Home » Sponsored » Pi Speakers » 4 Pi Build in San Luis Obispo - Flush Mounting and Bracing
Re: 4 Pi Build in San Luis Obispo - Settings for Flanking Subs [message #94068 is a reply to message #94063] Tue, 20 July 2021 10:52 Go to previous messageGo to next message
Wayne Parham is currently online  Wayne Parham
Messages: 18365
Registered: January 2001
Illuminati (33rd Degree)

It never hurts to use a high-pass filter for vented subs set at or just below the Helmholtz frequency. So if your sub cabinets are tuned to 20Hz, set a fourth-order high-pass at 15-20Hz.
Re: 4 Pi Build in San Luis Obispo - Progress [message #95582 is a reply to message #93009] Tue, 03 May 2022 12:08 Go to previous messageGo to next message
alexg is currently offline  alexg
Messages: 17
Registered: June 2019
Chancellor
Finally starting to make some progress...... I was hoping to post as I go but I tend to work in fits and spurts when doing these kinds of projects and although I found time to work on the speakers I fell behind on my posts and updates.

/forum/index.php?t=getfile&id=3041&private=0

In order to recess the wave guides, I ended up using the same template strategy that "Roger S" used. Thanks "Roger S!" At first I tried to use my jig to cut the shape of the wave guide directly into the baffle but really struggled to get the corners right. The jig was great for cutting the general shape of the wave guide but didn't allow me to effectively address the rounded corners. So, I ended up making the template per Roger S using my jig and router and then routed the corners by hand. It took me a several tries to get it right but after a few attempts I finally got one that I was happy with. From there I used the template to cut the baffle. Worked like a charm.

/forum/index.php?t=getfile&id=3042&private=0

/forum/index.php?t=getfile&id=3046&private=0
For the woofers, I beefed up the back side of the baffle with an additional piece of wood per Wayne's recommendation in order to give them a little more "meat" to attach to. Using my jasper circle jig I cut a round disc approximately 16.25" in diameter using some ¾" cabinet grade plywood that I had lying around and glued it to the back of the baffle. I then cut the recess and hole for the woofer.

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From there I attached the baffles and vents using clamps and kettle bells.

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For the most part I am pleased with my results thus far however I would like to point out a few issues.

#1 - Even though I had the local lumber yard cut my sheet of MDF to spec, after gluing up the box and then attaching the baffle my speaker was not perfectly square with some parts slightly hanging out over other parts. I ended up using a trim router to clean things up.

#2 - I pre-cut the hole for my vent with the intention of using a trim router to clean things up and make the opening flush and square however I got little too aggressive with the jig saw and over cut the opening in a few spots and then allowed the trim router to get away from me a few times so I now have to go back and fix the problem areas with some kind of wood filler. You can see it in the photo below and in some of the other photos in this post.

/forum/index.php?t=getfile&id=3055&private=0
Re: 4 Pi Build in San Luis Obispo - Questions for Wayne [message #95583 is a reply to message #95582] Tue, 03 May 2022 14:43 Go to previous messageGo to next message
alexg is currently offline  alexg
Messages: 17
Registered: June 2019
Chancellor
Some questions for Wayne.

1) Ok to use foam or wax strips for gaskets? I have a bunch from other projects.

2) Waveguide is recessed. Does it require "more meat" (backing) like the woofer)?

3) Can I install a larger piece for bracing?
- I was thinking of installing a more substantial piece of bracing that would touch all 4 interior walls, add more support, and give me something to attach the insulation to.

4) I have added some backing behind the woofer. I may add backing behind the waveguide. I would also like to potentially add the bracing that I described above. At what point should I be concerned about having a material impact on the internal volume.

5) I did see your article about how to properly install T-Nuts however I am wondering if it is ok to simply use larger wood screws in place of t-nuts especially because I used plywood as the backing for my woofers?
Re: 4 Pi Build in San Luis Obispo [message #95584 is a reply to message #95583] Tue, 03 May 2022 15:15 Go to previous message
Wayne Parham is currently online  Wayne Parham
Messages: 18365
Registered: January 2001
Illuminati (33rd Degree)

Your build is lookin' great!

I like the ring you've used to add "meat" behind the woofer for mounting screws. We do the exact same thing. It adds thickness where it's needed and eliminates the need for a double baffle. These speakers are heavy enough.

We do the same thing around the waveguide, which I think answers your question about that.

You could use wood screws to mount the drivers, sure. But I wouldn't. It isn't much more trouble to use T-Nuts and they provide much more clamping force without stripping. Not that you need much clamping force - 10 foot/pounds per screw is plenty - but still, the metal threads are much stronger and long-lasting.

You can add bracing if you want, but it's really only needed between the baffle and back. The rest of the panels are small enough to shift panel resonance way out of the passband. We tie the sides together at the same place - between woofer and tweeter - which is overkill but serves to provide a "perch" for the insulation that spans the cabinet interior. That's what is really important, to span the cross-section with insulation separating the midwoofer and the port. It prevents midrange from entering the port, but bass passes right through. That's its function.

As for gasket material, you could probably use your wax strips. I don't know - never used them - but the gaskets in vented loudspeakers aren't stressed so most anything that makes a decent gasket will work in this application. Almost any flat non-corrugated cardboard material is fine for a gasket. I like 40 mil PVC material, commonly used for making shower pans.
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