Questions, questions, from newb DIYer

Well, I guess I should start off by saying hello to everyone, Id also like to thank in advance those who help me :) I've recently decided to undertake my first DIY speaker project (well home at least, ive installed a stereo in my car, as well as a couple friends'). After some searching around, I decided on building the Bang! loudspeaker from Adire Audio http://adireaudio.com/misc/free_designs/the_bang!.htm
Theres the url for quick reference. Anyways, I decided on this kit based on price (headed to college next year :eek: so $$ is an issue) praise I have heard for the speakers, and lastly the reputation of Adire. I know I wont be dealing with Adire directly as I complete this project, but its just comforting to me i guess, to know that what Im building comes from a quality source. Wow, ok, Im thinking a lot of that was unneccesary, but Thanks to those still with me ;) . Now for my questions:
1. Do you guys have any better reccomndations for kits, considering that I think I can keep the budget on this one down to around $150 (not purchasing formica)
2. In the crossover, does the polarity of the components matter i.e. does the positive of the component face towards the source, or the speaker?
3. In the plans it calls for a 5uF Elpac Mylar Capacitor, Madisound no longer stocks this, and looking at Elpac's website, it seems silly ordering a single capacitor from a company that appears to deal mostly in bulk. So Madisound does have another 5uF capacitor, but its a GE, and is polypropylene as compared to mylar. So will the GE work?
4. The plans call for 5% 15W wire wound resistors, Madisound now stocks 10%. Heck I dont even know what the percent means, but will these new 10% work in lieu of 5%?
5. What gauge wire should i use for connections within the crossover itself, i was thinking 18-20 gauge, will that work?
6. When cutting out the panels for the cabinet with the..I feel like such a newb here, cant even think of the name of the saw, you know the handheld circular saw..anways, when your cutting with that, how exactly do you account for the kerfs it makes in your measurements on the cut sheet i.e. How do you measure the size of kerf it will actually make.

Whew, that was a lot of typing, well Im out of questions, though im sure i will have plenty more as this project progresses. Seriously guys, thanks so much for the help im sure Ill get, you have no idea how helpful a resource like this is. Thanks again.

Mike (the slightly overwhelmed newb) :D
 

Brett

Member
2002-01-07 6:02 pm
Howdy!

and welcome to the wild and wooly world of diy.

The Bang! is a good speaker for the money from the reports I've heard (caveat: not actually heard them myself). I think you will be hard pressed to get a better kit for the money. Adire have a reputation for making excellent products. It has a high sensitivity (how loud it will go for a certain amount of power) and they will go loud according to the site. Great. My only concerns are that you won't get huge bass from them: good, but not huge. But I gather they might be in a college room soon, so they'll probably be fine. Adire make some great subs which you can look into later if you find it lacking. The other is the impedance (the load the speaker represents to the amplifier: smaller number=bigger load) which dips to 3.5 ohms, which is a heavy load for some amplifiers. Do you have an amp yet, and if so, which one?

To your questions
<b>1. Do you guys have any better reccomndations for kits, considering that I think I can keep the budget on this one down to around $150 (not purchasing formica)</b>

I'll pass on answering and let the veterans in the US comment as they know prices better than me.

<b>2. In the crossover, does the polarity of the components matter i.e. does the positive of the component face towards the source, or the speaker?</b>

Resistors - no.
Inductors - no.
Capacitors - wrt the components on the list, no. The polyester and mylars (basically the same thing) are non-polar, ie, they can be connected either way around. For future reference, all plastic caps, poly-something, are non-polar. The Bennics in the list are also non-polar, but are electrolytic types. Most electrolytics are polarised and will have +/- terminals (future ref info) so they must be connected the right way around.

