I use a Windows 7, a Behringer UM2 DAI and Audacity as DAW… I am just a noob, hobby musician. I used an acoustic guitar with active pickups to record on a backing track. All settings are good (the only issue is I chose 41.4 KHz, as was discussed in this forum in the past). I adjusted amplification and loudness normalization as per requirement. My final exported wav clip (combined on a video, as per procedure, no mistake) sounds outstanding with a headphone / earphone, and on my Boss Katana min ami… but on a normal smartphone, the volume appears pretty low. What can I do, to make the volume loud on a cellphone too?? Tia 
the only issue is I chose 41.4 KHz
Hopefully 44100. 41400 isn’t a standard sampling rate.
What can I do, to make the volume loud on a cellphone too??
I’ll be watching this message. Your phone is displaying the video, right? Not just a sound track? So it may be going through video processing in the phone’s system.
The other problem might be the phone’s Compression Drivers (speakers). As good as they are, they won’t do all of the bass tones in a live guitar performance. So all those tones will be missing.
You could have stereo phase problems (unlikely). If you mixed and did all your production in stereo (headphones, speakers, etc) an out-of-phase stereo show will go right into the dirt the first time it was presented in a tiny mono-simulated system like the phone. The only evidence against that is that it sounds OK on the Boss Katana.
Accidental out of phase production still happens fairly regularly. I wrote to a production manager asking them if they got complaints about a recent interview. The interviewer was out of phase and would have vanished when played on a phone. They had and it did. They fixed it later.
An even more recent short tag video (“If you liked this show, you’ll really like…”) was out of phase and on my system, it sounded like the presenter was behind me. Again, you were using pickups and not actual microphones, so this isn’t likely (but still possible).
Reduce a copy of the performance to mono as an experiment and see what happens. Open the track. Tracks > Mix > Mix Stereo down to Mono. I don’t expect the volume of the track to change very much if you do that. If it does, that may be the answer. You have stereo phase damage.
Koz
but on a normal smartphone, the volume appears pretty low… sounds outstanding with a headphone / earphone
When the mono-mix (from the mono phone speaker) is reduced it’s usually the out-of-phase problem Koz mentioned. But that shouldn’t happen “accidently” with your Behringer set-up. That can happen if you use some kind of “artificial stereo widening”.
Another possibility is “too much bass”. If you reduce the bass (which the small built-n speaker can’t reproduce) you can Amplify or Normalize to a louder volume. But there shouldn’t be much bass from an acoustic guitar.
Or, it could simply be a combination of a quiet-dynamic recording and a small speaker and amplifier. Acoustic guitar is very dynamic, which means there is a wide-range between quiet and loud. And the “loud” peaks are short-duration so they don’t sound that loud. A normalized “clean” and uncompressed* acoustic recording won’t be as loud as a normalized recording of a distorted electric guitar. Most commercial music is highly compressed and it’s usually louder than home recordings. (Usually acoustic guitar shouldn’t be that compressed or you might not want it compressed at all if you want to retain the original dynamics.)
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- I’m talking about dynamic compression which tends to make “everything loud”. When you drive a guitar amp into distortion, that’s a kind of dynamic compression. This is unrelated to file compression like MP3.