Building a Tapped Horn with a NEJE laser

today we turn up the pressure as we assemble test and listen to a laser cut based [Music] we begin with this courtesy of ups which is where i can appreciate the abundance of packing material inside this box thankfully everything arrived unscathed as you can see in this lovely green shot but it's also worth noting that apart from the screws in the laser module everything in that front row is just accessories leaving precious little in a way of assembly the instructions call for a single m6 screw in each of the four corners followed by two more screws one at either end of the gantry the laser module slides in locks off and that's all she wrote this is the master 2s max from aj and it is big yeah yeah yeah it's not small no no no with an engraving area of 810 by 460 millimeters it just barely fits on the table the laser is rated at 7.5 watts that's the optical power though i may eventually swap it out for the 10 watt module offered by the company as one of the many upgrade packages one such upgrade is this air assist kit and we'll discuss in just a minute for now let us shift gears and talk acoustics right away i'll admit that the car is not where i get the most out of my listening experience not by a long shot which is why i haven't done anything about the factory speakers or this kenwood receiver likely dating back to the vehicle's original owner setting that aside however i do occasionally wonder about things like what might be the smallest base driver that a mobile sound quality enthusiast could get by with and in what type of enclosure well i've been chewing at that thinking about the laser drafting some ideas ultimately arriving at 4 inches oh my god i'm really sorry there there george it's the size of the sound that matters and will take care of it by coupling the driver's output to this nearly two and a half meter long expanding waveguide folded onto itself to form a tapped horn this particular example of a third order acoustic network benefits from low group delay lower in fact than that of a proportional base reflex simply because there is no compression chamber there to store and to release the energy out of step with the input signal this also lends itself to a phase response nearly as shallow as that of a proportionate sealed enclosure unfortunately the piston area of this 4-inch mid base isn't quite enough to run sealed at any chamber volume at least not as a subwoofer and this is precisely where the benefits of core loading come into play the high pressure low velocity vibrations of the throat are transformed into low pressure high velocity vibrations in the mouth allowing for something as small as this to acoustically impedance match with the surrounding airspace well into the base if not the sub-bass region you never go ask to mal tapped horns do if you'll pardon the analogy and here's the predicted income response at the headrest of my hatchback i've also modeled it in the corner of a small room and as you can see despite the difference in behavior from one listening space to the other both profiles are quite usable well into the upper 30hz region which is about as deep as i'm willing to go without simultaneously compromising the ability to play in volume or making the enclosure any larger than it already is speaking of which the final dimensions will measure 156 millimeters in width 450 millimeters in height and 580 millimeters in depth the build will comprise 24 quarter inch layers with 50 individual pieces forming the body of the waveguide including a pair of mostly double stacked outer walls these notches will serve to compensate for the cross-sectional blockage presented by the profile of the driver as it protrudes into the mouth of the waveguide not entirely but enough to matter also to keep everything in line during assembly each layer will be cut with this pilot hole pattern 22 screws will be threaded in to provide the alignment and some temporary clamping force along all the key areas corners midpoints etc basically all the places where a conventional ratchet bar should but won't reach finally a 3d printed terminal cup will complete the build portion of the project though before we get too far ahead of ourselves let's get this air assist figured out as you can see here it includes an m82m4 fitting reducer an inline shadow valve some screws a tiny stainless steel pipe and two meters of clear pneumatic tubing the idea is to direct a stream of compressed air toward the laser's focal point primarily to expel the carbonized burn residue otherwise left along the surface but also to evacuate heat reducing the risk of flare-ups one interesting point of note here is the lack of any mounting brackets in fact the product page instructs you to print your own assuming of course that you have a 3d printer which i do unfortunately the listed model appears to have been designed for something else and i can't exactly attach it in a way that would point the nozzle at the beam so i guess i'll just yank this back off take some measurements and model a bracket of my own afterwards some non-descript red pla wiggles its way down the gantry and into the extruder laying down 0.15 millimeter layers with full support and 100 info here's how the two printed pieces come together this is how the thing pivots and here's how it attaches to the laser the stainless steel pipe will serve as the air nozzle and once in place i can just lock it up at any angle the hose will run along the wiring harness which should keep