I found links to a few magazine articles in German testing the well known classic Fostex enclosures, and usefully also recommended filters to flatten the frequency response. These filters could be of interest as well in other enclosure designs as they work higher up in the frequencies.
This is linked from the site of a German dealer of horn speakers and kits, often using Fostex drivers.
It is interesting to see how the drivers and well known enclosures perform. These were articles from the magazine Hobby-Hifi which I like to buy whenever I am back in Europe.
Hence:
If I would build one of these enclosures I would use 3 terminal plugs so I can connect before and after the correction filter to experiment.
This is linked from the site of a German dealer of horn speakers and kits, often using Fostex drivers.
It is interesting to see how the drivers and well known enclosures perform. These were articles from the magazine Hobby-Hifi which I like to buy whenever I am back in Europe.
Hence:
- The elegant small FE103 horn. I was always curious about it. They say, as the measurement shows, that the bass is not impressive when measured properly in free air, but it is a lot more full sounding against a wall (as expected). Also useful is their recommended correction filter on page 4 (effect is shown in the frequency plot), plus an optional impedance correction when used with a tube amp:
https://eckhorn.com/bk-103.html?file=files/jpx/content/download/bk103.83.pdf - The BK108 horn for FE108EZ. Correction filter on p9:
https://eckhorn.com/bk-108.html?file=files/jpx/content/download/TESTBERICHT-BK108.pdf - The old enclosure for the FE206En. Unfortunately the shop’s filter is not published; however there is an interesting addendum measuring the FE206En in the FE208EZ enclosure. It has better bass in it and thus this enclosure is recommended instead, unless if you have a small room.
https://eckhorn.com/bk-206.html?file=files/jpx/content/download/bk206.82.pdf - FE208EZ in its enclosure with T900A super tweeter. The magazine publishes its filter next to the shop’s filter, the response looks better with the magazine’s filter.
https://eckhorn.com/bk208-mk-ii.html?file=files/jpx/content/download/BK208.pdf - FE166 horn with the FE168EZ or the rare limited FE163En-S and T90A tweeter. Filter including correction added on p9. Recommended to put this box against a wall.
https://eckhorn.com/bk166.html?file=files/jpx/content/download/BK166.pdf - BK83SOL enclosure also tested with FE83En and FF83WK. Correction filter on p10 is said to work well with any of the 3 drivers.
https://eckhorn.com/bk83sol.html?file=files/jpx/content/download/BK83Sol.pdf - BK12M with FE126En or now rare FE108-SOL (they really like this last driver). Correction filters on p8 (FE126En) and p9 (FE108-SOL). Best to put against a wall. They also compare with small FE103 horn and BK108 for FE108EZ. FE108SOL is the best sounding according to the magazine, and would be even better in the BK108 enclosure - more bass.
https://eckhorn.com/bk-12-m.html?file=files/jpx/content/download/BK-12m.pdf
If I would build one of these enclosures I would use 3 terminal plugs so I can connect before and after the correction filter to experiment.
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I understand that the Fostex enclosures are considered as suboptimal over here, yet following the measurements, I would be quite interested in building the BK208 box for a 8" horn-suitable Fostex driver. But, no space now!
I also like its looks and that it is quite doable to make with only straight angles to glue together.
I also like its looks and that it is quite doable to make with only straight angles to glue together.
From the parts I could translate it looks like an interesting project. Instead of the discrete stepped expansion in the BK206 I played with the hypex approximation tool in Hornresp which allows 4 segments and tried to eyeball the box dimensions to fit. I think David demonstrated a way to have Hornresp allow an additional segment utilising the throat chamber as the first segment too which may get close to representing all the stepped elements better. The coupling chamber volume is obviously smaller if the drukkammervolumen of 12 litres is the actual volume used somehow.
Your simulation is interesting - it shows the dip which was measured at 100hz but not the dip at 200hz.
Because of these articles, I do think it is worth building BK208 instead for the FE206 driver family, it has a better, fuller bass rezponse. You can see the measurement on p8 of the BK206 PDF at the bottom left; and at the right you see its response overlaid on the BK206 enclosure. It doesn't have the dip at 100hz and reaches at bit lower as well. Together with a relatively doable construction, I find this now a highly interesting box for the FE206 variants family.
Someone who understands horn physics might know if that 100 hz dip is real when listening in the room. I think MJK discussed this in one of his papers. Still not a 200 hz evident. I had throat resonances masked and used the some filling which flattens some of the resonances. Compare to the unfilled box with resonances not masked. I see further in the document how they measure the coupling volume and horn length so I updated dimensions with this. The Path is set to 55cm too which may be a factor?
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Yes it looks to be, as measured. The main differences appear to be the curved mouth exit, an effective restriction before the vertical chamber after which the cross section expands a little, and a closer driver and mouth exit “path” distance.
