Dual 18cf ported UM-18 Build Thread - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 137 Old 11-21-2016, 05:48 PM - Thread Starter
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Dual 18cf ported UM-18 Build Thread

This thread will detail the build of the two subs that are going behind my screen wall. This will be more of a discussion type thread than a how-to. I'm not going to show how to connect two panels together...it's not a tutorial.

Driver is the Dayton Ultimax-18 aka UM-18. Material is 3/4" MDF with a double front baffle, so a 1.5" front baffle.
Airspace is 18cf net, 21.7cf gross before driver, port and bracing displacement. These are not small boxes. External measurements are 47.5"w x 35.5"h x 25.5" d.
The port is 4" x 12" x 40" internal, giving the cab a 12Hz tune.
miniDSP for DSP, pro amps for power (QSC RMX2450a, one channel per sub @ 4 ohms = 800watts)

I don't know if these qualify as LLTs, but I can tell you they are large for sure and 12Hz is a lower tune than any other cab I've had.

Here's the WinISD SPL/FR graph. This is with 600 watts of power, 11Hz, 4th order Butterworth high pass and 80Hz 4th order Butterworth lowpass. No EQ applied to this graph. 108.5db at 12Hz. That's one cab.



I can't remember how many iterations of cab size/port size/tune I went through before arriving at this design. I had lots of great advice from @LTD02 , @More is Better and others. A big THANK YOU to all of you. I know I'm going to be happy with these. There will be two other subs in the rear of the room, same tune, but radically different in cab design. They'll be ported and tuned identically, but very different in appearance. I'll do a separate thread for those.

The mandatory "stack of cut panels" pic. This isn't all the panels for both cabs, just some of them.



These suckers are flippin' HUGE. Carrying them about 75 feet including a flight of stairs is gonna be FUN.




Internal width shot.



Here's the parts list and cut sheet from Cutlist. Best free program ever. Don't know why it's showing "1.38 x 97" for material. I'm using 3/4" MDF which is actually not 4'x8' but an inch larger all around at 49"x97". I used 5 full sheets of material for these two subs. Getting those sheets of MDF onto the table saw and cutting them accurately by myself was a heck of a workout.

*edit* If you want to duplicate these cabs, add TWO MORE Piece #15 or #16 (they are the same dimensions). You need FOUR TOTAL pieces at 40" x 4" for the port. The additional two pieces can easily be cut out of Supply Piece #4.




My first "Oh crap moment"...that didn't take long, did it? You may be wondering why there is a "port top and port bottom" but only one side. The port will use the rear panel and side panel as parts of the port. I want to roundover both the port and the outer edges of the cab itself. Trying to fit two 3/4" roundovers on a 3/4" panel won't work, so I need to double-up any port surface that also touches a cab surface. So, I screwed this part up. Darn! I'm missing another side piece for the port. Better to be missing a piece than to cut a piece incorrectly! No biggie as I have plenty of scraps and extra MDF too. So, add another Panel 15 & 16 to the parts list. Thankfully, I haven't cut the port opening out of the side panels yet. Didn't do any "panel machining" today, just cut them all to size.

This port will take up approx 1.7cf. Driver displacement is .250cf. That leaves 19.75cf, or, 1.75cf for bracing. Plenty.

Not sure how I'm going to do bracing, but it's most probably going to be simple stick bracing, using lots of the cutoffs from today....I save everything. With a cab this large, I'd feel better if I used 1" MDF, but way back when I bought this material, the lumber yard was out of 1" MDF...after they told me on the phone they "had plenty." They gave me a nice discount on the sheets I bought, so it all worked out. I'll just have to brace the snot out of it.

Next up will be gluing up the double front baffle and cutting the driver hole. As these cabs will be behind a screen wall, they will get a slathering of flat black paint and the driver won't be recessed. The other two cabs going in the rear of the room will be Duratexed and the driver recessed with an additional piece of 1/2" MDF laminated to the double front baffle.

