As a lifelong musician, i have to comment that when at 90dB, a 3dB change will neither increase, nor decrease amplitude by double. 3dB would not be very noticeable. A change of 5dB you might notice if you are sensitive to the sound of your truck. If you drop crusing volume from 95dB to 80dB, you will find the change absolutely heavenly.
Most Dodge Cummins engines idle around 94dB from outside at the fender. This is very loud. Permanent hearing damage can be expected with prolonged exposure to 85dB. A rock concert will likely be up to 120dB, which is why your ears will ring throughout the next day, perhaps making it difficult to hear things you normally could.
The ringing associated with an ear ache is usually associated with a condition such as Otitis Media, where your Eustachian Tubes are affected, likely clogged by mucus, and are unable to regulate air pressure. Prolonged ringing of the ears usually Tinnitus.
When i stomp on my truck at speed my digital SPL will read over 100dB. Around town it hovers around 97dB. Sometimes when coasting it will come down to the low 90s. My air conditioning blows well over 100dB. However, i don't always have to have the stereo loud, nor do i always have to shout to participate in conversations. This is because the frequencies are not competing at that moment.
As an example, a music producer doesn't mix each track by sliding the faders up and down. Instead, they pan and notch frequencies so that each instrument fits in its own place without bleeding or competing with the timbres of other instruments. Hearing a balance of these frequencies is why even a relatively flat (harmonically speaking based on the overtone series, not pitch) singer like Madonna sounds good. Your ears percieve the highs (treble) and the lows (bass), even if they're not coming from her voice, they're in the track from a supporting instrument.
Has anyone done before and after decibel testing with a Donaldson muffler on a 5" exhaust? A 10dB drop would be well worth $75. Has anyone tested with the Aeroturbine muffler? If anyone plans to try one of these mufflers, they can easily pickup an SPL from Radio Shack and report their findings. I've ripped out my entire interior and am currently covering it with sound deadening materials. This is my 3rd day on the project but i need to protect my ears.