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Discussion Starter #1
Hi Everybody!!

First post. I've been a'lurkin for about a month now soaking it all up like-a-sponge. I built sub boxes for cheapo (Pyramid anybody??) nasty thumping cars back in high school, but I was clueless. This will be my first attempt at a real DIY HT sub build. My woodworking skills / tools are pretty good, so that shouldn't be a problem (finding space to spread out will be though).

I'm currently using the PartsExpress Titanic Mk III kit that includes the parts in the Title line, along with a flimsy 3/4", ~90liter sealed enclosure (18" cubed). I've been very happy with it for a few years now. But one night, for no particular reason, I just decided I wanted to build a new box for it. Then I wound up here and fell in love with Steve's LLT sticky post. I have a small room in my new house dedicated to tv/movie watching. So size is no concern. Yes, my wife will hate having my coffin in the corner of the room, but she gets to control every other sq ft of the house. This one's mine baby.

So, at first I was going to just rebuild with my current kit parts, but while modeling in WinISD, I noticed a lot of over-excursion (xmax=20.5mm) at wattages far less than the 950W my amp can produce. So then I decided to go ahead and plunge into another Mk III (I want to discuss this decision in more detail since the driver is out of stock and I have a while to cancel if I'm convinced to by the guru's here).

So on to the design. Here's my first stab at it with WinISD/BoxNotes (well, actually my 50th stab after playing around for many many nights):

- Wire the 2 4ohm MkIII's in series for 8ohms, so ~425Watts total system power
- I set the WinISD signal power to 425W
- 600 liter
- 15Hz tune
- 3 - 47cm long, 4" pvc ports (13.5m/s-at-20Hz, 35m/s-at-13Hz)
- Vented out the top of the box, try to achieve 8" center-to-center spacing
- I'll flare the outside of the ports with whatever roundover bit that came with my router bit-kit (3/4" diameter I think), not going to spend $100 on a big honkin roundover bit or mess around with heated flaring (though those do look cool!)
- External dimensions: 650x700x1750mm
- 1" MDF (2 1/2" sheets glued together), 2" on front baffle
- 2 shelf braces, 1x1" edge bracing along the length of the 4 corners
- Forward-firing, both drivers on same face (???)
- Probably some open cell foam lined on the inside faces
- All glue, no screws from the outside. Screws on the inside wherever I can get them into something
- Plate amp mounted low on the face opposite the drivers
- I'll post some WinISD grabs/files in later posts if anyone wants to help out
- Equalization will just be with Onkyo Audyssey auto-eq unless I'm convinced otherwise
- My room is 14ft x 11ft x 8ft

I think that sums up my current plans. Start lobbing grenades at it. Please! I want to achieve 95% perfection. Ie, plenty good enough without delving into the region of diminishing returns.

I'm also using an REL 10" sub in another corner of the room, but I'll discuss what I should do with it in a thread elsewhere in these forums at a later date.

Note, this will be a slow-going build since I'm still settling into a new house and need to unpack/organize all of my garage stuff. I anticipate making first saw dust sometime during the Christmas holidays. I can't wait to start posting pics.

:duck: Looking forward to feedback!! :duck:
--Myles
 

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Hi Myles and welcome.

Here are a couple of OTTOMH suggestions from the points that leapt aout at me:

"- I'll flare the outside of the ports with whatever roundover bit that came with my router bit-kit (3/4" diameter I think), not going to spend $100 on a big honkin roundover bit or mess around with heated flaring (though those do look cool!)"


You could make a conical flare by routing out circles in mdf scrap using a 45° bit and laminate them together. This will get you most of a rounded over flare and you probably already have the bit.

"- Wire the 2 4ohm MkIII's in series for 8ohms, so ~425Watts total system power
- 600 liter
- 15Hz tune"


Could you not do two boxes of half the volume and the same tune and put one in each front corner? It will add the cost of an extra plate amp, but you could even build the enclosures tall and triangular in X-section, paint them like the wall and they'll blend in. Haven't modelled it though, so just a suggestion.

"- 2 shelf braces, 1x1" edge bracing along the length of the 4 corners"


Corners are the strongest area anyway, so i doubt I'd bother with the 1x1, but I would add at least another couple of braces horizontally and at least one vertically on each face.

"- Probably some open cell foam lined on the inside faces"

Won't do anything at all. Depending upon the final build config some fibreglass placed so as not to block the path port to driver will help tame the internal modes, especially the vertical.

