Ever wondered why acoustic guitars needs batteries but your electric doesn’t?
Acoustic guitars use batteries because the most common pickup systems used produce a weak signal that requires a preamp to boost the signal to line level. The preamp requires a power source, which in most cases is a 9V battery.
Not all acoustic guitars need to use a battery, and some electric guitars use a battery. It all comes down to how your guitar, converts the energy from when you play into a signal that gets sent to the amp.
In the following article we’re going to dive into the world of guitar amplification and explain why some acoustic guitars, but not all need batteries.
The problem with amplifying acoustic guitars
In earlier times the only way to amplify a guitar was to play in front of a microphone on a stand. In a recording environment, mics work well, capturing the natural characteristics, and subtle overtones of the instrument but in a live scenario it’s a different story.
For one, the guitarist is not free to move around as they play, as the volume is affected when the distance between the guitar and microphone changes.
Secondly, if playing accompanied, microphones tend to pick up other instruments and additional sounds. This results in a noisier output and a higher chance of feedback due to the increase in volume required to compete.
So while microphones are effective, they’re best suited to smaller venues or within a more controlled environment e.g. the studio.
Types of Acoustic Guitar Pickups
Pickups are transducers. What’s a transducer? It’s simply a device that detects a change and converts this to an electrical signal.
What’s this got to do with batteries? Pickups work by detecting change e.g. in the form of a standard magnetic pickup a disturbance to the electrical field created by the pickup is detected and then converted into an electrical current and transferred, by way of the guitar cable to the input jack of your amp.
There are three main choices of pickup available:
- Magnetic: Detects the vibration of the strings.
- Internal microphone: Detects the movement of air, in the form of sound waves.
- Contact: Detects changes in pressure brought about by the vibration of the soundboard
Within these three pickup categories, there are a variety of options. It’s also common to see combinations of the three used for amplifying acoustic guitars. In the following section we’ll look at all three and explain why two of these utilise a power source and one, at least in most cases does not.
Magnetic pickups are a series of magnets (pole pieces) that are contained within a wire coil. This combination produces a magnetic field.
When you play your guitar, the strings are vibrated over the pickup and the magnetic field is disturbed. This can be converted into an electrical signal and converted to sound, thanks to the electromagnet contained within your amplifier speaker.*Magnetic pickups wont work on nylon stringed instruments as nylon is not magnetic.
Magnetic pickups can be passive or active. If a power source is used to boost the signal, the pickup is active. If there isn’t a power source, the pickup is a passive pickup, which is more common.
The different between passive and active is the reason some electric guitars use batteries and also the reason why some acoustic guitars don’t use batteries.
Sound hole pickups
Most of the time if an acoustic guitar is utilising a magnetic pickup it will be in the form of a sound hole pickup.
Generally these won’t require a battery. However, Fishman (guitar pickup manufacturer) along with others do produce an active sound hole pickup in some of their models, which includes a small preamplifier, and requires a battery.
While sound hole pickups are a quick way to amplify a guitar that doesn’t have an internal pickup system, many people don’t like to play with them, and see them more as a convenience rather than an effective way to reproduce the tone of a guitar.
The reason for this is pretty simple.
Magnetic pickups work by detecting the vibration of the guitar strings. This works well on electric guitars, as they rely almost completely on the electronics of the guitar and amp for tone.
An acoustic guitar’s tone on the other hand is influenced heavily by the resonant nature of the soundboard, along with the construction of the guitar in general e.g. things like body shape and bracing.
Magnetic pickups only detect the vibration of the strings, so, some argue they’re not an authentic reproduction of the guitar’s tone.
Additionally, as already mentioned this type of pickup will not work on classical and flamenco guitars that utilise nylon strings.
Internal microphone pickups are small diaphragm microphones. They are also transducers and detect sound waves e.g. the movement of air, to produce a signal.
As a result mic placement is extremely important, with most placed in close proximity to the sound hole.
Microphones can be used on the surface of the guitar body or internally. The trade off is the external variety (which are less used), do not detect as much air movement (acoustical energy) and are prone to interference, but are easier to add to a guitar.
Internal mics on the other hand are more difficult to install but do not experience quite as many issues with interference.
Many people including guitarists such as Tommy Emmanuel prefer this type of setup.
However, many people also actively dislike the sound, which is often described as boomier and muffled. It really comes back to personal preference.
It is true that microphone pickups can produce a more authentic sound, but much like guitarists experienced when using mics on stands to project volume in the early days they are also subject to interference.They also require the addition of a preamp due to the weak nature of the signal they produce.
Contact pickups, also referred to as under saddle or more commonly as piezos – (pee-ay-zo) are the most common type of pickups seen on acoustic guitars and work equally well with steel and nylon strings. While also transducers, they operate by detecting changes in pressure, rather than air movement or disturbance.
Crystals are used to detect these changes in pressure and are called ‘piezoelectric’. This means that when change is detected e.g. in the form of a change in pressure e.g. compression caused by vibration, they can generate an electrical signal.
A good example of this is quartz, commonly used in clocks for time keeping. A circuit is used to vibrate the quarts with the rate of vibration determined by its size. In the case of the typical clock, the quartz is cut to a very specific size that determines the rate of vibration. The clock then uses the number of vibrations to accurately count minutes, hours and days.
In the case of acoustic guitars, piezos utilise a strip of piezoelectric crystals located beneath the guitar’s saddle. When you play the guitar, the vibration from the strings and sound board is detected by the change in pressure e.g. compression and an electrical current is generated which can be converted to sound.
While also seen on some jazz electric guitars, Piezos have been around longer than magnetic pickups but produce a much weaker signal in comparison. As a result they also require a boost in signal strength to work effectively with other devices such as mixing consoles and amplifiers.
So, why does my acoustic guitar require a battery?
In simple terms, guitars that use internal mics, contact or active pickups require a power source.
We’ve already covered why active pickups use a battery. In the case of internal microphone and contact pickups batteries are used to power the preamp that accompanies these types of pickup.
Acoustic guitar preamps
Preamps are circuits that take a weak electrical signal and increase it. They have three main properties, input resistance, (R in), output resistance (R out) and gain (A).
Resistance is a measure of how much opposition there is to the flow of an electrical signal. Gain on the other hand is a measure of the increase in the electrical signal, measured by dividing the output signal by the input signal. So, if the input signal was equal to 1 and the amplifier increased this to 20, the overall gain would be 20.
A weak signal needs to be increased to a normal operating level to work with amps, mixing consoles or audio interfaces.
Preamps are everywhere
While you might not realise it, if you play and record music you are very likely to be surrounded by preamps. They are used extensively in devices such as audio interfaces (the equipment you plug your guitar cable into for recording), mixing consoles, amps, mics and guitar pickup systems to increase their electrical output.
Preamps can be both external or attached to the guitar. In the case of many electric acoustic guitars, they are located on the upper bout of the guitar and will often include an equalizer to help control the tone.
Due to the addition of a power source you will also often find electric acoustic guitars also feature on board tuning and effects as demonstrated in the image below.
I hope the information above helps you to understand why some acoustic guitars require batteries and some don’t.
While most people probably don’t give a lot of thought to how guitars produce sound and how that sound can then be amplified, the world of guitar electronics is an interesting one, that is constantly evolving, since those early days when guitarists were forced to play in the same spot in front of a microphone. And while using a mic is still the preferred way to play and record, the development of pickups and powered preamps have allowed acoustic guitars to sound great when performing live and that can only be a good thing for all lovers of guitar.