Retro Vintage - Fostex FE208EΣ rear loaded horn loudspeakers

Fostex FE208EΣ rear loaded horn loudspeakers This was the start of my DIY hi fi journey. Finished cabinet with T90A supertweeters. Record added for scale... Background Whilst enjoying the beautiful hills in the Lakes in 2002 I was inspired by Paul Messenger's writings on some commercially available horn loudpeakers using Lowther (updated link) drivers, and was drawn to the positive comments about musicality and communication. Whilst Paul said they were not perfect they did possess a super communication. I started to search the net and quickly came across James Melhuish's Single Driver Website (dead link - did become fullrangedriver.com but this is dead too). This was a revelation and I spent quite some time reading the posts on the old forum and studying the projects. It had never occurred to me that I could actually build my own speakers, AND get a decent result. Lowther (updated link) drivers seemed to attract strongly polarised opinions, a love-em or hate-em reaction. They weren't exactly cheap either, a pair of EX4s cost over £1100 at the time. This was a little too rich for me - I hadn't even heard a pair of horns yet and it seemed a rather large risk as they might not be for me. Reading further, the Americans rated the Fostex (updated link) drivers, some even said they preferred them, but opinions expressed on t'Internet should be taken with a healthy dose of salt... But they were much more affordable. Fostex drivers weren't readily available in the UK at the time, but I got a pair of the new FE208EΣ (updated link) on special order from a Fostex supplier for £320 the pair. Not being used to a drive unit of this expense the construction of the cast frame, size of the magnet and overall weight was reassuring. Rear view of the FE208EΣ driver Whizzer-less banana fibre cone The supplied mounting gasket Choice of speaker I thought about design for some time, considering different flare types and horn lengths etc. I also considered Martin King's mass loaded transmission line (updated link - the old Fostex FE208 project is no longer available) enclosures but Martin felt the new drivers weren't sufficiently suitable and might give less than ideal results. In the end I decided to play it safe and build Fostex's recommended enclosure (updated link). Whilst not perhaps a true horn (more a series of coupled chambers) I figured that the good burghers at Fostex know more about speaker design than I do! Preparation So, looking at the recommended enclosure the first thing I did was convert the cutting list to a sheet size of 2400mm x 1200mm which is available in the UK. This worked out at four sheets for the two cabinets, which is a lot of 18mm thick birch ply. The best part of 10 stones, or 60kg, for each speaker! I weighed up using mdf but decided I only wanted to build them once so birch ply it was. There was a real benefit to rejigging the cutting list. The Fostex plans show a number of panels which are joined: the back, base and sides. Using 2400mm x 1200mm sheets allowed me to use single pieces which I figured had to give better rigidity as well as looking nicer. Cutting the sheets up at the local timber yard took about 10 minutes and saved no end of work. Definitely the way to go, provided the operator makes accurate cuts... The four sheets cost about £150. Two rather large piles of birch ply waiting to be assembled... Back in the shed assembly was pretty straightforward thanks to the square construction. Unlike many horns there are no varying width flares, which means the ends are square. This is supposed to help disperse any unwanted high and mid frequency sound that has entered the horn, so don't radius them. The square ends helped to keep things simple, and fortunately only minimal fitting of the panels was required as the cutting in the timber yard was pretty accurate. However, when working out my cutting list I did allow a few millimeters extra to some of the pieces to allow for trimming to size, particularly the side panels. This gave me the flexibility to make sure that the outside panels were a good flush fit. Construction Using the table saw the first job was to cut the numerous lengths of ply to the required lengths. Then the pieces were glued together in small sections using pva before assembling the small sections together. There were only two areas that required a little more thought. The first was the baffle for the driver. The second was the speaker binding posts, more of which later. The hole for the drive unit marked out prior to cutting out with a jigsaw. The outer circle is for the mounting screws. Beware the filler piece to the top left - used to patch knots. I spent quite a bit of time checking all the pieces of ply to make sure that the impact of any of the filler pieces was minimised. Unfortunately they were quite numerous and their complete avoidance was not possible. So, to start gluing up... First the front baffle and base of the back chamber. I decided to drill pilot holes for the driver mounting screws all the way through the wood to ensure the screws would drive home. I'm glad I did as the screws are a tight fit even so. Next the rear wall of the back chamber (face down on the bench) with the bracing to the first chamber sticking upright. The rear panel. The piece sticking up forms the third and fourth chamber. Note the two holes for the binding posts. I decided I didn't want to use a binding post tray, rather keep the natural birch look. It seemed like a good idea at the time... The internal vertical panel. And then the base panel and bottom front (on the bench). Glued up to one side panel. Note the circle cut from the outside panel for the binding posts. I did this for aesthetic reasons, and I think it looks very nice. 'Course, I'm stuffed if I ever want to change the binding posts or cable inside the cabinet... No, I wouldn't do it exactly the same again but I'd still wouldn't use a black plastic tray. The cabinet construction is easy to see now. Internal wire is two lengths per channel of HU1 (dead link) - silver plated ofc with ptfe dielectric from IPL (dead link). This is the same stuff I use for speaker cables. It's small so fits behind the carpet, and it sounds significantly better than the Linn K400 biwire cable I used to use with the Keilidhs. I only had a puny 18W Antex soldering iron which just wasn't big enough to heat the binding post to get the solder flowing. Fortunately, as I was building the speakers round at my parents I was able to press my mum's cooking blowtorch into service, and without burning too much of the wood either! First speaker almost complete except for the second skin to both sides, the bottom base panel, and proper cleaning up. Finished. Note the over-zealous sanding at 5 o'clock. Fortunately most of this is covered by the drive unit. Phew! Initial impressions Well, the first thing to note is that these are not small loudspeakers. Okay, that may sound obvious but they certainly make a statement in a room. Birch ply isn't everyone's choice, though Mr. Ikea has made a healthy living selling forests of the stuff. But it has the advantage over mdf that it only needs a varnish finish to protect it. And I can live with. Being a pretty impatient person, as soon as both cabinets were finished I moved the speakers in to my parents living room, mounted the drivers, connected my little Teac all-in-one job, and stuck a couple of test CDs on. The drive units were brand new and hadn't loosened up yet, and whilst this was quite audible, so was the open presentation and inherent "rightness" of the sound. My parents living room is a good size and I'm sure this helped the speakers to "breathe", but I was impressed straight