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items: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
items: Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)

Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Greetings everyone! This post will be mostly introduction and planning. At the time of this writing the 2Pi Towers are all but complete and in service, and the 6Pi mid-horns are in the last stages of construction. Introduction: Almost 20 years ago, I invested in a set of Athena Audio speakers for my home theater. They sat alongside my venerable Acoustic Research speakers which finally went to their maker about 5 years later. Acquiring a new set of high end speakers for music ended up getting put off because the cost of anything much better than the Athena's was cost prohibitive. I came across Pi Speakers 5 or so years ago, and giving them a try has been on my list of things to do ever since. Last year, one of the drivers in my surrounds packed up, I thought this was a good chance to test the Pi Speaker philosophy and built a pair of 1Pi's. These little speakers are really amazing for what they are. If you are in the market for a pair of nice monitors, I highly recommend them. A couple of months ago another speaker and the sub from my Athena kit failed, and I decided to go ahead and build corner horns and 2Pi surrounds. When I started planning this project, I realized I have a lot of unusual experience, and that this would make a very nice build thread. I have been working with wood since I was a little boy, and have had the pleasure of being a professional furniture maker, a semi-professional wood worker, and now a hobbyist wood worker. In more recent years, I have acquired a some machine tools, and become a fairly competent hobby machinist. I have also been blessed with almost perfect pitch and very good hand-eye coordination, which made me a passable acoustic guitar player. I returned to college after a serious back injury ended my 2nd career, and now hold degrees in Molecular Genetics and Mathematics and work in a research capacity. My intention is to write a detailed (and lengthy) thread on constructing these speakers, and I hope that my experience will benefit …
creator: joshua43214
date: 2018-05-22T02:09:38-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: After completing the model, I ordered up all the little parts that would be needed. Lots of threaded inserts, #10 cap head screws, banana plugs, etc. I also decided to replace my 20year old speaker wires. I sourced all the fasteners from McMaster Carr. I use them only because they are very reliable, there are cheaper places. I sourced the wire (Belden 5000UE) and banana plugs from Blue Jean Cable, and banana jacks (Dayton Audio BPA-38G) from Parts Express. Cutting the Parts: Cutting large panels that are both consistent in size, and square is always a challenge. Most big box lumber yards will cut sheet goods for you. My experience is that the cuts are never very dimensionally accurate, never consistent, and usually have damage to the edge from the operator not being careful enough. The raw edge of MDF is very rough, and when it is pushed through a vertical panel saw, it rocks around on the rollers, to make matters worse, the off cut is pulled down onto the blade by gravity. If you can't transport the full sheets home, I suggest only letting the lumber yard rough cut the panels into more manageable sizes, and do all the finish cutting at home. Store MDF flat on the floor, or as vertical as possible to prevent bowing. I stacked all my sheets on a pair of saw horses, then used pieces of scrap up elevate the top sheet for rough cutting. Label your parts! If you are like me, the rough cut parts at the end of the panel get left over-sized and easily get mistaken for a different part. Use stick on labels, blank labels and a sharpie are fine if you don't want to print them. I print my labels before I cut, and I know I am done when I run out of labels. I suggest not using pencil (it easily rubs off MDF), and never use a marker directly on the MDF (it bleeds through). I used 3/4" (19mm) MDF, and allowed 3/8" (10mm) between parts during the roughing. This gives me about 3mm of extra to trim off. Once all the panels are rough cut, I ripped them to final width on the table saw. …
creator: joshua43214
