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Discussion Starter #1
The VRK Midbass Modules are named after the initials of my 2nd Daughter. I bought the Magnum 12's on the evening she was born.

The box is 12.5" W x 18" H x 15.5" D with an ID cu ft of 1.47 cuft.
After bracing, port, and driver, I'm looking at 1.2 cuft.
It's tuned to 43Hz with an 11" x 1.5" x 7.5" slot port
HPF is a 2nd order butterworth at 35Hz
Powered by a Crown XLS 2002 at 375W RMS

The box is 3/4" MDF which will be veneered in walnut and stained to match my BDI media console and Paradigm LCR's. I will be experimenting with the impact on sound quality with a wooden grate that matches my media console to cover the driver (see attachment). If it impacts the sound I'll pivot on design and may even need to make a wider box

My Journey into DIY and mid-bass:

I have been annoying people on this DIY forum planning this build since the January of 2017. It's been over 18 months of discovering DIY and harassing people with questions like: "is there a difference in sound between a slot port", "will port placement impact tactile response at 8' away", "does the high excursion HST-11 sound boomy like the youtubes", "will a wood grate impact sound quality"...


You know, all the important things... I learned what I was missing, mid-bass, and heard of these Magnum-12 drivers. I did as much research as I could (primarily bothering folks with highly subjective questions)... Of course I learned about WinISD and T/S parameters (although I still don't know what the curve of transfer function magnitude is...)

On 8/11/2017 my second daughter was born and as my wife and her lay sleeping in the hospital bed, I was up salivating with DIY mania drawing pictures in Microsoft paint about various port placement options.... Out of complete DIY zietgiest, I pulled the trigger on these drivers. I contacted a friend that works at a instrument distributor and got a Crown XLS 2002, I contacted my local hacker space and was going to use their CNC machines because I can't cut a straight line to save my life...

I few months after my daughter was born the owner of the hackerspace got blown up in a propane accident (he's alive and well) but I was left to my own devices to cut straight lines. I got a router, cutting guide, and MDF for Xmas that year. I then waited for it to warm up and got busy, and then waited for it to cool down and had a day off.


Predictably, the cutting went terrible. I sold all of my battery operated tools on Craigslist and bought corded ones. Once again I wait for a cool day that I can take off which leads me to Monday July 2nd...
 

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Discussion Starter #2 (Edited)
Straight cuts! I used a Kreg Cutting Guide and the key for me was using a corded circular saw vs a battery operated one.

 

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Other tool notes: Don't over tighten the jig (I cracked mine already!), use the interior screw holes for a Ryobi (I made 3 trips to menards trying to get the right screws), I got a guide for a jigsaw to do a pocket cut for the port, I'll use a flush trim router bit to clean that up. I practiced cuts, straight routing, and roundovers as well. Given that I'm veneering, I don't think I'll be using and roundovers. Next simulation is going to be cutting with the circle jig but it's too dang hot!

 

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I remember you starting this a while ago around the same time as mine. My boxes are larger than yours, tune ended up around 42hz and I limit power to 300 Watts each with EQ. My model showed (with higher power) I shouldn’t go below 38hz at max power or i toast them, but I’m kind of starving them so I won’t hit excursion limits. Also I found around 35hz that I get some distortion. Ended up setting a 35hz filter and it’s been rock solid since.

My null around 55hz is still their though 😕


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What volumes do you listen to them at? I’ll listen at -20db (85dB) + 10dB LFE + 9dB hot

Max 104dB.
 

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Looking forward to this build coming together:)
 
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What volumes do you listen to them at? I’ll listen at -20db (85dB) + 10dB LFE + 9dB hot

Max 104dB.


Typical is -15, but that’s not pushing the inuke very hard. Eric told me these can go much higher. I look forward to eventually crossing them at 200+ and seeing how that goes.


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When you say you cross them at 200Hz, does that mean you set the crossover in your AVR to 200Hz? Or are you splitting the mains signal from the AVR and using DSP to low-pass that for the midbass? Thanks...
 

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When you say you cross them at 200Hz, does that mean you set the crossover in your AVR to 200Hz? Or are you splitting the mains signal from the AVR and using DSP to low-pass that for the midbass? Thanks...
+1
That’s a really high crossover. My plan is to do the LR Surround and tops at 100Hz and my center at 80hz. I may even try them at 120Hz.
I’ve considered making my 3 way LR a 4 way with these and may try that. However, I wanted the center channel FR too as well as LFE... I guess “double bass”
Using MSO will help. I may use the HPF on the amp and let MSO set my miniDSP filters between my full range subs (RythmikLVX 12’s) and these MBM’s
Then after that it’s Dirac
 

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When you say you cross them at 200Hz, does that mean you set the crossover in your AVR to 200Hz? Or are you splitting the mains signal from the AVR and using DSP to low-pass that for the midbass? Thanks...