away. Much better than the Keilidhs. Setting them up at home Lugging the speakers home was no mean feat at nearly 10 stones each. The speakers are positioned in the corners of my room, either side of a fireplace. There is little alternative, but fortunately they work pretty well here. I have them hard up against the corner, in theory giving better bass response, although the form of the speaker with the mouth in the middle of the baffle perhaps means the speaker doesn't get the full benefit of their location. The recommended enclosure (updated link, but in Japanese) helpfully refers to "sound absorbents" which should be placed in the back chamber, inside the bottom of the speaker, and inside the bottom front baffle. Whilst I thought about what to use for sound absorbents I connected them up the Exposure amps to see what they sounded like. I was still impressed, though the presentation was a little different from my parents' house as my room is half the size and I listen much closer to the speakers at home. Still much better than the Keilidhs. For the "sound absorbent" I got some Dacron-type fibrous pillow stuffing from the market for a couple of quid and filled the bottom of the speakers between the bracing ribs. But all this did was rob the life from the speaker, not at all good. There was an effect on the bass too. By the time I was experimenting with stuffing the drivers had just over 15 hours use. I remember this because at this point I was listening to David Gray's White Ladder and nice deep bass started to come from the horn mouth. When I put the stuffing in the cabinets the newly found bass was severely curtailed. So I took the stuffing out and had a think. I had some 2mm thick laminate floor underlay left over from the kitchen floor which I thought might be worth a try. I cut a number of strips and placed one thickness between each brace. As they were cut slightly oversize they wedged in nicely without any need for fixing. This cleaned the sound up a touch and preserved the life and bass. A good result that I was happy enough with to live with and forget about. I placed a piece of the same foam underlay on the back wall of the compression chamber but it didn't make much difference. I did, however, attach some self adhesive bitumen pads on the back of the magnet. Available from car parts places for a couple of quid a sheet, their principal use is for damping car panel resonances, but with the surface area of the driver's magnet being so large and the high pressures within the compression chamber they really helped damp vibrations reflecting back into the drivers. Although the pads are not easily removed once applied I think this was one of the biggest improvements I made, cleaning the sound up and revealing more detail. And that was as much tweaking as I did initially. I sat back and enjoyed the music. Listening impressions After listening almost exclusively to box loudspeakers for many years the Fostex horns came as quite a revelation. I suddenly (and shockingly) realised how coloured the box loudspeakers I had heard were. Not just the Keildhs, but other well known speakers costing the thick end of £2000. What was so surprising was that I hadn't really noticed the boxy colouration of the speakers when I had heard them, just that the horns stripped it away with a wonderfully organic sound. Bass was fast as you would expect from a horn, the driver coupled directly to the air behind it, though not particularly deep or extended, although the size of my room means I'm unlikely to get very deep bass anyway. Being a single driver there is no crossover. This has the obvious advantage of making the speakers more efficient, and I have come to the conclusion that more efficiency is generally a good thing (especially for SET valve amp enthusiasts). But I think the biggest advantage is having no components in the signal path - this seems to preserve the immediacy, detail and life of the speaker. And not spending money on any crossover components is an added bonus! There are some downsides though. The FE208EΣ is maybe better described as a "wide band" driver rather than "full range" as the treble rolls off from about 7kHz. I lived with the treble quite happily for a couple of years. It's amazing how much the brain can accommodate aural deficiencies, and my enjoyment of the speaker wasn't impaired at all during this time. Eventually though, as I heard other high quality speakers, notably Steve Shiels' Lowther EX4 horns and James D's Quasar open baffles with AER and Supravox drivers I became more aware of the missing treble and eventually added a supertweeter (updated link). The other downside is that due to the large 8" driver the speakers beam, and there is a very narrow sweetspot for the best stereo imaging, literally a few millimeters makes a large difference. How much this might affect you probably depends on whether you can sit in the sweet spot between the two speakers. That said, I can quite happily sit in the next room and listen to the music as the sound is, to my ears anyway, fundamentally right. Instruments just sound like they should. It would take a very good box loudspeaker to tempt me back. So, for under £500 these are a pair of speakers that sound better than anything I have heard commercially for £2000. Not perfect, but a nice balance of compromises that I can easily live with, and have done for nearly four years so far. And perhaps most significantly allowed me to start playing in the world of low powered single ended valve amplifiers... Improvements Well, I did end up adding a supertweeter, and as good as the speakers were the supertweeter improves them no end. See here (dead link). Probably the best value improvement is time. Time allows the drive units to run in and the performance does improve, quite markedly in some respects. Bass can thunder with the right material, given it's only an 8" wide band driver. What has been interesting is that as other components in my system have improved the Fostex horns have responded. For instance, connecting my WE91 type 300B monoblocks revealed lots of bass that hadn't been there before. At a recent meet in a decent sized living room the wooden floor really shook due to the bass energy produced by the speakers. Scottmoose was sufficiently surprised to model the speaker using Martin King's 1/2 space back loaded horn mathcad sheet... The red line shows the response has excellent sensitivity, nominally flat to 38Hz. There is quite a lot of ripple above 100Hz but this is not noticeable in practice: a combination of room acoustics and the internal square edges scattering the medium and high frequency waves in the cabinet helping here. Thanks Scott. The longer I listen to these speakers the more capable they seem to be. It will take something very special to replace them. December 2025 Update Ah these were good speakers. But they went to the recycling centre in the sky a few years ago. Eventually I heard the honk, it was subtle but it was there nevertheless. I tried to damp it with increasing amounts of absorbents, but I found that just robbed the life in the music. And there was a shrill peak around 3.5kHz which was a little uncomfortable if the wrong frequency was hit. Alison Krauss's vocal on Please Read The Letter was guaranteed to set it off. Subsequent experience suggests this is exacerbated by side walls close to the driver - my suspicion is the return wave on the cone makes it worse. My OB experiments changed this character for the better. I also found that if I hadn't listened to them a while they sounded pretty horrid until they'd had a few hours on them again. I love the full range character though and currently triamp so the amp is direct coupled to the 208EZ.

