Dual 18cf ported UM-18 Build Thread - Page 2 - AVS Forum | Home Theater Discussions And Reviews
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post #31 of 137 Old 11-30-2016, 02:43 PM - Thread Starter
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Originally Posted by NWCgrad View Post
A router spins much much faster than a drill. I would recommend a downspiral - or upspiral - router bit for this. They come in multiple diameters and shoukd be perfect for your needs.
I didn't think about that. Thank you! Even at it's slowest speed, I think my router does...16K rpm? Yeah, that's a lot faster than my drill press at 3K rpm or my cordless. I see many test holes in my future.
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post #32 of 137 Old 11-30-2016, 03:27 PM
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I like the router idea, just use the right sized router bit and you have a mini portable drill press.

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post #33 of 137 Old 12-02-2016, 11:51 PM - Thread Starter
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Experience is what you get when you didn't get what you wanted

A wise man once said that. My original plan was 4 subs, all ported and tuned equally, spaced very roughly at the 4 corners of the room. Well, it didn't work out that way. Didn't have enough...or any...room in the right, rear corner for a 21cf gross-sized cab.

So, I will have 3 identically-sized and tuned cabs up front and one cab with the same airspace/tuning in the left, rear corner of the theater. Between miniDSP and Audessey, I should be able to work it all out.

Tonight I cut all parts for the 3rd front cab, glued up the double baffle, glued up the port and rounded-over the inner edges of the ports for the other 3 cabs. I got stuff done.

There's something comforting about seeing a 1.5" baffle glue-up under a few hundred pounds of weight. I'll let it cure for 24 hours then cut the driver mounting hole.



I didn't plan on having a 3rd front cab. The existing (to be built) 2 front cabs have ports exiting on the left/right sides. With a 3rd in the middle there was only one direction to exit the port and that was up. This port will rest against the bottom of the cab and go up the rear panel, exiting the top. Here it is mocked up, no glue.




And being glued up.



Finally, I rounded over the inner port edges of the ports for the other 3 cabs.

One cab before rounding.




And after rounding.




All three ports after rounding.



Will these little details make any difference at all? I like to think that cumulatively, yes, they will make a difference. 1% here and 1% there adds up at the end of a project.

BTW, regarding those slab nuts/t-nuts: Did you know they come in "long flange and short flange" variants? And that the short flange variants have teeny-tiny little screw holes that basically, no screw visible without a scanning electron microscope will fit through? I didn't, but I found out today when my slab nuts got delivered. I did receive exactly what I ordered. Too bad I didn't surf the website closer to find these:

https://shop.stafast.com/sl14205h2130

THAT'S what I should've ordered in the first place. *flush* <--the sound of my money wasted on the first order But hey, live and learn. I have 100 of the correct slab nuts on the way.

Over the weekend I'll get started on gluing up the cabs and drilling baffles for t-nuts.
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post #34 of 137 Old 12-03-2016, 09:58 AM
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@michaelddd , PM sent regarding flange t nuts.
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post #35 of 137 Old 12-03-2016, 10:59 AM - Thread Starter
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@michaelddd , PM sent regarding flange t nuts.
And replied to. Thanks very much!
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post #36 of 137 Old 12-04-2016, 11:44 AM - Thread Starter
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Got the driver mounting holes (for t-nuts) drilled on 3 of the 4 baffles. As you guys know, it's not as simple as "mark the holes then drill them, duh."

While T-nuts are fantastic when they work properly, getting them to work properly can be a bear. The mounting holes have to be as close to perfectly spaced as possible and they absolutely have to be perpendicular to the face of the baffle. If the hole is "tilted" your mounting screw/bolt won't be able to thread properly into the nut. And that leads to the #1 issue with t-nuts; stripped threads on either the nut, bolt or both. Then you FORCE the screw to get it out or shove it in, which leads to a spun t-nut. If you've dealt with one of those, you just shuddered a little bit.