"I'm also using an REL 10" sub in another corner of the room, but I'll discuss what I should do with it in a thread elsewhere in these forums at a later date."

Use it mid wall or at another null somewhere in the room to help even out room modes. The Multi sub paper on the Harman site explains it all.
 

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The modeling looks good for your design, with a couple of points. These subs have much more potential which you may want to consider for the future. They can easily handle 1000 watts in case you may want to upgrade your amp. If that's a possibility, build a separate box for your current plate amp and set it on the floor behind the cabinet.

1000 watts would require four 4" diameter ports to control the air speed, or to simply things, one 8" diameter port which would have the same port area as four 4" ports. 8" diameter Sonotube is very cheap.

Corners are the strongest area anyway, so i doubt I'd bother with the 1x1, but I would add at least another couple of braces horizontally and at least one vertically on each face.
Agreed.

The biggest internal mode will be the vertical due to the cabinet hieght, 4' to 6" of compressed fiberglass insulation at the top of the cabinet will eliminate any resonance issue.
 

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Discussion Starter #4 (Edited)
Cool. Thanks for all the input! You got me thinking a lot. This was supposed to be a little $100 "Unbelievable!, let's just build a new box for kicks" project. But we all know how those turn out. I crossed the Rubicon once I hit Process Order on the 2cd Mk III.

Regarding amplification: Yes, agreed, I will not mount the amp into the driver enclosure. But I'm also not proud. I have no problem leaning the plate up against the box or throwing it on the bottom shelf of my component stack :coocoo:. Yes, running ~225W-max into each Mk III is gross underutilization. So I think I'll try running the Dayton amp into the parallel 2ohm load, and try to ballpark the gain control into the 800W'ish range. If I wind up melting it, oh well, then I'll get nasty with an EP4000 :hsd: (I'll order it while my wife isn't looking, else i'll be on the receiving end of :boxer:).

And after further consideration, I guess I'd have to be nuts not to build 2 boxes to help with room coverage. So I guess I'll do that too. And 8" Sonotube (or whatever brand my local HD/Lowe's has) is a good idea too. Now that I'm going with 2 shorter boxes, I think I'll stick with just the single shelf brace w/ no vertical bracing. So here are the new specs for the build.

- 2 boxes
- 340 liter each
- 15Hz tune
- WinISD signal set to 900W (in case I grab an EP4000 some day :spend:)
- 1 - 8", 112cm port (10m/s-at-20Hz, 28m/s-at-13Hz)
- No internal damping
- External dimensions (using BoxNotes' assumptions): 500 x 740 x 1345mm

I set the external height to port_length + 8" clearance + 1" = 1345mm. I may not have a full 8" of back-to-front clearance. I'll have to center it between the back wall and the back of the driver magnet. Let's seeee, Mk III is ~200mm deep. That leaves 515mm between magnet and back wall of box. 8"=200mm, so (515-206)/2 ~ 150mm clearance from port edges to back wall / magnet (to be cheated a little toward magnet since it's not as "obtrusive" as an enclosure wall). 155mm vs. ideal-200mm. I'll survive, right?

I'll try to think outside the box (pun intended) and weigh my options for getting the most flare I can easily achieve. But I'm not sweatin it too much with an 8" port.

Question: How can the Mk III claim to handle 800W if, according to WinISD, the excursion is 26mm at 25Hz (WinISD signal set to 800W, Mk III xmax=20.5mm)?

Re: the REL. Now that I'm going the 2-box route, looks like I best sell. I hope there's someone out there I can sucker into using a non-DIY sub. Who would do that?? :rolleyesno:

Thanks guys!
--Myles
 

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Question: How can the Mk III claim to handle 800W if, according to WinISD, the excursion is 26mm at 25Hz (WinISD signal set to 800W, Mk III xmax=20.5mm)?
Power rating of a driver is the amount of heat the voice coil, former and adhesives can stand before they start to fail. Better specs such as many pro driver datasheets will also include the time the diver is accepting this level of power under test without failure. It has nothing to do with excursion: you could put band limited pink noise through it at the appropriate level and get the same heating as a 30Hz sine wave with little excursion.
 

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In 340 liters tuned to 15 hz you are limited to 600 watts or over excursion will be an issue.

An 8" port was for 2 subs in one box, this would require a port 7" (or a bit less) which will help in reducing the port length. Sonotube is shipped one piece inside the other to reduce shipping costs, find a supplier and take a tape measure with you. Find a piece that is 6.75" or 7" diameter.

