Help Wiring two subs together for ?? Ohms

S

scotter98

Audiophyte
I have two Inifinity Kappa Subs (8 inch, 4 ohm impedance each) and one old amp I got from a friend to power them. He originally bought this amp from MCM but he can't tell me how many watts rms it pushes nor what the impedance limit is. I'm assuming it is four ohms, is this a safe bet for home audio? The serial number is 0031615, that's all i can find on the amp itself and MCM will not return my calls or emails for specs on it.

In any case I built independent, ported, enclosures for the subs and now just need to wire the speakers and mount them to enjoy the new addition to my home stereo. Can someone help me out?

How can I test my amp to see how many ohms it is rated for?
Should I wire the subs for 8 ohms just to be safe?
If 4 ohms is all right how can i wire them to get 4 ohms? It seems that series and 8 ohms or parallel and two ohms are my only options...

Thanks ahead.

Cheers,

Scott
 
M

markw

Audioholic Overlord
Without knowing anything about the amp, I'd recommend you play it safe and wire the subs in series for eight ohms.

As you correctly state, the only other option is to wire them in parallel for two ohms but that would be taking a leap of faith that the amp can safely handle this. Are ya feeling lucky, kid?

And, as you again correctly state, there's no way you can wire two four ohm subs and wind up with four ohms. Four, yes, but not two.
 
K

Knight

Enthusiast
You should be careful as most home amps don't work well with 2 ohms. Also since you built a ported box it will require slightly higher power, and if the ported box you designed is not just right you will not get the best sound. If you went by a box desigh that infinity recommends then you should be ok. If you want to measure the ideal impedance of the amp you can but it requires instruments that most people don't have. Since you have two seperate subs I'd wire one to each channel if it has two channels if not I'd get an amp that does. Building home subs is getting harder as the amp selection is getting harder. There aren't many affordable one channel hih power amps out there.
 
j_garcia

j_garcia

Audioholic Jedi
Ported boxes generally require LESS power than a sealed box.

I would wire them series to make the total load 8 Ohms, though you are still going to draw more current with there being two drivers. If you leave them 4 Ohms and aren't sure about the amp's capability, it could be a recipe for disaster.
 
D

Dolby CP-200

Banned
I agree wire in series otherwise you’ll hear a nasty clipping noise coming from the two when it reaches maximum peak or near depending on the program source or the output setting of the amplifier and where you’ve placed the volume.

“Series!”
 
K

Knight

Enthusiast
The ported box will take MORE power than the sealed box. The easier freedom to move will use less power in a ported box at low volumes however typically the ported box will allow for greater excursion that can be unattainable in a sealed box. So in general to keep the driver from clipping you need more power for the ported box because the driver becomes more power hungry at greater excursions. j_garcia is correct but this only holds true when comparing the same driver in a ported and sealed box at the same excursion. The reason for the change in power comsumption has to do with the change of impedance that occurs at high excursions, excursions that a sealed box might not be able to reach without very high power. In your case I would avoid high output applications since the amp at low impedance will not function correctly and could be damaged and at 8 ohms the amp might not give you the power you need and will cause driver clipping and damage.
 
j_garcia

j_garcia

Audioholic Jedi
If the amp is mono, then yes those are your only two options. If the amp is stereo, then you can hook them up one to each channel and get 4 Ohms on each channel.

Do you have specs for these subs? Did you calculate a proper box and port size? If not, you will get unpredictable results and as Knight touched on, if the box is not correctly sized and tuned, you could actually damage the drivers. Being 4 Ohm, they sound like car audio drivers which often have different specs than drivers intended for home use so your box design can be a little different.
 
K

Knight

Enthusiast
The way that you would measure the working impedence of the amp requires an oscillorscope and a tone generator of some sort. It really isn't practical for most people. As j_garcia said 8 ohms is the way to go for a mono amp. Most home amps don't work well with 2 ohm but if you are unsure be safe. Low impedence at high volume can cause all kinds of problems.
 
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