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Old 24th February 2008, 06:05 PM   #1
jwmbro is offline jwmbro  United States
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Location: München, Bavaria, Germany
Default Some last minute questions before ordering ZBM4s

Hi, thanks everyone here for your patience guiding a nooby like me to his decision.
I'm about to pull the trigger and order the parts for 8 ZBM4s (6 for me - 2 for a friend)
Here's a link to the article:
http://www.zaphaudio.com/ZBM4.html
Before I do so, I have a few questions.

1. X-Over Parts: I could order all the parts from madisound, or I could try to source similar parts locally. I can find poly caps with the according capacitances locally, however I can't find the exact R's and L's. For example I can find L's with .22 and .27 mH, but not with .25mH. Also their resistance is off too, so to get the right R, I'd have to pad with extra resistors. Is this worth the effort? or is it OK if it's a little off? For example, the closest to the .25mH, .1Ohm L I can find is a .33mH, .15Ohm for twice the price - probably best to just import then right?
And as for the Rs, I can't find 4Ohms or 5Ohms, but I can find 3.9 and 4.7, and also 0.1 and 0.3, but 2 Rs each means twice the price. Can I just use 3.9 instead of 4? Or should i make sure i get the 4?

2. X-Over: Where do I mount it - just to a board, which i put at the bottom of the speaker? Do I cover it with dampening material? how much energy does it dissipate?

3. Binding posts: what do I best use here - just the cheapest I can find? I'd like to use bananas with them, would this do?

4. Dampening: This I'd definitely like to get locally - what other than mineral wool can I use, and how much will I need for a speaker? Especially if any Germans can recommend something - it would be much appreciated.
Also, do I see correctly that there is also a thin strip of it between the box and the baffle on this picture?

5. Port: Does it have to be flared? Can I just use a PVC pipe? I'd like to make at least 3 of the speakers with a front port - will this sound worse than a back port (if I'm not using it as a nearfield - as Zaph mentions in the article)? My surrounds will be wall-mounted, so they can't have a rear port, and I was thinking might as well just make all 6 speakers the same... unless rear ports will be better? I s'pose I could just build a pair of test-speakers with front and back ports, and then experiment with plugging either port, but that would of course be more MDF, which is cheap, but not free. Hoping for feedback on this. Why are ports usually in the back anyway? Just for looks, or is it better that way?

6. Baffle: in this PDF John recommends a chamfer around the back of the woofer - will a standard 12mm depth work here? also, is it necessary to round off all 4 sides of the baffle? I could use MDF with veneer if I only needed to round the sides, but if the top and bottom are important also I'll just use wood or ply. Should I even make the baffle out of wood? I know wood is accoustically inferior, will I notice the difference in the baffle? The thing is, I'd like the baffle to be birch, so I'm wondering how best to achieve that.

7. Glue: John Krutke suggests you glue the woofer in place, to avoid leaks - if I do this, can I take the woofer out of the baffle again without damaging the woofer? Don't care if the baffle gets destroyed. (Same question goes for the tweeter, for that matter - since it is very fragile).

8. Baffle screws: I guess the easiest way to do this would be to sink a nut of some sort into the wooden triangles with the screwholes in them, and just screw a bolt through the baffle into them.

9. Enclosure: Here is where my lack of carpentry skills come into play Do I just glue the boards together, or do I use pegs and glue, or something even different? Is it worth the effort to miter the joints? How would you join to mitered boards up the best?

10. Cloth: To protect the tweeters from curious hands, I was thinking of covering the front of the speaker with some kind of cloth, what can I use that is accoustically as transparent as possible? I'd like to span it over a little frame on magnets, to attach to the baffle screws, so I can remove it.



OK, that's all for now, thanks in advance for any answers - by all means just answer one question if it's all you feel like, or all you can think of an answer for right now.
Also Thanks John Krutke for your excellent website if you read this!

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