Viva la Vifa! Curvy Cabinet DCR with TC9FD

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This project started over in the Foam Core sandbox: http://www.diyaudio.com/forums/full-range/223313-foam-core-board-speaker-enclosures-226.html#post3847794, but I think it deserves its own thread though as this design is special: it looks really cool, and is the first FC design I made using the single piece wrap around construction method suggested by Don Hills and also implemented by Grandcalmar on a rectangular box. Instead of making another rectangular box, I decided to make it curvy - inspired by Wesayso's glorious looking Twin Towers http://www.diyaudio.com/forums/full-range/242171-making-two-towers-25-driver-full-range-line-array.html. Anyhow, the construction method involves making ribs very much like aircraft wing ribs and wrapping it with the sheathing like an airfoil.

Here is the completed speaker:
404491d1394331762-foam-core-board-speaker-enclosures-dcr-vifa-photo-01.png


Preview of performance - here is what the FR and HD looks like with digitally applied BSC and bass smoothing with REW via miniDSP:
405087d1394537242-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-bsc-rew-hd.png


Here is the harmonic distortion performance with a speaker-level BSC and no DSP applied at the desktop listening position:
405849d1394805227-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-bsc-rew-hd-3in.png


In doing this I wanted to try a dual chamber reflex (DCR) - an alignment I have not tried before. Maybe not the best driver for a DCR, but I am using the venerable Vifa TC9FD to see if I could build a bold looking single point source with some decent bass as an all-in-one solution for excellent bookshelf, desktop, or even lower-volume stand-mount duties. I was not sure if it is possible with TC9FD, but my ultimate goal would be to be able to build a mini-monitor with flat response and low harmonic distortion (-20 dB) down to about 80 Hz, and better than -40dB HD above 300 Hz where the vocals and telephone band are.

I started with a model of the DCR in Akabak and used a typical volume required for such a high Qts driver like the Vifa. I also tried to keep in mind what a useful size would be for desktop of bookshelf speaker and set on no more than 14 in (35.6) high x 11 in (28 cm) deep. I set the width based on the minimal volume required to achieve significant bass extension (recommended volume by WinISD is 15 liters), while still keeping the profile small and attractive. I settled on a 50 Hz tuning frequency to really push this design below the 55 Hz tuning limit suggested by WinISD for BR design for a driver with an fs of 120 Hz. The HD may be terrible but we will have to see how it works out for nearfield (1 meter) listening at moderate 70 to 75 dB levels where cone excursion may be quite small and HD may not be too bad.

I arrived at a design that was about 12.5 liters total volume with dual ports each having 2.0 square inches (~13 cm^2) of CSA and a vent length of 4.7 inches. The volumes would be divided using the standard DCR design practice of 2/3rds for the upper chamber (where driver is located) and 1/3rd for the lower chamber. Normally, the interconnecting port is the same length but in the model I found that reducing its length helped to smooth the response in the 150 Hz region. So the interconnecting port is the same CSA but only 1.5 in (3.8 cm) long. In order to get an approximate volume required and have curvy corners, the maximum width was set at 6 in (15.2 cm) wide.

But there is another aspect to the design that I always consider: using the minimal amount of FC material as possible and making it so that it looks seamless from the front. I sketched the truncated teardrop (or airfoil) shape on a piece of paper ensuring that the flat front was wide enough to mount the Vifa - so I set it at 4.0 inches (Vifa is 3.5 in wide). I then rolled the template along a length of FC board to trace the circumference of the shape to make sure I could fit. With a little trimming I was able to achieve a shape with nicely rounded front corners, a gradual slope towards the back, a flat on the back for mounting the rear firing slot vents (and I think it looks better than a sharp knife edge), that fit in a 30 in long FC sheet length with exactly a strip equal to the rear flat left over. That is, the circumference of the speaker including the back is 30 inches. I had considered making the speaker 15 in tall but making it 14 in tall saves 6 in of material that will be needed for the top and bottom panels. The middle divider is not visible so I made that out of double wall cardboard. So this is a "1 FC sheet" design (or $1 in FC). This time, I only had the nicer thick paper facing Elmers FC on hand so I used that instead. It provided a much sturdier build and I would suggest that others use this too as it substantially improves the strength and durability of the structure once done.

The construction method is fairly simple but may be tricky for those new in FC construction. I would not recommend this as a first FC speaker build as the curved wall construction requires some experience. However, you can certainly practice and it doesn't cost anything if you mess up.

