Course:Phys341 2020/Steel Guitar

Ovation Guitars: Difference in Construction and Sound Quality

Having been founded in 1965, Ovation guitars self-describe themselves as "still one of the most advanced, forward-thinking and unique designs in the acoustic guitar market." The back of their guitars are made with a material they call Lyrachord (a composite material made out of glass filament and bond resin), which they claim to be more sound-reflectant and durable than wood. It is lauded by them as creating a "rounder, fuller sound" compared to wood guitars. A spectral analysis of the resonant qualities of an Ovation guitar and a wooden, classical guitar can yield a lot of information about the particular characteristics of these. For the purpose of this analysis, a Yamaha concert guitar made of Brazilian Rosewood was used.

Roundback

Starting in 1964, Ovation wished to innovate in the field of guitars and begin research into more efficient shapes for them. After 18 months of testing, they discovered that the best shape was a semi-parabolic (round) shape, as it reflected sound better and fuller. This acoustic shape can be found everywhere, from orchestra shells to even the human ear. However, this presented with the problem that wood cannot be bent into a circular shape without severe compromises, causing a structurally unstable product which dampened the sounds and caused unpleasant harmonics. As such, they turned to developing a synthetic material which would better support the shape they wanted. By 1966, they had settled on the Lyrachord which they continue to use to this day, and claim increases amplification. Their inspiration for materials was heavily influenced by its founder, Charles Kaman's previous work in aerospace engineering. His experience with helicopter blade engineering gave him a wide array of knowledge in material that had to be exposed to high vibrational stress. Because of this, he knew which materials would provide the best vibrations.

Later, in 1970, Ovation innovated further by modifying their soundboards. Originally made out of Sitka spruce (a wood widely utilized in instrument creation, including pianos, harps, violins, and guitar due to its sound conducting properties, as well as in early airplanes), they switched to a thinner, carbon-based composite laminated with a thin layer of birch. This soundboard is less than half as thick as a traditional, wooden soundboard, which gives the guitar a better sound quality They also feature models which 22 small sound holes across the upper body of the guitar, which they claim produces a louder sound.

Effect on Modes

Fig.1. Comparison of wood and air modes between a classical and ovation guitar (Own work)

The effect that this different material can be easily be seen through comparing an analysis of the wood and air modes of both a traditional wooden classical guitar with that of an ovation (Fig.1). The first thing that is immediately noticeable through this analysis is how much more resonant the air mode is compared to a classical guitar. This seems to align with Ovation's claim as to the resonant properties of Lyrachord in addition to the semi-parabolic back in comparison to a straight, wooden back (keeping in mind that the air mode is what makes the sound resonate much more than the wood mode). Even empirically, or by analyzing the decibel output of both guitars, it is easily noticeable how much louder the Ovation guitar is. In regards to the frequencies that it resonates, however, both seem to hover around the same area. The classical seems to have the highest resonance around 100Hz (G3) and the Ovation around 115Hz (A#2). The difference here is almost entirely in the loudness of the resonance and not with the frequencies that resonate.

However, when it comes to the" wood" mode (using this term here only to adhere to traditional notation despite it not being entirely made out of wood), the difference is much more pronounced. Here, the frequencies that resonate can be seen to be much lower than a classical guitar's by over an octave. In fact, looking at the brightest, most resonant frequencies for a wooden guitar (somewhere around 400Hz, or around G4 and G#4), one can see that there's a very noticeable dip in resonance in that same range of the Ovation. The Ovation's is much lower down, at around 180Hz (between F3 and F#3), or less than half of the classical guitar's resonance.

Difference in Timbre

Ultimately, the difference in timbre between the both instruments is very noticeable in the spectral analysis of their respective modes. An analysis of the difference in sound while being played was intentionally omitted as the strings themselves completely alter the sound between the two instruments (one having nylon strings and the other steel ones). As such, the scope of the analysis was limited to their air and wood modes, which are not altered in any way by the material of the strings attached to each instrument. Ultimately however, whether or not an Ovation's sound quality is "better" is ultimately a matter of personal preference. Through analysis, what can definitively be said that the sound resonates louder both due to the different shape and material.