Subwoofer Build -- 12" Dayton DVC

[Soundslike]

I set out to build this subwoofer to complete my daughter's 5.1 home theater system, which utilizes two TL variants of the popular Tritrix design for the front speakers, and the vented variant for center, and rear surrounds. I began while in the middle of building the 5.1 system for my daughter, and a pair of the Tritrix TLs for my son. That build is documented elsewhere in the Gallery forum -- the link may be found below with my signature.

Following the same logic as when I selected the Tritrix design, I first looked for a proven subwoofer design, believing that to be the surest path to a good sounding speaker. I was surprised to learn that subwoofer design wasn't nearly as exacting as a full-range speaker, and that I could expect a very good result by simply building a 3 cubic foot box, and using a 4" vent, with a 12" woofer. After looking around for a while, and asking for suggestions in the tech talk forum, one of the regulars, Chris Roemer, suggested that I go with the SA100 plate amp and the Dayton SD315-88 12" dual voice coil subwoofer (since replaced by the SD315A-88, which is in all important respects the same driver without shielding). His advice, I believe, was based on the fact that I wasn't striving for the world's best subwoofer, and that the point of diminishing returns wasn't far beyond the cost of the recommended components. The SA 100 was on sale at the time, and after paying the regular price for the subwoofer, I had all the necessary parts for about $140. The driver is here, and the plate amp is here.

I decided to make this a learning experience so I entered the TS parameters in WinISD and came up with a recommended 2.439 cubic foot box, tuned to 30 Hz with a 4" vent, cut to just under 12" in length. Next, I used Boxnotes to determine the optimal dimensions and elected to follow the recommended structural features, such as a double thickness baffle, shelf brace, and strategic placement of seams (by strategic I mean sizing the various panels so as to minimize the number of visible seams, in the event the dreaded MDF shrinkage occurs). Boxnotes calculates volume occupied by the driver, vent and brace, and recalculates the box tuning based on the area lost. Being a little concerned that most of the builders that responded to my questions predicted a box volume around 3 cubic feet, whereas WinISD recommended 2.4 cubic feet, I thought it would be wise to also factor in the area occupied by the plate amp. I produced the following drawing using metric dimensions for reasons that escape me at the moment -- I think it was because I drew the driver to scale and all dimensions were given by the manufacturer in mm. My early CAD program won't allow you to use both metric and Imperial units in the same drawing.

The shelf brace, shown as the cross-hatched area in the drawing, is cut from a single piece of MDF and resides in dados cut into the front, sides, and back. I elected to place the vent opening in the front, since I guessed that the subwoofer might well end up placed against a wall, or inside a cabinet -- as it turned out, that's where it ended up. I'll add more details tomorrow.



I can post a drawing showing dimensions in inches, if anyone is interested.

Those with sharp eyes, assuming anyone is reading this post, will notice that the vent is shown too high in the side view. I probably moved it when I drew the driver, and forgot to move it back into the correct position (which would have sullied my purdy drawing).

[Soundslike]

Re: Subwoofer Build -- 12" Dayton DVC

As mentioned in the first post, I used WinISD to determine the enclosure volume, tuning, and vent size.




I then turned to Boxnotes to determine the proportions and dimensions of the enclosure. Arriving at the optimal placement of the driver on the baffle required a bit of trial and error in order to avoid standing waves. At this point, I noticed that Boxnotes calculated the tuning to be 5 Hz higher, presumably because about 1/4 cubic foot would be occupied by the driver, port, and shelf brace. Perhaps I should have requested advice at this point, but I elected to move on with the design, thinking that the discrepancies noted by comparison of the two design programs either wasn't critical, or that WinISD had compensated for the lost volume in its calculations. Still, the prediction by Boxnotes that the box would be tuned to 35 Hz, rather than the 30Hz predicted by WinISD was troubling.



As I mentioned, I chose to go with the structural features recommended by Boxnotes. Here's a screen shot of the program's recommendations:



Notice that a double thickness baffle is recommended, which results in a rather hefty 1-1/2" dimension. Using two layers of MDF also makes full-size baffle possible, i.e., no seams on the baffle surface.

[Soundslike]

Re: Subwoofer Build -- 12" Dayton DVC

The enclosure is constructed with 3/4" (19mm) MDF, using but* joints and screws. In a previous thread, I wrote about the complications of using screws (they leave holes that have to be filled, they tend to show through a painted surface, and they're lurking just beneath the surface ready to do battle with your round over bit). But, a subwoofer enclosure is going to be subjected to more stress than your average enclosure. I think the added strength afforded by screws makes them well worth using.

