Amplifiers
Adding an external amplifier to a sound system that currently has its speakers powered by the head unit (or a factory fitted amplifier) is a great way to enhance overall SPL output (loudness), dynamic range, and clarity at higher volumes. Your system also benefits from the inclusion of crossover filtering for each pair of channels to feed to correct band of frequencies to the speakers – allowing them to play louder and clearer while being protected. Here are some tips to help you choose the perfect amplifier.
How many channels do you need?
If you are planning to amplify every speaker in your car then you’ll need at least one channel per front left & right, one per rear left & right, plus one for the subwoofer. This is why 5-channel amplifiers are so popular, as they house all the powered channels and all the signal processing you need into one chassis that’s easy to install.
It is also possible use a combination of the power built into your factory or aftermarket head unit at the same time as an external amplifier. An example would be a simplified system design of the same five speakers but employing a single 4-channel amplifier, where the front left & right speakers are powered by two channels of the amplifier, the subwoofer is powered by channels 3 & 4 in ‘bridged’ mode, while the rear speakers are still powered by the rear channels of the amplifier in the head unit. This is a great way to get started as you can upgrade by adding a dedicated mono amplifier for the subwoofer at a later stage then use the 4-channel amplifier to power the front and rear speakers.
If your car only has one stereo pair of speakers and a subwoofer then a 4-channel amplifier used in this 3-channel mode is a great option, with dozens of models available at varying price points and power outputs.
Alternatively, a more advanced system design may employ separate amplifier channels for each individual speaker in the car that includes treating the tweeters and midrange drivers as their own bespoke channels. The advantages of this are many, as you get to tailor and tune the sound for each speaker individually for both crossover filtration, time arrival, and even equalisation when DSP (Digital Signal Processing) is employed. Obviously, the number of channels here is determined by your specific sound system layout and your budget.
How much power do you need?
The amplifier power you need for each speaker in the system is governed by two important factors. The first is how loud or quiet the cabin of your car is when you are driving. An expensive luxury electric car’s cabin is much quieter than that of an old V8 muscle car with an aftermarket exhaust system. So, for any given target SPL (volume) level you’re seeking you’ll need a lot less power in the electric car than you would in the street machine.
Secondly, what are your own personal volume level targets once you’ve factored in the loudness of your car’s interior? If you want more loudness or dynamic head room, a more powerful amplifier will provide this for you.
In general, for a modern car with the ‘average’ quietness interior a power output of around 50WRMS per channel for the main speakers and 300-500WRMS for the subwoofer/s is ample. If your car is louder inside the cabin than normal, then doubling this power is a great idea. Frankly, it is better to have too much power than not enough. More power will manifest itself is greater dynamic range without distortion, which not only adds enjoyment but can reduce listening fatigue.
How does impedance and power output work?
All amplifiers have varying power output capabilities depending on the impedance load that is placed on their speaker outputs. Typically, as the impedance load reduces (from 4ohms to 2ohms, or 2ohms to 1ohm) the power output from the channel will increase. This ‘load’ is created by the speaker impedance of the speaker/s you have connected to the channels. Furthermore, you can wire multiple speakers or voice coils together in parallel or series to alter the total ‘load’ and, therefore, the power output from the amplifier channel.
Additionally, if you bridge two amplifier channels together each individual channel ‘sees’ half the impedance load of the total. So, a single 4ohm speaker bridged across two amplifier channels means that each individual amplifier channel of the bridged pair ‘sees’ a 2ohm load.
All amplifiers have a minimum impedance load they are capable of safely being connected to, and if you connect a load that is lower than recommended then the amplifier may go into protection mode and turn off, or it may get damaged internally. This damage is often not covered under warranty.
Ideally, you want to have your amplifiers operating at the minimum impedance load they are rated to work at, since this means they will be producing their highest possible power output. However, this doesn’t really apply to amplifiers powering your full range speakers since these speakers or almost exclusively 4ohms in impedance, whereas most amplifiers will happily make their best power at 2ohms per channel. That’s just the way it is.
For subwoofer amplifiers you have much greater ability to choose a subwoofer or subwoofers that offer the ideal minimum impedance load, so check what the minimum impedance load your mono amplifier suits and choose a combination of subwoofer multiples and voice coil types (and wire them accordingly) to match this.
What are gains and how do you set them?
The input sensitivity controls (gains) are to allow you to vary the input stage of the amplifier to suit the level on the incoming music signal from your head unit or processor that is upstream in the signal chain – as these can vary greatly. This then allows you to get the full power of the amplifier from any input voltage level.
As a basic guide these are the steps:
- Set all the input sensitivity levels to minimum
- Set your crossover filters appropriately for all channels
- Set your head unit’s tone controls to flat (no boost or cut at any frequency)
- Play a modern, well recorded music track that has good bass/midrange/treble
- Increase the main volume of the head unit until you get to around 2/3 total volume level
- Increased the input sensitivity levels until the speakers reach their maximum playing level that has no distortion
What are crossovers and do you need to use them?
