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
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
An externally hosted image should be here but it was not working when we last tested it.
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
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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
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
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
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
So I got one of the old FAST speakers out to have a play. Always interesting to revisit old projects.
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.
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.
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
An externally hosted image should be here but it was not working when we last tested it.
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.
An externally hosted image should be here but it was not working when we last tested it.
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.
An externally hosted image should be here but it was not working when we last tested it.
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
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
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
The box is currently 6"x6"x9", hwd. This design needs proper EQ (there's around 17dB of boost at 50Hz), so I won't be bothering with a notch filter. You'd probably need a Zobel, too, to counteract the inductive effect of the voice coil.
For my drivers, they need 6.6kHz, Q=10, -6dB. YMMV, since mine are phase-plugged and treated.
Chris
For my drivers, they need 6.6kHz, Q=10, -6dB. YMMV, since mine are phase-plugged and treated.
Chris
Okay, here's a couple of pictues. They're ugly, but they're very small and probably fairly well-sealed. A lot of PVA glue went in, since my cuts were, lets say, less than optimal.
I measure 85dB peaks (c-weighted, fast) on my SPL meter at 4m distance before the sound noticably "thickens" as distortion rises. At 1m (desktop use) that should be 97dB, which is more than enough.
The SPL test music was this: https://www.youtube.com/watch?v=0NFV8dHrZYM
Reasonable amount of stuff going on, but dubstep etc would punish the limited excursion so you'd probably get lower SPLs there.
Having listened for a while, I'm going to build some nicer cabinets, maybe with a little bracing, and make some attempt to finish them, maybe with some rosewood stain as I do with my PA speakers. There'll also be facilities to mount them on mic stands, as most small monitors do.
I do quite a lot of work involving recording/mixing on-location, and these are my new go-to.
Before, it was between some Bose MusicMonitor active desktop speakers (not bad, but stopped at 80Hz) and some Behringer B3030A monitors. The 3030A are pretty good, much louder than these Fostex ones, but the crossover is 3.4kHz - way too high for a 6.5" midbass, so there's an, er, interesting power response there.
I'm very pleased with how these came out. I'm going to mess with the PR tuning a little, but I think a box this small that's flat-to-50Hz is pretty impressive.
Just had a look at the phase plot on REW. Not quite horizontal (but this is no EQ), but close. 100Hz-12kHz fits into a 120 degree window.
Chris
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I measure 85dB peaks (c-weighted, fast) on my SPL meter at 4m distance before the sound noticably "thickens" as distortion rises. At 1m (desktop use) that should be 97dB, which is more than enough.
The SPL test music was this: https://www.youtube.com/watch?v=0NFV8dHrZYM
Reasonable amount of stuff going on, but dubstep etc would punish the limited excursion so you'd probably get lower SPLs there.
Having listened for a while, I'm going to build some nicer cabinets, maybe with a little bracing, and make some attempt to finish them, maybe with some rosewood stain as I do with my PA speakers. There'll also be facilities to mount them on mic stands, as most small monitors do.
I do quite a lot of work involving recording/mixing on-location, and these are my new go-to.
Before, it was between some Bose MusicMonitor active desktop speakers (not bad, but stopped at 80Hz) and some Behringer B3030A monitors. The 3030A are pretty good, much louder than these Fostex ones, but the crossover is 3.4kHz - way too high for a 6.5" midbass, so there's an, er, interesting power response there.
I'm very pleased with how these came out. I'm going to mess with the PR tuning a little, but I think a box this small that's flat-to-50Hz is pretty impressive.
Just had a look at the phase plot on REW. Not quite horizontal (but this is no EQ), but close. 100Hz-12kHz fits into a 120 degree window.
Chris
Here we go:
3'' Black Square Passive Bass Radiator Woofer Radiators Passive Speaker UK | eBay
Just a quick note to say I've got the measurement mic out and once again I'm horrified by what the average room does to any careful LF tuning.
Chris
3'' Black Square Passive Bass Radiator Woofer Radiators Passive Speaker UK | eBay
Just a quick note to say I've got the measurement mic out and once again I'm horrified by what the average room does to any careful LF tuning.
Chris
So, doing a little testing I think there's more to be had here. If I play a 50Hz tone, the excursion on the Fostex drivers is minimal, but the PRs move quite a lot. If you keep increasing the level, the Fostex driver suddenly undergoes huge excursions.
I think perhaps the PR tuning frequency is changing as volume goes up. In that case, its entirely possible that the bottoming out sound was also the PRs, and the Fostex drivers have more to give.
So I'm going to cut a couple more holes in one of these boxes and see what's what. I was hoping to keep the PRs just on the back of the cab, but that's now out. Maybe I can load them into slots or something on the finished product.
Chris
I think perhaps the PR tuning frequency is changing as volume goes up. In that case, its entirely possible that the bottoming out sound was also the PRs, and the Fostex drivers have more to give.
