1. Introduction

It is easy to enumerate the features[1,2]of an acoustic guitar comparing with other musical instruments. But there are many disadvantages of the guitar in the playing and the composing. Especially the worst weakness[3] is that the playing volume is too small.

However, the acoustic guitar fitted with pickups, a microphone or transducers which are enable to make high volume by the amplifier and a speaker is called an acoustic-electric guitar in America and an “Eleaco” in Japan. Usually, an “Eleaco” are fitted with piezoelectric pickups which are able to output a sound similar to the original guitar sound than the magnetic pickups.

Almost piezo pickups on the markets can capture only the vibrations of the strings, so natural guitar sounds could not be played because of no capturing the vibration of the top plate which influences most to the sounds of the guitar. But many guitarists were not satisfied with the sound of those piezo pickups.

In responses to the wish of all guitarists, the President Yamaya of Sonaresearch Co., Ltd, who is known as the famous developer of the pickup for piano and double bass pickups of YAMAHIKO brand[4]

among professional musicians and sound engineers, invented the Guitar Body Pickup(hereafter, GBP). The GBP was based on the studies by Sonaresearch Co., Ltd. and Projects for the Next Generation Musical Acoustics Systems in KAIT(Kanagawa Institute of Technology)[5] .

In this paper, experiences to compare with the spectrum of GBP outputs and usage of the playing and hearing test of the Guitar Body Pickup are shown under various conditions of changing positions to attach on the guitar body using the 3 different types of the guitar.

2. Force Mode Pickup (FMP) The first product of the pickup for the acoustic guitar

by our studies from 1999 was the Force Mode Pickup[6] (here after, FMP) . In Fig.1, (a) shows the inner cross section and (b) shows the photo of FMP.

In Fig.1(a), the piezoelectric element has the negative and positive polarization plane when the compression force is applied. Among the positive planes of the two donut-shaped piezoelectric elements, the center plate is arranged to sandwich, and is connected to the output connector. The two piezoelectric elements are connected in parallel, which are the poles of the respective signal output terminals.

In addition, the screwed bolt penetrates vertically in the center of the upper case and lower case, so the middle bolt, upper case, bottom case, the two piezoelectric elements and the center plate are mechanically fixed and compressed with the moderate pre-pressure as a block. FMP is the typical pickup with sensitivity to the vertical force of vibration from the top plate of the guitar.

New Type Pickup using Piezoelectric Elements for the Acoustic Guitar

Ichiro TOKUHIRO1,2, Shinji OGAWA1, Isoharu NISHIGUCHI 3, Kiyohiko YAMAYA 4 1 Department of Information Media, Kanagawa Institute of Technology, Kanagawa, Japan

2Showa University of Music, Kanagawa, Japan 3 Department of Vehicle System Engineering, Kanagawa Institute of Technology, Kanagawa, Japan

4Sonaresearch Co., Ltd., Kanagawa, Japan tokuhiro@ic.kanagawa-it.ac.jp

Abstract The new type pickup using piezoelectric elements for the acoustic guitar named “Guitar Body Pickup” was invented and have patented in the United States and Japan basing on the studies by both Sonaresearch Co., Ltd. and the Next Generation Music Sound System Research Projects in the Kanagawa Institute of Technology. All acoustic guitarists have been waiting for the appearance of the new and original pickups, which can make similar to real guitar sounds than commercially available pickups on the market now. It is the Guitar Body Pickup. In this paper, experiences to compare with the spectrum of GBP outputs and usage of the playing and hearing test of the Guitar Body Pickup are shown under various conditions of changing positions to attach on the guitar body using the 3 different types of the guitar. As results of the experiment and usage of the playing and hearing tests, the Body Guitar Pickup has the suitable positions to attach where are near “Front” and are not over the braces, so the Guitar Body Pickup is blessed with good performance and is found to be fully answered the expectations of guitarists.

