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Cerberus Subwoofer Build

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  • 50 watt head
    replied
    Re: Cerberus Subwoofer Build

    More outstanding work, Ron! That finish looks terrific :D

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  • Soundslike
    replied
    Re: Cerberus Subwoofer Build

    If you haven't already done so, check post #85 on this build string. Mikers got an outstanding finish using spray cans and color sanding techniques. On the other hand, subs are often out of sight anyway.
    Last edited by Soundslike; 06-11-2011, 12:40 PM.

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  • johnlinvell
    replied
    Re: Cerberus Subwoofer Build

    Thats beautiful............I will be building one of these in the am but my finish will not be as good as that...Great Job on this one..............

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  • Soundslike
    replied
    Re: Cerberus Subwoofer Build

    After sanding the primer to 400 grit, I sprayed on a single coat of three-part urethane automotive paint. I managed to produce a nice finish, but there are a few areas that could have been done better. Black is difficult to spray outdoors because it's tough to get the light just where you want it so you can view the build up from an angle to get a smooth, even application. For reasons I can't recall at the moment, I elected to finish all six surfaces which, of course, includes the bottom. Not wanting to hang the box for spraying, I used a method recommended in Jewitt's book on spray finishing -- I drilled four holes in a scrap piece of MDF and inserted four 8 penny finish nails to make a support. I sprayed the bottom first, and then set it on the nails while I sprayed the rest of the box. The method works fairly well, but of course you end up with four tiny marks in the paint -- not too big of an issue if it's on the bottom of the box. I also painted the Duellati speakers described in another build string at the same time.



    And here's a photo of the finished subwoofer.

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  • Soundslike
    replied
    Re: Cerberus Subwoofer Build

    Originally posted by fastbike1 View Post
    And folks actually like mdf better than plywood. Never ceases to amaze me. ;)
    Yeah, there are lots of things not to like about the stuff. I should give Baltic Birch a go, I guess.

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  • fastbike1
    replied
    Re: Cerberus Subwoofer Build

    And folks actually like mdf better than plywood. Never ceases to amaze me. ;)

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  • Soundslike
    replied
    Re: Cerberus Subwoofer Build

    After devoting most of my time to several other build strings, I'm back to the Cerberus. Picking up where I left off - the front two side corners were rounded off, using a 1/2" bit. All other edges were left square, but rounded off softly with light sanding. Earlier, I purchased a 1" roundover cutter for my shaper, planning to use it on this build. But the decision to go with the larger port, made it necessary to move things around, and the necessary real estate was lost. I perhaps could have used a larger radius, but that would mean getting fairly close to the port flare, and I was concerned that it would look odd.

    This next photo, is actually another Cerberus I'm building, but it illustrates how things looked after a 70/30 mixture of fiberglass resin and acetone was brushed on (70% resin). The 70% mix tends to leave brush marks that must be sanded out before paint can be applied, and the resin does take several days to cure thoroughly, before it can be sanded without excessive clogging of the sandpaper. The enclosure shown in the photo was coated with a 50/50 mix, which flows out much better, leaving minimal brush strokes. The enclosure in the photo uses the standard 1-1/2" port and the driver is centered.

    I like to use resin over the MDF, because it transforms the soft MDF surface into a more durable surface, and it seals very well. The result is a very smooth (after sanding) and relatively tough surface that resists dings much better. It is a messy process, and an extended drying period is necessary.



    In this next photo, we're back to the actual enclosure that is the subject of this build. Here, the enclosure has been sanded smooth -- the resin coat was sanded to 150 grit, fiberglass body filler was used to fill all the little inevitable defects, more sanding, then black lacquer based high-build primer was sprayed on, followed by sanding to 220, and finally 400 grit. The reddish stuff is glazing putty used to fill minor defects. You can see the the port required a little smoothing -- that's the result of two little errors. In an earlier post you can see where I had to add a ring around the port tube because I had mistakenly bored the hole too large. Then, when I glued the tube into the resized hole, I didn't insert it fully to the front edge of the baffle, because I had calculated the port length factoring in the port flare. Not too sure how much it matters, but I believe the port length should be measured from the middle of the flare, so I glued it in set back about 1/4". Unfortunately, the roundover didn't reach the tube, so I was left with a little ugly gap to fill.

