PC Speaker Amp

**Stooboy** · 09-03-2005, 04:18 PM

Ok, I havent seen any threads of anyone else doing this but, ive started to build my carpc system.

Im happy with the sound that my stock speakers in the car give, with the stock radio. however, im removing the stock radio so I can but an 8" oslon tft in there. I was going to run the line out from my sound straight into the loom of the car speakers but realised by reaading these forums that, this is not possible and would probabbly damage my sound on the laptop.

Like i said im happy to with the speakers that are in the car, and I have no amp, which to me is another big, peice of equipment I would have to power and find somewhere to put.

A friend suggested that you could take an amp out of a pair of old computer speakers, and kindlyu donated me a pair from his shed to dismantle

It turned out that the transfomer took 240V down to 12V AC, and there was a bridge rectivier on the board to convert this to DC, kool I though.

The speakers in my car are 4 ohms, and the speakers i took of the amp are 4 ohms. Thus I can only run the two front speakers from the amp I have.

What I was thinking of doing was putting the front right, and rear right speakers in series, giving me 8 ohms and put a 8 ohm resistor in parrallel with this to bring it down to the 4ohm output required. likewise on the other side. granted I wont have front and back control but at least I will have left and right with all four speakers. and a cheap solution.

My question is this, will that work, and if so how do I calcualte what wattage of resistor I will need.

Any help much appreciated...

**pancit175** · 09-07-2005, 10:03 PM

Power(watts) = Voltage(+12volts) * Current(Amps)
In parallel, It(Total current in amps)= I1 +I2
Voltage = current * resistance
But I wouldnt just throw a resistor in parallel just to bring it down for the amp, It wouldnt help sound performance You'd still be running the same amount of current to the speakers, and i doubt you'd be able to find a resistor that would be able to handle the amount of wattage that amp is putting out. If i attempted that, I wouldnt even put a resistor. Its a sound idea, but I dont think it would work well in automotive purposes.
I wouldnt do it. You'd probably get alot of static from the amp.

**roadhog** · 09-07-2005, 10:32 PM

:WHS:

I don't think it will matter if you wire the front and rear speakers in series though.

Or why not go quadrophonic?

Front as normal

Amp Left + to Rear Left Speaker +
Amp Right + to Rear Right Speaker +
Rear Left Speaker - to Rear Right Speaker -

Basically the rear speakers are in series but + - - + rather than conventional + - + -

It really can add a new twist to lots of music...

**Adam432823** · 09-08-2005, 04:47 PM

I agreee... putting in the extra resistor (yes they do make them large enough for this application, see ceramic) would give you the proper impedance, but you'd loose half of the output from the amp (think about it, you're converting energy into heat in the resistor).

You said you don't want to put in an amp cause you'd have to find a place to put it and run power.... um.... you're doing that with the guts of a desktop speaker now. Why? Go get yourself a inexpensive 2 channel amplifier. You can bridge your front and rears together and acheive a 2 ohm load. Any amp worth its salt can run 2 ohms. (1 ohm is usually out of the question).

If you absolutely have to use your desktop speakers amp, then I'd run it to both the fronts and rears at 2 ohm and make sure it has adequate ventilation to keep it from overheating. Maybe even slap a heatsink onto the amplifier ic.

**Bat** · 09-14-2005, 02:16 PM

Hi,
Visit your friends shed again, see if he's got another one, bingo! Or just run the front speakers with the one you've got?
Cheers,
Gavin.

**Stooboy** · 09-25-2005, 12:58 PM

Cheers for the replies guys,

I ended up just running the two front speakers from the PC speaker amp, it works well, at first but once I connected the screen into the same power loop I get intermittent crackle and whine from the engine so I guess I need to put a suppressor in.

The reason I continued with the PC speaker amp was because, this is my first install and I wanted to keep costs and complexity to a minimum, this will do for now but im so pleased with my install that, the next upgrade will be an amp (a real decent one) and possibly 5.1 audio!

Also the amp fitted perfectly in behind, the screen.