Liberal socialism wins over capitalism!
"Open source" High-End-Speaker-Killer design for everyone! (No joke)
What you see is a modified Fostex FE-208 Sigma, coated with aluminium foil in a Jericho-Horn, on the top is an array of five membrane-modified piezos (3xdirect 2xindirect), without their usual horns. This speaker is not filtered at all and has no audible colorations and an acceptable frequency response due to special damping behind the membrane, on the baffle front and positioning in the corner. This is a no-nonsense design based on technique of the 1930's. It gets loud and is reliable for many years. All drivers are wired in phase. Page made by Dragan Pavlovic, Germany 19.12.2000. Last, 11th update 23.12.2007. At the end of the page are links to the 2nd and 3rd page with the last modification of my Fostex as a point source without piezo array. New (03.12.02) added fourth page:
New ideas since my last update in 2005: You can use Denons Audyssey MultEQ to make the phase and amplitude response linear. (www.audyssey.com)
You can use analogue technique to do the same! Watch www.pfleid.de
There is a service provided by a german technician (sorry only in german!) who can make your speakers phase and amplitude coherent: www.hifi-klangservice.de
In my ears both techniques bring an end to the discussion about solving the "audio problem".
The glue used for the aluminium foil can not be purchased in the necessary quality any more from Noris Blattgold Germany. If you want to get the same glue with high damping capabilities you should search for the name: "Anlegemilch Schnellmixition Deutsch". The white glue is on a basis of silicone and water. You can get it from Wasner Blattgold, Germany.
There is a new website soon to come. A "Pfleid fan website".
Have a close look! It really looks like a 70's space age speaker!
The Fostex large band driver paper membrane is covered on both sides with aluminium foil. There is special damping (a thin layer of 3-4 millimeters of lambs wool fixed on the yellow spider. In the height halfed "Bofoam" is fixed on the blank metal of the chassis behind the membrane. This eliminates the first loud reflections which would disturb the sound. This effect is not taken into account by many designers but helps remedy the typical "horn-loudspeaker" colorations often critisized. No "nasal"-sounding colorations any more! You will be astonished when listening one modified speaker versus the unmodified (single-speaker demonstration). Look on the next photo:
Here you can see the chassis from behind. The aluminium foil covers the back side of the paper-membrane too (sandwich construction). On the spider is a thin layer of lambs wool. The lambs wool is fixed with only some drops of glue fuzzily spread. The lambs wool stays where it should. After some months of listening it did not drop down. I took lambs wool which is on the backside even, on the frontside "rough" and "open". (Old Visaton lambs wool was woven like that). Behind the membrane is a sort of "gap" between the spider (where the spider ends) and the metal-chassis. This "gap" I filled with damping material (foam). All potential first "loud" reflections are omitted by complete damping of all surfaces behind the chassis (I used also some "tesa-moll" halfed in height). Do not forget to dampen also the (approx. 2 cm) wood/chipboard of the hole for the loudspeaker. This area also contributes to unwanted reflections. The chamber in the back-loaded horn is covererd with one layer of "Bofoam" on all areas. Nothing else. (Latest update 21.12.02, now I added white baf-waddings on all surfaces in the back chamber). If you want to kill further unwanted middle-tone emissions you can put one layer of damping material (best is bofoam) into the wide horn opening at the end of the line. My expierience is that it does not disturb the bass but only reduces unwanted middle-tones (subjectively you have more bass). I covererd with bofoam the whole front of the speaker. This improves imaging and the frequency response.
Do not forget to cover the cone and the double-cone in the center from both/all sides! Even if you do not believe it: covering every part of the paper membrane changes dramatically the sound because sound velocity in the membrane material seems to be an important factor (regardless of the good stiffnes to weight ratio due to the sandwich-alike construction what ameliorates the impulse response a lot for itself). The glue used for the application of the aluminium foil is highly dampening the membrane (it is rubber-alike when dried). In the beginning I treated the membrane of the large band driver on both sides with hair-spray-liquid applicated with a soft brush. The liquid enters completely the membrane and evaporates fastly. Unlike with water-based liquids it is possible to penetrate the membrane completely with the hair-spray-liquid without having the fear that the membrane changes its form (I did "kill" several membranes in other projects by applicating too much water-based-liquids at once). The impulse response was better due to the stiffened membrane but the speaker was terribly sounding because of the absence of damping (harsh sound).
You should not try to dry the membrane in short time by using any sort of heat. It should dry under usual room conditions. If you force the membrane to dry fast after applicating the aluminium foil air-bubbles will cause optical losses and maybe audible ones. You need at least one week of drying because the water in the membrane escapes only slowly after having applicated the second layer of aluminium foil on the back of the membrane. I could not wait even two days. I tried listening very soon as you can imagine!
If you want to be anti-capitalist (and you do not like modern large-band drivers) you can buy old Radios of the 1950's or 1960's with two large-band-drivers for some dollars or try to get them for nothing by announcement. (Or two old radios of the same type).The amplifier/tuner does not need to be working - as long as the drivers are o.k..
