Triticum Agricolam Posted August 5, 2015 Report Share Posted August 5, 2015 How do you keep that area from leaking air though? My first thought is weatherstripping but unsure how that would hold up? I'd think a fat bead of silicone would do the trick and be easy to remove if need be. I've been doing some reading on the caraudioclassifieds 4th order thread. 1000+ posts actually. Thinking of going with a new ratio. 3:1 with 1 cube sealed per sub. So 4 cubes sealed and 12 ported. I ran across a formula for determining sealed resonance in that thread and am using it but coming up with silly numbers. The square root of Vas/Vb+1? Not sure I'm doing it right. My impression is that the answer to this formula will give me my best ported tuning frequency. Also, is it okay that I fire the subs at each other in the box? Soundqubed assures me that it won't cause any cancellation but I've heard one person say it's a general 'no-no'. Build begins this weekend BTW. Ratios mean jack. They were made as a (bad) shortcut for people who don't understand bandpass boxes. Using 1 cube per sub is going to give your subs a sealed resonance of about 46 Hz, assuming SoundQubes specs are accurate. The only difference between having a 6 cubes sealed and 4 cubes sealed is your low end rolloff is going to be a little steeper with the smaller sealed side, it won't make the box one bit louder. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
audiofanaticz Posted August 5, 2015 Report Share Posted August 5, 2015 Just read this entire thread looking for the guy that said shrinking the port and and lowering the port velocity would be bad... Only to find out this is the wrong thread.. I wanted to eat me some popcorn dammit! Link to comment Share on other sites More sharing options...
germanyt Posted August 5, 2015 Author Report Share Posted August 5, 2015 How do you keep that area from leaking air though? My first thought is weatherstripping but unsure how that would hold up? I'd think a fat bead of silicone would do the trick and be easy to remove if need be. I've been doing some reading on the caraudioclassifieds 4th order thread. 1000+ posts actually. Thinking of going with a new ratio. 3:1 with 1 cube sealed per sub. So 4 cubes sealed and 12 ported. I ran across a formula for determining sealed resonance in that thread and am using it but coming up with silly numbers. The square root of Vas/Vb+1? Not sure I'm doing it right. My impression is that the answer to this formula will give me my best ported tuning frequency. Also, is it okay that I fire the subs at each other in the box? Soundqubed assures me that it won't cause any cancellation but I've heard one person say it's a general 'no-no'. Build begins this weekend BTW. Ratios mean jack. They were made as a (bad) shortcut for people who don't understand bandpass boxes. Using 1 cube per sub is going to give your subs a sealed resonance of about 46 Hz, assuming SoundQubes specs are accurate. The only difference between having a 6 cubes sealed and 4 cubes sealed is your low end rolloff is going to be a little steeper with the smaller sealed side, it won't make the box one bit louder. Is it really so application dependant that there is no best place to start? Im going off of what most people seem to be doing. 2.5 cubes for an 18, 1.5 for a 15, 1 for a 12, .5 for a 10. And Im pretty sure indont need to go to a 4:1 ratio so i figured at 3:1 i could always add foam blocks to lower it if I feel like it's needed. If I stick with 1.5 or 1.25 how does that affect my resonant frequency and is that about what I should tune to? Current Setup : Nothing2014 Ford Focus SE Hatch Future looking like: Singer / XS power Crescendo BC3500D CT EXO 15 Pioneer 80PRS CDT HD-61PRO CT Sounds M75.4 CT Sounds AT60.4 Something along those lines. Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted August 5, 2015 Report Share Posted August 5, 2015 Is it really so application dependant that there is no best place to start? Im going off of what most people seem to be doing. 