I get a lot of questions about the acoustic properties of resonator guitars, so I thought I would spend some time explaining how they work. This is an attempt to explain the physics of resonator guitar acoustics in plain English (with a picture). I will try to simplify things as much as possible, and also make this article relevant to potential builders.
The pot is the primary resonating chamber of the resonator guitar. It is important to understand that the pot actually has very little effect on the volume or tone of the guitar. The vast majority of acoustic guitars (including resonators) are designed with an enclosed back and an open top, which allows them to use their body as a sound box where it vibrates along with the strings. There is no such thing in a solid body electric guitar: its body is solid and does not resonate along with the strings. On a resonator guitar, only the cone actually vibrates when you play (the top can also vibrate, but this will be discussed later).
There are many variations on this basic idea, including different size cones, different materials for cones and biscuit bridges, different types of metal bodies and tops, etc. In my opinion you can get away with using whatever looks good to you.
Before we dive into the acoustic and psychological reasons for why resonator guitars sound the way they do, I want to show you a picture of a few different resonators so you can get an idea of what I’m talking about.
A resonator guitar is one that has at least one “resonator” (often in the form of a metal cone) inside it. There are three main types of resonator guitars, each with its own distinct sound:
The Dobro style single-cone resonator. The signature “twangy” sound most people associate with resonator guitars.
The National Triolian style metal-bodied tri-cone resonator. This is probably the most famous type of resonator guitar and is most commonly associated with blues music.
The Dobro square neck style single cone resonator. A less common type of resonator guitar but still well known within certain circles (particularly bluegrass).
You may be wondering why these things have a metal cone in them in the first place if it doesn’t make them louder? Well, the answer is that it does make the guitar louder: just not like you might expect. Let me explain…
A resonator guitar’s sound is unique. It can be a very loud and cutting sound, but it can also be mellow and warm. A lot of people think that the resonator guitar is mainly played by blues artists and therefore sounds like a blues instrument. While it is true that the resonator guitar was invented to compete with the banjo (which had become very popular) in the 1920’s, which was the time of early blues, the resonator guitar has been used in many musical styles. The resonator guitar is still used today in many genres of music.
In this blog I will write about how the sound of a resonator guitar works and what makes it sound different from other acoustic guitars. I will also give you some examples of this type of guitar being used by different artists in different genres of music.
The first guitar I ever bought was a round-neck resonator guitar. I loved the way it sounded, but no one else could understand why. They were used to the regular acoustic guitar sound. It was just different. The resonator guitar is a very unique instrument that produces a distinctive sound like no other.
It’s not because of the style of the guitar or how it’s played, but rather because of its unique construction. I’m talking about the resonator itself, which is what sets this guitar apart from the rest and gives it its name. It’s a resonator that makes the difference!
What is a Resonator?
A resonator is basically an enclosure with one or more openings and mounted on the underside of the top of the instrument. Inside this enclosure are several components that work together to project sound out into the open air. These parts are:
Resonator Cone – The main purpose of this cone is to act as a speaker for the sound to come out through its opening in the top of instrument. There’s also an air space within this cone that amplifies and focuses the sound being produced by its strings down toward its opening.
Spider Bridge – The spider bridge rests on
A resonator guitar’s sound is, in many ways, a result of the materials used in its construction. A resonator is a device (a cone) that vibrates sympathetically with another vibrating device (a string). Resophonic guitars use a steel body and neck, but some have a wooden body and/or neck. The National Reso-Phonic Company offers steel bodied guitars with three different types of cones: spider, biscuit and tricone. The single cone models are called “single-cone” or “single-resonator” guitars.
The Acoustic Properties of Steel
Steel has a density of about 8000 kg/m3 (about 500 times more dense than air) and an acoustic impedance of around 100 Mrayl (about 35 times greater than air). These two properties contribute to what we hear as the “steel sound”. Besides giving the instrument its distinctive tone, the steel body acts as a huge resonator, adding sustain to the notes being played.
The Acoustic Properties of Wood
Wood has a density of about 600 kg/m3 (about 10 times more dense than air) and an acoustic impedance of around 6 Mrayl (about twice that of
All resonator guitars have a metal cone which vibrates when the guitar is played. This vibration is caused by the tension of the strings, the mass of the bridge and saddle, and the body of the guitar itself. The sound waves are amplified through a ‘resonator’ which is either a ‘spider’ or ‘biscuit’ bridge. These bridges are different in that they have a small resonating chamber inside of them to amplify the sound further. The gourd on a National resonator guitar also acts as an amplifier.
The resonator cone has two points where it is attached to the guitar: one at the center and one at its edge. There are two different types of cones – biscuit cones (which are circular) and spider cones (which are shaped like spiders). Biscuit-style cones tend to produce a brighter tone, whereas spider-style cones tend to produce a more mellow tone.
The three main parts of this instrument are the top plate, spider bridge, and resonator cone. Usually made from maple, mahogany or rosewood, these plates can be thick or thin depending on what type of sound is desired by the manufacturer. The thicknesses of these plates affect how much
The sound of a guitar comes from its body, not the strings. The vibration of the strings is just there to excite the soundboard (top) into making sound. By changing the shape and size of the guitar body, we change the way it resonates and therefore change its tone.
The simplest way of changing the tone is to make the body smaller. A smaller body produces a tighter, brighter sound. A larger body produces a deeper, mellower tone.
A second way of changing the tone is to change the depth or thickness of the body. A thin body produces more treble than a thick one.
A third way of changing tone is to adjust how much air is inside the guitar body. In general, more air in the body produces more bass response. This is why acoustic guitars sometimes have a hole cut in them at their deepest point: it lets out some of the air pressure that would otherwise be trapped in there, which in turn increases their bass response and widens their overall tonal range. If you want to hear what this sounds like, try this demo here on my website where I play three different guitars: one with no F holes, one with F holes but with no air chamber behind them (this will give you some idea about