Keywords: Guitar Body Pickup, Acoustic Guitar, Eleaco , Piezoelectric Elements, Force Sensor, Force Mode Pickup

Acrylic pedestal

Acrylic bar

Fig.1 Inner cross section (a) and Photo(b) of FMP

Screw for adjusting height

Force ModePickup

Upper case

Output connector

Center plate

Piezo element

Piezo element

Bottom case section (a)ottom case

Pieele

Piele

Upper ccasea

Outpuconnec

Centplat

ezo

iement

ezoment

iezoement

Top bar p p

(a) F

rr (b)

Bolt

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人間工学　第49巻　特別号

3. Guitar Body Pickup(GBP) After 10 years from the production of FMP, the GBP

was finally completed and produced. In Fig.2, the photo and the inner cross section of GBP are shown. The GBP is composed of the sensor mounting member, the adjusting screw, the top arm, the bottom arm, the output phone jack(1/4 inch) and the blastomeric intermediate member. And the principle of picking up the vibration of the guitar top plate is same as FMP.

It is important to determine the material of the silicone cover shown in Fig.2 and the attaching position of GBP on the top plate of the guitar. It can be easily estimated that the optimal position are different on the top plate of the different types of the guitar.

4. Reproducible Plucking Equipment There is no reproducibility in the experiment of the

guitar sound because of the plucking. The guitar string cannot be plucked exactly using the same strength, angle, speed and direction as before even by a professional guitarist. So we made the Reproducible Plucking Equipment shown in Fig.3.

This equipment is composed of 4 vices which can adjust the 3 dimensional positions and the silicone finger which has same shape, nail, hardness and

elasticity as one of the author’s finger shown in Fig.3. The silicone finger can pluck the string by a circular rotation in synchronization with the acrylic disc which is rotated by the leveling line and the falling weight.

The output signal of GBP is connected directly to Multi Data Station DS-0931 manufactured by Ono Sokki in which FFT spectrums are calculated by the Digital Signal Processing in real time. The output terminal of the acceleration pickup Type4393 B & K is connected to the charge amplifier CH1200 manufactured by Ono Sokki. The Output of the charge amplifier is connected to the input of DS-0931. The emitted sounds from the guitar body at the near position of the bottom and a sound hole are recorded in two PCs(OS:WindowsXP(32bit) and Windows7 (64bit), each SONY VAIO) by the condenser microphone C-800 manufactured by SONY.

5. Bracing of 3 Different Types of Guitars Three types of the guitar which were the classic, the

flamenco and the acoustic guitars were used in the experiment of GBP. The photo of the Flamenco guitar(TAMURA C30, 1972) set to the reproducible plucking equipment can be seen in Fig.3. The acoustic guitar is YAMAHA FG750s. From outside and inside, bracing photos of the classic guitar(RYOJI MASTUOKA M40) are showed in Fig.4. Top plate of Classic and Acoustic guitar is made of German Spruce and Flamenco guitar is made of Red Cedar.

Spring

guitabrac

Spring

Knob

Knob

Silicone cover

Guitar body

Guitar top plate

Guitar body sides

Top arm

Back arm

Sensor member

Sensor mountingmember

plate

Vibrationtransmitter

Guitar back plate

Adjusting screw

Fig.2 Photo and the inner cross section of GBP attached to the Guitar.

Blastometricitermediate member

Output phone jack (1/4 inch)

Fig 2 Photo and the inner cross

Output phone jack(1/4 inch)

VtraTop bracing

Back bracing

Falling weight

Siliconefinger

Fig.3 Reproducible Plucking Equipment and GBP

Acceleration pickup

GBP

7--F

2--B1--B

7--B

2--F1--F

Control rod

Leveling lineAcrylic disc

Fig.4 Bracing Photos taken from Inside and Outside of Classic Guitar(RYOJI MASTUOKA M40)

Outside Inside

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F. Author

Bracing of the guitar is an important component that affects the sound quality by the placing, the material and the shape. Top plates, etc., with the material of the other members, the shape and arrangement of the bracing must be fine-tune.

Fig.5 shows the photo of the bracings of 3 guitars, which are (A)Classic Guitar, (B)Flamenco Guitar and (C)Acoustic Guitar. Those photos were taken using a strong bright light of the Neo-halogen lamp(500W) manufactured by TOSHIBA.

