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Tim's 4Pi Speaker Build [message #80969]

Sun, 04 January 2015 01:42

timkur
Messages: 13
Registered: November 2012

Chancellor

Hey guys,

I've recently kicked off the construction of some 4pi speakers, and I thought I'd share some pics and my experience. I'd also appreciate any feedback if folks see I'm doing something horribly wrong. Smile

I consider myself a "weekend handyman". I've done rough framing, drywall, electrical, etc... but I'm not a skilled wood worker and I've been learning lots about cabinet building while doing this. I'm impressed with the skills of other folks I see posting in these forums, and am excited to see how close I can get to a good looking speaker. Hopefully it will sound great, no matter how it looks. Smile

Last year I build 2 3pi subwoofers, had a lot of fun building those, was impressed with what they added to my setup... see my dog George posing with them.

When I built those, I bought myself a router and a circle cutting jig, and learned how useful a router really is. Definitely something I had been missing before.

After hearing the 3pi subs for a year, I got the itch to replace my front 3 speakers. They are currently M&K 750THX speakers... I got them 12+ years ago and have been happy with them, but just wondering if there was something better out there. I guess we'll soon find out.

Thanks!

Tim

Attachment: subsSmall.jpg
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Re: Tim's 4Pi Speaker Build [message #80970 is a reply to message #80969]

Sun, 04 January 2015 01:48

timkur
Messages: 13
Registered: November 2012

Chancellor

For my 4pi build, this is what I'm targeting.

To cut down on costs, I purchased 4 JBL 2226H's used from eBay. The seller mentioned that they have been re-coned by a JBL authorized dealer, and they look in good shape. Only cause of concern is the seller mentioned they were originally 4 ohm speakers and reconed to be 8 ohms. However, I'm hopeful I'll be ok
I'm not an electronics guy, and I didn't want to learn how to build the crossovers myself. Instead, I ordered one, and my father in-law got me two of them for Christmas. Standard components... no upgrades for that.
I couldn't find the B&C DE250 used, so I ordered one new, and my parents gave me 2 more for a Christmas present (see a trend here?)
I like the look of the recessed speakers, but after doing the math, it seemed like recessing the JBLs would leave the frame around the front baffle very thin. There has been discussion in the forums about re-enforcing the baffle from the back, but I decided I'd do the same thing as I did with the 3pi subs, and do a double thick front baffle. Just cut 2 different sized circles, and be done.

I won't bore you with the details of the initial cutting of the wood, or gluing big pieces together. I'll just touch on the interesting things I picked up while combing through the forums and actually doing it.

When cutting holes, the only hiccup I ran across was the hole for the JBL. The plans called for a 13 15/16" hole, but that wasn't large enough for my speakers. I ended up going with a 14 1/16" hole. I didn't try a 14" hole, so I may have sacrificed more wood than needed, but the speaker fits now. Maybe the larger size is related to the original 4 ohm speakers I got. Who knows.

I'm excited to figure out how to recess the waveguide. The rounded corners look like they'll be fun to cut. Smile

Thanks

Tim

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Re: Tim's 4Pi Speaker Build [message #80971 is a reply to message #80970]

Sun, 04 January 2015 01:54

timkur
Messages: 13
Registered: November 2012

Chancellor

Port Construction

For the port, I built an actual little box that is 8.5" long. The double baffle will add another 1.5" of thickness to give me the full 10" port.

Once the boxes were built, I glued them to the baffle.

A nice tip in the forums about the port hole in the baffle is to do a rough cut first, and then use a flush trim bit on the router to get it nice and smooth. It works great and is an (almost) idiot proof way to do this, and is now my new favorite tool+bit combo that I own.

See the front... pencil marks is where the hole should be cut.

Through the back of the port... you can see the overlap that the bit will cut off.

And 20 seconds of using the flush trim bit. You can see my pencil lines were off a little bit. That would have been a pain to try and correct had I cut it where I marked. And not only that, but I've got rounded corners for the port. That looks cool. Smile

Thanks!

Tim

Attachment: PortBack.jpg
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Attachment: PortSmall.jpg
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Attachment: RoughPortFront.jpg
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Attachment: FrontPortSmooth.jpg
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Re: Tim's 4Pi Speaker Build [message #80972 is a reply to message #80971]

Sun, 04 January 2015 01:57

timkur
Messages: 13
Registered: November 2012

Chancellor

Cross Bracing

I see that a lot of folks built their 4pis and attached the back as the last piece. I thought about that, but then I couldn't figure out how to get the cross bracing installed, so I decided to leave the top for the last piece to glue on.

I had some leftover 1x2 maple from a cabinet I installed, and decided to use that. The plans say to install the cross braces with a "slight amount of preload". I took that to mean that they should fit really tight, so I cut the braces 1/16"-1/32" too long, and really wedged them in there. They weren't going to move easily, but I glued them in to be safe.

Thanks!

Tim

Attachment: FrontCrossBrace.jpg
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Attachment: TopCrossBrace.jpg
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Re: Tim's 4Pi Speaker Build [message #80973 is a reply to message #80972]

Sun, 04 January 2015 09:16

Wayne Parham
Messages: 18789
Registered: January 2001

Illuminati (33rd Degree)

Those are looking really good! Thanks for posting pics of your progress!

