German Piano Centres

An Introduction to Acoustic Design.

The acoustic piano has evolved by the twining of manufacturing skills with the science of acoustic tone.  

Manufacturing skills are acquired through generations of working experience. This experience is nearly always past down from the master craftsman and  given freely, into the hands of the apprentice.

 

And so it is here that we begin our brief report on acoustic design. What is detailed below is just the ‘tip of the iceberg’, however we hope that the following information will give you an insight into the way that quality pianos are made.

For a stringed instrument to produce an acoustic tone it must have three main parts.

i ) The first is the instrument's string. Once tensioned and struck it will resonate.  

ii) The second part of the production is the Bridge. It is the job of the bridge to transfer efficiently as possible, the sound of the string onto the soundboard.  

iii) The third is the soundboard and this part of the trio must amplify the sound of the resonating string.

  

These three points might at first sight seem relatively simple. However I will now go on to show that in life many things are not quite as simple as they first seem.

We begin with the third part of the trio….The Soundboard.

The reason that a good acoustic tone can sound so ‘alive’ is partially due to the soundboard. On a piano, this soundboard has to amplify frequencies that resonate from below 30Hz to over 4000Hz. So it is here that we have our first quandary ! A tone that is produced at the low end of the musical scale must have a reasonable volume and a good length of sustain. To accommodate this low frequency the sound board must resonate fairly freely i.e. be of low density. If we go up to the high end of the musical scale the requirements are completely opposite. To produce a clear sweet tone above  7thA the sound board must be held absolutely rigid i.e. be of high density.

One way to accommodate these varying requirements of density is of course to give the soundboard some curvature. So it is here that the experience of the designer and master craftsman comes into play. They will assemble the soundboard to produce a convex shape…..sounds simple, but it is not. and this is because we have not yet considered the material that the soundboard should be made of. Our options are few, but which ever material we choose we will find ourselves back to where we were just a moment ago ……‘Density’ !

Another very important aspect of design is that there should be an evenness (balance of tone) throughout the entire range of the keyboard. Some pianos, whether they are acoustic or digital, inherently have poor ‘balance’. On the digital side one can point the accusing finger at design, or at the use of low quality parts. On the acoustic side we have to reluctantly point the finger at mother nature ! Spruce is quite naturally ‘a product of nature’ ! A tree’s timbers, if grown in sandy soil will be denser than if grown in wet clay. It is because of this natural variation in density that some piano manufacturers are today seeking the assistance of modern technology to help create a better tonal balance. This can be done by the inclusion in the design spec. of an ‘Acoustically Laminated’ Soundboard.

Many years of acoustic research and development are needed to produce the type of soundboard. However once its fundamentals are understood and mastered it can help to give a very good level of tonal balance.

Now we come to the second part of the trio….The Bridge

As mentioned earlier it is the job of the bridge, or more precisely two bridges ( one for the tenor - treble and one for the bass ) to efficiently transfer the tone from the strings to the soundboard. This task is quite easy to accomplish. A skilled craftsmen can easily shape the underside of a bridge so that it freely contacts the curved soundboard throughout its entire length. The tenor - treble bridge is often called the long bridge and this is because it almost spans the entire width of an upright piano.

 

Number two quandary ! Where to place the bridge in relationship to the crown of the soundboard ( highest point ). Just for a moment, we must return to the soundboard, because in giving the soundboard a convex shape we have also given it a crown. Although this crown can be of use because it can help ‘colour’ the sound. If the bridge is placed directly on the crown then the tone produced will be shriller than if it were placed a little way below the crown.

So now we have worked our way back to the piano string.

To understand how a tensioned string resonates we must thank and use Brook Taylor's (1685 - 1731) established formula for calculating frequency in Hz

Fr = Length sq x Diameter Sq x Tensioned Sq x 3.14 x Specific Weight

                                               9.81

9.81 is the constant of gravity

For acoustic design, the shown formula acts just as a basis…..just the beginning. We must also take into consideration other factors that will come into play as we proceed with our calculations.

We must think about the breaking point of high tensile steel and how the string will be held in place at its extremities. The stiffness of a string is also an important factor because it too affects ' tone colour' by way of overtones (partials) that relate to the string's fundamental frequency.

We can now see from this introduction that a refined acoustic tone is not a matter of chance!

We hope that our web site has been informative and that your new piano will Inspire, Excite and Delight you and your friends for many years to come.

( Design text written by Robert Gregory )