[JCD]

The Fisher ST-828 Speakers that I have , Have a 15 inch woofer , I am going to have to replace the 5 inch midrange, and also replace the 3 inch tweeter.. Now the question is On ebay i can get CV crossovers for about 20.00 a pair.. Pretty good deal.. Now I looked at building a single order crossover similiar to what was in there something like 750/5000 ... The only thing I can figure is why does the caps and inductors cost so much .. What is in the speaker now is so wimpy and I cant even read what is on the caps and resistors.. the single order I am looking at building are about 18.00 per each.

I have read that I am supposed to use Mylar caps and at least 18 guage inductors..


The tweeter has a 3.3 uf cap in series with the + on the tweeter,, the Midrange has a 0.19mh inductor and a very expensive 29.88 uf cap in series on the + side of the midrange.. I have got to combined the caps here to get a 29.00 uf value( hooked in parrell ) then the woofer has a 1.7mh inductor in series with the + on the woofer and that is it .. and wow 18.00 per each just for that.. :yikes:

I'm not sure what a "cv" crossover is, but unless it's built specifically for the drivers your going to be using, I'm not sure you'll get the results you're hoping for.

And yeah, crossover parts can be might expensive. Caps in particular vary in price from sort of reasonable to flat out outrageous.
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[JCD]

Assuming you're looking at the Dayton metalized polyprolene caps at Parts Express (your prices are matching up with what I came up with), you can get a 30uF cap for $8.52 that is less than the cost of the three you have in parallel. It might be a little less accurate than your three caps, but you'd fall within the "accepted" +/- 5-10% -- and one cap is always going to sound better than 3.
I took a look at the inductors and found prices of $4.00 and $10.26 for inductors with values of 0.20mH and 1.7mH (Jantzen 18gauge aircore).

Total part cost would come to $24.47/speaker before shipping compared to your $28.85/speaker.

You may be looking at better quality parts, so maybe it'd be worth the extra $4.38x2, but it sounded like you wanted to do this one the cheap.

A few follow up questions:

1. Are you replacing the tweeter and mid drivers with the exact same drivers that were there before?
2. If so, I'm assuming you're using the same values for the speaker parts that were there before?
   
   [*]Or, are you using different drivers?​
   [*]If these are different, how did you determine the crossover values?​
3. If this is a new crossover, why a single order crossover? Why not go with a second order so you can get a better phase response?
4. I don't see any resistors -- that would only work if you have three speakers with identical sensitivities, which isn't usually the case.

As for the CV crossovers -- I think most premade crossovers don't work as you think they would. They, by necessity, assume a constant load (4 or 8 ohms) from the speaker drivers, which is NEVER the case. So, given that, I generally recommend against premade passive crossovers. Each crossover should be made for the specific drivers in your speaker and the speaker box.

 

[JCD]

Ok, so it looks like these are completely different drivers that what were there before.
I'm also assuming that the crossover you're trying to create is your own recipe.

Two things

1. I thought I saw you post that you made sure the internal volume of the current speaker is appropriate for the drivers you're using. If not, then more followup questions.
2. Given the cost of the drivers you're using, I think going with the CV crossover might not be such a bad idea. Generally speaking, a crossover that's about the same cost as the drivers seems a little extreme. With that in mind, I'd probably go ahead and try the CV crossovers. This would especially be the case if you haven't designed a crossover before. I have several spreadsheets that can calculate the crossover values for a variety of types and slopes of crossovers, but I consider that just a starting point as there is always a book v. real world difference.

And please don't think I'm denegrating your project -- but I do think a cost/benefit approach should always be taken.

I look forward to seeing how your project turns out.

 

[JCD]

Although the driver's may physically be similar, their T/S parameters could be completely different.

This won't stop you from being able to put the driver in the cabinent and then getting sound out, but it could adversely affect the quality of that sound. There are a handful of programs out there that calculate the internal volume of a speaker for a given set of TS parameters. WinISD is one of the programs you can download for free. Youl could play around with it to see how different T/S values affect the modelled output.

Again, it may be fine, but it may not be "ideal".

 

[JCD]

And...

the verdict?

:foottap: