Originally posted by TheBogie
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Prms = (Vps-1)2 / (2 * SPKr). That is W rms = (Power Supply voltage - 1) squared then divided by (2 times speaker impedance).
With two smaller 12 V batteries in series (i.e. 24 V) you can get 33 W rms per channel.
The system pictured is getting 66 W rms into the ".1" 4 ohm sub. You can see the two sealed lead acid batteries: 12 V, 18 aH. This plays for two days at 10 hours per day as there's no losses up converting a single 12 V battery and the 2.1 channel amp module is Class D (TI's TPA3116 amp chip). The batteries are roughly $45 each. And you'll need a SLA charger (~$35) to keep them topped off. You could then use many of the class D amp modules on PE's site. With the proper SLA charger, my first 12 V 18 aH battery lasted 8 years doing beach duty both days every weekend..
On another note, you may lack some bass since you outside w/o walls or floor to reinforce it. That's due to the "Baffle Step" phenomenon. The system below corrects for that in it's XOs.
(The system below is for sale including SLA batteries and two SLA chargers (and a second 24 V Li-ION battery and charger). Custom designed for lightweight, high volume beach parties, long battery life, and ease of transport with it's rugged case. In NJ).
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