Some facts about bass:

• "Very loud sounds can rip ear, lung and other vibrating tissues. A sound wave is a pressure wave; that's why you can sometimes feel your body vibrate during loud, low sounds. When body tissues resonate with the sound's frequency, the pressure increases."
  
  
• bodily resonances:
  • There is some evidence that a damaging resonance (lungs) occurs around 50 Hz.
  • Another damaging resonance is around 400 Hz (skull spherical shell resonance).
  • At what dB SPL level does bass make your vision go blurry?
  • The rumored brown note is in the 5 to 9 Hz infrasound range.
  
  
  
• It has been claimed that paper will burst into flames at a high enough SPL.
  
  
• Above 150 dB some rather strange things begin to happen; shock waves form, frequencies appear that were not in the original signal, and the speed of propagation exceeds that of "normal" sound.
  
  
• 140dB SPL is very dangerous, this much bass has made people break out sweating due to the pressure, some people have problems breathing, and heart arhythmia is also known to happen.
  
  
• world dB drag SPL records:
  • 2007
    • 180.5 dB, Alan Dante's concrete filled Volvo with a single Digital Designs 9918Z 18" subwoofer (3" dual voice coil 0.5 ohms) and four Stetsom 7KD amplifiers (26 kW) and fifteen Powermaster 16V batteries and a 61 Hz sine signal source. 
  • 1998
    • 172.2 dB, Alma Gates' Bronco has 64 PPI Pro 10" drivers and 32 PPI PC2350 amplifiers (45 kW).  The 1" thick plate glass windows have survived 172.8 dB.  Her signal source is track 61 on the dB jams CD, which is a 39 Hz Triple Tone Burst (unclipped sine, 50%, 100% clipped square) which was then ran thru a tripling gimzo to generate a 117 Hz tone.  From the outside, Alma Gates' Bronco was described as like "metal being beat to death, it sounds like a machine gun or something."  Rumor is that she is adding another 20 PPI 10" subs. 
    • 171.3 dB, 2nd place, Jeff ???, 12 Stroker 15D2's and 7.2 kW of power, only 0.9 dB behind team Gates with a fraction of the drivers and wattage.
  • 1997
    • 162 dB Alma Gates
  
  Here is an experiment for you auto SPL fans:
  • Go to the Piston Excursion calculator.
  • Lets assume Alma Gates Record of 172dB - 12dB of cabin gain/modes = 160dB SPL.
  • Enter 64 drivers, 10" diameter 117Hz at 160dB and look at the excursion you get?
  • Now with a little fiddling, you can see that 16 more drivers (80 total) is worth about only 2dB SPL more!
  
  
  
• Most drivers in Qtc=0.707 sealed boxes have their maximum SPL below 45Hz limited by Xmax excursion parameters and not RMS wattage. This isn't a rule but most of the time it is true.
  
  
• Just like top fuel funny cars, the name of the game is displacement (pi * r^2 * Xmax). It is all about how much air you can move. Wattage, Fs, Qts, Vas, sensitivity, ... are all nice, but ultimately it is the basic piston model that moves the air.
  
  
• In the early seventies the French military built a prototype sonic deathray called "Le Monstre." It was a phased array (row) of resonant tubes powered by a jet engine. Just like radio and medical sonograms, the phased array could be steered. The resonant tubes were 78 feet in length for an extremely directional 7Hz output. This horrific device could kill a man more than a mile away!
  • "A 7Hz tone of sufficient amplitude can crack the walls of a masonry building and can affect a phenomenon known as brain entertainment whereby normal brainwave frequencies are reclocked and vital processes are catastrophically disrupted. Individuals, thus 'down converted,' usually die within seconds, though not before experiencing excruciating pain as internal organs are literally churned by tsunamis of air. Terrifying indeed." - Dan Sweeny, WSR v6 n1 issue 32
  
  
  
• The maximum SPL level in 1 atmosphere is around 194dB (sine wave amplitude -1 atmosphere to +1 atmosphere).
  • A zero atmosphere vaccum is the absolute minimum pressure. So ±1 atmosphere would range from 0 ATM to +2 ATM. At what point is this considered an overpressure?
    
    
  • Will this dB barrier apply to the automotive dB SPL contests? Do the contest rules allow raising the internal cabin pressure up to 1.5 atmospheres or replacing the nitrogen-oxygen air with a heavier gas? In a closed vehicle all you have to do is keep on compressing the air up to 10 atm or what ever. If the speakers could displace half the cabin volume then you would be up to 2 atm.
    
    
  • "Another way to generate a 194dB sound pressure level, besides launching a Saturn rocket, is to detonate 50 pounds of TNT 10 feet away." - Alton Everest, Master Handbook of Acoustics
    • The power of the first stage of a Saturn rocket is on the order of 50,000k acoustic watts. This is more an overpressure, like an explosion, as opposed to an acoustic event.
  
  
  
• Stun grenades have been tested and measured to produce 175dB to 183dB at the ear. A Glock17 9mm pistol was measured to produce a peak of 163.5dB linear or 128.5dB(A) blast at the ear (fired at arms length). A Smith and Wesson Model 1000p 12 gauge shotgun produced 158.5dB linear or 131dB(A). A sawed off double barrel would undoubtly be even louder. Groovy.
  
  
• Muad'Dib is a killing word. Now where can I buy one of those weirding modules? Or a thumper?
  
  
• "An adult blue whale can generate 1/20 Hz (0.05 Hz) output at 200 dB ref 1 uPa @ 1 m (roughly equivalent to 187 dB SPL in water). THAT'S some low, powerful output..." - Daniel Wiggins
  
  
• The THX 0dB reference level can have peaks up to 105dB full spectrum. Now with the introduction of AC3 (Dolby Digital) and DTS; the LFE (Low Frequency Effects) channel is +10dB higher. This means with the LFE channel the bass peaks can now hit 115dB when played back at the reference level. Doing this in the bottom octave region (20Hz - 40Hz) will require several subs.
  
  
• Here is an experiment for you home theatre bass fans.
  • Go to the Piston Excursion calculator.
  • Enter five 18" drivers at 15Hz and 115dB and look at the Xmax.
  • Thats about 5 Velodyne F1800R's!!! See what happens at 10Hz?
  
  
  
• The most awesome bass I have ever experienced was when I was walking down the street one day and I went by a CalTrans crew doing some road work and re-paving. A huge steam roller was flattening the ground, and in addition to rolling, it was shaking. Some hydraulic/pneumatic thing. It was incredible. I was standing 20 feet away and the earth was just trembling. The bass was low (7 - 15Hz) and loud, I wish I had my SPL meter. This beats the couple of California earthquakes I've been through.
  
  
• Threshold of audibility:

  frequency	SPL level
  3 Hz	120 dB
  20 Hz	75 dB

  
  
  
• 8 minute recomended maximum exposure limits:

  frequency	SPL level
  12-20 Hz	140 dB
  11-8 Hz	145 dB
  7-1 Hz	150 dB