Driscoll - My Iowa DIY entry.

[johnnyrichards]

I am not sure what the general consensus was on these, but I received some nice compliments on them from various people.

Driscoll is a compact 2-way monitor using a 1" fabric dome tweeter, and a 5-1/4" paper cone woofer in vented enclosure tuned to ~65 Hz.

The tweeter is a buyout Vifa, model number BC25TG19-04. It is NLA, however the Vifa BC25SG15-04 is a drop-in replacement for this project.

The woofer is an Audax-made OEM unit for Max Fidelity. Last time I checked, they were still in stock and come in at $6.80.

The crossover is approximately 4th order LR acoustic with a 3rd order electrical on the tweeter and a 2nd order plus EQ/Zobel on the woofer. It contains eight components, and the crossover frequency is ~1800 Hz.

The enclosure is 0.30 cubic feet, net. I used the 2" Precision port, mounted on the rear of the enclosure. To get the proper length, I simply used a single joining ring and joined the two flared ends. This yielded almost exactly what tuning I was after.

The bass alignment yields an F3 in the mid 60's, with a slight hump above the Fb. This flattens out pretty well when high passed electronically at 80 Hz. These were designed with a full time subwoofer in mind.

The baffle size is 7.25" by 12" with a 1/2" roundover on the left, top and right sides. The tweeter is semi-flush mounted with ~1/16" of the flange protruding past the surface of the baffle.

The port tube is located more or less behind the tweeter, and there is a single brace running from left to right. I stuffed about 3 ounces of poly fill around the port and extending down to just above the woofer. This left me ~3" of clearance behind the woofer. I lined one inner wall with "egg crate" open cell foam.

The finish I received quite a few comments and questions about the finish so I will summarize it here:

Step one: make sure you have good, tight joints on your cabinet. I used a modified version of Dave Pellegrene's "trench method" on most of the cabinet. I was originally going to go with a removable baffle but changed my mind at the last minute and did not trench that seam. It shows, and the others I challenge any naysayers to find My "modification" was simply setting the table saw fence up and running the enclosure at the seams over the saw blade, set to a 1/16" depth.

Use plenty of Bondo on the seams, and work it into the cracks quite a bit. Sand it off with 120 Grit, and you will see any pinholes. Repeat this process at least twice. After you have used the Bondo twice, sand it smooth with 120 grit and go over all the seams with "glazing putty". Let this dry over night at least!. Sand the entire enclosure smooth with 220 grit.

This will leave you with a smooth, seam free finish. You are not done with the putty yet!

After it has been sanded smooth with 220 grit, visually inspect all seams for pinholes. If you find any, daub some glazing putty into them and wait for it to dry, again.

Step two: After double checking all seams, apply a very heavy coat of gray automotive "filler" primer over the entire enclosure, even the places you won't look at. This is important since wet sanding will occur in the future! I used almost an entire can per side on Driscoll, it needs to be that heavy!

Let this dry for at least two days. Sand it smooth with 220 grit paper, trying to keep the sander flat. If you have a variable speed random orbit sander, use the lowest speed setting. If you notice your sandpaper is gumming up, find something else to do for the next 24 hours. You should be able to quite a bit of sanding with one sheet, and you should be creating nothing but fine, gray dust. Sadly, You need to sand most of this heavy coat off to find any high or low places. If you find a low place (which will be indicated by oval shaped "islands" of gray primer in the yellow sea of MDF), it will pay off to grab the glazing putty again and apply a thin, flat coat over the island. It needs to dry overnight again, and carefully sand it smooth to match the rest of the surface.

The edges will soak up a lot of primer on this coat, so do not be afraid to liberally apply it along the edges. Runs will be sanded out in this step so pour it on. The edges are doing on a small scale what the low spots on the rest of it are doing on a large scale. If you look closely, you will be able to see flecks of gray in the exposed edges of the MDF. This is where the primers has filled and subsequently sealed the MDF.

Step three: Apply another coat of filler primer, taking care to apply it evenly throughout. After this has cured, sand it smooth with 220 grit trying to leave the entire enclosure coated this time. If you burn through, no problem - just apply more primer. This coat is very important as it acts as both a seal coat for the MDF, and the base coat for the finish. You are long ways from applying color, but a good finish starts at the bottom and you work your way up

Step four: Time to switch materials and apply a different color. I use black Rustoleum primer after the gray coat. Apply a moderately heavy coat over the entire enclosure, again. At this point, you can put the power tools away since you will not need them any longer.

If you do not have a 3M rubber "block sander", buy one. Also buy those packs of 3M wet/dry black sand paper in grits of 320,400,600,800,1000, and 1500. Get a large pan and put a few inches of water in it, a few drops of dish soap and start wet sanding. The 3M rubber block sander uses a 1/4 sheet of sand paper. Use light pressure in a circular motion, and sand the black primer until the gray undercoat just starts showing through. Start in one corner, and work your way across the other corner. For rounded over edges, grab a different piece of paper and using both hands, work the wet paper over the rounded edges - think of those boys shining shoes on the street corner, that is the movement needed.

