Fostex Fe206En: double bass-reflex or back-loaded horn?

Discussion in 'DIY' started by Kreshna, Aug 12, 2017.

  1. Kreshna

    Kreshna ...but I have to know.

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    I have never done DIY full range single driver before, but I've been recently interested in such thing. Then I started browsing the web, and was interested in Fostex FE206En.

    Anyway, there seem to be two popular enclosure designs of the said Fostex model: double bass-reflex enclosure, and back-loaded horn enclosure. The double bass-reflex enclosure seems to be much simpler to build. And based on the Youtube video I've watched, the double bass-reflex enclosure indeed has more bass.

    So it raises a question: what are the advantages of the back-loaded horn enclosure, then? If double bass-reflex is easier to build and has more bass, then why bother with back-loaded horn? And yet, back-loaded horn seems to be the most popular enclosure design for full range single-driver.

    I have listened to both models, but only from Youtube videos, so it is not the same as listening directly --not to mention my amp and speakers color the sound of those videos. Could anyone more experienced with single-driver enlighten me more about the difference between those two designs?
     
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  2. Lavane

    Lavane AK Subscriber Subscriber

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    Ive been wondering the same thing. Have you looked at the plans and flat pack cabinet kits at Madisound?
     
  3. Jim Shearer

    Jim Shearer Active Member

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    I have built a number of single full range driver speaker systems. IME, you can get much more performance from the FE206en in a BLH style than you could ever hope for w/ a BR. If you want a simple design, have a look at:
    https://speakerprojects.wordpress.com/cabinet-types/bib-loudspeakers/bib-calculator/
    I just finished building a pair of BIBs using Mark Audio 10.3 drivers, and can't believe the amount of bass these things produce. If you do a search for Bigger is Better or BIB, I suspect you can find lots more info, including my build. Note: I enjoy the A10.3 drivers very much, but they are, IMO, a bit on the fragile side and not for everyone.

    Cheers, Jim
     
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  4. Poultrygeist

    Poultrygeist Addicted Member

    I built these Frugal Horn Mk3's a few years back and they are probably the easiest DIY back loaded horns you'll find. There's a active thread on these at AC that goes back 6 or 7 years. The advantages of BL horns is they don't require any corrective circuits and run straight off the amp with nothing in the signal path to affect the sound. They use the Fostex FE126En which is not quite as efficient as the 206 but still only needs a few watts. BL horns can be corner loaded which increases bass output. Point source imaging is impressive and looks wise I think they're quite elegant.

    [​IMG]
     
    Last edited: Aug 13, 2017
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  5. Kreshna

    Kreshna ...but I have to know.

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    I thought baffle step correction circuit is needed when you are not using SET amp with your full range single-driver. For example, when you are driving Lowther or Fostex using solid state amps, the upper midrange will sound shrill, while the bass will sound weak due to overdamping. A SET amp tames the upper midrange region of such driver, and a SET amp also has such low damping factor. As such, baffle step correction circuit is not needed when using SET amp.

    Well at least that's what I knew from the articles I read. Have I been wrong?


    I have guessed as much. However, my listening experience to single-driver open baffle is limited to and by Youtube videos. In which areas does back-loaded horn enclosure perform better than double bass-reflex enclosure for such high sensitive full range driver like Fostex? Stereo imaging? HF details? Sound stage depth?
     
  6. Poultrygeist

    Poultrygeist Addicted Member

    The Frugals, Hornshoppe Horns, Lowther designs and Madisound BK's are just a few of the back loaded horns which require no corrective circuits. My single driver Fostex Tektons in bass reflex cabs don't use them either.

    The type of amplication doesn't matter. My class D amps all sound excellent with the Frugals, Lowthers and Tektons. Here's a TPA3116 amp driving a pair of Frugal Horn Mk3's.

    P5080006.JPG
     
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  7. Poultrygeist

    Poultrygeist Addicted Member

    The 206 also works well in open baffles but they need woofers to augment the bass. 2 way crossovers would be difficult in this combo but bi-amping is easier and would be the way to go.
     
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  8. slimecity

    slimecity Super Member

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    This comes down to your taste. I have this driver as a full-ranger in my OB's with an Eminence Delta doing bottom end (bi-amped).

    Theres absolutely nothing in between the amp and the Fostex. I switch amps often - and the Fostex sounds great with any amp. Some may find it "shrill", but I personally never have and have always found detailed and smooth. I think it depends on the kind of sound you are used to as well, ie: the perception of the sound that you gained from them
     
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  9. Jim Shearer

    Jim Shearer Active Member

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    Kreshna,

    The FE206en has Q(ts)=0.19, which rather begs for a BLH. I did once build a pair of BVR (big vent reflex, which I considered a big step up from simple BR) speakers using the older FE206e, and they did a respectable job, producing decent bass, but required significant BSC--otherwise they sounded overly bright and seriously bass deficient. In a good BLH design, you won't need any BSC or fiddling w/ tweeks to get a well balanced freq response. While I have no data to back this up, IME, the mids also sound a bit better when this driver is in a BLH rather than a BR. But others may disagree.