More to follow. Thanks for reading.

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post #2 of 137 Old 11-21-2016, 06:01 PM
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post #3 of 137 Old 11-22-2016, 01:13 PM
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Should be fun to follow...sub'd.

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post #4 of 137 Old 11-22-2016, 07:46 PM - Thread Starter
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Accomplished a few things tonight for both cabs. Got the ports themselves built and their exits in the side panels roughed out. Also laminated the double baffle.

The ports for these cabs are actual full, standalone slot/rectangular ports, for reasons outlined above.

Port is built.





Port location marked on cab side panel.



Port roughed out.



Port will fit like this. Once the port is installed in the cab, I will use a flush trim bit to bring the port opening in the side panel flush with the port's internal surfaces, then put a 3/4" roundover on the port.





Front baffle lamination.

First layer of one baffle..


Second layer applied..


Shot of both glued-up baffles under some weight to help them stick together.




Tomorrow I should be able to do work on the baffles. Need to get the driver holes cut out. As you know, that's a time-consuming task. Make the baffles 1.5" thick and it's a crappy time-consuming task with lots of MDF dust in your face. I will try out my new dust mask...though I will probably wind up not using it b/c when I wear dust masks, my safety goggles fog up. I'd rather inhale MDF dust than risk a broken router bit in my eye. After that, I need to drill the mounting holes and mount the t-nuts. I bought the special 6-prong t-nuts that PartsExpress sells. I've used them before and they are much higher quality than the stuff you pay $1 each for at Home Depot. I'll be using 1/4"-20 hex head bolts to secure the drivers.

Once the baffles are ready, the cabs will go together quickly...except for the bracing...I haven't given that much thought yet. I almost want to stick a few pieces of 2"x4"s in there and be done with it, vs. a hundred little 1/2" square sticks that I see in a lot of builds. Dunno what I'm going to do yet. And I still have 2 other cabs to design, cut wood for and build.

Stay tuned.

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post #5 of 137 Old 11-23-2016, 07:43 PM - Thread Starter
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I was planning on making a separate thread for the rear two cabs b/c technically, they are not identical to the front two cabs. And the two rear cabs aren't even close to identical to each other, physically, though all four cabs have the same airspace and tuning. But, the 3rd cab is very similar to the front two, in design so I'll just stick it here in this thread.

I was going to work on the two cabs that I started this thread about, but then I remembered that my table saw outfeed table is also my assembly table. Going to be hard to cut 4x8 sheets of MDF if there are two huge cabs-in-progress sitting on the table. So I need to cut all the wood for all four cabs before I start assembly. So tonight I cut the panels for Cab#3, the left rear cab. Effectively the same airspace (only .07cf difference) as the front cabs, just a different format to fit a different location in the room.

Cutlist printouts:





Not shown is a 48x38.5" piece of 1/2" MDF to recess the driver.

No point in boring you with pics of another stack of panels, so just two shots of the "internal airspace" for Cab#3. Looks like the cabs from above, but it's not. This cab is slightly wider and a lot taller, but not as deep.




Tomorrow I'll glue up the port for this cab and that'll probably be all I can squeeze in before company shows up.

Cab #4 will surely merit it's own thread as it will possibly be the thinnest LLT with a 18" driver ever made. How's a 11" internal depth for an 18" strike'ya? And that's all I'm saying for now.

On Friday I'll get the parts cut for the 4th sub and somehow find room for another huge stack of huge panels in the garage, then I can get to assembly.

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post #6 of 137 Old 11-23-2016, 08:41 PM
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post #7 of 137 Old 11-24-2016, 10:16 PM - Thread Starter
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Double baffle glue-up

Hope everyone had a good Thanksgiving! I've been on a roll these past few days, getting things done for the HT. No matter how little I accomplished for the HT today, any progress is still progress! So after company left and we cleaned up, I hit the garage to accomplish a small but significant task; gluing up the double front baffle for Sub#3, the left rear sub.

