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3 PI build [message #78971]

Thu, 16 January 2014 14:58

BFP
Messages: 48
Registered: May 2009

Baron

Hi folks

I've started a 3PI build. I am using the Eminence 4012HO woofer and a B&C DE250 horn driver. I have the PI H290C horns from Wayne. I am adding 4" to the overall height of the box and will house the crossover in the resulting compartment underneath. The internal dimensions are identical to the PI 3 plans developed by Wayne. I have some flared ports that are about 2 3/4" diameter that are long enough to be cut down to length for the 3.
I had some 3/4" Baltic Birch which will be used for the inner ply of a 2 layer baffle and also for the back panel. I will be using 3/4 MDF for the sides and top/bottom. Bracing will be a mix of the 2 materials as well.
I started by building the crossover board and back plate. I used 1/2 "MDF and some scraps of BB for bracing. I put a couple of thin pieces of particle board on the bottom to act as spacers for tie wraps or bolt head clearance.

index.php?t=getfile&id=1363&private=0

I am using a mix of parts. Coils are 14G Solen. Resistors are the 25w non inductive Mills heat sinked resistors. I mounted them on pieces of 1/4" Aluminium that I had in my scrap metal pile. For capacitors I had some North Creek Zen and Crescendo caps that add up to 7uf so they are doing duty as the first tweeter cap. The rest are Axon 250volt. Wire is mostly the component leads or 12 gauge OFC Anti Cable enamelled speaker cable wire. For the driver leads I had some 14g OFC wire for the woofers and 16G monster cable for the tweeters. This is mostly bits and pieces I had in stock but should get the job done. Solder was Cardas tri eutectic. Here is one under construction and also a top view of the finished unit. These will slide into the empty space at the bottom rear of the box.

index.php?t=getfile&id=1366&private=0

That's all for now. Next instalment will be starting to work on the box itself.

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Re: 3 PI build [message #78974 is a reply to message #78971]

Thu, 16 January 2014 19:08

BFP
Messages: 48
Registered: May 2009

Baron

Correction: The resistors used in the crossover are rated for 50w not 25w as stated above. There are 2- 25w resistors on the heatsink as well. They are in parallel with a 15ohm 50w to bring it down to the 13.5 ohm value required.

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Re: 3 PI build [message #78989 is a reply to message #78971]

Sun, 19 January 2014 16:27

BFP
Messages: 48
Registered: May 2009

Baron

There are many ways to build a speaker box. A lot depends on what tools you have at hand and what methods you prefer. I will be starting with a laminated baffle. The outside is 3/4" MDF backed up by 3/4" Baltic Birch. The inner baffle is inset so it will form a ledge for the front of the walls and top/bottom. The top/bottom are inset leaving no MDF joints visible on the sides. The back will be inset. I will be adding a cap to the top, making it 2 layers thick. I'm thinking of doing a black lacquer on the top. The rest of the box will probably be flat black covered with satin water based poly urethane. I plan on making a base to bolt to the bottom and a grill to keep dust off the drivers.
Heres some pictures of the inner baffle. I cut the horn through hole before laminating the 2 layers. I used a jig saw. The one I have is a Dewalt which I just got recently. A good jig saw is a great tool to have around. This one is capable of fast, accurate cuts without a lot of noise and vibration.
index.php?t=getfile&id=1370&private=0

Laminating the panels. You need lots of glue and clamps. You need to use a glue with a long open time. I'm using Lee Valley GF2002 which I have found to work well. Tite Bond 3 is quite similar.
index.php?t=getfile&id=1371&private=0

I also used drywall screws and brads in the centre section.
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Do yourself a favour and tape off both ends of one of the horn flares to prevent dust from getting in there. The static charge on the plastic attracts dust like crazy.
index.php?t=getfile&id=1373&private=0

Next job was to mark out the position of the port and woofer holes. The port I'm using requires a large hole at the front where the flare is. I decided to reduce the diameter of the hole in the inner baffle so I could seal and support the port with a snug fit in the baffle and some silicone.
index.php?t=getfile&id=1374&private=0

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Re: 3 PI build [message #78990 is a reply to message #78989]

Sun, 19 January 2014 17:31

Bill Epstein
Messages: 1088
Registered: May 2009
Location: Smoky Mts. USA

Illuminati (2nd Degree)

Classy work!

Given any thought to keeping that drawer from rattling?

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Re: 3 PI build [message #78996 is a reply to message #78990]

Mon, 20 January 2014 10:07

BFP
Messages: 48
Registered: May 2009

Baron

Bill Epstein wrote on Sun, 19 January 2014 17:31

Classy work!

Given any thought to keeping that drawer from rattling?

Thanks Bill

The rear of the crossover will be secured with 4 - 1/4" bolts and T nuts. I need to secure the front but haven't come up with a solution yet. I need to do that soon. I'm not sure how much it could rattle but if it can move at all there is a chance it will cause problems.

