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opinions on a portable 24v project

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jonaglon View Drop Down
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    Posted: 25 October 2016 at 7:15pm
Hi,

I've built sound systems before but am new to portable projects so am posting here to see what you make of my plans.

I am making what's best described as a robot jukebox, it will be built on the base of an electric wheel chair which needs 24v, so I think this is a 24v sound system not a 12v. I am more interested in building a rig which will sound really large for a couple of hours than a smaller one that lasts for ages, so power over efficiency is fine. I'll often have mains available but it needs to be portable.

I already have some parts I want to use, I have several nice 8ohm 8" drivers and nice 8ohm tweeters, I hope to run them all from this 24v class d amp. I am also lucky enough to have two of these 12NW100 B&c 12's.

The question is, could I power the two 12s portably? I have a budget and if I can use the audio parts I already have I could maybe blow it all on a very expensive battery. I am thinking maybe a lithium-ion battery like this, or a huge lifpov4 battery like this, then a powerful inverter to a mono class d amp running at 220v or 110v (would 110 be preferable?). I have a perfect mono 2000w class d amp but it's 220v.

Do you think that's ridiculous idea and I should add a leisure battery to the wheelchair batteries and power the biggest sub I can with the best 12v car audio amp I can afford with the budget instead? Suggestions welcome!

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bitSmasher View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitSmasher Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2016 at 11:24am
The easiest way would be a 4ch 24v chip amp like what Sure sell (model AA-AB33184)
MiniDSP for top/sub crossover and some EQ, run this from an isolated step-down power supply
2x 8" and tweeter tops, with passive crossover
2x 12" subs, tuned to boom a bit

Will be pretty loud, and fairly efficient too
"Battery Acid Sound System" blog hopefully happening in 2017
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jonaglon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonaglon Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2016 at 3:42pm
Thanks bitSmasher.

I've bought most of my components now - I bought a 24v chip amp just like the one you suggested but with 6 output channels - it's working brilliantly for the mids and tops. That won't power my bass bin though, I'm using a fairly large single 15" driver now. I have got a 24v lifepo4 battery and an inverter so I can power the big speaker with a proper 230v amp which seems to work. I didn't see how long the battery lasts yet, I don't have a cab for the driver so my tests are limited but it seems to work ok so far.

I hadn't seen a MiniDSP before, looks like a cool piece of kit. I already bought an kmtech active crossover, so I'll see how that sounds when I've built the cabs. Thanks for the reply, I'll post pics and results when I'm done.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2016 at 4:06pm
If I was after bass and a 15" for semi-portable use I'd be looking at a couple of class-D modules that could be bridged into a load. Series batteries as needed to get the voltage rails required for maximum output. Problem with an invertor is that you are just burning power in the DC-AC conversion process for no real reason. Stay DC all the way if you can and avoid the expense of a high power invert or + possible associated switching noise.

MiniDSPs are great for low poweer consumption tweaking and EQ'ing but your active will get you most of the way there.
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jonaglon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonaglon Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2016 at 4:26pm
I know what you're saying makes sense but I couldn't find a 12 or 24v amp that could deliver anything like the power I was hoping for. The battery I've got claims to be able to deliver 1500W peaks (it's meant for electric vehicles), the inverter is 2000W (4000w peak). I know the numbers are unlikely to be accurate but half of that is the sort of power I'm looking for. I'm hoping that is well matched for the amp and speakers and I'll be able to produce some proper bass. But for how long, and at what quality, are big unknowns at the moment. So far it seems to be working.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2016 at 5:11pm
Bridgable modules will double the power from a given voltage rail. Still only going to be a few hundred W but that will make quite a lot of noise Peaks draw figures don't mean a lot unless you know the time that said peak can be sustained for.

I would go for efficient bass drivers and less power, than the alternative. High power inverters and amps will add a lot of weight and bulk to a system, keeping it simple is a always a good design technique.

For example, why are you so sure a single 15" is the way to go? So you just feel it is a good idea or have you crunched some numbers? As long as you are reproducing 60Hz well and maybe a little below you will get the impression of decent bass. Every octave you go lower sucks more power from a system for less overall gain. So a compromise is sensible depending on how portable you wish this to be.

You could have 2 12" drivers that together could be run from 4 bridged amp modules, each getting a couple of hundred watts and together that have a larger surface area than one 15" driver. It is about selecting the right tool for the job!

What I am trying to get at is do not get hung up on figures of power. There is so much more to designing a good system than buying gear that claims to handle large amounts of power. Keep researching before you start buying stuff.

Just remember than a electric fire could be 3kW rated, but it does not make a lot of noise. If you buy ineffecieint drivers you will also spend most of your battery power heating voicecoils and not making much noise. Have a look at the relationship between driver efficiency, power, and resulting SPL.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sapro2 Quote  Post ReplyReply Direct Link To This Post Posted: 02 December 2016 at 9:37am
Originally posted by odc04r odc04r wrote:

Bridgable modules will double the power from a given voltage rail. Still only going to be a few hundred W but that will make quite a lot of noise Peaks draw figures don't mean a lot unless you know the time that said peak can be sustained for.