I used a smooth foam roller from Lowes marked as "cabinets and doors." It's a foam roller with zero texture, pictured below. Soaks up glue like a sponge though.

Layer 1 of the baffle with Titebond II liberally applied.




Stack the second layer on top of the first and let it cure/dry. But you need to squeeze out as much air as possible. After putting a few pin nails thru the bottom two corners so the layers couldn't move, you need to apply some weight. Being a bit gravitationally-challenged myself, walking around on top of the assembly was the answer, and what I usually do when laminating sheet goods together. Basically, you just walk around in circles, starting from the middle. Stupid looking, but effective.



A few more pins around the assembly and then you stack some weight on it. Preferably as evenly-distributed as possible. Note the nice squeeze-out.



So now all the panels for Cabs 1-3 are cut and laminated as needed. Tomorrow I will cut the panels for Cab#4, AKA "The Skinny 18 Ported Cab" and get that front baffle laminated as well. Over the weekend I can start assembling the cabs.
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post #8 of 137 Old 11-26-2016, 12:45 AM - Thread Starter
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That moment when...

It's time to cut the driver mounting hole in your carefully-glued-up double baffle...so much work and material...you can't screw this up...so you...

Check the manuf's mounting info...four times:



Then you triple-check the instructions for your circle cutting jig b/c you're using a larger bit than specified in the instructions:



Then you make a test cut in scrap:



And a second test cut in scrap because "there was way too much play" in the first test cut:



And after 6 passes b/c you don't want to burn the router bit or harm your precious double-baffle-glue-up, you have the cutout...and it looks good...but DID YOU CALCULATE EVERY DETAIL CORRECTLY?



That moment when two hours later, you drop the driver into the hole...and IT_FITS_LIKE_A_GLOVE




Mind you, that's an 18" driver. If it looks "small-ish" that gives you an idea of the size of this cab!

I cut the second driver cutout for the other front sub and stacked in on top of the first baffle for grins. Wouldn't it be great to have a 3" baffle? Talk about bullet-proof.



As shown in the screen shot above, PE specifies the baffle cutout for the UM-18 at 16.75. I can tell you that is way too large. There was a lot of "play" b/t the driver and a 16.75" cutout in my first test cut. I reduced the cutout by 1/16" in the second test cut. Still a lot of play. I reduced it by another 1/16" for a final cut out of 16-5/8", which is a much better fit. A smaller cutout than that MIGHT work, but I didn't test it b/c I ran out of scrap large enough to use for a 3rd test cut. Does that smaller cutout matter? I think it does. It leaves that much more material in the "mounting circle" for the t-nuts to bite into. Mass is always good when it comes to speaker cabs....moving them, non withstanding!

Tomorrow I will cut the driver hole for Cab#3 and get the t-nuts mounted for all three cabs. Then, assuming I have any steam left, I may start cutting panels for Sub#4.
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post #9 of 137 Old 11-26-2016, 01:55 AM
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Looking good!

Is it seated all the way down? Looks like its riding a little high in the shot from the side, though that might just be the gasket?

Reminds me of my baffles. I know how large and heavy those are. I had one of those standing up on my bench when I was test fitting it into the front of the enclosure and it rolled forward and fell onto my foot not fun.

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post #10 of 137 Old 11-26-2016, 02:07 AM - Thread Starter
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Thanks, @notnyt . Heck yeah, the double baffles are HEAVY! Mentally, I know that doubled 3/4" MDF should be double the weight of a single layer of 3/4" MDF, but when you're not used to moving 1.5" thick panels, it just catches you off-guard at how heavy they really are. It's like lifting a slab of granite or similar.