Start by cutting 3 of the rib shapes which define the internal curves. Locate that on a sheet of FC to establish where the two rounded corners are on the front. Then score cuts along along the 14 in length direction every 3 to 5 mm piercing through the first layer of paper with a razor. You will want a straight edge (or a metal drywall "T" is the perfect too to make this go fast) to make sure the lines are parallel. Do not score the flat 4 in wide section in front. The take a razor and remove a 1/8 in wide channel of paper and foam from the corner where the front is to allow a clean fold that does not crunch the paper. Now use a rounded object like a PVC pipe, a radiused countertop edge, etc to pre-curve the shape to allow it bend and wrap around the ribs without too much effort, being careful not buckle it and crease the FC this ruining the piece. Check that the curve can sufficiently follow the curve on the rib without too much force.

404867d1394457584-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-photo-03.png


Now glue the 3 ribs to the correct locations on the sheet (top, bottom, and 4.7 in from the bottom), add 90 deg braces to the ribs to set the squareness and reinforce them for the next operation. Then add a second layer of either FC or double wall cardboard behind where the driver goes to give the screws more material to grip.

404870d1394457584-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-photo-05.png


Now here is the tricky part, start gluing the outside panel to one side of the ribs a section (half the length from the front) at a time. You need to make sure the hot melt glue gun has a full stick of glue to start the operation (or have a spare ready and held in your teeth to reload quickly) as you do not have much time and there are 3 strips of glue about 5 inches long each that need to be applies, in addition there is the 14 in long gap where you removed the foam from the crease that needs to be filled with hot melt glue. Once you quickly apply the glue, use your hands to firmly hold and clamp the panel to the ribs to ensure a tight fit (including the middle divider rib). You only have seconds to work and hold it for a good 45 seconds before releasing pressure. Now use the glue gun to add fillets of hot melt glue internally to the joints to make an airtight seal. Next, repeat the hot melt glue and clamp with the remaining length all the way to the rear of the speaker. You may notice that because the speaker is curved and rounded, it is hard to hold steady while you apply hand clamp pressure. You may need to employ your knees, lap, and carpeted floor in combination. It wants to roll and squeeze its way out of your hands as you clamp it. Again, add hot melt glue fillets to seal.

404868d1394457584-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-photo-bracing.png


Now repeat with the remaining side, but before doing so, add some internal bracing to reduce the drum head resonances on the large side walls and the top and bottom panel. I used cardboard trimmed to size. You have to wait until the final side panel is glued on partially before adding final side bracing. If you have small hands (and a small hot melt glue gun) there is enough room to squeeze inside and seal the joints on the second panel before gluing the final stretch. On the final stretch, you have to apply copious amounts of hot melt glue to the divider rib because you cannot get to it after the fact so ensure an airtight seal there. The end ribs are not as critical as you can still seal it from the outside as needed.

404871d1394457584-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-photo-04.png


Once you have the curves single piece wrap around side on, it looks like a real speaker. Now trim the rear wall to have beveled edges to fit perfectly into the gap created by the one piece wall, cut two port slots (0.5 in x 4.0 in tall) in the rear wall. Make two slot ports out of FC or cardboard using hot melt glue and then glue them to the back of the rear wall strip. Either use binding post mount or poke a small hole and feed the speaker wire through the rear wall and seal with hot melt glue. Cut the driver hole with an xacto (it is 3.0 inches dia exactly), make sure you have enough wire coming out the front and attach crimped quick disconnect terminals. Add moderate stuffing to the top and bottom chamber (I used pillow stuffing) being careful to not directly block the vents. Then glue the rear wall on - the speaker is now finished except for the BSC circuit.

404872d1394457584-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-photo-02.png


Install the driver using wood or drywall screws. For those wanting to go the BSC route, put a 1.0 mH air core coil plus a 10 ohm x 10 watt resistor in parallel plus an optional 0.47 uF capacitor in parallel. Put all this in series with the posititive terminal to the driver. Hot melt glue this somewhere in the chamber (preferably at the bottom for stability) before you seal up the speaker.

I am going with the EQ'ing the speaker through my music player on the PC for now until I can get the BSC. It sounds really nice and I think you will like it and agree that the clarity and imaging will be superb. The bass is sufficiently deep at about 50 Hz when the speaker is placed near a rear wall such as when used as a bookshelf or desktop speaker. For in stand mount duties away from a wall, a sub woofer will most likely be needed to get sufficient bass.

