Portable PA Project

[Austin Translation]

Originally Posted by cyclecamper

don't think we're all talking about the same thing here.

torclausen, just add simple cheap filters. The power amp probably has a switch-mode power supply or inverter to get more voltage, and that may inject lots of noise on the battery. A cheap electrolytic cap across the power line of each (amp and bluetooth) usually do the job, maybe put a snap-on iron ring on the amp's power cord too, or you could make a ladder filter with inductors and capacitors if necessary. Or use an odyssey-type battery which behaves more like a capacitor to begin with. Usually just one small cheap electrolytic at each device cleans it all up nicely. Get the polarity right if you use electrolytics. It will also sound better while charging the battery. But for best results, filter both the device which injects the noise on the power system (the amp or charger) and also filter the supply to the noise-sensitive device (the bluetooth adapter). I'm talking here about two cheap little 20-volt electrolytics. Maybe a mica disc in parallel too...what does the noise sound like (high frequency or low).

Vivica,
Out skating as in ice skating or ice dancing, or more like rap for skateboarding at the local skate park, or do you need the sound system on your back as you strafe or during in-line skating to exercise & lose weight?

I'm assuming you want some stationary sound system that you can move in your car, not carry on your back? For use at some skating venue?

Consider an Odyssey brand of automotive or deepcycle marine battery if you don't have to carry it with you. It supplies surge current demands wonderfully, is clean, sealed, spillproof, has good charge density, long-lasting and can be run down nearly dead without sulfating and dropping lead to the bottom and shorting cells. If battery life becomes an issue, buy more and add them in parallel. Normal automotive batteries don't take well to major shocks or being discharged.

Stick with 12 volt automotive amplifiers, so you can power the system from a boat or car or charger plugged in, or power supply, or you can charge the PA batteries from your car. And automotive stuff can always be re-purposed.

Avoid a passive crossover if possible; they often waste a lot of power and require larger amplifiers. Consider a 1-way system for a very small system (Bose used to make some "rommmate" passive 1-way), otherwise use an automotive active bi-amp crossover. That will save you a lot of battery power. It also lets you dedicate one power amp channel directly to each woofer. Using several cheaper mass-produced right-sized power amps instead of really expensive higher-powered ones saves a lot of money in the long run. You might find automotive amps with built-in input active crossover swtches, so you don't need to buy an additional crossover device.

Use a class-D or "T" power amp. They are FAR more efficient, lighter, cooler. Saves battery power. Puts out more watts to the speaker.

Use efficient horns whenever possible.

Consider mono if coverage and clarity are more important than stereo soundstage image. Just mix the two channels into one. One good loud mono bi-amped system will be far better than a crummy inefficient 2-channel. Then you can add channels as you please later.

Would need to know more about the exact intended use to make better recommendations.

I know something about deep cycle batteries and would like to chime in here. There are NO deep cycle batteries that can be ran down nearly dead.

10.5 volts is as low as any deep cycle battery that is expected to be used more than once should be discharged, this represents about the half way discharged mark for lead acid batteries and any more (lower) than this WILL DAMAGE YOUR BATTERY!

[18Hurts]

Now it is down to batteries

There is one chemistry that can be run to dead--it actually likes to be run down to 0V on occasion--NiCad batteries.

Lead acid is cheap but don't like to be deep discharged, they are also very heavy and perform poorly in the cold.

The best battery to use in the cold, can be discharged to 80% without damage for thousands of cycles, is safe and non-toxic is Lithium-Iron-Phosphate. The code on the side states LiFePO4 so you know you have the right type. The size and weight savings over lead-acid is about 4 times lighter and 4 times smaller which allows more capacity and much longer runtimes.

Cheap? No--not yet but the prices have been falling for years and they can be charged from automotive chargers. Make absolutely sure the automotive charger does not have a trickle charge function, the only battery that likes to be charged at 100% constantly is lead-acid. Shut off the trickle charge function on the charger.

Most of the LiFePO4 batteries have a battery management board to shut down the battery once it gets down to below 20% charge--make sure you get one that does this so the pack can be used for many, many years without problems. Charge it up once a year when not in use and go.

[Bigun]

Originally Posted by cyclecamper

Consider mono if coverage and clarity are more important than stereo soundstage image. Just mix the two channels into one. One good loud mono bi-amped system will be far better than a crummy inefficient 2-channel.

+1