Splitting mains signal


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Splitting mains signal


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Got it. Thank you. Is it a pain to get the MBM mixed with the mains? I'd imagine you'd want to try and get the phase lined up as much as possible since essentially they are reproducing some of the same material.
 

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Painfully slow progressm (but I learned a bunch)

I finally finished my "experiments" on scrap wood with the router and the jig saw. Today I was cutting into my production rips.

A few tips:
1) take off your circle jig if you're having problems getting the bit router off
2) you can tighten your jig saw so it won't make angled cuts. I think my jigsaw guide would have worked better.

Experimental cut with the circle jig was clean. I used a 3/4 bit. However, in attempting to get the bit off so make my interior cut, I broke the already cracked jig.... The super glue is still drying.


I used a cut guide for my jig-saw to help cut a straight line for the slot port. Unfortunately, I didn't realize I could tighten my jig so I think it cut angles mid-way through. Also, I'm not sure why but the guide didn't seem completely straight either. I question the marks on my T-Square because when I stacked MDF to simulate the port the marks were much different...




Here's the final product! My slot port roughed in ready for the flush trim bit, a circle jig drying, and a trip to Menards to get more clamps that will fit. I only have 2 clamps that fit!


 

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Just think of it this way, you'll earn master status when you're done:)
 
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A tip - I cut out the slot port when the cab is assembled (minus the top). Drill a 3/4" hole, run my router with a 1/2" straight flush trim bit around the walls of the port. You can sort of see the process in my 1260 builds in my sig. Easy peasy, although there's more MDF to clean up inside the cab afterward.

Of course, YMMV.
 

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Got it. Thank you. Is it a pain to get the MBM mixed with the mains? I'd imagine you'd want to try and get the phase lined up as much as possible since essentially they are reproducing some of the same material.


It was very simple, didn’t even take an evening.


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Discussion Starter #15
Always hang on to the router!

My dried circle jig worked BUT I didn't anticipate that I could easily be off 1/16" on the center point for my jig. My plan was to have the circle cut just eclipse the sides and I'd put a grill over it. Well I was a 1/16" or more off and it looked terrible. While trying to fix it, I was monkeying with something and took my hands off the router it spun around the wood, and flew off the table!


Once again, I had to glue the jig for the second time!

 

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First box glued!

I changed my dimensions to 13" to accommodate having a little of leeway around the driver. I had to cut a new port, and 66% of my panels. Luckily I bought an extra sheet of 4x4 MDF in preparation for being terrible.


I carefully used my twice glued jig and my hand never left the router. I also decided to use a flush trim bit method on the port instead of terribly jig sawing it. Nevertheless, in spite of my lack of skill the jig worked!


The gluing was a mess! it was everywhere. I should have checked the forum how to glue. My strategy was to lay down the interior piece and put glue on all of the sides and fold it up. It was messy and I'm worried some of the glue scraped off. I tried to fill it via the outside. There's only 1 side (the "bottom") that is not flatly aligned. I THINK I can sand that down to make it 'normal'
After this dries, it's bracing and port. Then I'll glue the other box.
 

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Any suggestions on how to glue

Anyone have any strategies on how to glue the next box?

Given that I'm veneering this, could I use screws for the bracing?

If I scraped off too much glue in the chaos that was the first box, what are my options? I filled the gaps manually. I could use screws and caulk the inside too.
 

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USE A PLANER: Box 1 is braced (lessons learned); Box 2 gluing

With Box 1 I glued all sides with the exception of a panel that fits within all of the other sides which was a mistake. It's going to be very difficult to glue and I needed to plane the panel down to make it fit in the gap. It's proved to make some of the bracing more difficult

USE A PLANER INSTEAD OF SANDING OR JIGGING IF YOU HAVE ONE. I'll be recutting my port because it was too wide, so then I sanded unevenly, and cut too much with my jig saw trying to even it out. I own a planer, I should have planed it.

Consequently I needed to screw my port in which was not ideal. I would have rather glued it. Where stuff wasn't cut flush I needed to fill the gaps with glue. I think my circular saw is bent and tilted. Its a very small box so there's not a ton of room for bracing. I need to pick out a stuffing. I may go polyfill or I have some left over auralex... Seems like it'd be costly.
Here's my box and the bracing

Box 1 is nearing stuffing, porting, and wiring

With Box 2, I'm gluing it in a proper order. The last panel to be put on will be resting on the top of the sides and not fitting within the sides. I also have been using a foam roller to spread the glue and then use a bead of glue down the sides to fill if there are gaps. I think box 2 will be much smoother to build. Maybe I'll send up scraping box 1 and rebuilding it.
 

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One thing to never do with a router is release your hands. I’ve seen a router launch and smack a dude in the mid section when he took his hands off a router.


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One thing to never do with a router is release your hands. I’ve seen a router launch and smack a dude in the mid section when he took his hands off a router.
No doubt! I lucked out big time! I’ve screwed up on every turn of this build! After I get done, presumably I’ll be better but won’t be building any more subs for quite some time 😞
 
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