I would go for efficient bass drivers and less power, than the alternative. High power inverters and amps will add a lot of weight and bulk to a system, keeping it simple is a always a good design technique.

For example, why are you so sure a single 15" is the way to go? So you just feel it is a good idea or have you crunched some numbers? As long as you are reproducing 60Hz well and maybe a little below you will get the impression of decent bass. Every octave you go lower sucks more power from a system for less overall gain. So a compromise is sensible depending on how portable you wish this to be.

You could have 2 12" drivers that together could be run from 4 bridged amp modules, each getting a couple of hundred watts and together that have a larger surface area than one 15" driver. It is about selecting the right tool for the job!

What I am trying to get at is do not get hung up on figures of power. There is so much more to designing a good system than buying gear that claims to handle large amounts of power. Keep researching before you start buying stuff.

Just remember than a electric fire could be 3kW rated, but it does not make a lot of noise. If you buy ineffecieint drivers you will also spend most of your battery power heating voicecoils and not making much noise. Have a look at the relationship between driver efficiency, power, and resulting SPL.



+1000 to that. Every time you convert voltages you waste power. Better to have an efficient box than throw away your power.

(Best line ever 'Just remember than a electric fire could be 3kW rated, but it does not make a lot of noise.' ClapClapClapClapClap)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 02 December 2016 at 10:52am
Originally posted by jonaglon jonaglon wrote:


add a leisure battery to the wheelchair batteries and power the biggest sub I can with the best 12v car audio amp I can afford with the budget instead? Suggestions welcome!



This. Well on the battery/amp side of things anyway. Duck and dive your way through the car amp marketing bullsh1t .... remember the headline power ratings are usually into 1R load :-/  are usually "peak power" and are at supply voltages of 14.8V.
3000W car sub amp ..... will be nearer 2000W at 12V - more like 600-700W into 4R load and more like 300-400W RMS (whatever RMS means in car audio speak). So - if you want 400 real watts into (say) 4R load - look at car sub amps advertised as 3000-4000W.

I'd use the existing 2 good quality 12" drivers you already have (as a 4R load) - maybe add another one (as 2.66R load) - and make appropriate cabs ..... some kind of cab that enhances efficiency would be good (e.g. bandpass or cubo or some such) - but at the cost of some size/weight.
REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonaglon Quote  Post ReplyReply Direct Link To This Post Posted: 02 December 2016 at 11:25am
Thanks everyone. I did research and I do understand the accepted wisdom. BUT! There was a over a month before this post got it's first reply and I already blew my budget on an expensive battery and inverter from china so I will do some experiments and report back. I understand that I'm paying a hefty price (efficiency wise) using the inverter, but there is a payback - I can use a proper smps amplifier which will make up for some of that. And it does work, I've been powering an 8ohm 800W B&C Neo 15" speaker and properly moving some air - I think more than I've seen before from a battery powered sound system. But my cab was made from cardboard and shaking apart so I didn't test how long it lasts for or how it sounds. It may well not last long.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 02 December 2016 at 2:00pm
Wow - did you buy that $1300 battery ? If so I think thats probably the best battery bought by anyone around here !!


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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonaglon Quote  Post ReplyReply Direct Link To This Post Posted: 02 December 2016 at 3:45pm
I bought this battery - the one that came is actually quite a lot bigger than the one in that picture. It's not the one I originally linked to, it's lifepo4 rather than lithium-ion. Hopefully it will live through 2000 recharges (ideally! a lot anyway), have no memory effects, charge quickly and deliver more power at once than a standard leisure battery. It's an expensive step into the unknown, but I decided a good battery is a worthwhile investment. I need to power a electric wheelchair motors, leds, servos and a computer too so I may use more than one battery. But at least it should carry itself!

Edited by jonaglon - 02 December 2016 at 4:00pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 02 December 2016 at 10:57pm
Originally posted by jonaglon jonaglon wrote:

I bought this battery - the one that came is actually quite a lot bigger than the one in that picture. It's not the one I originally linked to, it's lifepo4 rather than lithium-ion. Hopefully it will live through 2000 recharges (ideally! a lot anyway), have no memory effects, charge quickly and deliver more power at once than a standard leisure battery. It's an expensive step into the unknown, but I decided a good battery is a worthwhile investment. I need to power a electric wheelchair motors, leds, servos and a computer too so I may use more than one battery. But at least it should carry itself!


Well that is a chunky battery then, don't short it!

Just to be a nerd and nitpick, it is still a Li-ion battery. LiFePO4 relates to the cathode material. In this case Lithium Iron Phosphate. There is a lot of ongoing research into different cathode materials. Lithium Cobalt Oxide is classic, then there's Lithium Manganese Oxide, and loads of other variants too. They all work the same way - intercalating crystal structures for Li ions.

Anyways, back to the sound nerding.
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