it out of the way then the shutoff valve can be spliced in just beyond the gantry finally we come to the fitting reducer which connects all that stuff we just did to a source of compressed air and here's where i'll point out that my own ability to identify a good air assist compressor does not extend much beyond this article by david tucker in which he compares several different options with the general consensus being that more psi is better so here's my personal pick for the middle ground concession between air pressure and quiet indoor operation it is the mac 100 q from akira claimed to operate at less than 60 decibels claim confirmed it also comes with a standard quick coupler socket which meant that i got to replace the fitting reducer with a four millimeter push to connect adapter made it to a quick coupler plug not included in kit so that goes in here and it looks like the pressure through the nozzle tops out around 6 psi eventually settling at around 4. as you can see this is just barely enough to form little air dimples on my fingers but whether or not it makes for an adequate air assist has yet to be established with a series of test kits the n4630 laser module comes with a focus adjustment knob which i do not plan to use so here i am rotating it all the way to the shortest focal point i also made this contraption to hold a piece of cardboard at a slight incline and now i'll run the laser across it from a set reference height say maybe 60 millimeters between the ground plane and the bottom of the heatsink here's my first try at 10 power and well that's not very definitive is it i can tell when the laser comes into focus but beyond that the nuance is all but lost so here we go again at five percent power and this time i can at least tell that the butter zone is somewhere toward the bottom so i'll just raise this thing up 20 millimeters and give it one final go there it is that's what i was looking for you see this mark here at the end is about as light as the one over here give or take and if these are the outskirts the midpoint represents the optimal focus let me just measure that and subtract from a reference height of 80 millimeters this gives us the target distance between the heatsink and the work surface a key measurement which i can now use to make a focal gauge anyway here's some quarter inch mdf here's how simple it now is to set focus and here's a test cut with the laser at full power 200 millimeters per minute and the air assist wide open this went on for a total of 16 passes at which point they decided to try again reducing the travel speed to 100 millimeters per minute unfortunately the beam never made it to the other side and after a closer inspection it looks like it hasn't even made it halfway through so there's our medium density materials performance in a nutshell and i have to think that we'll do better with plywood perch to be exact here's a quarter inch sample with the laser once again traveling at 100 millimeters per minute and already by the second pass the beam is shining through all the circular details released by the third pass and by the fourth we have an impressively clean looking test piece in fact now i'm curious about how this would have turned out without the air assist but first i want to make a pit stop by the way here's what 100 bucks will get you at harbor freight if you don't already have a dedicated makerspace this bench is right for all manner of customization especially if you don't mind design your own bits and pieces here it is in the garage setup for the laser hopefully inspiring a few modding ideas of your own the gantry is held in place and elevated allowing for oversized sheets to pass under the frame here's the birch ply from earlier and here's a repeat of that last test cut except now without the air assist needless to say while i didn't encounter any flare-ups the smoke released during the first couple of passes left a heavy coat of residue along the cut line what's more even after six passes nothing seemed ready to budge already positioned the air assist method as the obvious winner so with that established it's on to the feature build and it's probably worth noting that 100 millimeters per minute isn't very fast when the laser has to cover a distance of more than 6 000 millimeters per pass 6 passes per layer and all the travel in between the features at this rate each layer took about 7 hours to complete and if i may point out the obvious yeah this is hilariously impractical especially as i've only been able to supervise one cut per day but it's also the mother of all tests for diode laser engraver claiming to cut wood and this one does relentlessly even weeks into the project with a cooling fan matted full of grime and resin this thing just keeps on ripping through the ply though as you can see the elastic whip meant to hold the cables upright has eventually buckled under its own weight relying on some overhead assistance nevertheless if you're here for the review consider this the money shot nearly 200 hours had passed with the laser operating at full power a true testament to the machine's longevity and to a lesser extent my patience what's more there is still the small matter of putting the entire thing together which in this case meant a lot of gluing and screwing insert pun nobody is amused let's talk about this now with the screws pulling double duty as alignment dowels and as clamps everything relied on the consistency of the pilot hole pattern from one layer to the next so i