The driver is definitely fully-seated. In fact, I can grab the magnet and scoot the driver around in the mounting hole a bit as there is still play, even with a 16-5/8" mounting hole. The driver isn't bolted down in these pics and never has been, so the gasket is at full thickness. The gasket is kind of thin, and I am wondering if I should use a layer of gasket foam in addition to the gasket already mounted to the driver? As two of the four cabs will be Duratexed, the stock gasket might not be thick enough to account for the additional "hills and valleys" created by the Duratex.
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post #11 of 137 Old 11-26-2016, 03:39 PM - Thread Starter
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Got a little ahead of myself and almost forgot to laminate the driver recess panel to the baffle for the left rear sub. I started setting up to cut the driver recess in the panel, then I remembered. It wouldn't have been the end of the world, but it's much easier for me to cut the rebate for the driver and the cutout in one shot.

So, here's the 1/2" recess panel laminated to the 1.5" baffle, under a couple hundred pounds of weight. Nice squeeze out on this glue-up.



Having learned the hard way to never trust manufacturer's dimensions for mounting circle or driver diameter, I knew I had to make a test cut for the driver recess. Did that and PE's recommendation of 18.25" was spot-on.

Tonight I'll do up the Cutlist for the right-rear sub and get those panels cut and that cab's double-baffle glued-up tomorrow.
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post #12 of 137 Old 11-27-2016, 07:37 PM - Thread Starter
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I got some more work done tonight. I hit the baffle for Cab#3 with a flush trim bit to get the 1/2" recess panel nice and square with the underlying 1.5" baffle. I also got the driver hole and recess cut out.

The routing setup. I'm about 1/2 way through the recess at this point.



All done. It looks pretty...but will everything fit properly?



After measuring 10x before cutting once, everything turned out perfect. Well, there's that one little "oops" at the 6 o'clock position where I misjudged the depth of the bit, but that's only about 1/32" deep and there will be a t-nut mounted there anyway.





Here's the cutout disk. It took a long time to cut this out. 2.25" at about 1/8" per pass...so much dust. I wore a mask though.




A shot from underneath.



And a close-up of how the frame fits in the 16-5/8" cutout. The driver is roughly centered in the opening in this shot.



Next up will be the task I hate the most; laying out and drilling the holes for the t-nuts for the three cabs I've cut panels for so far...haven't started cutting for the fourth and final cab yet. I've gotten better at working with t-nuts over the years, and learned to use 1/4-20 bolts over 10-32 bolts if possible. Those fine threads on the 10-32 screws get cross threaded way too easily. I also thread a bolt into EVERY t-nut by hand first, before installing the nuts in the cab. I've weeded out far too many bad t-nuts and bolts over the years. Extra time now prevents frustration and possible project failure later. I also will be putting epoxy on the backs of the t-nuts as a preventative against them coming loose. These drivers are 45 pounds and I simply do not feel comfortable installing them with wood screws.

Thanks for looking.
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post #13 of 137 Old 11-27-2016, 09:10 PM
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post #14 of 137 Old 11-28-2016, 06:59 AM
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Looking good! What size bit did you use for cutting out the baffle cutouts? I'll be using a 1/4" straight bit.....but I can go up to 1/2". Which, I've read has less vibration along with better cutting. I bought a 1/2" flush trim bit specifically to try and see for myself.

Can't wait to see the finished product(s). Seriously jealous of your workshop.

Oh, isn't the cutlist program a life saver? I'm using it for my 1299 build. Great program!!

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post #15 of 137 Old 11-28-2016, 08:17 AM - Thread Starter
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Yup, Cultist is awesome. I use it for all but the simplest woodworking projects.

I use 1/2" bits almost exclusively, unless the workpiece is very small or I don't have a 1/2" bit in the style I need. I've never broken a 1/2" bit, but have broken a few 1/4" ones. It's easy to push the smaller bit too hard and break it. Expensive and dangerous. When using the larger bit with the Jasper circle jig you have to account for that, but it's easy to do.

