Traditionally steel string acoustic guitars have used hard maple or rosewood for bridge patches.
Conventional wisdom asserts that a hard maple bridge patch sounds “brighter” than a similar instrument with a “warmer” sounding rosewood bridge patch.
Rosewood is prefered by some for its added hardness over the maple because it reduces the wear that occurs over time from the ball ends of the strings. While some builders eschew rosewood due to its propensity to crack along the grain and its tendency to splinter when drilling.
This winter I did a deep dive into bridge patches, their sizing, materials and into alternatives and what i found convinced me that there were better woods for the job than the traditional materials that were probably chosen because they were cut-offs from materials already being used in the production of the guitar.
By searching reference works and browsing internet forums, I was able to come up with the following information on Martin instruments which is the style we build in our SIMSCal classes.
Because I was able to source resonably priced material, we chose to move forward with Persimmon (white ebony) as the material of choice for the bridge patches in the OM style guitars that our students are building in the 2025 class.
A sample of Indian rosewood thicknessed and sized for the OM bridge patch weighed in at 15.2 grams. Our Persimmon bridge patch only 9 grams. This weight saving and greater elasticity should improve the responsivness of our students guitars and coupled with the increased modulus of rupture and crush strength should also give their instruments a fighting chance at never needing a replacement bridge patch.
Sample Bridge Patch Thickness and Size Info
1936 D-18….. .078
1936 00-40H….. .078
1936 D-28….. .078
1939 D-18….. .078
1943 00-18….. .087
1964 D-28….. .097
1966 D-28….. .097
1968 D-28….. .096
1977 HD-28….. .098
Early OM’s had 1″ plates, but that shortly changed to 1 3/8″ (about the same footprint as the belly bridge).
Large Indian rosewood plates came in 1969
The 1 3/8″ maple plate first reappeared on the HD-28 in 1976.
Small maple plates were used on some limited editions in the 1980’s.
The D-45 got a 2″ maple plate in 1986.
The rest got a 2″ maple plate in 1988.
The GE Series got 1 11/16″ maple plates when it was introduced in 1999.
The Authentics were the first to get tucked 1 3/8″ plates since the 1940’s.
Wood Characteristics
Hard maple, sugar maple, rock maple
Scientific Name: Acer saccharum
Average Dried Weight: 44.0 lbs/ft3 (705 kg/m3)
Specific Gravity (Basic, 12% MC): .56, .71
Janka Hardness: 1,450 lbf (6,450 N)
Modulus of Rupture: 15,800 lbf/in2(109.0 MPa) Elastic Modulus: 1,830,000 lbf/in2(12.62 GPa) Crushing Strength: 7,830 lbf/in2 (54.0 MPa) Shrinkage: Radial: 4.8%, Tangential: 9.9%, Volumetric: 14.7%, T/R Ratio: 1.9
East Indian Rosewood
Scientific Name: Dalbergia latifolia
Average Dried Weight: 53.4 lbs/ft3 (855 kg/m3)
Specific Gravity (Basic, 12% MC): 0.73, 0.86
Janka Hardness: 2,350 lbf (10,440 N)
Modulus of Rupture: 16,680 lbf/in2 (115.0 MPa) Elastic Modulus: 1,783,000 lbf/in2 (12.30 GPa) Crushing Strength: 8,890 lbf/in2 (61.3 MPa) Shrinkage: Radial: 2.6%, Tangential: 5.9%, Volumetric: 8.6%, T/R Ratio: 2.3
Persimmon (Diospyros virginiana)
Common Name(s): Persimmon, White Ebony
Scientific Name: Diospyros virginiana
Average Dried Weight: 52 lbs/ft3 (835 kg/m3)
Specific Gravity (Basic, 12% MC): .74, .83
Janka Hardness: 2,300 lbf (10,230 N)
Modulus of Rupture: 17,700 lbf/in2 (122.1 MPa) Elastic Modulus: 2,010,000 lbf/in2 (13.86 GPa) Crushing Strength: 9,170 lbf/in2 (63.2 MPa) Shrinkage: Radial: 7.9%, Tangential: 11.2%, Volumetric: 19.1%, T/R Ratio: 1.4