Before the references and math for the above sound divergence map, consider that we all know what loud is; loudness is after all a subjective term, and what is loud to you has a great deal to do with your emotional response to that sound's features. dB-SPL however is completely objective. Few of us like the sound of freeway noise, but we are all familiar with it and have learned that we can tune it out—if nothing else it makes a nice neutral reference. For those reasons you will find it used below, to help you better correlate what a dB-SPL means to your earballs. Also, I'm asking you to trust your gut and your extensive experience with sound; those of us within a one mile radius of the former, community-sized Barker Park Amphitheater during a battle of the bands show know that live, amplified music inclusive of a bass guitar and drum kit carries pretty (cuss) far. Ask around if your gut is silent on this. Back to the map, rest assured (I know I'm funny, you might not think so) that anyone finding themselves even all the way out at the perimeter of the orange colored regions during a live music, DJ, or ruckus musical or film screening will be acutely aware of What's Going On* at the NO Amphitheater.

*Great album by Marvin Gaye. Maybe he could play No Amp—we have as good a chance of bringing him in (back) to play as any of the greats. LM(cuss)O. (No disrespect meant Marvin—I really do love that album, R.I.P.)

–Sean M Casey


NO Amphitheater 2018
Design: continues as a classic format amphitheater.
Gated diameter: ≈285ft [90m]. (Based on NOC Noise Levels Day dB(A) Map dated 8/22/2017.)
Stage to gate radius: 225ft [69m].
Spectator area defined by perimeter gate inclusive of tech booths: 64,000ft2 [5,945m2]
Usage: commercial—theater, music, weddings, movies; international and national touring acts, regional touring acts, local talent.

Sound Source Reference: Utah Symphony fortissimo (with half the players absent), easy country pop, soft classic rock…
most any not too loud live band inclusive of a drum kit as the power and bandwidth are similar.
Performers and sound system sound pressure level sum (L∑) @ stage perimeter.
Sound Power Level (SWL)≈141dB (isotropic).
SL (Lp) ∝130dBSPL @ stage source.

Bass [30→110Hz] Q = 3 (3 over 4pi r^2)
≥ 104dBSPL [Lp] @ 125 ft. from complex sum of stage (live Donny & Marie show).
≥ 98dBSPL [Lp] @ 250 ft. from complex sum of stage (live Donny & Marie show just outside the auditorium).
≥ 92dBSPL [Lp] @ 450 ft. from complex sum of stage (subway train at 300 feet away).
≥ 86dBSPL [Lp] @ 900 ft. from complex sum of stage (average motorcycle @ 35MPH 25 feet away).
≥ 80dBSPL [Lp] @ 1800 ft. from complex sum of stage (freeway noise 50 feet from pavement edge).
≥ 74dBSPL [Lp] @ 3600 ft. from complex sum of stage (living room music levels).


dBSPL [Lp] = 20 µPa (P–0 = 2x10-5 Pascals)
c (thermodynamic speed of sound) = 1130ft/s [344m/s]
Air temperature gradients are assumed to be zero.
Q is a directivity index quality factor.

Research Sources

Benade, Arthur H. (1990) Fundamentals of musical acoustics (2nd ed.). Dover (Origin 1976)
Everest, Alton F. (1994) The Master Handbook of Acoustics (3rd ed.) TAB
Helmholtz, Hermann L. F. (1954) On the Sensations of Tone (4th ed. Alexander J. Ellis, Trans.) Dover (Origin 1877)
Jeans, James, Sir (1937) Science and Music. Dover
Kinsler, Frey, Coppens, and Sanderds (1982) Fundamentals of Acoustics (3rd ed.) Wiley
Lamb, Horace, Sir (1960) The Dynamical Theory of Sound (2nd ed.) Dover (Original 1925)
Olson, Harry F. (1967) Music, Physics and Engineering (2nd ed.). Dover (Original 1952, formerly: Musical Engineering)
Randall, Robert H. (2005) An Introduction to Acoustics. Dover (Original 1951, Addison-Wesley. Principles of Physics, series.)
Rayleigh, J.W.S. Baron (1945) The Theory of Sound Vol. 1 & 2 (2nd ed.) Dover. (Original 1894)

Feynman, Richard P., Leighton, Robert B., Sands, Matthew (1964) The Feynman Lectures On Physics. Addison-Wesley
Halliday, Resnick, Walker (1997) Fundamentals of Physics Extended (5th ed.) Wiley