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Boomer1950

69 yr-old guy needs advice with 1st DIY sub

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I think the relationship between speed of the router blades & the speed of movement of the router are more related than I knew.  Just being aware of this will make things go more smoothly for me.  I have one brace to finish & then I start on the circle cuts.  I have definitely improved my technique to the point that my confidence about completing this job successfully is pretty high now.  Of course, I won't allow myself to become over-confident & lose my concentration.

I am using 3/4" MDF.  I don't plan to use anything but glue & clamps to construct the box. I've glued & clamped some scrap material just to get a feel for the amount of glue & the proper clamp pressure.  I think I have a good grasp of the technique.  A little more work before I start gluing.  It's moving along & I'm getting excited about the rest of the construction.

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Here's a picture of the progress I've made on the braces.  They look pretty good, if you stand about 10-15 feet away & squint slightly. I'm sure they will still be able to perform their function - bracing.

Braces-current-2.jpg

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I want to back up for a moment.  A lot of the build threads here & on other forums are done by people with woodworking skills or, at the very least, woodworking tools.  Other than a handsaw, hammer & a cordless drill I had nothing I needed to make the box - especially skills.  I bought a couple of Worx saw horses (that came with a couple of clamps) & a small router to start.  I made a work surface for the saw horses out of scrap material from the 3/4" MDF that was cut for me.

I went the more complicated way by designing the box myself using subbox.pro primarily.  I also learned how to use WinISD (well enough, I hope).  But, I had no background in engineering or 3D modeling software.  I did have some experience with Photoshop (I now use Pixelmator Pro on my MacBook), so I designed the pieces I needed using it.  That explains my rather colorful sketches.

I wanted to make sure everyone understood that there was little reason for me to think I could do this.  Of course, that discounts all the help you get from this forum which has been invaluable. I know this forum skews towards people with extensive sub building experience. The expertise here is stunning.  But (hopefully), I'll show that someone with no experience, no tools, no skills can still build a sub.

This entry will look terribly dumb, if I don't finish my sub or if it sounds like a piece of shit.  I'm assuming that neither of those things will happen.

Workbench2.jpg

Final braces1.jpg

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Looks like fine progress to me. Just take your time with the build (Measure 2 or 3x and cut once!) and apply advice from others who were in your shoes at one time. It's not that difficult. It just takes some experience and elbow grease. 

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Thanks, Ricci.  Things seem to be going well. I think your advice to take my time is crucial during a first-time build. 

But today I remembered what it's like to experience sublime pleasure from a very small event.  The evidence of my small accomplishment (that thrilled me no end because I've been so intimidated about cutting the baffles) is below.  Even though this was just practice I'm still happy I was able to cut my first hole successfully.  I used a Jasper circle jig.  I had to drill a new hole in the jig to make it work with my router.  Still worked like a charm. 

Obviously, this is the disk & not the hole, but the hole looks nice, too.

F5072549-A232-4BDD-AF7E-75D16221B1FB.jpeg

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Given my low skill level my decision to cut dadoes in the side walls might seem inadvisable.  But after watching a couple of videos, I thought I could do it.  The sidewall braces don't run from one wall to the other, so recessing the brace by 3/16" would not cause any problems.  I did a couple of practice cuts & discovered that my 3/4" router cut a dado slightly less wide than the 3/4" MDF.  I used the advice I found online & placed a strip of blue tape on the guide board & cut again.  Still doesn't fit.  Another strip of blue tape - another cut - and the MDF fits snuggly.  I started gluing the side braces into the dadoes - trying to keep each one square.

dado-1.jpg

Gluing dadoes.jpg

glued.jpg

still gluing.jpg

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After I glued all of the braces to the sidewalls I stood them up to create the 25" width of the finished subwoofer.  Then I propped up the long braces in approximately the proper location.  They run from the front wall to back wall & will be glued to the side braces.

Then I propped up the back onto the other pieces just to get a better sense of the size & future fit of these elements. The first picture with back piece in place shows how the side braces on the left & right are not spaced the same distances apart - to break up the symmetry.

I cut a couple of 6.25" holes for practice.  That's the size of hole needed for the 4" port flares I bought from Parts Express (which they got from Precision Ports).  I think I'm ready to start cutting the holes in the front baffles.  I'll be cutting the inner baffle first in order to have a little more practice before I cut the outer baffle.  But, it's much easier to cut the holes with a Jasper jig than I anticipated.  The peg inserted into the 1/8" hole drilled in the center of the circle & then inserted into the jig keeps the router on track really well.

Now it's time to cut holes in the actual baffles...

 

sidewalls.jpg

more sidewalls.jpg

with long braces.jpg

longbraces too.jpg

with back1.jpg

with back2.jpg

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Looks really nice for anyone but especially for a rookie builder.  Great work.  Only comment I have is you have really nice bracing on the left and right but what about tying the two sides together?

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Thanks for the kind words @dgage  I hadn't planned to have any pieces between the side braces. Certainly open to suggestion though. I could make pieces  2" wide to run between the sides.  How many braces like that would you recommend?