The best way to drill a perpendicular hole is with a drill press. I have one. But no way can I get a 47x35" baffle in there. Hmm. What else is like a drill press? A router. I'll use that! That was the plan until I realized a 5/16" drill bit can't be chucked into either a 1/4" or 1/2" collet. /facepalm I actually have a 5/16" straight bit with a 1/2" shaft, but it's only 1" long and I need to drill through 1.5" of baffle.

Which led me back to my original plan and the gadget I bought just for this task. Meet the Gator drill guide. Made of tool steel so the drill bits don't chew it up. It's about 1" tall and holds the bit perfectly straight.




You line it up on the mark.



Clamp it down good making sure it didn't move.



And drill.



Repeating this process for umpteeump (that's a real number) holes is slow going, but it works.



So I got 3 of 4 baffles drilled. Baffle #4 was still drying from glue-up. When it's only 60 degrees in the garage I like to let a big panel glue-up cure more than 24 hours before cutting into it. As of right now we're at about 36 hours, so I'll get that driver cutout and mounting holes done today. Might even get some actual assembly done.

Thanks for reading.

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post #37 of 137 Old 12-04-2016, 11:53 AM
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Nice job, that looks like a useful tool.

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post #38 of 137 Old 12-04-2016, 02:30 PM - Thread Starter
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Got the driver hole and mounting holes done in Cab #3. Won't bore you with pics of that.

Dry fit of Cab #4. Figured I'd start with this one as it takes up the most table real estate. Get it glued up and out of the way.




I will get this cab, at least the sides/bottom/top glued up tonight. Progress!
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post #39 of 137 Old 12-04-2016, 05:45 PM - Thread Starter
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Cue up The Imperial March Music...

Cab assembly has begun. And yes; it's a big cab. That assembly table is 70" square.



But before I got to that point, I glued up the four sides. BTW, those red Bessey right-angle clamps at the bottom make this a breeze compared to how I used to do it with homemade "W" shaped corner jigs. The smaller right angle clamps at the top are icing on the cake, but not necessary IMO. Cab is assembled with PL Premium and 1.5" brads for good measure. I will let the PL cure for 24 hours before I take off the clamps and move the cab. If I was building these in the summer, when it's 100F and 60% humidity in the garage, I could take the clamps off 8 hours later, but it's only 60F/50% humidity (yes, I have a thermometer and humidity gauge in my garage...don't you?) so 24 hours it is.




Then the back went on.





Still not sure what I'm going to do for bracing. I have four cabs total. Three are identical in dimensions, but the port is in a different place in one cab. And then there's this oddball I just started tonight. So I can't just bust out one set of braces and duplicate it for all cabs. What concerns me most is keeping bracing volume as close to identical as possible across all four cabs. I went through the trouble of making all four cabs exactly 21.7cf gross and tuning them all identically at 12Hz, so I don't want to throw anything off now. Any advice for bracing is appreciated.

My plan going forward is:
  1. Glue up all four cabs, minus the baffles and ports
  2. Glue in the ports for all four cabs
  3. Figure out the bracing scheme for all four cabs (two cabs will be identical, the other two will be one-offs)
  4. Cut braces, ensuring bracing takes up as close to equal airspace as possible, across all four cabs
  5. Assemble all bracing into cabs

I think that's going to take a few evenings. Thanks for looking!

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post #40 of 137 Old 12-05-2016, 10:09 AM
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I'm not a master sub builder. The bracing is slightly different in my two LLT's and Marty subs. As long as you are are not changing the over box volume, I don't think it makes a difference.
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post #41 of 137 Old 12-05-2016, 06:40 PM - Thread Starter
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Yeah, I know that .1 or .2 cf difference won't matter. Problem is that without actually calculating how much airspace each brace piece takes up, I really have no way of knowing just how much variance b/t cabs there is. Then again, I did allot 3.7cf for port, driver and bracing (the port alone takes up 1.6cf, IIRC).

