DIY Back Loaded Horn Speakers / BLH - Fostex FE206E in a Dallas III Cabinet Update 03 - Coral 8A-40

First off a very big thank you to Yeo of diyparadise for lending me a pair of his Coral 8A-40s to audition in my Dallas III cabinets. I was initially surprosed at how small the light the Coral 8A-40 drivers were compared to the Fostex FE206E. I understand that full range driveres depend on massive acceleration of the cone to deliver the entire range of frequency, so I wondered how Coral 8A-40's smaller magnet would compare to the Fostex206E's massive magnet that is at least 3 times larger and heavier?...I met Yeo one fine sunny weekend in January 2008, at his house. I took the opportunity to listen to his setup, the Coral Beta 6s in Hedlund cabinets. In terms of height the hedlunds are indeed an imposing pair of speaker, enough to give the "Tim the Toolman Taylor" in any of us the argh argh argh. But in real terms, both the Hedlunds and the Dallas III cabinets are similar in size, Hedlunds being a single fold horn and the Dallas III is a double fold horn. Once Yeo got his system up an running, we played some Led Zeppelin and cranked up the volume. Wow those speakers ROCK. They played loud and fast. That said, the first thing that hit me as odd was that the high frequencies were missing. Thus a lot of the "ambiance" in the music was lost. I would have loved to stay the entire afternoon and flip through different genre of music to see how the speakers would fare but I was in a rush. I listened to the speakers for less than 15 minutes in total. I know this is too short a time to form any real opinion. Here are the Fostex FE206E and the Coral 8A-40 front view. The Coral drivers a bit dirty as they are vintage stock....Now to my Fostex FE206E in Dallas III cabinets, I had the speakers installed in the cabinets for over 4 months now and I have been listening to them almost daily. I play music through them every evening even if I don't intend to sit down for a listen, just to give everything a daily workout. The wire leads were still sticking out of the cabinets in an unsightly manner. Not only is this unsightly, Ron, the Dallas III designer has said to me that this would cause a loss in the horn efficiency which translates to its ability to play low and loud. Why? you ask... Well its because the wires will prevent an air tight seal between the drivers and the cabinets. But still I procrastinated, I left the speakers unfinished because it sounded so good to me.

After some urging from my other half, I decided it was high time I finished off the speaker and tested the Coral 8A-40s that Yeo was gracious enough to loan to me. So I installed a pair of binding posts to clean up the wire mess. And I installed rubber gaskets so that I could create an air tight seal for the drivers and the cabinet.

The first order of business was to test the Coral 8A-40s. Being new old stock, I was conscious of the fact that the drivers would not sound their best initially. And as I had already surmised they did not sound good at all initially. I left them playing off and on for about 2 weeks. I estimate that the drivers must have played about 50-60hours. I could tell that they were improving. Even my other half commented that the speakers sounded good. With this affirmation I thought it was time for me to sit down for a listen.

The Coral 8A-40s sounded very similar to the Coral Beta 6s. Guess there is a family resemblance. These drivers can rock, put in some classic rock and you are good to go. Put on some slower Jazz numbers and I discovered that the vocals were good too. Music was "fast" and "tight". However, the drivers exhibited the same high frequency roll off, just like its more sort after brethren, the Coral Beta 6. And like I said earlier, the music was missing some ambiance. I could not get used to this especially when I had an pair of ESLs that excelled in this department. I know that there are many who will not agree with my evaluation of the Coral 8A-40's high frequency roll off. But these are what my ears are telling me. To all Coral owners, you have a gem of a driver, and for the price there is no speaker thant can compare.

So out came the Coral 8A-40s and back in went the Fostex FE206Es. If you have been observant, you would have realised that by this time I have been listening to the Corals 8A-40s in my bedroom exclusively for 2 weeks. Other than the High Frequency roll off, I had no other complaints about the Corals. At this point I could not compapare the Coral 8A-40s to my own Fostex FE206Es as I had trouble recalling what the Fostex FE206Es sounded like.