Here is the Freq Response from the ports and the integrated sound - far from walls:
404874d1394457660-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-1-meter-integrated-ports-no-bsc-spl.png


Here is response close to a wall and at 0.5m away and lower drive voltage:
404877d1394458995-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-integrated-no-bsc-spl-hd.png


Here is the Impulse Response:

404878d1394458995-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-impulse.png


I will build the matching stereo pair as soon as I get some time (about 4 hrs to make a piece) and more FC. have a listen to the sound clip and I think you will agree that it is a great sounding near field desktop speaker, or computers speaker.

404584d1394377264-foam-core-board-speaker-enclosures-dcr-vifa-photo-06.png


404601d1394377728-foam-core-board-speaker-enclosures-dcr-vifa-photo-07.png


Cheers,
X

Sound Clip Here:diyAudio
 

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I noticed this build last nigth xrk - and I agree with you it look quite nice! I shouldnt be feeling the temptation to build a pair at this moment but I do... I have done many similar builds (wrapped) but that was related to RC model aircraft, wings specifically :D

Not sure I can resist... :p
 
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Sims of DCR

Here is the simulation in Akabak without and with the 1.0 mH inductor + 10 ohm resisitor + 0.47 uF capacitor BSC. Also shown are the impedance and cone displacement. I used a 4 volt rms driver voltage which represents the max needed for the 80 dB sound level for the intended SPL at listening position of 1m near field.
 

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Founder of XSA-Labs
Joined 2012
Paid Member
I noticed this build last nigth xrk - and I agree with you it look quite nice! I shouldnt be feeling the temptation to build a pair at this moment but I do... I have done many similar builds (wrapped) but that was related to RC model aircraft, wings specifically :D

Not sure I can resist... :p

You are an expert at single sheet wrapped FC construction then - go for it!
:worship:
:)
 
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Joined 2012
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Wesayso,
I was thinking of making FC 25-driver towers believe it or not! I could make them in 5 driver modules (20 in tall) and wire them all in series with a banana binding post on the back. They will be quite lightweight and I was thinking of simply using velcro to attach and stack the 5 cabinets together, then run a bus up and down the banana plugs to parallel the 5 boxes for parallel/serial wiring. Now I have a tower that will is easy to make, costs nothing besides the drivers and banana jacks, and I don't have to worry about hurting the kids if it falls on them! :D
 
Same did I lol bit I decided against it :eek:
But this design is super sweet and deserve a go from my end... I love the design/look of the Magico Mini and this DCR design is similar, plus it utilize just a single Vifa - cant get any simpler than that ;) I have 54units on standby :cool:
 
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More measurements with BSC applied (via EQ)

I broke down and ordered a pair of 1 mH coils, a 10R 10 watt resistor, ad a 0.47uF coupling cap for the BSC circuit. They cost more than the drivers! I hate passive XO components for this reason but they let you keep a speaker simple in operation for hooking up to any amp.

In the meantime, I implemented the BSC using the PEQ in miniDSP but otherwise running fullrange just to see how it would look/sound. The measurements were made with the speaker 3 in away from a back wall (similar to how they would sit on my desk or bookshelf) at 42 in driver height above the ground. I used the TPA3116D2 amp and miniDSP for the EQ duties.

Here is a measurement of the speaker without any EQ (magenta), with the BSC applied (red), and with some auto-REW (blue) to flatten the response below 500 Hz.

405085d1394537242-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-bsc-rew-compare.png


Here is the BSC+REW result in detail with the acoustic phase shown. The phase is linear and flat above 500 Hz which means it will really be nice for imaging and sound stage accuracy.

405086d1394537242-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-bsc-rew-spl-phase.png


Here is the harmonic distortion which is great above 300 Hz but below starts to get a little ratty (especially that peak near 130 hz which is the fs of the driver) now that I have applied the REW. I wonder if I had just left those bass peaks alone if I would even hear them - it would keep distortion lower. I guess it si still pretty good considering I am asking the little 3.5 inch Vifa to pump out 50 Hz bass notes.