Your Dayton plate amp will not handle a 2 ohm load.
 

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Power rating of a driver is the amount of heat the voice coil, former and adhesives can stand before they start to fail. Better specs such as many pro driver datasheets will also include the time the diver is accepting this level of power under test without failure. It has nothing to do with excursion: you could put band limited pink noise through it at the appropriate level and get the same heating as a 30Hz sine wave with little excursion.
Awesome explanation!! :T
 

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In 340 liters tuned to 15 hz you are limited to 600 watts or over excursion will be an issue.

An 8" port was for 2 subs in one box, this would require a port 7" (or a bit less) which will help in reducing the port length. Sonotube is shipped one piece inside the other to reduce shipping costs, find a supplier and take a tape measure with you. Find a piece that is 6.75" or 7" diameter.

Your Dayton plate amp will not handle a 2 ohm load.
It might for a few minutes.... :dumbcrazy: Until it lets the magic smoke out. I really suggest using a good solid amp as clipping can be your worst enemy.

Matt
 

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Discussion Starter #9
Re: Power handling. Yeh, that's kind of what I figured. It's a bit misleading for most people that read Pe=500W-RMS and think that it can handle a 500W amp without bottoming/heavy-distortion.

Re: 2ohm load. I'm an analog IC designer, but I don't know the details of high power output stages. My guess is that the output stage is capable of a given voltage and current drive. As long as I stay beneath those (specifically the current limit), then I'll be shiny. I checked the manual and it doesn't specifically *say* that 4ohm is the minimum load. Anyhoo, no need to flame-up a perfectly good amp. I'll start out in series. That should give me at least the same SPL I'm getting with my current sealed box... which is a whole lot, but with far less distortion. Then, if I still feel the need for more pound'ola, I'll put my Dayton amp up for sale for ~$150. That'll ease me into a more capable amp (Behringer, Crown, etc)

Re: 7" port. Good call. Simulation looks good.

Re: All that nonsense I was talking about having enough clearance at the bottom of the box around the port. Duh :doh:, why was I even thinking of venting out the top? I don't want to be fishing my cat out of there some day (or having her claw her way out thru the cone). I'll down-fire the port. That'll leave all the room in the world at the top (middle) of the box for the port to breath.

Q: How high do I have to raise the box off the carpet if I'm downfiring the port? :dontknow:

Here are the new nightly specs:

- 2 boxes
- 340 liter each
- 15Hz tune
- WinISD signal set to 500W (xmax limited)
- 1 - 7", 85cm port (10m/s-at-20Hz, 28m/s-at-13Hz)
- No internal damping
- External dimensions: 500 x 640 x 1510mm
 

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Discussion Starter #11
I'm going to try to start construction this week. I started a few other threads to gather some more design input (LLT vs. higher tune, and cheapo finish techniques). Since earth breaking is nearing, I'm finalizing some of the design decisions. Here's the latest state of the union:

* Going to use a Reckhorn B-2 to add a 4th-order (24dB/octave) cut at 15Hz. (Because I read that some jokers in movie sound design actually put 10Hz and lower info in the LFE tracks (War of the Worlds, etc); thanks dudes)
* Up'd the tune to 17Hz. The anti-LLT crowd got to me, so I split the difference. Comments??? :help:
* BUT, I'm going to add a thinga'muh'hookie to the box that will let me change the port length if I want to. Can't commit :scratch:. I could even seal it in a monstro-box :coocoo:.
* 373 liter working volume.
* 2 boxes (my 2cd MkIII arrived and is sitting on my dresser; I kind of like it sitting there looking intimidating :flex:).
* I'm going to run the 2 beasts in series with the Dayton SPA1000 (~450W total system power) until I can sell my REL-10" sub, and the SPA1000/stock-kit-box), then I'll upgrade to an EP4000 or similar and rock da house.
* Each MkIII should be able to handle 700W of input cleanly (~Xmax), so 1400W total system top limit.
* Chose the box dimensions such that no panels are wider than 24" so that I can get 2 panels from each sheet of MDF.
* Here's my spreadsheet to calculate working volume. Similar to Boxnote's calculations, but slightly more customized. Let me know if anyone wants the source code to the sheet. I'll Google-docs share it with you. https://spreadsheets.google.com/pub?key=0AjwCXbS5q2UGdFJ2VThjWjhhZER3cllacHRXNWR1T0E&hl=en&output=html
* 1" MDF w/ 2" thick front baffle.
* Outside dim's: 600x660x1300 WxDxH
* 7.25" port, 646mm
* 3 shelf braces and probably a few 1" dowels placed vertically between shelfs and outer panels.
* Going to try and use my biscuit joiner for the first time.

