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Discussion Starter #41
Did some re-modeling. If I include the side port rails and increase the port height to 4" (with the side rails it goes to 15.5" wide), the effective full length goes to 52" or about ~16hz with fpr at 130hz. If I knock off 15" of the port the tuning goes to ~20hz with fpr at 180hz. Vb goes down to 10.5cuft unless I go wider to 32", then it bumps back up to 11.5cuft. I think doing a 16hz and 20hz tune(s) is the way to go. Internally tunable to keep it as simple as screwing in a board on the inside.

Hmmm..This is starting to look a lot like the box Mark Seaton designed for this driver except the low tuning of this box seemingly pays no port velocity or port compression penalty(s). Only measurements could prove that though. Note: I'm referring to the data-bass.com test of the 21DS115 where Ricci tried an unintended use with Mark's box design. I know Mark and Ricci could do 100 times better than me at this. Lucky crappy weather Kellie me from going to get wood to build today so plenty of time for additional analysis/paralysis.
 

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Discussion Starter #42
if the port is built for the full height 48" tall cab, then the effective port length (the red line) will be 48" + the port height. so with a 4" port, the effective length will be about 52".





I didn't double check your calculations for internal volume and I'm not quite sure what your plan is with respect to how many port braces will be in there, so I'm not quite sure how deep your port will be.


IF, your internal cab volume is around 11.25 cubic feet (after everything) and your port is roughly 17" deep (20" cab depth - double baffle, one port brace, one rear panel) and 4" tall, then winisd shows a tune of about 16.6hz.
measured results sometimes come in an additional half a hz lower even after all this, so my best guess for your cab would be 16-16.5hz.
port velocity is under 17 m/s all the way down to 18hz with enough power to drive the driver to 15mm excursion, so that is going to be just fine.


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edit: I just checked the cab volume and it looks like 11.2 cubic feet or so with a 4" tall port, so I'd probably subtract 0.5 cubic feet for the driver and bracing for the net internal volume (for winisd).
with no other adjustments that would raise the tuning of the cab (after everything) by about 0.4hz, so call it 16.5-17.0hz tuning.
You posted while I was typing it all out. :). Question is it worth it to go wider to pick up another cuft? I can squeeze 32" wide but 30" would be easier.
 

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that would lower the tune a hair, but wouldn't really do anything for increasing performance, so if 30" wide makes life easier, I'd go with that.


I'm not sure that anybody would do 100 times better than you have. your design looks good to me.
 

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Discussion Starter #44
Here is the final layout and options to tune internally to 19hz or externally to 19hz. If you make the port around 15" shorter on one side OR the other (not both) then you should come in the ballpart. The rails would allow you to play with this as you wish by changing out boards again internally or externally. If you do this make sure you use some sort of gasket material for leak free operation. The Box is 10.5cuft after you account for the space the driver takes up (.5cuft it is huge) and the bracing takes up (.25cuft guessing) and the space the port takes up. If i build it full size the tune will come in at ~16hz and since i upped the port to 4" tall it should flow plenty of air and compress very little at very high power. I'm going to be powering each of these with an iNuke 3000 DSP which i've modeled at 1800w. Design details and graphs attached.
 

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I haven't double check your port length for the higher tune, but if the external port board will be removable, I'd increase the size of the board that it will mount to from mdf slabs to 2x4's since the mdf isn't going to accept screws being inserted and removed too much before they start to strip out.
 

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Discussion Starter #46
I reworked things a little since I realized that with the port on the side the giant 21" driver would not be centered on the baffle and that started to drive me a little crazy. Since the weather has been rediculous I've had the time. Port is now 3.5" wide and tune should come in right around 15hz. I'm undecided if I'll make mine tunable but will have the option. I've decided I'm going to make these out of plywood that is .689" thick so the files all reflect working with that thickness and maintaining the dimensions of 30"w x 48"t x 20"d. I've attached a bunch of screenshots and if you want moar, here is the dropbox link to my sketchup file and cutlist files: https://www.dropbox.com/sh/d9a8ps0em2i671t/AAAroQlQDaMT6HF-ZqHa33Dka?dl=0

Pete
 

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cool.


on your cutlist, it looks like the panels are summing to 97" or so.


with ply, you probably don't get the extra inch that mdf provides vs. nominal.


a minor allowance for the saw blade as well if not cutting down the center of measured lines first. in other words, if cutting all panels on the right of the cutline to their listed size (and working from left to right across each panel), you may end up quite a bit short on the very last piece.
 

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Discussion Starter #50
braces 18, 20, and 21 could be moved to the waste area 14/15/16/17 if you are careful not to cut that piece up prior.
Thanks, I'm going to need to adjust things as I didn't buy the wood I planned. I bought red oak veneer 11ply because it looked better and was on sale for $46 a sheet. I think it is .703". I'll measure in the morning.
 

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What's the rush? You'll have bass forever, but it won't be long before the kids won't want to hang out with you.

I'm camping out at a 6 hour swim meet, lol. :D

Nice derby cars!
 
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