The Acoustics of Voicing: Analyzing the Spectral Effects of the Voicing Process

Updated: Jun 16

Part 2: Building Power and Core

By Jason Cassel

Dynamic Range

In Part 1 of this series, we observed how changes in dynamic level effect which partials are engaged, and thus, the timbre. If the piano is properly regulated and voiced, the instrument should allow for controlled use of all dynamic ranges. In his book Under the Lid, Stephen Brady explains, “The task of the piano hammer is to transfer energy from the action to the strings, and to do so in such a way that the overtone series of the string develops naturally – that is, with the various string partials in balance: A powerful fundamental sound strengthened and made more interesting by middle partials and the sparkle and brilliance of higher partials.” In order to measure this control, I played the same note ten times – starting at the softest possible dynamic level and increasing each time until the highest possible dynamic level was reached. 

During this process, I listened to see if the dynamic level would reach its climax too early. For example, if the dynamic climax was reached on stroke 7 of 10, then improvement could be made. When this occurs, the Renner Technical Manual suggests deep needling the low shoulder (see Photo 1).

Deep needling the low shoulder.

Graph 1 shows the dynamic range of F4 played by a hard-pressed hammer at ten dynamic gradations before and after needling. Graph 2 shows this same dynamic range played by a soft-pressed hammer. The blue columns show the amplitudes before needling. The orange columns show the effects of the needling on the dynamic range. Again, I recognize the possibility for human error in these graphs as I was unable to utilize my “thumper” device. All the same, the graphs are still informative. (Note: The numbers above each column are for comparative use only, and are not indicative of any specific unit of measurement.)

Graph 1: Dynamic range before and after needling (hard-pressed hammer).

Graph 2: Dynamic range before and after needling (soft-pressed hammer).

Notice how in Graph 1, before voicing, the hard-pressed hammer quickly increased in its dynamic range and maxed out around stroke 8 of 10 (see the blue columns). However, after voicing, Graph 1 shows how the dynamic range increased more gradually – omitting the significant leaps in the lower dynamic levels, and even accessing softer dynamic levels than before (see the orange columns). Video 1 demonstrates this audibly: 

Graph 2 on the other hand, shows how the deep needling in the lower shoulder had little to no effect on the soft-pressed hammer (the blue and orange columns are basically the same). Any differences between the before and after columns could easily be attributed to human error. This might be expected, as manufacturers of soft-pressed hammers generally recommend the building of power and dynamic range through the use of hardening chemicals. The Steinway World-Wide Technical Reference Guide clarifies this, stating, “New York Steinway & Sons hammers [soft-pressed] are designed to use lacquer as a stiffening agent, the time-tested method by which tone is built.” Later, the Technical Reference Guide addresses Hamburg Steinway & Sons hammers, which are more hard-pressed in their design, stating, “needling [in the shoulder] can gain power and brilliance for the tone while increasing the elasticity for more dynamics at the same time! The more elastic the felt is, the more dynamically variable the tone will be.” 

Building Power with Needling 

In Part 1 of this series, we defined tone as having three parts: 

  1. Low Partials: Approx. Partials 1-9 – Defining the Core or Power of the Tone 

  2. Middle Partials: Approx. partials 10-20 – Defining the Body or Presence of the Tone 

  3. High Partials: Approx. partials 21+ – Defining the Color or Attack of the Tone (as determined by their absence or presence)  

Notice how the core and power of the tone are established in the first 1-9 partials. In their eBook Complete Piano Voicing, Jim Busby and Vincent Mrykalo reference the need to develop the right “core” sound. In this process they explain, “getting more core sound usually means opening up (needling) the shoulders.” This high shoulder region is shown in Photo 2. In his book The Voice of the Piano, André Oorebeek clarifies this further, stating, “by creating an area with less tension the hammer will open up and become less stiff. The cushion that has now been created causes a sudden transformation of the partial spectrum because from that moment, lower partials become more pronounced.”

Needling the high shoulder.

Graph 3 shows the partial spectrum for F4 played by a hard-pressed hammer before and after needling in the high shoulder. Remember that the x-axis shows the partial number and the y-axis shows the volume of each partial at that moment. The blue line represents the tone before needling. The orange line represents the tone after needling.

Graph 3: Needling high shoulder (hard-pressed hammer).

With this in mind, we can look at the graph and see that true to Oorebeek’s words, the first 8 partials (which constitute the core and power of the tone) were slightly increased. Video 2 demonstrates this aurally:

With this observation, it is important to add that the Renner Technical Manual warns, “Proceed with caution [when deep needling in the high shoulder], one stitch at a time, checking often, and do as little as possible. Too much needling in this area will reduce the power.”

