Amplifiers Glossary

Ampere

Ampere is the unit of measure for current or electrical “flow” through a circuit. It is commonly abbreviated as “amp” or “A” and should not be confused with the word “amplifier,” which is also commonly abbreviated as “amp.” Current increases with decrease in impedance.

Bridged Power

Some power amplifiers, allow you to combine the power outputs of two channels into one channel. By bridging, you can drive one speaker with more power than the amp could produce for two speakers. Because of this high power output, bridging is an ideal way to drive a single subwoofer.
If your amp is bridgeable, the owner’s manual will have directions that tell you how. Usually, an amp is bridged by connecting the speaker leads to the positive (+) terminal from one channel and the negative (-) terminal from the other channel. However, you are advised to consult your owner’s manual before attempting to bridge your amp.Most amplifiers need to see a 4-ohm load when bridged to mono operation. This is in other ways, specified as “4-ohm stable”. If you want to bridge your amp, you should use one 4-ohm speaker or, if you prefer multiple woofers, wire two 8-ohm speakers in parallel. (Again, consult your manual before operating your amp in bridged mode.) Some amps are 2-ohm stable, and even 1-ohm stable also.

Bass Boost Circuitry

Increases the output of low frequencies. Usually centered somewhere between 40 and 90 Hz, many amps have variably controlled circuits that allow you to increase the bass level in dB increments (ie. 0-12 dB at 45Hz). Variable bass boosts allow you to adjust the center frequency, changing the character of the bass. Some recent receivers have Bass Boost Circuitry in the head unit’s amplifier.

Built-in Crossovers

Crossovers consist of both a high-pass and low-pass filter. A low-pass filter prevents high-frequencies from reaching a subwoofer, by allowing only frequencies below the crossover point to be amplified. A high-pass filter allows only frequencies above the crossover point to be amplified — useful for keeping low bass away from small speakers, so they can play more efficiently. Crossovers are usually listed as variable or selectable. Continuously Variable means the crossover can be freely adjusted to any frequency between the listed end points. Selectable means that you can choose from several preset crossover points.

Capacitor

Capacitors are reservoirs of power. Heavy-duty capacitors act as a buffer zone between your amp and your car’s electrical system. They store up a reservoir of power, which can supply the amplifier’s peak demands without having to get additional current from the battery, which otherwise would impact badly on car’s battery. All amplifiers have built-in capacitors, though high-performance amps use larger, more effective ones.

External capacitors are recommended when you have high-powered subwoofers. External capacitors connect to the power cable just before it reaches your amplifier.

CEA-2006 Compliant

CEA-2006 is a standard published by Consumer Electronics Association, on May 28th, 2003. This standard imposes a “Testing & Measurement Methods for Mobile Audio Amplifiers.”, a uniform method for determining an amplifier’s RMS power and Signal-to-Noise (S/N) ratio. Using 14.4 volts, RMS watts are measured into a 4-ohm impedance load at 1 percent Total Harmonic Distortion (THD) plus noise, at a frequency range (for general purpose amplifiers) of 20 Hz to 20,000 Hz. Signal-to-Noise ratio is measured in weighted absolute decibels (dBA) at a reference of 1 watt into 4 ohms. This applies to both external amplifiers and the amplifiers within in-dash receivers.
CEA-2006 allows consumers to be able to compare car amplifiers and receivers on an equal basis. Manufacturers who choose to abide by the new standard are able to stamp their products with the CEA-2006 logo that reads: “Amp Power Standard CEA-2006 Compliant.”

Class of an Amplifier

Amplifiers are categorized into different classes based on their performance characteristics. Each class determines a specific design employed in the amp circuitry. And each design has different performance characteristics such as, power dissipation (in the form of heat) and distortion characteristics determining the efficiency of an amp.

