Check exposure and hearing protection

The SPL tab answers two questions the crew asks and nobody has the table for: how long can we stand at this level, and how much does this plug actually help. RoomSense shows both major rules side by side because they disagree, and shows protection after the derating the lab number never mentions.

Run the damage timer

1. Open the SPL tab and find Hearing Damage Timer.
2. Choose the weighting of your reading: dBA (the default and what most meters report) or dBC. With dBC selected the card shows the conversion it applies.
3. Enter the Current SPL level.
4. Read the two results:
   • NIOSH (3 dB) — 85 dB reference, 3 dB exchange rate: every 3 dB more halves the allowed time.
   • OSHA (5 dB) — 90 dB reference, 5 dB exchange rate: the more lenient regulatory rule.

Both are shown so you can quote whichever applies where you are — and see how far apart they are at a typical 103 dBA show.

Check hearing protection

The Hearing Protection card estimates the level behind a plug or muff.

1. Pick the HPD type: Foam plug (NRR 33), Earmuff (NRR 25), IEM (NRR 26), ACS Pro 15 (NRR 12), ACS Pro 20 (NRR 17) or Custom (ACS-style). Custom lets you enter per-band attenuation in dB.
2. Read Effective SPL (dBA) behind the device, and the NIOSH (3 dB) — protected and OSHA (5 dB) — protected exposure times.

The rating is derated per NIOSH because real-world fit is worse than the laboratory fit, so the actual protection is lower than the number on the box. The card says so: NIOSH-derated estimate. Actual protection depends on fit. If the NRR is too low for the level, a warning says NIOSH derating predicts no usable protection and suggests Custom mode for a per-band look.

The other SPL cards

• Inverse Square Law — level at a new distance from a reference reading.
• Back-Row Level — what the last row hears, distance loss included.
• Source Combiner — the combined level of several sources.

The Results tab pulls the SPL reference into Critical Distance and the back-row HF loss.

Print it

Print A5 at the bottom of the tab prints the SPL cards on a sheet sized for the workbook. It is a handy thing to tape to the FOH desk before a loud run.