2.5 cubes for an 18, 1.5 for a 15, 1 for a 12, .5 for a 10. And Im pretty sure indont need to go to a 4:1 ratio so i figured at 3:1 i could always add foam blocks to lower it if I feel like it's needed. If I stick with 1.5 or 1.25 how does that affect my resonant frequency and is that about what I should tune to? When it comes to bandpass boxes, just because other people are doing it doesn't make it "right". Bandpass boxes have to be one of the least understood things in car audio and I see lots of people doing ill-advised things with them. Also there is definitely more than one "right" way to design a bandpass box, it really depends on what kind of sound you are trying to get out of it. If you are looking for a starting point, here is my suggestion. Start with the sealed side, ideally you want it sized to get the QTC at .707 or below and you want the Fb to be close to where you want to tune the front chamber to (45 Hz is a good starting point). Not all subs will allow you to accomplish this. In your case 1.15 cubes per sub will get the Fb to 45 Hz. The Qtc is still higher than ideal but there isn't much you can do about that since the subs QTS is already above .707 and all you can do is raise it. Now for the ported side, tune it to around 45 hz to start with and size it whatever it needs to be to get the amount of bandwidth or efficiency you want. 4th order bandpass boxes trade wide bandwidth for efficiency, you can have a combination of the two but you can't max out both at the same time. With 12 cubes for the front chamber the box is going to be very efficiency around the tuning frequency, but will have a narrow bandwidth. I like smooth response, so if I were building it to sound how I like things I'd use about 4 cubes for the front chamber, but I don't mind giving up output to get decent response and in this case going from 12 to 4 cubes is going to cost about 7 db. Neither 12 or 4 cubes is right or wrong, it just depends on how you want it to sound. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
germanyt Posted August 5, 2015 Author Report Share Posted August 5, 2015 I understand what you mean about trading efficiency for bandwidth but I don't have a reference point. The owner of this truck is probably equally concerned about them. He really only listens to rap so I figure most of that bass is in the 30 -45 hz range. He's also excited, as am I, about the possibility of approaching 150db. Even 145 I think would make him happy. Current Setup : Nothing2014 Ford Focus SE Hatch Future looking like: Singer / XS power Crescendo BC3500D CT EXO 15 Pioneer 80PRS CDT HD-61PRO CT Sounds M75.4 CT Sounds AT60.4 Something along those lines. Link to comment Share on other sites More sharing options...
CleanSierra Posted August 5, 2015 Report Share Posted August 5, 2015 You'll get a 145 for sure. I'm not sure what resonant frequency of that cabin is, but I'd guess 35-40 Hz. What ohm load are you going to run on that amp with the 4 subs installed? Im not the one you want to try to troll. Just a fyi for you. Link to comment Share on other sites More sharing options...
germanyt Posted August 5, 2015 Author Report Share Posted August 5, 2015 Subs are D4 so 2ohm. Current Setup : Nothing2014 Ford Focus SE Hatch Future looking like: Singer / XS power Crescendo BC3500D CT EXO 15 Pioneer 80PRS CDT HD-61PRO CT Sounds M75.4 CT Sounds AT60.4 Something along those lines. Link to comment Share on other sites More sharing options...
germanyt Posted August 6, 2015 Author Report Share Posted August 6, 2015 Ok so i finally finished my design. Took me 3 days, 8 pages of scratch math, and a few hundred forum pages. This is what i came up with. Front top and side view. 4.702 net sealed 10.95 net ported 224.5 sq inches port 11.06 inches long 49hz Materials being picked up Friday. 300 screws, 4 sheets mdf, 16oz glue, 12 tubes caulk, 1 galon fiberglass resin, 50 sq ft fiberglass mat. Then off to get bedlinered. Will start a build log on Sunday and update as I build. Hoping to get it done in 2 sundays. Current Setup : Nothing2014 Ford Focus SE Hatch Future looking like: Singer / XS power Crescendo BC3500D CT EXO 15 Pioneer 80PRS CDT HD-61PRO CT Sounds M75.4 CT Sounds AT60.4 Something along those lines. Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted August 6, 2015 Report Share Posted August 6, 2015 Looks like you have quite a project ahead of you! I hope it all goes well. One suggestion, I would play test the box as early in the construction process as possible. Just in case you want to make any changes, the earlier you discover that the easier it will be. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
CleanSierra Posted August 6, 2015 Report Share Posted August 6, 2015 The design sound like a SOLID starting point. I'm not double checking the math or anything but the projected numbers you have seem like a great start. Im not the one you want to try to troll. Just a fyi for you. Link to comment Share on other sites More sharing options...
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