• Class A amplifiers are desirable for the high quality of their sound but inefficient and runs very hot. This is because even when there is no audio signal, the output transistor(s) always have current running through them. The current flowing through the output transistor(s) (with no audio signal) causes the amp to heat up unnecessarily, and “waste” input energy. Most car amplifiers that boast “Class A” circuitry are really Class A/Class AB hybrids.
• Class AB amplifiers are most commonly available amp design. They allow current to run through the output transistors when there is no audio signal, but at a much lower level. A class AB amplifier runs cooler, and therefore, more efficiently than a class A, with low distortion and high reliability.
• Class D amplifiers boast higher efficiency, produce less heat, and draw less current than traditional Class AB designs. They use output transistors as switches to control power distribution — the transistors “turn off” when there is too much voltage across them. Class D amplifiers produce higher distortion than AB designs due to the high-speed switching on and off of the transistors, but this distortion occurs at high frequencies that are typically removed by a low-pass filter.
• Class T amplifiers are bit expensive and provide the sort of sonic advantages of conventional Class AB designs, combined with the high power efficiency and low heat production of a Class D design. Class T amps are able to generate 2-4 times more power than a comparably-sized Class AB amp.

Clipping

When Clipping occurs in amplifier, it literally cuts off the tops and bottoms of the musical waveforms that it’s trying to reproduce. This occurs when your amplifier is asked to deliver more current to a speaker than the amp is capable of doing. This introduces a huge amount of distortion into the output signal. Clipping can be heard as a crunching sound on musical peaks. And more over, in that time, your subwoofer will have to operate at its peak power handling ratings.

Crossover Point

In high-pass filters, low-pass filters, and crossovers, the crossover point is the frequency at which the level of the output signal has been reduced by 3 dB.

Crossover Slope

Slope is expressed as decibels per octave. Crossover Slope is the rate at which the crossover attenuates the blocked frequencies. A 6dB per octave crossover reduces signal level by 6dB in every octave starting at the crossover point. This means that every time the frequency of the audio signal is changed by a factor of 2 (one octave), the level of the audio signal will change by 6dB.

Suppose, your low-pass filter is set at 80Hz with a 6dB slope, you will see a drop in level of 6dB at 160Hz. With slopes of 12dB and higher, you’ll hear little output beyond the crossover point.

Damping Factor

The ability of an amplifier to control the movement of a speaker — the higher the damping factor, the greater the accuracy.

Damping factor = speaker impedance / output impedance of the amplifier. An amplifier’s damping factor will decrease as the speaker’s impedance decreases.That’s why an amp running at 4 ohms will provide tighter bass than at 2 ohms.

Discrete Output Devices

Three basic types of output devices are found in car audio amplifiers: integrated circuits (or IC), bipolar transistors, and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). An IC cannot pass enough current to work on a more powerful amplifier and is not considered a discrete output device. It is found only on relatively low-wattage (20 watts RMS per channel or less) amplifiers called “bridged transformerless” amps.

Bipolar transistors and MOSFETs are fast enough and can handle enough current to send wattage greater than 20 watts per channel to your speakers. They are found on the output stages of high-powered amplifiers. Both of these types of transistors are considered discrete output devices. Usually there are two per channel, but some amps feature as many as four per channel.

Impedance

Impedance rating is the total opposition to the flow of audio signal in an electrical circuit at a given frequency. It is measured in Ohms. Most car audio elements have 4-Ohms of impedance. Although car audio manufacturers label the impedance of most car speakers and subs at 4-ohms, the impedance of a speaker is actually not a constant. It’s actual impedance changes with frequency and can vary greatly. Therefore, though 4-ohms is the standard impedance in car audio, this standard is more of an average impedance for speakers and amplifiers when driven within the part of the audio spectrum for which they are designed. “Nominal Impedance” is the minimal impedance that the amp. Or speaker can handle.

Mono Amplifier

Mono (or monaural) amplifiers are single channel amps, well suited for low-frequency applications since the human ear cannot distinguish stereo in the extreme bass range. Also, since mono amplifiers are stable to 2-ohms, you can connect them safely to two 4-ohm woofers (wired in parallel). These are also called generally as monoblocks.

