Something small and cute - Fostex FE126eN

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chris661
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#1 Something small and cute - Fostex FE126eN

Post by chris661 »

Hi all,

Thought I'd share this, since it effectively cost £20 to do (already had the drivers, wood, etc), but I'm getting really good sound here.

The standmount full-range + sub cabinets have been sat for a while, which is a real shame because the cabs are nice, and so are the drivers. Trouble is the Fostex doesn't work nicely with the Tang Band mini-subs. Just when the subs are getting going, the Fostex drivers have gone all shouty - the Fostexes aren't meant to go loud.

Picture of those cabs, finished by our own Toppsy:
Image

So, I've taken the Fostex drivers out and put the rest aside for a moment, and I got to thinking - can I get full-range out of this single cone?
Of course, you can build a big horn and call it good. That's one way, but I don't have space or inclination for anything like that. I want something small that still does bass. We know these Fostex FE drivers have tiny rated Xmax, but generally go to a couple of mm travel before anything nasty happens.

I wanted to tune low, and use a small box. That means passive radiators. A port that still fits the box would run into chuffing as soon as the driver thought about moving.

So, went on eBay and found some of these:
Image

Decided on 2 per side for now, which is only just enough. Stuffed the Fostex driver and a pair of PRs into a box around 6"x6"x9", and put plenty of filling in. Measure twice, cut once really applied here. My hand-saw skills are bad, but double-checking measurements would've made this look neater.
Image
Image

Plugged them in and fired it all up, and its obvious some EQ would be needed. That's okay, my simulations suggested the same.
Here's the response of the drivers in the sealed compartments of the old speakers:
Image
The response with the PRs installed looks quite similar, with a little more at 50Hz and a little less below.

The spike at 6.6kHz is the signature of these speakers, but I want something reference-flat, so off it goes. There's a couple of low-Q filters to tilt the response to my liking, and a bass boost. The passive radiators with no added mass tune to 50Hz. Adding mass will take the tuning down, requiring more bass boost to get them flat, and more excursion used. That's a compromise - maximum SPL vs LF cutoff. 50Hz is good for now, though I do plan on messing with that.

With EQ added, they sound very very good. The phase response fits in a 120-degree window from 100Hz-10kHz. No time-domain problems due to crossovers - there's still that purity to the sound. Bass is solid, treble is smooth and detailed.
However, I'm still squeezing an honest 50Hz out of a box I can get my hand around. The compromise there is that, when playing material with some LF content, maximum SPL is limited to around 85dB peaks at a 4m listening positionn(my test was One Day Like This by Elbow). Above that, there's an obvious "woof" sound when the kick drum happens - the driver has run out of travel. That usually happens before the midrange gets shouty, which is nice.
That said, 85dB peak is enough for most listening, and you can play whatever you like. The Fostex shout is effectively tamed, and you've got a very nice little monitor.

In summary:
- had the parts, paid £20 for some passive radiators on eBay
- not much SPL, but what they do is very nice
- tiny box

If anyone has some of these Fostex drivers around, I'd highly recommend you give this a go.

Chris
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#2 Re: Something small and cute - Fostex FE126eN

Post by Toppsy »

Ah, I remember building those for you Chris. Here is a better photo of the finished cabinets without the drivers:
Image
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#3 Re: Something small and cute - Fostex FE126eN

Post by chris661 »

Bit of an update - the passive radiators were replaced with bigger ones, since the 3" ones were going nonlinear when the volume went up - as they get near the end of their travel, the suspension gets nonlinear and messes with the tuning.
I'm now using some butchered 4" Wharfedale drivers from the Modus cube speakers. 2x PRs per cabinet, so they're working in their linear range.

I added a lot of mass (3x M10 nuts per PR) and got the tuning down to 40Hz. With a lot of boost at the bottom end, they'll go flat to 40Hz, which is really cool from such a small box. The problem is, though, that now the PRs are helping right at the bottom end, the 55-80Hz region is effectively being handled by just the little Fostex driver, so there's quite a lot of cone excursion being used in that range. They'll go to just above talking volumes at a 10' listening distance before distortion happens.
They'd be great for desktop speakers where going loud just isn't a concern, but I've hit the end-stops here. It would've been nice to get 30Hz (as low as most music goes), but the Fostex driver would be struggling at background volumes, which is no fun.

So, I think the experiment is nearly finished. I plan on getting the passive radiator tuning back up to around 60Hz, which is where most of the thump is in music. That'll mean the passive radiators will be reducing the Fostex driver's excursion where it's needed most, so I'll gain plenty of headroom.


The rest of the system is a bit of a hodge-podge at the moment, but I've just finished working on a GL78 (on long-term loan from Emma's dad), replacing the stylus and the tonearm bearings. The turntable is sitting on top of the subwoofer, but that's okay - the sub is dual-opposed, so the cones move in opposite directions and the vibration cancels out. Running a full-power 10Hz sine wave, I can't feel the cabinet moving at all. The phono preamp is borrowed from Dad, an old NAD one. That's running into a Behringer UMC202HD soundcard which I'm just using as a volume control before sending to the amps.
I'm going to play with adding a second sub to the setup today (by one of the seats so it'll double as a table), mostly to help smooth out room modes.

Eventually I'd like to have some kind of integrated amp with a MiniDSP in between the pre/power sections, but that can wait for when business picks up some more.