date: 2018-05-22T13:17:28-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: If this was the carcass for a cabinet, one would typically glue the 4 sides in one go, then glue on the top and bottom. A speaker though has bracing and stuffing, both of which would be very difficult to install from the ends. I used a somewhat unconventional method of assembly that both allowed me to keep everything square, yet still gave access for installing braces and stuffing. My milling machine has a DRO, so I used the hole pattern feature on it to drill the mounting holes, then used a circle guide and router to cut the rabbit and cut out for the drivers. The mounting holes are deep and close to the cut out, a drill guide is a really good idea if you do not have a drill press large enough to accommodate the baffle. I should mention that I am a huge advocate of the "file to fit, and paint to hide" school. This is the essential element to "as built" construction. I also believe that it is almost impossible to dry fit parts too many times, and large glue up should always be practiced. Glue seems to turn into a first class lubricant at the worst possible times leaving parts that joined up perfectly hopelessly out of alignment. Making a dry run will not only ensure you really can assemble things in your planned order, but also put clamps where you plan too. It will also ensure you have everything on hand. My plan was as follows: glue the sides to the baffle, glue the top and bottom on, install the stuffing, install the bracing, glue in the rear panel. My design has the front and rear panel fully captured on all 4 sides. I choose this to take advantage of the extra surface area of the doubled baffle even though it puts the raw edges of the sides to the front of the speaker. I also want the sides, top and bottom to be very slightly proud of the baffle so they can be sanded back flush. Since the back and baffle are fully captured, it is important that the speaker carcass be glued up so the back can be installed last - in other words, the carcass cannot be allowed to t…
creator: joshua43214
date: 2018-05-22T15:07:05-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: After about an hour has passed, I removed the clamps. I scribbled pencil at the ends of the carcass and passed a large hard sanding block over them. It is important that the ends are planar and there is sufficient surface are for a good airtight glue joint. I placed one of the top panels on and made sure it did not rock. At this point, it is just possible to knock the carcass apart with a mallet if something went really wrong. If the ends are not planar but can be fixed, consider letting it dry overnight. In my case, the ends came out very well, and just some minor dressing with the sanding block gave a near perfect join. My sanding block is a piece of MDF cut to use 1/3 of a sheet of sandpaper longwise. I use a light coat of spray adhesive to hold the sheet in place. I also have an MDF sanding block covered in heavy felt that uses 1/4 sheet of sandpaper. I only use soft block for finer grits and finishing. Leveling surfaces is best done with a hard block even though it wears out the paper faster. Next I glued the top and bottom on. once again, the order of operations is important. I set the carcass face down on some scrap to keep it off the bench slightly, and applied glue to all the parts. I set the back in place with no glue. I placed the top and bottom, and gently clamped crosswise to bring the sides tight to the back. I then placed pipe clamps top to bottom and lightly tightened them. I then slightly loosened the bar clamps holding the sides against the back and slightly tightened the pipe clamps so the carcass could relax or twist as needed for the top and bottom to go on square. Once everything was aligned, I tightened up the bar clamps, then the pipe clamps. I removed the bar clamps, and used the port as a handle to pull the back out. The off cuts I said to save in an earlier post are used as spacers, and clamped between the sides. Once again, it sounds much more complicated than it is. The important thing is that the clamps go on in such a way that the carc…
creator: joshua43214
date: 2018-05-22T16:26:15-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Here are the pics from the 6Pi parts. Those with sensitive stomachs beware... The Crossovers got hammered to death by one of the Compression drivers. Wayne asked me to send them back for assessment, and UPS managed to sit on them for so long they didn't get back to him til late last week. They look even worse in person, even the resistors got bent and almost ripped off the boards. The Delta 10 is about 1/4" out of round and the Delta 12 is bent over 1/4" out of flat. Wayne also asked me to send the compression driver back since it was probably the hammer that caused the problems. All in all, it was a very sad day. Hoping the replacements arrive before the 6Pi's are complete, the race is on
creator: joshua43214
date: 2018-05-22T16:47:08-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Great build thread! Keep 'em coming! This kind of stuff is so useful for everyone on the forum.
