Fostex FE126En / FE108Sigma driver measurements and related DIY

Discussion in 'Speakers' started by Serious, Oct 8, 2016.

  1. Serious

    Serious Inquisitive Frequency Response Plot

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    MOD UPDATE:

    Fostex Small Driver Measurements


    Fostex FE126En
    http://www.superbestaudiofriends.or...measurements-and-related-diy.2976/#post-85124

    Fostex FE108EZ
    http://www.superbestaudiofriends.or...measurements-and-related-diy.2976/#post-85502





    Wasn't my plan, but seems like the thread went into the DIY direction.
    That would be fantastic.

    I've been wanting to buy Beta 15s and use some weird 1970s East German "full range" drivers that are in a 2-way bookshelf speaker that I have to make a 2-way OB speaker (just for kicks). Those drivers are too bright for me on-axis and off-axis they have too much roll-off above 10kHz for me, so I thought something cheap like the 3 or 4" Fostex drivers could be perfect and wouldn't be too expensive to just try it out. I could try to design a filter for the drivers I have and it would probably work, but I figure if Gaurav uses the Blumensteins, the 3" Fostex driver must really be something special. The Sigmas are too expensive to just try something dumb for me right now and at that point I would rather save up for something better. I can always repurpose the Fostex driver later on, or give it to a friend or so.
    For this purpose a smooth response and good treble extension is actually more important than utmost clarity and resolution for me.
     
    Last edited by a moderator: Oct 11, 2016
  2. purr1n

    purr1n Finding his inner redneck

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    Fostex FE126En driver measurements

    Did this really quickly.

    WARNING: This is an an open baffle 24" wide. 50" tall. The driver is centered on the baffle. This means there will be a dip at around 800Hz and a bump at 400Hz taking into account the room boundaries and 100% leakage (open garage door). Here's rough simulation of what a perfect driver will look like mounted on the baffle and measured from 3" away.
    Total1.gif

    FE126en FR meas.jpg

    Here is the on-axis measured response 1/9 octave smoothing.
    Fostex FE126En frequency response. On-axis. 3 feet away from 2' open baffle.
    FE126en FR 0.png

    Here is the response slightly off-axis, about 20 degrees.
    FE126en FR 15.png




     
    Last edited: Oct 11, 2016
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  3. batriq

    batriq Probably has made you smarter

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    When the woofer is engaged, where do you cross it at? I've built the Martin King OBs with the Eminence 15" woofers and the 108Sigma, but I feel the crossover is holding it back (bass is too weak).
     
  4. purr1n

    purr1n Finding his inner redneck

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    I'd cross it over at 400Hz to 500Hz based on this. Depends upon crossover slope. But things head south (distortion) really fast below 400Hz for this driver. This driver is simply too small to handle even upper bass. Note these distortion measurements are taken at levels about 7db lower than the headphones measurements. Blasting 80db is already pretty loud in a real life environment.

    FE126en dist 20.png
     
    Last edited: Oct 10, 2016
    Serious and ultrabike like this.
  5. Cspirou

    Cspirou They call me Sparky

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  6. purr1n

    purr1n Finding his inner redneck

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    Not really since the Y axis is more compressed on my graphs. The 7kHz is less problematic slightly off axis, which is how the driver should be used.

    Haha. I have a similar project in the works, but with driver positions reversed. Will post pix in a bit.
     
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  7. purr1n

    purr1n Finding his inner redneck

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    Fostex FE108EZ Measurements

    It's the driver on top. GOV2 used for scale purposes. Small driver is so cute!
    fe108sigma.jpg

    Here is the on-axis measured response 1/9 octave smoothing.
    Fostex FE108EZfrequency response. On-axis. 3 feet away from 2' open baffle.

    fr108 FR.png

    The 800Hz dip is slightly more pronounced and 400Hz peak is less than expected from the OB / room predictions. Similar 7kHz peak as fe126, smaller in magnitude. Will take off-axis and 80db distortion measurements when I get a chance. Don't want to freak out neighbors with loud sine sweeps.

    This 4" driver is badass BTW.
     
    Last edited: Oct 11, 2016
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  8. Cspirou

    Cspirou They call me Sparky

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    I've seen very large builds using these small drivers. Like this:

    http://www.wodendesign.com/Valiant.html

    Do you know what the interest is? If going through that much work, wouldn't you want a bigger driver?

    Cruising through the craigslist market I saw a pair of fe103-SOL 16 ohm for 90 euros. I want them bad. Especially since reading the Jotunheim can push 7.5 W into 16 ohms.
     
