Un­der pres­sure

Pilot - - PILOT -

I fear there will be some con­tro­versy over your de­ci­sion on a win­ner of the Light­speed head­set com­pe­ti­tion (yes, I have just en­tered with what are the cor­rect(!) an­swers).

Q2 asks for units for mea­sure­ment of sound (acous­tic) pres­sure. The cor­rect an­swer is of course Pa in SI sys­tem. And sound pres­sure level (SPL) is nor­malised on a log­a­rith­mic ba­sis rel­a­tive to the ref­er­ence level, p0, of 20 mi­cropa = 2 x 10- Pa, that cor­re­spond­ing to what is con­ven­tion­ally con­sid­ered to be the ap­prox­i­mate thresh­old of hu­man hear­ing at 1 khz. This ref­er­ence level is nor­mally de­noted 0 DBSPL (zero deci­bel rel­a­tive to p0). So con­ver­sa­tion lev­els cor­re­spond to ~50 DBSPL, long term hear­ing dam­age level ~85 DBSPL etc. Un­for­tu­nately this nomen­cla­ture is of­ten lazily writ­ten as ‘db’ and not ‘DBSPL’. Or rather the ref­er­ence level (0db) is not de­fined (dbs are just rel­a­tive, not ab­so­lute val­ues). Even Poo­ley’s PPL train­ing man­ual on Hu­man Per­for­mance Fac­tors has this wrong.

I sus­pect you as­sumed the cor­rect Q2 an­swer is dbs. But the ques­tion is ill-posed for this; it should have asked how sound pres­sure lev­els are mea­sured rather than sim­ply sound pres­sure.

In the era of Trump, your as­sump­tion and wrong an­swer can be con­sid­ered pop­ulist! POTUS In­ter­rup­tus knows no more of physics, avi­a­tion and en­gi­neer­ing than the man in the moon, which is why he is propos­ing to bug­ger up the FAA.

Pedan­ti­cally yours re­gard­less David S James PHD

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