creator: Wayne Parham
date: 2018-05-22T21:03:57-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Josh, Great read! I already picked up several pointers for an upcoming build. Paul
creator: ggnarley
date: 2018-05-24T02:28:17-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Before I even began making the CAD drawings, I was worried about finishing. If the hulking monolith of the 2Pi gets a low WAF score, the 6Pi Cornerhorn gets a total fail. Fortunately, I no longer have to worry about WAF scores, but I do prefer things to look good. Veneering was definitely an option. I have several hundred board feet of "African Mahogany" that I let my lumber supplier talk me into a bunch of years ago. The stuff is so awful to work with I have never sold it, but I would be otherwise "free" material. After much consideration, I decided that it just has too much figure and would serve only to draw attention to the speakers. Not such a problem with the 2Pi's but I don't really want to make the 6Pi's stand out too much. I have close to a thousand board feet of White Oak, and a fuming chamber large enough to hold even the largest parts. Fumed oak is wonderful, and would match my house nicely. Fuming veneer creates an entire new set of issues because the ammonia will attack the glue if it is too thin, and veneer thick enough to fume has a major effect on construction and joinery. I am knee deep in projects already, and I need new speakers more than I need yet another showcase piece. In the end I decided to paint the speakers, and after looking at thousands of pictures of painted speakers, I settled on black paint. What I want is for the eye to not be drawn to the speakers. Flat chalk black actually creates a negative space that the eye is drawn too. Likewise, gloss ivory black demands attention because it is so lovely. I also knew I wanted some texture to the paint. I wanted just enough eggshell to prevent reflections, but not so much it once again creates negative space. This eliminates using my spray equipment, and eliminates high texture paints like Duratex. I started experimenting with paints the day after I began sawing up materials, and was still experimenting with paints while I was applying primer. I finally settled on Sherwin Williams satin black …
creator: joshua43214
date: 2018-05-24T03:52:23-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: So, how do they sound? Good. How good? Very. They sound so good that I felt compelled to take a break from working on the 6Pi's so I could deal with acoustic treatments. Flaws in my listening room suddenly became intolerable. They sound so good I found myself using mostly well engineered music for critical listening (the audiophile rabbit hole). My first thought when I hooked them up was "wow, that is big sound." Very reminiscent of the big speakers that where so popular in the '70s, the kind of speaker you want to play blues, rock, or soul through. Not to say they do not work just as well with orchestral music. Piano and cello are reproduced with amazing accuracy. Most impressive to me is how well they handle percussion though. They handle percussion almost as well as acoustic suspension speakers (which is even more impressive considering these do not have a Zobel circuit). So far they have been put through three critical listening sessions with my son (who is musician of some skill and an audiophile), and we shared a relaxed listening session last week. For reference, I relied on 4 songs: Tori Amos Pretty Good Year. This song is a good test because it has a fairly wide range of octaves, and it is difficult to produce the low piano notes, Tori's husky voice, and the backup vocals simultaneously. It also was very useful for speaker placement - the song will bring out room issues very quickly. The CD is very well produced, and has very good sound. The majority of the signal is inside the 2Pi Towers "sweet spot" and they effortlessly push the music into the room. A sub would be needed to fill out the bottom fully, but the Towers never sound like they are straining on this track. Massive Attack Group Four. This song will test any speaker. The nice thing about Massive attack is that every bit of sound in the track is put there by hand, and it is clear when something is out of place. The music itself also hints at what is missing if your system is not able to reproduce i…
creator: joshua43214
date: 2018-06-11T01:16:11-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: As I write this post, the replacement drivers have arrived safe and sound, and I am still waiting on the replacement cross-overs and my 3Pi Subwoofer parts. All the major construction of the 6Pi is complete, and only a handful of small parts need to be made, and some holes drilled. I have begun painting what is ready to be painted, and I expect to spend the next week or two on painting the rest. I aggravated my back injury lifting the bass bins last Thursday, so I have been working at a slower pace since then. I have also begun work on the 3Pi Subwoofer, but can't proceed until the kit arrives. I will prolly interrupt the 6Pi build with a post or two on its construction at some point. The vast majority of this portion of the thread will be given over to the midhorns. The Tweeter boxes and bass bins are fairly straight forward, and do not require much additional to the 2Pi Towers. This forum limits the number of images you can upload for each post, so this will also be broken up into many posts since I have many pics. During one of my previous lives, I was a furniture maker. During this time, I spent a few years making percussion instruments. I have probably tried about every method possible for cutting and gluing tapered joints. I know from experience how difficult it can be to get a proper glue joint on something like this. Proper glue joints depend on two things: surface area, and clamping pressure. It takes very little error in the cut angle to reduce the amount of surface area below the required amount, and it is almost impossible to clamp perpendicular to the joint. I consider the horn section of this build to be a somewhat advanced project, that should be doable by anyone with moderate experience in woodworking. Mostly it requires patience and fussiness at a few key points, as well as the proper tools. The method I used is one of the methods I worked out for making tapered drums, and it works extremely well. I decided not to make a full sized jig because it wo…
creator: joshua43214
date: 2018-06-13T03:14:48-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: 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.
