Patented Jasper Device
A discovery so revolutionary, we built a guitar around it.
While each of our guitars is individually made to meet (and exceed) high benchmarks for quality, craftsmanship, and sound, what really separates a Jasper from any other guitar on the market is our own proprietary, patented, resonance apparatus built into each and every instrument.
The documentation for our hardware, U.S. Patent No. 10607579 B1, describes a radically unique take on the semi-hollow electric guitar that includes a specially-chambered body, sidewall venting, and an adjustable resonance plate on its back. The official name on the books is "Adjustable Musical Instrument Body", but around here we like to call it the "device". The interior chambers and grilled vents are an integral part of the device's acoustic functionality, but the carbon fiber back plate is what really steals the show. Under tension, the plate resonates in unison with the top of the guitar to dramatically increase the sustain of notes and chords. Adjusting the tensioning bolt in the center of the plate will actually change the guitar's resonant frequencies and even restrict the unwanted feedback inherent to semi-hollowbody guitars played at high levels of amplification. This incredible technology, standard among all our guitar models, is what makes Jasper guitars, truly, unlike any other in the world today.
In-Depth Technical Talk
Carbon Fiber Back Plate (Figures 5 & 3)
This was initially just an aesthetic addition to cover the large opening we created in the back of the body for easier access to our electronics. Over a few prototype modifications, the plate eventually became flexible and adjustable in a way that can help inhibit feedback and change the resonant frequency of the guitar.
Sidewall Air Vents (Figure 1, #4)
These are a critical design aspect of the Jasper guitar body. Traditionally, semi-hollowbody guitars, or chambered guitars, have f-holes on the top of the body, which are primarily decorative; however, when the guitar is electrically amplified at high volumes, they also function as a pathway to move and vent air mass within the guitar body. During the design phase for our prototypes, we eliminated the traditional f-hole vents from the top. With strategic placement and a fresh look, we transferred the vents to the side walls of our guitar body. This venting alteration also helped make the guitar top stronger, stiffer, and less vulnerable to feedback.
String-Through Bridge Assembly (Figures 4 and 6)
This is comprised of three primary parts: 1) The top piece found on the top of the Jasper guitar body that adjusts string height and intonation; 2) A middle piece, installed in the core of the body, that adjoins top and back parts with machined bolts; 3) The back piece, installed on the surface of the carbon fiber back plate, that connects and tightens to the middle piece with a machined tensioning bolt that passes through the back panel. With these three primary parts connected together, one can flex or tighten the back panel inward by applying clockwise turns to the bolt that passes through the back portion of the bridge assembly.
— Tony Louscher (Jasper Guitar Company - Owner, Operator, Luthier)
The Problem
Historically, electrically amplified musical instruments, like acoustic and semi-hollowbody guitars, have been difficult to amplify reliably at high volume levels. When musical instruments are amplified, they often produce undesirable audio feedback frequencies, such as high-pitched squealing and squelching. Playing such amplified guitars in smaller venues and at lower levels of amplification will not always produce this undesirable feedback. While performing in large concert halls, auditoriums, and arenas, however, there is typically the need to amplify guitars at a much higher volume, increasing the risk and likelihood of generating feedback.
Audio feedback, also known as acoustic feedback (or the Larsen effect), is a special kind of positive loop gain which occurs when a sound loop exists between an audio input (e.g., a microphone or guitar pickup) and an audio output (e.g. a power amplified loudspeaker). In the example diagram above, a signal received by the guitar is amplified and passed out of the loudspeaker. The sound wave from the loudspeaker can then be received by the guitar again, amplified further, and then passed out through the loudspeaker again. This reaction from guitar to amplifier to speaker repeats itself and is incrementally augmented. The frequency of the resulting sound is determined by resonance frequencies in the guitar, amplifier, loudspeaker, the acoustics of the room, and the directional pickup and emission patterns of the guitar and loudspeaker, as well as the distance between them. In physics, resonance is the tendency of a system to vibrate with increasing amplitudes at some frequencies of excitation. These are known as the system’s resonant frequencies (or resonance frequencies). The resonator may have a fundamental frequency and any number of harmonics.