Chris
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#4 Re: Something small and cute - Fostex FE126eN

Post by IslandPink »

Good effort ! Nice driver in many ways. I'd still like to try something with these fostex units as mentioned in one of the other threads - find which part of the cone is resonating when you hit one of those annoying treble peaks , and try & place a mechanical mask ( phase plug or ring ) in front of the cone ( not touching ) to see if you can effectively create a mechanical 'notch filter' . Anyway, that's another story !
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#5 Re: Something small and cute - Fostex FE126eN

Post by Scottmoose »

Up to a point, that's what the cone modifications to Chris's units are aimed at. You can see the damping added to the cone (glossy ring) in addition to the EnABL mod. The latter has progressed significantly since those units & Dave, until his health issues, had gone even further in targeting excess modes.
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#6 Re: Something small and cute - Fostex FE126eN

Post by Ali Tait »

IslandPink wrote: Fri Apr 21, 2017 12:50 pm Good effort ! Nice driver in many ways. I'd still like to try something with these fostex units as mentioned in one of the other threads - find which part of the cone is resonating when you hit one of those annoying treble peaks , and try & place a mechanical mask ( phase plug or ring ) in front of the cone ( not touching ) to see if you can effectively create a mechanical 'notch filter' . Anyway, that's another story !
Never mind that, get those horns finished! :D
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#7 Re: Something small and cute - Fostex FE126eN

Post by chris661 »

IslandPink wrote: Fri Apr 21, 2017 12:50 pm Good effort ! Nice driver in many ways. I'd still like to try something with these fostex units as mentioned in one of the other threads - find which part of the cone is resonating when you hit one of those annoying treble peaks , and try & place a mechanical mask ( phase plug or ring ) in front of the cone ( not touching ) to see if you can effectively create a mechanical 'notch filter' . Anyway, that's another story !
I think the 6.7kHz peak is a full-wave radial cone breakup. The frequency of the breakup peak coincides pretty much exactly with the distance from the cone neck to the edge. That assumes that the speed of sound in that particular paper mixture is the same as it is in air (IIRC someone said it's similar in paper and in air, but I haven't checked).
Scottmoose wrote: Fri Apr 21, 2017 1:21 pm Up to a point, that's what the cone modifications to Chris's units are aimed at. You can see the damping added to the cone (glossy ring) in addition to the EnABL mod. The latter has progressed significantly since those units & Dave, until his health issues, had gone even further in targeting excess modes.
Damn, now I wish I'd held out for updated treatments. A little electrical EQ gets these units sounding very nice, though.


As a thought, I'm pretty sure microphones use a series of holes cut into a plastic disc to create a set of resonances to alter the high-frequency response. Perhaps it's possible to do something similar, and tune them to cut down a specific peak..?
I'd have to have a think about that, though it seems plausible. Then again, it'd likely put a lowpass filter on there above the desired notch frequency, so even if you could flatten the 6.7kHz peak, you might lose out above that. Not great. Might be worth an experiment or two, though.

Chris
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#8 Re: Something small and cute - Fostex FE126eN

Post by Scottmoose »

As I recall it is (a radial mode). It's always a balancing act & Fostex were targeting a mechanically efficient cone (vis-à-vis the transverse wave) at the price of some linearity.

Well, you know how these things are Chris; they tend to develop over time & you have to pull the trigger at some point or you're forever waiting for 'the next thing'. I don't think it's been a night / day upgrade over what you have -subtle improvements, but you've probably got 98% already.

As in a variation on a grill? Sure, quite a few [hard] dome tweeters & others do exactly that to improve linearity. Some pull double-duty including a small Helmholtz to prop up the inevitable mass-induced HF drop-off of an aluminium dome.
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#9 Re: Something small and cute - Fostex FE126eN

Post by IslandPink »

Ali Tait wrote: Fri Apr 21, 2017 1:21 pm Never mind that, get those horns finished! :D
Better not mention that I'm printing photos instead now !
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#10 Re: Something small and cute - Fostex FE126eN

Post by ed »

hey Mark

you printing photos now?
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#11 Re: Something small and cute - Fostex FE126eN

Post by Ali Tait »

:mrgreen:
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#12 Re: Something small and cute - Fostex FE126eN

Post by IslandPink »

Yeh actually the stuff's hanging up drying in the back kitchen now :D
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#13 Re: Something small and cute - Fostex FE126eN

Post by Dave the bass »

You and Robert Johnson, I think he was into photography as well cos he sang about coming into his kitchen (cos its gonna be rain'in outside).
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#14 Re: Something small and cute - Fostex FE126eN

Post by chris661 »

Last update - I've got the PR tuning to 65Hz, which needed a single M10 nut per passive radiator, held with a glued-in M5 T-nut and a bolt.

They go pretty loud on their own, and go reasonably low. Switch on the sub amp and it's flat to 10Hz in-room. It took a while to get right, but there's no obvious change to the sound. It just goes lower.

I'm very happy with the sound I've got here. There's a couple of different presets saved since sometimes the speakers are on the mantlepiece, and sometimes they're on stands. Difference is about 6dB below 150Hz ish.
The subs are a pair of JBL GTO1214 in a dual-opposed sealed box on the left, and a P-Audio 21" monster on the right, also in a sealed box, pretending (badly) to be a side-table. The turntable (GL78) is on top of the JBL sub, near the amps (NU3000DSP for the Fostexes, NU6000DSP for the subs).

Chris
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#15 Re: Something small and cute - Fostex FE126eN

Post by cressy »

chris661 wrote: Wed Apr 26, 2017 6:59 pm The turntable (GL78) is on top of the JBL sub, near the amps (NU3000DSP for the Fostexes, NU6000DSP for the subs).

Chris
You might get a bit of rumble from it during playback our chris :D
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