Other Things To Consider When Choosing An Amplifier
Ohms (Ω): Also reffered to as impedance. This is the measurement of resistance that the speaker adds to the circuit. In car audio, typically the full range, mid range speakers, and tweeters are almost always rated at 4Ωs.
It is very important to match your amplifiers impedance to your speakers impedance. Since most multi-channel, full range amps are configured for 4Ωs, this is mainly a concern when dealing with subwoofers.
When and amplifier meets very little resistance it then begins to produce more output (power) than it was designed for and will cause damage or failure to the unit. Conversely, if you power 8Ω speakers with a 4Ω amplifier you will have reduced output.
For example, connecting an amp that produces 1000 watt at 2Ω to 2 subwoofers that are rated at 500 watts each but are wired in an 8Ω configuration. The reality is that most of the power from the amplifier will be consumed by the resistance of the 8Ω configuration and the speakers will likely only see about 250 watts. So it is important to make sure that your amplifier impedance matches the impedance of your speaker configuration.
Under Powering Your Speakers
When a speaker is underpowered there is the potential of overdriving the amp. This happens when the volume is turned up so loud that the amplifier can no longer produce a constant signal, resulting in audio breakup or distortion known as clipping. Most people think that it’s because the speakers are distorting, but in this case it is the amplifier failing. When this happens the amplifier sends harmful signals (square waves) to the speakers, and these signals can not be reproduced by the speaker resulting in damage to the speakers themselves causing loss of output or even failure. This is especially harmful on smaller, more delicate speakers such as tweeters.
When the amplifier is driven to the point of distortion (peaking or clipping), not only is it harmful to the speakers it also causes damage to the amplifier as well. When an amplifier reaches the point of clipping it can result in permanent damage or failure.
How much power do you need?
Matching the exact RMS Power of your speakers to the RMS Power of your amplifier seems like the logical thing to do, and yes it allows for great sound. If you over-power your speakers by 20%-50% this creates headroom within the amplifier, and will produce a fuller sound when played at all volumes. The additional headroom will enable your amplifier to contend with any sudden spikes in the audio signal. When an under powered amplifier receives an audio spike, it will not have enough power to reproduce the signal, instead it will produce a distorted signal.
The image below is an example of the output volume of an audio signal played at ¾ volume. If you have an amplifier that is rated at 50 Watts RMS (the Red horizontal line), you will notice that there are plenty of spikes in the audio that surpass the 50 watt range of your amp. These spikes will still be audible, but they will most likely be distorted and will cause your amplifier to produce excessive heat when they are reproduced.
If you had an amp that was rated at 75 Watts RMS (the Green horizontal line), you will notice that none of the audio spikes reach the 75 watt range, and the amplifier has plenty of power to reproduce the audio signal clearly without distortion. You will have the same volume without the distortion. The space between the Red and Green lines is what is referred to as Headroom. Headroom is basically how hard you can push your amplifier before it will distort. It is always a good idea to have plenty of Headroom within your system for this exact reason.
It is true that your 50 watt speakers may produce some distortion since the amplifier has a 50% higher power rating than the speakers. One way to accommodate for this is to dial the amplifier’s input gain down slightly, as this will allow your amplifier to perform efficiently and not generate too much power for the speakers.
Will a More Powerful Amp Make Your Speakers Louder?
A more powerful amp will give your audio system more headroom, and improve the sound quality of the audio. The more power will let you turn up the music before the amplifier distorts. However if the speakers can not handle the additional power they will distort. With a more powerful amp and speakers that handle the power, you’re speakers will definately be louder.
Wiring: Manufactures recommend wiring specifications in terms of gauge (thickness) and material of wire for their products. Using wiring that is too thin or made of inferior material wire will starve the amp of the power that it needs to perform at its optimum, thus limiting the amplifier’s performance.
Bridging: When 2 channels are combined to create one channel. This process cuts the ohm load in half therefore providing more power to the speaker that the amplifier is powering. This practice is commonly used to power subwoofers on a multi channel amp. For example if you have a 4 channel amp, channels 1 and 2 are used to power your left and right speakers, channels 3 and 4 are bridged to power a subwoofer. Note: Not all amplifiers are capable of bridging.
Audio Filters: Filters are an electronic device that can be found within amplifiers that control what frequencies are sent to your speakers. This is extremely helpful because they allow you to fine tune your amplifier to your speaker selection and your vehicle. Filters are available in both Fixed and Variable. A Fixed Filter is a filter that has only has one setting that is predetermined by the manufacturer. A Variable Filter allows you to adjust the setting of which frequencies are affected by the filter.
High Pass Filter: An electronic filter that allows signals higher than a specified frequency to pass through its circuit, frequencies below the specified frequency are muted.
Low Pass Filter: Exactly opposite of the High Pass Filter, this filter allows all frequencies below a specified frequency and all frequencies above the specified frequency are muted.
Subsonic Filter: Mutes the ultra low frequencies that are not in audible range, this reduces the workload of both the amplifier and the speakers. Why have your audio components reproduce audio that you cannot hear?
Adjustable Input Level: This function allows you to boost or cut the signal that is sent to your amplifier from your car stereo. This helps you dial-in the input signal strength to your amp to help minimize distortion within your unit.
Adjustable Output Level: This provides control over the signal strength that the amplifier sends to the speakers, to ensure that your speakers are not inadvertently overdriven and protects the amplifier from distorting or overheating.
High Resolution: Because of High Resolution Audio’s ultra-wide frequency response (up to 100 kHz), most standard amplifiers cannot reproduce all of the audio. Some of these tones may never be heard individually but when they are combined with the original audio of a recording, it breathes new life into the recording, offering more depth and ambiance.
Speaker Level Inputs: Enable you to use the speaker outputs from your car stereo to send signals to the amplifier. This is especially helpful when you do not have line level outputs (RCA) on your car receiver.
DSP (Digital Signal Processing): Some amplifier manufacturers offer models that feature onboard DSP. The DSP component allows you the ability to tune your amplifier to your vehicle by means of adjusting the EQ, Signal Delay, and Phase so you can get the best sound out of your vehicle’s audio system.
Although there are many different classes of audio amplifiers, only a handful of amp classes are commonly used in the world of car audio. Without going into a lengthy explanation on the physics of how each amp class works, it is much easier to understand the pros and cons of each amp class.
Listed below are the most prevalent amplifier classes used within the industry.
Class A: An analog amplifier. Mainly used in higher end car audio installs.