Home » Sponsored » Pi Speakers » Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center) (Building some Pi Speakers)
Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center) [message #88172 is a reply to message #88057 ] Wed, 13 June 2018 07:17 Go to previous messageGo to next message
johnnycamp5 is currently online johnnycamp5
Messages: 200
Registered: June 2015
Location: NJ
Master
Awesome build!

Just a couple of observations-

You had mentioned the six pi Corner horn being smaller than the seven pi.
I believe it is the other way around, with the six pi tuned to about 1/2 an octave lower.

As far as the two pi's lacking in punch.
It has been my experience that woofers (especially high sensitivity) will loosen up and break-in, improving in just that range (mid bass).
My four pi's slowly broke in, increasing in the mid bass.

Experience also tells me that amplifier topology also has a part to play in this.

I used an Adcom 555, with moderate punch.
Then a set 300 b with a bit less punch.
Now two medium size mono blocks using Kt 88 tubes, they pretty much punch you in the face.

Ymmv.
Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center) [message #88173 is a reply to message #88172 ] Wed, 13 June 2018 11:46 Go to previous messageGo to next message
Wayne Parham  is currently offline Wayne Parham
Messages: 17186
Registered: May 2009
Illuminati (33rd Degree)

Seriously cool build thread, Josh! I've been meaning to say a few words, but I've been slammed lately. So I just read without comment. But here are the things I've been meaning to say, or at least thinking about as I read your notes:

As John said, the six π cornerhorn is actually a smidge taller than the seven π. But it's only just a little taller - Less than 2". So I didn't say anything when I read your post about that. They look exactly the same to the eye.

Same with the three π and the four π speakers. If they're not side-by-side, they look the same size. But the three π is slightly larger.

It's just the tuning required for the drivers I've chosen. Both have an alignment that is slightly overdamped, just the way I like it - Controlled. The system can't shift towards underdamped (peakyness) even when the power levels are high for extended periods.

The threads in the "Models, Upgrades and Driver Characteristics" section of the FAQ talk about all that stuff in more detail so I won't belabor it in your build thread.

Lastly, I saw that you would have liked gold "π" decals on your tower twos so I sent a couple in the package with the three π sub kit. I also sent the replacement crossovers for your cornerhorns.

I'm still amazed how much damage those parts suffered. UPS does a pretty good job, but I have to make claims in about one out of every thousand shipments. So I'm hoping I'm good for two thousand shipments 'cause you had two packages damaged. Laughing

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center) [message #88175 is a reply to message #88057 ] Thu, 14 June 2018 06:51 Go to previous messageGo to next message
joshua43214  is currently offline joshua43214
Messages: 25
Registered: October 2016
Location: USA
Chancellor
@johnnycamp5
@Wayne Parham

Thanks for the feedback.

Sorry about the confusion on speaker size, I was actually referring to the size of the drivers as opposed to the cabinet. My intuition was that the 15" woofer in the 7Pi is just too big for my room. I do not need the extra sensitivity, and I already knew the 8" 1Pi can fill my room. So I resisted the "if some is good, more is better" logic. I did not know the 7Pi was physically smaller than the 6Pi, though either one has a smaller foot print than the 4Pi because they need no wall spacing or flanking subs.

Good advice on amps. I have had the nagging feeling that this might be the case as well, and my son also has the same contention. I dusted off my venerable Marantz 1030 that I purchased used as a teenager and hooked it up. It produced lovely sound for less than a minute before it started making crackling noises. I can't find my old Harman Kardon amps.

I am somewhat tempted to snag some cheap Ebay kit amps of different classes to see how they affect the performance before building something high-end (more projects...).

That is great news about the crossovers being on the way. I suppose this means I have to get back to painting.

-Josh
Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center) [message #88176 is a reply to message #88170 ] Thu, 14 June 2018 17:19 Go to previous messageGo to next message
ggnarley  is currently offline ggnarley
Messages: 12
Registered: May 2018
Location: Ohio
Chancellor
Josh,

Thumbs up on the great posts. I have read them over a couple times and keep picking up solid build tips; not just for speakers, but carpentry/woodworking in general.

