Bookshelf speakers build

[AlanY]

Are you planning on veneering the speakers that you're assembling with screws? You're going to have to be especially careful to avoid show-thru, especially if you're using paper-backed thin veneer. It may be worth asking on a woodworking forum for more advice about hiding the screws. They might suggest using Bondo above the screw holes.

[guzziguy]

Also do yourself a favor and use pre-filled and pre-sanded veneer.

[aerius]

Speaking of crossovers I'm not quite sure how to mount the crossovers, the SR-71 kit XO came on two boards and my initial design aimed for a stacked crossover with a horizontal platform to mount the second XO board. After deciding to do a crossbrace, I found that the XO would be in the way so I may just mount it on the side.

Or go with external crossovers, as is done with the Living Voice OBX-R. Build a nice shiny box for the crossover and separate it from the speaker entirely. This gives your more freedom for laying out the boards and it also gets the parts away from the vibration and magnetic fields in the speaker. The downside is you'll need extra sets of speaker cables to hook it up to the amp.

[swt61]

Are you planning on veneering the speakers that you're assembling with screws? You're going to have to be especially careful to avoid show-thru, especially if you're using paper-backed thin veneer. It may be worth asking on a woodworking forum for more advice about hiding the screws. They might suggest using Bondo above the screw holes.

Sinking the screws about 1/32-1/16" below the surface and filling with Durham's Rock Hard Water Putty will work great, although Bondo is perfectly acceptable as well.

Then I'd use a bearing guided straight bit to flush up the top and bottom plates.

[Nebby]

Sinking the screws about 1/32-1/16" below the surface and filling with Durham's Rock Hard Water Putty will work great, although Bondo is perfectly acceptable as well.

Then I'd use a bearing guided straight bit to flush up the top and bottom plates.

I had thought of doing that since I did that for my subwoofer when prepping for paint, but I didn't realize that the screws would show through with veneer! Thanks for the warning AlanY, I'll make sure to put a few screws on my test piece to see how much of an effect it has. The veneer I have also isn't paper backed, so hopefully that helps. I don't have access to that Durham's putty, but I have something that seems to be the Japanese equivalent of Bondo.

Btw, thanks swt for the tip with the dovetails, that makes perfectly good sense!

aerius: I have given external crossovers some thought, but personally I think it's best to keep the cable length between the crossover and the speakers as short as possible so I'm planning on keeping the crossovers internal. Thinking back now I was simply over-thinking the crossover placement, it really won't be much of an issue if at all.

[HeadphoneAddict]

Nebby that bottom dovetail is damned near perfect, I doubt you could get it any closer.

A little tip for your finished product...After cutting and fitting the dovetails, take some 220 grit sandpaper and lightly go over the joint. This will fill any minor flaws or voids with fine dust the correct color. Then use a jersey rag (old T-Shirt) to lightly wipe down the area (no compressed air here obviously). Take a can of spray lacquer and very lightly spray over the joint from about 12-14 inches away. Just a very light touch, and if you have no lacquer around hair spray will substitute well as long as it's the aerosol type. Give that time to dry and very lightly sand with 400 grit. This won't interfere with your chosen finish, and will give you a perfect joint.

Your box plan seems reasonable to me.

Give me a powertool over handwork any day! As long as new tools are invented to speed up the woodworking process, guys like me will keep buying them. I have great respect for the woodworkers of the past, but we gots 'lectricity now baby!

Those are some GREAT tips about getting the perfect joint!

Too bad it will be covered by a veneer.

[Nebby]

Who said anything about my DAC box being veneered? I'm crazy, but not THAT crazy Speakers = veneered, future DAC box = dovetailed and dado's.

[Dusty Chalk]

aerius: I have given external crossovers some thought, but personally I think it's best to keep the cable length between the crossover and the speakers as short as possible so I'm planning on keeping the crossovers internal. Thinking back now I was simply over-thinking the crossover placement, it really won't be much of an issue if at all.

What about mounting it externally? Just in case you run out of room...

[luvdunhill]

personally I think it's best to keep the cable length between the crossover and the speakers as short as possible so I'm planning on keeping the crossovers internal.

You're building someone else's design on the one hand, and on the other hand making blind judgments on what is a good idea and what's not?

There are a lot of good reasons to do external crossovers... the added resistance of the wire is pretty much trivial, but if this concerns you, it's easy enough to compensate for it.

