TuningLedger Field Guide
Piano Pitch Raise Service Log
How acoustic piano soundboard tension dictactes double-pass tunings when pitch drifts ±15 cents from A440.
The Physics of Soundboard Crown and String Tension
An acoustic piano soundboard is an arched wooden diaphragm of spruce crowned upward against the strings. The 220+ steel and copper-wound strings exert roughly 35,000 to 40,000 pounds (18 to 20 tons) of aggregate downbearing tension.
When a piano sits unserviced across multiple humid summers and dry winters, the soundboard wood swells and contracts. As moisture leaves the spruce in winter, the crown flattens, reducing string tension and dropping the pitch—often by 15, 25, or even 50 cents.
If a technician attempts to pull a flat piano directly to A440 in a single fine pass, the increasing tension of the bass and tenor strings compresses the soundboard further, causing the treble strings tuned earlier in the hour to immediately sag flat again.
The ±15 Cents Pitch Raise Threshold
In professional piano technology (PTG standards), an initial drift of ≥ ±15 cents represents the definitive threshold where a single-pass tuning will fail to hold pitch stability.
Why 15 cents?
Pulling an entire piano up by 15 cents adds approximately 300 to 500 pounds of new downbearing force onto the bridge. A quick overpull pass (roughly 25–33% beyond target pitch in the tenor and treble) is required to pre-stretch the strings and compress the soundboard before fine tuning can begin.
TuningLedger bakes this exact standard into its pricing and service workflow:
- Deterministic Quoting: Entering an initial offset of ±15 cents automatically adds a standard$45.00 pitch-raise surcharge and extends the bench duration by 30 minutes.
- Bench Logging: During closeout, the technician records initial cents drift, final target Hz (e.g. 440.0 Hz), and room relative humidity.
- Automated Client Care Notes: The on-device engine automatically generates transparent client explanations: “Due to significant pitch drift, a double-pass rough pull was completed. Because strings and soundboard settle under new tension, the piano will drift faster than usual over the next 90–120 days.”
Soundboard Climate & Pinblock Health
A pitch raise is only as stable as the wood anchoring the strings. TuningLedger requires logging two critical environmental factors during service closeout:
Relative Humidity (% RH)
Ideal room humidity for acoustic pianos is 40% to 50% RH. If humidity falls below 30% (winter heating dry-out) or spikes above 65% (summer humidity), soundboard wood shrinkage risks cracking bridges and loosening tuning pins. TuningLedger shortens seasonal recall suggestions to 120 days when extreme humidity is logged.
Pinblock Torque Rating
Tuning pins are held in laminated hard maple pinblocks by friction. Pins holding tight torque (70–90 in-lb) hold pitch through vigorous playing. Loose pins (< 50 in-lb) require CA glue treatment or oversized pins. TuningLedger tags loose pinblocks with high instability warnings.
Built for Fast Bench Documentation
Instead of scribbling cents drift on paper invoices or losing records in messy email threads, TuningLedger keeps the entire instrument lifecycle on your mobile phone or tablet:
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