I got one of the front 3 cabs glued up. That port is actually the top of the cab. It's going to be fun trying to glue a 31" long L-shaped port into a 31" tall space. Yeah, I didn't think that step through well enough. I see lots of brads and lots of smeared PL in my future.



I also scraped the PL squeeze-out from last night's cab both outside and along the inside corner where the port will be glued to both the side and rear panels. Here is that cab. For reference, that's a standard 16oz bottle of Titebond II. Not a tiny cab. I think the baffle for this cab (2" thick) weighs as much as this assembly. you can see the baffle on the floor, on the left. It's the top-most panel, closest to the cab on the table.



Tomorrow I'll get another cab glued up and hopefully get the ports installed in these first two cabs. Then I can start planning bracing.
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post #42 of 137 Old 12-07-2016, 06:53 PM - Thread Starter
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Slight delay due to the angled port for the front, middle cab not...well, not fitting inside the cab. /facepalm

I made it as long as the overall height of the cab, not the height of the interior. After all these years, you can still make a n00b mistake. No big deal. I cut the right amount off the straight end and tacked the cutoff onto the folded end. Overall port length is now 1/8" shorter. Absolutely inconsequential. And probably, the PL makes up for 1/16" so REALLY inconsequential. It looks ugly but it's airtight, so who cares?

So now I have the shells of two cabs and their ports assembled. Tomorrow for sure I will get the remaining two cabs glued up, then the ports for them on Friday and start cutting bracing. But here's some pics from tonight's work.

This is the front, middle sub (I will have three front subs). The port has to exit the top, so this is the top of the cab.



Here's the angled port and lots and lots of PL. Two things matter with ports: They are the correct airspace and they are airtight in their fitment to the cab. This is both. And ugly. But both. The case weighs about 30 pounds and is just there for weight while the PL cures. There are 1.5" brad nails strategically placed as well. If you look closely, you can see the tack-on job at the front of the angled end of the port.




This is the left side/rear cab. This worked out well. It just took 3/4" of a tube of PL to make damn sure it was glued in there and airtight.

This pic is the port exit at top, right rear corner of the cab. The port exits will be flush-trimmed with the interior of the ports before I put the baffles on, FYI.



And the port after glue-up, underneath the ports that will go in the L/R front subs for weighting it down while curing. BTW, there's about 3/4 tube of PL underneath and on the side of this port. After the PL cures, it's not going anywhere. Probably a dozen brads in there too for good measure.



For reference, all ports on all four cabs are 4" x 12" x 40" (interior airspace). Three of the ports are straight shots and one is folded, but all have the same effective length/tuning.
And yes, I write notes to myself on the parts that need them. It's how I keep things straight. Most of the time, anyway. Thanks for looking.

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post #43 of 137 Old 12-10-2016, 10:28 AM - Thread Starter
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Warts and all...

What fun is a build if you don't have at least a couple of "Oh *****" moments?

My "epiphanies" have all been port-related so far. Guess that's what happens when you wind up with 3 different port designs for your 4 cabs. First issue was the folded slot port for front sub #2 being too long. Took care of that. This latest one is for front sub #3. I cut the port exit in the side panel incorrectly and it was too late as the cab was glued up already. The old saying "Experience is what you get when you don't get what you wanted" rings true here and actually came in handy as I figured out a fix after staring at the problem for a few minutes.

The port sits inside the box like this, against the top and side panels (the box is upside-down on the bench in this pic)



In this pic you can see the port exit in the side panel of the cab. But as the port is constructed of 3/4" material, you can see that the lower long edge of the port exit is too low. 3/4" too low to be exact. I laid out the port incorrectly.



So, some port surgery was in order. I flush trimmed the side panel with the top of the box, did some sanding in other places and cut a strip of MDF to take up the 3/4" gap.

Patch glued in. Also in these pics, I've already cut the top long edge of the port about 1/2" higher to line up with where the port opening actually should be in the side panel.