I flush mounted the driver and the plate amp.

Perhaps I should have mentioned this earlier, but if you haven't noticed, I am usually cautious about design decisons when I'm not certain what effect might result from something I'm considering, if the effect could be significant and difficult to undo. I also keep in mind, that seemingly insignificant errors and adverse effects, can accumulate and combined can produce an effect that is significant. Translation: Excrement tends to pile up into bigger piles.

You'll notice that I didn't round over the port opening. I chose not to, primarily because I was concerned that doing so might alter the port length significantly, and further degrade the tuning. Earlier, I had determined that port noise (chuffing) was not likely to be a problem owing to the dimensions recommended by WinISD. In retrospect, I think the appearance of the port would have been improved, and that the lost port length wouldn't have detracted from the sub's performance.

The port opening is sized on the inner surface to the outside diameter of the 4" PVC drain pipe I used. The outer opening (that which goes through the outer layer of 3/4" MDF), is sized to the insider diameter of the port. I was able to achieve a smooth transition by cutting the inner hole before the two baffle pieces were glued together. Then, the outer layer of MDF was glued to the inner layer and the port was epoxied into the hole, butted-up against the outer layer. A small pilot hole was drilled through the outer layer, from the inside, to transfer its location to the outside of the enclosure., Then a smaller hole (smaller than the inside dimension of the pipe) was cut around the pilot hole. A router with a flush trim bit was used to match up the outer port opening to the pipe.

Inside the enclosure, you can see the automotive carpet padding I used to line the interior, on three sides. Other than that, no other material was used. Here again, I was concerned about further loss of enclosure volume.

The shelf brace is visible inside the enclosure. I rounded it over, because, well, it seemed like the thing to do.

I used a paste filler made from sawdust and white carpenter's glue to fill the screw holes, and wherever filling was needed. The resulting paste is very strong, and adheres well, but as I cautioned in the Tritrix HT thread, the stuff is hard to sand. It's not an ideal filler, except as a first layer, and I will switch to automotive body filler (commonly referred to as Bondo) on my next build. On the subject of Bondo, several posters have advised to avoid that particular brand because it is not easy to sand, as compared to other products, notably Evercoat's Rage Gold. It's harder to find, it's more expensive, and I wasn't able to locate it in quantities smaller than a gallon -- but it's said to be superior to other choices. Run a search on the Internet for body fillers and see what you think... I've yet to use it, but I will report the results in a future build thread, probably for two pairs of Carmody's Ovenight Sensations I've started on.





Here's a lousy flash photo (I hate flash photos) looking through the opening for the plate amp, showing the interior of the the enclosure, with the driver installed. You can see the probably minimal sound absorbing material I used (automotive carpet padding about 5/8" thick). It does work well in cars though. You'll also notice the parallel wiring of the dual voice coil woofer. I've noticed in may builds that it's almost become standard practice to bevel or chamfer the inside of the woofer cutout. I didn't do that in this case, because the driver appears to have adequate clearance (Is anyone aware of any measured data showing showing an improvement resulting from chamfered edges?).

The 4" PVC drain pipe I chose is thin walled, as compared to a schedule 40 pipe. I considered that an advantage as 4" schedule 40 is going to be needlessly bulky.



I'll continue in another post...

[Soundslike]

Re: Subwoofer Build -- 12" Dayton DVC

This next photo shows the assembled subwoofer, ready for primer. The final finish would be a high gloss black. As you can see, the corners were rounded.



This photo shows the enclosure after two coats of Zinsser's BIN, shellac based primer. The primer was sprayed on with a gravity feed gun. This product does seal very well, and it dries quickly. Too quickly in fact, if a smooth surface for a high quality finish is desired. In the summer heat of Arizona, the fast drying quality resulted in an orange peel finish that no amount of sanding could rectify. If the primer is sanded to a smooth finish, then spots of bare MDF will result, which will require another coat. Of course the next coat produces another orange peel surface. BIN primer is very effective at sealing the exposed bare edges, but it's not intended to flow out and produce a smooth finish. Zinsser's website touts the primer for covering stains, adhering to most common materials, and drying fast.

[benhinkle711]

Re: Subwoofer Build -- 12" Dayton DVC

Very nice looking build so far. I haven't had a chance to use/hear any of the new SD series subwoofers but the previous version were very nice, the only drawback being 5 mounting holes. The Zinnser looks like it is working out well. Would it be possible to sand smooth and then use a different primer on top of that so the edges are sealed and you still get a smooth finish?

