I'll just search Google and the forum for the answers that I need, you guys have been great, thanks so much!!
I meant for cutting the hole for the face.. I've picked up a a table saw, circular saw, sawzall, I've also got the router with a few tips.. learned to set up jigs for circles and square cuts..I don't think a jigsaw will suffice for cutting a slot port, unless you are REALLY good with it over long distances. If someone can cut the long side or if you can pick up some wood pre-cut like with a saw at Home depot assuming it is accurate enough, this is doable.
I meant for cutting the hole for the face.. I've picked up a a table saw, circular saw, sawzall, I've also got the router with a few tips.. learned to set up jigs for circles and square cuts..
Correct/square cuts are no longer a concern.. I may actually go so far as to remove all the carpet, hit it with orbital, spray bedliner on the box, route the edges smooth..
I'm just not sure if I'm supposed to be working with/ inputting inner or outer dimensions for port calculation..
If the port has to be a long and shallow, running lengthwise along the bottom of the box, would probably make my life easiest..
Appreciate all the trouble, the JPG made it clear..Ah, looks like you're in the clear with a table saw and so on, then.
So yes, always measure INSIDE, that's all the air "cares" about. Any 90 or 180 degree bends or whatever, use the middle measurement for the number. Example, a 4x8 port, turns 90 degrees... you'd go in that port and visualize the 45 degree angle of each piece of wood it would take to make it, and use the measurement from the inside middle of that. Simpler done than even explained.
edit: Here's a pic to explain better than words
Again, use of WinISD Pro can provide necessary info.I just skimmed through this thread, apparently I missed the part about passive radiators..
I know what they are, but I would not know how or where to begin with calculations...
I missed this too!Just wanted to say, if it hasn't been already, be extremely careful with your table saw and make shift fence. With your self admitted limited wood working experience and a fence that isn't properly secured, that saw becomes extremely dangerous. Just look up table saw kick back and you'll see what I mean. I'm 40, been a carpenter and cabinet builder most of my life and I've had a couple of kick back scenarios even with a good quality fence that was properly secured. Any shift in the work piece while it's being cut can catch the back of the blade and it can be shot back at you. It happens so quickly you have no time to react. If your hands are near the blade they can be pulled in to the blade, seriously not a good thing. I've once had a piece of 1/4" plywood shot back at me and it hit me in my upper thigh, just below of my waist and just shy of my "area". It caused a welt the size of a golf ball and a cut requiring 18 stitches. Just saying, be careful...better yet, get a proper fence or a saw with one. The most killer sub box isn't worth the risk.
Again, use of WinISD Pro can provide necessary info.
They aren't cheap but it works great because you don't take up space with ports, AND they are tune-able.
OK so I modeled an approximately 8 cubic foot box with two subs, and two 15" CSS passive radiators. With 500g of added weight on the the radiators, this matches (roughly) a 24hz tuned port.
Comparatively, that tuned port requires Three 4" round ports to avoid heavy chuffing.
In both of these sims, I used a 15hz infrasonic filter to keep excursion from possibly being an issue.
At 500W total power, SPL for either of these options is about 115.5dB anechoic.
Since I dug up a brand new 4" holesaw which I forgot I had, I've already purchased the 4" PVC..
I'm having a nightmare of an ordeal fixing broken tools (turns out the router I purchased brand new from Lowes was returned by previous owner with broken handle and broken height adjustment lock release..
Since I decided to make it a Sat night project, I was relegated to trying to rig a router.. Threw in the towel after I mangled the doubled up plywood panels..
Sorry I put you through the hassle of researching passive radiators, I'm not sure why I even posed the question, I was hoping to get the box done tonight..
Anyway, Matt from Parts Express modelled my subs in whatever program they use over there..
Showed a decent plot with only 500 watts, calls for 2 4" ports and 7.5 cf internal..
Plot showed a minimal dip below 0 from 22hz all the way to 50 where it hits the 0 line..
I asked about port velocity, according to his program, the pair of 4" PVC ports won't be a problem..
Not sure if it makes a difference that I'm actually running 500 rms per sub, not sure if he was aware of that when plugging in data..
Anyway, time for a movie Thanks again guys, I'll keep you posted!
OK, this is the last I will trouble you with this.. I have figured out how to quickly make straight square cuts for building slot port..Matt from PE mis-calculated, unless you are operating under 400W. 34 meters / second is the target at least as far as the most you'd probably tolerate. Bear in mind, that is ~.1 MACH.
With two ports 4", you'd be best off adding a large infrasonic filter @ 25hz. By doing this, you'll be able to keep port chuffing below crazy levels.
OK, this is the last I will trouble you with this.. I have figured out how to quickly make straight square cuts for building slot port..
So port velocity will be too high @ 22hz regardless of the quantity of ports? Adding a few ports won't solve the problem will it? I'm assuming it won't, or the port lengths required will equal some absurd type length..
I don't have a box building program, hence all the badgering.. I will check back later today, if 4" down to 22/24hz is an absolute moot point, I'll build a slot port..
Heading downstairs to work on the box.. Will check back later!