This does create some additional extra work in that I have to re-scrape the PL from the edges inside the box, so the port fits flush, but it's better than a ruined cab and having to start over. At this point I hadn't yet glued up cab#4 so I check that side panel and yup, same stupid mistake. So I had to recut a new side panel for that cab, but that was easier than having to do this same port surgery over again on another cab. If you catch your mistake before it becomes a problem, it doesn't count. Right?

This is what I mean about scraping the PL off. Normally, you just leave the squeeze-out there as it helps to seal the box. In my case, I will have a "square box", the port, that needs to sit flush against the rear panel. You can see the PL scraped away from where the back and top panels meet.




So now I have all four cabs at least glued up and two of them already have the ports in.

3 cabs.



And #4 glued up last night.



I also got my baffles completed. A big shout-out and thank you to @NWCgrad for graciously providing the slab nuts I needed for this build. Thanks again, NWCgrad.

The slab nuts are a tight press-fit in a 5/16" hole. Here I'm drilling pilot holes for the #5 x 5/8" screws that secure the nut.



Slab nuts being installed.



And done. I now have 4 baffles that look like this.



This weekend I'll get the final two ports glued in and hopefully flush trim all ports into their respective port exits. After that, it's time for "Brace-fest 2016"...something I'm not looking forward to, but "labor of love" and all that jazz.

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post #44 of 137 Old 12-10-2016, 10:43 AM
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Adapt and overcome! Nice recovery effort for the port. I am so jealous of your kicka$$ work surface. The ability to hold down work pieces looks exceptionally handy.

Glad the slab nuts worked for you!

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post #45 of 137 Old 12-10-2016, 11:20 AM - Thread Starter
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Thanks for the compliments on the table, NWCgrad. I built it earlier this year, specifically for this project. That assembly table takes up a third of the garage, but if you build stuff regularly it really comes in handy. Long ago, I built my own workbench...might be in some of the pics and while it's sturdy, it's not flat. It's strong as heck, but not FLAT, which is what you need when building cabs or bookshelves, etc.

My workbench...pic taken in our old house. BTW, that's a Bill Fitzmaurice OTop12 being assembled.


But I needed something bigger and flatter. Also needed it to double as an outfeed table for the table saw, which my workbench cannot do b/c it's too tall. When you're cutting 4x8 sheets of MDF you really need a large outfeed table.

I discovered Kreg's DIY bench/table kits. Basically, you can make ANY size/configuration bench you want in a square or rectangular configuration up to a whopping 64" x 64" base, which is what I have. And the kits really aren't expensive at all. Here's the Kreg page for them: https://www.kregtool.com/store/c42/u...d-height-legs/

I wanted a practical work surface, not just a big table, which required a lot more work on my part. The top is 1.5" thick MDF top (3/4" material glue up) with a laminated layer of white Formica. Then I had to route the channels for the t-tracks. Laying all that out and doing it was a lot of work, but the end result was worth it. The Rockler clamps can be positioned anywhere on the table. I think I have a pic of the table after I completed it...lemme see here....

Nope, no photos of the "just completed" table, but do have some in progress pics.

1.5" MDF top glue up. Check out all glue on the floor, dripping off the edges. It was not fun scraping that off the floor.


Formica lamination.


Laying out the t-track. In this pic you can see the 2x4's that span the opening where the bottom shelf is. There's also 2x4's underneath the top, which were necessary considering there would be a 64" square piece of 1.5" thick MDF being unsupported. The table is very strong. I've had over half a ton of weight on it with no bowing, creaking or any bad effects.


I had to figure out all kinds of jigs to keep the router cutting straight for the t-track...it was a ton of work, but I'm glad I did it.
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post #46 of 137 Old 12-10-2016, 11:46 PM - Thread Starter
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Lots of progress tonight. All four cabs now have ports. Two of four cabs ports are now flush-trimmed with their exits. OK whatever...where are the pics? Right here.