creator: johnnycamp5
date: 2018-06-13T12:17:13-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: 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.
creator: Wayne Parham
date: 2018-06-13T16:46:30-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: @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
creator: joshua43214
date: 2018-06-14T11:51:32-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: 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
creator: ggnarley
date: 2018-06-14T22:19:15-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: 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…
creator: joshua43214
date: 2018-06-15T02:30:20-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: 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. 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. Dimensions clarifications A pro-tip on modeling. When I drew the horn core,…
creator: joshua43214
date: 2018-06-15T05:54:27-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Hello everyone, please accept my apologies for the long delay on continuing this thread. Along the way to finishing the project several things happened that took away my time on one hand, and took the wind out of my sails on the other. I continued to have issues with the paint, I will go into detail later, but I found it extremely hard to continue to muster enthusiasm for a project I was already getting tired of knowing that I was going to have real issues with the final finish in the end. My experience with the 3Pi Subwoofer only put me off more (more later). On a more positive note, I was able to sneak a nice trip to the Painted Rocks area of the Upper Peninsula, and took a horizontal transfer where I work. I have the same title and description, but I am taking over a brand new lab and all that entails. The new position also came with a nice pay raise, and very real opportunity for further advancement. I don't recall if I mentioned it already, but I hold degrees in Molecular Genetics and Mathematics, and work in a semi-academic research capacity. The down side is a lot of hours until I can get everything working as it should, and by then we will have 2 post-docs I will have to nurse along Also, if you could hear my 6Pi Cornerhorns, I am sure you would also prefer to relax and enjoy the music rather than write a build thread... That said... We interrupt this 6Pi build thread to knock out a 3Pi Subwoofer... The 3Pi Subwoofer is truly a weekend project, and is quite a simple build. If you are looking for a good project to get your feet wet, this, or the 1Pi speakers are an excellent choice. After a brief email exchange with Wayne over what plate amp to chose, I settled on the Dayton Audio SPA250 from Parts Express. The Eminence JOB12 that the Pi3 Sub is built around is a serious beast, and I was worried about pairing a 250W amp with a 400W driver. There is a huge price jump when you cross the 250W threshold, and I did not want to spend a ton of money on an amp whose …
creator: joshua43214
date: 2018-07-14T18:10:38-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: The horn box is a bit more challenging than it looks at first glance. Clamping the 45degree sides will be very difficult. The method I detail below was not my first choice, but it worked quite well and was of minimal hassle. The best method in my opinion would be to rabbit grooves in the top and bottom that are a snug fit for the sides. This would allow clamping the angled portion without having to worry about everything getting pushed out of alignment. If you opt to get the parts CNC cut, I highly suggest this as a method. Setting up a router guide/jig as way more hassle than the method I used, but if your work style goes in this direction, follow your urges. It is really important that the miter joint in the sides be cut perfectly square to the top and bottom edges. If this joint is not square, a joint somewhere in the box will not close fully. If this happens, just spread some 5 minute epoxy on the inside of the joint to seal it. The Midhorn is the heart of the 6Pi, it is important that the box be fully sealed and airtight. Taking the time to get all the joints perfect will pay off in the end. I also made a design change at this point. In my original design, the rear portion of the sides entrapped the front - the assembly method I visualized would have been easier that way. I decided that I preferred the front portion to entrap the rear so less end grain would be visible. My parts had already been rough cut, so I played with the parts to convince myself that I could still make it work. Prudence being the better part of valor, I stopped everything and changed the design in Fusion 360. What looked to be fine on the bench, turned out to not work. After some fiddling, I was able to find a way to use the parts I had already cut. In the end, I settled on using the venerable screw and glue method for getting the sides to close up at the miter. After some experimentation, I found that 5/8" #6 screws (3.3mm x 16mm) worked well. The back is screwed onto the box, and in my …
creator: joshua43214
