Tools · TOOL · REV 2026-10-06
Sound pressure calculator
Level at a new distance from a known level at a known distance. Free field, point source, and the room is absent from the equation.
What this gate is
Lp2 = Lp1 + 20 log₁₀(r1 / r2).
It is not a cabinet sensitivity unless your input already is. No directivity, no array, no reflection, no air.
What is published now
The equation is visible
The calculator writes the law above the result so it can be checked.
Limits are written
Each tool names what it ignores: the room, the code, or the manufacturer’s sheet.
An editable example
The starting values are for understanding. Change them to your project, then discard the result when a measurement arrives.
When to open this gate
Before a meeting
To turn a verbal dispute into a calculation whose assumptions everyone can see.
Not in a tender
A result from this page is not pasted into a bill of quantities.
How to read the subject
- 01
96 dB at 1 m becomes about 84 dB at 4 m, then about 72 at 16 m, in free field only.
- 02
Read the warning under the result. If the assumption does not apply, stop.
- 03
Replace any textbook coefficient with a laboratory sheet or a measurement.
- 04
Ask it again inside the project brief: what is success, and in which room condition?
What this gate does not do
Copying the figure
A figure without the volume, the distance, or the condition is meaningless in a contract.
Mixing tools
Adding decibels is not RT60, and throw ratio is not brightness.
SPL
Level at a distance
Lp2 = Lp1 + 20 log₁₀(r1 / r2). A point source in a free field. It ignores the room, directivity, arrays, air absorption, and the sum of more than one source.
A preliminary figure for understanding and comparison. Not a measurement, not an acoustic model, and not something to paste into a specification or a quotation.
Questions designers and owners ask
Is the result approved?
No. It is a preliminary calculation on a stated assumption.
Why are there no product numbers?
Because a product’s performance is copied from its test report, not from an article.
Can I save the calculation?
Copy the result into the study brief. The page does not send it to a server.
Technical sources
- The law written inside the tool
The law written inside the tool
- ISO 3382-1 and IEC 60268-16 when the subject is the room
ISO 3382-1 and IEC 60268-16 when the subject is the room
- The local code and the manufacturer’s sheet
The local code and the manufacturer’s sheet
Last editorial review: 2026-10-06. Review means the text was checked, not that a project was measured.
Turn the question into a brief
A study starts from room volume, use, and existing condition, not from a product name. Fill the brief and copy it.
Project study form