    In the long run, I decided that I preferred a whizzer-less driver, and built a pair of what I call transmission line speakers which are similar in design to the FH3 mentioned above by Poultrygeist. Using Fostex FF225wk supplemented by an Eminence APT-80super tweeter XO'd in at 8,000 Hz (where the FF225wk dies out), I achieved what I regard as my best build to date. However, I should note that I designed it to suit my taste and my room, so others may not like it. If you want a reference to the build thread, please PM me.

    If you wanted to use them as mid-tweets and XO to some nice woofers, then skip the big BLH and proceed!

    Cheers, Jim
     
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  10. Kreshna

    Kreshna ...but I have to know.

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    I see. Thanks, everyone. I indeed noticed no BSC mentioned on the BLH page.

    It is this article, though, that gives me the impression that you need a SET amp --or at least tube amp, to make single driver sounds good..

    ================================================

    During about this same time, Kent and I began playing with full-range drivers, those loudspeakers which deliver bass, midrange and treble from one single cone. In a number of ways, they don't measure as well as multiple specialized drivers particularly at the bottom and top of the audible range but there is something aesthetically appealing about the simplicity of the idea - and on many occasions, they manage to sound very good especially driven by tube amplifiers.

    Most interesting are the full-range high-efficiency drivers that deliver the goods with only a watt or so. It's a big design challenge to produce a good sounding full-range acoustic transducer with 100dB/watt efficiency. When it is properly achieved, you get a wealth of detail, exceptional dynamic range and a sense of musical 'aliveness' that you don't often hear elsewhere.

    Tube amplifiers seem to bring out the best from such drivers. They have more bottom end, a warmer mellower mid- and upper mid-range and often more top octave. By comparison, the 'best' solid-state amplifiers make them sound more like transistor radios - less bottom end and an occasionally strident upper midrange. If you are a solid-state kind of guy like me, you start wondering how that could be. If you are a tube aficionado, you smirk and say, "I told you so." The solid-state guy probably starts fixing the response with a parametric equalizer and the tube guy enjoys his music with a nice glass of wine.

    Critical damping -- that resistive combination of electrical source impedance, suspension friction and acoustic load -- occurs when you apply a step pulse to the voice coil and the cone's motion doesn't overshoot. Under-damping results in bass notes that hang around a little longer than the amplifier intended. Over-damping has good transient bass control but also suffers a significant loss of bottom end response. Generally, we want something in-between, something closer to critical damping. Whether we slightly over-damp or under-damp seems to be a matter of taste.

    The need for electrical damping is different for each type of loudspeaker and acoustic environment. High-efficiency full-range drivers are more easily damped than other types due to their powerful efficient motors and light cones. Looking at their bass response curves, we conclude that they are easily over-damped, resulting in excessive loss of bottom end. This partially explains the preference for tube amps with such loudspeakers.


    ================================================
     
  11. Poultrygeist

    Poultrygeist Addicted Member

    The designer of the HS Horns when asked what amp he would suggest for his BLH's will often recommend a Sherwood receiver :eek: from Best Buy.

    But that's Ed for you.
     
  12. Jim Shearer

    Jim Shearer Active Member

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    Kreshna,

    Ah, amplifiers! This is another difficult question...

    For me, the choice of amp depends on the specific speaker. Some of my experiences:
    1) I built a pair of Metronomes using Fostex F120A drivers because I wanted to see what this 'Alnico magic' is all about. So I get them built & broken in, and they sound truly mediocre. Plenty of bass but the highs are missing. I had them running with my trusty old Yamaha CR-1000 receiver (vintage 1976). My friend Martin (MJK of Quarter-Wave.com) comes over to hear them, bringing along a custom PP EL-34 tube amp and home made speaker cables (using CAT-5e). He says he has also bought a pair of F120A is terribly disappointed by them. He is also very disappointed with the tube amp--every speaker he has tried them on is totally lacking in bass. So he connects the tube amp to the Mets w/ the CAT5e cables. Unbelievable! It was as if the heavens opened and the angels began to sing! It's all there in spades: perfect bass, mids to die for, and lovely highs. How can this be? Why did the Yamaha (typical direct coupled output topology) fail on the F120A when it works great on all my other speakers (including single drivers)??? Why does that tube amp only work well w/ the F120A, not with other single driver or multi-way speakers??? I have no clue...

    2) I built a Dynakitparts.com ST-35 tube amp for the F120A Mets. Works great! I tried the ST-35 w/ my FF225wk equipped PTLs: not so good; bass is loose & flabby. Why??? No clue...

    3) A few years back I bought a little Miniwatt S-1 SEP amp based on some wildly positive reviews. It sounds good on the F120A Mets, but really doesn't have enough power, as it's just 2.5 wpc (and that may be an exaggeration). The S-1 has been mostly sitting around...until a few months ago when I came across it & asked myself why haven't I tried this with the PTLs? The FF225wk has a sensitivity of 93 dB/w, better than the 89 dB/w F120A. As it turns out, the S-1 is a GREAT match for the PTLs! Bass is not only plentiful, but firm & articulate. The S-1 now rotates with the Pass designed ACA class A mono-blocks; can't decide which is better.

