Questions about this small sound system

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LongWayUp
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Questions about this small sound system

Post by LongWayUp » Mon Aug 11, 2014 10:18 am

I'm working on a small-scale sound system that I'll be carrying with me on a bike cart, consisting of the following:
-12v deep cycle battery, 105 Ah
-1200 watt inverter
-300 watt receiver
-Peavey PR15 speaker
-Laptop, or MP3 player if I don't feel like DJing
-Big Boy EL wire driver

Couple of questions about this system:

1. My calculations indicate that this battery will power my receiver, laptop, and lights for about 3-4 hours before being completely discharged, which I might do over the course of an evening. Is it ok to run down a deep cycle that much, or should I add a second battery if I can handle the weight? I could also go with a lower-wattage efficient DC amplifier--I mail-ordered a Topping TA2020, but it hasn't arrived yet so haven't tested--but that won't give me as much volume.

2. The receiver seems vulnerable because it's got vents all over the top to let the dust in, and I'm also worried that it's likely to overheat. I'm thinking about putting it and the battery in a 3' x 2' x 2' black tool box mounted on the bike trailer to protect it from dust. Will the receiver overheat if it's in a closed plastic box like that? Cover it with a cardboard box instead of putting it in the toolbox?

ShreddinPB
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Re: Questions about this small sound system

Post by ShreddinPB » Mon Aug 11, 2014 5:22 pm

Im am pretty sure you are not supposed to completly drain the batteries. Deep Cycles are designed to go lower than normal batteries, but if you take them too low, like any battery, I think you damage them.

I have a boom box type thing on my tricycle, I used all car stereo equipment to put it together since its more energy efficient.

Did you calculate in the amount of loss you will get using an inverter? Everything I have read says thay are very poor at converting.

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BBadger
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Re: Questions about this small sound system

Post by BBadger » Mon Aug 11, 2014 5:45 pm

Those batteries only want to discharge to about 50%, otherwise it can damage the battery. It will depend on if you care if you damage the battery too. Maybe you'll only be using it for this event, and not need it to last after? Your call.

Also, you'll probably be able to last the night on only a 50% discharge if you're just going by the receiver rating. You're not going to be pulling 300W constantly. Even at reference volume, you'll probably only peak at 300W -- though I'm not discounting that my assumptions may be wrong and you've measured it with a Kill-a-Watt or something and know the real power usage.
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daft
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Re: Questions about this small sound system

Post by daft » Mon Aug 11, 2014 6:31 pm

They weigh an awful lot. Maybe use it for awhile and then kill it, party, take it home to recharge. Two must be like towing me around and I can entertain that.

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Captain Goddammit
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Re: Questions about this small sound system

Post by Captain Goddammit » Mon Aug 11, 2014 11:11 pm

You can't discharge your battery all the way, the inverter probably won't work when the battery voltage drops too much.

Forget the 300 watt number. Your calculations will only have any meaning if you measure the actual power draw. If you got the 300 watt figure from the receiver's claimed output, there are a whole lot of variables there. Power output is often listed as RMS, which is .707 of peak power. The power output is also relative to the distortion level. The more you turn it up the more distortion. A receiver that manages 50 watts per channel at only 0.05% distortion is a lot louder amp than one rated at 100 watts per channel at 20% distortion. They simply took the power reading at a higher volume setting where it's all distorted. Car stereo gear is notorious for inflated power claims because there's no standard for distortion level.

INPUT power to the amp is another matter, and that's the figure the battery cares about. That also depends on a few things. The only way you can know is to hook up a meter, like a Kill-A-Watt. Or hook it all up, crank it up, and see how long it plays.
The next best guess is to look at the specs on the amp for it's 120VAC power cord. The input figure in amps or watts is the number you need, but that's usually a maximin possible number. Your actual average will be less.
It'll probably play quite a while on that battery. Two would be awful heavy on a bike cart!
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Re: Questions about this small sound system

Post by Fan C » Mon Aug 11, 2014 11:31 pm

I have AN answer for question 2.