<b>3. In the plans it calls for a 5uF Elpac Mylar Capacitor, Madisound no longer stocks this, and looking at Elpac's website, it seems silly ordering a single capacitor from a company that appears to deal mostly in bulk. So Madisound does have another 5uF capacitor, but its a GE, and is polypropylene as compared to mylar. So will the GE work?</b>

The GE will be fine. All poly caps are just basic variations on a theme. Many consider PP caps to be better than PE anyway, but I'll opt out of that discussion at the moment.:D

<b>4. The plans call for 5% 15W wire wound resistors, Madisound now stocks 10%. Heck I dont even know what the percent means, but will these new 10% work in lieu of 5%?</b>

The % refers to the tolerance with which it's manufactured. A 100 ohm resisteor as it comes from the factory, will not be <i>exactly</i> 100 ohms. A 5% tolerance means it can be anywhere between 95-105 ohms, and 10% between 90-110 ohms. The closer to exact is always better IMO, but it's often not critical. I would try to get the correct tolerance, as it will help you get it working as close to the way the designer meant. There are other sources for these in one-off quantities, such as Digikey, Mouser, Parts Express (all in the US) etc.

<b>5. What gauge wire should i use for connections within the crossover itself, i was thinking 18-20 gauge, will that work?</b>

Should be fine. A cheap tip for speaker wire is Cat5 computer cabling, which you might be able to scrounge for free depending on the length of your speaker runs from an electrical contactors offcuts. Power cable also works, as of course does the standard zip-cord. With Cat5, strip all the ends and twist them all together, and use that for +ve for one speaker, and another length for -ve. Another two runs are required for the other speaker.

<b>6. When cutting out the panels for the cabinet with the..I feel like such a newb here, cant even think of the name of the saw, you know the handheld circular saw..anways, when your cutting with that, how exactly do you account for the kerfs it makes in your measurements on the cut sheet i.e. How do you measure the size of kerf it will actually make.</b>

I think you got it with hand held circular saw. By "kerfs" I assume you mean the loss of timber (blade width) caused by the cut itself. That'll depend on the particular blade/saw. The more experienced woodworkers will be able to be more exact.

My advice for the timber cutting would be to spend a few extra dollars and have it cut on a proper saw at the place where ou buy the timber. They will be straight and square and the right size, and will save you a lot of grief in the building. I <i>can</i> do it myself, but I get much better results faster by getting a pro to cut it. Print out the cut-sheet on the Adire site and ask the timber yard how much extra it'll cost. Shouldn't be much as they're all rectanglular pieces.

When you actually build it, take your time, measure everything twice (at least), and relax. Expect to make mistakes, but with care it should be straight forward. Ask for help here or from experienced friends etc. Oh, and RELAX: this stuff is supposed to be FUN.

I hope that answered your questions OK. If not, ask for clarification. There are a lot of knowledgable people here who are willing to share their experience.

Cheers
 
4. You could always buy a bunch of 10% resistors and measure them and use the ones that falls inside the 5% margin. Not so cheap to do with 15W resistors though...

6. Take a piece of scrap wood and try the saw. Then you will know. I don't really see why you need to have that measure. You cut out one piece and then from the new end you measure and draw the outlines for the next piece.

You could always practice your skills on some scrap wood so you don't have to make so many misstakes on the real thing. ;)

/Marcus
 
Woodworking issues...

I'll tackle your woodworking question, as that's one of my favorite hobbies...

First, I'm assuming the saw you're referring to is a 7 1/4" circular saw (Pretty standard saw for more people) and not a jig saw. (jig saw has the long thin blade that goes up and down and not around) Unless you have a special thin kerf blade (which I doubt) the kerf is basically 1/8".

Okay, I just took a look at the site, and now understand why you're asking about the kerf. They run a VERY tight cutting arrangement. My suggestion for cutting that sheet would be as follows.

1) lay out the left most long cut, namely 12 1/2" from the edge. A suggestion here on cutting straight lines, especially on such a long length, when you're buying the sheet goods, also pick up a long metal straight edge. (I assume you're going to Home Depot, Lowes, etc.) It should be cheap, come with clamps and be long enough to cover the 8' sheet. (I think mine was under $20, and is DEFINATELY worth it.)

2) measure the distance between the saw blade and the edge of the bottom plate on the saw. Now it gets a little tricky, depending on which side you place the rail, you'll either need to add on the thickness of the blade (1/8", remember?) or not. (Think carefully about which side the cut piece will be on)

3) clamp down your straight edge, double check the measurements at both ends. Think again whether you have to add the thickness of the blade, check that measurement again. (trust me on this, I've screwed this up several times)

4) make the cut. Measure the cut piece. (Hopefully you got the measurement right and its not 1/8" short) If all goes well, you should have the first long piece cut now!

