n00b here: Tell me why my build isn't as loud as I expected please?

I tried taking this amp 4 x 100W Class D Bluetooth Audio Amplifier Board - TSA8498
Powering it with this battery KLUOSI 10S6P 36V 19.2Ah for LG18650MH1 1000W with 30A BMS 36V Lithium Battery Pack for Ebike Electric Car Bicycle Motor Scooter|Battery Packs| - AliExpress
And using it to run 4x cheap Walmart 6x9 Scosche speakers Scosche HD Speakers for Cars 6x9" Set | Walmart Canada
Enclosed in speaker boxes that are 21x15x12 plywood containing baffling. Imgur: The magic of the Internet
Would you expect that these components would be right for each other or did I **** up?

I've been told that the shape is wrong, that they would be louder if they were more wedge shaped.
I've been told that the gauge of the wire from the battery to the amp is too small. It starts at 14 but then I dropped it unknowingly. The amp starts cutting out at maximum volume, possibly because it cannot draw enough power.

If I change these 2 things and it doesn't make it loud enough I'll probably take the components and put them into a suitcase to make something more portable to suit the lower than expected volume, but I still want a -really- loud battery powered sound system.
 
> I've been told that the shape is wrong,

Ignore that "expert". The shape is only minor difference.

> I still want a -really- loud battery powered sound system.

You can't fill the ocean with a teaspoon. BIG sound needs big efficient speakers. The most accessible may be guitar amplifier types. I used to do large parks with about that much amplifier and four JBL E-130 (yes, this is way past your budget).
 
> I've been told that the shape is wrong,

Ignore that "expert". The shape is only minor difference.

> I still want a -really- loud battery powered sound system.

You can't fill the ocean with a teaspoon. BIG sound needs big efficient speakers. The most accessible may be guitar amplifier types. I used to do large parks with about that much amplifier and four JBL E-130 (yes, this is way past your budget).

I wanted to quote only the last but the first deserves some attention... Well, shape... Shape of the wavefront might catch some attention. Since I recall that the bass is fairly good from 2X 6x9 drivers in an open baffle - yes, a car rear-the problem is the 2 x tweeters associated with the cones. Electrical compatibility for 2 drivers in one channel Plus extra tweeter drive makes new problem... 🙄
 
OH yes, the amplifier is 4 channels
/QUOTE]
New frontiers!
X-over techniques, active/passive and mixed, mon9/stereo and bypass/Eq 😱

Really many possibilities... I would make it the usual woofer(2 in this case) plus full range in the 300-500Hz cut 🙄;
The FR driver would need an additional amplifier since I see the 4x100 W is employed for driving the woofers
 
Let me telll you something. No you did not F*** up.
You just got what you paid for. that's all.
This kind of Loudspeaker aren't made for HOME USE, or similar, because of BAD to VERY BAD SPL. SPL = Sound Pressure Level. Calculate that Size which moves the air around that 6X9 Inch Loudspeaker. and the calculate the AIR in the room or even worse, if you go outside, and the you can ask yourself, does this makes sense.. Answer will be simply = NO.!These are speakers to build into the trunk in your car or the car doors, then may they sound good.
So save your money and buy some Bazooka made AMP and speakers.. May it will be better but I doubt it..Don't waste more money than you already did, us this as it is and save your money.,
A very smart man told me something., Unless you are going to win a contest in SPL, there is no reason to turn up loud that all the city can hear.

And another one said, the first watt is the most important watt.
Buy a good home stereo or build yourself one, sit down into a good chair where it's comfortable, and listen - Within this first WATT - because that's real loud already for a ROOM by 4x5 Meter. *Neighbors will hit the wall, because they do not want to hear your music.* This of course is only true if you are not DEAF.. Hey don't get upset at my writing.. try it and then you know.
I hope you find what you are looking for,

Regards and good Luck
Chris
 
Learn about SPL.
Learn the difference between a 90dB and a 100dB speaker connected to the same amp, playing at the same Volume and You'll find some answers.
That's why good PA speakers are in the 97-100dB range.
PA Compression drivers are more efficient and have usually higher SPL figures.