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New project - Fostex FE126eN in a small PR enclosure
New project - Fostex FE126eN in a small PR enclosure
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Old 18th January 2017, 02:15 PM   #1
chris661 is offline chris661  United Kingdom
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Default New project - Fostex FE126eN in a small PR enclosure

I have a pair of Fostex FE126eN drivers treated by Dave at P10, and it seems a shame to have them sitting around, not doing anything.

A little history on how I've used them so far...

- Small folded Voigt pipes. Good down to 100Hz or so, but probably needed some BSC. Great for small-scale acoustic music. Got better with subs. See the end of this post for a picture.
- Standmount FAST speaker with TB W6-1139 mini-subs. That was pretty good, but the Fostex driver got shouty before the sub got going. Bit of a mismatch there.
- Running full-range in the small sealed compartment of that FAST. With EQ, it worked pretty well, but had very limited power handling down low.

After that lot, I went multi-way for a while. I do feel there's something not-quite in the midrange, though, so I'm back to these Fostexes.


With the very low Qts, this driver doesn't ask for much in the way of cabinet size. First up, I ran a simulation of an ML-TL, which suggested I could get to 30Hz in a small floorstander. The problem is, however, that you've run out of Xmax at less than 90dB. That's not great for a floorstander.
I wonder if we can get that sort of performance out of a desktop system...
So, I played around with Hornresp and modelled a 5L ported box, with a port with a very small area and fairly long length, tuning down around 30Hz. Not bad. A rather sloped down response (15dB down at 30Hz), but usable. A port that small (2cm^2 area) will chuff as soon as any bass comes along, so I started looking for PRs.

I went on eBay and found some 3" passive radiators going pretty cheap, so I've picked up 6. The plan is to have 3 in a line down the back of the enclosure, build a box just about big enough to fit everything in, and then EQ the result.

It won't be loud, but 30Hz from a smallish desktop speaker would be cool.
If not, I'll change the mass on the PRs and raise the tuning until I like the balance between low-frequency output and maximum SPL.

I plan on using a Behringer NU3000DSP for initial testing and listening. I can apply all the EQ I'd ever want with that. If I like the result, I might see about getting a small amp in a box from eBay and building the EQ into that.

Something to play with, anyway.

Chris

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Old 21st January 2017, 12:21 AM   #2
Jeffrey 01 is offline Jeffrey 01  United States
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Sounds like you have done your home work. I was going to use passive radiators but, my engineering friend told me it's to much time and work to get it right? So I never got into it. Also the only designs I have heard with P.R. are the vendersteens and the golden ear speakers. please keep us updated. I am wondering how it will turn out? Jeff

Last edited by Jeffrey 01; 21st January 2017 at 12:23 AM.
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Old 21st January 2017, 02:52 AM   #3
chrisb is offline chrisb
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FWIW, I've played with these little buggers in a few designs myself- actually only just BLHs of some variant, including the horrid little hybrid design from Fostex -well, at least I thought they were.

Hornshoppe Horns -"roughly based on" the Buschhorn MkI, if I understood one of Ed's long ago posts on the Decware forums. If I got that wrong, I know he'd forgive it.
Ron Clarke A126 - not a tiny thing
Scott Lingdren's Valiant, BK12, and Frugel-Horn Mk3. I'm sure he has other designs for this driver I've not seen, or just couldn't get around to.
Properly executed and situated in a corner for reinforcement, a rear mouthed BLH, or BIB for the FE126 probably don't need any extra help via PRs, but high-passing them and using separately powered (sub)woofer(s) almost never hurts anything except the budget and WAF
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Old 21st January 2017, 03:55 AM   #4
Jeffrey 01 is offline Jeffrey 01  United States
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The fostex fe126en will always hold a soft spot for me. I have enjoyed it over the years from stock and modded by me. Jeff.
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Old 22nd January 2017, 09:02 PM   #5
chris661 is offline chris661  United Kingdom
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So the PRs have arrived, and I've also ordered some neodymium disc magnets. I'll glue the first magnet to the back of the PR, and then I can add pretty much any mass I like. Easy to remove, too.
Though I can see that the magnets might add distortion by pulling towards the steel frame of the PRs. Hmmm. Maybe blu-tak instead.