When the entire enclosure is wet sanded with 320 grit, use a towel and wipe it completely dry. You will notice the water gets everywhere, which is why I apply primer heavily to the edges of driver cutouts, and even inside the cabinet.

Step five: Change colors again. For this coat, I switch to Rustoleum "ruddy red" brown primer. Repeat the process above, but when this coat is dry wet sand with 400 grit, and then repeat with 600 grit. Wet sand each area until the color below the one you are currently doing starts barely showing through. If you see the gray showing through, you went too far!

Step six: You will need another color. I use a flat paint for this coat, in a color that will stand out in contrast to the final color. For example, on Driscoll I used a flat blue paint. If your primers are properly wet sanded up to 600 grit, this coat will look ultra smooth with hardly any "orange peel" or other artifacts. This coat needs to be wet sanded twice with 600 grit and 800 grit. The same rules WRT to color bleeding apply here.

Step seven: Apply your color coat. Apply at least six good coats of color, spraying every 1/2 hour, but a "wet" coat is not needed. Avoid using "gloss" paints, as these tend to A: take forever to cure and B: go on really heavy with heavy orange peel. This is the only mistake I made with Driscoll was using a gloss paint. I prefer using a "satin" finish.

Let dry for about a week.

Step eight: Wet sand the color coat with 1000 grit, and watch for the orange peel to start to disappear. You will notice when it does so. Be careful at this point, as the paint is actually pretty thin and if you see the next color show through you will have to paint it again and wait again blah blah blah. When the orange peel is pretty smoothed out, block it out one last time with 1500 grit. This will take the orange peel almost all the way out, and if you have enough paint on it - it is safe to go to a glassy finish. While the color coat is still wet, look at it under different light angles and you will see areas that need more work.

Step nine: Dry completely and buff with a clean, dry cloth. It is time to buff the finish out, and for this step I use Meguiar's "Ultimate Compound". Follow the directions on the bottle, but be warned that this step also takes off a thin layer of paint!

Step ten: Polish the surface with Meguiar's "SwirlX" swirl remover. This is a very fine rubbing compund, but it, too will remove paint.

Step ten: Finish the surface with a good paste wax. I use Mother's California Gold.

You should now have a "reasonable facsimile" (to use a phrase I heard in Iowa) of a piano finish.

Anyways, the crossover is like this:


The schematic shows Poly caps in the woofer circuit, but they are actually the mylar caps.

This is the crossover everyone heard at Iowa. I am going to do a little work on the tweeter, but I think it isn't at all bad the way it is. I am also going to build an "upgrade" crossover using poly caps in the woofer circuit rather than the mylar caps.

Tweeter (replacement): 264-1026
Woofer(until it is NLA): 299-071

I purchased all crossover components at Erse Audio.

My garage measurements show the peak at 5K which is why the tweeter might have seemed a little much:


This would make a decent center channel when laid on it's side.

This is a 4 ohm speaker.

[Pete Schumacher ®]

You definitely got DoubleTap's attention Johnny.

As we were heading back, he was recollecting his experience with them running full range without an enclosure. Running them side by side with a Scan Revelator left him unimpressed (go figure . . .). But after hearing them put into a final system, he told me he was ready to build up a set of 5 for his TV room.

Nicely done sir. They definitely sounded very nice.

[johnnyrichards]

Thank you Pete.

[evilskillit]

Sounded as good as they looked.

[mikejennens]

Great sounding speakers... and cheap too. It was nice to meet you Johnny. Thanks for sharing your knowledge and insight.
Mike

[johnnyrichards]

Thank you, gentlemen. It was nice meeting you all.

[arlis_1957@yahoo.com]

very, very nice write-up john.

i was able to listen to these a bit more then ya'll. they ARE nice sounding speakers.
before he left this morning, we modeled up a two-way with the 8inch silverflute that i bought in grinell. could be really sweet. thanks.

[johnnyrichards]

Arlis, I think those 8" Silverflutes will make a killer small floorstander Thank you for the kind words, the steak and the Grainbelts. I had a great time this weekend.

[6thplanet]

Nice write up, but where's the pics of the final speaker?

[johnnyrichards]

[6thplanet]

Ahhhh....

[2leftthumbs]

It looks like the tweeter is offset....how much?

[johnnyrichards]

It looks like the tweeter is offset....how much?

I'll get a baffle print up, maybe tonight yet. It has all the pertinent measurements

[theLinks]

Looks like your hard work paid off. Good job!

[johnnyrichards]

Oops, forgot about this:


Depth is 11.5", and I used 5/8" material on all sides except for the baffle which is 3/4"

[howard]

Johnny,
That Is a very attractive speaker with a professional looking finish. I would be proud to have that in my home; even more proud to have built it. I enjoyed your write up. I think the only way I will ever get a finish like that is to buy the cabinets from PE.
Howard

[johnnyrichards]

Thank you, Howard.

[anunnaki]

Those look wonderful Johnny! Great job on the finish!

[christianb]

Wow. Great looking speaker!

[johnnyrichards]

Thanks for the compliments, guys.