First off, cutting MDF is one thing and routing MDF is another completely when it comes to dust. After years of dealing with MDF you get tired of a nose-full of MDF dust and coughing that crap up. So you wear a good dust mask. This mask was worn for roughly 5 hours of work...nasty.



Got the ports glued into the last two cabs.



Some weight holding them down while the PL cures.




BTW, when you're routing MDF (flush trimming, rounding over, etc) and you don't look like this, YOU'RE DOING IT WRONG.



Fluish trimming the back panel of one cab with the sides of the cab.



One port flush trimmed.




BTW: Here's the cab with the "surgery port exit" with the port glued up. I completely saturated the side panel area with PL...can you tell? LOL! This will suck to scrape off...



Finally; there are four cabs in this pic. At 21cf each they aren't too hard to find.



The next step is bracing and I'm really confused on which way to go. I could do a few window-type braces or I could put three or four 2x4's in on the X and Y axis' and be done with it. I'm not looking to beat the world record for bracing here...just want it to "meet the standard" and that's it.
Thanks for looking!
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post #47 of 137 Old 12-11-2016, 01:41 PM
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Geez, monster cabs. And I thought my two 12cuft cabs were big.

Very interesting build. Subd.

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post #48 of 137 Old 12-11-2016, 03:36 PM - Thread Starter
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Yup, they are huge and HEAVY...and the baffles aren't even on yet. It's going to take 3 guys to get these up the stairs to the HT. I'm not even going to install the drivers until the cabs are upstairs....that's 45 pounds less per cab to carry. I've never had cabs tuned this low or even remotely this size before. I'm hoping that four 18's cures my upgrade-itis for a few years, at least.
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post #49 of 137 Old 12-11-2016, 06:36 PM - Thread Starter
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All four cabs now have the ports installed and the ports are flush-trimmed with the port exits. I also flush-trimmed the back panel on all four cabs. They sit nice and squarely now.

Here's the "surgery cab" port trimmed up. Just need to take some 80-grit sandpaper to that patch and make it level with the rest of the side panel and it'll be invisible. *edit* No idea why the port looks "squished" in this pic. It's perfectly square IRL...really.



And cab#4.



As only one cab will be visible, that one cab is getting the full cosmetic treatment; spackling of nail holes, heavy coat of primer and two heavy coats of Duratex. The other 3 cabs will be slathered in stunning flat black paint and will live their lives behind the screen wall.

Here's the lucky cab with it's nail holes and minor dings in the port exit area all patched up (but not sanded yet).



I've got some ideas for bracing but need to think about it a little more before I start making sawdust.

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post #50 of 137 Old 12-11-2016, 06:36 PM
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I have used this style bracing in my two LLT's and other sub. This is not as extensive of bracing as some guys used but, it has held up well and works.
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post #51 of 137 Old 12-16-2016, 05:55 PM - Thread Starter
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Welcome to BraceFest 2016!

BraceFest? Brace-A-Palooza? Brace-A-Thon? Ah, you get the idea. It's time to brace these cabs and get that much closer to completion.

But first, some gratuitous clamp shots. I know what you're thinking, and you're right; never enough clamps! The "clamp rack" is a re-purposed telco rack I used to use and almost threw away. One day I hooked a clamp on there just b/c the rack was next to where I was working and *ding* the little, dim light bulb went on over my head.




I spent a few hours marking off the space the driver will occupy inside each cab and I marked/drew/scribbled accordingly. I have four cabs and three different designs (same airspace for all four cabs, though), ergo only three pics to cover all four cabs.





And the BRACING. A whole lot of it. .75" x 1.50" strips. I cut up all the scraps the cab panels were cut from that were long enough to be useful and half a full sheet of MDF into these strips. OMG...THE_FREAKING_DUST!!!! So glad I wore a dustmask/goggles! I have dust collection on the table saw and there was still a 1" high pile of the stuff everywhere.