Use as old an analog receiver as you can find. Our camp stereo is '80s vintage and just keeps working. In '12 it was buried under about 3 inches of dust and the music was still going.

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Re: Questions about this small sound system

Post by Captain Goddammit » Tue Aug 12, 2014 4:50 am

I took a similar older receiver to work as a shop stereo in a shop where they cut and grind granite all day, with playa storm dust levels. Damn thing just kept working.
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Re: Questions about this small sound system

Post by nixiebunny » Tue Aug 12, 2014 8:13 am

I have built a 300 watt sound system for my bike. It uses a Class D car trunk amplifier, and it runs for 8 hours on about 20 amp hours of 12V power.
Details here:

http://www.cathodecorner.com/loudbike/

I highly recommend this Pioneer amplifier. Of course, it's discontinued, so you will need the modern replacement, the GM-D8604.

No worries about dust, and no need for that inverter!
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LongWayUp
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Re: Questions about this small sound system

Post by LongWayUp » Tue Aug 12, 2014 11:12 am

I haven't measured the draw yet. Thanks for the Kill-A-Watt suggestion, I'll pick one up today. Would this tell me anything about the inverter's efficiency, or just how much power the amp is pulling from the inverter once it's transformed the voltage? Seems like it would be the latter.

The reason why I was worried about >50% discharge is that I did this math:
300 watt = 12 volt * X amp
X amp = 25

add 2 amp for a conservative estimate of the power draw from the EL wire driver and/or laptop

With a 105 Ah battery, if I run this system for 2 hours then I'll have used 54 Ah--won't that be a >50% discharge?

Regarding the amplifier: I'm leaving for EA on 8/19, so at this point it's unlikely I'll be able to get another amp to swap in (nixiebunny's idea of a DC car stereo amp is really good, though, might poke around at some car audio shops for that). Some other threads suggested covering the speaker with pantyhose--would that work for the amp as well, or is it even necessary if I'm storing it in the tool bin?

EDIT: I know everyone's saying that the amp probably will draw less than 300w, but I'm trying to plan for worst case scenario because I plan to push the volume as high as possible.

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Captain Goddammit
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Re: Questions about this small sound system

Post by Captain Goddammit » Tue Aug 12, 2014 12:19 pm

12 volt car stereo amp is a very good idea.
It will be more power efficient, smaller, and more durable.
That's what I use on my M/V.
I've used the same one many years on the playa. It looks pretty playafied but still works great.
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Re: Questions about this small sound system

Post by ShreddinPB » Tue Aug 12, 2014 12:43 pm

nixiebunny wrote:I have built a 300 watt sound system for my bike. It uses a Class D car trunk amplifier, and it runs for 8 hours on about 20 amp hours of 12V power.
Details here:

http://www.cathodecorner.com/loudbike/

I highly recommend this Pioneer amplifier. Of course, it's discontinued, so you will need the modern replacement, the GM-D8604.

No worries about dust, and no need for that inverter!
I love it!
Did you design and make a small class D amp?
I think I bought one from you

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Re: Questions about this small sound system

Post by nixiebunny » Tue Aug 12, 2014 5:52 pm

I have one of those 300W Pioneer amps on hand, if you want to go that route.

My other bike stereo is the 30 watt rear rack mount unit called the Bike Boom Box. I sell a lot of those to RAGBRAI riders in Iowa. It has a class D amp board that I designed and build.
--David Forbes

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Re: Questions about this small sound system

Post by postal003 » Tue Aug 12, 2014 9:00 pm

Not to add confusion but the people we got our deep cycles from said they are fine with being run dry and then recharging them again. I guess we'll see if he's correct or not out there. Because music has transients, you won't be running the 300 watts constantly depending on the music playing. The less bass the less wattage used cuz that's the biggest power draw. If you stick with the constant 300 watt usage estimates, you should find yourself with extra battery life depending on the music played (less bass, longer battery life). Google bill fitz-maurice who designs speakers, there's a wealth of knowledge from similar projects over there in the forums.

Cheers.

