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  #1  
Old 01-11-2006
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Ohms, Amps and Subs.

I have asked questions about stereos and ohms and subs and still have a hard time understadning it. I dont really think I am dumb, but have NEVER really invested time into learning about stereos, so its almost like I am learning a new laguage. Someone may tell me, but until it sinks in, I might have to ask again.

Anyways, my question is this.

The sub I want to get is 500w RMS. I dont want to pay almost $400 for a mono amp to push the sub at 4 ohms, so I was figuring I could do this (run 2 ohms for much cheaper).

I could buy this sub:
http://www.onlinecarstereo.com/CarAu...roductID=14955

and this amp (and run it at 2 ohms for 600w RMS):
http://www.onlinecarstereo.com/CarAu...roductID=14927

Now my question is this. When it gets hooked up, will it be hooked up like this?



Thats what I am thinking is what needs to be done, but I may be wrong. That is how I am understanding getting the 300w RMS 4ohms to run at 600w RMS at 2 ohms.

is this set up going to sound bad? Would it be worth just getting the 700w RMS 4 ohm amp and getting a 4 ohm sub?

Let me know if this is right, please.
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  #2  
Old 01-11-2006
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I'll be interested to see the responses to this also, as I've always been really bad with electricity. My next physics class is PHYS 218 - Electricity and Magnetism though, so hopefully I'll get a better understanding.
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Old 01-11-2006
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If you hook up a subwoofer with dual 2 ohm coils in series like you have on the diagram the amp will be presented with a 4 ohm load. That amplifier will push 300W RMS when it has a 4 ohm load on it. If you have your heart set on that amp, you would be better off getting the dual 4 ohm version of that sub, hook the coils in parallel, and enjoy the 600W it will push at 2 ohm.

EDIT: Or, you could just hook up to only one of the 2 ohm coils...and one day if you blow it, switch to the other coil

Your drawing is correct, but you will get 300W, not 600W.

Last edited by fuze; 01-12-2006 at 12:01 AM.
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  #4  
Old 01-12-2006
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Quote:
Originally Posted by fuze
If you hook up a subwoofer with dual 2 ohm coils in series like you have on the diagram the amp will be presented with a 4 ohm load. That amplifier will push 300W RMS when it has a 4 ohm load on it. If you have your heart set on that amp, you would be better off getting the dual 4 ohm version of that sub, hook the coils in parallel, and enjoy the 600W it will push at 2 ohm.

EDIT: Or, you could just hook up to only one of the 2 ohm coils...and one day if you blow it, switch to the other coil

Your drawing is correct, but you will get 300W, not 600W.
Then what I would need to do is get the amp I am talking about from above:
http://www.onlinecarstereo.com/CarAu...roductID=14927

Then get a 4ohm Sub:
http://www.onlinecarstereo.com/CarAu...roductID=14954

and then connect it like this:

(I am assuming this is how you would make a 4 ohm amp run as 2 ohms)

Is that Correct???
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  #5  
Old 01-12-2006
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BTW, welcome to the sight, fuze. and thanks for the help.
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  #6  
Old 01-12-2006
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Correct. Or, like I said, keep the dual 2 and only use one side.

You might consider a cheaper amp also. Really, once you pass a certain level of quality there isn't a lot of difference. I bought a 1200W Lanzar amp for <$300 back in high school. It was driving the previous version of that 12" Type-R sub. I have the dual 2 ohm version and I had that amp loaded with 1 ohm. It pounded. Granted this was more power than the sub was rated for, although amps are usually over rated, but it ran like that for about 3 or 4 years and still does. As long as the sub can cool somewhat and you are careful not to allow distortion, it won't complain. Distortion and heat kill. Too much power = heat...turning it up too loud = distortion...and on and on I can go but you didn't ask all of this...

I could easily be persuaded to part with that Lanzar amp for a reasonable price btw...

But yea, back to your question...if you wire the sub and amp in your second post according to the second diagram it will work.
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  #7  
Old 01-12-2006
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Quote:
Originally Posted by 3906brad
BTW, welcome to the sight, fuze. and thanks for the help.
Thanks...and I'm glad to help so ask away
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  #8  
Old 01-12-2006
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I am trying to build a full Alpine system. This will be my thrid vehicle witha nice system, always wanted to build one up from the same Manufacturer.

