opinions: building a subwoofer cabinet

[ksmith63]

hey guys

So i've got these 4x 8" dual voice coil (2 ohms a pop) subs that were made to be stock car subwoofers. I also have an 80 watt car amp along with plywood scraps. How well do you think this would do for an extension cabinet for my marhsall (2x15 watts into 8" speakers)? The marshall itself isn't that bad but it cannot handle any low frequencies. Any thoughts/ opinions on me buying a dc power converter and building a powered 4x8" sub extension?

 

[Quencho092]

Re: opinions: building a subwoofer cabinet

If you really want to go for it, you should run the headphones out of your marshall into the input of the car amp, then into all of the woofers.

What does the amp handle impedence wise? (how many ohms does the amp want to see?)

 

[ksmith63]

Re: opinions: building a subwoofer cabinet

car amp is 4 ohms and 80 watts (so if i run all 8 voice coils in parallel this will end up being 4 ohms). does it matter that i run the headphones out to the amp? this amp (not sure if all do) has a 'high level input' that is supposed to connect to the speaker terminals in your car eliminating the need for rca cables. If this is true then couldn't i run the signal from the marshall speakers to the high level input?

 

[Quencho092]

Re: opinions: building a subwoofer cabinet

try it using signal first.

If you run the speaker terminals from your amp to the car amp, output transformer might freak out because it wont be seeing any impedence.

Best bet is to run pure SIGNAL into the power amp.

 

[ksmith63]

Re: opinions: building a subwoofer cabinet

good point. i'll give it a try when i get around to building it. maybe i'll wake the neighbors up tomorrow at 7 am with a table saw.....

 

[Quencho092]

Re: opinions: building a subwoofer cabinet

oh and-

If each voice coil is 2 ohms, and you're running 8 of them in parallel, that's 1/16th of an ohm not 4 ohms. The only way to get 4 ohms is to run them as 2 series pairs in parallel. (4 speakers in series-8 ohms. 2 8 ohm sets in parallel-4 ohms!)

 

[ksmith63]

Re: opinions: building a subwoofer cabinet

wait for it......wait for it........wait.....WOO HOO! 100 Posts!
- thanks for that last bit of advise. lol i'm an idiot. forgot that in parallel the resistance is 1/r1 + 1/r2 = 1/rtotal. forgot the 1/rtotal part. a 4 ohm amp running at 1/16 ohms wouldnt be good.