date: 2018-07-14T19:45:07-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: I trimmed the extra material off the horn flares, and sanded the joints flush. The flare was then inverted over the mouth of the box, and the long edges marked out for trimming I used one of the supports for the bass bin as a sled to run the flare through the table saw. I first made a cut that I was sure would be ok, then tapped the fence over as much as I dared and cut to the line. Fitting the long edge is just a matter of sanding until it fits, while being extra careful to sand to the line, and to keep the edges parallel. Once the flare is close to fitting, extra care should be taken to not split the box. MDF is a very weak material in tension, and you will split it with almost no effort. Patience is the key, it does not take any special talent or skill. Just check it often, wear a glove, and think happy thoughts. The human eye is remarkably adept at spotting regular shapes and shadow lines. Measure over and over as you go to make sure the top and bottom edges are the same width, and they are not tapered. Trust your eyes. If it looks like this when you sight down the edge, you have done very well. Next: Finishing up the flare
creator: joshua43214
date: 2018-07-14T20:09:40-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Fitting the short edge is much the same as the long edge with a couple differences. Trimming of the bulk is not easily done on the table saw. I trimmed it off with a handsaw. unlike sanding blocks, handsaws to require a bit of skill to use well. Just stay inside your comfort zone and use whatever tool you feel most comfortable with. Before I marked out the cut line, I spent some time fussing about getting the flare even in the box. I used a dial caliper and levered the flare with a chisel until I had less than 0.005" (.127mm) difference. All of my earlier fussing was so I could make this particular measurement well. If the box or the flare are not square and flush at the fronts, then getting this alignment will be difficult. The more out of alignment this is, the more the flare will be aimed off axis, and the more the driver will be out of vertical. How much does this really matter? Hardly any if there is only one speaker. The point is not that the horn and driver must be in some perfect plane, it is that the pair should be as identical as one can make them. One again, just sand to the line, think happy thoughts, and check often. When fitted, the flare should fall in with minimal friction. Just enough to prevent it from free falling, but not so tight that it produces a starved glue joint. This next image is actually out of order, but the operation can be done at this stage. Sorry, it is the hazard of writing a build thread after the project is completed. I used a fly cutter on the mill to trim the throat of the horn flat. This can also be done using straight edges and rulers, which is the method I used for flattening the back of the box. Still it is a cool pic with a scary tool Once the flare was fitted. I glued it in place and used some spring clamps to keep the joint tight. It is important to work quickly doing this, Tight Bond grabs and starts to set very rapidly. Make sure you have a mallet and an assortment of scrap for beating the flare into place. Before I gl…
creator: joshua43214
date: 2018-07-14T21:12:28-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Once the glue dried, I used a router to flush trim the sides only. The front I sanded just enough to remove the glue, and the back I left untrimmed. The back takes a gasket, delaying trimming as long as possible delays any damage it might receive during construction. I had saved all the offcuts from the horn to be used as internal bracing. I fitted one brace by trial and error using the bandsaw and a sanding block. Once the brace is close to being a good fit to the taper, one can hold the brace in place against one side, and scribe a line with a pencil laid flat on the other side. Then it is just a simple matter of trimming the edge parallel to the pencil line until it fits properly. The fitted brace is then used as an angle guide for cutting the remaining braces, by taping the blanks to the fitted brace and running them past the blade. Done wrong, this can be a very dangerous operation. Note the wide part of the guide is closer to the blade. If the tape fails and the part being cut slips, the taper will cause it to move away from the blade. If the taper is run the opposite way, the part will wedge between the blade and fence causing a kick back. The braces are then trimmed to length. Note the stop block is making contact with the taper, not the end. Each horn has a total of 6 braces, 4 for the longs sides, and 3 for the short sides. As uniform as these horns came out, they are not perfectly alike. Because of this, I chose to use 5 minute epoxy to glue the braces in. Un-adulterated epoxy is very hard and brittle, so not suited for this application because it might crack from the vibration of the driver. The stuff sold in hobby stores to the model airplane crowd is the right stuff, or the general purpose epoxy sold at the big box hardware stores. People often have trouble measuring epoxy, especially when it comes in tubes because the hardener and the resin have very different viscosities. Follow the directions, if it says equal volumes, do not use a scale. I invert t…