I used Inkscape to draw up my cut sheets. Highly recommended. Easy to learn for simple application like this. Looks like it's going to take 5 sheets total (for both boxes).

I'll post a few WinISD traces tomorrow night. But suffice to say that a single box will get me [email protected] -3dB is @ 16Hz (assuming 50Hz is 0dB & 700W input). [email protected] w/ 225W. Need that new amp!!! :crying:

Counting down to liftoff....
 

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Discussion Starter #12
I've been cutting panels the last couple of days. This is my first sub box since high school 20+ years ago. Back in them good ol days, I drew a line and tried to hand-track it with a skil saw :duh:. Needless to say, my methods have improved. I want to start a detailed thread elsewhere to help other noobs like me. I made a lot of goofs, but eventually got so that I could get within +/-1mm of my target dimension.

I want to get a little farther along. Then I'll start posting some pics.

Warning: this will be an entirely uninteresting build. Boring, cheap and ugly all the way. I just want the sound baby.

After mucho deliberation and a minor flame war, I think I'm going to stick to my LLT guns and tune to 15Hz. If I want more "punch", I'll eq it in. I'm adding the ability to change the port length. So if I want it bad enough, I'll create new ports and stick them in.

The final specs are:
* 365 liters
* 15Hz tune
* Going to run at low power for a while without HPF (225W to each MkIII), but I think I may need to add one after I get a Behringer EPX3000 (900W to each MkIII).

Here's my spreadsheet (I highly recommend Zoho):
http://public.sheet.zoho.com/public/smprather/rectangular-ported-subwoofer-box-dimensions-calculator

There are a total of 20 panels to cut (6 sides + 3 braces + 1 for double-thick front baffle)*2. I have 19 of them done already. Need to get more MDF for the last panel since I miscalculated on my cut sheets. Just a $50 miscalc. No big deal :doh:. Well, at least I'm guaranteed to have enough scrap to build a box for an 8" Dayton I've had laying around for years now.

Next step is to fire up the router and start slotting for bracing. Opening up the braces. Driver opening. Etc etc.

Looking for recommendations for:
1. Feet. I have to raise these suckers ~7" to let the bottom firing ports breath.
2. How to design the holes in the braces that the port will pass through keeping in mind that I need to be able to pull a port out and put a new one in, and I want to avoid the possibility of rattling.
3. I plan to use biscuit joining. Worth the trouble? Or should I just glue/screw? I don't think my panel cuts are accurate enough for glue only. I foresee some small gaps that I'll need to fill before painting.

I'm currently thinking:
1. Either simple L's created out of MDF, or maybe aluminum tubes (4*2"x7" for $12 at speedymetals.com; sweet!)
2. Oversize the holes enough to line with some dense-foam weather stripping. Use finishing nails to secure well enough that it'll never come off. Will the rubber degrade after 10'ish years?? Or should I just oversize-a-plenny (~1" clearance all-around). Ports don't really need internal support, do they? Especially if they're positioned vertically?

Man this is time consuming stuff!! 3 days so far to make my guides and cut 19 panels. Still a lot of work left to do. And now I have to go back to work after 2 weeks off :crying: :crying: :crying:.
 

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Discussion Starter #14
And away we go. I have no clue why I took some of these pictures, but I've yet to read a build thread with too many pictures. I'm about 70% finished. I'll post some pics tonight and more as time goes on.

Here are some shots of:
- The MkIII
- Port tubes (~7.25")
- Shelf brace (2 per cab, 4 total)
- The just about complete bottom panel (more pictures to follow later). The 4 L-grooves will be receiving 1"x7" MDF feet to give the down-firing port room to breath.
- My home-brew circle jig. Note how i recess the holes for the screws that go up into the router base. This gives me a smooth ride on the board I'm cutting the circle in. This jig has performed very well after cutting, hmmm, ~11 circle holes of various sizes.

