This link got me thinking:
"HEARING DAMAGE FROM LOW FREQUENCY AND INFRASONIC SOUND
Extremely low frequency sounds do not follow the tables above, because the weighting curves used for the sound measurements above are based on audibility. But it is now thought that frequencies under 60 Hz, and especially those approaching DC impulse transients, cause hearing damage, even though they are not very audible. This damage begins in the "rock range", starting between 2 KHz and 6 KHz, and expanding in frequency range as exposure continues. So the following precautions should be taken:
Infrasonic filters rolling off at 30 Hz should be inserted in all subwoofer, house, and monitor feeds.
Subharmonic generators (bass enhancers) must not be used.
If the sound is felt in a person's chest, it is too loud in the infrasonic region. It is causing hearing damage even though it is not heard to be that loud.
Infrasonic filters should be inserted in the instrument outputs of certain instruments. For example, some Yamaha instruments are known to output DC transients.
A new weighting curve, Z weighting (dBZ), has been created for SPL meters so this hazard may be measured.
Often the damage is done to people farther from the speakers. A 20 Hz wave does not fully form until the sound is 28 feet from the speaker."
"The NIOSH-ANSI Recommendation
NIOSH (National Institute for Occupational Safety and Health) and ANSI (American National Standards Institute) have adopted a stricter standard based on equal amounts of energy. Here is their scale of the amount of sound a person may be exposed to in a 24 hour period:
Use the dBZ scale if available. Otherwise use dBC.
A formula for calculating these times follows:
NIOSH max time (hr):
N_time = 2 ^ ((94 - SPL) / 3)
A formula for calculating the portion of the maximum dose used by a given sound exposure follows:
N_dose = time (hr) * 2 ^ ((SPL - 94) / 3)
LEVEL NIOSH MAX TIME
> 115 dB SPL NONE
115 dB SPL 28 seconds
112 dB SPL 56 seconds
109 dB SPL 1 minute 52 seconds
106 dB SPL 3 minutes 45 seconds
103 dB SPL 7 minutes 30 seconds
100 dB SPL 15 minutes
97 dB SPL 30 minutes
94 dB SPL 1 hour
91 dB SPL 2 hours
88 dB SPL 4 hours
85 dB SPL 8 hours
82 dB SPL 16 hours
80 dB SPL 24 hours (continuous)
NIOSH recommended maximum exposure times"
So, do the general tips apply to bass/subs too? and can our ear handle more SPL in the bass region before damage occurs vs. mids and especially highs?