405087d1394537242-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-bsc-rew-hd.png


So how does it sound with the BSC and REW applied? In a word - Fantastic! I really like the clarity of the mids and highs and the presence of the adequate bass which sounds good for most listening at near field. Nearfield at desk is more like 0.5m away so the SPL levels needed are very low. This is good because with the BSC circuit applied the efficiency is like 75 dB 1 watt at 1 meter. Good thing I have 8 watts on tap and I am listening at 0.5m :D

I can't wait for the BSC circuit parts to arrive and to find time to make the stereo pair. These are turning out to be a very simple great sounding alternative when I want to just relax with simple music and simple speakers without all that digital hoohah and stuff :)

If you want to hear what the speaker sounds like before and after BSC applied, listen to this clip which demonstrates the effect in real-time. It starts out raw with no BSC (kind of unpleasant and unlistenable) and halfway through, BSC is applied and it just smooths out... ahhh that is what the music was supposed to sound like!

The second clip is an example of what this speaker sounds like with BSC and the REW applied.
 

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Very nice plots xrk!
I already have a pair of 1.0mH coils / MOX 10W 3.9ohm resistors on hand so the BSC is already sorted... :) Need to build a pair of these... :superman:

Since foamboard is difficult to obtain around here and 3&6mm Depron (XPS foam) readily available I might use that to build these. However Depron is not as stiff/rigid as Foamboard but the curved shape will help in that regard. Could preshape 6mm gypsum boards to act as support, they add great weight also :scratch:
 
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Halair,
Thanks. I am glad you will give this a try. Yes, the curved shape gives it much additional rigidity like a cylinder. I think Depron XPS sheets can work - just add something form for the backing on the front panel for the driver to mount. The Gypsum board sounds perfect for this. You can use that for the flat top bottom and divider panel. I am quite amazed how full bodied the bass sounds. I got a chance to put a bunch more test songs through and it is handling them all well - that is, it appears to be a good all around we speaker. I discovered the PEQ dialog in Jriver that lets me apply the identical PEQ I used in miniDSP - so that is great. If you plan to drive this purely from a PC you probably don't need BSC as it can be done all digitally in software.
Good luck!
X
 
If you plan to drive this purely from a PC you probably don't need BSC as it can be done all digitally in software.
Good luck!
X

Indeed! None of my personal speakers have any passive filters built in. I have been using DSP filters exclusively for some years now. Of course, I have to design the passive filters to include in my commercial sales, as DSP is not yet widespread.

Bob
 
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Bob,
I know you use nanoDIGI in hardware. What software player packages do you use that have the DSP PEQ capability built in? Jriver works great but I was wondering if a free alternative is available.
The quality of the sound from Jriver player going through DSP to perform the BSC is really good - it may have to do with the lossless compression format that it uses - APE. Big files compared to mp3 (4x to 6x larger due to circa 700kbps nitrates), but it sure sounds good.
 
Prior to the miniDSP, I used the 31-band "Graphic Equalizer" in Foobar2000. I think it is FIR, but I am not sure. I know it isn't PEQ, so.... I found the EQ at least as good as passive filters and a lot easier to implement. The secret, of course is be gentle. I am using the miniDSP/nanoDIGI primarily because I need a digital XO for my 2-way's.

Bob
 
Bob,
I know you use nanoDIGI in hardware. What software player packages do you use that have the DSP PEQ capability built in? Jriver works great but I was wondering if a free alternative is available.
The quality of the sound from Jriver player going through DSP to perform the BSC is really good - it may have to do with the lossless compression format that it uses - APE. Big files compared to mp3 (4x to 6x larger due to circa 700kbps nitrates), but it sure sounds good.

You could use Foobar Download foobar2000 and optional components coupled with the VST wrapper here yohng.com Foobar2000 VST Wrapper to run the EasyQ PEQ RS-MET.

I can always post help/instructions if you run into issues with any of the above.
 
The problem with the Yohng wrapper is that it is not very stable. I have tried it with some different plug-ins and always have found the results not worth the bother. I don't use many plug-ins. At the moment, all I have is an SRC, the graphic EQ and the advanced limiter. Even the SRC may go. My next quest will be to see if there is any difference between coming out of the computer USB or HDMI. Always something else to try.

Bob
 
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What is SRC plugin? Now that you point out some potential instabilities that may plague shareware - it may make sense to buy Jriver for $50. It is a pretty slick package that comes with most of the popular plugins already preloaded. I am still using the soundcard built into the desktop PC motherboard - which seems to sound pretty good. I bet switching to an external DAC might just blow me away. I only have USB and 1394 interface on this 8 yr old PC though. Even my newer laptop has HDMI. MiniDSP has an HDMI input DSP now.