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Multi-Way Conventional loudspeakers with crossovers

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Old 4th July 2002, 09:53 AM   #21
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What i was thinking when i said rigidity was if the box would flex at all compared to MDF. Also, is either material more conducive to better sound, or will I not notice a difference in sound between the two? So looking around, Im thinking im going to want to get the PS 1-95 grade plywood, is any preperation required for staining plywood, im thinking of using an opaque stain by the way. Geez, i just keep getting more and more questions, thanks a lot for sticking with me guys

Mike
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Old 4th July 2002, 03:11 PM   #22
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To be honest, for making relatively small boxes like yours, as long as the box is well braced, there is very little difference between ply and mdf.

When finishing any box, do as much sanding as you can be bothered with, it always makes the biggest difference to the success of the final result.

When staining, always apply plenty of stain, and leave for a minute or so then wipe off any excess, that way you will not get brush marks in the finish.
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Old 4th July 2002, 03:54 PM   #23
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The only thing to watch out for with plywood is voids, due to irregularities in the ply you can get voids of various sizes that can have an impact on sound. This is why you'll see baltic birch plywood come up again and again in speaker construction simply because it is void free.
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Old 4th July 2002, 04:01 PM   #24
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I couldn't find the word void in my dictionary. What does it mean in this case?

/Marcus
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Old 4th July 2002, 05:00 PM   #25
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Holes, usually due to knots that fall out of the veneer during manufacture, or gaps when two interior sheets do not quite meet before the sheet is glued and pressed.

Cabinet, or furniture grade ply, as well as baltic ply is usually certified free, from knots and voids, and usually has at least one clear side, free from any knots or other defects.

Ply can also be bought with either one or both sides finished with a hardwood, such as oak, beech or mahogany, or other decorative woods, (as can mdf in some places).
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Old 6th July 2002, 03:26 AM   #26
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Allright, thanks so much for the insight guys, I think this weekend Im gonna head to Home Depot to buy all my supplies, and will decide on mdf vs ply there, probably mostly due to the cost differences between the two, and the way i want to finish them(painting and staining respectively). Thanks again.

Mike
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Old 6th July 2002, 09:42 AM   #27
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Just a thought since you father does have a table saw and can presumably show you how to do precision cuts is to have Home Depot cut every thing with some overlap, take it to Dad and then cut it perfectly. It will be easier to handle already cut to close to what you need.
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Old 7th July 2002, 02:33 AM   #28
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Default You can have Home Depot do the cuts for you . . .

you just have to be smart about it. You have to know which lengths are critical and don't mark up the piece it makes things complicated.

What I do because I don't know how much volume bracing and cross-overs and other things take up, so I have them make the cuts so my final speaker will 2 or 3" taller, so I give myself some leway so I can just cut the bottom to the length that I need. Now for my front and back I only need to worry about the width. For my sides I only have to worry about my depth. And for my top and later after I cut the bottom I only worry about the width surprizingly because I only want to worry about one measurement instead of 2 make for a good 90 degree box. So what I do is I have the right width for the top and bottom and I leave the depth longer and after I screw and glue the piece I cut it with a hand saw, since it's easy to hold the saw against the front or back while cutting and use it as a guide cause they're straight and it makes everything flush.

When you go to Home Depot tell him you need 2 pieces 28" and 2 or 3 pieces 9.5." But but you don't want him to measure it everytime he cuts, it's better if there's a ruler on the saw and if there isn't have him (or you can do it) mark the wood holding braces at 28, 11, 12.5, and 9.5." If he measures it with the tape measure and markes it with a pencil every time he needs to cut and then eyeballs and saw to see if it lines up with the mark, you will go home with a bunch of wood that is all different sizes. Go up to him and say " I need 2 cuts 28," he gets done with that say "I need 3 cuts 9.5," he gets done with that take the cut wood and say "I need 4 cuts 11," and etc. Making sure he does all the same size cuts ONE AFTER THE OTHER, IN A ROW. That way they'll be accurate, trust me I've done this a bunch of times. It's common sense but the first time you walk in there you don't think about these things. You can have him cut the tops and bottoms if you don't like my way of cutting them.

