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First off I'd like to say hello to everyone. I have been reading these forums for quite some time, but this is my first post. The amount of help given here is great and hopefully I'll be able to add to it as well.

So for some time I have been toying with the idea of a bookshelf speaker made with the following drivers from CSS, SDX7, FR125, and the RT1. My idea is to arrange in a mtw arrangement all sealed.

I have looked around and have planned to have the SDX7 in 7L sealed, the FR125 in a 9.4L sealed and the RT-1 in its own small compartment.

So now the question where I hope someone with more experience will come in - the crossover. To start will all be passive. The following pic shows what I have come up with for values. Crossover points are 500 and 4000 Hz.





The crossovers will all be wired in parallel. They are based on a butterworth arrangement, and the values for caps and inductors were calculated based on the impedance at the crossover frequency.

So if someone could help me out and have a look over, let me know if I'm way off base here. I'm also flexible to the crossover points and any other recommendations about my preliminary design.

Below is the plan for the speakers, curved sides, with a walnut veneer finish on sides and top, and a curved leather wrapped front baffle. Not a very good pic to start but I'll find another and post it soon.



I know it's a long first post, but I look forward to hearing your feedback and I'll be posting pics of it when I get it started.

Thanks again to everyone here!!

Sam
 

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Elite Shackster , HTS Moderator Emeritus
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2,216 Posts
So far it looks good. Crossover points are nice, 4k is out of the critical "sensitivity" band (1k to 3k, where oddly enough most speaker elect to put a crossover point).

As for the values and such, I would check out the FRD Consortium (google that for the link). They have a lot of free Excel based tools for calculating actual crossover values using the real data for impedance and frequency response, not just the single point. You can spot things like low impedance, weird phase shifts, out of phase behavior in the crossover, etc. Sometimes a little bump or dip in the FR can screw up an otherwise good crossover design. Since it's free, it would be worth it to play around with your design to see how it fares.

The only other thing I would recommend researching is baffle step compensation. Any closed-box speaker will have this problem, but thankfully there are many ways to deal with it. In short, the lower frequencies will have less output due to the width of the box. Wider boxes have less of a problem, but are often impractical. There are electronic solutions, like a Baffle Step Compensation circuit across the crossover (BSC for short), and if you don't mind a small redesign, an extra woofer can make up for the loss. Read up on it, it's nothing to be too concerned with, but you do have to plan for it in the original design.

Good luck.
 
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