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You’ve tied the sides into the top and bottom but cross-bracing has been shown to be most effective.  It may not need the sides tied together but if it were me, I’d probably tie the two sides together at least near the middle.  

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Thanks for the suggestion.  Putting a couple of braces across the middle won't be difficult.  It's comforting to know someone is looking over my shoulder.  

It's going to take shape pretty quickly now.  After a year & a half of imagining what it will look like, it'll be strange to see the actual box sitting in my house.  Initial impression?  Pretty damn big.  I know people make much larger subwoofers, especially on this forum, but my current 12" ported sub is about a 2.4 cu.ft. box.  This one is a 9.25 cu.ft. box. Bigger.

 

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Dang, that’s almost as big as our sealed 24 at around 10 cuft.  Our standard cube version is 28”x28”x27”deep but we’ve also made an end tableversion, which gets pretty big.  Pretty much 30”x30” 32” tall.  

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Great progress, and I agree the work quality looks nice from the pictures.  You got this done a lot faster than I did.  :)

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I have questions about some details concerning the construction of the box:

When should I install the threaded inserts for the feet for the box?  If I want to use T-nuts or Hurricane nuts, how do I tell if they work with 3/4" MDF?

Do the Precision ports need threaded inserts to mount them to the outer baffle?  Or, do I just use wood screws plus glue to mount them "permanently"?  The 4" flares have a 1/2" flange with holes drilled into it for mounting purposes.

I bought a SpeakON panel connector (Neutrik NL4MP-UC 40A Speakon Connector 4 Pole Panel Mount Part # 092-067).  Do I use wood screws & glue to attach the SpeakOn panel mount or should I use threaded inserts?

I'm waiting to receive my SI driver before I can determine the location of the inserts to mount it.  But, am I able to buy the inserts & screws now - meaning, is there a standard insert that will work with SI drivers?

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I'm using wood screws+gasket tape on anything but driver and hatch. Since you don't have an access hatch I'd only use hex inserts for the driver. Don't forget to line the driver with gasket tape. I wouldn't glue any hardware to the cab.

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I've completed the installation & gluing of all of the internal braces - including 6 new braces (2" x 6.5") between the braces running from front to back (& also back to front) as was suggested by @dgage.  The goal was to tie the 2 sides together & it appears they've been successful.  

Question:  Should I cover the internal walls with 1" acoustic foam?  (like the picture below) 

acoustic foam.jpg

headon braces.jpg

last braces1.jpg

lastbraces2.jpg

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1 hour ago, Boomer1950 said:

Question:  Should I cover the internal walls with 1" acoustic foam?  (like the picture below) 

acoustic foam.jpg

Doing so will dampen resonances and make for a better frequency response at the cost of a fraction of a db of output. It's not always needed, but generally a good thing to do. Especially when maximum output is not a key factor. You can put the foam anywhere where it does not obstruct the airflow. With your port pretty much on all side walls.

I used spray adhesive to glue the foam to the Skhorn and staple gunned the foam to my Z21. I personally hated working with spray adhesive.

What are you doing with the PVC pipe? Will that be part of the port?

 

NiTa6Wl.jpg

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1 hour ago, Boomer1950 said:

Question:  Should I cover the internal walls with 1" acoustic foam?  (like the picture below)

I doubt it would make any difference.  Bass waves are just too long and will go through that foam like it isn’t there.  For speakers, sure but for subs, don’t think you’d be able to measure a difference with the foam.

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5 minutes ago, dgage said:

I doubt it would make any difference.  Bass waves are just too long and will go through that foam like it isn’t there.  For speakers, sure but for subs, don’t think you’d be able to measure a difference with the foam.

Ricci did just that some time ago iirc. There was a meaningful difference even below 100Hz if I'm not mistaken. Remember that reflections will pass through the foam multiple times on all walls. I think it was even published as article here on data-bass.

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I tested with my sealed 18” and 24” subs filled with blue jean insulation.  I was able to measure a small difference but was able to use a very minor DSP entry to get the non-filled sub to match the filled sub.  So yes there may be a minor difference but in the scheme of things, it won’t really matter and since you yourself said you didn’t like dealing with the adhesive, I say pass.

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I personally would suggest thicker foam --- 2" or 4" for more out of the way places.  I do concur about avoiding foam in the path between the driver and the vent.  I honestly don't know how much output will be lost going from 1" to 2 or 4", but I don't think it'll be much if it's not placed too close to the vent (where air may be moving a lot more) or in the path between the driver and vent.

In my view, the primary reason to install foam or other acoustic absorption is not to alter the frequency response in the operating range but rather to remove unwanted sound inside the cabinet that's above the sub's operating range, to keep it from leaking out through the vent or interfering with the driver.  This unwanted sound is caused by distortion and noise produced by the driver.  The distortion can drive standing waves and other resonances inside the enclosure, which can amplify them and cause unevenness in the sound, particularly when the sub is being pushed harder.

A thicker 2" foam will absorb much better below 1000 Hz than a 1" thick foam.  The standing wave resonances inside that cabinet will start at around 250 Hz, and even 2" thick material doesn't do much there, but it's a big upgrade from 1".

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