creator: joshua43214
date: 2018-07-15T22:19:20-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: The driver mount should be just a smidge shorter than the box sides otherwise there will be no room for any glue and it will be difficult to put in. I cut mine when I cut the sides, then sanded one edge back until it fit right. I test fitted the mount, and scribed the throat opening. The holes for the driver mounting screws are laid out from the scribed line. Once again, I took the easy way out and drilled the holes and made the cut out on the mill. Note I stayed very far from the line. This extra material is important later. I managed to remember to install the inserts before I glued in the mount. Forgetting this would be a disaster since they cannot be installed later. I also lightly moistened each hole, and added a touch of Gorilla Glue, having these unscrew would also be a disaster. After gluing in the driver mount, I glued 3/4" (19mm) square pine strips to the top and bottom of the box at the back. These strips will hold the inserts for the back cover. I also glued in some 3/4" (19mm) braces along the driver mount to top/bottom joint. I then taped some brown construction paper inside the assembly to prevent sawdust from getting down into the stuffing. Using one of the bass bin supports as a sled, I ran the whole assembly through the table saw to trim the excess off the back. This is when having a dial caliper and dial indicator come in really handy. I measure how much material is remaining. Then use the dial indicator to bump the fence over a few thousandths short of the target distance. I then placed the assembly mouth down on the table saw, and found the lowest point on the back. I scribed this height all the way around the box, and clamped straight pieces of scrape to the box along the line. Then it is just a matter of sanding and checking with a straight edge until the back of the box is flat. It is not so important that the back be parallel to the front, what is important is the back is flat. A gasket is only as good as the surface it seals. The rear cover…
creator: joshua43214
date: 2018-07-15T22:53:06-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Dealing with the throat of the flare is something I spent quite a bit of time thinking about. I read about every paper published for free on horn theory, and learned a huge amount in the process. It seemed self-evident that having sharp edges where sound entered the horn would not be a good thing. This turned out to be a subject that others have done some research on. In the end, I decided to be guided by a whitepaper by Charles E. Hughes for Peavey called "The Quadratic Throat Waveguide." Reading this paper alongside Wayne's own whitepaper on horn theory will probably all one needs to know about horns in general unless you want to take the deep dive into it. In short, the paper contends that the transition from the backside of the horn, to the inside of the horn should be a circular arc, whose edges are tangent to the back and side faces. The paper goes onto contend that the corners where the sides meet the top/bottom of the horn should be a parabolic profile whose origin is relative to the width of the side at any given point. The first part is simple enough, and can be done easily with a compass, the second part requires real working knowledge of calculus, and implementing will be a nightmare. Fortunately, we are making a 6Pi Cornerhorn, not a Peavey horn. My other research showed that above a certain size diffractions inside of horn become inaudible even when measurable, and that standing waves inside the horn are a far bigger issue. The 6Pi midhorn is just over that threshold for size. I honestly do not know how much of a difference this will make verses just eyeballing a radius, but it make me sleep better, which makes my girl friend happy, and a happy girl friend makes me happy Returning to Fusion 360, I exported the midhorn core to a new design, and created a model just for the arcs. I then created a shop drawing from the new model and printed it out. I trimmed a piece of scrap to be equal to the distance from the front of the driver mount to the tangent lin…
creator: joshua43214
date: 2018-07-15T23:24:37-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: I spent some time trying to figure where to put the crossovers. I know it is common to put them in a box, and set them on the floor next to the speakers. I am not the neatest person in the world, and this sort of thing just creates more mess in my world. I did want ready access to them, so putting them inside the bass bin seemed a bad option. After experimenting in CAD for a while, I settled on putting them in boxes, and mounting the boxes on the back of the midhorn. The pros of this are the crossovers are easily accessible, the box can be used to brace the back panel eliminating the need for a rubber ball behind the driver, and the crossovers are near the drivers making for a clean set up. The cons are that if I need to unplug the midhorn for testing, I will