Crossovers are the filters that ensure each speaker in your system is only receiving the precise band of frequencies they are design to play. In a basic sound system with full range main speakers and a subwoofer, the main speakers would have a high pass (HP) filter set for their channels at around 80 – 100Hz so that frequencies below this are diminished, while the subwoofer would get a commensurate low pass (LP) filter set at around the same frequency so the higher frequencies are diminished. In this way, all the frequencies are represented in the playback and are replayed by the correct speakers.
In a system design where there is no subwoofer employed at all, then you may prefer to leave the crossover disengaged altogether. This means that the full range speakers will be receiving low bass information all the way down to 20Hz. In this instance be mindful that at higher volume levels you could cause damage if excessive bass is present, and that any use of bass boost can exacerbate this.
While most multi-channel amplifiers will cater to this basic 2-way HP/LP system layout, some amplifiers offer a wider range of filter frequencies than others, or steeper filter slopes, or both. Your amplifier choice may change because some models feature more flexible or more advanced crossovers than others do and may suit your needs better.
How do you set bass boost or sub-sonic filters?
Bass boost is only recommended to be employed for subwoofers, as it typically is centred at between 40Hz and 50Hz which is too low a frequency range to be safely used on full range speakers at higher volume levels. Bass boost is designed to emphasise the ‘kick’ of a bass drum and can work well if used carefully. Remember that bass boost can’t make an amplifier any more powerful than it already is, so for any amount of boost you apply you need to reduce the input sensitivity a commensurate amount to avoid distortion and potential damage to the subwoofer/s.
Subsonic filters are high pass filters commonly found on mono amplifiers and are designed to protect the subwoofer from ultra-low frequencies when you are using a ported subwoofer enclosure. This is because below the port tuning frequency the mechanical power handling of the subwoofer is greatly diminished. As a rule, set the subsonic filter at just below the port tuning frequency of the enclosure. If the enclosure is tuned to 40hz, then set the subsonic filter at 30Hz for example.
Do all amplifiers sound the same or do expensive models sound better?
It has never been conclusively proven that one amplifier sounds better than another one, that a more expensive amplifier sounds better than a cheaper one, or that a specific amplifier topology (Class A/B versus Class D for example) sounds better or different than another one. There are, however, other factors that will make amplifiers sound different to each other that may cause you to perceive that one sounds ‘better’ than another one.
The single biggest differentiator between the perceptions of the sound ‘quality’ between amplifiers is their power outputs. Any amplifier that offers more power than another will sound ‘better’ – all other things being equal.
What is conclusive, is that different amplifiers behave differently when pushed beyond their limits, and that this can affect how they sound while at this output level. This can be clearly observed when they are connected to an oscilloscope to observe their AC audio waveform. Some amplifiers become over-driven and distort gently, while others distort the music signal more markedly that would be clearly audible.
The argument then is, why push an amplifier into distortion in the first place? If you are, then you obviously need a more powerful amplifier. Since amplifier power is so affordable, there is no merit in seeking a supposedly ‘better’ sounding amplifier when you can simply buy one powerful enough to avoid distortion in the first place.
By far the most influential aspects that differentiate how amplifiers sound compared to each other are the crossover filters they employ, and to a lesser extent the added signal processing they provide like bass boost. Even a minute difference between either or both attributes will colour the resulting sound, and therefore its perceived ‘quality’ to the listener.
If there is no power output difference, there is no distortion, and the signal processing is the same - all amplifiers sound essentially the same.
What else do you need to buy to do the installation yourself?
The primary addition you’ll need when buying an amplifier is an appropriate wiring kit to connect the amplifier to your source unit, and speaker wire to connect the outputs to your speakers. We offer a host of wiring solutions in our ‘Amplifier Installation Parts’ section where you can piece together a bespoke wiring and connection solution for a detailed and elaborate system design or find a one-kit solution for a simpler system design.
A basic solution requires a power cable from the battery to the amplifier’s location, with a main fuse placed within 30cm of the battery’s positive terminal. You’ll need an equal gauge earth cable from the amplifier to a chassis point close to the amplifier’s mounting location. You’ll need either RCA interconnects or speaker wires from the head unit (depending on if you are using RCA or speaker level). You’ll need a single small gauge wire for the 12V trigger unless you are employing speaker level input and your amplifier has remote signal sensing turn on/off. You’ll also need speaker wires to connect from the amplifier to your speakers.
We offer ‘Amplifier Power Kits’ that come with just the parts required to connect power and earth, or ‘Amplifier Wiring Kits’ that also include RCA cables. Make sure you check what’s included in each kit we offer to ensure it has everything you need to get the job done. If you require additional speaker wires you’ll need to purchase these separately.