Alpair 12P MLTLs - Day 8

Day 8 - 3 hours

Time to cut out the absorbent material and glue it in both cabinets. It's starting to feel like I'm getting somewhere now.

First, of course, temperature watch. Even I'm getting bored of this now. Anyway 9 degrees today.

Here's both cabs together after the cramps were stripped from the second.

The absorbent is old fashioned carpet underlay, roughly 10mm thick. It's not so easy to get these days, fortunately Dave the Bass had some spare he let me have. Thanks Dave :-). The top, back and one side is lined; here it's cut to size and trial fit.

I used some spray adhesive to mount the material. I was a little unsure what to use, some of the cans sounded like the bond might be a bit temporary or light, and I don't want the linings to come loose in the future. So I used a contact type adhesive, sprayed on to the cabinet and a couple of coats on the material. It comes out as a web and the fibrous nature of the lining meant it webbed up almost immediately without really making contact with the body of the material. On the other hand I found it difficult to get an even coverage on the plywood. I think it might have made quite a mess if I was trying to glue laminate, but it's good enough for this job.

Once the coats had dried so they were no longer tacky (the can says 2 to 5 minutes but it took more like 10 due to the low temperature) the pieces were placed carefully. As it's a contact adhesive it tends to grab as soon as it touches each other so steady and careful positioning was required. Then pressure was applied to ensure the two substrates made good contact. And that's it. Hopefully.

All done.

And here are the two cabinets together.

One last job for today, glue on the side of one of the cabinets. A little more time today to get a photo as there's a lot less glueing for just a side.

And here it is cramped up.

That's it for today, no more cramps.

Alpair 12P MLTLs - Day 7

Day 7 - 1 hour

Dad was round again yesterday so as well as clearing leaves from the gutters it was important I got the other cabinet glued up - it's always easier glueing with two!