There will be a lot of custom-fitting each brace to its' respective location in each cab. I did notice that due to my excessive clamping pressure, that basically the center of each cab is "Pinched". Basically the center of each cab is about 1/8" - 1/4" shorter than the ends. Not sure if I should force the space open...don't want to risk cracking the PL. The cabs seem happy like this and I'm happy to flush-trim the baffles. We'll see what happens.

Tomorrow, all four cabs get braced. After at least 24 hours for the PL to dry I'll start cutting the mattress toppers I bought a year ago into strips and stapling them into the cabs. After that, it's drilling the holes for the Speakon connectors. Then baffle attachment, truing up edges, rounding over edges and painting!

Thanks for looking.
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post #52 of 137 Old 12-16-2016, 08:45 PM
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Slab nuts being installed.



And done. I now have 4 baffles that look like this.


Another alternative to the slab nuts used above are aircraft nut plates or anchor nuts. They come in both fixed and floating and most incorporate a thread locking method so no lock washer is required. They come in various sizes from 6-32 up to 3/8"-24.

One example is the MS21047-4 which is a fixed nutplate in a 1/4"-28 size with a locking thread. They can be purchased here for less than $0.90 each. Also, aircraft flat washers are smaller diameter than hardware store washers, so they should fit within the mounting recess of the woofer flange without trouble.

To install them, I would drill the holes through the baffle just large enough to clear the bolts, then mount the woofer using the bolts and screw the nut plates down from the back side of the baffle until slight resistance is met, then push the nut plate flush against the backside of the baffle so the bolt protrudes a bit and secure the nut plates in place with two small screws. In this fashion you will be assured that all of the nut plates will be aligned. Note that these nut plates are intended to extend away from the backside of the MDF rather than recessed into the MDF as @michaelddd did with his slab nut installation.

Lastly, these are readily available worldwide.



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post #53 of 137 Old 12-16-2016, 09:09 PM - Thread Starter
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Note that these nut plates are intended to extend away from the backside of the MDF rather than recessed into the MDF
Thank you, @mhutchins , it's great to know there's another alternative to the evil t-nuts. Funny: Just when you think you know what's going on and you stop buying hardware from the big box stores, yet another unknown piece of hardware shows up.

I could see these being useful for IB installs, where access to the backside of the baffle may be easy. At least with an IB install, you can fairly easily thread them on after the bolts are placed through the driver and then secure the nuts more easily than T/Hurricane/Slab nuts, due to the fact that the barrel extends outwards vs. having to be recessed into the baffle. Never knew these things existed!

Hopefully, all my slab nut holes are drilled on-center and perpendicular and there will be no "FML moments." I can say that having discovered slab nuts for this build has been a huge event for me. I spent years learning the trickery of t-nuts. Then I learned some tricks to keep them from backing out or spinning. And I thought that was end-game. Then slab nuts showed up which incorporate half the tricks I used to use and add in that the ability for the tricks is built into the design of the fastener to begin with. *mind blown*
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Some more pics taken tonight just because.

Braces from a different perspective; all laid-out/stacked on top of the TS. Note: These braces are not "pre-cut to fit." I cut them all 2-4" longer than where I think they need to go. I'll use the miter saw (chop saw) to cut them to approximate length, then PL/brad nail them into place. Should be interesting as I've never done bracing like this before.




And all four cabs before bracing.




What is this? A medieval wood burning stove? Nope; it's the center, front sub with the port exiting the top of the cab.



I think I'm more psyched to get the bracing installed than to have the cabs completed. Once the bracing is done, 99% of the hard part of cab construction is done. I tell you, I'm ready for these cabs to be finished!
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Great looking build. Are you sure you've enough clamps there?
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post #56 of 137 Old 12-17-2016, 06:33 PM - Thread Starter
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Bracing begins. This is by far my least-favorite part of the build. Mainly b/c it's just so complicated. You cannot just stick a brace wherever. You can't block the airspace the driver will occupy. You can't block the port. You have to ensure the braces aren't too long or they'll bulge the cab walls outward. If they're too short they won't be strong. If they don't line up with each other you'll have trouble with the braces that cross them at a 90-degree angle. SMH...I have the skills to do this, but I'm not happy about doing it. I guess everyone has a "least favorite part of the build." Now you know what mine is.

