Bending MDF

fokakis1
fokakis1 Posts: 36
edited May 2012 in DIY, Mods & Tweaks
I recently purchased a pair of Polk Rti-a9's. These beauties are fairly large and have a curved teardrop shape, as they taper from front-to-back. I like the look, and the bass performance is solid, so I've set out to build 2 matching subs to complement the low end. [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6047.jpg[/IMG]"]CIMG6047.jpg[/URL]

I've been researching different ways to bend MDF so that I can form arcs for the sides of the enclosures. My budget is tight and tools are limited, so I can't afford too many failed experiments. I've read about kerfing, but I'm afraid that I won't get a smooth outer finish, and that I'll go through several sheets of wood trying to get it right. I've also read about bending several thin sheets then laminating them together, but the only sizes available at the local lumber yards are 1/2" and 3/4" in MDF, and birch is expensive. I've even heard of someone going so far as to cut out the perimeter of a tree trunk to get a rounded finish.

The idea that intrigued me the most came from terryj at home theater shack in his thread http://www.hometheatershack.com/forums/diy-speakers/19571-my-speaker-build-about-time-i-showed-you.html Thanks for the idea. I set a 4X8 sheet of 3/4" MDF on 2 sawhorses. As you can see, the board is very stiff and hardly bends even with about 80 lbs. of weight on it. [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5798.jpg[/IMG]"]CIMG5798.jpg[/URL]

I used a bottle of household ammonia mixed 50/50 with water and rubbed it on with a washcloth. I applied the ammonia/water mixture evenly across the board until it had soaked about 1/3 of the way through. I flipped the board over and applied the mixture to the other side until it soaked 1/3 of the board's thickness. This left the inner 1/3 dry. Amazingly, the board began to bend! [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5802.jpg[/IMG]"]CIMG5802.jpg[/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5810.jpg[/IMG]"]CIMG5810.jpg[/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5815.jpg[/IMG]"]CIMG5815.jpg[/URL]

I increased the weight on top of the board over the next few hours. I was careful in that I increased the weight in small increments as the board bent, and I spread the weight evenly to keep the bend consistent (a template would have been helpful here). [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5829.jpg[/IMG]"]CIMG5829.jpg[/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5836.jpg[/IMG]"]CIMG5836.jpg[/URL]

Drying only took a few hours. I was surprised to find that the board was still smooth to the touch.
The gnap of the wood was still in tack and sanded as smooth as the other panels on the subwoofer.
Performance wise the arced side panels actually feel stiffer than the flat panels! This is amazing considering that they are also the largest panels. After bracing, I can't feel any vibrations coming from the side panels while producing heavy bass passages.[URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5857.jpg[/IMG]"]CIMG5857.jpg[/URL]

The pics below are of the finished product. I have applied cherry veneer and wood conditioner, but they lack stain and finish. Thank you for reading my thread. [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6027.jpg[/IMG]"]CIMG6027.jpg[/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6034.jpg[/IMG]"]CIMG6034.jpg[/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6037.jpg[/IMG]"]CIMG6037.jpg[/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6040.jpg[/IMG]"]CIMG6040.jpg[/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6030.jpg[/IMG]"]CIMG6030.jpg[/URL]
Full 8.2 with:
Onkyo TX-NR818
Emotiva XPA-3
Audiosource Amp One/A
Behringer EPQ2000 w/quietfan mod
Panny BDP310
3TB NAS
Ethereal ESP601R
Monster HTS 1650
Epson HC-3020
120" DIY 1.0 Gain Screen
Polk Rti A9 fronts
Polk Rti 6 surrounds
Polk Rt/Fx rear surrounds
Polk Rti 4 front heights
(Phantom center):wink:
SVS 12's x 2 (DIY passive):eek:
ATS Acoustics DIY panels
Harmony 650
Nostalgia Electronics CCP-510 MovieTime Popcorn Cart
Post edited by fokakis1 on
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Comments

  • geoff727
    geoff727 Posts: 546
    edited May 2012
    Fantastic read, and wonderful looking woofers! Educational and inspiring. Thanks for sharing.

    G~
    Polk SDA SRS 2
    Polk RTA 15tl
    Polk Monitor 7C
    Polk Lsi9
    Infinity RS-II (modded)
    Infinity RS-IIIa (modded)
    Infinity RS 2.5 x 2
    Magnepan 1.6QR (modded)

    System: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1290711373
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  • chumlie
    chumlie Posts: 8,658
    edited May 2012
    Absolutely beautiful work. Thanks for the time & effort it took to post and welcome to Club Polk. ( hope you stay ). How do they sound ?
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  • [Deleted User]
    [Deleted User] Posts: 1,225
    edited May 2012
    Nice job, looks impressive especially when you add that you did it yourself.
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  • Toolfan66
    Toolfan66 Posts: 17,303
    edited May 2012
    Beautiful!!!