Paul
Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center) [message #88177 is a reply to message #88057 ] Thu, 14 June 2018 21:30 Go to previous messageGo to next message
joshua43214  is currently offline joshua43214
Messages: 25
Registered: October 2016
Location: USA
Chancellor
The horn flare requires the sides to be cut at a compound angle. The work must be fed through at an angle, and the blade itself must be angled. There are a number of ways to accomplish this, all have pros and cons. The number of methods shrinks rapidly when they are constrained to a high level of precision and consistency. Ideal methods will use a single set up on the saw.

Before I began cutting parts, I took the time to make sure the rip fence was parallel to the blade, and that the miter gage was square. I use the dial indicator to adjust the fence. I turn off the magnetic base, and hold the base firmly against the fence with the plunger near the gullet of one of the teeth on the blade. Zero the indicator, then move the base up the fence and check the far side of the blade. Best practice is to mark the gullet with a felt tip pen, and use the same gullet for each check. I prefer this method to using the miter gage as a mount for the indicator.
To square the miter gage, cross cut as wide a piece of scrap as you can. Tape a piece of paper to the table next to the rip fence. Hold the reference edge against the fence, and strike a line along the edge that was cut. Flip the part over front to back, hold it against the fence and strike another line alongside the first line. The difference between the two lines is the double the error.

These two checks are the first of the critical things that I was fussy over.

Accomplishing a single set up is best done using a sled that positions the work, and once the rip fence and blade angle are set, all the cuts can be made. My sled is just a piece of MDF with 3/16" (4.5mm) brass pins spaced exactly 10" (25.4cm) apart. To get the pins "perfectly" parallel to the fence, I ripped a piece of scrap approx 2.5" (64mm) wide, and placed it ontop of the sled between the pins and the rip fence, then just ran the sled through the saw. The fresh cut edge is now the edge used against the rip fence for cutting the flare parts.

The image shows the sled on the saw. Note the larger holes are the hole pattern for the bass bin driver, so the sled does double duty as a drill guide.
index.php?t=getfile&id=2145&private=0

The flare sides are trimmed to length. Note the work is elevated off the table saw so the tapered edge on the other end can register properly on the miter gage stop.
index.php?t=getfile&id=2146&private=0

Three holes are drilled in each horn flare side. These holes do not need to go all the way through, but mine do. They are filled later with 5minute epoxy.
I used my mill to drill the holes. These holes need to be very accurately placed, and my mill has a DRO that makes it painless. This can be done with a compass and a trammel. I will go into details in my next post about locating the holes accurately with primitive tools, and finding the cut angles.
index.php?t=getfile&id=2147&private=0

The flare is then placed over the pins, and the edges are ripped.
Note the large piece of MDF clamped on the left side of the blade. This is to prevent the offcut from falling onto the angled blade and getting kicked back.
index.php?t=getfile&id=2148&private=0


The part is then reversed, and the other side ripped.
index.php?t=getfile&id=2149&private=0

You might notice that there are no clamps holding the part to the sled. None are needed. The holes are drilled to be a tight fit, and hand pressure is more than enough to hold it down. In practice it feels no more dangerous than making any other rip cut.

Up next: Finding the angles and marking the holes.

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center) [message #88178 is a reply to message #88057 ] Fri, 15 June 2018 00:54 Go to previous message
joshua43214  is currently offline joshua43214
Messages: 25
Registered: October 2016
Location: USA
Chancellor
This next part is difficult to describe in words. I will do my best, but I tend to fall into the pedantic style that science and math papers are written in, so please accept my apologies in advance if this post is a difficult read.

Many of you probably noticed the flare sides where rough cut as rectangles rather than as trapezoids. At first glance this might appear to be grossly wasteful of materials. It is, but the offcuts will be used later as bracing, mitigating some of the waste. The main reason they are cut as rectangles is so that the mouth and the throat are parallel to each other. This would be very difficult to accomplish otherwise. This ties back to my earlier post about constantly asking myself "how am I going to cut that, and how am I going to install that." Planning the cutting and assembly during the design stage is a huge benefit.

I will go ahead and describe part of the process for creating the CAD model for the flare in Fusion 360. My feeling is that most people who are willing to take on a speaker cabinet project will probably be also interested in using CAD. CAD has a bit of a learning curve. I dumped many thousands of dollars into CAD programs since the 90's, and I have found that Fusion 360 is the best all around tool for the work I do (and it is free).