As for the 4 ohm amp and 4 ohm sub. I will probably use whats in the diagram. I think that will work pretty good.

600w RMS on a 500w RMS sub - just need to turn the amp back some.
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  #9  
Old 01-12-2006
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http://www.audio-n-more.com/subwoofe...ormation.shtml

Found this.


Quote:
Connecting the two voice coils of the driver in parallel (+ to +, - to -) will result in the following impedances:

(Dual 6 ohm) Subwoofer: 3 Ohms

* This would be the most commonly used method of connecting a single 6 ohm DVC to a mono-bridged amp. Check to be sure your amp can handle a 3 Ohm mono (1.5 Ohm stereo) load. Check out the NEW 'Class D' and 'High Current' amplifiers.

(Dual 4 ohm) Subwoofer: 2 ohms

* This can only be used with "high current" amplifiers rated to handle 2 ohm mono loads. Check out the NEW 'Class D' and 'High Current' amplifiers.
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  #10  
Old 01-12-2006
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Yea, I can understand that since right now I'm swapping out my amps to make everything Kenwood...except for the Alpine sub. I wouldn't worry about matching the power. Just use your ears and make sure it doesn't distort and you will be fine.
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  #11  
Old 01-12-2006
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Yea, if you connect loads in series you just add the impedances up. If you connect loads in parallel...lets say two loads for example...the formula is 1/[(1/A)+(1/B)] where A and B are the impedances of the two loads. If you had 3 the formula is 1/[(1/A)+(1/B)+(1/C)]. Notice the pattern? just keep adding (1/X) for however many loads you have. Usually you don't need to get the formula out unless you're using those 3 ohm subs or just a lot of subs in some strange combination.
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  #12  
Old 01-12-2006
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Holy beginning posts with "yea" Batman!
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  #13  
Old 01-12-2006
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For loads that are all the same impedance the formula becomes even simpler.

Ohms/number of loads

So, three 4 ohm speakers in parallel would be 4/3 ohms, or 1.33 ohms for example.

The correct but more complex formula that Stephen posted is usually only used for loads of unequal impedance (or resistance in non-reactive circuits). That is, when you are connecting a 4 ohm and 8 ohm speaker in parallel for instance.

You might have noticed that speakers are not rated as "4 ohms resistance", but instead "4 ohms impedance". Both are measured in ohms however.

The difference between impedance and resistance is based on what the load does when driven by AC current (like an amp feeding audio to a speaker). A load like a coil or a capacitor works differently with AC than DC. Though impedance is still measured in ohms, but it PRESUMES a certain frequency of AC.

A load which is resistive reacts the same way to AC and DC. A load which reacts differently to AC and DC is said to be "reactive" and will usually have different resistance at DC versus it's impedance at AC.

One of the more interesting aspects, often overlooked, of speaker design is the "smoothing" of the impedance curve. That is, at different frequencies the speaker always presents the same load. That's actually one of the things a good speaker design should do.

A speaker in free-air, or improperly "baffled" (enclosed) will not show 2 ohms or 4 ohms or whatever at all frequencies. This can stress the amp, and/or cause resonances or "drop outs" in the response curve.
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  #14  
Old 01-12-2006
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This is one stupid question...but is less ohms more power or does it have nothing to do with that?
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  #15  
Old 01-12-2006
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The basic formula for power is current squared divided by resistance ("I squared R") which also works for impedance.

All things being equal, a 2 ohm sub would pull twice as much power from an amp as a 4 ohm sub. This does NOT however mean it would be twice as loud. To handle that extra power, the wire has to be heavier, and the speaker has to be able to handle the physical stress of being driven harder. This sometimes results in a "higher power" speaker having less "sensitivity" than a lower power (and perhaps higher impedance) one.

But all things are not equal, lol. So sometimes it doesn't work that way.

For instance, a given amp might or might NOT be able to provide the same amount of current to a 2 ohm load as it does to a 4 ohm load. That is often reflected in the specs of an amp where the power at 2 ohms is not twice the power at 4 ohms.

