Samps Posted April 26, 2018 Share Posted April 26, 2018 About half way done with my ported DS21. Thought I'd share some pics. 23.5 x 23.5 x 49.5. = good use of ply. 13.4 internal -1.0 for port -.5 for driver -.15 for bracing = about 11.75 net cubic feet port is 8 x 8. Length is a guess at this point. It's 22.75 in actual length, but the effective length I'm sure is going to be longer. Hoping for 20-22 hz. I built a jig to measure, but can't get a good reading yet. Going to be painted. Bridged on a 3000dsp. Link to comment Share on other sites More sharing options...
Ricci Posted April 27, 2018 Share Posted April 27, 2018 Looks good. Yes I would expect your port to act a bit longer than what you have calculated for the length plus 90deg turn since it is close to the back wall. I'd guess it acts a good 3" longer than expected. Impedance measurement should show where it lands. Link to comment Share on other sites More sharing options...
maxmercy Posted April 27, 2018 Share Posted April 27, 2018 Make sure you put a finish on the cab before you install the driver. I have had cabs that went without finish for 3 years, b/c after the driver goes in, it is so easy to just listen to it. JSS Link to comment Share on other sites More sharing options...
Samps Posted April 27, 2018 Author Share Posted April 27, 2018 I built and sold two THTs that were never finished. I figure you have to test it before you spend all that time finishing, but then it never gets done. My impedance jig isn't working correctly. It will make a sweep but the level is super low and the graph doesn't look anything like what I've seen before. Pretty sure I built the jig correctly, but not sure I'm using the correct settings in REW and or computer. Been testing a little bookshelf for practice. Link to comment Share on other sites More sharing options...
lilmike Posted April 28, 2018 Share Posted April 28, 2018 6 hours ago, maxmercy said: Make sure you put a finish on the cab before you install the driver. I have had cabs that went without finish for 3 years, b/c after the driver goes in, it is so easy to just listen to it. JSS Three years.... Weak.... I am still rocking the OG MicroWrecker (since 2013)... No finish, not even sanded, still has big PL boogers on it. Link to comment Share on other sites More sharing options...
lilmike Posted April 28, 2018 Share Posted April 28, 2018 5 hours ago, Samps said: I built and sold two THTs that were never finished. I figure you have to test it before you spend all that time finishing, but then it never gets done. My impedance jig isn't working correctly. It will make a sweep but the level is super low and the graph doesn't look anything like what I've seen before. Pretty sure I built the jig correctly, but not sure I'm using the correct settings in REW and or computer. Been testing a little bookshelf for practice. PM me. I can help you work through it. They're pretty basic. Might be as simple as L and R channels swapped. Link to comment Share on other sites More sharing options...
Samps Posted April 29, 2018 Author Share Posted April 29, 2018 Would there be any benefit to adding a deflector to the back corner of my port? Currently there is a pretty big difference in volume of that corner vs the rest of the port. Link to comment Share on other sites More sharing options...
Samps Posted April 29, 2018 Author Share Posted April 29, 2018 Test from a random htib speaker. Link to comment Share on other sites More sharing options...
lilmike Posted April 29, 2018 Share Posted April 29, 2018 3 hours ago, Samps said: Would there be any benefit to adding a deflector to the back corner of my port? Currently there is a pretty big difference in volume of that corner vs the rest of the port. Possibly. Looks like it is something where you could try it and see. Heck, just cut a piece and set it in place for testing. Won't be 100%, but will give you an idea. Link to comment Share on other sites More sharing options...
Samps Posted April 29, 2018 Author Share Posted April 29, 2018 Yeah, that's what I was thinking. Now that I can do the impedance test ( thanks Mike ) I feel like I can test things and make useful decisions. I doubt it will make a big difference unless I'm pushing things pretty hard. But it's simple enough to try. Link to comment Share on other sites More sharing options...
Ricci Posted April 30, 2018 Share Posted April 30, 2018 Cheers Mike for helping Samps out. Link to comment Share on other sites More sharing options...
Samps Posted May 3, 2018 Author Share Posted May 3, 2018 Took a impedance sweep. Looks like it's currently around 23hz. Not sure if that might change once the driver gets broken in? It may shift a little lower when the cab is standing upright. It's currently laying on its back because I didn't want to screw in the driver. Once it's standing up, the port may act a little longer since it's on the very bottom. I was hoping for a little lower but not sure if I want to mess with it. 22hz in the model works out pretty well with the inukes 20hz HPF. Adding length to the port isn't a problem, I left myself plenty of room to extend it. I did add the corner deflector in the back corner, but didn't get the impedance test of the before and after. Link to comment Share on other sites More sharing options...