    To make smoothing the port on the second enclosure easier, I used a different installation process (the one shown in the photo above of the resin coated enclosure with the standard port). On the second enclosure, I first located the port and drilled a 1/8" hole through the baffle so it would be possible to determine where to drill/bore/rout from either side. I then bored the hole with a Forstner bit from the back side, to within 1/4" of the front surface. I epoxied the PVC pipe into the hole, which left it positioned 1/4" behind the surface in order to leave a bit of MDF for the roundover. I added a collar made from 3/4" MDF around the PVC on the backside in order to increase the glue surface area. After everything dried/cured I enlarged the center hole to 1/2", and then used a flush-trim bit to create an extended hole through the MDf that matched the inside of the port. That hole was then rounded over.



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  • Mikers
    replied
    Re: Cerberus Subwoofer Build

    nice work on the flush mount.

    button this thing up so we can see some finished photo's.

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  • Soundslike
    replied
    Re: Cerebus Subwoofer Build

    I forgot to acknowledge the comments by 50 watt head, and djd. Thanks for the nice words and encouragement.


    I installed the vent inside the box, and it fit as planned in the drafting process, so that it's supported by the bottom and sides. I insulated the box with 1/2" automotive felt carpet padding on both sides and the bottom. There was very little area on the back that could be covered, once the plate amp was installed, so I didn't bother there. I was still concerned that I was using up too much of the little box's volume with the large port and all of the insulation I had added, and to do any good on the back, I would have needed to insulate the cover on the plate amp. So, I opted to leave well enough alone.

    In the photo you can see that the driver was moved to the left, and up in the box, in order to make room for the vent. The vent was positioned to take into account the dimensions of the elbows, and a planned roundover of the terminus.

    What looks like a ring around the PVC, is actually a repaired goof. I made the hole too large for the PVC, and rather than throw the baffle away, I elected to make a disc from MDF, sized to fill the hole. I was careful to place a pivot hole in the center, before cutting it out. After the glue dried, I went back with my router and circle guide and cut the correctly sized hole.



    Here's a view through the cutout for the plate amp. As you can see, I've flush mounted the driver and the plate amp. Pay no attention to the little notch, that will soon be gone.:o

    I used a bushing for routing the recess for the plate amp. The easiest method I've found to make this cut is to clamp straight edges for the bushing to follow. It's also necessary to clamp on stops to avoid going to far, and it's important to use a bit with a radius that matches the rounded corners of the plate amp face. To get a bushing with a hole large enough to not interfere with the bit I used, yet shallow enough to for the overall length of the bit, I ended up modifying one. I'll include a longer explanation and a photo, or drawing later, for those who aren't familiar with the process.



    Here's a view with the plate amp in place.

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  • Soundslike
    replied
    Re: Cerebus Subwoofer Build

    Randall,
    I just used a rattle can on the port tubing. It's Rustoleum's "Professional" line, and it actually does a good job on small pieces. I was painting the inside of the port so it would be black when viewed from the outside of the finished enclosure when I thought I might as well paint the outside too. A complete waste of time I'm sure, but I didn't like the looks of the long port with PVC elbows. Even though it would be inside and out of sight it looks like something from underneath your floor, or inside a wall.

    I'm using a table saw to make the rabbets. I've got a vertical fence jig I made for making the cuts with the panel in the vertical position. I didn't bother switching over to the dado blade, so two cuts are necessary. I manage to get sufficient accuracy for a project like this. I know you don't need a photo to understand what I'm talking about here, but for the benefit of anyone I may have confused, I'll insert a one here taken by Mark65 during another project we've got going.



