Acura Legend Forum banner
1 - 10 of 10 Posts

·
Registered
Joined
·
217 Posts
Discussion Starter · #1 ·
I wanna use two jlw0s on a 4ohm amp. does that mean i have to buy 8ohm jls? the amp is 4 channel. (2 2 channel amps) im going to bridge em to run the subs. if u run 2 8ohms, they turn into 4ohms or something?? im confused. plz help
 

·
0000$$$$0000####0000
Joined
·
4,943 Posts
It depends on how you wire them. You can combine the two 8 ohm JL subs in parallel and get a 4 ohm nominal impedence, or you can combine two 2 ohm subs in series and still get a 4 ohm nominal impedence. Also, are the JL's you plan on buying a single voice coil, or a dual vioce coil? The last JL sub I used was the old W4 series, so I am no longer familiar with the JL speaker line.
 

·
Registered
Joined
·
103 Posts
Most four and two channel amps are "stable" to two ohms stereo. Meaning you could run two four ohm subs off of each channel. It's when you start bridging that things get hairy. Most amps, unless they are a mono sub amp are only stable to four ohms bridged. So you would have to get two eight omh subs wired parallel to get your four ohms.
Add like this: two 8ohm subs equals 16. 16 divided by # of subs: 2 that equals 8. A bridged amp sees half of that. You get 4. Now if you were doing the same thing in stereo the amp would be seeing 8 ohms. Only when you bridge the amp does it "see" half. Now if you ran your subs in series wiring it would be completely different. Like Chris said you would need to get two 2ohm speakers. If you ran two four ohm subs in series you would be getting 8ohm impedence at the amp.

Since you have a four channel amp get two 4 ohm subs and run one to each bridged channel to get what you want. Or get two 8 ohm dvc subs and wire those in parallel to each bridged side to get four

If your completely lost right now have a car audio shop hook them up for you.:)
 

·
Registered
Joined
·
217 Posts
Discussion Starter · #4 ·
cool, thx. parallel and series? whats the difference? series is when both are bridged across on left and right channels. parallel is ones bridged on left, ones bridged on right?
 

·
Registered
Joined
·
307 Posts
wyolegend said:

Add like this: two 8ohm subs equals 16. 16 divided by # of subs: 2 that equals 8. A bridged amp sees half of that. You get 4. Now if you were doing the same thing in stereo the amp would be seeing 8 ohms. Only when you bridge the amp does it "see" half. Now if you ran your subs in series wiring it would be completely different. Like Chris said you would need to get two 2ohm speakers. If you ran two four ohm subs in series you would be getting 8ohm impedence at the amp.
I'm not hating on ya, but your calculation is wrong. This is how you calculate impedance (resistence). Remember, nominal impedance or resistence is not constant and will vary. The number and calculation that I will provide assumes constant and static conditions (i.e. voltage, current, etc...). The number that the amplifier manufacturer provides is sort of an "average" of what the amp can and will handle safely without overheating. Generally speaking, the lower the load that you run on your amp, the hotter it will get. You can run an amp lower than it's recommended load rating, but you run the risk of burning up your amp. However, if you could devise a way to keep the amp cool, you might be all right.

At any rate, here are some calculations:

Parallel:

This is when you run a speaker wire from the positive terminal on one speaker to the positive on another, and the negative to the negative on the other. Then you take the positive and negative from one of the speakers (the same speaker) and run them into your amp :).

1/R = 1/r(1) + 1/r(2) + 1/r(3) + . . . 1/r(n)

R = Total resistence
r = resistence on each of the speakers

So for example, if you have 2 4 ohm speakers you have:

1/R = 1/4 + 1/4
1/R = 2/4

Take the inverse of both sides (simple algebra):

R = 4/2
R = 2

With 3 4 ohm speakers, you have:

1/R = 1/4 + 1/4 + 1/4
1/R = 3/4

Take the inverse of both sides:

R = 4/3
R = 1.33333333333333333333

Series:

This is when you take a wire and connect the positive terminal on one speaker to the negative terminal on the other speaker. Then you take the remaining terminals and wire them to the amp.

I hope this makes sense to you. I'll try this way, speaker A has a + - and speaker B has a + -. You take a wire from A+ and wire it to B-. You then wire A- and B+ to your amp. This is a series connection.

Calculating Resistence on a series circuit is easy. My variable are the same as above.

R = r(1) + r(2) + r(3) + .... + r(n)

So for 2 4 ohm speakers you have:

R = 4 + 4
R = 8

With 3 4 ohm speakers you have:

R = 4 + 4 + 4
R = 12

I hope this helps.
 

·
Registered
Joined
·
99 Posts
SushiLicious said:


I'm not hating on ya, but your calculation is wrong. This is how you calculate impedance (resistence). Remember, nominal impedance or resistence is not constant and will vary. The number and calculation that I will provide assumes constant and static conditions (i.e. voltage, current, etc...). The number that the amplifier manufacturer provides is sort of an "average" of what the amp can and will handle safely without overheating. Generally speaking, the lower the load that you run on your amp, the hotter it will get. You can run an amp lower than it's recommended load rating, but you run the risk of burning up your amp. However, if you could devise a way to keep the amp cool, you might be all right.
somebody did there homework:cool:

next lesson: electrical current and resistance; from theory to practice. we will discuss why those equations are correct. hehehe

ok, ok...i'll spare y'all the booooooooring disertation
 

·
Registered
Joined
·
307 Posts
koper187 said:


somebody did there homework:cool:

next lesson: electrical current and resistance; from theory to practice. we will discuss why those equations are correct. hehehe

ok, ok...i'll spare y'all the booooooooring disertation
LOL, yes please educate me. I dropped out the Electrical Engineering program before we got to the practical part of the curriculum. I got my degree in CIS instead :D, make more dough selling than I do designing the product, go figure....
 

·
Registered
Joined
·
99 Posts
SushiLicious said:


LOL, yes please educate me. I dropped out the Electrical Engineering program before we got to the practical part of the curriculum. I got my degree in CIS instead :D, make more dough selling than I do designing the product, go figure....
it's been over four years since I took E&M, and since I haven't really used any of it, I'd have to go find my lecture notes. Plus, I hated that class: too much damn maths!:mad:

oh-well
 

·
0000$$$$0000####0000
Joined
·
4,943 Posts
I wish I had stuck with it when I was youger :( Currently I'm a lowly technician, but I am now back in school to get my EE. It sucks because I have a full time job in the Engineering departement at a local TV station, I'm married (no kids for now thankfully), and I go to school full time. I'm tired as heck now days, and I have to retake a lot of things that I no longer remember :) The positive side is that everyone is so young compared to me (30yrs in May), that I have much less distractions on my mind when I'm in school then when I was younger :) I no longer wish to be elswhere when in class and can concentrate better.
 

·
Registered
Joined
·
103 Posts
Thanks sushi!
My explanation was of course very basic, and I'm always curious to learn more. More info=better installer! You sure cleared that up for me!:D
 
1 - 10 of 10 Posts
Top