Speakers - by Eddie Runner (NU5K)

The terms and specs used to describe speakers (specially car speakers) are sometimes confusing.

Watts, mostly a bullshit advertising number (specially in car audio). The watts doesn't mean the speaker will play louder. If the wattage rating for car speakers was done correctly (and it usually is not) then it would only give you the amount of power you should not exceed when powering your speakers. If your powering your 100watt speakers with 50 watts then changing to a 200watt speaker may not make any difference. At least not just because of the power rating although the 200watt speaker might have other differences that might make it sound better or worse.

Sensitivity, this is usually how load the speaker is when you put 1 watt of power and stand back 1 meter. A speaker with 97dB sensitivity might be louder than a speaker with 94dB sensitivity, 3dB louder. Considering you would have to double your amplifier power from 100watts to 200watts to get a 3dB increase, this difference in loudspeakers could be quite considerable! However, some manufacturers do not measure this the same way and like everything else, some lie about it. Even one major car speaker manufacturer rates their speaker at 1/2 meter instead of the industry standard of 1 meter, this makes their sensitivity ratings appear much higher than they really are.

Frequency Response,  this is the RANGE of sounds the speaker will play. The human ear can on average hear from 10Hz to 20000 Hz. So check your speakers and see how much of the sound they can reproduce.
Frequency response should be given with a (+or- db) variance listed, many in car audio don't list the variances in their frequency response specs and they should. By not listing the variances they can stretch their claims a bit.

ORDER, The order of the speaker system is equivalent to the number of energy storages it has. This is very confusing to many folks, so many folks avoid the use of the term ORDER.

Impedance, most car audio speakers are 4 ohms, most home speakers are 8 ohms. The reason car speakers are usually 4 ohms is because in the early days of car audio it was difficult for amp designers (or powered radio designers) to make much power from the measly 12 volts the car has to offer from the battery. So they by using 4 ohm speakers the amps make more power with less battery voltage.  Now there is starting to be a push toward the 2 ohm capable amplifiers for even more available power. Check your amplifiers rating to see what impedance the amplifier will be happy with, and buy speakers that have he recommended impedance.  Running a speaker with an impedance less than your amplifiers specs recommend will give you more output power at the speaker but may damage your amplifier from the added heat caused by increase in current caused by the lower impedance, do so at your own risk...

Thiel-Small Parameters

FS - Natural resonant frequency of the woofer

Cas - Acoustic compliance

Vas - Volume of air having the same compliance as the woofer suspension.

Qms - Mechanical Q

Qes - Electrical Q  

Qts - total Q  Qts=1/(1/Qes)+(1/Qms)

Vab - Air volume of box

Cab - Acoustic compliance of the air in the box

Fb - Resonant frequency of a vented box

Qb - Q of a vented box

Qtc - system Q of a sealed box

RE - Voice coil resistance

VB - volume of enclosure

VP - Peak Displacement

FB - resonant frequency of vented box

F3 - the 3dB down point