[Nebby]

Hey thanks for pointing out my mistake there! I did some more reading and found out what I thought was an issue with external xo's was mostly false. I was worried about emi/rfi but that would only really take effect in long runs which wouldn't be the case.

I'm treating this project as a learning experience. Admittedly my own knowledge of the subject is minimal and really only limited to what I've read (including the speaker cookbook...that's one great book)

What are some of the good reasons to do external crossovers? The benefits I can think of moving the XO out of the speaker enclosure:

1) move the XO away from the magnets of the speaker, taking any negative interactions out of the picture

2) If you're playing loud for long periods of time having them external would allow more cooling

3) remove the odd shaped xo from inside the enclosure, though the effect of that can be reduced by putting the xo into a sub-compartment within the enclosure

4) Easier access to the XO for tweaking purposes

5) possible conversion to active crossover (but for a project in this price range I don't think it's worth the hassle)

Possible cons?

1) Separate enclosure required for crossovers

2) Length of the cable from XO might provide more opportunities for emi/rfi, but I would guess that this is a non-issue unless we're talking about very long cables

I would like to keep the speakers one piece though, since I move somewhat often and having extra parts to worry about every move would be a hassle.

[swt61]

)

Possible cons?

1) Separate enclosure required for crossovers

2) Length of the cable from XO might provide more opportunities for emi/rfi, but I would guess that this is a non-issue unless we're talking about very long cables

Building custom stands with the crossovers mounted inside them is an easy fix here.

I'm building such a project for Marc.

[luvdunhill]

2) Length of the cable from XO might provide more opportunities for emi/rfi, but I would guess that this is a non-issue unless we're talking about very long cables

yup, this isn't really an issue at all. Take for example the following topologies: active crossovers, PLLXO crossovers, digital domain crossovers (Behringer devices, etc.). All of these have the potentially long cable in the same location in the circuit with no detriment.

From my experience, there are no negatives. The positives that I've personally measured are:

less inductive coupling due to more room to properly layout inductors. If you're building a large floorstander, this is less of an issue, as you have more room. But if you have a small three-way with 30 odd components per channel, there is no way you can cram it in a speaker enclosure without detriment in this area. Even more to the point, is I have a small three way with four inductors per channel. There is no way that you can space these out properly. This is pretty easy to measure and verify. This also includes interaction with the drivers own inductance, as you pointed out.

less microphonics from the capacitors. Well, I guess this may be harder to convince people of, but it's really noticeable when your in the trenches designing a crossover. The best way to mitigate this if you want to stick the crossover in the enclosure is the use of box caps, as I've found they are far less susceptible.... yes, you'll need a lot of them in some cases, but they are well worth it. Some people damp the hell out of the axial capacitors with silicon, but this just doesn't work so well I've found.

Anyways, have fun!

[Nebby]

Thanks for taking the time to write all that out luvdunhill. In your testing, what was the distance before inductance wasn't affected by neighboring inductors? The only testing I've seen done has been this link: Placement of coils in crossover networks: Does that mostly match up with your findings?

I have read about capacitor microphonics, but didn't realize it was that noticeable. I think I'll have to do some more reading on that. Perhaps for my next project I'll be using an external crossover!

I'm definitely having fun thinking out the logistics and learning about everything involved with a speaker. Worst case if it doesn't work well I can always make a new enclosure. Afterall, it's not the destination but the journey isn't it?

[Nebby]

Didn't go into the woodshop, felt too under the weather to trust myself with the project. So instead I did went ahead and tried out a bit of veneering. The veneer I did the test with was a scrap piece of 1/40" figured bubinga.

Main objectives of this test were to find out:

1) How difficult the process is

-not very

2) If screws or puttied countersinks showed thru the veneer

-1/40" thick veneer I expected they wouldn't, and they don't

3) How hard it is to work with the veneer

-it's a bit tough, sharp tools help; went with a simple score and snap method for removing excess veneer with this test piece, will probably cut it properly with a router on the real thing or 2nd test

4) Overall melt/solidify time for the heat-lock glue

-I used my snowboard wax iron, set to 160C, the glue initially melts/hardens within seconds although the instructions recommend letting it harden for 24hours.

On to the pictures:

Extra countersunk screws

Flush countersunk screws (left one is slightly low)

Extra countersunk screws haphazardly puttied

Glue rolled on to both surfaces. You'll notice that the veneer bent quite a bit from the glue. I read in a book that you can prevent this by spraying the opposite side with water to equal the expansion. The book didn't say what would happen if you didn't, so I decided to find out.

