at converting electrical power into acoustical power 112 dB is an impossible goal to reach. It's just being used as a reference point. Most guitar speaker SPLs fall between 92 and 104 dB.
Decibel / dB. For our usage it's a number used for direct comparison of sound pressure levels received by our microphone 1 meter in front of the speaker. Note that the scale used to measure in decibels is logarithmic rather than linear. It's not a straight line. It's a curve that becomes more pronounced as the value increases.
For electrical power output from the amp to the speaker we'll use the amps RMS wattage rating. We'll just go with a 100 watt amp delivering 100 watts of electrical power to the speaker.
The shape or curve of a speakers frequency response is refering to the shape displayed on those fancy looking graphs speaker manufacturers include on the spec. sheets.They represent how loud or prominent different frequencies are produced by the speaker.
Ok. I've just over simplified a lot of fancy shit that folks go to school to get educated on in a proper manner, but, please remember that Dinosaurs lived in the wild without the benefit of schools. They had tiny little brains and always preferred to cut to the chase. At least the big ones did. The little ones..........well.........not really looking forward to the chase. But that doesn't matter. We're all big Dinos here.
So. Now let me mess with your head. The sound pressure level produced by running a 50 watt amp into a Celestion Vintage 30 with a sensitivity rating of 100 dB equals the sound pressure level of a 100 watt amp run into a Celestion G12T-75 with a sensitivity rating of 97 dB. You've run twice the wattage into the G12T-75 yet the microphone received the same sound pressure level. The sound pressure level is what the microphone would have picked up as loudness you would have heard had your ear been located at the same place as the microphone. Amp Wattage and Speaker Sensitivity work together to create the loudness coming out of the speaker. Each time you add 3 dB to a speakers sensitivity you can cut the amplifiers wattage in half and still get the same loudness.
Important note to clarify something that many players misunderstand. A 3 dB increase in speaker sensitivity does not double the loudness you hear just as doubling the wattage of an amp head doesn't double the loudness you hear. Doubling an amps wattage or increasing the speakers sensitivity by 3 dB changes the loudness in near equal proportions.
I've created a list below of how a Duelling Dino Guitarist would react to changes in the amount of decibels he hears coming out of his bands other Dino Guitarists amp rig.
One decible increase in loudness.......Hmm?
Two decible increase............I know I heard that. Quit screwing around.
Three decibel increase.........I told you. All Dino ears hear it louder.
Four decibel increase..........Dude. Your starting to drown me out.
Five decibel increase..........Don't make me come over there.
Six decibel increase...........After the show I'm eating you!
Seven decibel increase.....Fuck it. I'm eating you after this song.
Eight decibel increase.......Hey, Dick! The soundmans ears are bleeding!
Nine decibel increase........Did you see that guys head explode?
Ten decibel increase.........Your 100% twice as loud as when we started!
The next section explains why speakers with the same sensitivity are not always identical in the amount of loudness your ears perceive.
Along with a speakers sensitivity rating another specification also has an effect on how loud the speaker sounds. Not to be confused with the Frequency response numbers, Example 75 Hz to 5000 Hz, it's the shape or curve of the frequencies specified for the speaker. The graph included with a speakers specifications run the frequencies left to right from low end to high end. They run the decibel level from bottom to top with the quietest level at the bottom and the loudest level at the top. By looking at one of the graphs you can see that a speaker does not reproduce all of the frequencies at the same level of loudness. That's where the shape of the curve comes into play. The graph shows which frequencies the speaker being represented produces loudly and which frequencies it produces at a softer level. Without going into tonal or voicing effects and staying strictly with the loudness aspect, the human ear does not pick up all frequencies as equal in loudness. A speaker with it's average levels in frequencies that the human ear doesn't pick up on very well will not sound as loud as one that has it's average levels in frequencies that the human ear hears very well. Thus, two speakers with the same sensitivity but with the peaks and valleys of their frequency curves in different areas of the frequency range may very well be perceived as producing two different levels of loudness. The microphone picks up the same levels and produces the same levels but our ears decide which speaker is louder because of which frequencies they are most attuned to and how loud the speaker is offering them.
Lastly, it often comes up in conversations among Dinos about the loudness gains through the use of multiple speakers in one cab. To put it simply, assuming a sameness of cab design and all speakers of the same type, If one speaker produces a cab loudness level of 80 dB then two speakers with produce 83 dB and four of them will produce 86 dB. Every time you double the number of speakers in the cab you up the decibels by three. How much is three decibels to the human ear? My friend Tim at Ear Candy Cabs explains the increase this way. With one decibel being the lowest increase in volume the average human ear can detect, three decibels would be described as slightly louder. So, 2 speakers are slightly louder than 1 speaker and 4 speakers are slightly louder than 2 speakers.
Now for the simple examples of how this information can be utilized for speaker selection to match a Dinos need for more or less loudness from their amp.
