I realize any answer to this is subjective, but I’ll take what I can get. That said, I’m about to replace a portion of my Dodge Challenger’s exhaust system. The manufacturer of the product says the exhaust note will increase by 6 decibels. Can anyone somehow describe what such an increase would be like?
According to this site it seems a 6dB increase means about a 1.5X increase in perceived loudness.
An increase of 6db means therefore that the power has increased by 10[sup]0.6[/sup], or roughly fourfold. However, that measures the “acoustic intensity”, and the way we perceive sounds means that it won’t seem four times as loud, as zombywoof’s link shows.
[aside] I found it pretty neat that it’s actually a ‘deci’ Bel–the unit measurement is the Bel (should that be capitalized? Is it named after Alexander Graham Bell? Why is there only one ‘l’?). The ‘deci’ bit means that the measurement is one-tenth of a Bel. I think I came across this wondering why my stereo went into negative dBs for most listening levels.
Or I could be wildly misinformed–this is the place to check such things 
This list of examples may help.
If your exhaust was as loud as a library, it’ll now be as loud as home conversation.
If it was as loud as a Bell J-2A helicopter at 100 ft, it’ll now be as loud as a Boeing 707 at one nautical mile before landing.
You’re right about the Bel, why it’s only spelled with one L I don’t know, but that’s not the reason for negative dB. Without a reference a dB value is just a comparison - for sound levels, 20 dB means a tenfold increase in sound pressure or voltage. Because it’s a logarithmic scale, negative dB just mean the ratio is less than 1 (-20 dB is one tenth).
Thanks. The explanation I’d heard was that the unit was calibrated to 1dB. Turning the attenuator[sup]*[/sup] down meant it was decreasing the volume by that much.
I love believing everything I read on the Internet.
[sup]*Is there any difference between ‘attenuator’ and ‘volume’, or is it just marketing to make the receiver seem more hoity-toity?[/sup]
Decibels are used for all sorts of measurements. It is usually 10* log base ten of power divided by reference power. So 0db is calibrated to something. What the power measured and the reference are need to be discovered from context.
So Rhythmdvl the only thing wrong with what you read on the internet is the unit should have been calibrated to 0db.
Here, 0db would be the reference power output of the amplifier. i.e. If the amp is rated at 100 watts per channel, then that is the 0db point. The volume control then shows output power relative to that point. -20 db is 1 watt (100th power relative to 100 watts), -30 is 100 milliwatts and so on.
[QUOTE=Rhythmdvl]
Is there any difference between ‘attenuator’ and ‘volume’, or is it just marketing to make the receiver seem more hoity-toity?
[/QUOTE]
There is a technical difference, but for the most part, it sounds intentionally complicated and fancy.
An attenuator reduces a signal level. If you’re familiar with “L-pad” volume controls for distributed systems such as Muzak in an office, that’s an attenuator - the signal being distrubuted around the building is at full volume, and the attenuator reduces it to something tolerable.
A volume control might reduce a signal, or it may adjust the amount of amplification or gain. Exactly what it’s doing depends on the design of the particular system or piece of equipment.
Just in case it’s not clear, the dB as power output from your stereo (possibly displayed as the volume setting) is not measuring the same thing as the ‘dB’ in the OP, measuring the noise level. Much of the time when dB is spoken of it is these sound levels - technically SPL (Sound Pressure Level). On that scale 0dB means a very low, but specific, sound level (it’s around the minimum that most humans can detect in the range of voice frequencies) and other sounds are much louder relative to it, so the dB will be positive.
For the power output of the stereo, the scale would normally be calibrated so that 0dB is the maximum output, and the volume cuts that down (hence negative dB). The actual SPL measured in dBs varies widely depending on the speakers connected and the stereo itself, but might be expected to be somewhere close to 100dB for a decent system.
The reason they’re both using dB is that it’s a simply a logarithmic scale. Since volume is perceived logarithmically, it makes sense to have your stereo vary its output on that scale when you change the volume knob linearly.