What's the biggest thing I've learned while doing this build? That it takes an incredible amount of time. For instance, it took me ~4 hours just to route the grooves for the feet. Basically, one day of weekend work. Just for the feet grooves!!! I cut my first driver hole tonight. ~2hrs. And that's not counting ~2hrs to prep my driver (had to cut away some of the mounting gasket rubber, and drill the metal mount hole, to make the holes big enough for the hex-head screws I got from PE), and precisely drill the mounting holes (driver face down on wood, drill bit right through driver holes into the MDF). Time time time. And lots of sawdust on the neighbors cars :devil:.





If anyone knows how to get these images into the thread at higher resolution, please let me know. I've seen bigger pictures in other threads, so I know it's possible. I'm using the HTS Gallery to do my uploads.

Good night all! More later!
--Myles
 

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Discussion Starter #15
More pictures tonight. BTW, I know I'm posting a lot of junk shots, but as a noob reading this forum, I picked up all sorts of ideas that's old news to most of you. Tonight, I'll talk about my changeable port construction. I'm porting out the bottom, so I didn't care about how it looked. This will all be out of sight.

First, I cut out my port circle - inside half of the MDF is the OD of the port, the outside half of the MDF is the ID of the port, then a 1/2" roundoff. Then I cut a square out of the bottom panel that captured my port opening. Then I cut a sheet about 2" larger (on all sides) than the square I cut out of the bottom panel. I cut a circle in that square the OD of the port. This sheet will be mounted on the inside of the bottom panel. I dry clamped everything together and drilled 4 holes through the port-holding-panel and the port-assembly-mounting-panel. Then I installed hurricane nuts (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=081-1084) on the inside. Man I love those hurricane nuts. Highly recommended, especially for MDF usage where spiked t-nuts won't penetrate good. Then I drilled out some space for the hex bolt head to countersink (the bolts weren't long enough to reach the threads unless I allowed for some countersink). With the 4 hex bolts screwed in, the panels are rock solid connected. Absolutely air-tight and structurally sound.

Anyhoo, clear as mud? I think the pictures will help clear it up. (sorry, not in chrono order).

- Square containing port hole cut out of bottom panel.
- Cutting out the the receiving sheet with the port OD circle in it.
- Just before I glue the receiving sheet to the inside of the bottom panel.
- Mounting the hurricane nuts.
- Getting ready to drill the holes through both panels at the same time to guarantee alignment.
- Finished shot. Shows 1/2" roundover. Tip: For a little "bonus" radius, let your roundover bit sink a mm or 2 into the MDF, then round off that step with some coarse sandpaper.
- Another look at the finished bottom panels along with my stack of other panels.
- L-grooves will hold the MDF feet.
- Obligatory kid shot.

Again, my apologies to those of you expecting pictures of museum-grade bass launchers. These things are going to be big, black, rectangular coffins. But I'm betting they'll sound just as good / better than the hand-carved laminate stacked warp drive woofer we all loved reading/looking at :clap:.







More tomorrow...
--Myles
 

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Discussion Starter #18
Is that the inside diameter?
Yeh, it's ID. 7.37" (187mm) to be exact. The wall thisckness is only 2.4mm though.

Thanks for the encouragement guys. Forging onward. Glued my 2cd shelf brace in place tonight. I'm clamp-poor, so I'm taking it slow. One panel per day. It's all I have energy for after work anyway.

Time for more pictures!
- This is where the magic happens. This was day-1, building circle guide and gluing my sawboard together (http://www.subwoofer-builder.com/sawboard/index.htm). I have some "wish I'd thought of that before" tips on making a sawboard. I'll try to get around to detailing that some day.
- This was my basic setup for cutting all of my panels. I put a sheet of $10 junk plywood under my 1" MDF (2 1/2" sheets laminated). Then I set my saw depth to be 1.5"+a_smidge - 1" for cut, 1/2" for sawboard thickness, plus a little to make sure I get through. Can't stress how handy it is to have a 30lb weight handy. I've used it about 100 different ways. Note also that I used a parallel board to support that wide part of the saw base.
- Just a shot of clamping so that the saw motor could run over the top of it ok (if I did it over again, I think I would've made my sawboard wider to prevent clamps getting in the way; big pain).
- For the times (quite often) when I needed to space my sawboard edge 1 blade width from my desired line, I used a sliver of MDF that I sanded down until it snugged into a blade width test cut.
- Then I used that sliver to set my spacing.
- Ready to cut.
- And here's an out of place shot of testing my router depth to get 5mm rebates for my shelf braces.





Till tomorrow...
--Myles
 

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