Linearteam WinISD Pro
An octave is any doubling or halving of a given frequency. A dB (decibel) is a unit of measurement which is "referenced" to some value. I believe that the official definition of a decibel is "A logarithmic means of measuring a gain or a loss". Decibels are funny, and a little hard to understand at first. Decibels apply to sound loudness, power, or voltage. The best way to think of decibels is to think "compared to what?". When speaking of sound (loudness), a 1 dB change is the minimum amount of change perceptible by the human ear. If you were sitting blind folded in my living room, and I snuck over the volume knob and slowly changed it, the point at which you would say "Ah! I can tell you've changed the volume!" is a 1 dB change in sound. If I continue to "crank the knob", I would have to change the sound level by 10dB to make the sound twice as loud as it was from where it started. This is true from any volume level. Decibels simply define a ratio of change from "what was" to "what is" in either watts, volts, current, or SPL. A 3dB increase of sound is about the increase you make when you turn the volume up to the next reasonable level, like when someone says "turn it up a little, I can't hear it". The price of bringing the volume "up a notch" --- twice the power.
Here's a little secret...if you see a 100W amp next to a 130W amp in a store, those 30 "extra" watts are meaningless as far as loudness is concerned. Those extra 30 watts may provide a small of amount of reserve power (useful for reproducing deep bass notes that happen in rapid succession), but a properly designed amp will have large enough capacitors to fulfill that need anyway. Remember that 3dB I told you about? Well, it actually takes a DOUBLING of power to reach that 3dB! In other words, if you're cranking out 100W of power from your amp, and you go to the volume knob to "crank it up a notch", you will actually need to DOUBLE the power output to increase the volume up enough to take it to the next "level". That's right, to increase the volume so that the increase is plainly noticable requires a DOUBLING of amplifier power! So, your 100W amp is probably every bit as good as that 130W amp! If you have a 100W amp, and want a LOUDER amp, you must at LEAST double your power. You need a 200W amp! If you want the sound to be "twice as loud", then you must increase your power tenfold! A 1000W amp will only be twice as loud as a 100W amp! So the next time a salesman tells you that those extra 30 watts will make the difference, you can tell him to pack sand (in fact, go ahead and ask him about "reserve power"). ;)
The human ear can detect (in young people) a frequency range of 20 Hz to 20,000 Hz. In reality, the average person can hear frequencies from about 28 Hz to 18,000 Hz. And to top that off, the average musical song will only cover frequencies from 35Hz to 15,000 Hz.
For you "need to know" types, Frequency correlates to the actual movement of a given speaker. Imagine placing a D cell battery across the terminals of a speaker. The speaker would respond by moving either in or out with a little "pop". Reversing the polarity of the D cell battery would cause the speaker to now move in (if it moved out the first time) or out (if it moved in the first time). If you were the 6 Million Dollar Man, and could switch the battery back and forth at incredible speeds, the speaker would start to make sound. If you could switch the battery back and forth at a rate of 30 times per second, the speaker would play a 30 Hz note (albeit with an insane amount of popping as the battery continued to make and break contact, but you get the idea)...and so on.
Passive crossovers serve to "funnel" the output frequencies from your amp to the appropriate speaker in your box. Sending low frequency notes to your tweeter will smoke it in no time flat. Sending high frequency notes to your woofer wastes high frequency power that would be better utilized by your tweeter. Your midrange fits in the middle there, and is subject to both problems.
Passive crossovers are installed in series with the speakers in your box, and offer varying amounts of impedance (A/C resistance) to the amplifier. A capacitor's impedance is very high at low frequencies, and very low at high frequencies. Placing a capacitor in series with your tweeter will serve to "block" the very low frequencies, while allowing the very high frequencies to pass almost for "free".
An outward moving speaker increases the air pressure in the room, whilst an inward moving speaker decreases it. This rise and fall of air pressure in the room pushes little hairs inside of your ears back and forth (imagine tall weeds in a grassy field being pushed by the wind..only not just any wind, but a strange wind which blows one way for an instant, and then the opposite way the next instant, continuously). These little hairs in your ear perceive these changes in the "wind", and pass this onto your main noodle, which processes this as sound.
These little hairs, however, can only move so fast. At frequencies above about 18 kHz (or below about 25 Hz), the little hairs can't dance...and this is the reason why you don't hear sounds outside of that frequency range. Also, if the INTENSITY of the "wind" is too great for too long (you "jam out" at mind blowing volume levels all the time), those little hairs begin to get "stuck" in the bent over position (just like the weeds in the field would naturally do if the wind got high enough). When this happens, you lose the ability to detect sound.
At first, the high frequencies vanish (the tallest, most sensitive weeds go first), and eventually all of them "die". There is no cure at this time for this hearing loss. Hearing aids are available, but they only serve to CRAM the now defunct freqs down your ears' "throat", and is the equivalent of walking on crutches. Bottom line is this...if your ears ring right after you've been jamming out, then you've just killed some weeds (in your ear ;) ). I myself have fallen victim to this trap (thanks to too much AC/DC, Frampton, RUSH and the like).
So, a word to the wise (to those who are smart enough to heed it). Your average senior citizen on the street today has a hard time hearing, and he wasn't exactly jammin' out to a Rockford Fosgate Punch amp when he was young, right? So, here's something to dwell on..."Ya ain't gettin' any younger"....and neither are your ears...you WILL age, and you WILL live to regret any abuse you subject your ears to... Make it "thump", not BLARE! If your friend is showing off a system, and it's either distorting OR blaring loud, then promptly stamp a big, fat "L" on his forehead and move on. Keep your sound in the "comfort zone".
'Nuff said.