[Soundslike]

Re: Subwoofer Build -- 12" Dayton DVC

Very nice looking build so far. I haven't had a chance to use/hear any of the new SD series subwoofers but the previous version were very nice, the only drawback being 5 mounting holes. The Zinnser looks like it is working out well. Would it be possible to sand smooth and then use a different primer on top of that so the edges are sealed and you still get a smooth finish?

Thanks for your comments -- great avatar, by the way. Regarding the new SD series, I haven't compared the specs, and I haven't listened to one either, but I'm guessing they will be very close. From what I've read in the Tech Talk Forum, Parts Express is striving to offer equivalent drivers, sans shielding. I'm sorry to the shielding go, if only from an appearance standpoint. They're much more impressive looking with a shield, but that of course, isn't a good reason to offer a shielded woofer. As for the five mounting holes, the frame is a bit light and would likely benefit from a few additional mounting points. I might consider drilling additional holes next time, but of course that will mean ten screws -- might look a bit overdone...

About the primer -- I mention it because I've seen more than a few posts where various builders suggested using it. I want others to know of it's limitations should they consider using it. If one looks at what Zinsser has to say about it on their website, it's pretty clear that this primer is intended for house painting. I think you're right, it could be sanded smooth and then painted over with a better-behaving primer. That's probably what I should have done. But, I can't help thinking that there are better choices. I ended up with automotive paint and primer.

[Soundslike]

Re: Subwoofer Build -- 12" Dayton DVC

For most of the painting projects I have done in the past, I have managed to make do pretty well with what's available at the local home improvement store. Seeking to improve however, I decided to get my paint for this project, and the Tritrix project described in another thread, at a paint store. I assumed that by going to a paint store, the personnel there would be able to suggest well-suited products for the high gloss black finish I was seeking. I had been thinking about using shellac based primer for some time, and when the paint store salesman suggested BIN primer, I decided to give it a try. I also chose an oil-based alkyd paint for the final finish. Here's a photo of the paint and primer I purchased.

.

Frazee has a number of stores in the Phoenix area, and at one time at least, their products were often used by house painters.

[Chris Roemer]

Re: Subwoofer Build -- 12" Dayton DVC

This next photo shows the assembled subwoofer, ready for primer. The final finish would be a high gloss black. As you can see, the corners were rounded.



This photo shows the enclosure after two coats of Zinsser's BIN, shellac based primer. This product does seal very well, and it dries quickly. Too quickly in fact, if a smooth surface for a high quality finish is desired. In the summer heat of Arizona, the fast drying quality resulted in an orange peel finish that no amount of sanding could rectify. If the primer is sanded to a smooth finish, then spots of bare MDF will result, which will require another coat. Of course the next coat produces another orange peel surface. BIN primer is very effective at sealing the exposed bare edges, but it's not intended to flow out and produce a smooth finish. Zinsser's website touts the primer for covering stains, adhering to most common materials, and drying fast.

You're in a hangar? Expound.

[Soundslike]

Re: Subwoofer Build -- 12" Dayton DVC

You're in a hangar? Expound.

I live at what's called an "airpark," a term recognized mostly by pilots. It's a place where the houses are built on lots connected by taxiways to the runway. Everyone has a hangar and all but a few have airplanes. I've got a couple -- a vintage Cessna 172, and a Scottish Aviation Bulldog visible in the background in several photos. The Bulldog was used by several European air forces as a trainer, including Britain where mine is from, and Sweden. The hangar makes for a nice roomy shop -- except for those pesky airplanes in the way.

[Soundslike]

Re: Subwoofer Build -- 12" Dayton DVC

I think I mentioned earlier that it was summertime, here in the greater Phoenix area, when I started this project. It was hot and dry when I started the finishing process; you have to move right along when spraying if you are to keep a wet edge and avoid overspray. The materials I was using were not formulated for the high temps common here in the summer. Still, it's manageable provided you're not in direct sunlight, and not painting during the hottest part of the day.

After the first coat was applied, I could see things would not be going well. In the next photo you can see the results after one coat. It doesn't look too bad, but it's certainly not up to the standard I was looking for.


I let the project set for two or three days before attempting to sand in preparation for the next coat. Not being satisfied with the smoothness of the first coat, I had planned to sand fairly aggressively in order to achieve a smoother surface for the second coat. But even though it had been sitting in 105+ heat for a couple of day, I soon began to clog sandpaper. When that happens, you can easily make matters worse so I settled for a less than perfect surface.

I was careful to apply the second coat during the morning hours, before the temperature got too high. In the next photo you can see that things were to go from bad to worse.




