12V RIG - Help, knowledge & Advice appreciated

HHi, regards the battery, the capacity is calculated at the C20 rate (5 amps for 20 hours). You are proposing a C5 rate. Battery capacity is significantly less at this rate. You'll probably need to double you battery size. Check the web for C rate versus capacity

= 100/5 or 20

so 20A for 5 hours?

Thanks for the pointing me in the direction of C rate vs Capacity, I will read into this 

No rush for a reply with a broken screen, and thanks for your comments so far 

DDeep cycle is a bit of a marketing hype.

True deep cycle battery is extremely heavy due to thick plates and very expensive.

Pioneer offer some more powerful models, have you looked at the GM-A5702? About four times as powerful as the one you mentioned, but only 2 channels - not necessarily a problem if you passively cross over to your bullet tweeter? It's not class D, so might drain your battery rapid. That would have to be worked out in the field, unless Pioneer start providing more useful specs like quiescent current draw and efficiency figures.....

A lot of us on this forum have had good success using modules from Sure Electronics (aka Wondom) out of China. They can sell you a 2x300w/4ohm amplifier for about £50 and a power supply for it for about £45. These arrive as bare circuit boards so you need to mount them in a case and do a little wiring, but otherwise they are very easy to work with. It's not going to be cheaper or easier than the car amps, but potentially more efficient and much lighter weight.

Don't be too confused by speaker RMS ratings. In the world of 12v you will often be powering quite a large speaker from a relatively small amplifier. The dB-for-one-watt efficiency figure is the important thing as it determines how much of the input power the speaker can turn into sound. A lot of car subwoofers have the efficiency of a rubber chicken, and need great big amps to get them to move at all. This one at "105dB" is apparently almost as sensitive as a high quality compression driver, so I would basically doubt that figure hugely and assume that it is actually more in the region of 90dB output for one watt. Anything above 90 is OK, anything in the 80's is rubber chicken territory, anything above 100 is very good indeed. You can increase the efficiency by putting the driver in a horn (eg a tapped horn).

Finally consider that Hobbyking are now selling 10Ah, 14.8v lithium packs for about £35 and they are *so* much better than lead-acids in terms of power to weight ratio. Plus they are much happier with constant high current draw. I'm not totally sure a car amp would be happy with them at full charge (about 16.7v)- might trip its over voltage protection. But they are the future ;)

If size and weight isn't an issue and you really only care to get 5 or 6 hours of playback from a 115ah battery (how do you plan to transport this thing exactly?), then sure, go for a large box reflex design (but seriously consider tapped horns or hybrids like the Cubo series as they're a good compromise), but then you're going to need a lot more than 45W to drive it.

If it's actually going to be playing outside of a car like a normal PA system then the only place car audio components should come into it is for the amplifiers, and you'll need a much bigger one than specified (think 500w RMS monoblock for the bass if you want to produce 35Hz - Something from Vibe or BassFace that actually outputs the specified amount).

For mids/highs you would do well to look at the Fane 12" 12-250tc full range drivers. They're efficient, sound good, reasonably cheap, no need for a separate tweeter, no need for a crossover, you can put them in a small closed box and cross them from subs, possibly with a crossover built into the amp if you can find one like that. That's about as fool proof a set up as I can think of for what you're trying to do anyway. Other options can produce better results but get progressively more complicated the more components you try to incorporate.

If you're trying to produce 35Hz then you may as well get a 15" driver for the bass because the real size and weight is going to be the box size, and you'll want the efficiency. You probably don't actually need 35Hz but I won't try and convince you of that.