MOSFET

Metal Oxide Semiconductor Field Effect Transistors have a higher switching speed than bipolar transistors and generate very little heat. MOSFETs offer fast response and high efficiency.

Ohm

The unit of measurement for impedance or resistance. It tells you how much a device will resist the flow of current. If you take two signals of exactly the same strength and send one to a 4-ohm speaker and the other to an 8-ohm speaker, twice as much current will flow through the 4-ohm speaker. In other words, the 8-ohm speaker will require twice as much power (wattage) to play at the same volume.

Power Handling (RMS)

The maximum continuous sine wave power that can be dissipated by a speaker without failure, measured in watts RMS. Most speakers fail for one of two main reasons:

• A speaker is driven with too much power, beyond its rating, and it overheats.
• The amplifier is driven into clipping, producing square wave distortion that destroys the driver.

Remember that, clipping of an amp, forces the speakers to work at double power!

Preamp output

A preamp output lets you pass the preamp signal to additional amps, and in many cases the internal crossover from the first amp can send a filtered signal, eliminating the need for additional crossovers.

Resistance

Is the opposition to the flow of electrical current. Resistance is measured in Ohms.

RMS Power vs. Peak Power

The amount of continuous power, measured in watts, that an amplifier produces is called RMS power. This is very significant rating one should pay attention to, while buying the amp. The higher the RMS figure, the louder and cleaner your music sounds. Also, keep in mind that some manufacturers calculate the RMS power ratings of their amplifiers at different input voltages. For example, an amplifier rated at 100 watts RMS at 12 volts can produce considerably more power than an amp rated at 100 watts RMS at the more typical 14.4 volts.Stereo manufacturers often display peak power ratings on the face of their products. The peak power rating tells you the maximum wattage an amplifier can deliver as a brief burst during a musical peak, like a dramatic drum accent. The RMS figure is more significant.

RMS Power at 2 ohms

This rating tells you how much more power your amp delivers when a 2-ohm stereo load is presented. You can achieve a 2-ohm load by using parallel wiring of 4 Ohm speakers or by using 2 Ohm speakers.

Theoretically, amp output should exactly double as the impedance drops from the usual 4 ohms to 2 ohms. However, amp makers use different degrees of regulation on power supplies, which can restrict the actual increase in output.Less regulated power supplies come closer to doubling their output into 2-ohm loads. An amp with little regulation can achieve higher wattage into lower impedances. An amp with stiffer regulation maintains rated output from your amp as other electrical accessories demand voltage from the battery.

Signal-to-Noise Ratio

Measured in decibels (dB), this specification compares the strength of the desired audio signal to the level of background noise. A higher value indicates less background noise.

Sound Pressure Level (SPL)

SPL is measured in dB — an acoustic measurement of sound energy. One dB SPL is the smallest audible difference in sound level. 0dB SPL is the threshold of human hearing, while noise measuring 120dB can damage your hearing. In some countries, the maximum SPL of audio systems are restricted to specific values.

Speaker-level input

Number and type of speaker-level inputs. Speaker inputs let you connect an amp to a receiver that lacks RCA preamp outputs.

Subsonic Filter

A subsonic filter or an infrasonic filter, cuts off extremely low bass (below the range of human hearing) that many speakers cannot effectively reproduce, thereby making the amp’s power supply and output devices, and the speaker, more efficient.

Total Harmonic Distortion (THD)

Amount of change in harmonic content of the signal as it is amplified. A lower figure indicates less change and a more accurate amp. THD below 1% is inaudible.

Tripath

Tripath Technologies is the developer of the Class-T® amplifier design, which combines the low distortion and excellent sound quality of the Class AB design with the efficiency advantages of the Class D design. Tripath uses switching transistors to achieve very high power efficiency (around 90%), low heat production, and compact chassis-size.

Tri-Way Output

Also called as Dual Mode, this setup powers a pair of stereo speakers and one subwoofer simultaneously from the outputs of a single 2-channel amplifier. It’s an affordable way to drive a subwoofer. It requires an external Tri-Way adapter that is connected in-line between your amplifier and your speakers.