As for the screws get drywall screws. Esspecially if you use MDF, it splits very easily. If you have the misfortune of having to take your box apart you will see. I use drywall screws because looking at them length wise they're just as wide with the threads as regular screws, but the shaft holding the threads is more narrow. So you have a very nice margin of error when you decide how wide a drill to use when you pre-drill holes for the screws. Normal screws you have to decide should I risk spliting the wood if the hole is too small or losing the grip from the thread and having the screw spin if the hole is too big (another good reason for long screws, if you can drill straight). Only thing better about normal wood screws is that you can get them with no thread for the first .5" or 3/4" so that the threads don't hold the wood apart.

Check this link out for box construction http://www.lalena.com/audio/faq/build/

Hope this kind of makes sense. I think this is my first contribution to this forum only because I have gone to Home Dept so many times for this reason and I believe with the way I do it I get more accurate cuts than I could do myself (probably, I never tried because I just got a circular saw) everytime.
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Old 7th July 2002, 10:58 AM   #29
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Jimmy. your way makes a certain amount of sense for a basic home constructor, with limited tools...

But, what I would do is re-arrange the cutting list, so that each set of panels with the same dimension is cut at the same time, successively, so that even though each panel may be a fraction off in one direction, they will all be the same in that dimension.

So, for instance, first make all the cuts for depth for the box sides and top/bottoms, then the cuts for width for the fronts and the final width cut for top/bottom. Then finally cut all 4 sides to the right height.

Although you box may not be the same, I hope this gives you the ideal, all similar cuts should be made without changing the settings on the saw, as this is where errors creep in.

Box volume can quite easily vary by 5- 10% without causing too many problems, from design parameters, so an odd couple of mm either way on a
cut will not be problematic, as long as all the cut dimensions are the same.

Personally any new boxes I build tend to use biscuits and clamps for assembly, it keeps things accurate and aligned, and saves having to fill any screwholes before finishing.
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Old 9th July 2002, 08:32 AM   #30
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Question Crossover Troubles

Thanks for all the replies on the woodworking aspect, im sure they will be put to good use

Now sticking with the trend of of being the most perplexing area of this endeavour, (to me at least) the crossover has thrown me another curveball. I sat down to map out how i would lay out the crossover board, and noticed that the inductor values looked a little funny, so then i looked at the parts list, and saw that some of the values called for in the crossover schematic were not listed in the supply list. Here's what is called for in the supply list:

.55 mH air core inductor, 19g (2)
.45 mH air core inductor, 19g (2)
.30 mH air core inductor, 19g (2)
.20 mH air core inductor, 19g (2)
.15 mH air core inductor, 20g (2)

Now in the schematic for building the crossover, (url for kit is : http://adireaudio.com/misc/free_designs/the_bang!.htm schematic is about halfway down the page) it calls for: .15 , .27 , .41 , and .20 mH inductors. I've heard something about combining crossover components to get a different value, but have no clue as to how to do this. Also, two of the values of inductors in the schematic are the same as those called for in the parts list, while two are not. But if you have to combine two different inductors in order to get a different value, that would require 4 total inductors to get the two different values, that 4 plus the 2 whose values remain the same equals six inductors, for one speaker. But the parts list only has you buying 2 each of 5 inductors for both speakers. I hope you see what Im trying to convey here

...ok, after doing some reading, I see that you can either put inductors in a series or parallel circuit in order to alter their values, much like speakers now that i think about it. Actually just like speakers, seeing as the equations are the same(Ltotal=L1+L2+L3 for series and Ltotal=1/L1+1/L2+1/L3 for parallel, but im sure you guys knew those equations) But still like i thought before, this requires at least two inductors for each value I want to change, and that leaves me on short according to the supply list, plus, i see no way of obtaining these odd values using the values listed on the supply listed and the aforementioned equations. Oh well, Im sure if anyone got to the end of this book of mine they might be able to figure it out..Wow, muchos gracias to anyone who even reads this far, let alone even attempts to solve this. I really mean it, thanks a lot guys.

Mike
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