decided to drive the screws in through an alignment jig further ensuring that the pattern doesn't stray as we advance upward this appears to have worked well enough in fact the very next layer seals the whole thing shut taking advantage of this last chance to access the internals armed with some wood filler and a power tube selfie inspected the walls for any pinhole gaps formed by the occasional imperfection along the surface of the wood afterwards a bit of sanding on the outside a bit more on the inside just to scrape away some of that loose residue a quick wipe down with a rag and it's on to the driver mounting plate it's a double snack after a fashion with a couple of m4 bolts serving as binding posts an ample bit of glue around the landing wires first and the whole thing just settles into place afterwards some jb weld is prepared and the cable is run along the waveguide to the terminal plate in the back then just as a proactive measure another batch of jbl is spread around the bottom of the driver mounting plate the difference in pressure from one side of this panel to the other is projected to reach nearly 0.05 bar at the 30 watts that the driver is rated for which may not seem like much until you consider it happening no less than 35 times per second and that's a lot of incentive for the air leaks to make themselves apparent needless to say a gasket of blue tack around the driver is also a must and with everything wired up we can finally seal the waveguide there's the inner layer some more glue and the outer layer right on the mark in fact this entire pilot hole pattern approach has made the assembly effortless albeit still very time consuming even with a power tool at any rate once the two remaining layers have been sanded down the enclosure is essentially ready to be tested so here i've stuck it in the corner of my office which is about as small a room as i have on hand for this and after all the effort i am relieved to see it perform as expected certainly along the base in the sub-base region with a shallow dip between the two above the last however it's the distinct unequivocal base horn presence that ultimately defines the listening experience and i'm wondering if any of it could be relayed over youtube so what i've done here is set up a dsp with a high pass around 38 hertz everything below 80 hertz going to the sub and everything else being sent to an extended range speaker you may recall from an earlier video this along with some recording gear is dragged into the living room where i hope to demonstrate how the enclosure projects across a larger space the microphones are set up about a meter away from the near field demo then about 8 meters away from the midfield demo and just to showcase a bit of the organic detail across the timbre before my regular tracks here's a few bars of some upright bass [Music] so [Music] foreign [Music] foreign [Music] so as you could hopefully tell under the right circumstances a loan some 4-inch mid-base can absolutely fill the listening space with some weighty well-controlled bottom end but now let's move it up to the car and since i still have these rcas ran from the head unit i can just plug into the dsp sending 38 to 80 hertz through the reference amp to the sub with everything else coming through the curve speakers i will however bypass this until after the frequency response test and things continue to line up as expected then again it's a little late for surprises though if there's one thing that continues to stand out it's the forward sounding character of the lows and how effortlessly they carry even beyond the immediate listening space so much so in fact that i elected to include a midfield vantage point for the in-car portion of the demo as well with the microphone set up on the bench once again starting off with the operating base [Music] um [Music] so [Music] [Music] [Applause] foreign [Music] [Music] foreign [Music] [Music] oranges [Music] so [Music] and scene all right some final thoughts right away i like the idea that one day my wood cutting machine will be something that i can just hang on the wall for storage and the master 2s max from aj is a practical step toward that future with a seven and a half watt laser it is already fit for minor projects around the house things like plywood furniture shelving and as it turns out a fully functioning tapped horn just to demonstrate some basic principles of acoustic impedance matching along the way speaking of which i am looking forward to seeing what you've picked up on during the demo as well as your choice of listening gear the voiceover for this video was recorded with the au am 200 bundle thoughtfully provided by milano it includes a podcasting console and this large diaphragm side address studio condenser mic which interestingly enough doesn't actually require phantom power anyhow thank you for watching and i may as well thank you for waiting as it does take some time for me to put these projects together in my spare time so don't forget to rate this one as you see fit subscribe for more and i'll see you in the next one cheers

Channel: HexiBase

Views: 115,056

Keywords: HexiBase, Pete, Peter, Kulicki, NEJE, Tapped Horn, Bass, Horn, Subwoofer, Tang Band, Speaker, Midbass, Woofer, Acoustics, Amplifier, Demo, Enclosure, Design, Car Audio, Audiophile, Prusa, Creality, 3D Printing, Harbor Freight, Makita, Compressor, Laser, Engraver, Cutter, Woodworking, Birch, MDF

Id: ipHH2GUgT5g

Length: 19min 19sec (1159 seconds)

Published: Mon Mar 28 2022