I began by modeling a core that is the inside of the flare.
The image shows the core with the right side and the bottom. The base sketches for the core are visible inside the core.
index.php?t=getfile&id=2150&private=0
To model a side, I selected a side of the core as the reference plane, then just sketched a rectangle bigger than the core and extruded it to my material thickness. The adjacent faces of the core are then used as slicing planes to split the side, and the extra parts removed.

I found that I could not get the dimensions and angles in the plans provided by Wayne to work together. I am providing the link to the thread I started again for reference.
A pro-tip on modeling. When I drew the horn core, I began by making the base sketch for the core in the XY plane. I stopped the sketch without extruding it. While making sure the first sketch was visible, I started the base sketch for the YZ plane. By doing this, the first sketch will "auto-project" into the new sketch allowing one to constrain the intersections of the lines to be coincident. That way, when a change is made to one base drawing, it will force the other base drawing to adjust to it. Once both base drawings are completed, I returned to the first drawing and extruded it oversized. I then extruded the second drawing also oversized (ensure you are making a new body). The two 3D bodies are then used to split each other, and the offcuts removed leaving nothing but a single body.

One of the limits of Fusion 360 is that it is purely a 3D modeling program. 2D modeling is limited to base sketches that are extruded into 3D shapes. The software is meant for producing models that are made either by 3D printing or CNC machining. As such, the tools for producing shop drawings are limited since shop drawings are 2D.
When the 3D model is imported into the tool for generating shop drawings, all the parts are projected from the cardinal directions of top/side/etc. Parts that are not planar with one of the cardinal views will appear angled or foreshortened in the drawing space. Search YouTube for tutorials on creating custom views (it is very simple), and select the appropriate view when creating the shop drawing for the horn parts.

The angle that is needed for the saw blade is referenced to the bottom face of the flare, and is measured along the line perpendicular to the cut edge. There is no reliable way to create this reference in the shop drawing space.
index.php?t=getfile&id=2151&private=0
I found the simplest method to get this angle was to sketch a line on the inside face of the right side perpendicular to the cut, and use that line to create a new plane at a 90 degree angle. I then split the part with the plane, and copied the new part to a new model space, and used "undo" to remove all the edits (don't forget to break the link to the old model). The new part was exported to the drawing space as its own file, and my angle measurements taken from there. The angles for the mouth and throat can be taken from the main drawing.

Where to place the three holes for the pins will depend on your tooling. The digital read out on my mill resolves to 0.0001" (0.0024mm), so I just put them where they looked ok. All of the dimensions of the horn work together, so it is important to cut and measure as accurately as possible. Your dial indicator will scribe marks very accurately up to its capacity, but making marks 12" or so inches from the edge are problematic.

Here is my suggestion for making the layout. This assumes you acquired a machinist combination square that does not suck. It is a really good idea (like really good) to go through all the horn parts and mark all 4 edges on both faces right/left/top/bottom/inside/outside, and to group them as horn #1 and #2.
Cut the mouth and throat angles, cut the parts as close as you can measure. Reading glasses make nice magnifiers when using precision rulers (I think I forgot to include a 24" machinist scale in the tooling list). Strike a line perpendicular to the mouth bisecting the part. The 12" scale that comes with the combination square can be used to place the hole closest to the throat. Use a dial caliper to scribe a line parallel to the mouth that passes through point A in the pic below. Set the trammel to 10" (check and double check this, get fussy). Strike an arc across the part with the point near the throat and the center. Use the dial caliper to scribe the points closest to the mouth (distance H). Those of you without a flag on the Moon will have to use whatever metric dimensions are standard on tools in your location.
index.php?t=getfile&id=2152&private=0


Lightly center punch, and drill with a drill press. I like to use a center point in the drill press to locate the part, then swap in the drill bit. It takes a bit of extra time to swap out the drill before each hole, but there is only 12 holes to drill. Following any method similar to this reduces you to making one questionable measurement (the 10 distance for the trammel), but this distance is only measured 1 time. Even if it is off a bit, the horns will be identical to each other.

