Headphone „limiter“ on iPhone

Is this correct?  Someone please correct me if this is wrong.  

The apple DAC dongle has about a 1 volt (RMS) output max.  So multiply the efficiency of your headphones( db/Vrms) times the 1 volt and obtain the volume at max output.  

I use IEM with about a 117 dB/Vrms (t 1 KHz) so I try to keep it at about 50 % power to be safe and account for peaks or energy at other frequencies.  I don't like it louder anyway.  Plus, I only listen for about 1/2 hour at a time.  

https://www.kenrockwell.com/apple/lightning-adapter-audio-quality.htm

Is this the right way to calculate it and be safe?   My younger days were not easy on my ears with motorcycles, construction, and concerts.  

As an aside, if you’re using the Apple Camera Adapter do yourself a favor and order this dongle from LavriCable.  It uses 5N silver wire and sounds much better than Apple’s adapter.  Very worthwhile upgrade for not much $$$.

https://www.lavricables.com/cables/reference-silver-lightning-interconnect-cable-for-oppo-ha-2-centrance-mini-m8/

Do you use it? When I set it on 80 db and listen with my dt 900 pros it seems like it’s not loud enough, but I also don’t want to destroy my ears.

Is the volume with this settings really pretty low or are my ears already bad?

https://vshare.onl/

I got this,..