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A nice pair of loudspeakers
The Mni-TML
The Cobtas RBT
The EOS

A protection fuse

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A nice pair


The Mini-Transmission Line



Mini Transmission Line - Atkinson

Firstly, afaik, this ingenious concept of a very compact TML was published in 1978 by Atkinson in Hi-Fi News & Record Review and was brought to Germany in 1979 by Herbert Klinger in paperback RPB 311.

The original kit used a KEF B110 for bass- midrange and a KEF T27 (or an Audax) dome tweeter. The B110 became famous when used in the BBC LS3/5a loudspeaker. A very compact studio monitor that still finds enthusiasts today. KEF discontinued the production and one only can find used copies. Except: Falcon Acoustics in Oxford England are claiming to produce and sell exact replacements.

 I already had built this TML 35 years ago. But due to a tight budget I at that time used cheap Peerless alternative chassis. Despite this limitations I can remember a beautiful sound. So the plan arose to rebuild them again by assembling technically up to date chassis. The main challenge is to find a suitiable replacement for the B110. KEF had produced two types of the B110. A SP1003 type and a SP1057. To make things worst the SP1003 received three variations along it's production line.

But after a long search I luckily found a chassis with parameters (Thiele - Small) close to the B110 SP1003 ones. And the best part is that it is used in a pretty good reviewed DIY-kit - the "Bodega" from Bernd Timmermanns published in Hobby Hifi - April 2016. 

   This definitly is a job for very experienced hobbyists. You'll get an impression by looking at the pictures below. But what will you get? How do they sound? First let me mention that the line's damping is essentiell and critical. Unfortunately it's effect is hard to measure so experimenting and close listening is inevitable.

When playing contemporary music you'll initially start looking out for the subwoofer because you never would expect such a deep bass from a loudspeaker in such dimensions. Midrange and treble? Nothing spectacular here. Overall the sound is natural and you'll get what's in the record's grooves. Listening to excellent studio recordings is pure fun. Especially live concerts show a wonderful spatiality both in width and in depth.

And now, that I've bought a Superlux 888 B microphon, I can show  a frequency response. Please keep in mind that this is a gated measurement at my listening room with HOLMImpulse. 1m distance at an angle of 0 dgree (blue line) and 30 degree (red line). This is really impressive. The frequency goes linear down to 30Hz. Due to bass resonances inside my listening room I can't get better results.
 

Mini-TML-Frequeny response


But if you prefer hard Rock or Heavy Metal this loudspeaker is not for you. Switch to the Cobras. The TML's effeciency is very very bad. Thus said I developed special protection fuses to prevent them from being damaged (maybe I'll show them here later). So, now that we want to hear harder and louder, let's hook up the Cobra-Horns.


 Cobra Horn RBT

Cobra Horn 2 - RBT


  Again it's Mr. Bernd Timmermanns who developed this hyperbolic back-loaded Horn. It is big, it is heavy and it is loud. But with a kit price (enclosure excluded) of about 160 € worth a try without the risk of losing too much money if you don't like it's sound.

 When it comes to sound I have observed a very special tone whenever I had the opportunity to listen music over horn speakers. This is hard to describe but I am able to identify horn speakers watching even bad quality Youtube videos wherein owners are presenting their horns - with closed eyes. A very thorough and decent damping can mitigate this effect but in a direct A to B  comparison with a vented or closed enclosure it is unmistakable. Additionally horn speakers have to be huge to deliver bass below 60Hz. Do a search for "Schmacks-Horn". You will be convinced.

So why do these speakers have so many fans and why did I build them? Because they deliver a sound that is best described as "immediate," "fast," "present," and "direct". Close your eyes and listen to Malia & Boris Blank's "Celestial Echo" and do it loud. After a few seconds you will open your eyes being scared by Malia who is standing right in front of you. There is an excellent article on Wikipedia about horn loudspeakers and I recommend to read it before building a pair.

      Again Mr. Timmermanns did an outstanding job and I am very pleased with the listening experience these loudspeakers can transfer. It is amazing how well these cheapos perform. I could reduce the special distortions to an acceptable amount by using four different damping materials applied to four different locations inside the horn. This has been my twentieth pair of loudspeakers I have built and I'm satisfied with this nice pair - for a while!


Some impressions of the building process


Mini TML Atkinson    Mini TML Atkinson    Mini TML Atkinson


Cobra Horn RBT    Cobra Horn RBT    Cobra Horn RBT


The history of EOS


EOS loudspeaker


In 1998 I decided to replace my big and loud 3-way pyramid loudspeakers. Mainly because the bass driver's cone surrounds were starting to deteriorate. Secondly because their low WAF. Or may be vice versa. Whatever! I got a new job, we had to move and rented an appartment with a pretty large listening room.

In DIY-magazines and tests the Focal Temptation was highly praised and in May 1999 Klang + Ton came up with an ultra-high-end-DIY kit: The EOS. Bernd Timmermanns had developed a both challenging and uncommon 2-way speaker. A nearby shop gave me samples and so I started to compare them. This was a long hard process because both speakers came really close to what I was demanding. Let WAF decide and I built the EOS.