    Very nice work thanks for sharing!!
    Polk Audio SDA 2.3tl Fully Hot Rodded. 😎

    SVS SB16 X2

    Cary SLP-05/Ultimate Upgrade.
    Cary SA-500.1 ES Amps
    Cary DMS 800PV Network
    OPPO UDP 205/ModWright Modification
    VPI Scout TT / Dynavector 20x2
    Jolida JD9 Fully Modified

    VPI MW-1 Cyclone RCM

    MIT Shotgun 3 cables throughout / Except TT, and PC’s
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  • drumminman
    drumminman Posts: 3,396
    edited May 2012
    Outstanding! I would not have guessed fro the "after" pics that this is a DIY effort.

    Never heard of that technique for bending MDF - way cool :cool:

    How do they sound - are you pleased with the performance?
    "Science is suppose to explain observations not dismiss them as impossible" - Norm on AA; 2.3TL's w/sonicaps/mills/jantzen inductors, Gimpod's boards, Lg Solen SDA inductors, RD-0198's, MW's dynamatted, Armaflex speaker gaskets, H-nuts, brass spikes, Cardas CCGR BP's, upgraded IC Cable, Black Hole Damping Sheet strips, interior of cabinets sealed with Loctite Power Grab, AI-1 interface with 1000VA A-L transformer
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  • mdaudioguy
    mdaudioguy Posts: 5,165
    edited May 2012
    Very, very cool! Thanks for sharing!!
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  • zane77
    zane77 Posts: 1,696
    edited May 2012
    Beautiful job! What drivers are you using and what are you powering these with?
    Home Theater
    Onkyo PR-SC5508 Sharp LC-70LE847U
    Emotiva XPA-5 Emotiva XPA-2 Emotiva UPA-2
    Front RTi-A9 Wide RTi-A7 Center CSi-A6 Surround FXi-A6 Rear RTi-A3 Sub 2x PSW505
    Sony BDP-S790 Dishnetwork Hopper/Joey Logitech Harmony One Apple TV
    Two Channel
    Oppo 105D BAT VK-500 w/BatPack SDA SRS 2.3 Dreadnought Squeezebox Touch Apple TV
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  • VR3
    VR3 Posts: 28,746
    edited May 2012
    WOW! Just wow!

    Great job!
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • Drenis
    Drenis Posts: 2,871
    edited May 2012
    Boy that looks slick. I would LOVE something like that. Just the right size.
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  • strider
    strider Posts: 2,568
    edited May 2012
    Well done, thanks for the link to the write up on how to do it as well.

    I must admit, when I saw the thread title I didn't think I was going to see finished results like that.
    Wristwatch--->Crisco
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  • fokakis1
    fokakis1 Posts: 36
    edited May 2012
    Thank you to all for your replies. I hope this thread proves helpful to someone out there.
    Absolutely beautiful work. Thanks for the time & effort it took to post and welcome to Club Polk. ( hope you stay ). How do they sound ?

    I could not be more pleased with the sound. Music is deep and detailed, and movies are a whole new experience.
    Beautiful job! What drivers are you using and what are you powering these with?

    The drivers are the old DB12 (2002) out of some 20-39's. The edges are spray painted silver to match the rti's. I'm powering them with a Behringer EPQ2000, which seems to be plenty of juice.
    Full 8.2 with:
    Onkyo TX-NR818
    Emotiva XPA-3
    Audiosource Amp One/A
    Behringer EPQ2000 w/quietfan mod
    Panny BDP310
    3TB NAS
    Ethereal ESP601R
    Monster HTS 1650
    Epson HC-3020
    120" DIY 1.0 Gain Screen
    Polk Rti A9 fronts
    Polk Rti 6 surrounds
    Polk Rt/Fx rear surrounds
    Polk Rti 4 front heights
    (Phantom center):wink:
    SVS 12's x 2 (DIY passive):eek:
    ATS Acoustics DIY panels
    Harmony 650
    Nostalgia Electronics CCP-510 MovieTime Popcorn Cart
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  • newrival
    newrival Posts: 2,017
    edited May 2012
    Very nice work. Perfect companions to your new Polks. Very refined look.
    design is where science and art break even.
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  • SCompRacer
    SCompRacer Posts: 8,505
    edited May 2012
    High marks! Beautiful work. I would have thought getting the MDF wet would cause more surface problems than kerfing. I've never attempted it, but the manufacturer of my hybrid speakers folded transmission line bass module uses kerfing to get the rounded shape. But they do it on a set and forget CNC machine and use hardwood now.

    cabinetsonrouterweb.gif
    Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ * Signature Series Sonore Music Server w/Deux PS * Roon * Gustard R26 DAC / Singxer SU-6 DDC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *
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  • Face
    Face Posts: 14,340
    edited May 2012
    Great job!

    FYI, bendable MDF does exist: http://www.bendymdf.co.uk/ My local exotic wood/lumber yard carries it.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • cnh
    cnh Posts: 13,284
    edited May 2012
    Absolutely beautiful work. I want me one of those! Wonderful complement to the RTi-A series. Maybe Polk should take a long hard look at this and think about something similar? Hint! Hint!