Thanks for the kind words on the shop. I'm happy with it. Spent many years working on a Black and Decker Workmate on my apartment balcony, so I appreciate the advantages a shop offers.
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post #16 of 137 Old 11-28-2016, 08:26 AM
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Quote:
Originally Posted by michaelddd View Post
Next up will be the task I hate the most; laying out and drilling the holes for the t-nuts for the three cabs I've cut panels for so far...haven't started cutting for the fourth and final cab yet. I've gotten better at working with t-nuts over the years, and learned to use 1/4-20 bolts over 10-32 bolts if possible. Those fine threads on the 10-32 screws get cross threaded way too easily. I also thread a bolt into EVERY t-nut by hand first, before installing the nuts in the cab. I've weeded out far too many bad t-nuts and bolts over the years. Extra time now prevents frustration and possible project failure later. I also will be putting epoxy on the backs of the t-nuts as a preventative against them coming loose. These drivers are 45 pounds and I simply do not feel comfortable installing them with wood screws. .
Have you considered slab nuts? Easier to use and more secure since they are connected to screws at the back of the baffle to keep em from spinning, they "should" work with your triple baffle as well, think thats how @dgage uses them in his Mariana subs.....
@dgage here will sell you a set of 10 for like 12 bucks shipped...... I bought a bunch so here are pics from my UM18 build of the install...



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post #17 of 137 Old 11-28-2016, 01:11 PM - Thread Starter
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@EndersShadow. Those slab nuts are perfect. I ordered 100 of them for $27 on stafast.com. $11 of that was standard shipping. So the price was not bad at all. What size screws did you use to attach the nut to the baffle? Did you predrill?

My standard method of attaching tnuts is to use a bolt to pull the nut into the wood vs. hammering them in, so these slabs will save me a lot of time.

Thanks for the suggestion!
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post #18 of 137 Old 11-28-2016, 03:12 PM
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@EndersShadow. Those slab nuts are perfect. I ordered 100 of them for $27 on stafast.com. $11 of that was standard shipping. So the price was not bad at all. What size screws did you use to attach the nut to the baffle? Did you predrill?

My standard method of attaching tnuts is to use a bolt to pull the nut into the wood vs. hammering them in, so these slabs will save me a lot of time.

Thanks for the suggestion!
@dgage sold em to me as a full kit with screws and lock washers.

If you look at the hyperlink in my first post it shows the parts he uses including screws.

I believe my buddy did predrill but not sure.
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post #19 of 137 Old 11-28-2016, 04:13 PM
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Great stuff in this build. I've just passed the part in my own build where the cabinet stuff is done, thereby eclipsing my own personal experience. You're a few steps ahead of me, and seeing how you tackle some mundane stuff smartly (walking in circles during your baffle lamination!) has been helpful.

Thanks for writing the thread, and keep up the great work. I dig your attention to detail!!
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post #20 of 137 Old 11-28-2016, 06:23 PM - Thread Starter
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Thanks, @DougUSMC : I'm happy to hear that this thread is helpful to you. AVSFORUM has been a huge help to me with myriad projects and research over the years; so many awesome people here and so much collective knowledge!

Best advice I can give for someone building their first cabs (or having built not many things) is to take you time and don't rush. Stop and ask questions if you're not sure. The only stupid question is the one you don't ask and then regret it. Better to have a day or two delay than screw something up and waste material and progress or worse, injure yourself.

@EndersShadow : Thanks for mentioning the lockwashers. I've never used them before when mounting drivers with machine screws and t-nuts, but with the weight of these drivers and the amount of force they will exert during movement, it's probably a good idea. Only problem I can foresee is how to fit the lockwasher down in the mounting recess where the bolt goes thru the frame? Most 1/4" lockwashers I've seen are considerably larger in diameter than the screws they work with, and there's barely room for the hex head screw to begin with. Hmm, though the lockwasher you have in your pic above is about the same diameter as the hex head and would fit. So they do exist. (magical unicorn moment)
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post #21 of 137 Old 11-28-2016, 06:25 PM
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That's why I bought it all as a package from dgage. It was plug and play. Also the lock washer I believe goes between the bolt and the speaker basket not the MDF. In my case you don't even see them...

