Scrappydue Posted November 29, 2015 Share Posted November 29, 2015 (edited) 13 sheets of baltic birch. ! What the hell. About talked myself into putting two of these behind me, but 13 sheets??? http://www.hometheatershack.com/forums/ported-subwoofer-build-projects/69710-dougs-dual-gjallarhorn-build.html not sure if you know but this is the doug that lives really close to me. You could hear these as well at othorns if you come back up.Also can hear the noesis 215's. And there is also a guy close with an erskine designed room. He's rich lol Edited November 29, 2015 by Scrappydue 1 Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted November 30, 2015 Author Share Posted November 30, 2015 (edited) not sure if you know but this is the doug that lives really close to me. You could hear these as well at othorns if you come back up. Yeah I didn't figure there were two Dougs near Kansas City who both have two G-horns. Find out his BBQ competition schedule beforehand next time. That room is nothing like what I pictured though. There's no way I can tear into something like that until my pole barn is up. Just a ridiculous idea. Edited November 30, 2015 by MetropolisLakeOutfitters Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 30, 2015 Share Posted November 30, 2015 Can't wait to see the builds. Yes, MDF is stinky. After the driver is installed and the box coated, there's very little smell, even with ported or horns. 1 Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted November 30, 2015 Share Posted November 30, 2015 (edited) Yes, MDF is stinky. See my little friend below. Edited November 30, 2015 by derrickdj1 1 Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted November 30, 2015 Author Share Posted November 30, 2015 Wish there was one resource with all the rules for ports: 1. prevent loading issues by not having the back of the port face the driver. 2. keep the port close enough to the driver as to not have issues with the frequency in question, and I forget how to calculate this. 3. keep the port's side and back clearance at least the size of the port away 4. slotted ports need to be at least a 1:8 ratio 5. don't get lazy on the bracing (but there's a hole in the box!) because at the tuning frequency the internal pressures are nearly twice that of a sealed box due to port backpressure. 6. for the cleanest sound, but is likely hard to do on subs, face ports away from the listeners so that artifacts coming from inside the box aren't directed at their ears through the port but are instead dissipated What else is there? Pretty sure there's more. 7. Apparently the consensus is that ports need at least 14 square inches per cubic foot of box size, probably ideally more like 15-16. That means for the 8 cubic foot box I was about to build, the not-quite 50 square inches would need to be over twice as large to be optimal, and over 3 times as large as the 37 square inches that Parts Express is recommending. You'd have to have four 6" round ports for a single 18 if you went by this rule. I don't really understand this. Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted November 30, 2015 Author Share Posted November 30, 2015 Yes, MDF is stinky. See my little friend below. Don't nobody go in the bathroom for about 35, 45 minutes. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 30, 2015 Share Posted November 30, 2015 Apparently the consensus is that ports need at least 14 square inches per cubic foot of box size Cubic inches? Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted November 30, 2015 Author Share Posted November 30, 2015 Apparently the consensus is that ports need at least 14 square inches per cubic foot of box size Cubic inches? No like port area as to eliminate huffing and whatnot. I'm guessing that only applies to towers and booming car audio, that's a ridiculous rule for large boxes with low tunes. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 30, 2015 Share Posted November 30, 2015 A slot port would be 24x5 then. That doesn't sound unreasonable. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 30, 2015 Share Posted November 30, 2015 I guess port size is relative. 1 Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted November 30, 2015 Author Share Posted November 30, 2015 (edited) A slot port would be 24x5 then. That doesn't sound unreasonable. Until you realize that this port in an 8 cubic foot box would have to be 90" (7.5') long to be tuned at 20 hz. Your port alone would take up 7.2 cubic feet of space for an 8 cubic foot box. After bracing, driver, and port displacement, suddenly you've got a 16 cubic foot box on your hands, just to hit a measly 20 hz in a traditional ported box, with only one 18. Edited November 30, 2015 by MetropolisLakeOutfitters Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 30, 2015 Share Posted November 30, 2015 (edited) A slot port would be 24x5 then. That doesn't sound unreasonable. Until you realize that this port would have to be 90" (7.5') long to be tuned at 20 hz. Your port alone would take up 7.2 cubic feet of space for an 8 cubic foot box That