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4Pi Center Channel Build

1K views 23 replies 6 participants last post by  NWCgrad 
#1 · (Edited)
Many of you know but, for those that don't, Pi Speakers deals in high efficiency, constant (or controlled) directivity speakers based on primarily pro sound drivers. These were around before the Econowave and SEOS movement. I decided on the 4Pi design for my home theater/basement living room about 5 years ago. SEOS was a bit unproven for me at the time and I felt Wayne's design was mature and well thought out. Lots of great info on the designs here and on the forums. I built my main LR channels about 3 years ago and have been running a phantom center ever since (which has sounded great BTW). I had all the parts and some leftover ply for the center and I finally decided to give it a go.

This build is a center channel where I've decided to go with a sealed design and the waveguide centered. It's been done before and the bass response simulations show only minor differences when crossed to a sub.

DISCLAIMER: I am a poor excuse for a cabinet builder and I don't have a DSLR for photos so I apologize in advance. I do my best and it is a constant learning experience for me.

OK, the plan is something like this (below). I won't give specific dimensions for my build because Wayne want to have control over disbursement of his design which is understandable. I generated my own plans and I believe my design is unique in some ways.

Oh yeah, forgot to mention, this will be a "stock" version with the Eminence drivers. Can't afford the JBL woofer. Wayne claims he only hears a minor difference in distortion/fatigue after listening at high volumes for extended periods. My "stock" LR channels certainly sound great and much lower distortion than the Klipsch RF-82's I previously had. Much more "laid back" too, not harsh at all.
 

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#2 ·
Some panels cut

I gotta figure out how to embed photos :mad:

Prelim cuts and dry layup...
 

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#3 ·
Cut rabbits? and braces. I messed up on the "window" brace and cut out the side to side panel center brace. Oh well, the front to back one was the important one. Here's dry layup and glue and clamp. For some reason assembly is the hardest part for me. Oh yeah, I know why. The plans I drew up were for MDF and I used ply but forgot about the dimensional thickness difference. That took some extra adjusting...

Forgot to take photos of the front baffle cuts for waveguide and woofer but I did break my jigsaw and took a photo of that. Cuts better now!
 

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#4 ·
Assembly of the box. Most edges have overhang thanks to dimensional disparity between MDF and ply. That's cool I will use a flush cut bit to trim around the box. Here is what she looks like in rough glued up shape.

Next I will install second front baffle for recessed cutouts.
 

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#7 ·
gluing the front baffle on to the box

I don't have enough clamps! I put 300 lbs of weights on it but in psi I don't think that's anywhere near what a clamp will do. Also some examples of how my good and not so good joints came out. This design was more difficult to cut than a butt joint design but it made my assembly easier. Plus I learned some stuff about joinery. I don't have good tools or a lot of skill but I'm pretty sure this box will be solid and air tight.
 

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#9 ·
Thanks dude,

Originally I drew up these plans with intent to have a local CNC router shop cut these out of MDF. I solicited 5 quotes and only got one back. They wanted $1200! My buddy is a carpenter and he uses a guy to do cabinet builds for cheap but it was still gonna be $400 for the build. Not a bad price at all but I already had purchased some baltic birch so I finally decided to give it a go! When I get rich I can commission a build, lol
 
#10 ·
Baffle cutouts

OK, so I got the front baffle glued on. I overhung a fraction on all sides thanks to some of the trimming I had to do on account of the difference between MDF and ply thickness. Then I trimmed up the baffle using a flush cut bit with the router.

Woofer cutout is something that I've done several times and I have a pretty good process for it. I made a circular cut jig out of a piece of 1/4 MDF. I can drill a new hole at any diameter I need. One tip I would suggest is to position your router in the center of the jig lengthwise so that the end opposite your router (180 degrees azimuth) overhangs the cutout for better support when finishing the hole cut.

Forgot pics of the setup. Here are a couple showing the cut.





Cool, figured out that image imbed problem.

Pencil layout for the waveguide layout, blurry sorry

 
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#15 ·
Yeah, I've seen your build thread(s). Nice work.

Sealed center looks better but I have to admit another reason was I wasn't too keen on assembling the rectangular port again. I did not have a good method for that.

We have similar setups in our basement, at least in that we both have living room setups rather than dedicated theaters and my open end is over to the right. My surrounds are not as aggressive as yours though :D
 
#13 ·
Waveguide recess

Thanks for the comments guys.