As soon as I had the Fostex FE206Es installed, and had music playing through them, I realised that they were a whole order more musical and also clearer compared to the Coral 8A-40s. It was like a veil was lifted. Just the clarity of the music was astounding. To make sure this was not a figment of my imagination, I swapped between the Corals 8A-40s and Fostex FE206Es a couple of times and even asked my other half to have a listen. And both of us preferred the Fostex FE206Es. However I noticed that the Coral 8A-40s had a slightly fuller mid bass, which made male voices and rock music sound forward. Both drivers played quite low, Corals 8A-40s till about 49hz and the Fostex FE206E till about 43Hz before dropping off. Here is another view of the Fostex and Coral Full Range Drivers. Not all 8" FR drivers are made equal... the massive magnets does make a difference....

And u know what, I slapped on some Def Leppard, Queen, ACDC.... the Fostex FE206E in the Dallas III cabinets ROCKED too... as hard as the Beta 6s in Hedlund cabinets.

Feel free to leave your commets. Or Return to Home.

DIY Electrostatic Loudspeakers / ESLs - Problem with Treble Frequency Solved

The ESLs have been performing very well up till about 3 months ago. One of the speakers developed a problem. The volume on one of the pairs was softer than the other, not by much but enough to shift the stereo image over to one side. After more listening I deternimed that it was the treble frequencies that sounded softer compared to the rest of the frequency. With advise from the designer I proceeded to trouble shoot the faulty speaker:

1. Thoroughly clean the diaphragms and stators using a vacuum cleaner.
2. Visually checked all surfaces to ensure that was no dust or insect causing a leak between the diaphrams and stators.
3. Rechecked and tightened all connections.

Still the problem persisted. I then proceeded to ensure that none of the other equipment that was connected to the speakers caused the problem. To do this I did the following:

1. Swapped the speaker cables
2. Used another amplifier
3. Used another CD player

Again, no change, the problem persisted. With all the possible culprits eliminated, the finger pointed at the electronics, and since the problem affected the treble frequencies, it must be one of the 1.2ohm resistors connected in series with the speakers. Rob had replacement resistors sent to me, free. I promptly replaced the offending resistors and the problem is gone. The ESLIII are now 100% again.

Thanks goes out to Rob of ER Audio for the great support.

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DIY Subwoofer - Rythmik Audio DS12 kit - Listening Impressions

After living with the Rythmik Audio Subwoofers for a few months. I have come to the following conclusion:

This DIY subwoofer has exceeded my expectations. They are perfect for my Home Theatre setup... rattles the furniture and ceiling boards when the need arises. I have the subwoofers crossed at about 80Hz using the AV receiver.

However I am still working on integrating them into my Hifi setup. For my Hifi setup I rely on the plate amplifier's cross over adjustments. I have the crossover set at about 100hz. I am still experimenting with the subwoofer placement, but right now, it is sitting in front of the room right in between the ESLs. For Hifi purposes, there is no doubt that the subwoofer produces non bloated, accurate and articulated bass notes. On most pieces of music, integration with my ESLs are seamless where I don't even know if they are turned on or not. However on certain pieces of music, commercial pop mainly, the producers mix an awful lot of bass and when played thru the ESLs and the subwoofer, the bass sounds over emphasised and exagerated.

Here are more of my observations:
1. Clarity of the bass is top notch. No boom or just a deep rumble... you can actually tell the instrument and the note that is being played. This alone quality alone sells the subwoofer!!
2. The subwoofer adds a lot of "atmosphere" to the music. The music seems "fuller bodied".
3. The subwoofer produces bass that is "tight and fast" enought to keep up with my ESLs.
4. The ESLs and subwoofer setup sounds best on accoustic pieces, classical (pipe organ music is fantastic) and some slow rock pieces.
5. Bass extension is great despite the size of the driver and the cabinets... roughly 2.1cuft. Saves space while not sacrificing extension or SPL.

I don't have any real testing equipment except for the ratshack analog sound analyser. And from some of the frequency sweeps I have done, the frequency response is flat down to 13hz 3-5db when damping set to High and extension set to 14hz.

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DIY Subwoofer - Rythmik Audio DS12 kit

Here is another of my speaker projects from 2007. What is it you ask, well its a subwoofer.My primary objective was to use a subwoofer to bolster the lowest frequencies of my DIY ESLs. But this was a unique situation as I did not want to have a situation where the bass sounded disembodied from the rest of the music like the Martin Logan ESLs!! So not just any subwoofer would suffice. I have listened to many subwoofers in my day. What I considered great in my youth (head-banging days), I now consider bloated and woolly, lacking definition and musicality. All the commercially available subwoofers just play catch up with the rest of the music. My ESLs called for a subwoofer that is both musical and accurate (some might even call it "fast") So my search for such a subwoofer thus began.