However, lower impedances are one of the easiest ways to get the most power. Each amplifier system has a "source" or "excitation" voltage (the power supply) and the total potential power is based on that. Amps which use 12 volts alone internally can only produce limited amounts of power to a load.

Most really powerful amps have switching regulated "boost" converters that supply a higher voltage from the 12 volt automotive system. This boosted voltage for the output circuits allows the potential for higher currents -- provided the system can handle the additional current.

So the answer to your question is: yes. But design factors limit the amount of extra power you get, if the amp can handle 2 ohms at all (which most can nowadays).

The disadvantage of very low impedance speakers is losses in the wiring. That's why you use obscenely thick wires to subs -- thinner wires would have enough resistance to actually waste a significant fraction of the power going to the speaker. For higher impedance speakers, the wire resistance is less of a factor proportionately.
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  #16  
Old 01-12-2006
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This is awesome. This cleared up alot of things and helped me to understand alot (and i think it sank in).

Thanks for the help guys.
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  #17  
Old 01-12-2006
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^^Im right there with ya. Thanks!
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  #18  
Old 01-12-2006
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Much more complete answers than mine...but mine were at like 2am or something...lol
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  #19  
Old 01-12-2006
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ok, here is another question. I called to get pricing on wiring for what I need and I was told I would need other things. Capacitor/s is what I think he said I would need. He said "Just like modifying an engine, there is no stopping, its what you want."

My question is, Would this System be enough? Do I NEED to add anything else?

Rear Doors:
http://www.onlinecarstereo.com/CarAu...roductID=14757

Front Doors:
http://www.onlinecarstereo.com/CarAu...roductID=14754

Sub:
http://www.onlinecarstereo.com/CarAu...roductID=14954

Amp for Doors:
http://www.onlinecarstereo.com/CarAu...roductID=13202

Amp for Sub:
http://www.onlinecarstereo.com/CarAu...roductID=14927

Deck:
http://www.onlinecarstereo.com/CarAu...roductID=14775

I am going to be using 0 Guage wire for power running into a splitter and using 4 guage from there for power. Then I will be using some large guage wire for the sub (i will see what I need) and some fresh wire for the 4 speakers.

Is that good enough? If not, tell me what i would NEED and why. please.
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  #20  
Old 01-12-2006
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Well, you're running a VERY good power feed for such a relatively low power setup. That power feed you're making may make it unnecessary to use a capacitor.

A capacitor is an energy storage cell, when used as they want you to. It allows brief spikes of very high current to be drawn at the amps power input without excessive "droop" of the 12 volts going into it. It's not a bad idea to have -- but may not be absolutely necessary at those power levels.

A general rule for "biamped" systems is 2 to 3 times the power in the bass amp as in the mid/treble amp -- you appear to have that.

You'll probably want to use the electronic crossover to block the bass to the main speaker amps so that it doesn't waste power trying to reproduce sounds the sub is responsible for. Basically, it's like the filter in the sub's amp that blocks highs, except you need to block lows. The amp you've shown has such a crossover/filter built in at 80 hz. You want to set it for "high pass", and tune the subs filter (which is low pass) to about the same frequency. You can tune the subs filter up or down a bit to get the smoothest response.

Looks good to me. Sure beats what I have, lol!
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  #21  
Old 01-12-2006
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you Don't need a Cap, spend the same amount ( for a decent Cap 1.5-2.5 Farads) instead on a Yellow top and you'll be fine.

Like John said caps have a purpose, but they are more for extremely high drawing systems or just for looks in show cars.

I'd upgrade the H/U a lil if you can afford it, unless you really like that one.

are you gonna do anything cool or wild with the isntall or just a MDF and carpet box?
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  #22  
Old 01-12-2006
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Quote:
Originally Posted by KARPE
I'd upgrade the H/U a lil if you can afford it, unless you really like that one.

are you gonna do anything cool or wild with the isntall or just a MDF and carpet box?
I really liek the HU. I had the 9845 in my Ranger and this one is basically the same, but allows me the access to XM if I want, since my truck is set up for it from the factory.

As for the system, nothing special. No lights or anything like that. No special boxes. I really dont want anything that is going to draw attention while it sits.

I had intentions of showing my Ranger when I got it cleaned up, but no intentions of doing that with this truck. Just going to get Wheels and a System.
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