Now on to the waveguide recess. Probably the correct way to do this is make a router template from the waveguide. I don't have the equipment to do that. I decided to setup a straight edge to cut the four straight lines then do the corners by hand following my pencil lines. Pretty risky method plus I've never tried this before.

Here's a pic from my straight edge setup...



Turns out my method was a poor choice and I messed up one corner. The router grabbed a little and I cut too far into the corner. Two other corners came out OK and really only one turned out really well. To compensate I had to open up the cutout top and bottom of the waveguide a little so I could cut more material and try and blend in my screw up.

Hopefully some sanding and a black Duratex finish will hide my errors.

Here you can see the finished cutouts for woofer and waveguide and the fit around the waveguide. The big mistake is in the lower left corner of the waveguide. Sorry for the poor image quality on these.



 
#14 ·
Terminal Cup installed

Not much to it. Cut a square hole and mount with four screws. This one came with my 4Pi kit. Internal speaker wire comes with kit cut to length and terminated. Nice touch in a kit. Terminal cup has a gasket to seal itself so no work required there.

Notice in the pics at the bottom left and top right when flush cutting the cabinet my router bit ripped out the laminate at those locations. :frown: Fortunately not on the front baffle. Not sure how to fix this or how to prevent in future.



 
#17 ·
Most people won't use a 15" woofer for a center speaker build because it won't fit under most TV's and the WAF is around zero. I have a DIYSoundgroup Cheap Thrills with a 15" woofer and the 12" SEOS and DNA-360 CD. When it is set on its side, the mid-range is absolutely fantastic for a center, the best I've ever heard.

Your setup looks great and I bet it sounds just as good.
 
#20 · (Edited)
That setup does have some compromises but it bet in the right sitting/standing positions it sounds great. (wait, not sure about SEOS vertical directivity) Do you get good left to right response when on it's side?

My setup has its own compromises but I did get the WA!
 
#18 ·
here's where the speaker will be installed...


 
#21 ·
More driver fit checks

Here are some more pics of the compression driver and woofer, checking for fit, and the cabinet in general at this stage...









 
#22 ·
Crossover installation

Normally at this stage I would round over the corners and get to sanding but instead I'm going to fall prey to the typical DIY mistake of listening to the speaker before finishing the cabinet. I know, I know.

I knew I wasn't going to be able to work on this cabinet for a couple weeks and figured I could spend a couple quiet hours assembling the crossover, wiring, insulation and drivers so that I could enjoy this speaker in the meantime.

Crossover:
The crossover network comes from Wayne at Pi Speakers pre-assembled on a printed PCB. It's a pretty nice piece. During shipment to me, a lead on one of the capacitors (top right) broke. Wayne sent me a new one right away so I could solder it on. He offered to do the repair but this was not a difficult thing for me. He has also made a slight change to the crossover since I purchased them about 3 years ago so I had to add the 9th resistor across the compression driver terminals. The PCB traces and the leads on these things are so large they are really quite easy soldering work. For reference, I think the long dimension on the PCB is about 12 inches.



I put foam weatherstripping tape underneath the crossover and screw it down to the bottom panel of the cabinet. You can also see the large 100W resistor. All the speaker wires come with the kit pre-cut and terminated which I think is a nice touch. The crimp terminals are soldered to the wires. I thought about soldering to the crossover and/or drivers but I haven't had any problems with my other two speakers so I didn't do it.

 
#23 ·
Insulation and driver installation

R13 on one side, top, and across the brace between woofer and compression driver. I also had a little of the 2-inch ultra touch laying around so I stapled some to the back and left side between the two braces. The R13 sits/stuffs in there great and holds on its own. This was paper backed so I made sure to remove paper backing from the stuff on the window brace.



I just use wood screws to install the woofer. I like these cabinet screws from GRK. I will paint them black when I finish the cabinet. The Eminence woofer comes with gasket installed so no need to do anything extra there.



I put weatherstripping tape on the back of the waveguide to seal it. Some black pan-head wood screws from PE to install it.

Here's the (unfinished) speaker. Already looks not half bad because the front and side panels I used pre-finished Baltic Birch that I had laying around. I was planning Duratex finish for these but I will wait to see how the sanding and filling of imperfections goes before I make a final decision. If I get it to come out pretty decent I might consider black stain. Lots of mistakes on this cabinet but still my best one so far. Definitely heavy and solid!



 
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