So I'm going to cut a couple more holes in one of these boxes and see what's what. I was hoping to keep the PRs just on the back of the cab, but that's now out. Maybe I can load them into slots or something on the finished product.
Chris
There's a rule of thumb around that says the passive radiators should have 2x the volume displacement of the active driver.
Lets investigate, using one of my favourite online tools: Piston Excursion calculator
We want equal SPLs from the passive radiators and the active cone. The difference is that the excursion peak for the active cone happens at a higher frequency than the passive radiators.
Lets say we want 85dB and we're gonna EQ everything flat. The passive radiators are tuned for 50Hz, so to get 85dB at 50Hz from a single 4" PR, you need 4.9mm one-way travel. The main driver's excursion peak happens at 65Hz, give or take. To hit 85dB at 65Hz, you only need 2.9mm of travel for the main driver. That's just under a factor of two in the displacement requirements. This seems to hold at every frequency I tested.
No wonder the 3" PRs I have at the moment are struggling - the pair of them have half of the volume displacement of the Fostex driver.
I've ordered a set of 4x 4" PRs. They'll need a new box making for them, but that's okay. I have lots of bits of MDF lying around and this is rather fun.
Similar layout, 2x rear-firing PRs, front-firing Fostex driver.
Then I'll do some measurements, apply EQ and have a listen.
If I get another few dB from these little boxes, I'll be very happy.
Chris
Lets investigate, using one of my favourite online tools: Piston Excursion calculator
We want equal SPLs from the passive radiators and the active cone. The difference is that the excursion peak for the active cone happens at a higher frequency than the passive radiators.
Lets say we want 85dB and we're gonna EQ everything flat. The passive radiators are tuned for 50Hz, so to get 85dB at 50Hz from a single 4" PR, you need 4.9mm one-way travel. The main driver's excursion peak happens at 65Hz, give or take. To hit 85dB at 65Hz, you only need 2.9mm of travel for the main driver. That's just under a factor of two in the displacement requirements. This seems to hold at every frequency I tested.
No wonder the 3" PRs I have at the moment are struggling - the pair of them have half of the volume displacement of the Fostex driver.
I've ordered a set of 4x 4" PRs. They'll need a new box making for them, but that's okay. I have lots of bits of MDF lying around and this is rather fun.
Similar layout, 2x rear-firing PRs, front-firing Fostex driver.
Then I'll do some measurements, apply EQ and have a listen.
If I get another few dB from these little boxes, I'll be very happy.
Chris
The 4" PRs arrived with a resonance in the 80Hz region, and my attempt to add mass by gluing an M6 nut in there went wrong (don't use PVA), so I'm waiting on another set from a different manufacturer.
Further design tweaks:
- PRs on opposite sides of the box for force cancellation. The new PRs might have quite a lot of mass added, so this will help to stop them walking around. One PR on the front, one on the back.
- 35mm tophap stand mount. Ultimately, these will be used for on-location monitoring, so being able to get them to a good working height easily is a good thing. I'm not lugging HiFi stands around with me.
- SpeakOn socket(s) on the back. The "master" one will have a 4-pole in and a 2-pole out, and the other will just have a 2-pole in. 4-pole cable from the amplifier keeps things neater, though there's still the option to run 2-pole cables direct from the amp to each speaker.
I haven't finalised the tuning yet, still waiting on the correct PRs. I'll also either build or buy a little case to put them in. Maybe something like a 6U amp rack with the amp in the bottom, and then foam inserts to sit the speakers into.
Chris
Further design tweaks:
- PRs on opposite sides of the box for force cancellation. The new PRs might have quite a lot of mass added, so this will help to stop them walking around. One PR on the front, one on the back.
- 35mm tophap stand mount. Ultimately, these will be used for on-location monitoring, so being able to get them to a good working height easily is a good thing. I'm not lugging HiFi stands around with me.
- SpeakOn socket(s) on the back. The "master" one will have a 4-pole in and a 2-pole out, and the other will just have a 2-pole in. 4-pole cable from the amplifier keeps things neater, though there's still the option to run 2-pole cables direct from the amp to each speaker.
I haven't finalised the tuning yet, still waiting on the correct PRs. I'll also either build or buy a little case to put them in. Maybe something like a 6U amp rack with the amp in the bottom, and then foam inserts to sit the speakers into.
Chris
I think I ended up with the PRs tuned around 60Hz. They were good for desktop use, but wouldn't get loud enough to fill a room to a satisfactory level. I'm working on other things at the moment, but I do have them around somewhere.
The Fostex units were my first "HiFi" drivers, so while they're difficult to work with, there's also a little sentimental attachment which means I can't quite bring myself to sell them on.
Chris
The Fostex units were my first "HiFi" drivers, so while they're difficult to work with, there's also a little sentimental attachment which means I can't quite bring myself to sell them on.
Chris
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