Portable stereo speaker (digital amp) 5V 3-5W

I was never a fan of internal speakers on phones, even the best of them. the sound is always jarring and too strong in the 1-5kHz band. whilst they rarely can reproduce frequencies under 500Hz. and that is mainly due to the fact that physics is a harsh bitch (the size of the speaker and speaker box dictates the resonance range and hence power output at various frequencies).

So, what's a man to do? well that depends to the type of man. some go and buy a cheap compact speaker that sounds shite, some buy expensive ones (ex. Logitech UE series $100-$400) and live with what has been made for them, OR, he makes his own damn speakers! with all the features he wants and none of the nonsense he doesn't. 

[after 9 months of regular use]

So, here are my criteria:

Want

• Simple and robust
• Wired connection
• Potential for upgrades and add-ons
• USB rechargeable
• Long runtime
• Repairability
• Modular

Don't want

• Complication (fidgeting with bluetooth, pairing, hold buttons for on/off or functions, etc)
• Loads of controls that rarely get used
• Large or heavy
• Short battery life (high standby current)
• Heat management 

Our chip of choice is PAM8406, class-D amp with %90 efficiency and 3W Output at 10% THD with a 4Ω Load and 5V Power Supply. (originally I had made this with PAM8403, it turned out my parts could handle more so I upgraded).

Parts:

• ABS project box (ebay) ~$5
• Speakers (ebay) ~$5
• Amp module (ebay) ~$4
• Boost circuit (ebay) ~$1
• Battery li-ion 1000mAh (salvaged off rc toys)
• Caps 6.3V, 1500/1800µF x 14 low ESR (salvaged off old motherboards)
• Sockets, pot, leds, resistors (almost all salvaged)
• Wires (pc power supply quality cables - salvaged)
• Copper Heatsink (made of reclaimed metal)
• Paint, hot goop, cardboard, screws, etc (more or less free :D)

Notes:

• Battery has protection circuit on it
• Amp doesn't make enough heat to cause trouble with the battery underneath
• Boost circuit gets a bit toasty at full output (used what I had handy, needs upgrade)
• Panel could have been done cleaner, alas, "ain't nobody got time for that" :D
• Base funnel/tube was helpful but not hugely. according to online calculators, with my box size and the low frequency response I wanted, to achieve resonance, tube needed to be +60cm long. my box is 16cm long total soooo ¯\_(ツ)_/¯ 
• This speaker has much fuller sound than a phone speaker and gets much louder but it's no sub-woofer (physics being a bitch and stuff) lower band is around 200Hz before output starts to take a dive

Future upgrades

• Replace the battery with one 18650
• Swap the charger module with one that has micro usb (instead of mini) and has onboard battery protection 
• Redo the volume knob
• Redo the lights and light pipes