  9. Serious

    Serious Inquisitive Frequency Response Plot

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    Oh btw: I got the FE83En in yesterday. I don't get who would make a single driver speaker with a 3" driver. I was hoping for better treble extension. Drops off 5db after the 9kHz peak. Right now I actually replaced the mid/tweeter driver in my vintage bookshelf speakers (don't laugh) with it. They were crossed at a low 900Hz or so and the sensitivity matches almost exactly. Impedance seems close enough. The FR is now better than before LOL.
    There's a pronounced, super narrow (narrower than smoothed spec sheets suggest) 10db 2.2kHz dip, probably from the big magnet covering most of the driver back. Don't know if you can do something about it. There's a tiny 9Khz resonance that bothered me a bit yesterday coming from my HD800, but overall the driver seems to be impressively neutral. Burnt them in overnight. I just wish it extended to 20kHz. It actually drops off even more after 16kHz.

    Will see how this goes. The 4" (or even bigger) full range would have been better for my purposes, but also more expensive. I was worried about bad treble extension with the bigger drivers but it seems like even the small ones don't go to 20kHz without dropping off. This was supposed to be super cheap. Waiting for the woofer.

    BTW: Not sure if you will see driver measurements from me soon. It's cold and rainy in munich right now.
     
    Last edited: Oct 12, 2016
  10. spwath

    spwath Collegiate hijinks master

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    Or all the frugal horn designs use this and similar drivers.
     
  11. purr1n

    purr1n Finding his inner redneck

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    @Serious:

    The rolloff does seem odd as the 4" above are hitting 15kHz.

    Chamfer the baffle to get better airflow. I know, it's a bitch.
     
  12. Serious

    Serious Inquisitive Frequency Response Plot

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    Yep. If the 3" driver doesn't extend any better than the 4", then there's hardly any reason to use the 3" except maybe for a different flavor of peakage (6.5/9kHz vs 5.5/8kHz). Maybe the 5" with its rising response combats the rolloff better?

    I only have them taped to a piece of cardboard for now, so I doubt it's that. I think it had the same rolloff even with no baffle at all. Had to use cardboard because the driver that was in there before was bigger (and I didn't expect it to work). We will see when I put them in the actual baffle tomorrow. Going to use 18mm thick piece of wood, which will probably be too thick to use without chamfering.

    The extension to 20kHz actually seems to be better than the bigger drivers, it's just the drop after 9kHz that's slightly annoying. Drops off about 5db after 9kHz and then after a slight bump at 16kHz drops off another 5db. The 5" and the 4" Sigma seem to drop off more than 10db to 20kHz. Subjectively the rolloff bothers me coming from the HD800. Subjectively it did seem to get better with some burn-in.
     
  13. purr1n

    purr1n Finding his inner redneck

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    What's the size of the baffle? W x H. Also how far off floor and walls? The deep depression in the mids could be caused the OB / baffle leakage / room.
     
    Last edited: Oct 12, 2016
  14. Serious

    Serious Inquisitive Frequency Response Plot

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    Oh, it's not in an open baffle yet. It's in a pair of old bookshelf speakers. They were sealed, so not a good idea to close the front-baffle with a piece of cardboard, but it's only temporary anyway.
    Front baffle is 23cm (9in) wide and 38cm (15in) tall. The driver is almost centered in the middle and 8.5cm (3.3in) from the top to the center of the driver.

    Driver is sitting about 1m from the floor and only about 45cm from center of the driver to the side-walls, but I have lots of absorption on the walls (and even the floor, just not the ceiling). The dip wasn't there with the other driver, either. Maybe it's made worse by a fucky crossover interaction (probably not, at least not at 2-3kHz). The crossover in this speaker seems to not be optimized at all, not even for the original driver. The original drivers were wired so that there was a dip at the crossover frequency at the height I'm listening at, with both drivers wired in positive polarity.

    The strong 2kHz dip does seem to get better (but never goes away) at some angles off-axis, so could be partly a baffle thing. I think it's mainly the driver. Even the spec-sheets show it.

    Anyway, we will see tomorrow. I plan on mounting them 95cm from the floor. The baffle I bought is 60cm wide and 120cm high, but I want to use a thicker piece of wood for the woofer (28mm) and the 18mm one for the Fostex. Have to see if I can salvage enough big coils to make a low-pass for two woofers, especially with its high inductivity and 2kHz peak.
     
    Last edited: Oct 12, 2016
  15. purr1n

    purr1n Finding his inner redneck

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    Holy crap. The spec sheets do show it. You know that dip's going to be worse in RL because the Fostex sheets aren't brutally honest like the Seas sheets.
     
  16. fierce_freak

    fierce_freak Friend

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    This crossed my mind, too.

    -edit- Schiit was pretty clear about not doing this, though haha
     
  17. Cspirou

    Cspirou They call me Sparky

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    How do these drivers handle high frequencies? Isn't there issues with cone breakup?
     
  18. purr1n

    purr1n Finding his inner redneck

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    Fostex FE108EZ frequency response. 3 feet away from 2' open baffle.
    Here is the response slightly off-axis, about 20 degrees.
    Distortion measurements are taken at levels about 7db lower than the headphones measurements.


    fostex 108 20.png
     
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