# Caps and Woofer Replacement



## Tiny (Oct 17, 2007)

I have 4 vintage speakers that I am using for surround and surround backs on my 7.1 system. 2 are Criterion VI and two are of unknown make but the inside of both cabinets is marked Cerwin Vega though they don't look like any cerwins I have ever seen. That is neither here nor there at the moment anyways. I want to replace the 12" woofers in all four with 4 new Cerwins I bought for another project. While I am at it I am going to recap the speakers. Should I be replacing the caps with the same kind that are all ready in them or should some sort of upgrade?


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## Doug Plumb (Mar 16, 2007)

By "cap" I assume that you are talking about a capacitor in series with the woofer.

This provides an additional order of low freq roll off. A second order (closed box) becomes a 3rd order, a 4th order (vented) becomes a 5th order. 

This performs the function of an HP filter and reduces the ultra low frequency cone movement - movement that you can see clearly with the naked eye. Reducing this reduces distortion and can increase power handling. Overall I think its a good idea and have used it myself.

If its a closed box I say keep the cap and try the sound with and without it. If its a vented box, make it a closed box when you replace the woofer and use a cap with 2 X the existing ones stated value.


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## Anthony (Oct 5, 2006)

I agree with a lot of what Doug said, but it's impossible to know what value of capacitor you will need without the Thiele-Small parameters, impedance plot, and box type/dimensions.

In general, the same size cerwins should be similar to the old ones, however, if the new ones are for a different line -- they would have a different response. The same capacitor value might not be enough "rumble" filtering, or would be too much and limit the low end extension.

If you are up for some experimenting, just do the swap and play with different capacitor values until you get one that seems to work. Non-polar electrolytics are pretty cheap and you can use them to prototype. Once you find a value that works you can swap it out with a polypropylene cap (more expensive but doesn't degrade over time and some argue the sound quality is better).

If you can get some numbers off the old driver, we may be able to help with the replacement.

Good luck.
Anthony


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## Tiny (Oct 17, 2007)

Anthony said:


> If you are up for some experimenting, just do the swap and play with different capacitor values until you get one that seems to work. Non-polar electrolytics are pretty cheap and you can use them to prototype. Once you find a value that works you can swap it out with a polypropylene cap (more expensive but doesn't degrade over time and some argue the sound quality is better).
> 
> 
> Good luck.
> Anthony


I probably will have to do some experimenting I finally got the speakers apart and a good look at the "cerwin" caps and can tell you they are shot and used to be blue. I have never seen a cap so badly coroded come out of a working speaker. I think I will start with going to my electronics guru and shop owner and saying, "Roger I need to replace these". If they are identifiable he will know exactly what they used to be if anyone will. (This is my usual method of finding capacitors) 

The cabinets have a little more than 1.8cf inside each (24x15x12 outside).


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