“Watts” Up with the Volume?

A primer on the relationship between Watts, Decibels and Volume

Nigel Tufnel: The numbers all go to eleven. Look, right across the board, eleven, eleven, eleven and…
Marty DiBergi: Oh, I see. And most amps go up to ten?
Nigel Tufnel: Exactly.
Marty DiBergi: Does that mean it’s louder? Is it any louder?
Nigel Tufnel: Well, it’s one louder, isn’t it? It’s not ten. You see, most blokes, you know, will be playing at ten. You’re on ten here, all the way up, all the way up, all the way up, you’re on ten on your guitar. Where can you go from there? Where?
Marty DiBergi: I don’t know.
Nigel Tufnel: Nowhere. Exactly. What we do is, if we need that extra push over the cliff, you know what we do?
Marty DiBergi: Put it up to eleven.
Nigel Tufnel: Eleven. Exactly. One louder.
Marty DiBergi: Why don’t you just make ten louder and make ten be the top number and make that a little louder?
Nigel Tufnel: [pause] These go to eleven.

Watts, Decibels and Volume

Dialing in the right volume of music and sound effects for your haunt or escape room is essential to creating a great immersive experience for your customers.

At one time or another we have all been faced with the dilemma of determining how many watts are needed for our rooms or displays.  Will more watts give me greater volume?  Will it be enough to be heard over a crowd of people up to 30 feet away?

Volume, like music, is often subjective to the listener.  What is loud to one person, may be a perfect listening level to another.  And as we talk further about the variables involved, the answers may not be cut and dry, but the information provided should help develop a guideline in amp and speaker selection moving forward.

Decibels

Let’s start out with what we know about Decibels

SPL (Sound Pressure Level) calculates the pressure of sound waves traveling through the air from a source of noise in units called Decibels (named after Alexander Graham Bell).  The Decibel unit is actually logarithmic. For now, we will use dB (Decibels) as our reference to sound pressure levels in this primer.

Also note that 0 dB is the unit we use to represent the lowest threshold of human hearing.  In the following chart, pay special attention to entries with distances as well as the Decibel level indicated.

 

Noise Source Decibel Level Decibel Effect
Jet take-off (at 25 meters)
Recommended product: Outdoor Noise Barriers
150 Eardrum rupture
Military jet aircraft take-off from aircraft carrier with afterburner at 50 ft (130 dB). 130
Thunderclap, chain saw. Oxygen torch (121 dB). 120 Painful. 32 times as loud as 70 dB.
Steel mill, auto horn at 1 meter. Turbo-fan aircraft at takeoff power at 200 ft (118 dB). Riveting machine (110 dB); live rock music (108 – 114 dB). 110 Average human pain threshold. 16 times as loud as 70 dB.
Jet take-off (at 305 meters), use of outboard motor, power lawn mower, motorcycle, farm tractor, jackhammer, garbage truck. Boeing 707 or DC-8 aircraft at one nautical mile (6080 ft) before landing (106 dB); jet flyover at 1000 feet (103 dB); Bell J-2A helicopter at 100 ft (100 dB). 100 8 times as loud as 70 dB. Serious damage possible in 8 hr exposure.
Boeing 737 or DC-9 aircraft at one nautical mile (6080 ft) before landing (97 dB); power mower (96 dB); motorcycle at 25 ft (90 dB). Newspaper press (97 dB). 90 4 times as loud as 70 dB. Likely damage in 8 hour exposure.
Garbage disposal, dishwasher, average factory, freight train (at 15 meters). Car wash at 20 ft (89 dB); propeller plane flyover at 1000 ft (88 dB); diesel truck 40 mph at 50 ft (84 dB); diesel train at 45 mph at 100 ft (83 dB). Food blender (88 dB); milling machine (85 dB); garbage disposal (80 dB). 80 2 times as loud as 70 dB. Possible damage in 8 hour exposure.
Passenger car at 65 mph at 25 ft (77 dB); freeway at 50 ft from pavement edge 10 a.m. (76 dB). Living room music (76 dB); radio or TV-audio, vacuum cleaner (70 dB). 70 Arbitrary base of comparison. Upper 70s are annoyingly loud to some people.
Conversation in restaurant, office, background music, Air conditioning unit at 100 feet. 60 Half as loud as 70 dB. Fairly quiet.
Quiet suburb, conversation at home. Large electrical transformers at 100 feet. 50 One-fourth as loud as 70 dB.
Library, bird calls (44 dB); lowest limit of urban ambient sound 40 One-eighth as loud as 70 dB.
Quiet rural area. 30 One-sixteenth as loud as 70 dB. Very Quiet.
Whisper, rustling leaves 20
Breathing 10 Barely audible

 

Lets Translate

So how does all this translate into volume or “loudness”?  The dB (Decibel) scale is logarithmic because that’s essentially how our ears respond.  A 10-fold increase in sound intensity, measured as a 10dB increase with a sound meter, would feel like a doubling in loudness to our ears.  Another 10-fold increase (another 10dB increase) would feel like another doubling. And so on and so forth.