Example 1). Lets say the Dino amp you own is a 50 watt Marshall DSL and your speaker cabinet is a Marshall 1960A with G12T-75s on board and your the lead player in the band. The rhythm player in your band owns a 100 watt Marshall DSL and he owns the same exact speaker cab. You don't want to buy a different head. You love the tone of your Marshall DSL 50. Using the complicated crap I explained earlier along with Celestions specs we know that a G12T-75 has an SPL rating of 97 decibels and a 4 X 12 cab loaded with these would have an SPL cab rating of 103 decibels. A 50 watt head into this cab would produce 120 decibels. A 100 watt head from the same manufacturer going into the same cab would produce 123 decibels. Your rhythm players setup is 3 decibels louder than your setup. Neither one of you, being the Dinos your are, want to turn down. In this situation what's the Dino lead player to do? You could kill and eat the rhythm player and find another one that plays through a Marshall 401 40 watt amp or you could increase the loudness of your own rig by swapping those G12T-75s, sensitivity 97 dB, for four Vintage 30s or G12Hs, sensitivity 100 dB. Your DSL 50 powering a cab loaded with four of either of these speakers, (or any other sensitivity 100 dB speakers), would bring your rigs overall SPL up to 123 dB. The same loudness level as your rhythm player. Or, you could trash the bastard by loading your cab with four Eminence Redcoat Wizards, sensitivity 103 dB, and get your rig to put out an overall SPL of 126 dB. Now your 50 watt rig is noticeably louder than the rhythm players 100 watt rig.
Example 2). Lets say you've come to the conclusion that Big is to much and you've decided to go for less loudness while retaining your Dino tone. You've dumped your 50 watt Marshall DSL head and 4 X 12 cab and bought a 15 / 7 watt Orange Tiny Terror and your running it into a Bogner 1 X 12 cube with a vintage 30 on board. You've got it set for 7 watts and the neighbors are still bitching about the loudness. What's a Dino to do? Well.......You could just eat the neighbor and be done with it or you could swap the Vintage 30 speaker out for a G12M Heritage. With the Vintage 30 rated at 100 SPL and the G12M Heritage rated at 96 SPL you would be able to lower the loudness of your rig without adjusting any of the knobs on your amp. A four decibel difference is very noticeable and might easily cause your neighbor to shut the fuck up and let you play the music you love.
Example 3). Let's say you've discovered your amps sweet spot is with the volume control set at 7 1/2. Your band has just gotten a job as the house band at the local S&M club. The problem? The size of the club is forcing you to limit your amps volume setting to 5. When you play at 7 1/2 the patrons can't hear the crack of the whip or the screams of pleasure from their partner. The management says this will never do. You love your amp head and you love it set on 7 1/2. Option? Swap your speaker's out or change cabs to one with a set of speakers that have a sensitivity rating that's three, four, or five decibels lower than what your currently using. The overall output volume from your rig could very well drop to a point that you wouldn't have to decrease the volume knob's 7 1/2 setting. The slap of a spanking and the resulting aah is now audible to the patrons, the management is happy, and you get to run your amp on 7 1/2. Everybodies happy. Some are way past happy.
Here's a list of some Dino speaker combinations. Note the differences in loudness, overall SPL / dB ratings. Lower numeric values are quieter. Higher numeric values are louder.
2 X 12" speaker cab combinations. High Wattage.
Two Celestion G12T-75. Total sensitivity for the pair is 100 dB. Can handle up to 150 watts.
Two Celestion Heritage series G12-65. Total sensitivity for the pair is 100 dB. Can handle up to 130 watts.
Two Jensen Blackbird. Total sensitivity for the pair is 101 dB. Can handle up to 200 watts.
Two Celestion Classic Lead 80. Total sensitivity for the pair is 102 dB. Can handle up to 160 watts.
Two Eminence Texas Heat 8 ohm. Total sensitivity for the pair is 102 dB. Can handle up to 300 watts.
Two Electro Voice EVM 12L Classic. Total sensitivity for the pair is 103 dB. Can handle up to 400 watts.
Two Electro Voice EVM 12L Black Label. Total sensitivity for the pair is 103 dB. Can handle up to 600 watts.
Two Celestion Gold. Total sensitivity for the pair is 103 dB. Can handle up to 100 watts.
Two Celestion Vintage 30. Total sensitivity for the pair is 103 dB. Can handle up to 120 watts.
Two Fane Revival 12-100. Total sensitivity for the pair is 103 dB. Can handle up to 200 watts.
Two Eminence Texas Heat 16 ohm. Total sensitivity for the pair is 103 dB. Can handle up to 300 watts.
Two Fane Revival 12-75. Total sensitivity for the pair is 104 dB. Can handle up to 150 watts.
Two Fane AXA-12. Total sensitivity for the pair is 104 dB. Can handle up to 200 watts.
Two Eminence Governor. Total sensitivity for the pair is 105 dB. Can handle up to 150 watts.
Two Eminence Swamp Thang. Total sensitivity for the pair is 105 dB. Can handle up to 300 watts.
Two Eminence The Wizard. Total sensitivity for the pair is 106 dB. Can handle up to 150 watts.
2 X 12" speaker cab combinations. Lower Wattage.
Two Celestion Heritage series G12M. Total sensitivity for the pair is 99 dB. Can Handle up to 40 watts.
Two Celestion G12M Greenbacks. Total sensitivity for the pair is 101 dB. Can Handle up to 50 watts.
Two Celestion Heritage series G12H. Total sensitivity for the pair is 103 dB. Can handle up to 60 watts.
Two Celestion Blue. Total sensitivity for the pair is 103 dB. Can handle up to 30 watts.
Two Celestion G12H Anniversary. Total sensitivity for the pair is 103 dB. Can handle up to 60 watts.
Two Fane Revival 12-35. Total sensitivity for the pair is 103 dB. Can handle up to 70 watts.
4 X 12" speaker cab combinations of any of the above pairs just add 3 dB to the sensitivity and double the wattage handling ability.
I'm gonna stop now. My tiny Dinosaur brain hurts. I do hope this explains the very strong role speaker sensitivity plays in the loudness of your Dino performances and the way it works in conjunction with amp wattage to achieve the overall volume your audience is presented with.
Mistress Ana Conda? I'm finished here. So............... Where were we?