An argument for cutting the mouth and throat angle first, as opposed to leaving them square and trimming them later: If the mouth and throat are left square, it will be more difficult to align the top to the sides. Trimming later requires sanding a substantial amount of MDF away, and it will be difficult to ensure the entire face of the flare is flat because of its size. Cutting the angles first does require an extra machine set up, and leaves you referencing from a sharp and fragile edge, but saves time and increases accuracy at the same time.

Use a precision protractor to set the table saw blade. It is vitally important that the protractor be perpendicular to the blade when the measurement is made. I use the miter gage to hold it square. Put a light at the back of the saw, and see how much light leaks between the blade and the protractor. Slide the protractor over, and then back to the blade to double check. This is a point to get fussy over.

At this point, you should have horn sides that are cut to size on all 4 edges, and tops/bottoms that are cut only at the appropriate angle at the mouth and throat.
The flare top and bottom are identical, so I will only talk about the top from this point forward.
Using a framing square (you did Google up how to square a square, didn't you?), bisect the inside face of the top using the mouth as the reference, and taking care the square is referenced on the edge and not on the bevel. Cut some scrap exactly 4.5" as spacers for the horn throat. Use a compass to draw a 4.5" circle near the throat on the bisecting line. Very carefully measure out from the bisecting line the distance to the outside edge of the side, and set the trammel to this distance. Use the trammel to repeat these marks to all the tops and bottoms. Doing this will ensure the horns are identical even if your measurement is slightly off.

Mark a line on the outside of the top that will be directly over the center line of the sides.

Clamp the spacer using the compass circle to get it aligned. If you took your time and where very careful, the throat will be laid out exactly over the center of the mouth.
Dry assemble the horn. It took some playing around to figure out how to hold everything together.
Get the whole horn lined up. With some patience, you will find that it will come together properly. Carefully drill a hole for a 1/4" (5mm) dowel near the throat. Trim a piece of dowel, sand it enough that it can be lightly tapped in with a mallet, and then re-align everything (it will have shifted when you drilled). repeat until you have a pair of dowels on each glue joint (8 total). Plan to spend some quality time doing this.
Line the drill up carefully, there is a strong optical illusion that will lead you astray.
Once all the dowels are in, drill holes for #10 screw threads. Dismantle the horn and drill out the screw holes in the top to clear the threads. Counter sink the holes on the inside of the joint.
Dry fit the parts again using screws and dowels. Tighten the screws just enough to pull it together. inspect closely for gaps or poor fitting. If all went well, you should see no issues. If the joints are not well fitting, you will have to clean them up by hand with a sanding block.

Apply glue and screw it all together. Measure corner to corner at the mouth to make sure the assembly is square. Yellow glue is a good choice with this. If the glue joint is not tight, use epoxy. Do not use polyurethane glue on a poor fitting joint. Polyurethane glues are very weak on joints with gaps, and they are highly porous because of how the expand.
index.php?t=getfile&id=2153&private=0
index.php?t=getfile&id=2154&private=0
Make sure you remove the 4.5" spacer before it gets glued in place. After about 40 minutes, clean up the glue with a chisel.

Remove the screws and trim the top and bottom flush with a handsaw.

Congratulations, you just built something awesome.
Many years ago I subscribed to Fine Woodworking Magazine (when it was still a mag for professionals). Every month they would feature a "Master Class" where some master craftsman would make something awesome. One month, the feature was about making a feed trough. Is it essentially the same thing as this horn flare only about 3 times the size. Everyone was amazed at how difficult the project was. It turns out that there was a class of woodworkers similar to coopers who did this type of work. It is difficult enough that specialists existed at one time for doing it.

Up Next: The Horn box

Previous Topic:One Pi speaker plan request
Next Topic:4Pi Rough concept
Goto Forum:
  


Current Time: Mon Jun 18 19:42:31 CDT 2018

Sponsoring Organizations

AudioKinesis
AudioKinesis
BuildAnAmp.com
BuildAnAmp.com
Crescendo Systems
Crescendo Systems
DIY Audio Projects
DIY Audio Projects
OddWatt Audio
OddWatt Audio
Pi Speakers
Pi Speakers
Prosound Shootout
Prosound Shootout
Smith & Larson Audio
Smith & Larson Audio
Tubes For Amps
TubesForAmps.com
Lone Star Audiofest