How can i improve the sound of Iphone 11?

Portable DAC is big improvement. Personality I use AQ Dragonfly Cobalt and very happy with it. Also if you using Apple Music hi res service you can improve SQ with the phone Settings. Go to Phone Settings then to Music where in Audio section you could play with Audio Quality, EQ, Dolby Atmos etc.

Happy listening.

I struggled with this question for a long time. Traveling with amps and a DACs. It was heavy and bulky or a mass of interconnections.

My solution was to switch to highly efficient headphones designed to be driven by low power. I bought a pair of Ultrasonde Edition 8 that sound great driven directly from the iPhone.

The best solution depend on the circumstances you use the system. In particular, the ambient noise you will be experiencing. I enjoyed this solution for many years. But I realized I was fine leaving “high end” sound at home and traveling in comfort (+200,000 miles a year) was more important and switched to Bose QuietComfort. Not highly accurate but really enjoyable (like your favorite inexpensive wine as opposed to a $250 bottle of Bordeaux) to listen to and incredibly comfortable and could be worn with noice cancelation only in airports and airplanes. 

So, depends on your usage.

epz,
I've been using the Hidizs S9 dongle with an iPhone and I get great results.   There are both single-ended and balanced outputs, and a lot of power.   It sounds great and it also measures quite well.
Dave

Thank you for all the replies. I am seeing a lot of love for the Dragonfly solution. The Hidizs and Helm are much less expensive. I am thinking i would be able to get much of the purchase price back on a Dragonfly if i did not like and sold it on the used market.

 - What is a jitterbug? Only one user mentioned having it.

" One thing I’d recommend is trying Qobuz — I switched from Tidal and am much happier, and no MQA crap to deal with."

When using the BluOS app, Tidal tracks list either CD or MQA.
When using the TIDAL app, tracks show M (master) or nothing.

Is MQA something to be avoided due to reduced sound quality? I have been unable to hear a diff between any of the formats (when the same song is listed twice - CD and MQA. I am paying for the TIDAL HIFI level which should not limit my choices.

Is MQA something to be avoided due to reduced sound quality?

Currently I’m subscribed to Qobuz, Tidal and Apple Music I have to admit that SQ of Tidal Masters is very close to SQ of Qobuz Studio Premier (album varies) some albums better on Tidal some on Qobuz…both services have their pluses and minuses. For me as a practical listener the MQA is definitely not a thing to avoid a specially on mobile setup. Don’t hesitate to try it yourself. It’s not big deal to get trial subscription for both services for one month so you could figure out yourself. I don’t yet have proper equipment to check Apple Music on my main system but using Dragonfly Cobalt DAC with Senheiser HD650 let me conclude that Apples Hi-Res Masters SQ is better than both Tidal Masters and Qobuz SQ (same album)…so the issue is yes practical for the listener… we r just choosing the better option and at some choices MQA is exist.