It disables the standard Digital Signal Processing (DSP), meaning the speaker skips default sound optimizations to create a raw, loud, low-end sound.
On many portable speakers like the JBL Flip 4, this is activated by pressing and holding the and Volume Down (-) button simultaneously for about 10 seconds.
Are you asking about a specific type of device (like a JBL speaker, Nikon camera, or software) when you mention low-frequency-2.7z ? Let me know so I can give you more specific details. JBL Flip 4 - How To Activate Low Frequency Mode ! "DSP OFF"