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Re: 3 PI build [message #79010 is a reply to message #78996]

Tue, 21 January 2014 10:43

BFP
Messages: 48
Registered: May 2009

Baron

Just a few general notes/comments on building speaker boxes.
Safety is important. I use a cartridge respirator when cutting MDF and Birch. Even though I have dust collection there is still enough dust to be very irritating. I also wear ear protection and safety glasses. Having all your equipment in good working order and keeping the work area clean are good practice as well. Try not to rush and quit working when you are tired.
I usually start by making a cut list of all the parts. I then have a look at my tools, making sure what I have what is needed and that the blades and router bits etc. are in good shape and clean. This helps avoid problems as you work through the project. .
After establishing the size of all the parts, I determine how they will be cut. Set the saw once and cut all the parts that size, then move on. For instance, in these boxes the tops, bottoms, inner baffle, back panel and braces are all the same width. Having them identical in size is very important. Doing one set up and cutting them all minimizes any differences. Precision is more important than accuracy in this case. If the width is off by a small amount it's not a problem as long as all the pieces are the same width.
Another issue can be the thickness of the MDF or Birch. I knew the BB was 18mm not 3/4" but did not realize that the 2 different lots of MDF I used were not the same thickness. I didn't check this and have some minor issues to deal with because of it.

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Re: 3 PI build [message #79021 is a reply to message #79010]

Wed, 22 January 2014 14:37

BFP
Messages: 48
Registered: May 2009

Baron

The next job was to cut the woofer holes and make the recess for flush mounting the horn.
The woofers were pretty easy. I used a Jasper Jig mounted on a plunge router to make the recess then the through hole. For a 4012 HO woofer I went with the 11 1/16in. size for the through hole and for the recess I went 12 7/16 in. The recess is about 9/16" deep. The woofer is listed as 12.38" diameter so you may get it to fit with 12 3/8 but I went with the larger hole to be sure. Since I am going with a black baffle any small gap will not be noticeable.
To do the recess for the horn I made a pattern and used a bushing on the router to cut the recess from the pattern.
It's a 3 step process. First you rout around the outside of the horn flare. In the post above you can see the horn flare face down, bolted to a piece of 1/4" MDF which became the first pattern.This creates an over sized pattern. You then rout around the inside of that pattern to create a second smaller pattern. That pattern is oversized by the diameter of the bit used to create the patterns. You then use the smaller pattern to rout out the recess around the horn opening in the baffle. You need to use a bushing to compensate for the size. So if you are again using a 1/4" bit you use a 3/4" bushing which gives you the correct offset and a perfectly sized recess for the horn. It's a lot of work and may not be worth it for many people.

Here you can see the large pattern clamped down and the just routed 2nd pattern in the centre.

index.php?t=getfile&id=1375&private=0

The recess and a gasket. Don't forget to add depth to the recess for a gasket.

index.php?t=getfile&id=1376&private=0

With the horn in place.

index.php?t=getfile&id=1377&private=0

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Re: 3 PI build [message #79022 is a reply to message #78971]

Wed, 22 January 2014 14:50

BFP
Messages: 48
Registered: May 2009

Baron

OK, It's time to stick the drivers/port in a baffle and see what they look like. Pretty nice! These woofers are a really nice looking driver. They look very well made and the magnet/voice coil and venting are all huge.

index.php?t=getfile&id=1379&private=0

Next the T nuts get installed in the baffle. I used 1/4" t nuts for the woofer. The woofer mounting holes will take 1/4". However, it's a close fit without much room for error. I set the woofer in the baffle, shimmed it tight, marked it's position and used a 1/4" forstner bit in a portable drill to make centre marks for each hole. I then used a drill press to drill the through holes. This ensures a hole perpendicular to the baffles. The tolerance is too close to hand drill these IME. If I did not have the drill press I would use the smaller #10 T nuts which leave room for error. The holes all lined up fine in the end. I also cutout the crossover access hole in the back panel and added the 1/4" Tnuts for the crossover cover.

index.php?t=getfile&id=1382&private=0

I wanted to add T nuts to the bottom so I could add spikes/feet or a base/stand. I used 3/8" T nuts and installed 8 of them to make sure I could securely bolt up a stand if needed.

index.php?t=getfile&id=1383&private=0

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Re: 3 PI build [message #79046 is a reply to message #78971]

Thu, 23 January 2014 17:26

BFP
Messages: 48
Registered: May 2009

Baron

Now it's time to build the box and brace it. I started by gluing the top and sides to the baffle then added the bottom. Clamps were left on for a few hours and the boxes left for 24hrs before being handled.

index.php?t=getfile&id=1384&private=0

Next up, bracing. I'm a fan of using a lot of bracing inside cabinets, especially large ones. I decided on 2 window braces, one below the horn and one between the port and the woofer. I also added a brace at the mid point of the woofer and stick braces on all the panels. Cutting or routing braces can be a lot of work. I cut this down by gang drilling the corners of the 4 window braces and cutting as much as possible on the mitre saw. I only had to do the short sides with the jig saw.

4 brace blanks stacked and clamped in place for drilling with a forstner bit.
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