5) Now repeat for the next cut. When you get to the last piece, it should be less than 1" off of its final size.

Using this technique, you don't have to worry as much about the saw kerf, as you're measuring each piece from the already cut edge. The biggest thing they're trying to emphasize on the web page is to not just measure and mark all of the cuts at once without taking the kerf into account. If you use my method, you'll come out fine.

As to their logic on using Particle board over MDF, don't let price be the deciding factor on that, it should be less than $10 difference between the two. (I just recently bought a 4x8 sheet of 3/4" MDF for $20 at the local lowes)

Good luck with your project, and let me know if you need more help!
 
Thanks for the prompt replies guys. As per Brett's question on my current amp, i am far from an audiophile at this time, and thus dont have quite the best equipment. Right now I am using an older Technics reciever that used to be my dads, the model number is SA-410. I will be using this for at least a few more months, but then will be buying a new a/v reciever. Schaef, thank you for your directions on cutting the panels, but I think im going to go with Brett's recommendation of having the store i buy the wood at cut the pieces for me. It just seems like one less thing to worry about, and this being my first project I think its a good idea, I will definately save your directions for reference in future projects though :) . Once again, my sincerest of thanks.

Mike
 
Well it looks like Schaefs directions will be going to use after all. I just got back from visiting the local Home Depot and talking to one of the people there, I found out that the price was right, 25 cents per cut, but the accuracy was not, he informed me that the measurements could be off anywhere from 1/16" to 1/8". So I politely thanked him for his time, and headed back home. Looking around in the garage I found that my dad does have on of those long metal straight edges, so that makes things easier. I was just wondering if there were anymore suggestions on building these cabinets, pointers, lessons youve learned the hard way, whatever you think might help :p Also how long, and what type of nails work best with 3/4" MDF? And one last question for the time being, I was wanting to finish these cabinets by painting them black, preferably with a glossy finish, does anyone know how I would go about doing that? Thanks a lot.

Mike
 
About cutting the wood. If you have a straight edge use it. Take a piece of scrap wood and put the straigth edge on it anywhere, clamp it down. Now take the saw and just make a small cut in the wood, having the saw guide run up against the straight edge. Okay, now measure from the inside of your cut to the edge of the straight edge. Now every time you want to make a cut, mark the cut, then place the straight edge the distance from the line that you just measured, and clamp it down. You should now be able to run the saw up against the straight edge and make a pretty accurate cut.

Hope that kind of made sense. If not let me know and I will try to find another way to explain it. A table saw would be ideal, maybe a neighbor has one that you could use. If not this method is one way that you should be able to get fairly accurate cuts if you take your time.

As for nails in mdf, don't use nails. Screws would be best but maybe that is what you meant. I have found that wood screws and dry wall screws work pretty well. You will want to pre drill the holes so you don't split the mdf as the screw goes in. Also countersinking the screws is a plus. In case you don't know countersinking a screw is when you use a speacial "drill bit" to basically make a space for the screw head to sit in so it is flush with the surface it is screwed into.

That is a lot of typing for now. I am tired and probobly ranting, so if you need any clearing up about this stuff just ask.

Mark
 
Thanks markkanof, that thing with measuring after making the cut in scrap wood sounds like a good idea. heh, yeah i did mean screws, but what size would work, should it be twice the thickness of the wood, so 1 1/2"? My dad has a table saw, but it wont work for this since im going to be working with a huge sheet of MDF, and he was no extensions for it to hold the wood, ya know what i mean? is there another way to use a table saw without those extensions? THanks everyone.

Mike
 
I'll try to answer each of your questions as best as I can.