As you can see, the piezos are embedded in "Bofoam" and have some red foam around them in the black plastic housing. The membranes are coverd on the front side with one layer of aluminium foil, no foil on the backside. (So they sound the same like the large band drivers what is important for homgeneity of sound). The piezos must be positioned approximately in the height of the voice coil of the main driver. The space and the chamber behind the piezo-membrane is damped with (optimal) very soft fibres which I collected from the filter of drying-machines for clothes (in german: Textilreste/Ansammlungen vom "Flusen-Filter" von Wäschetrocknern). It was a good idea! The fibres are the best of all I know - it is a composite material of all kinds of fibres from cleaned clothes at no cost. There is no damping material on the market which is so soft. I put this material in direct contact with the membrane from behind to dampen the membrane. Do not forget to put some damping between the piezo-element and the membrane, too. Slight stuffing is o.k.. As you can see this speaker is a true socialist design. Now my Fostex is working without piezo array. On my third page (link at the end of page) is a photo of the point source. One piezo crystal glued/added onto the backside of the membrane. This gives the relatively "slow" large band driver a fast rise time and attack (even faster than most tweeters).
This is what you need for covering paper (and other!) membranes with aluminium foil. I purchased the special glue and the special thin aluminium foil in germany at "Noris Blattgoldfabrik, Rennmühle 3, 91126 Schwabach, phone: 09122-98930, fax: 09122-73245." The glue is called "Noris-Anlegemilch" and has 500ml content. The foil is called "Blattaluminium", 250 foils, 14cmx14cm. I did not try out the products of others. They may be as good but I do not know. I hope that this glue has worldwide comparable charateristics. The foil is sufficient for lots of speakers.
Use glue with water 1:1
Treating the membrane: The foil is extremely fragile. Do not do this job if you can not stand difficult work with your fingers. For the center of the Fostex - not included the double cone(!) I need 45 min of work. One chassis takes for beginners 10 hours of intensive work. You need only one soft brush. You cut the paper (with the aluminium foils between them) into adequate pieces. First you take one paper (no aluminium foil) and you can take "measure" directly on your object by putting it on the paper membrane of your driver and slightly moving the pencil along the edge. You get easily the perfect shape. This paper you put back to the block of papers (with foils) and fix it with "tesa" stripes. So you can cut with a cissor a portion of foils. Overlapping of the pieces of foil of 5-7 mm on the paper membrane. First you wet the membrane with one layer of thinned glue with the brush. Before you "drop" the cutted aluminium foil on the _outer_ edge of the paper membrane and lower it slowly from the outer edge to the center you put a second layer of glue on the membrane. You do not need to put glue on the aluminium foil before applying. It would be impossible to work like this (foil sticks to your fingers when glue on). The paper membrane must be "wet" with glue so you can correct a little bit the aluminium foil in its position or put it off in order to restart the "landing". If the glue is not enough liquid it would be difficult to correct the positioning. Your hands must be kept clean from the glue. Dry your fingers regularly. With the brush which must always be wet with glue you "press" the foil onto the paper with slight moves. Omit air bubbles under the foil. Do not make too much moves with the brush - you will destroy the very thin foil. Try to get a very soft brush. You can use two brushes. But after some time of work the one used to press the foil on the paper gets wet and becomes unusable before cleaning and drying. My experience is that a "coat" of glue on the aluminium foil does not disturb sound reproduction when working with one wet brush.
Speakers I treated with aluminium foil:
Old German Dual Speakers from the good old seventies. I removed the complete filter so the woofers are working large band. Speakers wired all in phase with only one capacitor of 2.2 mikrofarad for the tweeter - sonds nice! The special glue of Noris Blattgold Germany can be used to treat the foam surrounding of the chassis in order to prolongue its longeivity. I made a small hole into the back of the baffle (1 cm) so that is no air compression in the enclosure. Sounds better. A look closer:
No comment to this delight. Just space age feeling. - - -
Do you see
the
shining/shimmering aluminium foil? I can! I bought the used
speakers for 4 dollars/pair. The speaker is from the seventies
(from Japan) and a typical large band design with added tweeter.
Only one capacitor.
Here a close look for those with less fantasy. Yes, even tweeters do profit of the aluminium treatment. I did not believe it myself. But subjectively the tweeter gets the sound velocity and "speed" of a metal dome (!) without having their ringing problem. All membranes treated became the same fast sound - even the polypropylene-membranes of my car-speakers. The titanium tweeter and the coated polypropylene-main-driver got the same homogeneous sond. You can build up a system with old speakers of different type, but the sound they make is very close due to the same membrane treatment.
This speaker is made in 1975. You see the shimmer? All speakers get the same analytical sound.
This low priced super-woofer (because of its phenomenal membrane stiffness) is from Radiotehnica/Russia/St. Petersburg (named "GDN-75"). The membrane gets the typical sound like all the other aluminium-treated cones, too! I could not believe my ears because this is a true woofer and not designed to make the mids. (In my eyes you do not need to buy high-tec woofers from Eton or Podzus-Görlich). I will try out this chassis without any filter, combined with modified piezos in horns. (I want to know if the big dustcap allows acceptable mid reproduction. The frequency response falls - analogue to loudspeaker theory - with 12db/ocatve beyond 2 Khz).
More fotos and scientific information
Much more fotos (liberal socialist open source loudspeaker show)
Excuse me for my german-sounding english. If you have got some ideas/comment, you can send me an email. You can contact me by
Email: religi%onskritik AT gmx.de (take out percentage sign)
If you have questions about how to build a (horn loaded) large band speaker. I can recommend to visit www.melhuish.org and look there under "Audio". Its the best Do-It-Yourself (DIY) speaker page I ever came to know! Please get there for the first your information before asking me questions. They have a mailing-forum where you can pose your questions.