These subwoofers also had a second duty, which was to serve as the subwoofer to my Home Theatre setup. This double duty required a truly spectacular subwoofer, and at one point I considered DIYing 2 subwoofers. After much reading I came across a category of subwoofers using SERVO technology. Now subwoofers utilising servo technology is nothing new, several commercial maufacturers use it in their offerings. Servo subwoofers utilise feedback sensors to ensure that the driver is performing as it should. In addition to this servo tehcnology, I also opted for a sealed subwoofer as this sounded most accurate and musical to me. Enter a direct to consumer manufacturer called Rythmik Audio. Rythmik Audio offered DIY Subwoofer kits based on TC Sound's drivers and specially modified plate amp.

The kit of my choice is the DS12 Standard kit for a sealed subwoofer design. The driver and plate amp were modified to utilise Direct Servo technology. In addition, the plate amp had adjustable circuits for bass extension and SPL. Wow this was the 2 subs in one that was needed to pull double duty in my setups.

Here is an extract from Secrets of Home Theatre and High Fidelity article about the kit:

"There are many advantages to using a servo-controlled system for a subwoofer. As previously described in the review of the Titan sub, the servo design allows you to use a smaller cabinet to achieve the low-end response. The feedback controller also protects the driver from being overdriven, which would cause damage to the voice coil.

The feedback loop in the Rythmik sub is a combination of current sensing and velocity sensing feedback. Unlike most servo designs on the market, Rythmik takes on a minimalist's approach. There are no active devices in the feedback paths. The feedback path is purely comprised of resistor and capacitor networks. In contrast, in accelerometer based designs, op amps are used to amplify the motion signal, therefore, becoming a possible source of audible degradation.

The way Rythmik designed the extension filter was such that, without the extension filter, the frequency response (from the sub, not from the amp) will be flat to below 10 Hz. However, this type of design would not be practical. So Rythmik inserted an additional single 2nd order high pass filter with adjustable fs and Q values by changing the resistor and capacitor values of the filter. That sets up the ultimate extension of the frequency response, which allows the user to select between maximum extension and maximum playback SPL."

Having never heard these subwoofers and armed only with glowing reviews from owners, diyers and magazines, I proceeded to contact the designer, Brian Ding. A pleasant fellow, ever willing to answer your questions and help you in anyway possible. After several correspondenses with Brian Ding via email, I felt convinced that this was the kit for me. Musical, accurate, articulate, goes down flat to 10Hz, adjustable extension and SPL what more would I need. So I made the plunge and promptly ordered the DS12 standard kit. Shipping to Malaysia was not cheap. But after a couple of weeks, the kit arrived.... comprising of 1 12" driver unit and a 350 watt plate amp with humongous toroidal transformers and a bank of 4 caps!! Here are some pictures...

The DS12TC 12"TC Sounds based driver, and notice the large 2" magnet. This baby is heavy. Its not the most impressive driver from TC Sounds' stable, but it does its job well.
Top View. This version comes with a Black Anodized Aluminium Cone.Side View, showing the Sensor Coil. The sensor coil sends feedback plate amplifier's servo circuit about the cones movement and position. TC Sounds specially manufactures this sensor coil based on Rythmik Audio's design.Side View, showing Driver Coil.Bottom View.Here is the 350 watt A370 plate amp.So what's missing? The Cabinets of course. Cabinets were a simple affair, a cube with cross braced internals, thick walls.... and an open/glass top so that I can see what's inside. I made them using facilities in my Uncle's woodworking shop. I had them made out of MDF as that was all we had lying around. Here are the pictures of the cabinets. The internal cross braces.Front quarter view.Many people ask if I make the cabinets by myself. I do make it myself but I get a lot of help from my Uncle who is a carpenter by trade. He has a woodworking shop where I make use of the many equipment a home builder would otherwise have no access to. Here is a picture of part of the workshop. The installation of the plate amp and driver units were a simple affair, everything is sealed using silicone adhesives and screws. I use silicone as I had to ensure that it was air tight. The top glass cover is 1cm thick temperred glass. It is attached with nothing other than silicone. Here is a picture of the installed plate amp, notice the large toroid and bank of 4 caps!!Front view showing the 12" driver unit.Another view from the top showing the internals. Incidently, the internal walls of the cabinets have now been lined with 1cm thick foam to reduce internal reflections.Another view from the top showing the driver's backside. The rear view of the cone moving during high excursions is a sight to behold!!Feel free to leave your comments. Read my Listening Impressions or return to Home.