First, screw length (don't nail MDF, you'll regret), I prefer to go with a screw that's at least double the thickness of the material. Longer won't hurt. Also, as markkanof suggested, counter-sinking the screws is a really, really, really, good idea. (Get the hint?) Before you start work on the final sandings, fill the holes with putty, allow to dry, and then do your final sandings, and after painting, the screws are gone! (if done well, of course) I'd also recommend gluing the panels as well as screwing them. (In addition to strengthening the joint, it helps seal it as well)

As to the table saw, while it IS a good idea, I would recommend against using it for this, unless you buy two pieces of MDF or have at least one other person around to help while cutting. (As you've probably found out, MDF is HEAVY!) The circular saw/straight edge combo should be good enough. (I've built numerous things using this method, they've come out quite nice, if I do say so myself)

On to painting, you'll quickly discover that MDF can act like a sponge. It'll take the finish you apply and suck it right up, until you've completely sealed it. So, I'd suggest at least two coats of a good primer followed by at least three coats of your paint. If you want a really smooth gloss finish, I'd recommend sanding between every coat. (No power sanding, hand sanding with 220 grit or higher sandpaper or 0000 steel wool, and yes that's four zeros before the steel wool, not a typo)

Finally, take your time and things will come out fine. Also, remember, you'll be the single most critical person analyzing your work. (Unless you happen to be married, then you'll be the second most critical:D ) Also, be patient when working on the finish, if you rush it, it won't look good. (I generally allocate at least a week of time for finishes, but then again, I'm picky when it comes to finishing a work)

Oh, and another thing, have fun! This should be a relaxing thing to do as well! Let us know how it turns out and if you have any more questions!
 
Thank you once again for your help Schaef. There were just a couple things I was wondering on the paint about. What kind of paint works best? and is it spray or brush on? Also, to ge the high gloss finish, how much do you sand between coats, just lightly, or do you go pretty deep? And do you get the glossy finish from just the paint by itself, or is there some clear coat you put over it to make it shiny? Once again, thanks a million

Mike
 
Okay, slight confession here, I've not painted MDF yet, I'm giving advice based on information I have read here and in woodworking bulletin boards, so I have no personal experience with painting MDF. Having said that, my finishing experience is tied to my woodworking projects. (right now, a small table/desk for a second computer made from maple, finished with a tung oil mixture and top-coated with poly, already looking real good with only two coats of oil!)

As to which paint is better, that's hard to say, partly because I'm not sure if you want a name brand, or if you're looking at oil vs. water based. I can't help a lot there, as my finishes have mostly been of the oil or shellac or poly variety. I will say that with current technologies, the differences that once existed between the paints are getting smaller and smaller. However, one piece of advice I CAN give, is to not skimp on the quality of the paint. Based on the size of the speakers, (you are building just two, right?) a gallon of paint should be more than enough.

As to spray versus brush, if you can spray and know how, it should produce a smoother finish. (I'm talking HVLP gun, compressor and what not here, not spray cans) If you take your time with a quality brush though, you should be able to get a really nice finish with a brush as well, it'll just take a little more work.

As to sanding, you just want to sand enough to make the surface smooth again. It should feel pretty smooth before you rub/sand it, but afterward, you won't believe the difference! One other key item, is to put on thin coats, don't try to do a one coat coverage, it'll look like it. Do multiple thin coats, it'll come out smoother and look better.

As to the shine, you can do a couple of things, and here, you should experiment a little with some scraps. (Just finish a couple scraps along with the main piece, so you can try these things) This will help you decide what looks best to you. When you get to the final step, you want rub out the final coat with the steel wool, then switch to a very fine grit sand paper (600+), and then you can try going further with using rottenstone paste and a rag. Alternatives to the last step include using car wax and buffing it out. (It can look quite nice and if you have a power buffer, it can look even nicer) Basically you want to polish the finish for the last step, this will give you the high gloss you want. (In addition to using a gloss paint to begin with)

Hope this helps you out!
 
Hi Mike

Well, I have some experience with mdf, (real wood is so very expensive in the UK), so I might be able to help.

The main problem with mdf finishing is getting a good base, as the plane surface can cause primers and paints to pinhole due to the mixture of woods and resins used.

The endgrain is also very very absorbant, and will suck up paint like there is no tomorrow!

