The Gertz Tension Resonator

FROM THE MUSIC TRADE REVIEW, VOL 40, NO. 9, MARCH 4, 1905, PG 21

Secures Patent This Week Whereby the Tension on the Rim Supporting the Sounding Board of the Piano is Easily Adjusted and the Adjustment Maintained Regardless of Atmospheric Changes.

                        Washington D.C., March 1, 1905.

An improvement patent, bearing the No. 783,781, was this week issued by the Patent Office to Richard W. Gertz, of the Mason & Hamlin Co., Boston, Mass.  It relates to pianos, and has for its object to provide a novel construction whereby the tension of the rim supporting the sounding board may be easily adjusted and the adjustment maintained regardless of the hydrostatic changes in the atmosphere.

In patent No. 658,985, granted to Emil A. Gertz and R.W. Gertz, is illustrated and described a piano in which the rim to which  the sounding board is secured, as usual, is maintained at the proper tension by means of tension members, which pass through the rim and have suitable heads on their ends which engage the outside of the rim (outside of the inner rim – Vince).  The rim in said patent is constructed of a plurality of layers of wood placed with the grain running longitudinally thereof, and therefore the strain on the tension members is across the grain rather than in the direction of the length of the grain.

In order to keep the sounding board under proper tension, it is FREQUENTLY NECESSARY to tighten the tension members to such an extent that the heads on the ends of the tension members are apt to crush the grain of the wood against which they lie and to be drawn into the rim to some extent (Emphasis mine. We are told not to ever tighten those tension members).  The result is especially apt to occur whenever the rim swells any, due to moisture in the atmosphere or otherwise, for it is a well known fact that whenever wood swells or shrinks, the swelling or shrinkage takes place transversely to the grain rather than longitudinally thereof, and any swelling or shrinkage of the rim of the piano therefore causes it to increase or diminish in thickness or width.  Such increase or diminution in the thickness or width of the rim not only operates to increase or vary the tension on the tension members, but frequently causes the flat heads on the end thereof to become embedded in the rim.  As soon as this occurs the tension on the rim is reduced, and it becomes necessary to readjust the tension members (Again, my emphasis) in order to bring the sounding board up to its proper pitch.  It is to obviate this difficulty and to provide a construction in which the head on the end of the tension member will not become embedded in the wood of the rim under any circumstances that Mr. Gertz made his present invention.  This object is accomplished by providing the ends of the tension members with tapering heads, which are received in correspondingly shaped recesses in the rim.  The taper on the heads, while sufficient to prevent the latter from being pulled through the rim, is such that the strain on the tension members is transmitted to the wood substantially in a direction parallel to the direction of the grain of the wood.  With this construction the strain on the tension members will not crush the wood, as is the case where the pressure of the head comes transversely to the grain rather than longitudinally thereof, and therefore there is no danger of the heads becoming embedded in the rim and the tension on the latter relaxed due either to swelling of the rim or to any other cause.

END OF ARTICLE

So it appears that any Mason & Hamlin grand piano made prior to 1905 with the tension resonator present should be checked for tightness of the tension members, but those made after 1905 shouldn’t be. . .