String Leveling 101! (a.k.a. String Mating)

What is String Leveling?

String leveling is the process of adjusting the strings in a grand or upright piano so that all strings in a unison are struck by the hammer at the exact same time. This ensures consistent tone, power, and resonance. It's not something you do at every appointment. Rather, it’s typically reserved for:

• Full action reconditioning or rebuilding jobs
  
  

• Pianos that have just had their hammers surfaced
  
  

• Concert prep work
  
  

• Instances where the tuning is relatively close, and spacing has already been addressed
  
  

Tools You’ll Need

1. String Hook (T-handle puller): Used to lift individual strings.
   
2. Wooden Shank or Dowel: Used to tap strings downward.
   
3. File or Sandpaper: Used to carefully reshape the hammer if needed.
   
   

The Basic Procedure

• Prepare the Action: Remove the fallboard, cheek blocks, and key slip. Add a strip of felt under the knuckles so you can block the hammers against the strings without tripping let-off.
  
• Lift the Hammer: Gently press the jack upward until the hammer makes contact with the strings. Use the sostenuto or damper pedal to lift the dampers.
  
• Test the Strings: Pluck each string in the unison. If one rings out more than the others, it’s too high. If it’s muted or doesn’t ring, it may be too low.
  
• Make Adjustments:
  
  
  • To raise a string: Use the string hook about 1–2 inches past the termination point (near the pressure bar or agraffe) and carefully pull upwards.
    
    
  • To lower a string: Tap it down using the wooden shank and a light strike from your tuning hammer.
    
    
  • If needed: Slightly file the hammer to better match string height.
    
    

*Pro Tip: Be careful not to get your face too close—string hooks can slip and snap back with surprising force. That’s the near-tooth-breaking part.

Upright Pianos

In uprights, string leveling is often easier. You simply press the hammer up to the strings, lift the damper pedal, and test by plucking. You typically won’t use a string hook—just tap the string down or lightly reshape the hammer.

A Word on Effectiveness

Pulling strings upward or filing hammers usually gives longer-lasting results than tapping strings down. So when in doubt, lift the others to match the highest string. After adjusting, always tune again.

When to Use This Skill

You probably won’t use string leveling on most tuning jobs. But it’s a powerful tool when:

• There's a weird zing or overtone
  
  

• Tone feels thin or inconsistent
  
  

• You’re performing high-level voicing or tonal refinement
  
  

• You're prepping a concert instrument or doing full rebuild work
  
  

It takes time. On a full piano, expect about four hours for tuning, string leveling, and a follow-up touch-up. That’s not a small service—often bundled into larger packages or restorations.

Final Thoughts

This isn’t a beginner task—but it’s a vital skill in your piano technician toolbox. You’ll be surprised at how much fuller and more beautiful a piano sounds after proper string mating. It’s the kind of subtle change that transforms a good piano into a great one.