how do I calculate tuning voltage on 3 woofers?

[mrpep]

I just bought 3 RFP4212 woofers in a sealed box, See link :

Rockford Fosgate HE2 RFP4212 12" Dual 4-ohm Voice Coil Component Subwoofer at Crutchfield.com

I want to tune them correctly , They are 400 watt RMS @ 4 ohms. My amp seems to be handling them well , THE AMP HAS 1000 WATTS RMS AND 2000 MAX. but wanna make sure that I am tunning in a safe zone.

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[CSCStang]

Wha? How do you have them wired and exactly what amp are you using? If they are all wired parallel, that's 1.3 ohm. If they are series/parallel, that's 2.7 ohm.

 

[mrpep]

Wha? How do you have them wired and exactly what amp are you using?

Rockford Fosgate RFP4208 Installation & Operation Manual (Page 7 of 12)

look at 2.67 ohms, thats how theyre wired and I am using this amp:

Alpine Electronics of America, Inc.

 

[CSCStang]

So you mean what ohm load is safe....the way you have it is ideal.

 

[mrpep]

I am trying to tune teh amp though , what calculation should I use?

400 watt rms x 2.67 ohms = 1068 volts square root = 32 volts.

Does that sound right?

 

[CSCStang]

You have to calculate the rms of the amp x 2.67, not the subs. At that ohm load, you are closer to 800rms. on the amp.

 

[jnewnam88 10+ year member]

You have to calculate the rms of the amp x 2.67, not the subs. At that ohm load, you are closer to 800rms. on the amp.

Negative ghostrider. You use the wattage you want the amp to put out. if you use rms of the amp that will tell you what voltage of that amout of watts. OP you are correct find the rms you want coming out of the amp and use that number times 2.67.

 

[CSCStang]

Negative ghostrider. You use the wattage you want the amp to put out. if you use rms of the amp that will tell you what voltage of that amout of watts. OP you are correct find the rms you want coming out of the amp and use that number times 2.67.

The amp is 1000 rms@2 ohm. At 2.67 it's closer to 800rms. So 800x2.67 is what you calculate.

 

[mrpep]

So it doesn't matter whether there are 2 or 3 woofers the formula remains the same ? I use the rms of the woofer because I don't to blow it if the amp is too powerful.

 

[jnewnam88 10+ year member]

The amp is 1000 rms@2 ohm. At 2.67 it's closer to 800rms. So 800x2.67 is what you calculate.

Yes, correct if you want to output 800 watts. However, he does not want to output 800 watts rms he wants to output 400 or whatever op wrote. You tune for what you want the output to be hence ohms law. Use the equation to find the missing piece.

 

[mrpep]

It doesn't seem to make sense to me though cause if you have one woofer and add a second don't you need more power / gain?

 

[CSCStang]

So it doesn't matter whether there are 2 or 3 woofers the formula remains the same ? I use the rms of the woofer because I don't to blow it if the amp is too powerful.

You have 3 400rms subs. With that amp load you are not running too much power at all.

 

[CSCStang]

It doesn't seem to make sense to me though cause if you have one woofer and add a second don't you need more power / gain?

You are safe under powering those Fosgates.

 

[jnewnam88 10+ year member]

So it doesn't matter whether there are 2 or 3 woofers the formula remains the same ? I use the rms of the woofer because I don't to blow it if the amp is too powerful.

Correct op. Just use your final impedence multiplied by the rms you WANT to output and take the square root of that to find vac

 

[CSCStang]

Ohm load x amp rms=voltage.