fmrazoroller Posted September 5, 2018 Report Share Posted September 5, 2018 So I’ll start off saying I used to have subs when I was younger about 10 years ago. Fast forward now and I’m married and have workshop now and love to build stuff. Well searching YouTube I saw a guy built sub box for his Silverado so I thought hey why not. So this has all been new to me because in the past I just had an audio shop hook all my stuff up. So I built a sealed box for my truck. Extended cab 99 Silverado. It has 2 8” skar ix8s dual 4 ohm. And I have a boss 1500 mono. Yes I have recently watched YouTube showing how little power this amp actual puts out so I’m in the process of getting a new amp. I’ve calculated I’m prolly only pushing 46 watts to each sub. They are 150 Rms a piece. My box originally had .60-.65 space for each sub, it was a sealed box, which is what the specs call for. So I’ve recently decided to add ports to the box. I’ve added the pvc and built the small kick outs u can see. I’m looking for help checking to see if I did it right. Each space is roughly 20x10x8 = 1600/ 1728 = .92 i have 4 Inch pvc pipe going into each space total length of each pipe is 18 inches that includes a 4 inch 90 I have the pipe straight back then 90d to go behind the subwoofer on the back wall the pipe is about 2 inches away from wall and the magnet on the woofer. I really didn’t know how to calculate pipe so I just took 4x4x18 = 288 - 1600 / 1728 = .76 which is almost right dead on what skar calls for in a porter box. I think I may be calculating pipe wrong. Now I didn’t factor in my sub woofer displacement but it’s so small didn’t think it mattered. Does this seam right? I don’t feel a ton of air moving in and out of port but I know the subwoofer is getting 1/3 if it’s power to it. Is it ok to run the pvc pipe right behind the subwoofer? When the bass hits it sound like the sub it hitting really hard against the box wall like a hollow wood sound it’s not bad I’m just not used to hearing that this is the first ported box I’ve used or built Most of the box Is mfd but the add ons are just wood I had at the shop. I’m not worried about a perfect box. haven’t sealed anything yet and haven’t glued the pvc pipes yet I plan on Bedliner The entire thing. The white peices on the front are just 4 inch toilet flanges lol I haven’t seen anyone use those yet hey it flares the pipe I have them wired to 4 ohms at the amp because this amp isn’t stable at 1 ohm Link to comment Share on other sites More sharing options...
YukonXL04 Posted September 6, 2018 Report Share Posted September 6, 2018 LOL oh my.... toilet flanges, havent seen that one before. Since you havent sealed and glued everything yet, those pieces moving around are probably what your hearing. Honestly you need to start that box over from scratch. While your at it, run the ports out each side, those trucks like side firing ports. Calculating round airspace, (RxRx3.14) x length but your 4" pipe is probably 4.5" OD so 2.25x2.25x3.14 18 Sierra 6.2 Z71 : 3 F8L's, DD M2a @.67, 1.95@33 05 TL build log SOLD 04 YukonXL : jvc kw-v51bt , RE 6.5c, 4 jbl gt5 12s, Memphis pr1000.1 5.5 cu.ft. sealed Link to comment Share on other sites More sharing options...
Joe X Posted September 6, 2018 Report Share Posted September 6, 2018 20x10x8 of gross internal airspace with a port which is 4"x 18" results in 0.75@46Hz, port area of 12.6 square inches. Hope you don't like rap (and such) or even try to play it on higher power on those boxes. Link to comment Share on other sites More sharing options...
fmrazoroller Posted September 6, 2018 Author Report Share Posted September 6, 2018 Joe. I looks like I’m not to far off on my numbers. .75 — .75 41 — 46hz 13in port — 12.6in port the sub is listed .41 I’m at 46hz. Is 5hz a lot? Or is this sub not good for rap music? I believe I’ve heard low 30s is good for rap. If true how could I get the box to that? any input on modifications would be nice. Yes I know best case scenario is built an entire new box but I’m looking for help tweaking this box to just make it better. Link to comment Share on other sites More sharing options...
shredder2 Posted September 6, 2018 Report Share Posted September 6, 2018 Re- baffle the whole thing if you want to stick with what you got... cut new holes and try doing your calculations with a 3" round on each... you'll find it will be easier to tune lower with a given length of port and the port area should be fine. A side fire ported would be best in that truck but if I had to work with what you got, that's what I'd do. Really... I'd just re-do the thing and get a better amp if it was me. Link to comment Share on other sites More sharing options...
Joe X Posted September 6, 2018 Report Share Posted September 6, 2018 Let's see some modeling plotsnet volume of 0.75 cubic feet: With a 32Hz tuning you see the extension to the low end you get: This is the cone displacement vs frequency, 32Hz and 46Hz , when you see the plot go dark you are about to bottom out your subs notice that with low tuning you can play lower without damaging your subs: This is your vent airspeed at 32Hz and 46Hz respectively, your sub can play on lower port area: Lastly here's vent airspeed for a 3" port vs a 4" port, you can see that at 32Hz tuning you could use a flared port and still avoid port noise as long as you keep within rated power: So what I would recommend is to fully glue your box parts and ports and test if you like it you are done and will be louder to the ear than the following, if you need some extra low end go for 3" ports and tune as low as possible to get the internal 3" port clearance, aiming ports sideways as suggested, it won't be as loud but it will be much nicer to listen. Link to comment Share on other sites More sharing options...
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