    Regarding the room where I'll use the Cerberus, I have a smallish office about 13 X 13 where I'll use it with whatever speakers I'm listening to, for music. Currently, I'm using it with a pair of Paul's Overnight Sensations and it does a great job. It doesn't produce as much punch as the 12" Dayton subwoofer I made, but it makes more than enough for music played at reasonable levels, and it's about 1/4 the size of the 12" Dayton.

    Ron
    Last edited by Soundslike; 04-25-2011, 01:18 PM. Reason: Inserted photo

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  • Randall Kepley
    replied
    Re: Cerebus Subwoofer Build

    Ron, I also meant to ask you, how are you making your Rabbets? Are you cutting them w/ a dado blade or Router bit. I can usually tell by the cut , but at the angle of the pix I cant quite make it out. Which ever your using it looks like your dead on. BTW what size of a room are you planning on using this sub in. Thanks bud, R.K.

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  • Randall Kepley
    replied
    Re: Cerebus Subwoofer Build

    Ron, what did you spray that PVC w/? It looks smooth as butter R.K.

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  • djg
    replied
    Re: Cerebus Subwoofer Build

    I made some ONSs and a Cerberus sub for my girlfriend's nephew. He keeps asking for more bass. Your build is very nice.

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  • 50 watt head
    replied
    Re: Cerebus Subwoofer Build

    The rabbets look great, Ron.

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  • Soundslike
    replied
    Re: Cerebus Subwoofer Build

    This next photo shows the assembled box. I strongly recommend dry fitting the panels together beforehand, and marking them so you can more easily see which joints go together. Then lay the panels in logical order around the piece you'll start with. Also, think about which surfaces will need glue and mark them so you'll know where to spread the glue. There are three surfaces to apply glue to, on each edge -- note that the side panels are different because they fit inside the other panels..

    The baffle covers the entire width and height, as does the back panel, an arrangement that puts the part lines on the top and sides.



    Referring back to the drawing in the first post, you'll note that I used the drafting program to determine the port segment lengths, and locations. Working inside the confines of this small box, with such a large and long port, made it necessary to utilize at least two elbows. Although I can't recall the source, I've read that a sufficiently accurate method of determining the distance through an elbow is to simply measure from where the two imaginary centerlines intersect within it. But, being a persistent skeptic, I decided to do a little cipher'in.



    A close examination showed that a PVC elbow isn't necessarily perfectly formed, but I came up with the measurements you see on the masking tape. From the tattered appearance you'll probably surmise that I handled it quite a bit flipping it around, measuring and remeasuring. The total straight line distance is 2-9/16" + 2-9/16", or 5-1/8". I also measured the length of a 45 degree path, which you see marked on the tape. This bit of simple measuring convinced me that the straight line method is not accurate. Perhaps it's accurate enough, but knowing that an inaccuracy is introduced with every elbow, was enough to convince me that I should limit the layout to two elbows. I originally considered a different route that would have placed the interior port terminus further from the driver, but rejected it because a third elbow would have been required.

    Rounding over the port terminus on the baffle, adds another variable. For the first horizontal segment, I started my measurement in the middle of the baffle, i.e., 3/8" in.

    For those who might be interested, I've since calculated the actual distance, using a different method. According to my calculations, the actual length of the path through a 2" elbow is closer to 4.57", as opposed to 5.125". Either calculation, by the way, depends on accurately cut pipe lengths and full insertion into the elbow.

    Probably what really matters regarding port length calculations, at least at a theoretical level, is the volume that results from whatever dimensions are used. Even though there is a potentially significant difference between the two methods of calculating elbow length, whatever affect that has on volume could be altered one way or another if the interior dimensions vary through the arc. I'm sure this question has been adequately covered a number of times elsewhere -- if anyone has a link, that would be welcomed...

    This last photo shows the port after assembly. I rounded over the edges on the elbows and inside the opening, because it seemed like the thing to do.;) I'm holding the port where it will be inserted through the baffle. I'll be sure to report the acoustical benefits of the paint job.:rolleyes:

    Last edited by Soundslike; 06-03-2011, 12:25 PM.

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