How long does 100 g of desiccant actually last?

A: Count openings, not days. Each admits about 0.3 g and 100 g of gel holds 12 g at 40 percent RH, so 40 openings: ten days at four a day, three at twelve.

Why three dots instead of five on the card?

A: In the wireless microphone & soundcard moisture-proof case the three mark dry, working ceiling and replace. Large patches read through the lid; five-dot cards need the eye close enough to separate neighbours.

Does a 6 kPa valve become a leak path?

A: No. The membrane is expanded PTFE: air passes, water does not, and 10 kPa of 1 m head will not push through; the 6 kPa point targets temperature, not water.

Wireless microphone & soundcard moisture-proof case

Q: Why does the seal in a wireless microphone & soundcard moisture-proof case fail first?

A: Because every opening compresses it again: an 8 mm lip at 22 percent gives 1.76 mm of squeeze, and after 3 000 openings it sits at 18 percent, where 1.44 mm cannot hold 10 kPa.

Quick answer: Wireless microphone & soundcard moisture-proof case: 420×320×180 mm outside, 370×270×140 mm inside, an 8 mm seal squeezed 22 percent, 100 g of desiccant.

Three parts in series, not one rating
An 8 mm seal at 22 percent
100 g of desiccant, counted in openings
Three dots on the humidity card
A 6 kPa valve, a 1.0 m drop and −10 °C to 55 °C
FAQ

1. Three parts in series, not one rating

Moisture control in a wireless microphone & soundcard moisture-proof case is three parts in series: seal, desiccant, indicator card. They fail in a fixed order: seal first, desiccant second, card last, so a card at 60 percent means the other two have been failing for a while.

The wireless microphone & soundcard moisture-proof case is 420×320×180 mm outside with a 3.0 mm wall, 370×270×140 mm inside, 3.0 kg empty, 6.5 kg loaded, 9.5 kg in total. The cavity takes three grey foam pockets; the lid carries 20 mm egg-crate foam.

Table 1: what each barrier does

Barrier stage	Job	Key figure
Seal	keeps vapour and splash out	8 mm wide, 22 percent squeeze
Desiccant	absorbs what openings admit	100 g, 12 g usable
Indicator card	reports internal humidity	3 dots, 10 / 40 / 60 percent
Pressure valve	equalises temperature differential	opens at 6 kPa

Only the seal wears; the other three are spent by count.

2. An 8 mm seal at 22 percent

In the wireless microphone & soundcard moisture-proof case the seal is an 8 mm EPDM lip in a lid groove. Closed, it is squeezed 22 percent, 1.76 mm, leaving 6.24 mm. The line runs 2×(370+270)=1 280 mm and reacts at about 200 N; two latches at 280 N give 560 N, a factor of 2.8.

Wireless microphone & soundcard moisture-proof case in sand colour, lid open on concrete, black gasket ring and a long foam channel

The squeeze falls: EPDM takes a permanent set, and after 3 000 openings the same latch closes on 18 percent, 1.44 mm, 0.32 mm below new. Under 10 kPa of a 1 m water column that gap is a continuous path, which is what IP67 at 1 m for 30 min tests.

Starting at 25 percent lifts the reaction to 240 N; the latches still hold, but the lid is harder to break open, so 22 percent sits between a 3 000-cycle life and one-hand opening.

3. 100 g of desiccant, counted in openings

The wireless microphone & soundcard moisture-proof case cavity is 0.014 m³. Air at 30 °C and 80 percent RH carries about 24 g/m³, so one opening exchanges roughly 0.3 g of water. Openings, not days, are the real budget.

At 40 percent RH 100 g of silica gel holds about 12 g, not half its weight. Twelve grams over 0.3 g gives 40 openings: ten days at four a day, three at twelve. Same shell, same sachet, a threefold spread the opening count explains.

Table 2: three ways the barrier fails

Failure mode	Early sign	When it appears
Seal takes a set	groove looks shallow, lid closes light	3 000 openings
Desiccant saturates	card turns at the 40 percent dot	about 40 openings
Lip scratched	local leak, card jumps to 60	grit left in the groove

The second is the one people miss: nothing moves, only the card knows.

4. Three dots on the humidity card

In the wireless microphone & soundcard moisture-proof case the card carries three patches: 10 percent dry, 40 percent ceiling, 60 percent replace. Three rather than five is about reading cost: large patches read through the lid, five-dot cards need the eye close enough to separate neighbours.

Wireless microphone & soundcard moisture-proof case open on a steel bench, egg-crate foam in the lid and four latches along the front

Forty percent RH is a band, not a floor to chase. Below 10 percent the foam and seal stiffen and the lid keeps a permanent groove. The card also drifts with heat, reading about 5 points drier near 55 °C; read it two minutes after opening.

5. A 6 kPa valve, a 1.0 m drop and −10 °C to 55 °C

The wireless microphone & soundcard moisture-proof case valve opens at 6 kPa, a figure about temperature rather than altitude. A sealed box moving from 20 °C to −10 °C crosses 30 K, roughly 10 kPa across a 3.0 mm wall, and past 6 kPa it vents; without that the lid is sucked down and the latches release without lifting it. The membrane is expanded PTFE, so air passes and 10 kPa of 1 m head does not, which is how IP67 and a valve coexist.

Drop tests run at 1.0 m with 9.5 kg aboard, once per face: no latch opens, no pocket collapses, no lid gap beyond 1.5 mm.

IP67 at 1 m for 30 min rests on the seal plus 0.3 mm of lid flatness. The −10 °C to 55 °C range is what PP and EPDM take: at −10 °C the seal needs a moment to seat, at 55 °C compression set accelerates and the 3 000-cycle life is discounted.

Table 3: control values and how to check them

Control value	Pass condition	Check method
22 percent squeeze	1.76 mm closed, 6.24 mm left	feeler gauge at the lid line, quarterly
40 percent RH inside	40 percent dot unchanged	look each time the lid opens
12 g usable absorption	replace after 40 openings	count openings, not calendar
IP67 at 1 m / 30 min	lid flatness 0.3 mm	3 units per batch

Conclusion

A wireless microphone & soundcard moisture-proof case holds 40 percent RH through three parts that fail in order, not a water rating alone. The 8 mm seal closes at 22 percent and falls to 18 percent after 3 000 openings, and the 0.32 mm difference is where the leak starts. Desiccant capacity of 12 g against 0.3 g per opening sets a 40-opening change, and the three card dots watch the band from 10 to 60 percent. Keep the three in sequence and the 6 kPa valve keeps its meaning.