Turns out there's nothing wrong with just letting it dry. I think with a thinner veneer or with veneer that's more unstable you would need to spritz with water, but the bubinga turned out just fine. This is after letting it sit for 30minutes:

After scoring and snapping off the edges (yes, it was rough but it's just a test) and then doing a quick sanding job with 320grit:

Planning on doing a coat or two of spray lacquer to see how it looks/reacts to a finish tomorrow.

[swt61]

Beautiful veneer Nebby!

I like to use a veneer trimmer like this...

A+ Edgebanding Trimmer now in stock at VeneerSupplies.com

They trim it perfectly flush, but be sure to trim within 1/16" first with a utility knife and straight edge. If you try to trim more than that it can get hung up and cut too deep into the grain.

[Nebby]

Ah, can't believe I missed that item! That's the exact store I bought my glue and softener from.

Here's the test piece coated with two coats of semi-flat deft clear lacquer (unsanded)

[swt61]

That's gorgeous!

I'd give it about 3 more coats buffed with 0000 steel wool between each one. That will give it some depth for that crazy, fantastic graining. Excellent work!

[Nebby]

No updates for a while since I've been a bit busy lately. But this just came in yesterday:

Japanese veneer saw - works great.

[Nebby]

Did trial run of the baffle cuts today, first I tried to do the tweeter:

As you can see, it didn't work out too well. The stopper on the router got loose halfway and as I went the router went deeper and deeper until at one point it just went right thru the piece. After getting a feel for how tight was "properly" tight, I went on to go for the woofer.

It turned out a bit better this time, although I went too deep and the cutout got loose when I went to complete the circle. Next time I'm going to make sure to leave a tiny bit left over so the piece is intact, then route that out on the other side.

After placing the woofer in, the frame was acceptably flush with the baffle. It's difficult to see, but the frame has a bevel to it, so getting a proper measurement of the thickness was a bit difficult. I went with what the specs gave me and it ended up alright IMHO.

Lessons learned:

1) Check router stopper is properly tightened, then check again.

2) When doing the cutout, leave a bit of wood so the piece doesn't go loose at the end.

3) Working with measurements given in metric is a genuine PITA when all your equipment are in imperial units.

[swt61]

When I get toward the end of a circle cutout I apply a bit of inward pressure on the router. That pushes the cutout section against the circle wall you just cut, and keeps the router from running into the outside of the circular cut.

Did that make any since?

Your way will work fine too. I'm assuming you're using a Jasper circle jig?

[Nebby]

You assume correctly sir, I'm using a Jasper circle jig. I was somewhat worried about the metric -> imperial conversion until I found their calculator on their site. Unfortunately the tweeter cutout will be .5 mm larger than the tweeter, but I'm hoping that some generous primer and paint will close that gap. I was hoping to test that with this test baffle, but completely fubar'd it this time.

The method you describe does make sense, I'll give it a try on my next test. Thanks for the tips, they're much appreciated!

[swt61]

I would think that after finishing the .5mm would hardly be noticable.

Thanks for the conversion tip, I didn't know it was on their site either.

As usual great work!

If you decide to stick with it, you're going to be an awesome woodworker! Your patience and detail are your strong suit. I love following your threads!

DIY turntable in the future?

[AlanY]

Unfortunately the tweeter cutout will be .5 mm larger than the tweeter, but I'm hoping that some generous primer and paint will close that gap.

MDF swells a bit once you apply sealer. You want a small gap like that after routing otherwise it can be hard to get the drivers in. So it sounds like what you have is perfect.

[Nebby]

Actually, patience is not my strong suit. I cope by working on multiple projects at once, so I can distract myself from frustrations by being productive on something else. It's worked well for me so far

No turntable in the near future, I'm mostly satisfied with cd's and digitial audio...maybe in the distant future?

AlanY: Totally forgot about the MDF expanding from the moisture, I'll definitely watch out for that on the test.

[Nebby]

I did some stain testing the other day and totally forgot to post pictures, so here you go:

Dark mahogany, reg. mahogany, and keyaki. It's hard to tell but the dark mahogany has a nice red glow on the figure, I rather like it however the stain is a bit dark. For a later project I might thin it out some and use it. For the speakers I'm sticking to the natural color.

Here's a closeup of the corner. The joint line is extremely thin and is very difficult to see, especially with a slight chamfer on the corner.