Please 'Boom' Responsibly As most of you have noticed, the noise ordinances have become much tougher lately. Most of this is due to idiots, yes IDIOTS, who drive through residential areas with their windows down while their system is playing at full power. To make things worse, the music they listen to has all sorts of foul language that's not suitable for small children, (who may be playing outside). There are even a few people, who are even beyond idiot status, that play their systems at full power through residential areas after 10:00 PM (when many people go to bed). I don't believe that this type of behavior is good for the industry. If the fines get too stiff, people will stop buying large systems. If this happens, more people will get out of car audio (who wants a mediocre system). People get interested in things because they're exciting. A deck and four 6.5" speakers are not going to interest many of the younger car audio enthusiasts. If car audio enthusiasts keep annoying more and more people, the fines will keep getting tougher. All of this will only reduce interest in the equipment that fuels the industry. If you want to listen to your system at full volume, get out on the highway where there's little chance of bothering anyone. When you get to a red light, turn it down. If the only thing attractive about you is your 'system', you have some work to do. Bottom line... Think about what you're doing. Think about other people. It's not the end of the world if you have to turn the volume down for a little while.

Decibels:
The term decibel is often used but not often fully understood. If a level is stated in decibels, then it is comparing a current signal level to a previous level or preset standard level. A value given as decibels always has a reference, otherwise it is meaningless. If you are talking about sound pressure levels (SPL), the reference is considered to be the lowest level that can be heard by human beings. A one decibel change is considered to be the smallest change that can be percieved by the human ear. If a value is given as negative decibels (-dB), it means that the value is below the reference. You will notice that the "B" is capitalized in dB. This is because it refers to the last name of Alexander Graham Bell.

There are some common reference values in electronics for dealing with decibels. A few are listed below. Pay special attention to the upper and lower case designations of each term.

dBV referenced to 1 volt
dBW referenced to 1 watt
dBm reference to 1 milliwatt
or
.775 volts into a 600 ohm load
dBf reference to 1 femtowatt
or
.2739 µvolts into a 75 ohm load
dBv
dBu		 referenced to .775 volts with
no load parameters given

The following calculator will convert a known voltage level into dBf, dBu, dBm and dBV. You can change the load for dBm if you like but 600 ohms is fairly standard. DBf is used in tuner specs. It is 1 femtowatt (0.000000000000001 watts or 0.00000027386 volts) into 75 ohms (generally).
Data Input:
Voltage?
Data Output:
dBu = Referenced to .775V
dBm = Referenced to 1 mw into ohms
dBf = Referenced to 1 femtowatt into ohms
dBV = Referenced to 1V

The two formulas below are helpful when comparing voltage or power levels.
10*(log(power level # 2/power level # 1))
20*(log(voltage level # 2/voltage level # 1))
EXAMPLE:
First power measurement: 100 watts
Second power measurement: 200 watts
Difference between measurements, in decibels=10*(log10(200/100))
Difference between measurements, in decibels=3dB
In this case it was a positive number because it was an increase in power. If you reverse the first and second values, the answer would have come out as -3dB. Just realize that, if you have an increase, the result will be a positive number. If you have a decrease, the result will be a negative number.
As you may have heard, doubling the power output level of a source (such as an amplifier) is a 3dB increase in its output.
This calculator may help you to better understand how the difference between two values translates into decibels. You'll notice how doubling the voltage results in a 6dB increase and doubling power will result in a 3dB increase.

Data Input:
Value One? = (reference)
Value Two? =  
 
 
Data Output:
Difference = Decibels

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