have to remove the box, and the fasteners are pretty expensive. Because the box bolts to the back of the midhorn, the box is the same size as the back. I focused heavily on ensuring the front of the box and flare where as square as I could make them, this came at the expense of squareness at the rear cover. Both of them are very slightly out of square. I began by ripping the backs for the midhorn and crossover box to fit their individual horns. I then taped the back cover and crossover back together, and cross cut them to fit the midhorn. I used layers of tape on the miter gauge to adjust the angle as I cut them. This is much simpler than adjusting the miter gauge, and just as accurate in this case. I then marked out and drilled the 4 holes for mounting the box through both parts. The holes in the horn back gets drilled over sized later to take the 1/4" threaded inserts. After separating the parts, I drill the holes for the binding posts. I have a rolling cart that I use for my drum sander that turned out to be just the right height to put under my drill press for drilling the mounting holes for the back cover. This was easier than attaching an oversized table to the drill press. I also have a bench top drill p…
creator: joshua43214
date: 2018-07-16T00:06:04-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: I designed and discarded a number of tweeter enclosures. The problem is that the horn itself is simply ugly and utilitarian, and putting an enclosure around it just makes it that much more obvious you are hiding something. In the end, I just decided to embrace its ugliness, and wrap it in a box that looks like it is serving some puropose. The tweeter boxes are "as built." I began by marking out the dimensions of the top. I used a piece of scrap that I ripped to be parallel to set the angle of the miter gauge. The scrap is held against the rip fence, and the miter gauge is adjusted until the other edge lays on the pencil line. The fence is then moved out of the way, and the tops are cut to the line. The driver is large enough that a relief is needed in the top. I cut the relief with a dado. A bit of trial and error was able to locate the position of the material so the relief would be centered. The pic below has all the details. A stop is clamped the to the fence with a large C clamp. A piece of scrap is clamped above the work to prevent it from shifting upward when the dado head is raised. The work itself is held in place with a bar clamp. A large piece of scrap is clamped at the front of the saw as a last safety device should the worst occur, and it will prevent the work from hitting me in the face as I kneel to raise the blade. After the cut is made on both sides, the fence is moved over about 3/4" (19mm) and the operation repeated. Once the angles are cut, the top itself is then used to set the blade angle for cutting the sides. The bottom is little more than a brace to keep the front end of the sides positioned, and the back is just a cap. After glue up, I used the horn to scribe the radius at the front, and sanded the taper with a long hard sanding block and 80 grit sandpaper.
creator: joshua43214
date: 2018-07-16T00:37:14-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: This forum has a 5 image limit, so here are some bonus pics for the tweeter. It is clear the mold was not up to temperature when the horns where cast, but A mold that size would take a while to warm up and add to the cost greatly. It is a good idea to dress the area where the driver mounts, since it is anything but flat or smooth. Here is an image of the completed tweeter showing the rope caulk wrapping, and rubber glued to the bottom to prevent it from moving around.
creator: joshua43214
date: 2018-07-16T00:47:52-00:00

Re: Build Thread: 2Pi Towers, 6Pi Corner horns (and possibly a sub and center)
type: item
description: Very cool looking tweeter enclosure! As an aside, the compression driver has a gasket that provides seal even with some of the casting marks on the mount. The casting marks simply press into the gasket. Still, it doesn't hurt to take those down with sandpaper as long as one isn't too aggressive. Earlier versions of the horn had an aluminum throat mount that was machined from billet. The current H390C wood horn still has this mount. It has an O-Ring immediately outside the throat. But I found this was extreme overkill. The gasket on the front of the compression driver works very well. Another example of something similar: Some people press modeling clay into the slight separation between compression driver and throat mount. They think the tiny gap might be a problem, like a larger discontinuity would be. But it's acoustically too small - Small compared to wavelength. It's kind of like how you can't see the mesh of a screen door. A better analogy would be a large tire rolling over a small crack which passes without disturbance. There are no anomalies that can be detected from the tiny gap between compression driver exit and horn throat entrance; There are no measurable differences made when using the modeling clay. So while it doesn't hurt, it doesn't help either.
creator: Wayne Parham
date: 2018-07-16T14:50:11-00:00