This is topic Stereo help please in forum Tech Talk at Northern California Ford Owners  .


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Posted by 532Fastback (Member # 1482) on :
 
I installed a 4ohm sub in my 96 Explorer that came with an 8ohm sub/amp. When i turn up the volume my sub sometimes turns off depending on the music i was told its because the amp thinks there is a short with the sub since the amp is an 8ohm and the new sub is a 4ohm. How do i make the 8ohm amp think its giving power to an 8ohm sub even though its really a 4ohm?
 

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Posted by 532Fastback (Member # 1482) on :
 
ttt
 

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Posted by RioredGT (Member # 2300) on :
 
if the amp is designed to play at 8-ohms (8-ohm stable) than you are damaging the amp by using a 4-ohm load. With a 4-ohm load the amp sees a lower resistance and is drawing a higher current (even higher when the bass gets lower or you turn the volume up) which it is not rated for causing it to overheat which is why it is shutting down (usually amps have built in thermal protection). If you do this enough times the thermal protection circuit will eventually blow and your amp won't turn on.

As for fooling the amp into thinking it sees an 8-ohm load, I'm not too sure it's possible with one 4-ohm sub. You can get another 4-ohm sub, wire the two in series to produce an 8-ohm load and that will work.

If you want to be adventurous and try something AT YOUR OWN RISK, you can try putting a high wattage resistor (or two) in series with the sub to increase the resistance the amp sees. I've seen this done when building a low wattage speaker but never seen it done on a sub that was already built and not sure how it would effect the power of the sub???. The resistor would be something like these , but you would need to find one that matches the wattage of the amp.

[ April 19, 2009, 09:55 PM: Message edited by: RioredGT ]
 

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Posted by 532Fastback (Member # 1482) on :
 
what if i did some kind of bridging?
 

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Posted by RioredGT (Member # 2300) on :
 
Is it a two channel amp? Bridging is used when you combine two channels from an amp into one. Is this a factory amp or is it aftermarket? If you can post the amp specs I could possibly help you out some more...

Easiest thing might be to find an 8-ohm sub. Not as common as they used to be, but I see them from time to time on ebay.
 

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Posted by stanger50 (Member # 1665) on :
 
http://www.rockfordfosgate.com/rftech/woofer_wizard.asp?submitted=true&woofer_qty=2&woofer_imp=1

http://www.rockfordfosgate.com/rftech/woofer_wizard.asp?submitted=true&woofer_qty=1&woofer_imp=1
 

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Posted by 92stangLX (Member # 3252) on :
 
You will probably need an 8 ohm sub for it to work correctly
 

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Posted by venomous99 (Member # 1917) on :
 
you can also look at some dual voice coil subs where you'll have more wiring flexibility to alter the effective impedance. only thing is you may be underdriving the subs depending on what amp you have. majority of aftermarket amps on the market are 4ohms and is a good reason why you see lots of 4ohm subs.
 

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Posted by asskickn88 (Member # 4957) on :
 
You either need an 8 ohm sub or a 4 ohm dual voice coil that you can wire in series to make 8 ohms. By cutting your ohm load in half your allowing the amp to make more power but also causing it to overheat and shut down. I know others have posted correct advise, I'm just trying to throw out a simple explanation
 

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Posted by 532Fastback (Member # 1482) on :
 
Ok. I don't think I explained it good. My explorer comes stock with a 6 in sub. The stock sub was blown so I replaced it not thinking about ohms. The stock sub was an 8ohm I installed a 4ohm. What can I do besides replacing the amp or new sub? And if nothing anyone know of a small 4ohm amp I can buy that will be an exact replacement of my stock one?
 

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Posted by 532Fastback (Member # 1482) on :
 
anyone know?
 

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Posted by Blind (Member # 3052) on :
 
http://www.zeroimpedance.com/products.html

or, as asskicken88 said, you can get a DVC speaker and wire it in series to show the amp an 8ohm load

[ April 25, 2009, 12:55 AM: Message edited by: Blind ]
 

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Posted by WildFire532FB (Member # 1482) on :
 

quote:

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Originally posted by Blind:
http://www.zeroimpedance.com/products.html

or, as asskicken88 said, you can get a DVC speaker and wire it in series to show the amp an 8ohm load

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