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Batteries, amps, and watts, oh my! Help with my speaker build? Answered

Hey guys, first post here, so be kind, I suppose. :P

I'm building a set of speakers, loosely based off of the super loud, super long lasting speakers instructable (found here https://www.instructables.com/id/super-portable-super-loud-long-lasting-battery-/ ) I wanted to take these, and make them significantly better.

First of all, I was going to substitute in car speakers. The upside of that is that I also get bass without having to go out and buy woofers and wire up a crossover. I've been looking around on partsexpress, and it seems like most have an impedence of 4 ohms, and range from 75 to 150 RMS. I'm aware that the general rule of thumb is that you double the RMS for the amplifier. However, I'm not sure about soe of the other parts. Should the speakers be wired in series or parallel? If they're wired in parallel, should I be looking for an amp with 2 ohms of resistance, since it's two speakers at 4 ohms? If not, can speakers be easily wired in series?

Next question, batteries. Where in the hell do I get some good LiPo batteries? I know this thing is going to go through electricity like candy, so I want high wattage and high capacity.

The wattage brings me to my last question. These speakers are rated for a maximum input of 70 watts or more. I can't get a battery to go anywhere near that capacity. Will the speakers be harmed by a lower wattage supply? Significantly lower, I might add, most probably not more than twelve, even if I array the batteries into my own pack. How will that affect the speakers?
EDIT: I could realistically reach more than that, although it'll start getting really expensive really fast.

Sorry, one last; concerning the rule of thumb in which you should double the voltage of the speakers RMS for your amp, if I can't find an amp that does that exactly, should I have my amp be slightly overpowered, or slightly underpowered?

Thanks for all the help on this one :)

Discussions

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steveastrouk

9 years ago

Your amp should generally be AT LEAST twice the honest power rating of your speakers, too much isn't a problem - except you may blow your speakers if you get too enthusiastic. Car speakers are not "better" they are a space efficiency based compromise, given the limits in a car. If you have the space, a separate woofer is a better option. I'd wire 'em in series, so your amp needs to deliver its payload into 8 Ohms. The AMP has as close to zero output impedance as the makers can manage, over its normal range of operation, which is partially specified by its ability to dump X watts ino Y Ohms. How much budget have you got for batteries ? How much ACTUAL energy are you REALLY going to pull. 70W of sound is almighty loud, if your speakers are well mounted, and you are not in the wild outdoors. And you won't damage your speakers if the amp is underpowered.

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headinmysightssteveastrouk

Answer 9 years ago

Sorry, forgot this and there's no edit button, I read somewhere that it's very difficult to wire up speakers in series, is this true? I don't see why it would be.

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steveastroukheadinmysights

Answer 9 years ago

Neither do I. Most amps are specified into 4 or 8 ohms though. How many.speakers are you intending to wire to each amp ?

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headinmysightssteveastrouk

Answer 9 years ago

I suppose that if I use a woofer, and I intend to create stereo sound, then I'll have a total four speakers, two woofers and two tweeters. Would it work to use two mono amps? If I can't, since they're all likely to have an impedance of four ohms, could I use a combination of series and parallel wiring to attain the correct impedance level?

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steveastroukheadinmysights

Answer 9 years ago

Yes, you need two mono amps, and you'll need a crossover for each pair.

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headinmysightssteveastrouk

Answer 9 years ago

Thanks for the help. It might actually work better to do the woofer, even if I have to do a crossover. Easier to find an amp that works out. Out of curiosity, when the manufacturer has an efficiency rating, so many decibels per watt, can that be trusted as being correct? Anyways, thank you very much. :)

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steveastroukheadinmysights

Answer 9 years ago

Don't do a passive crossover, make an active one from a couple of op-amps, then pipe the output of your "crossover" to an amp for high frequency (which can, in general be lower power than the low frequency one) and to a Low frequency amp. Makes it much easier to tune your speakers too. A manufacturer will place the speakers in an absolutely optimum enclosure if they are quoting dB/ Watt, and it'll probably only be at one carefully chosen frequency. Speakers are much of a muchness unless you are into serious hifi, bigger is better for bass performance, smaller units work better at treble conditions.