What you see is the result of high temperature and a gun with a partially clogged strainer (at the bottom of the paint cup). It was obvious that the gun wasn't applying the paint evenly, but once you've started, there really is no stopping unless you want to wait a few more days, then resand, etc. Besides, I've had similar problems before and managed to salvage the paint job. It was not to be this time -- this is the worst finish I have ever produced.

By this point, I was getting more than a little frustrated, but I was determined to get a good finish. It was painfully obvious at this point, that I was going to need a better paint.

While waiting the week or so it took for the globbed on paint to dry well enough for sanding, I went shopping for paint. I ended up at an automotive paint store where I told them about my tale of woe. They suggested that I use a high-build lacquer primer, and an automotive urethane type paint. I'd always wanted to try an automotive grade paint on a wood project so I purchased the products you see in the following photo:



While I was at it, I decided to upgrade my spray gun. I purchased a Devilbliss HVLP gun to replace both the inexpensive gravity feed gun, and my old-faithful Binks gun. After all, the inexpensive gun did clog up on me :o

As I imagine you can tell, the paint is a three part product -- the urethane paint, a reducer, and the hardener. The hardener comes in several different formulations that adapt the paint to the temperature range you will be in when the paint is applied.

I expected better results, and I wasn't disappointed. Even though I wasn't able to use the lacquer primer (it would likely have curdled the underlying alkyd enamel I had started with) the urethane paint performed beautifully. I highly recommend this type of paint.

Here's a photo of the finished subwoofer:



A closer view -- what looks like a smudge on the side of the enclosure is actually a reflection of the camera sitting nearby.



And one that gives an idea of the overall size..



The next time I build a sub (and it won't be too long) I'll most likely flare the vent or at least round it over. I'll also want to paint the inside -- somewhere I've got a link to a thread where a builder has discovered how to stain PVC. That might be a better way, since spray painting a long tube isn't going to be easy, and I could end up with sags and runs. Hopefully, I'll be able to find a flared black tube of sufficient size.

The performance of this subwoofer reallly impressed me. I know it must have its deficiencies, but to date I haven't heard any. I didn't want to give it up, but.... a promise is a promise. My son-in-law tells me that when the family is watching a movie with the volume turned up to theater levels, he often retreats to the other end of their 3200 sq. ft. house, where he watches TV at saner volume levels, while the plaque on the wall shakes and rattles. When I started this project, one poster told me I wouldn't be disappointed -- he was right, I'm not. Makes me wonder what the 240 watt amp, and a Reference Series woofer would do...

[[email protected]]

Re: Subwoofer Build -- 12" Dayton DVC

this is an excelent build summary. you and your airplane did a fine job. nice camera collection. is john travolta one of your neighbors?

[Soundslike]

Re: Subwoofer Build -- 12" Dayton DVC

Thanks for the compliment -- the airplane was good company, except I kept looking at it and thinking about all the things I needed to do to it, rather than building speakers. I've absolutely loved airplanes (and motorcycles) all my life but, speaker building has diverted much of my attention.

John doesn't live here, but this is an amazing place for anyone who loves aviation. We've had as many as three P-51s based here at the same time (we're down to one now). There are Stearmans, an AT-6, a Super Corsair, an L-39 Albatros http://aviasales.com/, an NA-50, http://www.google.com/imgres?imgurl=...ed=0CFgQ9QEwCQseveral Citations, several RVs, -- it's almost like living at an airshow.

The cameras you see are part of a larger collection -- another thing that irritates my wife. I think I've got about 120 vintage cameras. If I ever get them all dusted off, I'll probably post a few photos on Photobucket.

[RDR75]

Re: Subwoofer Build -- 12" Dayton DVC

.......Makes me wonder what the 240 watt amp, and a Reference Series woofer would do...

Once again an excellent job....It's always helpfull to see someone else's approach before you begin your own.....I have a 240w amp and a reference series woofer sitting in my basement, I'm just waiting for some nicer Canadian weather before I get started in my garage:D

[greywarden]

Re: Subwoofer Build -- 12" Dayton DVC

this is an excelent build summary. you and your airplane did a fine job. nice camera collection. is john travolta one of your neighbors?

Haha, he lives in South FL, he was considering buying an Antebellum mansion/plantation with 300 acres in my home town at one point, too.

[tech9_79]

Re: Subwoofer Build -- 12" Dayton DVC

wow..that paint is pricey.. but man it does look sharp.. is that with a clear coat? polishing? and i really kinda like the contrast of the white port..gives me ideas...