The attaching positions and position names of the top plate where GBP was attached are shown in Fig.5. Those attaching positions were determined in consideration the usability and the bracing position. The character “F” in the position name means the Front and “B” means the Back. Bracings of the classic and flamenco guitar are almost symmetrical, but the acoustic guitar is not symmetrically as shown in Fig.5(C).

6. Determination of Setting Position for GBP It is clear that different guitars have different optimal

setting positions of GBP. Two experiments to determine the suitable position for playing the guitar with GBP were performed. One is the way to use the power spectrum of outputs from GBP, and the other is the way to evaluate the amplified sounds from the speaker.

The power spectrum of GBP outputs for attaching

position 1B on the classic guitar is shown in Fig.6. In Fig.6, the line of None means the natural sound of the guitar and numbers of 1 7 means the attaching position of GBP shown in Fig.5.

In the Fig.6, it can be found that the spectrum envelope at 2B is smoother and higher value than other position. So the best setting position in 1B 7B are founded to be 2B. But the spectrum value at 2B is smaller than real guitar sound in the frequency domain over 1.5[kHz]. At all positions shown in Fig.5, by checking spectrums shown as examples in Fig.6, the suitable position to attach GBP on the guitar are chosen and shown in Table 1.

The power spectrums of four outputs (Microphone on the Guitar Hale, Microphone near out on the bottom of the guitar, Accelerator and GBP) from the Acoustic guitar at positions 10F and 14B are shown in Fig.15. From Fig.7, the 10F is better position than the 14B comparing spectrums on high frequency range using the plucked open 1st, 3rd and 5th strings.

From Table2, it is found that suitable positions for GBP are biased to “Front” of the all guitar body.

Classic Flamenco Acoustic optimal position

2B,3F

5F,6F,7F

10F,11F,12F

1B 1F

B 2B

2F 3B

F 3F B 4B

7B

FB

4F

6B

5F B F5B

6B66FF

7B7FF

(A)Classic Guitar

1B 1F

2B

2FF

3B 3FF

4B

7B

4FF

6B

5FF 5B 6FF

7FF

(B)Flamenco Guitar

1B 1F

4B 4FF

7B 7FF

10B 10F

13F 13F13B 15B

13B13B15B

15F

(C)Acoustic Guitar

D i i f S i P i i f

( )Fig.5 Attaching Positions of GBP

Fig.7 Power Spectrum of Four Outputs from Acoustic guitar

-120

-100

-80

-60

-40

-20

0 1 2 3 4 5 6 7 8

Mic.Hall

Mic.Out

Acc.

GBP

-120

-100

-80

-60

-40

-20

0 1 2 3 4 5 6 7 8

Mic. HallMic.OutAcc.GBP

rum of Four Outputs from A2 3 4 5 6

→Frequency[kHz]

2 3 4 5 6→Frequency[kHz]

GBP: Position 14B

GBP: Position 10F

20

-100

-80

-60

-40

-20

→Po

wer

Spe

ctru

m[d

B]

-12

-10

-8

-6

-4

-2

-12→→

Pow

er S

pect

rum

[dB

]

-120

-100

-80

-60

-40

-20

0 1 2 3 4 5 6 7 8 9 10

None 1

2 3

4 5

6 7

Fig.6 Power Spectrum of GBP Output for Attaching Position on Classic guitar

→Frequency[kHz]

-12

-10

-8

-6

-4

-2

→Po

wer

spe

ctru

m[d

B]

GBP:Position 1B-7B

Table1 Suitable Positions decided by Spectrum

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7. Playing and Hearing Test of GBP The final experiment of GBP is the playing and

hearing test by 3 guitarists whose experience periods of the electric guitar are 3, 6, and 7 years. In Fig.8, the photo of playing and hearing test of the sound from the L1™ model I system speaker manufactured by BOSE is shown.

Guitarists evaluate the speaker sound comparing the natural sound of the guitar evaluated 7 using the rating scale method with 7 ranks. The sound using the plucked open 1st, 3rd and 5th strings with the pick were used.

The averages of evaluated values of GBP’s sound by guitarists were arranged in descending order in Table2 and showed the evaluated top three positions for each guitar in Table3.

In the top six of Table2, the character “F” can be seen in great quantity. And it is the fact that Table3 is similar with Table1(underlined positions were same). Also the position with the character “B” had generally low evaluations.