SME Posted May 3, 2018 Share Posted May 3, 2018 Driver break-in may shift the impedance peaks ever so slightly, but it won't affect the tune, which depends only on the cabinet volume and port characteristics. Edit: I think you're closer to 21.5-22 Hz. The tuning frequency is precisely where the phase crosses zero. Link to comment Share on other sites More sharing options...
Samps Posted May 3, 2018 Author Share Posted May 3, 2018 Thanks, I'm going to put in a few screws tonight, and test it upright to see if that changes things. Link to comment Share on other sites More sharing options...
Ricci Posted May 3, 2018 Share Posted May 3, 2018 Not having the driver bolted in will probably make the system a bit lossy too. I'd expect that standing the cab up and properly bolting in the driver and sealing it will probably sharpen the lower peak a little and perhaps lower it a bit more. Link to comment Share on other sites More sharing options...
lilmike Posted May 3, 2018 Share Posted May 3, 2018 Yeah, that lower peak is a bit "soft", that generally means losses or leaks (or, as I learned, a really useless port). With a typical reflex box, we want the peaks to be about the same height. Link to comment Share on other sites More sharing options...
Samps Posted May 3, 2018 Author Share Posted May 3, 2018 I thought the peaks would only be the same height if the tune was at the drivers FS? Winisd predicts similar lopsided peaks as I'm getting, but the lower peak is not quite as bad. Hopefully it all works out once I add screws and stand it up. Link to comment Share on other sites More sharing options...
SME Posted May 3, 2018 Share Posted May 3, 2018 The lower peak substantially depends on the suspension compliance, which is probably the least accurate T/S parameter given and the most likely to change with break-in as well as temperature and humidity. Link to comment Share on other sites More sharing options...
Samps Posted May 3, 2018 Author Share Posted May 3, 2018 Looks better screwed in and standing up. The trace has more wobble in it, but the impedance minimum came down to 21.27hz. And the lower peak is a bit higher and sharper. Also added a comparison between unscrewed laying down and the screwed standing up. Link to comment Share on other sites More sharing options...
SME Posted May 4, 2018 Share Posted May 4, 2018 Can you run a slower sweep? That might help reduce the ripple. Otherwise, looks good. It looks like you hit the tune you wanted right on the mark. Link to comment Share on other sites More sharing options...
Samps Posted May 4, 2018 Author Share Posted May 4, 2018 I ran the slowest sweep REW allows and the result was exactly the same. Not sure where that waviness comes from. It didn't show up in any of my tests of other speakers around my house. Possibly still some air leaking out, I didn't use any gasket material under the driver since this is still under construction. I'm pretty confident this is working out as planned, so I'm going to move forward with sanding and paint. It won't be a show piece, but decent anyways. Thanks for all the help! Link to comment Share on other sites More sharing options...
Ricci Posted May 4, 2018 Share Posted May 4, 2018 Wobbles could be reflections from surfaces and vibration/resonances. I put about 150lbs on my speaker stand to drop the vibration resonance of the top section down below 5Hz. Otherwise it shows up in the impedance measurements. You'd be surprised what adding some weight and turning the cab just 15 degrees might do sometimes. I bet that desk isn't as stable as you'd think. I usually put my cabs on a bar stool if measuring in my garage and angle them towards the far corner then add a couple 50lb dumb bells and some sandbags on top. Larger cabs like Skhorns, MAULS, etc. get done outdoors. Link to comment Share on other sites More sharing options...
Samps Posted May 4, 2018 Author Share Posted May 4, 2018 Lol, that desk is not stable at all. Cheap IKEA type construction. I added some braces to it just so I could make it useful, but I wouldn't call it stable in any way. Maybe I'll try sitting it on the floor. I'm also planning on making my own grill for this, since nobody makes a damn 21" speaker grill. I guess all the pro audio guys using these either have them in horns or make their own grills. So, question is, how much clearance should I leave above the surround? Link to comment Share on other sites More sharing options...
Ricci Posted May 4, 2018 Share Posted May 4, 2018 I'd do xmech rating +2mm or something. You'd never ever hit that but you don't want to take that chance either. Link to comment Share on other sites More sharing options...
lilmike Posted May 5, 2018 Share Posted May 5, 2018 Admittedly, I oversimplified the statement regarding equal peak height above. The relationship between the driver parameters and the box tune dictate the relative size of the two peaks. What matters most is that the peaks you're measuring are a decent match to what your simulation software is predicting. As far as the grille spacing? Yeah, make sure things won't hit. X-mech plus a few mm is a great start, I'd look at the thickness of nominal pieces of plywood or other scrap stock. Make sure the grille does not rattle. Foam weatherstrip and lots of screws. Link to comment Share on other sites More sharing options...
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