    It would certainly have a high WAF!

    cnh
    Currently orbiting Bowie's Blackstar.!

    Polk Lsi-7s, Def Tech 8" sub, HK 3490, HK HD 990 (CDP/DAC), AKG Q701s
    [sig. changed on a monthly basis as I rotate in and out of my stash]
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  • pdxfj
    pdxfj Posts: 376
    edited May 2012
    That is truly impressive work! Very, very nice.
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  • Eusebio
    Eusebio Posts: 16
    edited May 2012
    awesome awesome job. congrats on the finished product
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  • mrbiron
    mrbiron Posts: 5,711
    edited May 2012
    Quite impressive. When we use MDF for window sills and wall caps, we have to make sure nobody puts anything wet on them as it will bubble quite easily. That is a neat technique for bending.
    Where’s the KABOOM?!?! There’s supposed to be an Earth shattering KABOOM!!!
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  • bmbguy
    bmbguy Posts: 416
    edited May 2012
    Very interesting post, and very impressive results. Congrats on some wonderful work.
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  • ken brydson
    ken brydson Posts: 8,772
    edited May 2012
    Very nice!!!
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  • halo71
    halo71 Posts: 4,604
    edited May 2012
    Wow, that is one of the best DIY subs I think I have ever seen! Simply stunning build!
    --Gary--
    Onkyo Integra M504, Bottlehead Foreplay III, Denon SACD, Thiel CS2.3, NHT VT-2, VT-3 and Evolution T6, Infinity RSIIIa, SDA1C and a few dozen other speakers around the house I change in and out.
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  • skrol
    skrol Posts: 3,387
    edited May 2012
    Wow, that looks excellent. We need one of those jaw-drop smiles.
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Benchmark DAC1, Monster HTS3600-MKII, Grado SR-225i; Technics SL-J2, Parasound PPH-100.

    HT:
    Marantz SR7010, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW110 , Marantz UD5005, Pioneer PL-530, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, AVR-888, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, 5B, TSi100, RM7, PSW10 (DXi104 upgrade); Pioneer: CT-6R; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, CDR-615; Parasound C/PT-600, HCA-800ii, Sony CDP-650ESD, Technics SA 5070, B&W DM601
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  • Oldfatdogs
    Oldfatdogs Posts: 1,874
    edited May 2012
    Very nice work.
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  • polk500
    polk500 Posts: 1,171
    edited May 2012
    Awesome skills, I'm sure if you wanted to make a few sets of these you would have no problems selling them. Just awesome are you a finish carpenter or do it for a hobby?

    I was for a long time but I don't think I could have pull this off who am I kidding I wouldn't be able to.

    Great work.

    Cheers Roger
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  • [Deleted User]
    [Deleted User] Posts: 1,394
    edited May 2012
    Amazing work! Wow..
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  • SDA1C
    SDA1C Posts: 2,072
    edited May 2012
    I'm with Halo on this one. That is some of the most impressive DIY work I've seen. Just WOW!
    Too much **** to list....
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  • falconcry72
    falconcry72 Posts: 3,580
    edited May 2012
    I take it those are Polk OEM feet to match the A9's? Nice touch.:cool:
    2-Channel: PC > Schiit Eitr > Audio Research DAC-8 > Audio Research LS-26 > Pass Labs X-250.5 > Magnepan 3.7's

    Living Room: PC > Marantz AV-7703 > Emotiva XPA-5 > Sonus Faber Liuto Towers, Sonus Faber Liuto Center, Sonus Faber Liuto Bookshelves > Dual SVS PC12-Pluses

    Office: Phone/Tablet > AudioEngine B1 > McIntosh D100 > Bryston 4B-ST > Polk Audio LSiM-703's
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  • TECHNOKID
    TECHNOKID Posts: 4,298
    edited May 2012
    IMHO, this has to be the thread of the month if not the thread of the year. Very cool project, lots of details and passion put into the project. Very skillfull too! Thanks for sharing! :cool:
    DARE TO SOAR:
    “Your attitude, almost always determine your altitude in life” ;)
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  • mrbigbluelight
    mrbigbluelight Posts: 9,787
    edited May 2012
    ^^^ Very good points mentioned.

    Besides the very impressive results (NIIIICE !), one of the really neat things about this DIY project is that it doesn't get much more DIY than this.
    Sheet of MDF. Sawhorses. Bottle of ammonia. Sponge. Patience. Etc.

    ... and, in this case, an artistic eye. A very artistic eye.

    "Okay, both sides 1/3 wet, .... lemme half load some empty computer paper boxes towards the edges, probably go with a fully loaded Meat Master box in the middle ....".

    :eek:

    The bendy MDF site posted by Face mentioned the use of the bendy MDF as templates. Perhaps something to consider if you ever decide to produce more in the future. Or I should say "create" more in the future.

    Brilliant work.
    Sal Palooza
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  • love2listen
    love2listen Posts: 172
    edited May 2012
    WOW!!! Congrats on a wonderful job..looks great!!: :cool:
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