How to figure out OHM load?

[Nova]

I tried searching this one but couldn't find it... Maybe I'm retarded. Anyway, how do you know what OHM load your amp is at? I know there are diagrams and stuff to show you how to get different OHM loads but how do they figure it out?....

[HaMSaMMiCH]

Let me Google that for you.

Ohm's Law

[Burbarry]

It has to do witht he resistance of the speaker. If you speaker is Dual 2 ohm and you bridge them together in Parallel, meaning all the positives together and all the negatives together. You will then be at a 1 ohm load for that speaker. If you hook that one speaker up to the amp you will have a 1 ohm load. Now if you hook one of the positives to one of the negatives on the speaker you will be at a 4 ohm load. Then hook that up to the amp you will be at a 4 ohm load at the amp.

[Nova]

Let me Google that for you.

Ohm's Law

I didn't know it was Ohm's law... Thank you

[audiofanaticz]

I tried searching this one but couldn't find it... Maybe I'm retarded. Anyway, how do you know what OHM load your amp is at?

Really all you know is what your speakers at like the one guy said. If you have a dual 4 ohm woofer wired in series, its 8 ohms, if its wired in parallel (both positives and both negatives wired together) its at 2 ohm.

If you parallel two dual 4 ohm drivers together it will be a 1 ohm load, if you series them together it will be 16 ohm load, if you series/parallel the 2 drivers together it will be at 4 ohm.

Tho that really doesnt answer your question at all, and I dont think the ohms law will help much at all if any for your main question of "what ohm load is your amp at?"

Tho you may have your amp wired at 1 ohm it rarely ever plays 1 ohm.

The ohm load of a driver (subwoofer, tweeter, midbass, midrange, etc) is a variable. When the driver moves the ohm load is constantly changing. So your setup that is wired at 1 ohm is actually being played anywhere from 1 ohm to 5 ohms (maybe even higher)!!!

If you take a DMM (digital multimeter) and set it to display ohms and connect it to a speaker you will see the impedance/ohm of said voicecoil. Now if you tap on your speaker or move the cone you will see that number (ohm load) change. The same thing happens everytime the driver moves forwards and backwords, thus changing the ohm load your amp is playing at.

You see people claiming 10,000 20,000 25,000 30,000 wrms etc. That is not the case at all. All they are doing is adding the RMS value of their amps together at a said ohm load.

They are not including the variable change of the woofers impedance. In reality there amp(s) are probolly doing half that rated rms power on a daily beating system that plays music.

A example is my buddies Honda CRX. They have 2 12 inch woofers, and 1 cactus 12kw amp. Its rated at 12000wrms by 1 @ 1 ohm, but when they clamp the amp to see the actual power it makes after impedance rise, it only does 5900wrms. But it still burps a 156.5db legal.

Then you have box/impedance rise. Depending on the size of your box, how your box is built yada yada yada, effects the ohm load your amps play at too making your amps put out even less power.

All these is is part of the reason I build my boxes on the larger side (larger then manufacture specs) to help fight impedance rise to get more power from my amp(s) and to make the driver more efficient (louder with less power).

But if you ever heard people saying they run their Sundown SAZ-3000D amps daily at .5 ohms without problems, its because of impedance rise which constantly changes and is almost always higher then the woofers impedance.

There is something else I wanted to say, but it totally slipped my mind now. Oh well, I think I covered most of it.

[audiofanaticz]

There is something else I wanted to say, but it totally slipped my mind now. Oh well, I think I covered most of it.

Just remembered what it was.

Amp rating. Many amps say they will do said amount of power at said ohm at said voltage.

Example: 3000 watts rms by 1 channel @ 1 ohm 13.8 volts.

But what many companies dont disclose is the frequency that their test is done at.

and Ive seen this in LOTS of tests too.

Many times these tests are done at 60 hz.

Now we are talking about sub amps here, and most of us dont drive around in our cars bumping music that plays at 60hz. Most of us daily beaters are tuned in the 25hz- 45hz range. So a amp that is rated at said 60 hz that is being used on a system that plays rap music in the 30hz frequency range isnt going to as much power as it could at 60 hz.

I even seen some tests on the big sound digital amp, and the person who tested it claimped like 13 or 14 thousand watts from the amp at a benchtest, but he also played a 100hz tone!! Sure that power is great and all, but its a useless benchmark to any of us that are tuned low.

[HHR Ed]

Really all you know is what your speakers at like the one guy said. If you have a dual 4 ohm woofer wired in series, its 8 ohms, if its wired in parallel (both positives and both negatives wired together) its at 2 ohm.

