by: Kevin Smith

Hz: The unit of measurement for frequency. 1 Hz is equal to one cycle per second, or the complete cycle of an alternating wave form per second.

Fs: The frequency at which a speaker naturally resonates in free air. (measured in Hz)

Fb: The resonance frequency of the air in a port and the stiffness of air in a ported system. This is commonly referred to as the Tuning Frequency of a ported enclosure. (also measured in Hz)

Fc: The resonance frequency of the Closed-box system.

F3: The frequency at which the acoustic power output from a system has fallen to half of its reference value. This is what we call the systems 3dB down point. (again, measured in Hz)

Fu: Yes, this is commonly used in the industry, but not to describe ANYTHING technical. This is commonly used in response to someone badmouthing your favorite product.

Q: Yes, this is the guy that made all those fancy gadgets for 007, but that isn't what we mean here. This is actually the ratio of reactance to resistance in a series circuit, or the ratio of resistance to reactance in a parallel circuit.

Qes: The Q of a speaker at its free air resonance, considering only its electrical losses.

Qms: The Q of a speaker at its free air resonance, considering only its mechanical losses.

Qtc: The total Q of a woofer and sealed enclosure (Fc) at the system's resonance frequency, considering ALL resistive losses.

Qts: The total Q of a woofer at Fs, considering all driver (speaker) resistances.

Vas: Volume Acoustic Suspension. This is the volume of air having the same acoustic compliance ("stiffness") as the speaker's suspension. (measured in cubic feet or liters)

Vab: Volume of air having the same acoustic compliance as the enclosure. No this isn't one of those posers from Milli Vanilli, that was Fab.

: Compliance Ratio

NO: For many of you it may be what your gf says to you after a date, but it really means Reference Efficiency (H Greek eta).

CAS: This the Acoustic compliance of the driver suspension.

CAB: Ok, this MIGHT be how some of you get around after your Driving Under the Influence tickets, but this really means, Acoustic Compliance of the air in the enclosure.

Xmax: The maximum excursion of a speakers cone in ONE direction while maintaining a linear behavior. (measured in inches or millimeters) This could also describe the fatter porn stars.

Vd: NO not Venereal Disease! This is the volume of air displaced by the speakers cone during an Xmax displacement.

BL: The product of a drivers gap flux density and the length of the voice coils conductor in the gap. (measured in Tesla meters) Not to be confused with BS which is commonly spouted by many persons on RAC and IRC (you know who you are).

Sd: The active radiating area of a speaker cone, including the surround. (measured in square inches or meters) Sd is also known as EPA no, not the Environmental Protection Agency, it's "Effective Piston Area"

Re: The ACTUAL DC resistance of a speakers voice coil/s as measured with a standard volt/ohm meter. Not to be confused with Nominal impedance. A 4ohm speaker will commonly measure only 3.2ohms and an 8ohm will measure around 6.4ohms. You can use a volt/ohm meter to measure the impedance of the coil on a speaker that you are not sure the impedance of. (measured in Ohms)

Le: The electrical inductance of a speakers voice coil. (measured in mH also known as millihenries) Also a small asian man in South Central that killed many would be thieves during the riots.(possibly related to our own Sulkee P. Chandler)

Impedance: The total opposition to the flow of alternating current in an electrical circuit. The measure of the magnitude of an electrical load when using alternating current, such as in audio. This is the combined effect of resistance, capacitance and inductance. (measured in Ohms) Not IMPOTENCE, a not uncommon problem experienced by more than ONE of our members I can almost assure you!

RMS: This is the continuous power that the speakers voice coil can handle without failure. (measured in Watts) Maybe it means REALLY MONDO SOUND

S Factor: A description of a bandpass enclosures frequency response in the pass band. It is a general indicator of the bandwidth.

SPL: Everyones favorite. This is an acoustic measurement of sound energy. (measured in dB aka decibel) High dB levels (above 120dB) can cause permanent hearing damage and according to some on RAC, pain in the testicles! Ladies, you won't have to worry about this one. Although it may cause similar results in breasts, but we haven't done any studies, YET. Feel free to join any teamROCS member in their vehicles for a test. :0)

SPLo: The speaker's reference efficiency measured with 1 watt input at a 1 meter distance from the center of the cone.

dB: The basic unit of measurement in electronic and acoustic work. It can be referred to as a measure of loudness.

Damping Factor: The ability of an amp to control the load without overhang. This applies to how tight the bass is. The higher the number the better, but anything over 50 is said to be inaudible. Damping factor is calculated by dividing the load (speaker impedance) by the output of the amplifier. As a speakers impedance decreases the amplifiers damping factor will also decrease. (not to be confused with DampENING, aka getting your amps wet, as this is a very, very, BAD thing to do to your amps)

Vb: Internal Volume of air in an enclosure. (measured in cubic feet, or liters for you foreigners)

Volume: The total internal airspace of an enclosure calculated by multiplying Length x Width x Height. (also measured in cubic feet or liters) (to calculate the cubic feet you must do your multiplication as described above and then divide by 1728 <---cubic inches in one cubic foot)

HD: Hole Diameter, no, not the anal orifice of our own teamROCS member RocketJohn, but the Actual cutout size in your baffle so your speaker will fit properly.

MD: No, not your Doctor. This is the Mounting Depth of your speaker.

Series: A series connection is two or more speakers or voice coils wired with the positive from one speaker/coil to the negative on second speaker/coil, thus leaving a positive from one speaker/coil and a negative from the other.

Parallel: A parallel connection is achieved by taking all the positives from each speaker/coil and wiring them together and then doing the same for all negatives.

A formula for calculating your final Series, or Parallel impedances can be found in another tech article on our site. Please take a look, as it will explain this further and can possibly save you from making an expensive mistake. Go There

DC: "Direct Current" describes a circuit in which current travels in one direction only. This current will always flow from Negative to Positive.

AC: "Alternating Current" describes a circuit in which the voltage potential fluctuates so that current can flow in both directions through the circuit. Your amplifiers put out Alternating Current to drive your speakers.

THD: This is Total Harmonic Distortion and represents how much a certain device (amps, etc.) may distort a signal. This is usually shown on spec sheets as .005% THD. You will want to pick a product that has low THD numbers, as these will offer the cleanest signal. It is said that THD of less than .1% is inaudible, but even though your ears may not hear it, it doesn't mean it isn't there and possibly doing damage to your speakers. Distortion is the LEADING cause of damaged speakers!

EBP: "Efficiency Bandwidth Product" is used to help in the design of the correct enclosure for a particular driver you will be using. EBP=Fs/Qes. Numbers below 50 will be best suited for Sealed enclosures, while numbers from 50-90 are fairly flexible as far as enclosure options, and 90 and up are best suited for Vented enclosures.