This is the reason why the positions of “B” were placed near the bracings with the specific modal frequency, but the position of “F” were placed near the side plate of the guitar which vibrate with all modes of the top plate.

Classic Flamenco Acoustic optimal position

7B,6F,4F

1F,5F,5B

1F,10F,11F

8. Modal Analysis of Guitar with FEM Optimum attaching positions of GBP are different

from the type, the material and the internal structure of guitar. Especially, the bracing placement will affect the mode shape of the top plate and all modes will affect the output of the GBP.

Fig.9 shows the mode shape of the classic guitar (RYOJI MASTUOKA M40) from 1st to 4th mode with the modal frequency using the FEM(Finite Element Method) software “Abaqus” manufactured by SGI Japan,Ltd. The tail part of the 2nd mode in Fig.8 has become a node of modes, so the attaching places of the GBP should be avoided.

Using shapes from the 1st to the higher order modes, the GBP attaching position on the top plate of the guitar is obtained so that nodes may be placed in a location that does not exist in all modes.

9. Conclusion Experiences and usage of the playing and hearing

test of the Guitar Body Pickup are examined under various conditions. As results of experiments and tests, the Body Guitar Pickup has the suitable positions to attach where are near “Front” and are not over the braces, so the Body Guitar Pickup is blessed with good performance and is found to be fully answered the expectations of guitarists.

References [1]OGAWA S. Guitar Dictionary , , Ongaku no

Tomo sha Corporation(1954)[in Japnese] [2]http://www13.plala.or.jp/yutorist/06yomoyama/

guitar02.htm[in Japnese] [3]http://www.guitarra.co.jp/cl02_01/detail -7.html

[in Japnese] [4]http://www.yamahiko.info/[in English and Japanes] [5]http://www.kait-acoustics.jp/[in Japnese] [6]TOKUHIRO I.,OSHIMA N.,YAMAYA K.:Plate Vibration and Sounds of Acoustic Guitar-Application of Force Mode Pick-up to Guitar-, MA99-11,

Acoustical Society of Japan, 1-9, 1999[in Japnese] [7] TOKUHIRO I., KAMATA K., NISHIGUCHI I.

and YAMAYA K.:The Guitar Body Pickup using Piezoelectric Elements for the Acoustic Guitar,The 5th AEG, JES Meeting on Auditory ErgonomicsAEG2011-04,17-24,2011[in English]

Fig.9 Mode Shape of Classic Guitar by FEM

f2=308[Hz] f1=186[Hz] f1st Mode shape 2nd Mode shape

3rd Mode shape f3=341[Hz]

4th Mode shape f4=498[Hz] Table 2 Evaluated Values of GBP’s Sound

low middle high balance low middle high balance low middle high balance1F 3.33 4.33 2.67 3.33 4.33 4.67 3.67 4.33 2.67 2.67 3.33 2.33 3.47

10F 3.67 3.67 3.67 3.67 3.00 3.00 3.33 2.67 3.00 3.33 3.33 3.33 3.3111F 3.33 3.33 3.67 3.33 2.67 3.33 2.67 2.67 4.00 3.33 3.33 3.67 3.2811B 3.33 3.33 3.33 3.33 3.33 3.33 3.67 3.67 2.67 3.00 3.00 3.00 3.2512F 3.33 3.67 3.00 3.00 3.33 3.00 3.00 3.00 3.33 3.67 3.33 3.33 3.254F 3.33 3.33 3.00 3.33 3.00 3.67 3.00 3.33 3.00 3.33 3.00 3.00 3.192B 2.67 3.00 3.00 3.00 3.67 3.67 3.33 3.67 2.33 2.67 2.33 2.33 2.97

1st string 3rd string 5th stringaverageposition

Table 3 Suitable Position by Playing Test

Speaker

Amplifier

GBP Evaluating sheet

T bl 3 S it bl P iti b Pl i T t

Fig.8 Hearing Test of GBP using the L1™ model I system of BOSE

attbrpeex

Classic Guitar (RYOJI MASTUOKA M40)

Woofer BOSEL1™ model I system

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