Use APKPure App
Get Bass reflex old version APK for Android
Bass reflex vent calculator
This app can be used for vented speaker box design (bassreflex tube length calculation) or for reverse analysis of existing solutions.
Wikipedia: A bass reflex system (also known as a ported, vented box or reflex port) is a type of loudspeaker enclosure that uses the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical closed box loudspeaker or an infinite baffle mounting.