So, most amplified acoustic guitars and semi-hollowbody electric guitars share the common element of having holes on their tops. The holes on acoustic guitars are designed to produce volume, whereas the holes on semi-hollowbodies do little more than simply vent the moving air mass that gets generated within the cavity or chambers of this type of body design. These two types of guitars are inherently plagued by the menacing feedback loop that is created when electrically amplified. Part of the problem is that when the sound wave returns to the guitar it not only excites the top surface but also penetrates into the top via the hole(s) and exacerbates or intensifies the feedback, which will continue to increase exponentially. Various products and remedies have been used to suppress this problem, from stuffing towels in the guitar cavity, to placing a thick rubber-like disc in the sound hole, to even taping over the f-hole to impede the nasty squelching. Needless to say, none of these solutions is ideal and each has its own varying levels of success.
Our Solution
During a brief epiphany in the late spring of 2018, I decided to create a prototype semi-hollowbody with no f-holes. Now, f-holes on a semi-hollowbody guitar are primarily just decorative air vents, and they really aren’t designed to produce much volume. However, with no f-holes, the guitar’s inner air mass will still need an exit path, so I decided to eliminate the f-holes from the top and move the vents to the sidewalls of my proto design. Without the venting on the top, the integrity of the guitar top was preserved, making it stiffer, stronger, and less vulnerable to the feedback loop.
In addition to relocating the top vents to the sidewalls, I started experimenting with various materials for the back access plate. I liked the option of carbon fiber primarily because of its aesthetic value, but it’s also easily sourced and has been used in guitar manufacturing for decades. This choice of material turned out to include a tangible bonus, as the carbon fiber would prove to be flexible and adjustable, significant factors to producing its exclusive results.
The tensioning bolt affixed to the carbon fiber back plate has an integral design function, as well. As clockwise turns are applied, the bolt is threaded into an internal metal block, which is attached via bolts to the bridge unit that rests on the top of the guitar. When the desired turns are applied to the tensioning bolt, the carbon fiber plate is forced to flex inward producing resistance that creates a counteractive effect. The result is that the resistance created by the flexing carbon fiber plate will, in effect, pull back on the guitar top, making it stiffer and inhibiting feedback.
— Tony Louscher (Jasper Guitar Company - Owner, Operator, Luthier)
The information that follows is the result of a test performed by Tony Louscher and Max Kresch in March, 2020. The purpose of the test was to determine the resonant frequency that the chambered body of the Jasper prototype guitar would produce by measuring its internal air mass.
If we stretch our imaginations a bit, the body prototype may be thought of as a simple air cavity. Specifically, the hollow portion of the body (seen as a gumdrop shape in Fig. 1 and covered by a carbon fiber plate in Fig. 2) serves as the cavity, and the ports (seen in Fig. 2) serve as the (singular) opening.
With this idealized picture, the guitar is basically a simple cavity and we may use the corresponding equation to calculate the resonant frequency of the guitar body. An illustration of a simple cavity and the equation are shown in Fig. 3 (from http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/cavity.html).
The resonant frequency, then, is related to the physical spatial characteristics of the cavity and the opening port.
In order to determine the volume of the cavity, it was filled with sand, which was then leveled, and then the volume of the sand was measured. Using this process, a volume (V) of 1450 cm3 was found. Fig. 4 shows an enlarged and idealized version of one of the ports shown in Fig. 2. Caliper measurements were used to determine the length (l = 2.5 cm), width (w = 3.8 cm), and diameter (d = 0.8 cm) of a single port. The diameter and width were then used to determine the overall area (A = 7.08 cm2) as seen in Fig. 5. This is just the area of the rectangular portion of the port added to the area of a circle, multiplied by 2, because there are two ports on the guitar.
Lastly, we took room temperature to be 20°C with the speed of sound in air at room temperature (α) to be 34,600 cm/s. Given the volume, the length, the area, and the speed of sound, we may use the equation from Fig. 3 to determine the resonant frequency (f resonance = 243.4 Hz) in Fig. 6. The playable frequencies of a normal guitar in E standard tuning range from 80 Hz for low E to about 1200 Hz on the highest frets of the high E string. This places the resonant frequency for the prototype squarely in the playable range of the guitar. Given that the guitar has more variables than a simple cavity, we might be hesitant to read too much more into this result. However, if one insists on taking this as the resonant frequency, it corresponds roughly to open B on the guitar, which should be 246 Hz.