DIY Back Loaded Horn Speakers / BLH - Fostex FE206E in a Dallas III Cabinet Update 02

I asked Ronc if the radiused corners of the Dallas III would have a detrimental effect on the sound compared to the angular Dallas II designs. Ronc had this to say:

"Nope! just a gain in efficency because there is less turbulance in the wavefront as it traveles. Down side is a slight increase in mids coming thru the mouth. However the actual horn action begins a slow roll off at 247 hz and ends at around 400 hz. From there the baffle action takes over (overlaps with the horn roll off) and as the frequency increases finally hands off to the driver. The absolute lowest frequencies are a TL action which blend into the lowest horn action at around 120 hz. The higher frequency TL ripples are then blended with the horn action. This results in a smoother mid bass."

So I am really glad that the desicion I made, which were originally based on aesthetics, did not result in an inferior sounding speaker. Especially considering all the effort that has gone into the build.

Feel free to leave you commets. Read on to my next update 03 or return to Home.

DIY Back Loaded Horn Speakers / BLH - Fostex FE206E in a Dallas III Cabinet Update 01

I submitted my speakers for a public critique on various DIY forums. I have also had the luck of making contact with Ronc, the designer of the original Dallas, Dallas II and Dallas III. He has confirmed that he designed the Dallas III. So I credit these speakers to Ronc.

I have received the following advise:

1. The side walls and internal structure could do with more Support or Bracing. This is something I probably could not do without massive cutting up of the cabinets as they are already sealed up.

2. Seal up the drivers to the driver flange using silicone as leaks would affect Low Frequency performance. I will do this as soon as I have installed the binding posts and also after I have tested the Coral Flat 8 / 8A-40... courtesy of Yeo from diyparadise. I know that these cabinets have been designed for the 206, We just want to experiment with the Corals that seem very versatile.

3. Add 1-4ohm resistance in series with the speakers. It will bring up the LF response by raising the Qes which in turn raises the Qts. With the efficency of the 206/Dallas, this loss of efficiency should not be notice.

That's it for the time being. I am adding pictures of the internal side profile for comparison. Presenting the Dallas II...
and the Dallas III... much more attractive, but does the radiused corners affect the parameters and so the sound.... negatively?Feel Free to leave your commets. Read on to my update 02 or return to Home.
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DIY Back Loaded Horn Speakers / BLH - Fostex FE206E in a Dallas III Cabinet

Horny, I'm home. Funny? I have been waiting a longtime to say that... And I have also been waiting equally long to complete these BLH speakers. So why did I choose to build a horn speaker since I have already completed the ESLs... basically I wanted to experiment with the various speaker technology and designs. I have never been satisfied with the multi coned, multi way speakers. They have never sounded right to me, save for a few very well integrated 2 way speakers. That is why I am attracted to full range drivers and ESLs. The ESLs produce music from a single surface which makes the music "cohesive" for lack of a better word. The music is accurate, fast, with pin sharp imaging and well... they are musical. Instruments sound as they should, piano sounds like a piano, guitar is a guitar... it just jives. I love my ESLs to bits.

The "not so good" of the ESLs are that they are a pain to drive, needing serious wattage and current from a amp that puts out heat like an oven... I kid you not. A monster amp with 200watts with ample current and able to deal with the quirky impedance of the ESLs are what they need to perform their best.


Now on the other end of the scale are these eccentric full range drivers. My first memorable experience with them were in an Audio Note showroom. I forget what amp was on show, but I am quite sure it is one of the famed amps from Kondo's stable. There were also some funny looking speakers singing in the back room. I asked the sales attendant and found out that they were.... Lowthers was the name. They resided in some cabinets huge cabinets that I mistook for a chest of drawers!! They sounded lucious and "complete"!! What do you do when you don't have a couple of hundred thousand to plonk onto one of Kondo's famed amps with a matching lowther driver and those very fine cabinets... DIY of course...