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Several years ago I built the Fostex enclosures for the FE208 EZ, completely following its design except for the rear panel, now completely removable (see drawings)
In this way the damping of the various volumes can be set up and changed step by step to the desired tuning. The "Nagaoka" enclosure seems to behave more like a chain of Helmholtz resonators than an usual BLH.
Thanks to an expert friend the procedure was to first make a convincing equalization with my parametric Technics SA 9010, then simulating the results just due to the damping + diffraction prisms in the various volumes.
Note pls that the goal was to have convincing voices from the solo instruments and not an extension of the basses, so presently it sounds anything but a horn speaker.
It also incorporates the Fostex notch filter, but I don't use almost never it because it veils somehow the sound of a 300b SET (as did the equalizer, completely undetectable instead with SS amps)
carlo
hope this may help someone
In this way the damping of the various volumes can be set up and changed step by step to the desired tuning. The "Nagaoka" enclosure seems to behave more like a chain of Helmholtz resonators than an usual BLH.
Thanks to an expert friend the procedure was to first make a convincing equalization with my parametric Technics SA 9010, then simulating the results just due to the damping + diffraction prisms in the various volumes.
Note pls that the goal was to have convincing voices from the solo instruments and not an extension of the basses, so presently it sounds anything but a horn speaker.
It also incorporates the Fostex notch filter, but I don't use almost never it because it veils somehow the sound of a 300b SET (as did the equalizer, completely undetectable instead with SS amps)
carlo
hope this may help someone
Attachments
This is a gorgeous realisation and indeed a good idea to keep the back removable.
Do you add damping behind the driver? It looks to me that a lot of the backwave would be reflected through the speaker cone.
I am also curious if those fostex deflectors made an audible difference?
Frankly I remember very little because the all the credit goes to my friend, I understand very little about speakers, and about much else.
To begin with, the FE 208 is not a full range (fortunately it is without a whizzer cone but with a very light and rigid cone). So the T90 tweeter is usually recommended but I took the F17 mainly because it is cheap and has the same sensitivity; spending a lot of money on a hyper-efficient one and then strangling it with resistors did not seem too smart to me.
The damping treatment is implemented with different means, and differently from chamber to chamber; there is a sort of closed-cell foam tablecloth immediately behind the 208 and in the transition surfaces between the chambers (highs diffraction). Then there are layers of synthetic wool, open-cell polyurethane foam and closed-cell polythene wedges, especially in the final port. The three vertical ducts before the port are interrupted by very compact wool cylinders at different heights (agaist booming). The whole process took a lot of time and attempts, especially for the first and the final chamber.
Killing the mooing cow inside a BLH is not easy, as known. And it requires sacrifices; for me it was enough to hear a plausible flute, or human voice.
Not that easy.
carlo
Found just these notes. and a tablecloth photo
To begin with, the FE 208 is not a full range (fortunately it is without a whizzer cone but with a very light and rigid cone). So the T90 tweeter is usually recommended but I took the F17 mainly because it is cheap and has the same sensitivity; spending a lot of money on a hyper-efficient one and then strangling it with resistors did not seem too smart to me.
The damping treatment is implemented with different means, and differently from chamber to chamber; there is a sort of closed-cell foam tablecloth immediately behind the 208 and in the transition surfaces between the chambers (highs diffraction). Then there are layers of synthetic wool, open-cell polyurethane foam and closed-cell polythene wedges, especially in the final port. The three vertical ducts before the port are interrupted by very compact wool cylinders at different heights (agaist booming). The whole process took a lot of time and attempts, especially for the first and the final chamber.
Killing the mooing cow inside a BLH is not easy, as known. And it requires sacrifices; for me it was enough to hear a plausible flute, or human voice.
Not that easy.
carlo
Found just these notes. and a tablecloth photo
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Thanks for your valuable feedback! I gather that the sound was truly suboptimal before you started tweaking and taming the beast.
Sorry I didn't explain it clearly.
It's just a matter of taste, many would find absurd this kind of treatment because it sounds more like a closed box (but with an unheard dynamic and transparency, near to Sennheiser open headphones) than like usual horn speakers.
What I wanted to explain is that these boxes, with their 7 chambers, are much more flexible than normal BLHs, that should be taken as is, with their own character. Here, with patience, you can adapt the sound to your preferred kind of music and tastes without using active or passive electronic filters.
As I already said, the simple notch filter indicated by Fostex is enough to steal the magic of the Sigma speakers.
c
It's just a matter of taste, many would find absurd this kind of treatment because it sounds more like a closed box (but with an unheard dynamic and transparency, near to Sennheiser open headphones) than like usual horn speakers.
What I wanted to explain is that these boxes, with their 7 chambers, are much more flexible than normal BLHs, that should be taken as is, with their own character. Here, with patience, you can adapt the sound to your preferred kind of music and tastes without using active or passive electronic filters.
As I already said, the simple notch filter indicated by Fostex is enough to steal the magic of the Sigma speakers.
c