Here is what I am trying to do. I have a few decent quality car speakers laying around and would like to finish off my home theater system. I would like to build some decent speaker boxes and have nice surround sound system. I am a college kid, so $ isnt exactly flowing like rain. However, yesterday after doing some research I found that my receiver has to have a min. of 6 ohms per channel. All the of the car speakers that I have are 4 ohms.

What I would like to do is just put in a 2 ohm resistor and call it a day. The guy at radio shack gave me the dear in the headlights look when I told him this and said there was a lot more to it then just throwing on a resistor, but this is where I am at a loss because he didnt really know himself. What else do I need to look into? What kind of resistor do I need to make this work? I dont really want to run a 2 speakers in a series as I dont have 3 extra laying around! I would be building LR RR and a center speaker to finish off my system.

thanks-

Blaze

 

What the guy at radio shack wanted to tell you but didn't know how to say is that speaker coils are inductors as well as resistors, which means that, while they do have some resistive properties, they are able to take WAY more current than the traditional resistor. Basically what this means is that while you could throw the resistor in, it would probably burn up before you got the first sound out of your speakers. You could try putting in a wire-wound rheostat adjusted to 2-ohms to balance it out but I really don't know if that would work. Maybe someone else has an idea?

 

Probably true about burning it up, but I have used resistors inline on speaker cables without issue. Just be sure to get one that can handle at least the amount of amperage the amp will be pushing through it (50A resistor FTW).

You can also run 2 4 Ohm speakers in series on each speaker channel for 8 Ohms total resistance. This will also avoid over driving the amp, and doesn't require adding inline resistors. Or run the 4 Ohm speaker in series with a 2 Ohm tweeter (should be cheap enough to source), for a 6 Ohm load.

 

2 ohm tweeter? maybe a home audio, but i have never heard of a 2ohm car audio tweeter ever, i know you don't have the extra speakers to do it, flat line.. your best solution is a pair of 4ohm speakers in series, plain and simple. Trying to add resistance using a resistor is just not gonna suffice very well, because 1/3 of your amps power output is going to soak the resistor, so if your ch output is 20w rms, your resistor is gonna see 6.7w rms, constant.. and like the guy up about said, it is also has inductive properties and is not going to really be what you want, third option, run 4ohms on a 6ohm min ch, maybe the amp can handle it, who knows.. its definitely not recommended, and the unit may run hot and turn off, sq will probably be crappy, but it may work.

again to add to the 8 ohm load on the 6ohm ch- more resistance is gonna result in better sq.. if you don't really care about the speakers and amp, try what you want, but the best way is going to be the 8ohm load per ch alternative.

 

Here are the wattage outputs for my receiver

70.0 Watt - 8.0 Ohm - THD 0.1 % - 1.0 channel(s) ( Front ) , 70.0 Watt - 6.0 Ohm - THD 0.1 % - 2.0 channel(s) ( Center ) , 50.0 Watt - 6.0 Ohm - THD 0.08 % - 2.0 channel(s) ( Rear ) , 30.0 Watt - 8.0 Ohm - THD 0.08 % - 1.0 channel(s) ( Front ) , 50.0 Watt - 8.0 Ohm - THD 0.08 % - 2.0 channel(s) ( Rear ) , 20.0 Watt - 6.0 Ohm - THD 0.1 % - 2.0 channel(s) ( Center )

Since I already have the 2 front mains setup, there is no problem there. Since this is a low budget setup, I am leaning towards just doing an inline resistor. I dont mind that the RR and LR and center wont see that much wattage but if the sound quality is just terrible then I might beg to differ but we wont know till after I build the box and set it all up. As for a resistors, should I run one 50 amp 1 ohm on the negative and positive side before the cable reaches the speakers? Or is there some other way to wire it up? How do I know what amperage resistor to get? All the resistors that I have worked with (wiring up 450cc injectors) are always rated in watts, are there specifically resistors that just do AMPs and ohms only? I do not want the RR LR and Center to see more then 4ohms cause I dont want a toasted receiver or speaker. Thanks for all the help! Any guidance on what resistors to get for each speaker would be appreciated. I want to play it safe ohm wise while still allowing for maximum wattage delivery.

-Blaze

 

put a 12ohm parallel with the 6

---- 12 ohm ---
-----| |----
---- 6 ohm -----

these are what I've learnt from my EE class

 

Meh, Just add another 4ohm driver, or tweeter with a cap, wire them in series, and call it a day.

 

A resistor is the WRONG way to go. Most home recievers want to drive an 8 ohm load. Wire two speakers in series and call it a day.

Good luck finding a 70 Watt resistor LOL.

 

um, you don't buy resistors according to the amperage, you buy it in according to the resistance and wattage, i just ordered some 50 and 100 ohm resistors at work the other day, they are rated for 225w each and the are 13" long and about 1.5" in diameter, but we have 100w resistors the same size. they are about 10 bucks each at www.alliedelec.com

 

oh and your gonna wanna buy the clips for it to because they are gonna get hot, really hot.

 

Use two sets of speakers wired in series and call it a day, best way to do it.94

 

I beat you to the punch old man

 

I'm curious as to the accuracy of such a device +/-30%? Why whould you need such a device, why not use a couple mosfet transistors where you could dial in the resistance to whatever you wanted?

What do you use this for?

 

the company i work for make medical grade computer carts and as well as computers www.howardcomputers.com our carts have a battery/power supply setup on them so that they are mobile throughout a hospital, well we have to do strenuous testing on our equipment, so instead of hooking up devices such as heart monitors, computers, scanners, etc to create a draining load on the power supply, we used a large resistor instead to keep a steady resistance on the charger, because the charger will not kick into an output stage without seeing a load. Also those resistors are coated but some are not, some are variable and you can slide a strap up and down the resistor to get a desired resistance.

 

I see seems like a strange way. You must have an engineering department with entirely to much to do. A mosfet load would be rather simple and probably take up less space. With mosfets you would be able to drive a dynamic load which would provide more info then a static one. Real world most loads are dynamic. I guess whatever works works.