Jeff, this is a try-it-and-see sort of project. I have plenty of measurement gear here, so will be finding and adjusting the LF tuning that way. Of course, I'll be posting graphs and listening impressions when they happen.

Chris, I've heard them in a couple of BLHs. Wasn't keen on them in the FH3 compared to Mark's Alpair 7 drivers (might've been first gen, not sure). For sure, adding woofers helps these drivers at moderate SPLs. However, I did find that, when turned up, the harmonic distortion from the Fostex drivers means they sounded louder than the woofers I paired them with, so I was constantly messing with the relative levels. I'm hoping that using them for the entire range will mitigate that.

I also plan on seeing what the midrange and treble looks like with these drivers. I've never measured them before, but I know there's some peakiness up there.

Chris
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Old 22nd January 2017, 09:07 PM   #6
Jeffrey 01 is offline Jeffrey 01  United States
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Sounds good. I can't wait to see the progress of this project. Cheers Jeff
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Old 23rd January 2017, 01:09 PM   #7
chris661 is offline chris661  United Kingdom
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So I got one of the old FAST speakers out to have a play. Always interesting to revisit old projects.

Click the image to open in full size.

A few tasting notes, before the graphs.
- The Fostex shout is obviously there, with a combination of upward-sloping response and a 6dB narrow 6.6kHz peak.Going to around 30-degrees off axis levels out the rise a little, but the peak is ever-present.
- The ported enclosure for the woofers isn't quite working right - there's no obvious notch in the nearfield cone measurements. Oh well.
- The Fostex driver unloads pretty gracefully. You get 3mm p/p travel before they sound "woofy" when the kick drum happens.
- EQing the sealed Fostex down to 50Hz blows through the excursion quickly.

On the latter point, I sim'd a sealed and ported box for excursion with Hornresp. It looks like the ported box has very little excursion below 70Hz or so. Applying a fairly steep high-pass filter at 70Hz to the sealed + EQ'd box meant it'd go much much louder before excursion became a problem. That gives me hope for this project.

Click the image to open in full size.

Here's a nearly-on-axis measurement of just the Fostex driver, with EQ simulated. In practice, the EQ helps the midrange a lot - by knocking down the peak, the waterfall plots etc all clean up. THD rises steeply towards 50Hz, but stays below 10%. I hope PRs reducing the excursion will help lower that.

This is in-room, around 2' away, 1/24octave smoothed.
Click the image to open in full size.

I'm going to make some sawdust now. Having seen how little excursion you get with the Fostex drivers, I'm going to try just two PRs in a smaller box. The PRs are good to more like 5mm p/p until the suspension noticably changes compliance, so two will be more than enough.

Chris

Chris
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Old 23rd January 2017, 02:12 PM   #8
chris661 is offline chris661  United Kingdom
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PS - one last shot with the passive radiators.

Click the image to open in full size.

Sawdust making is going okay, but the making of usable panels, not so much. That's the last time I clamp 4 layers together and cut them all with a hand saw.

Chris
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Old 24th January 2017, 02:46 PM   #9
chris661 is offline chris661  United Kingdom
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They're up and running. The passive radiators with no added mass tune to 50Hz, so I've EQ'd accordingly. Set them up in the living room, and I'm very impressed. The maximum volume 4m away leaves something to be desired - when you're listening to some music, not loud, but above background level, that's where Xmax just starts to become a problem. You can play acoustic guitar + singer music and go louder, but where's the fun in that?

The limited volume has one up-side, though - you can't run loud enough for midrange distortion to be a problem.

In conclusion - they're tiny, drop low, and the mid-high range still has the magic. They won't go loud, but they will go loud enough for what I'm after.

I was planning on messing with tuning for the next hour or two, but that really can wait. What I'm hearing is too good.

Chris
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Old 25th January 2017, 12:37 AM   #10
mor2bz is offline mor2bz  United States
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Box size please? I have a pr of these drivers in their factory boxes and it seems that
nobody except ed knows quite what to do with them.

will you take a stab at a passive notch filter? I tried once and did not hear any difference.
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