The only way I ever achieved a good piano black finish on mdf was very time consuming, but was done as follows;

1) round over any sharp edges with a router or power sander

2) sand, sand, sand, and then sand some more

3) fill all construction screwholes and minor gaps, as well as running a thin layer over any exposed engrain, with 2 part car body filler

4) sand some more, and then wipe down with thinners

5) spray on a couple of thin coats of car body primer

6)lightly sand, and then fill in any new holes/ marks that you can now see with more filler

7) spray on more primer in thin coats, lightly rubbing down with very fine wet and dry paper between coats, until you can no longer see the difference where the endgrain starts and the face material. When you do this, use a sanding block and warm slightly soapy water, then wipe with a slightly damp cloth and allow to dry fully.

8) when satisfied you have a flat finish, apply 4 or 5 coats of colour, knocking the finish back as above between coats.

9)apply 3 or 4 coats of laquer ( making sure you use the same paint maker as your body coat, as some paints can react), knocking back as above

10) allow to dry for a minimum of two weeks

11) very lightly sand, as above, for one last time

12) polish using firstly a cutting compound such as T Cut, and then buffing with wax by hand, as many times as you like...


This is why I now veneer all my mdf boxes!
 
Hi Mike

Well, I have some experience with mdf, (real wood is so very expensive in the UK), so I might be able to help.

The main problem with mdf finishing is getting a good base, as the plane surface can cause primers and paints to pinhole due to the mixture of woods and resins used.

The endgrain is also very very absorbant, and will suck up paint like there is no tomorrow!

The only way I ever achieved a good piano black finish on mdf was very time consuming, but was done as follows;

1) round over any sharp edges with a router or power sander

2) sand, sand, sand, and then sand some more

3) fill all construction screwholes and minor gaps, as well as running a thin layer over any exposed engrain, with 2 part car body filler

4) sand some more, and then wipe down with thinners

5) spray on a couple of thin coats of car body primer

6)lightly sand, and then fill in any new holes/ marks that you can now see with more filler

7) spray on more primer in thin coats, lightly rubbing down with very fine wet and dry paper between coats, until you can no longer see the difference where the endgrain starts and the face material. When you do this, use a sanding block and warm slightly soapy water, then wipe with a slightly damp cloth and allow to dry fully.

8) when satisfied you have a flat finish, apply 4 or 5 coats of colour, knocking the finish back as above between coats.

9)apply 3 or 4 coats of laquer ( making sure you use the same paint maker as your body coat, as some paints can react), knocking back as above

10) allow to dry for a minimum of two weeks

11) very lightly sand, as above, for one last time

12) polish using firstly a cutting compound such as T Cut, and then buffing with wax by hand, as many times as you like...


This is why I now veneer all my mdf boxes!
 
Thanks for the great advice on the painting guys. I think instead of the high gloss finish, ill try for more of a semi-shiny finish ;) Im just going after a smooth nice looking black here, so even flat would probably work. Thanks once again guys, gonna start ordering all the pieces for this here in a couple days :) Regards

Mike
 
ook, plywood, im sorta new to the lingo ;) My only concern with plywood is its rigidity as a building material, as compared to MDF, also, does it come in 3/4" sheets? Oh yeah, eye protection is a must, and as for the facial mask, i didnt know MDF was that harsh, thanks for the heads up :D . Thanks for all the help.

Mike
 
Just want to second the comment before about the use of masks when cutting mdf, the glue in that stuff is pretty nasty, and the dust from it is so much finer than wood dust.

Plywood definetly comes in 3/4 thichness, as well as 1/2 inch, and 1/4 inch. As for it's rigidity, I guess that kind of depends what you mean. Is it as dense as mdf, no not at all. Now this part is just my thoughts, the ideas are fact, but might not translate to reality in this case. So here goes, Plywood is made of thin sheets, obviously each known as a ply, which are glued together under pressure to create the final product. Now these plies are normally glued together with each layer's grain going perpendicular to the last layer's grain. This is intended to increase what I would call rigidity over regular wood in which the grain goes all in one direction. The reason I mention this is because to me working with plywood is much preferable to working with mdf because I feel it is worked much easier. Meaning it isn't as rough on my table saw blades, it doesn't have as nasty a dust, it takes screws well, it can be finished nicely, etc. So my thought would be if mdf isn't much more rigid than plywood, then plywood might be the material of choice for easiest construction.

Thoughts??

Mark