First temperature watch, a little cool for glueing really, barely 5 degrees

Here's the first cab we glued last week now stripped of the cramps. Not bad, but there's a very slight bow in the front baffle. Either there's a slight bow in the bench or the composite of the ply and mdf has expanded or contracted at slightly different rates in the year it's been sat in the garage on the bench subject to the natural moisture in the air. This wouldn't have been a problem if I'd realised when glueing up, but I missed it and the side is a little "short" in centre of the baffle. It shouldn't be a problem as I think I'll have to make a cover for the baffle as the greeny grey look of the 12Ps hasn't gone down too well...

And here's the second cabinet glued up. Note the damp wood where the glue that's been squeezed out has been wiped off. Best not to get the wood unduly wet as it lifts the grain. Light sanding should fettle this.

And that's it for another day.

Alpair 12P MLTLs - Day 6

Day 6 - 1 hour

It's nearly a year since I last made any progress with these speakers. It's been a very busy time in the garden this year making trellis fences, gates, arches and a shed from scratch. But now it's winter it's audio time again!

After a long overdue tidy up in the garage I could see the bench again so I could finally start to glue up the first speaker. But first, temperature watch. It was a particularly mild and pleasant morning - 14 degrees in the still of the low slanting sun.

Not too much to talk about but here's a photo of the first gluing up. You can never have too many cramps. One side is left off as three of the internal faces are to be lined with absorbency material. Still a fair bit to do.

Alpair 12P MLTLs - Part 5

Day 5 - 5 hours

As is customary let's start with temperature-watch - much cooler today, 6 degrees.

The first job was to finish off the holes for the pseudo tweeter and port for the second baffle. And then rout the holes for the Lpad and speaker terminal in the rear panels. Here's the front baffles with the finished holes.

With all the holes complete the next job was to rout 45 degrees chamfers around the holes for the 12Ps on the rear of the front baffles. This allows the driver cones to "breathe" as the front baffles are quite thick.

Then it was time for a trial fit to make sure the 12Ps and Monacor RBT-95SQ pseudo ribbons fit okay. First a sand with 70 grit to clean things up a touch before mounting the drivers. Only one of the pseudo ribbons was tried as they needed unsoldering from the Quasars as well as unscrewing.

And then it was back to sanding. All surfaces are now sanded to 120 grit both inside and out, I'll finish with 240 grit when assembled. I did test a patch that will eventually be inside with the finer grit and finish was lovely and smooth.

It's taken a while but the speakers are starting to come together now.

Alpair 12P MLTLs - Part 4

Day 4 - 4 hours

Goodness, it's over 7 months since my last blog, and over 10 months since I last had chance to play with the speakers. It's fair to say audio has been on a back burner for much of this year, but today I made a little progress with the MLTL speakers :-). But first let's have a look at temperature-watch.

Parts of the country are experiencing terrible flooding, no doubt made worse by the unseasonably mild weather which is probably retaining a lot of moisture. 12 degrees C, mild for the end of December.

So first job was to have a quick tidy, then remember where I'd got to. I'd made a start on routing the first hole for the 12P at the end of the last session, but I was rushing and hadn't noticed that the template had slipped slightly and was no longer centred. Fortunately I noticed in time before serious damage was done. So I marked out the circles with a compass to be sure, then carefully reset the template and clamped well.

More haste less speed. Lesson learnt - measure twice cut once.

The first hole needed three phases. The first was to rout the inner hole for the driver to pass through, 170mm diameter. The plunge cutter only reaches part of the way through the baffle though, so needs cutting from the other side too - the third phase.

The second phase is to rebate the driver, 203mm diameter and 11mm deep. This was a bit of a laborious process as there was a lot of wood to cut away. Here's the finished hole. Note the misalignment from cutting from the front and then the back. This was largely due to the initial cut that had slipped. It shouldn't be a problem though, as long as the driver passes through and the driver makes an air tight seal.

Next was the hole for the Monacor pseudo ribbon I'm going to use to fill the treble out over 12k Hz. I started to cut away the all the wood so the unit sits within a cavity...

...but then decided that I was probably going over the top so then cut full depth before turning over and finishing the cut. Ideally I guess I would have preferred to isolate the driver from the main chamber and the air pressures within, but hopefully it shouldn't make too much difference. I might even add a plate to the back just to seal it.

And here's the two holes viewed from the rear.

Next the 3" port, which requires a 79mm diameter hole. This is perhaps just a little slack, but probably better than being too tight and struggling to insert the port. I can always use a bit of glue or silicon to secure them.

From the rear

And here's the first baffle with the initial holes made. It needs a good clean up and a rear 45 degrees chamfer cutting on the rear of the hole for the 12P. And a check to make sure everything fits of course.

For the second baffle I fully marked out all three holes both front and back first, now I had a little more confidence with what I was doing.

And started with the largest hole for the 12P. Here's the first 170mm diameter hole cut and the start of the wider 203mm rebate.

The finished hole from the rear.

And from the front.

And that was the end of the today's audio fun.