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String Termination experiment
the effect of duplexes on the sound

2004

 

 W hat I wanted to determine was the influence of the string termination on the sound. So I constructed a very simple monochord, made of a spruce board, 2 grand piano agraffes, hitch pins, tuning pins and a brass string, as seen below:

The agraffes [1] form the main terminations of the speaking length.
I used two mobile wooden blocks [2], each with an iron nail (with the head cut) placed on it's top for providing the secondary termination point after the agraffes. This point is set higher, so the string segment between it and agraffe is at an angle to the speaking length. I have also used paper wedges [3] for muting the string segments (white and orange in the picture).

 

 T he following set-ups were used :

Situation 1 = secondary terminations (wooden pieces) set such as to form 2 duplexes in tune with the speaking length (2 octaves above it's frequency)

Situation 2 = secondary terminations set such as to form very short free string segments, at no more than 1 cm from the agraffes.

Situation 3 = string segments between agraffes and secondary terminations (duplexes) muted with some paper strips (as shown in the picture).

Situation 4 = no secondary terminations and waste lengths muted.

 

 O bservations:

1. The worst sustain and tone quality has been achieved when the secondary terminations (wooden pieces) were missing and waste lengths were muted, because the string segments after the agraffes formed a very shallow angle to the speking length (Situation 4). An angle seems to be necessary to achieve a good string termination.

2. The second worst was with the secondary terminations in place and duplexes
muted (Situation 3).

3. The best sustain and tone quality was achieved when the string segments between agraffes and secondary terminations were not muted => Situations 1  and 2.

There were different tone qualities:
Situation 1 had a good sound, with an audible ringing from the duplexes, sounding 2 octaves higher.
Situation 2 had also a good and open sound, but without the extra ringing (harmonics) heard.

 

 C onclusions:

I can't really say which set-up I prefer, among these two (sit. 1 & 2). they both sound good, but different, which becomes a matter of taste. Further experimenting is needed.

The main conclusion that I drew is that the secondary termination is crucial for the sustain of the string, because a lot of energy bleeds through the agraffe. Touching the duplex segment (both when tuned and when kept very short - Situations 1 & 2) with a finger and plucking the speaking length produced much less sustain and overtones than without touching it.

Note: this experiment doesn't exactly reproduce the way a string is fixed in a piano, because I used 2 agraffes instead of 1 agraffe and 2 bridge pins.

You can see how the conclusions of this experiment were applied to a Steinway O grand piano here.

© Calin - Do not reproduce or distribute without my written consent.

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© Calin
Last update: 14.10.2006