Fast forward 10 years or so, I finally decided that it was high time I got my tube amp plus a pair of horns setup to recapture the magic. So I shopped around for an amp and speakers. I thought I was going to DIY a tube amp, but I came across a deal for a Made in China tube amp that I could not let go. So I bought myself a Little Dot III tube amp with switchable modes between Triode and Pentode. This amp sounds beautiful and only produces 2 - 3 watts, but what beatiful watts they are. All parts of the amps including the tubes are made in china save for the volume control which is from alps and power connectors from amphenol. I may yet DIY a tube amp in the future.... you never know. Now for the star of the show, the speakers.


After scouring the internet I considered, various forms of full range drivers... in bass reflex, open baffle, and various flavours of horns (spiral was really interesting). I settled on one of the best bang for the buck Fostex FE206E full range drivers that work best in a back loaded horn configuration. People tell me that Corals are better, they probably are better but I could not find much information about them. The pair of Fostex 206E drivers cost me less than RM600 shipped from Japan. The only drawback with these full range drivers that I garnered from all that reading was the inherent "shout" that had to be dealt with or tolerated..... As for the BLH design, I can't design any speaker to save my live. So I scoured many sources and forums for something that I could build. I came across several designs and of course there is the recommended design for the 206E from Fostex. I then happened across http://www.fullrangedriver.com/ . This site contained much information about horns and full range drivers, horn calculators, designs and a collection of people passionate about them. After much reading I was taken up by a BLH design made specifically for the Fostex FE206E called the Dallas II. The completed cabinets looked like the usual box type folded BLH. The designer goes by the name of Ron in the fullrangedriver forum. While I have never listened to these speakers, something about this guy just struck a cord in me. In addition several DIYers had built the Dallas II and were very happy with the result. I must admit that the rectagular/boxy Dallas II did not appeal to me aesthetically.


Then from out of nowhere the Dallas III surfaced. Now I am not sure if the Dallas III was actually designed by Ron himself or drawn by a fellow enthusiast. But the Dallas III was a much more aesthetically pleasing speaker. The externally the Dallas III had discarded the boxy look for a curved and flowing design. The internal folds are smooth as well, containing no sharp angles. For all intents and purposes the dimensions of the Dallas II and III were identical. So I thought I'd try to build this. The fact that it looked nice, gave me an oppurtunity to blend my music into my surroundings. After showing the desings to the Home Minister, we desided it would be nice to have them in our bedroom, as a sort of functional Art Deco piece.


These sepakers sound as beautiful as they look, they are really enjoyable and can go really LOUD. Who new what 2 watts could do? As luck would have it I have a large bedroom which suited these speakers fine both visually and sonically. Bass while not prodigious is fast and accurate. It goes down low to about 35Hz. The inherent shout is only evident when you are listening on axis, with the speakers suitably toed in/out, its hardly noticeable. It plays all music with equal aplomb. Bach's Dorian sounded great, Dire Straits' Money for Nothing was really rocking, Janet Seidel's Agua De Beber was pure liquid.... I am listening to CCR as I am writing this post, very nice!!


Presenting the Dallas III and Fostex FE206E.
Front view of the speakers, I placed a 6 inch ruler so you can get appreciate the scale of these behemoths, while not as big as my ESL, they are still more than a handfull. They stand about 1.2m tall 45cm deep and 30cm wide. The backside.... pretty uneventful here... A view of the business end of the horn. The wires are hanging out coz I have not installed the binding posts yet. Standing next to the Dallas III are my old faithful... TDL's RTL2 transmission line speakers. They just sound dull and wooly compared to the Dallas IIIs. The Dallas III twins, sitting pretty in my room, with the tube amp that in then middle. Internally, the Dallas III back loaded horn is a folded horn... 3 folds to be precise. Here is a picture that shows the folding. How did I make the bends? Trade secret! And here is a side profile showing the beautiful curves...Also presenting the Little Dot III, this little 2 watter is a beauty, just ignore the cheesy blue leds. Comes with an external power supply. (The Little Dot III amp that drives the Dallas III... coincidence... I think not!!)And finally a closer look at the Fostex 206E, the cone is made from banana pulp. The music is achieved thru massive acceleration of the cone using this massive magnet. The magnet measures almost as large as the speaker basket.... More of the driver unit... Feel free to leave your comments. Read on to my update 01 or return to Home.
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