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Re: Questions about this small sound system

Post by Captain Goddammit » Tue Aug 12, 2014 9:10 pm

I'm still saying that arbitrary 300 watt figure is next to meaningless for the reasons I already outlined.
You gotta actually measure the INPUT power consumption.
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BBadger
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Re: Questions about this small sound system

Post by BBadger » Tue Aug 12, 2014 9:38 pm

LongWayUp wrote:EDIT: I know everyone's saying that the amp probably will draw less than 300w, but I'm trying to plan for worst case scenario because I plan to push the volume as high as possible.
It's good that you want to plan for the worst-case, but the fact of the matter is that you don't even know what this worst case really is. Your receiver spec is only for the output power delivered, not the power consumed on input. They're made for connecting to "limitless" power sources like wall power or even your car, which is a power plant. Even that wattage rating a marketing number. Rarely do receivers actually deliver on their "300W" rating. Some unscrupulous manufacturers will use the rating measured under conditions where the amp would catch on fire. That's why higher end models will "only" have 60W or something per channel, whereas cheap-ass ones will have really high ratings.

Even if your wattage rating is 100% legit, again, that's the output wattage. Your receiver might be using a class A amp that uses 1.5x the amount of current that your speakers do when just plugged in with no signal. Or maybe you're using a class D amp which can have 80-90% efficiency. Or maybe you're in the middle somewhere. You just don't know because these amps aren't designed for running on batteries in the desert.

You also don't know what volume you'll be running your receiver at. As the Captain mentioned, the distortion increases as the volume increases. Maybe 100% volume is so terrible that you can't stand using it. Maybe you adjust some of the equalizer settings to reduce the volume at certain frequencies, and that saves or uses more power. Maybe your speakers have mismatched impedance and you have to use more power to drive them.

I mentioned above that you'll probably be able to run the whole night. That's under the assumption that you'll probably not be driving them at full volume due to it sounding terrible, that your receiver is relatively efficient, and that your music will not be using full power all the time. Even then, that's just a guess.

I think the real solution is to just measure how much power you do use and build around that. As daft mentioned above, those 110AH lead acid batteries are heavy. You probably only want to bring one regardless of the duration you can actually use it. Plan your project around your battery limitations, not the other way around. Regardless, you'll only know when you actually measure the power you consume.
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Re: Questions about this small sound system

Post by Elorrum » Tue Aug 12, 2014 10:21 pm

I like the Watt measurement of Watts WLS, when lightening strikes. Some car amps have ridiculous ratings on them, I have a nice 600 watt Kinter amp (it says so on the case,) cost about 10 dollars, that is more realistically 15 watts, and so distorted at full volume, that it is as loud as I'll allow at about 2/3 of it's volume range. It will run for two whole days on a weekend camp out, with 8 D cells, around 1.4 Ah. For ten dollars I don't care if it gets destroyed. It's not going to power a dance or blow away an MV rolling by, but it's decent for a small area, and just regular music you can still talk over.
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Re: Questions about this small sound system

Post by nixiebunny » Thu Aug 14, 2014 10:15 pm

For what it's worth. I hooked him up with a spare 300 watt Pioneer Class D car trunk stereo. We'll see how it works.
--David Forbes

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Re: Questions about this small sound system

Post by BBadger » Thu Aug 14, 2014 10:38 pm

Those Class D or "Class T" amps are pretty power efficient. They just need some capacitors to help them get through some of the power issues, but that's needed for any amp.
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Re: Questions about this small sound system

Post by LongWayUp » Mon Aug 18, 2014 12:45 pm

Update on this:

Nixiebunny hooked me up with a sweet amp and gave me some quality tech support to help me install it, and I tested the system this weekend. With the amp, speaker, and an 80 Ah deep cycle battery (they didn't have 105 Ah at the auto parts store), it's still pretty lightweight; I was able to pedal it around on my bike cart with no trouble at all. It's louder when I'm riding past a large structure (like a wall or an RV) so there's something to bounce the sound off of, but that's to be expected.

Looks like this is a go! I look forward to doing my part to make up for the dire scarcity of loud electronic dance music at Burning Man.

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