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Old 21st September 2012, 09:25 PM   #11
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+1 on what Cal said.

The 15" woofer seriously isn't up to much.

It has low sensitivity (87dB @1w is very low for what you want), which means the rest of the speakers will over power it easily.


Get 4 of these
, read up on crossovers, and then build something like the Boominator, but scaled down a little.

Chris
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Old 8th October 2012, 11:38 AM   #12
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kind of like this?
Click the image to open in full size.
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Old 9th October 2012, 11:25 PM   #13
dangus is offline dangus  Canada
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Buy a TA2020 or TA2024 T-amp board from eBay (under $10), or be a big spender and get one in a case with volume knobs and all that for around $20. They'll do about 10 real RMS watts into 4 ohms, which happens to be almost exactly the same as a "high power" car head unit (which usually claim 30 to 40 "watts" where "watts" are not precisely defined).

For speakers, use the first quality pair of 4 ohm car speakers you find at a thrift store, yard sale, or abandoned Honda Civic in a gravel pit with bullet holes in the doors that miraculously missed the speakers.

Power this with 12V from a 7AH sealed lead acid battery (commonly used in computer UPS, some ride-on toy cars, emergency lighting), bunch of NiMH cells in series, or some cordless tool battery in the 12V to 14.4V range. I'd be tempted to add some frills like a cheap LED voltmeter module from eBay wired with a push switch to allow checking battery voltage, a lighter jack for powering other 12V accessories, and something that can charge the battery and/or run the unit from 120V AC.

If light weight is a concern, with some luck or perseverance you may find car speakers that have neodymium magnets and composite frames. (I found a pair like this at a thrift store: looks like an OEM speaker, but no identifying brand. It's slightly possible that asking around at car stereo installers will get you a pair that have been pulled from a new car.) OEM car speakers don't have a great reputation, but if you put them in a box that doesn't rattle or buzz, has stuffing to prevent internal resonances, and maybe add a tweeter, it could sound good.

For a lightweight but stiff enclosure that's strong enough to sit on, try a plastic foam-insulated picnic cooler. Those can be very cheap at thrift stores. I've also seen some plastic water-resistant boxes at a hunting/fishing supply store that resembled ammo boxes, like this one: http://www.amazon.com/Action-Product.../dp/B001DZLL5Y

Last edited by dangus; 9th October 2012 at 11:51 PM.
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Old 31st December 2012, 10:28 PM   #14
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Quote:
Originally Posted by dangus View Post

For speakers, use the first quality pair of 4 ohm car speakers you find at a thrift store, yard sale, or abandoned Honda Civic in a gravel pit with bullet holes in the doors that miraculously missed the speakers.

Power this with 12V from a 7AH sealed lead acid battery (commonly used in computer UPS, some ride-on toy cars, emergency lighting), bunch of NiMH cells in series, or some cordless tool battery in the 12V to 14.4V range. I'd be tempted to add some frills like a cheap LED voltmeter module from eBay wired with a push switch to allow checking battery voltage, a lighter jack for powering other 12V accessories, and something that can charge the battery and/or run the unit from 120V AC.
Dont mean to hi-jack the thread... But I figure it'd be best to ask the relative questions here than start a new thread.. I'm new to this stuff too, but have some understanding...

My questions are
1) Why do you reccomend 4ohm speakers as opposed to 8ohm? Price? Avaiability?

2) The most confusing part to me now is power. What do you need to do to get a power source from the wall to both charge a battery as well as power the system... Do you simply wire the battery in series with the power source and then to the amp? Would that be fine to charge the battery? Or would you need to make up a circuit or add a component to "trickle" charge the battery

Thanks
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Old 1st January 2013, 11:21 PM   #15
dangus is offline dangus  Canada
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All things being equal, 4 ohm speakers will draw twice as much power from the amp compared to 8 ohm speakers. Car speakers are nearly always 4 ohms. "Twice as much" isn't a lot when expressed in dB, though, so if you stumble over a nice pair of 8 ohm speakers, give them a try.

SLA batteries like to be charged at about 13.8 to 14.4 volts, but the charging current should usually be limited to less than C/5 (where C is the ampere-hour rating of the battery). The battery would be wired in parallel with the charger and with the load. At low to moderate listening levels, the charger would supply current to the amplifier, but with the volume cranked, the battery would do the work. But if the voltage sags when the bass hits (from 13.8 to 12V), that could have audible effects, or possibly confuse a smart charger.

Maybe it's safer to run the amp from a separate 12V supply while the battery is being charged. 12V switching supplies don't cost much from eBay or a thrift store. On the other hand, if T-amps will tolerate 15V, a 15V laptop supply could run the amp, and the 15V would be dropped (using a series diode) and current limited (resistor?) to charge the battery.

Or, a switching supply could boost the 12V from an AC adapter to charge the battery. That would have additional benefits: you could charge the battery from a car lighter jack, or use the boombox battery to boost a flat car battery.

Last edited by dangus; 1st January 2013 at 11:45 PM.
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Old 2nd January 2013, 12:42 PM   #16
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I wanted something similar. I bought a Lepai TA-2020+ and a pair of the cheap Dayton B652 speakers to start with. I then bought a piece of 1x8 pine board and some threaded rod to clamp it all together. I screwed the amplifier to the center of the bottom board. Then I used those rubber furniture leg pads to cushion the speakers. The threaded rod goes through the top board and screws into blind nuts attached to the bottom board. I put a handle on top.. and that is about it. All in, about $70 and it sounds pretty decent. I am going to make a place to mount a battery once summer comes.

Click the image to open in full size.

I also plan on tinkering with the Daytons to try to make them sound a bit better.. although that it not the real purpose of the rig. The purpose was to make something portable, that I could also disassemble and use as a near field system if the mood strikes me.
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Old 3rd February 2013, 02:51 AM   #17
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so what happened with the OP?
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