    4) The BVR cabinets w/ FE206e drivers that I built for my daughter years ago sound good to me with most decent amps, including the Dayton DTA-100a she is currently using. However, when I was breaking in those drivers, I connected them to a Radio Shack amp that I picked up on close-out. That amp made the FE206e un-listenable! It was horribly sibilant. I have no clue why...

    IMO, you can try a number of amps that you have on hand and see what you like. It is possible that a SET or SEP might be better, but who knows? The technical reasons for amp/speaker synergy are beyond my understanding.

    Cheers, Jim
     
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  13. slimecity

    slimecity Super Member

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    Jim has some good points.

    These Fostexs are incredibly efficient and easy to drive, so a low powered tube amp will work fine - however theres no reason why a decent SS amp cant sound great also with them. There are many factors involved including technical points on amp design involved, room configuration, enclosure design, as well as quite simply what sounds best to you subjectively.
     
  14. Poultrygeist

    Poultrygeist Addicted Member

    I love the Volt+ ( TPA3118 ) from India with my full range single driver speakers. The sound is SET like but with a bit more power. What wonderful times we live in where $39 can buy this level of performance.

    https://allo.com/sparky/volt-plus-amp.html
     
  15. Kreshna

    Kreshna ...but I have to know.

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    Sounds very, very interesting. Does monoblock version exist?

    I see. I wonder why Nelson Pass wrote that SS amps make full range single driver sound like transistor radio. Perhaps overdamping?

    Thanks Jim. Many interesting points being made. I understand difference between amplifiers is audible, even with conventional, crossovered, multi-drive loudspeakers. My JBL 120Ti, for instance, sounds best with Sansui AU-7900, while it sound harsh on other amps like Yamaha RX-V663 and NAD C326BEE. However, it seems difference between amplifiers is more severe in full range single-driver, perhaps because full range single-driver is more sensitive (heavy magnet, thin cone) than conventional speakers.

    Am I correct so far?

    Then, the problem with SS, as Nelson Pass has described. It seems to me full range single-driver sounds harsh in SS amp is due to overdamping. Too bad Allo Volt+ specs doesn't mention its damping factor, but perhaps it's low enough, that it sounds good with full range single-driver as Poultrygeist mentioned?

    But it also seems overdamping is not the only factor. I think the reason SET amps sound really good with full range single-driver is because SET amp has minimalist design. I remember reading somewhere, that non-SET tube amps tend sound ugly with full range single-driver, distortion become audible, etc. Perhaps the Allo Volt+ amp sounds very good with full range single-driver, because the said class-D amp has minimalist design?


    Back to the speakers...

    The reason I become very interested to try full range single-driver is because I read the such speakers have outstanding stereo imaging and sound stage. They also have great dynamics due to their high sensitivity.

    Now, back to the topics. So, double bass-reflex enclosure has more bass than back-loaded horn enclosure, but back-loaded horn is better otherwise. My question is, how much better is back-loaded horn enclosure compared to double bass-reflex enclosure? Or rather, how much worse is double-bass reflex enclosure compared to back-loaded horn?

    How about sound stage and stereo imaging? How much worse is double-bass reflex enclosure compared to back-loaded horn in terms of sound stage and stereo imaging? But single-driver in double-bass reflex enclosure still has better sound stage and stereo imaging than typical multi-driver, doesn't it? And how about dynamics?
     
  16. Jim Shearer

    Jim Shearer Active Member

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    Kreshna,

    You said: "However, it seems difference between amplifiers is more severe in full range single-driver, perhaps because full range single-driver is more sensitive (heavy magnet, thin cone) than conventional speakers."

    I think it has more to do with the cross-over. The XO adds another layer between the amp and the driver, altering the impedance and phase VS freq curves. And I don't put much store by 'damping factor'; I believe that the interactions between amp and speaker are way more complex, and I make no pretense of understanding them. Perhaps if I were a young EE student looking for a PhD thesis, I might explore this topic.

    I have never explored double-bass reflex cabinets, but I would expect most of the differences to be in the region below 300 Hz. The design of the baffle will have significant effect on sound stage and imaging: baffle width and diffraction effects (including those caused by grills) are areas for you to research.

    Cheers, Jim
     
  17. Kreshna

    Kreshna ...but I have to know.

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    I see.

    I'd really welcome opinions and/or observations regarding Fostex Fe206En double-bass reflex cabinet. I hope its stereo imaging and sound stage are still better than those of conventional, crossovered, multi-driver loudspeakers.
     
  18. Poultrygeist

    Poultrygeist Addicted Member

    Have you considered open baffle speakers?
     
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  19. Kreshna

    Kreshna ...but I have to know.

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    Isn't open baffle less sensitive and does require even more power?
     
  20. mkane

    mkane AK Subscriber Subscriber

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    DSC_0007 (1).JPG Using less than 2 here
     

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