If you parallel two dual 4 ohm drivers together it will be a 1 ohm load, if you series them together it will be 16 ohm load, if you series/parallel the 2 drivers together it will be at 4 ohm.

Tho that really doesnt answer your question at all, and I dont think the ohms law will help much at all if any for your main question of "what ohm load is your amp at?"

Tho you may have your amp wired at 1 ohm it rarely ever plays 1 ohm.

The ohm load of a driver (subwoofer, tweeter, midbass, midrange, etc) is a variable. When the driver moves the ohm load is constantly changing. So your setup that is wired at 1 ohm is actually being played anywhere from 1 ohm to 5 ohms (maybe even higher)!!!

If you take a DMM (digital multimeter) and set it to display ohms and connect it to a speaker you will see the impedance/ohm of said voicecoil. Now if you tap on your speaker or move the cone you will see that number (ohm load) change. The same thing happens everytime the driver moves forwards and backwords, thus changing the ohm load your amp is playing at.

You see people claiming 10,000 20,000 25,000 30,000 wrms etc. That is not the case at all. All they are doing is adding the RMS value of their amps together at a said ohm load.

They are not including the variable change of the woofers impedance. In reality there amp(s) are probolly doing half that rated rms power on a daily beating system that plays music.

A example is my buddies Honda CRX. They have 2 12 inch woofers, and 1 cactus 12kw amp. Its rated at 12000wrms by 1 @ 1 ohm, but when they clamp the amp to see the actual power it makes after impedance rise, it only does 5900wrms. But it still burps a 156.5db legal.

Then you have box/impedance rise. Depending on the size of your box, how your box is built yada yada yada, effects the ohm load your amps play at too making your amps put out even less power.

All these is is part of the reason I build my boxes on the larger side (larger then manufacture specs) to help fight impedance rise to get more power from my amp(s) and to make the driver more efficient (louder with less power).

But if you ever heard people saying they run their Sundown SAZ-3000D amps daily at .5 ohms without problems, its because of impedance rise which constantly changes and is almost always higher then the woofers impedance.

There is something else I wanted to say, but it totally slipped my mind now. Oh well, I think I covered most of it.

Your buddy's CRX isnt getting full power out of that amp also because of voltage drop.

Probably drops below 10 volts DC huh?

The most power I have seen out of an amp in a street class setup is about 7000w. and thats on a 12K

[HHR Ed]

Just remembered what it was.

Amp rating. Many amps say they will do said amount of power at said ohm at said voltage.

Example: 3000 watts rms by 1 channel @ 1 ohm 13.8 volts.

But what many companies dont disclose is the frequency that their test is done at.

and Ive seen this in LOTS of tests too.

Many times these tests are done at 60 hz.

Now we are talking about sub amps here, and most of us dont drive around in our cars bumping music that plays at 60hz. Most of us daily beaters are tuned in the 25hz- 45hz range. So a amp that is rated at said 60 hz that is being used on a system that plays rap music in the 30hz frequency range isnt going to as much power as it could at 60 hz.

I even seen some tests on the big sound digital amp, and the person who tested it claimped like 13 or 14 thousand watts from the amp at a benchtest, but he also played a 100hz tone!! Sure that power is great and all, but its a useless benchmark to any of us that are tuned low.

Actually, manufacturers test amp output at various frequencies and also test a frequency curve. Most sub amps have a relatively flat frequency response from 20hz to 200hz.

Edited October 6, 2009 by HHR Ed

[Jman08]

well said man

[audiofanaticz]

Your buddy's CRX isnt getting full power out of that amp also because of voltage drop.

Probably drops below 10 volts DC huh?

The most power I have seen out of an amp in a street class setup is about 7000w. and thats on a 12K

Looks like they are running 10's in the car now. Last time I was at hughes house, they where testing with 12s. Didnt know they changed it up.

They are running 1 NSB75 with drop to 10.3 volts, and 4900watts.

http://audioforum.termpro.com/topic/4/20431/2.html

Actually, manufacturers test amp output at various frequencies and also test a frequency curve. Most sub amps have a relatively flat frequency response from 20hz to 200hz.

I didnt say that all tested at higher frequancys. Just a thing Ive noticed with some companies. I was trying to find the exact post on Termpro that I seen it, and the freq was 100hz. It was just used as an example. Not something to base every amplifier off of.

Edited October 6, 2009 by Bangin Caddy