Appreciate all of this! I know I sound like such a noob, been doing this a while although I've always had boxes built to order as per manufacturers recommendation.. (with great results) I can install, I can tune, not great with fab, have always outsourced.. Another thing I want to point out, I was active 5 or 6 years back, fell out of the loop, back in the saddle, much has changed, much remains the same..It isn't trouble, so please don't think of a conversation of this stuff like that. Nobody is born with an innate ability to figure out audio, we all learn it. My first box was a fucking mess, as was my second, and third, and around the 4th I started getting a grip on it, etc.
Port velocity drops with the addition of ports. However port length will increase per port. Just stay accurate with your calculations, and remember that the ports take up room so you're working with a moving target. The trick is to calculate, think it through, re-calculate, etc before cutting a single board.
When you say you don't have a box building program:
Now you do.
OK, so here's where I'm at.. Again, I have very limited prior experience with box building/woodworking, I'm on a super limited budget, I am working on the street with cheap tools which I had to "rig"You need to basically shoot the moving target.
In other words, you're best off doing plans several times, taking the calculations into consideration. For instance, find the displacement of your ports (break out your math for cylinder volume). I actually use SketchUp all the time for this. It gives square area of a given space, and then I just multiply by height. I can also use plugins for volume with "weird" shapes. But you can do this on paper as well. For instance, 3.1416 x radius squared x height, and on a 4.5" (outside diameter), it would go like this:
2.25^2 = 5.0625
x 3.1416 = 15.904
x 40" = 636.174 cu inches displaced. And then x6 for four ports, and you get 3,817.04 cubic inches, which is 2.2 cubic feet of displacement.
Which is one reason when I modeled your stuff, I tried using 7 cubic feet instead of ~8.
Now unless I have incorrect specs (not sure about that), I modeled these subs again (on my new laptop computer, ergo new software), and I calculate you'll be able to get acceptable velocities with 3 4" vents. Again, using an infrasonic filter (18hz in this sim), and I'm using 1000W total power, this reduces the velocity at the very bottom end, and it keeps the sub out of excursion limits. If you go with 4 vents, port velocity drops down into very acceptable limits, likely not audible even at full boogie. For instance (again, guessing box size around 7 cubic feet final), 4 vents would be at 27.91" and 3 would be 20.2". That will end up being much less displacement due to ports, giving you a bigger box overall. IMO, if you can swing it, go with the 4 vents and the reason is, even if you don't flare the ports or anything, you're likely not going to hear much port noise if any. 4 vents with this size would turn out to be a tick over 1 cubic feet of port displacement, at 1.027 or so. Remember your bracing should be extensive with subs like this, but that shouldn't take up too much space. You can "buy" some space back by using Polyfil or other kinds of batting-type stuffing. The jury is out on how much space you can pretend to increase with, but my recommendation is to line the box heavily just to reduce impedance even if you don't need the space.
Have fun, be safe!
Oh and if my numbers aren't adding up, throw me the specs of this driver, I'm using WinISD's W12GTi specs but they may have changed over time.
Thanks so much for info!I think you'll be just fine with a total of (4) 4" ports.
I just modeled it myself, 7.5 cuft box, 25Hz tune. With 1000 watts of system power, air velocity peaks at 29m/s at 23Hz. With 2000 watts, it peaks at about 41m/s, again at about 23 Hz. In that alignment, response models great, flat to 25Hz and -3dB at about 21Hz. Most music, even modern electronica, rarely reaches much lower than 25-30Hz.
Cone excursion also looks good in that model, they'll stay below xmax at 1000 watts until 21Hz. With 2000 watts, they'll exceed xmax once at 35Hz by only about 1-2mm, then again at 22Hz and below.
Keep in mind, you'll rarely reach full system power with typical music listening unless you just crank the shit out of it on a regular basis. So, both excursion and vent air velocity will stay well below these limits most of the time. Also, if you have the capability of a highpass on the subs, that will also help tremendously with keeping the excursion and vent air speed in check.
As an example, I use 2 W15GTIs in my home theater. The box is 20cuft with a 17Hz tune, powered by pro amps currently capable of 750 watts per driver. There are (2) 4" ports and they are located at the ends(sides) of the box along with the woofers, so (4) 4" vents total. I used a large(2") round over bit in my router to ease the end of the port at the baffle to help with any chuffing. Modeling this without a highpass in place, I exceed xmax once at 25Hz and then again at 15Hz. According to WinISD, my vent velocity reaches 27m/s at 20Hz, 25m/s at 18Hz, 40m/s at 17Hz and finally peaks 49m/s at 15Hz.
With a highpass at 15Hz, vent velocity peaks at 35m/s at 16Hz. Xmax peaks twice by 2-3mm, once at 25Hz and then again at 13Hz where it drops off again due to the highpass filter in place.
I never hear any chuffing what's so ever. The only time I hear the woofers struggle a bit is when I'm cranking it and the amplifiers start clipping. Again, this is in a house and a room that is waaaaaay bigger than the cabin of a car and in a box tuned lower and bigger than these woofers are meant to be in. I think your 7.5cuft box with a 25Hz tune and (4) 4" ports would be excellent.