doesn't sound right at all. Where are you getting the numbers from? Have you run them in winisd? Edited November 30, 2015 by CECAA850 Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted November 30, 2015 Author Share Posted November 30, 2015 (edited) That doesn't sound right at all. Where are you getting the numbers from? Have you run them in winisd? The 14-16 square inches doesn't sound right? Just do a Google search, a whole bunch of DIY stereo and SPL car audio guys are repeating these numbers left and right. Makes no sense. I'm sure WinISD would disagree. I think that's what Parts Express uses to come up with their recommendations. If the port length doesn't seem right, you can play with this calculator. http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm Edited November 30, 2015 by MetropolisLakeOutfitters Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 30, 2015 Share Posted November 30, 2015 Are you talking about the UM18? • Vented (home theater): 8 cubic ft. (net internal, not including driver or vent) tuned to 20 Hz, with 3 flared vents 4" diameter by 28.5" long, for an f3 of 18 Hz If you're talking about the HO,, it's 7.5 cu ft. The port would be slightly smaller than above as well. Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted November 30, 2015 Author Share Posted November 30, 2015 (edited) Yeah talking about the ultimax ported 8 cubic foot box just as an example. Their recommendations are way off of the 14-16 square inch per cubic foot recommendation that some people often repeat. Not sure why that rule is considered to be legit. As soon as you make the port have a larger area, you have to make it longer to keep the same tuning. Edited November 30, 2015 by MetropolisLakeOutfitters Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted November 30, 2015 Share Posted November 30, 2015 An 8 cu ft box may need a lot of port length to tune that low. Larger boxes may not. Have you looked at the Marty sub enclosuress? Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted November 30, 2015 Share Posted November 30, 2015 (edited) The Marty tuned to 17 is around 11 cu ft. and the slot port is 3 in. X 24 in. The port sizes that you mention seem off. Is that the box you are making in the pic? That's what I call a home theater monster. Unless the sub/port is poorly design I don't think you will hear a big difference with it on the front, side, or back. Most of us don't have that good of hearing. Edited November 30, 2015 by derrickdj1 1 Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted November 30, 2015 Author Share Posted November 30, 2015 (edited) An 8 cu ft box may need a lot of port length to tune that low. Larger boxes may not. Have you looked at the Marty sub enclosuress? Yeah two full Marty's laid on their sides may end up behind me eventually. They're the same situation with what I was asking though, port is 3x22.5", 67.5 square inches total. With 11 cubic feet, the 14-16 rule that I've seen several times would be more like 165 square inches, then of course the box size would be even more ridiculous. I don't know where people came up with that. Is that the box you are making in the pic? That's what I call a home theater monster. No I'm making four sealed up front because that's all I can figure out that will fit in the footprint that I wish for. Only got to work on it maybe 4 hours total but I got this far. Going to finish it when it stops raining and dries up. These will be end to end, internally will net 16 cubic feet total after displacement. I like my potentially somewhat directional bass from music to come from up front so I'm pretty adamant that something goes under the screen. Unless the sub/port is poorly design I don't think you will hear a big difference with it on the front, side, or back. Most of us don't have that good of hearing. I just have limited space up front so those ain't going up there. However I did have some ported boxes up front before, for whatever reason they weren't very impressive, but put them behind me, and whatever it was about the room modes, it just kind of unleashed them. But, I put my sealed ultimaxes behind me and they sound like crap. Put them up front, and they're super tight for rock music and the low end is still there. I don't know what the deal was there, wish I knew why the ported ones performed so much better behind me. Edited November 30, 2015 by MetropolisLakeOutfitters Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted December 1, 2015 Share Posted December 1, 2015 Very cool. Quote Link to comment Share on other sites More sharing options...
Paducah Home Theater Posted December 6, 2015 Author Share Posted December 6, 2015 (edited) More from the ghetto build, trying to slap some braces in. Just one of these is already too heavy for me to pick up, I have to move it around with a hand truck/dolly. Going to put some square dowels in as cross braces and call it good. Edited December 6, 2015 by MetropolisLakeOutfitters Quote Link to comment Share on other sites More sharing options...
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