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Re: Tim's 4Pi Speaker Build [message #81016 is a reply to message #80973]

Wed, 14 January 2015 23:20

timkur
Messages: 13
Registered: November 2012

Chancellor

Thanks Wayne. My day job has me sitting at a desk all day, so it feels great to actually build something in my free time. I'm looking forward to getting this all together and hearing what I built!

Tim

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Re: Tim's 4Pi Speaker Build [message #81017 is a reply to message #81016]

Wed, 14 January 2015 23:39

timkur
Messages: 13
Registered: November 2012

Chancellor

T-Nut installation.

There is a great thread http://audioroundtable.com/forum/index.php?t=msg&goto=71620#msg_71620
about installing T-Nuts. I thought I'd add some pictures and post some of my experience.

It wasn't clear to me if the T-Nuts should go on the frontside of the baffle, or the backside. When I built my 3pi subs, I put them on the front side. They were easy to install and easy access if something should go wrong. Even though that causes the mounting surface to not be smooth, the gasket helps seal it up real nice.

6 months later the sub failed in my M&K sub, and when I went to replace that, I noticed those T-Nuts were located on the back side. Additionally, one of the T-Nuts had come loose, which turned a 5 minute replacement job into a multi-hour ordeal to get that speaker out. Ugh. I wish M&K added glue to their T-Nuts like Wayne suggests.

This time around, I decided to mount the T-Nuts on the backside. The big reason why I decided to do that is that I may have cut my hole a bit too big. I guess I should have tried a 14" hole instead of a 14 1/16" hole. However, with the T-Nuts on the back side, and the taper of the speaker, this wasn't a problem.

The above thread mentioned 2 different ways to install the T-Nuts... one with a screw, and another with a C clamp. I couldn't quite visualize the screw method, so I went with a C clamp.

In order to get enough torque to push the T-Nut in, I needed to use one of the "crank style" clamps. I couldn't generate enough pressure with the "handle style" clamps I was using to glue the boards together.

Since I put these on the backside, I figured it would be easier to do this before I glued the box together, so I could see what I was doing. Unfortunately, at this point, I had already glued one of the baffles to a box, so one of them I needed to do blind. It turned out not to be as hard as I would have expected, but it was definitely easier to do it when I could see it.

Here is one of the baffles with the T-Nuts installed. I made sure I glued them in. Before I put in the T-Nut, I wet the area with a paper towel, added a drop of gorilla glue, and clamped them in.

Pretty straightforward, but putting in 24 of these things took some time. Smile

Tim

Attachment: TNutOverlap.jpg
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Attachment: TNutClampPress.jpg
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Attachment: Clamp.jpg
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Re: Tim's 4Pi Speaker Build [message #81018 is a reply to message #81017]

Thu, 15 January 2015 00:06

timkur
Messages: 13
Registered: November 2012

Chancellor

Insulation

This was pretty straightforward. The only R13 insulation I could find at Home Depot was faced (has the brown paper backing on it), but that made it really easy to install. For the back, side, and top, I glued the paper backing to the inside of the speaker box. Pretty simple. For the insulation on the cross brace, I removed the paper, so as not to interfere with the absorption of the insulation.

I installed the insulation before I glued on the top of the speaker box. It made access very easy.

Insulation on the back and side.

Insulation sitting on the cross brace.

And then I glued the insulation to the top before I glued the top onto the box.

Next up, the 2nd baffle, and cutting those curved corners for the waveform. I was able to successfully do it on a test piece. We'll see how it works when I do it for real. Smile

Tim

Attachment: InsulBackAndSide.jpg
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Attachment: InsulOnBrace.jpg
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Attachment: InsulOnTop.jpg
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Re: Tim's 4Pi Speaker Build [message #81019 is a reply to message #81018]

Thu, 15 January 2015 10:39

Wayne Parham
Messages: 18789
Registered: January 2001

Illuminati (33rd Degree)

That looks really good, Tim. Thanks for showing us your build as it comes together.

I usually remove the paper backing because I worry it might buzz. But I suppose if you press it firmly onto the cabinet panel while the glue is drying, it would prevent that.

And I agree with your observations about T-Nuts. I've seen enough of 'em get loose that I always glue them in. I pull them in place with a clamp just like you did, or by tightening a screw to pull them in place. I never hammer them in.

The reason I mount T-Nuts from the inside is I don't want to pull them out the front when tightening. I suppose the glue will probably prevent this, but I prefer the added security of having them inside the cabinet, where tightening the fastener pulls them further in rather than further out. It puts the joint in compression rather than in tension.

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Re: Tim's 4Pi Speaker Build [message #81032 is a reply to message #81019]

Sun, 25 January 2015 18:55

timkur
Messages: 13
Registered: November 2012

Chancellor

Thanks Wayne.

That makes complete sense about mounting the T-Nuts on the inside... makes me feel kind of stupid for not thinking about it sooner. Smile

I'll keep my ears open for buzzing. If I hear it, I'll go in and remove the paper.

Thanks!

Tim

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