FE126eN Folded Voigt pipe - construction thread

[chris661]

Hi guys,

Been saving up for a while, and I've ordered a pair of fully done up FE126 drivers off Dave (who has been a great help, as well as Scott and the others).

Here's a link to the construction plans...

http://www.diyaudio.com/forums/attac...e-ml-voigt.gif

Anyway, got most of the pieces cut at a CNC place near me (£30+VAT for all the cutting and a sheet of 15mm MDF). When Dad picked them up, they were 18mm MDF, so, after a brief phone call, they sent someone over with the parts in 15mm.

Well, I'm off to start building. Pictures will be posted shortly.

Chris

[chris661]

Some pictures for you...

The fronts aren't glued on (neither is the internal partition - I need the driver to be able to cut it accurately, and test fit before gluing - wouldn't be easy cutting it down when it's in situe), they're just being used to spread the weight a bit.

So, it's a waiting game now...

[doorman]

Looks good!
I'd also suggest a round-over on the backside of the driver cut-out, and T-nuts, or equivalent are a must in MDF!
Nice job. be sure and follow up when complete!
Don

[planet10]

Looking good (much as i hate MDF)... the transit time should give you some time to apply multiple layers of something on the inside to stiffen them up.

What Don says about fasteners and driver cut-out.

At least 1 set of this design by Tim Forman has been built with good reported results.

dave

[chris661]

Don - the plan is to 45 degree chamfer them from about half way. Hopefully, that'll suffice.

I'm thinking of keeping the front temporarily removable (hold it down with duct tape or maybe just get some rope around it, so I can experiment with stuffing/lining when the time comes.

I have a question. In a "standard" Voigt pipe, the expansion is kept linear, as it's effectively a triangular prism. However, with the design being folded, the expansion isn't linear any more. Perhaps some 45 degree batons of the appropriate size should be added?

[planet10]

You could add deflectors, but they are probably unnecessary. the expansion at the corners act as a low pass, meaning either less ripple, or less stuffing leading to greater bass support.

dave

[chris661]

Brilliant, thanks Dave.

[chris661]

Well, I've rounded the driver cut-out with a router, and had been sanding one of the panels down (glue has thickness that I failed to account for) when the rain came. So here I am posting pictures.

The last picture is the panel before I started. 30 minutes later and it's nearly there.

[mcr483]

is there any chance to put the driver at the narrower side?

this is very intresting enclosure but small size means bass limitation.
what is the lowest frequency?

[chris661]

Hi,

I built these some time ago, and the drivers have (just!) finished bedding in.

I'd say they're rolling off around 70Hz in room, after stuffing the tapered end (to me, stuffing the tapered end and around the driver gave improved midrange, with small losses in the bass). Without stuffing, they'll hit more like 60Hz with some authority. Ideally, these would need a subwoofer, but for smaller-scale music, the low frequency re-enforcement isn't missed.

Here come some listening impressions...

- the higher registers are fantastic, cymbals sound suitably metallic, you can tell exactly when they're damped and when they're hit and allowed to ring. Snare drums snap with appropriate "speed" and impact. Sibilance was a problem during bed-in, but has now settled down after a good thrashing (went to ~6mm p/p of cone travel, a few hours at a time).
- the midrange, especially vocals and guitar, are amazing. Anyone contending the full range magic hasn't heard something like this. Stereo imaging extends to the corners of the room (instead of the 1/3 of the room between them), with some singers managing to be waaay off to one side (past the speaker), and yet still part of the music. Impressive stuff, I've not heard much like this.
- the lower registers, which not all there, goes low enough to cross to a subwoofer (they're rolled off electrically at 80Hz, but as I said earlier, they're good for a little lower). The tonality and texture of instruments like bass guitars is still there, despite the missing fundamentals.

The stuffing experimenting I did:
- first I tried no stuffing at all. Pretty good, bass was reasonable out in open space, but began to boom when put near a wall. While impressive for all of 5 seconds, the sound quickly became annoying, so I moved them into free space again.
- Next, I tried stuffing the tapered end, and some loosely around the driver itself. The midrange cleared up a little (perhaps there were some reflections comming back through the cone), at the expense of a little bass in free space. Moved a little closer to the wall and this came back.
- Finally, I moved the stuffing to the ported end of the cabinet, leaving some around the driver. This left a thin-sounding speaker, where the voigt pipe design wasn't contributing enough to the lower midrange. This would've meant crossing over to the woofer at more like 200Hz, at this point, they'd be easily locatable.

So, I moved the stuffing back to the tapered end, added a capacitor to the amplifier input, then played with integrating them with a subwoofer.



I know the picture isn't the best of quality, but you get the idea. Since that was taken, I've added Neutrik SpeakOn connectors to the back. More pics will follow later.

Chris

PS - thanks to Andrew for taking the last picture at a recent meet.