So I drew lots of lines on the inside of the cab panels and did the best I could. These are only the braces that run long-ways....vertical or horizontal, depending on which cab. I'll give them 18 or so hours to dry then I'll install the front braces that run from the rear panel to the front baffle. It help that it's 75F/52% humidity in my garage...gotta love south Texas in December!

The "short bracing" is where I'm planning on "bracing the snot out of the cab." IMO the hard work is done. All I need to do is cut the short braces about 1/8" short so that the baffle sits flush and the PL will fill that 1/8" gap b/t the brace ends and the baffle.

It may be overkill to some, but I used a level to ensure these braces were level on both the X and Y axis'. I did this to ensure I could easily hit more than one long brace with a short front-to-back brace. Even still, I had a little shift due to the slippery PL. That's OK; I'll just PL the snot out of the braces from here out.






Stapling the mattress topper inside the cab will not be easy or fun. If I wasn't a big believer in cab lining I wouldn't bother, but IME, it makes a difference. Stay tuned.
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Ricci meausred the affects of dampening material in the cabs.

Overall it reduces output, but if you have any long sides, it will deal with standing waves in the cab. just remember with subs not to use too much.

Personally, I don't use any material in my ported subs. If you do, you might want to take before and after measurements to see what it does for you.
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Ricci meausred the affects of dampening material in the cabs.

Overall it reduces output, but if you have any long sides, it will deal with standing waves in the cab. just remember with subs not to use too much.

Personally, I don't use any material in my ported subs. If you do, you might want to take before and after measurements to see what it does for you.
+1.

I did this with my sealed car subs. It was easiest to hear/feel output differences without measurement gear.
No stuffing, overstuffed and then just right.
Gotta Goldilocks those cabs.

------------------------------------------------
Receiver : Denon x5200
Front Stage : L/R - Statements by Jim Holtz
Surround Speakers : Klipsch RF-82II x 4 / RP-280F x 2
Subwooferage : 6 UM18/4 HT18 Subwoofer Log
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Thanks guys. All four cabs have very long sides. I know that 48" or greater is the danger zone for standing waves in the sub-frequency zone. My tallest cab has a long side of 46" so that's right near that danger zone. The three shorter cabs have 42" sides, IIRC. I don't think I'm at the point where I need to stuff pillows in the middle of the cab to break up any standing waves.

I'm planning on a single layer of mattress topper (1.5" thick IIRC) on the back panel, outside of the port and the sides. Do you think that's a waste of time? I bought 4 King size mattress toppers a year ago in preparation for this. LOL! Too late to return them now...
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Thanks guys. All four cabs have very long sides. I know that 48" or greater is the danger zone for standing waves in the sub-frequency zone. My tallest cab has a long side of 46" so that's right near that danger zone. The three shorter cabs have 42" sides, IIRC. I don't think I'm at the point where I need to stuff pillows in the middle of the cab to break up any standing waves.

I'm planning on a single layer of mattress topper (1.5" thick IIRC) on the back panel, outside of the port and the sides. Do you think that's a waste of time? I bought 4 King size mattress toppers a year ago in preparation for this. LOL! Too late to return them now...
I'm not sure what they're made out of, but they'd probably work. stuffing a pillow in would also get the job done.. either way.

Just for reference with my monster enclosures with a 48" side, I didn't run into any resonance problems in the band they're used. There's a port resonance at 108hz which is only barely noticeable when graphing csd. You can calculate the resonances based on the enclosure size fairly accurately using online calculators if interested to see where you'll get a resonance.

dip at 80 is room mode

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