As a point of interest, the high shoulder needling made no significant measurable change in the partial spectrum for the soft-pressed hammer. 

Building Power with Lacquer

As mentioned, manufacturers of soft-pressed hammers generally recommend the use of hardening chemicals to build tone and power. Hard-pressed hammer manufacturers in contrast, do not recommend the use of hardening chemicals on their hammers. André Oorebeek explains, “The European style compression hammer is made mellower through voicing with needles, while the American style softer hammer is made harder through the use of lacquer… The lesson to be learned from this is that there are different methods of manufacturing hammers which call for different voicing treatments.”

In spite of these differences, the region of the hammer where these techniques are applied remains the same, as lacquer is generally applied to the shoulder of the hammer (see Photo 3). Thus, generally speaking, power and dynamic range are built in the shoulder, either through needling in hard-pressed hammers or by applying hardening chemicals to soft-pressed hammers. 

Where to apply lacquer to the shoulder.

Graph 4 shows the tonal spectrum for E2 played by a soft-pressed hammer before and after lacquer was applied and left to dry overnight. Similar to the hard-pressed hammer in Graph 3, the lower partials appear to be where the most significant changes occur, although a fair number of middle partials were also increased.

Graph 4: Lacquer to the shoulder before and after (soft-pressed hammer).

Video 3 presents a before and after recording: 

Note: There are varying ratios of lacquer solution. The solution used in this study was approximately 3:1 lacquer thinner and lacquer solution. 

Building Attack and Color with Keytop Solution 

While not a substitute for lacquer, a few drops of keytop solution (generally 1 keytop to 8 ounces of acetone) can be applied to the crown of soft-pressed hammers (see Photo 4). In this study, after 15 minutes, the hammer was played multiple times while moving the una corda pedal. This was done to break up the solution to avoid any unwanted noise. After some additional drying time, the recordings were made.

Where to apply keytop solution to the strike point.

Graph 5 shows the tonal spectrum for G4 before and after keytop solution was applied. Unlike the lacquer solution which brought out lower partials, the keytop solution dramatically increased the amplitudes of the middle and higher partials (which constitute the body, color and attack of the tone).

Graph 5: Keytop solution to the strike point (soft-pressed hammer).

This is demonstrated aurally in Video 4:

Conclusion of Part 2

From Part 2 of this study, we can observe that the core and power of the tone are established in the low partials (or the first 1-9 partials in the mid-range and bass). Additionally, it is clear that in both soft and hard-pressed hammers, the shoulder is where the most significant changes to the core and power of the tone are made. In our keytop example, we saw how adding chemicals to the crown of the hammer drastically increased the middle and higher partials – while leaving the lower partials relatively unchanged. In Part 3 of this series, we will discuss common techniques used to “voice down” a piano hammer and will focus primarily on needling in the crown and strike point. 


Baldassin, Rick. Selecting & Voicing the Renner Hammer. Scottsdale, AZ: Renner USA, 


Brady, Stephen H. Under the Lid: the Art & Craft of the Concert Piano Technician. 

Seattle: Byzantium Books, 2011.

Busby, Jim and Vincent Mrykalo. Complete Piano Voicing: Pragmatic, Intuitive and 

Inclusive. Piano Technician Tutorials, 2018.

Oorebeek, André. The Voice of the Piano: A Piano Technicians Definitive Guide to 

Voicing. Nanaimo, BC: Crescendo Publications, 2009.

Steinway & Sons. World-Wide Technical Reference Guide. New York: Steinway & 

Sons, 2017. 

Jason Cassel, RPT, M.A.

Brigham Young University - Salt Lake City, UT

Jason Cassel currently serves as a Piano Technician for the Brigham Young University School of Music. Before accepting this position, Jason Cassel graduated with an MA in Piano Technology from Florida State University – a distinction shared by only a dozen technicians in the nation. He earned his BM in Commercial Music from BYU while working as a student apprentice in the university’s piano shop. Jason has received training at the Steinway & Sons Factory in New York, the Mason & Hamlin Factory in Boston, and from Yamaha Pianos in California.

Jason is a Registered Piano Technician with the Piano Technicians Guild and has presented at local chapter meetings and attended various regional and national conventions. Many of his articles on piano technology have been published in the Piano Technicians Journal and his work on the revolutionary On Pitch DVD Series has been considered “an unprecedented tool to propel the next generation of fine tuners.” (Anne Garee – Former Head of Piano Technology at FSU)


Most of our photography was done by the talented ChiaYu Lee.

 To see more of his series from Heart One Pianos, visit his website. 

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