Perceived Loudness

  • +10dB = 2x the loudness
  • +20dB = 4x the loudness
  • +30dB = 8x the loudness
  • +40dB = 16x the loudness

Now, while these numbers represent a good approximation in perception, they are often meaningless without taking distance into account.  And the most useful tool for us is the distance from the source of music and SFX.

  • 2X the distance from source = -6dB
  • 4x the distance from source = – 12dB
  • 10X the distance from source = -20dB

This is called the Inverse Square Law of Sound.
Find out more at http://hyperphysics.phy-astr.gsu.edu/hbase/Acoustic/invsqc.html#c1)

So Watts Watt???

Now, the real question we are looking to answer here is how the rated wattage of, let’s say, an amp and speaker combination (sound source) might play into determining how loud your music and SFX may be.

Wattage is a measure of electrical power.  When an amplifier processes sound, the output is measured in watts.  Same with speakers.  All speakers have a threshold of watts they can handle.  Look for these key specifications when making you amp and speaker selections.  Also, you will run into amps and speakers operating at particular Ohms.  It is always a best practice to match Amp and Speaker Ohms as to not damage either unit.

For amplifiers: 

  • RMS = the power an amplifier can deliver over a long period of time.
  • Peak = the power an amplifier can put out in short bursts or peaks.

For speakers:

  • Nominal power= what a speaker can handle long term without being damaged
  • Peak power= what a speaker can handle in short bursts without being damaged

And finally (arguably most importantly), look for the Sensitivity of the speakers you are evaluating.  Sensitivity helps determine how well a speaker can process power (watts) into volume (dB).  The more sensitive the better.  The measurement is usually taken from 1 meter (~3ft) from the speaker and you will see it expressed most often in the specs as dB.  Anything less than 85dB is rather inefficient so I’d recommend keeping between 85 and 94dB for the sensitivity as you make your decision.  This will help keep the following numbers more accurate in association to Decibels.

Watts to Decibels

Watts Decibels
2 93
4 96
8 99
16 102
32 105
64 108
128 111
256 114
512 117
1,024 120
These numbers are indicative of a distance measured 1 Meter (~3 Feet) away from the sound source.

Look at the 2-4 Watt range.  Did the numbers surprise you a bit? Looking at our table earlier in this primer, at 1 meter (~3ft) away from a 2-4 watt amp/speaker combo, your sound source will be comparably as loud as a power mower, motorcycle at 25ft away, or standing near a newspaper press.  As the watts doubled, did you see how the dB level changed by only +3dB ?

For a real life comparison, I’ll use a Scream Box that I carry.  I get a lot of questions about how loud something of that “size” is, and my customers are often surprised.

The Screambox can produce about 1 Watt of power and is in the 85dB range of sensitivity.  So with 1 Watt of power you will be able to generate approximately 88-90dB at 1 meter away with only a 1 Watt amp and speaker!  Pretty cool huh?
Now granted there are many other variables to consider here.  Other noise in the vicinity, groups of people absorbing sound, room absorption (furniture, walls, reverb), etc.   But when used as a jump scare or with a prop where people are within 3-5 feet of the Screambox, they will definitely get a great effect!

But if we think about a room, let’s say, 10×10 and you want to fill it with sound, taking in the variables is really important.  The more furniture you have, or possibly actors, reflective surfaces such as walls and ceilings, as well as your customers will impact the amount of air you can move.  My rule of thumb tends to be to get something that is loud enough that you have to turn down, not up, to get the desired result.

Let’s say in the same room you have an amp/speaker on one wall and because sound emanates in a sphere, you want to throw it at least 10 feet across the room and still be plenty loud to hear.  This is where the Sound Inverse Square law comes into play.

So, let’s say we have a 60 Watt amp/speaker combo that gives us about 105-108dB 3 feet away.   If we double that distance to 6 feet away, we now have about 99dB.  Double that again and we now have 93dB left over and just about to the edge of the farthest distance in the room.  Still pretty loud at this point!

NOTE:

Remember that for you, your actors and your audience that prolonged exposure to loud audio can cause ear damage.  As a rule of thumb, prolonged exposure above 70dB can cause fatigue and anything above 90dB at more than 8 hours can cause permanent damage.

Summary

Overall, the point to remember in this primer is that there are LOTs of variables involved in assessing the right amp/speaker setup for a room and it is almost always subjective.  The numbers given in this article are meant to be used as a guideline for determining the needs of a room or display.

But one thing remains very certain.  Bigger does not always mean better in this case.  A quality amp and speaker are going to produce much better sound and volume at lower wattages than lower quality amps and speakers at higher watts.  It’s all about the details.

Looking to find out more or get additional details?  Just ask!  And if you are in the area, I will be teaching a class on amp and speaker selection at the West Coast Haunters Convention in April, 2018 in Portland, Oregon.

Oh, and if you’ve never seen “This Is Spinal Tap”, here’s the scene I’ve referenced in the introduction to this primer.  Enjoy!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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