I think it goes Bolt Head | Lock Washer | Speaker Basket | MDF
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post #22 of 137 Old 11-28-2016, 07:01 PM - Thread Starter
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Yup, that's the order they go in. And I found them locally! At least online, it shows that my local Fastenal store has them. Here's the product; please LMK if these look like what you've got. The outer diameter is .360" which isn't much larger than inner diameter.

https://www.fastenal.com/products/details/1133686

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post #23 of 137 Old 11-29-2016, 05:46 PM - Thread Starter
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Didn't get any physical work done on the subs today, but I did get associated tasks accomplished.

Bought a gallon of Duratex and a 4" textured roller from PartsExpress. The gallon is more than I will need/use, since I'm only Duratexing the two subs that will be seen, but I didn't want to risk running out with just a quart. DTex goes a long way, especially if you prime first, but still, I'll be coating two fridge-sized cabs.

I also bought the slab nuts that @EndersShadow has in his pic, above. Also bought a bunch of #5 x 5/8" panhead wood screws from www.boltdepot.com Those screws are to secure the slab washers. I'm going to put a dab of epoxy over the screws and slab washer for good measure. They will never come out when I'm finished with them. BTW, you're not finding those screws at HD or Lowes, that's why I ordered them online. Finally, I stopped by the Fastenal store in my area which happened to have just one bag of the washers in the pic above. Some pics of the washers...they are "hi-collar lockwashers". I never knew there was such a thing. *shrug*

Fastenal bag. The part number is 1133686.


Washer close-up. You can see how they are not as flat as normal lockwashers but they are much thinner cross-sectionally.


Washer on 1/4" hex head screw. Washer is barely bigger than the screw itself. Not the best pic, but you get the idea.


I'm off Thursday, and the goal is to get the 3 baffles drilled for t-nuts and the parts cut for the fourth and final cab...maybe even do the glue-up for the double baffle if I've got the energy. More to follow.

Last edited by michaelddd; 11-29-2016 at 05:50 PM.
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post #24 of 137 Old 11-30-2016, 09:21 AM
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I have a few large subs and they are a bear to move. I have them all on wheels. Some wheels will make life easier later if going into a basement with carpet. You are going to love the output of those monsters!!!
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Thanks, derrickdj1. I wish I could put them on wheels and roll them into place. They are going up a couple of flights of stairs, unfortunately! I'm certainly hoping they are everything they model to be, and then some. Cabs this large are no small effort!
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Tell me about moving large cabinet's, what a pain in the butt.

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@NWCgrad : Yup, I saw your JBL 2242 build thread. Those things must weigh a ton! But I'll bet they sound sweet. I haven't ventured into that end of DIY....yet. Even though I built the smaller cabs a year ago, after 3 88 Specials and 4 Volt10s and now these four subs, I'm all DIY'd out...and I still have a screen wall and a screen to build. It's a labor of love though, as well all know.
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BTW, I (think) I came up with a smart idea to drill the holes for the t-nuts. As these baffles are too large and heavy to fit in the drill press, I figured why not use a router with the drill bit chucked in it? After all, a router really is just a big drill, right? It's perfectly 90-degrees to the work surface. I'll just have to be careful plunging it. Should be way more accurate than trying to hold a drill level, while I hold a level next to it to make sure it's level and then drilling and not moving in the X or Y planes at all.
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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.
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Quote:
Originally Posted by michaelddd View Post
@NWCgrad : Yup, I saw your JBL 2242 build thread. Those things must weigh a ton! But I'll bet they sound sweet. I haven't ventured into that end of DIY....yet. Even though I built the smaller cabs a year ago, after 3 88 Specials and 4 Volt10s and now these four subs, I'm all DIY'd out...and I still have a screen wall and a screen to build. It's a labor of love though, as well all know.
I added a T-shaped brace to the bottom of my cabinets. I wanted three contact points to avoid rocking. Works really well BUT it makes moving them really sucks as they are very tippy (but not enough to actually fall over).

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