My job became stressfull and I attended my son growing up so there was less time to listen to music. One or two years later, I remember exactly, I heard a strange sound when listening to Kate Bush - Lion heart. To cut a long story short: Some internet search revealed that many builders had sent complains to Klang + Ton about what I had discovered too. Meanwhile Bernd Timmermanns had left K + T and had founded his own magazin Hobby-HiFi.

Heinz Schmidt and Udo Wohlgemuth, the new editors of K + T, had taken the complaints seriously and meanwhile had developed/added a mid range section to the EOS. A new crossover, the new mid-range chassis and an additional enclosure was all I had to built. This speaker covers a range from 30Hz (-3dB) to 20KHz. It is fast, direct and sounds neutral and natural. Whenever I build new speakers, I compare them to the EOS and so the Cobras had to leave and the Mini-TMLs will stay.

 Heinz Schmidt and Udo Wohlgemuth weren't able to physically measure the cause of all complaints and they didn't confirm them. They guessed that both chassis had been driven to their limits and that the tweeter therefor was producing distortions in the transition range at high levels.

I've later discovered two possible other causes: The tweeter's construction. It wasn't properly sealed on it's backside which I told the distributor. He recommended a small seperate chamber. The distance between the diaphragm and the middle bar was too small. A second revision was then released to fix this flaw. Both faults could have led to the described disstortions.


Protection fuse

 
A loudspeaker protection fuse


A loudspeaker protection fuse


You may ask: Why a fuse to protect my loudspeakers?  Recently I was watching a movie (The 15:17 to Paris) when suddenly, as the scene shifts into the train, a terrifying loud crack popped up. I was using the TML as main front speakers in a 5.1 sorround system and it turned out that the extremly deep and loud low frequencies had pushed the bass speaker to it's limit.

The difference in sound level between normal talk and underlying effects is insane. I have never heard anything like this before. We enjoy these seat  shaking subsonic waves in theater but want to protect our speakers. Besides that, we want to  respect our neighbour's sleep at night. So switching to "night mode" on the receiver is an option. The chassis did survive but I wanted a more reliable and general protection and after a series of experiments with different kinds of fuses the above construction came out.

It is a PTC (1,3A Itrip, 0,37 Rmin) parallel connected to a festoon lamp (12V, 5W - soffitte). This goes in a serial connection to either Plus or Minus of the speaker cable. If current reaches a certain limit the PTC will increase it's resistance, the festoon then will glow and indicate an overload. If the high current is removed the PTC will self reset to it's initial state. The parts are cheap. The whole thing has cost me under 5€.

But there are some disadvantages: This is a slow-flow fuse so you are better off to use a standard fast flow cartridge glass fuse if you really want to be safe. Of course you have to replace this fuse if the emergency occurred. Secondly we don't want to use it as part of the crossover protecting a single chassis, e.g. the tweeter, because it will change the crossover frequency. Thirdly, it is a bit hard to find matching parts. I did some measurements with sine waves and an 8Ohm (phantom) resistor. The calculation leaded to a current value of 1A - 1,5A. But I ordered 6 different PTC with Itrip between 1A to 2,5A and used soffitte bulbs in a range from 5W to 18W. It was a lot of fun to experiment with and I have learned something again.


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First things first. I discovered a gem from the past in my record collection. Albums from Steve Harley and Cockney Rebel. If you wikipedia this band you'll find that S.Harley has written almost all songs by himself. His voice is unique, his style is extremly various. Alan Parsons did some studio work, so you can expect a decent sound.

I use an ACER ASPIRE ONE D270 as media server. This Netbook surprisingly has a very good sound chip which's frequency linearety is pretty good from 20Hz to 20KHz.

Use AUDACITY to record your album. Make sure the record level doesn't exceed 0dB. Record both album sides seamlessly. Now we have two options: Splitting the entire audio file to it's tracks or converting it to whatever format you prefer.

Here is what I did. I exported the file as a single WAV file and left Audacity open. Then I opened the WAV in FREAC and converted it to a single Flac file. On discogs I looked for the specific record and copy - pasted the relevant information into a cue sheet which I had created with notepad (A simple ABC.txt file renamed to ABC.cue). My media player is able to read cue sheets so this this technique for me is the fastest and easiest one. Below is an example. In a last step, that is not necessary but useful, I properly tagged the audio file with MP3TAG.  Please make sure that ABC.cue and ABC.flac are in the same folder.

REM GENRE Rock
 REM DATE 1976
  PERFORMER "Steve Harley and Cockney Rebel"
 TITLE "Love's a primadonna"
 FILE "Love is a primadonna.flac" WAVE
 TRACK 01 AUDIO
TITLE "Seeking A Love"
INDEX 01 00:00:00
TRACK 02 AUDIO
 TITLE "G.I. Valentine"
 INDEX 01 04:17:52


 

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