Summer Project - Replication of MBL loudspeaker 101mkII

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Magnasanti


I admire all the cleverness and skill in all this- but I look at the tweeter and the possible mass of the moving lamella......wouldn't a dy version of one of these be worth a look..?

AudioStereo -- ELAC ELECTROACUSTIC -- Technology: ELAC JET ribbon tweeter , ELAC 4Pi omnidirectional tweeter , ELAC ribbon tweeter , ELAC X-JET coaxial-coplanar design, ELAC LLD, ELAC AS-XR Crystal cone driver, ELAC AS cone driver, ELAC ESP subwoofer


what you think?
Hey George a Thanks for the interest. By "dy" do you happen to mean a diy version? A clone version of the tweeter is on my to do list but at this moment I am focusing on the mid-range. Also cool link seems like a very innovative company interesting stuff.
 
Hi Magnasanti

Yes I did mean DIY..

I been thinking of building a pair of these using something like these ring magnets spaced abt 1/2" apart

http://www.magnet4sale.com/Neodymiu...-4-NdFeB-Rare-Earth-Magnets-p-17081.html.Such a device could easily be built with thin aluminium foil as the diaphram -formed into a shallow "cylinder" and suspended between the magnets.

Again - moving mass would be very low ....
Yes an impedence / matching transformer would be needed as the resistence of the ribbon diaphram would be very very low.


I like the lamella construction emulating a "pulsating sphere" but can't help wonder if a device such as the elac ribbon ring tweeter would avoid some of the problems in construction.(and resonances etc.)
It possible emulates a pulsating toroid rather than a pulsating sphere.

I haven't heard the MBL 's at all (and am unlikely too) and they by reports are brilliant. but I've played with ribbons and have come away impressed...

Cheers
 
Hi Magnasanti

Yes I did mean DIY..

I been thinking of building a pair of these using something like these ring magnets spaced abt 1/2" apart

http://www.magnet4sale.com/Neodymiu...-4-NdFeB-Rare-Earth-Magnets-p-17081.html.Such a device could easily be built with thin aluminium foil as the diaphram -formed into a shallow "cylinder" and suspended between the magnets.

Again - moving mass would be very low ....
Yes an impedence / matching transformer would be needed as the resistence of the ribbon diaphram would be very very low.


I like the lamella construction emulating a "pulsating sphere" but can't help wonder if a device such as the elac ribbon ring tweeter would avoid some of the problems in construction.(and resonances etc.)
It possible emulates a pulsating toroid rather than a pulsating sphere.

I haven't heard the MBL 's at all (and am unlikely too) and they by reports are brilliant. but I've played with ribbons and have come away impressed...

Cheers
Seems like an interesting project to undertake. A couple of others have done what you are proposing. such as Raal with their Eternity, as well as others on this site.
I fell in love with the mbl sound as well and the look and mystique of their products.
If i wasn't so entranced i would probably be doing something similar as the Elac.
 
Magnasanti,
What country are you located in. Depending on where you are I may be able to help with materials but some of these would get me in trouble if I sent them to the wrong place. Somewhere I had a very extensive article on the construction of the original speakers.

On the centering of the voicecoil if you are not going to use a spider of any sort I would think that you would then use a ferrofluid as the centering method. Forming aluminum and not having it crack while forming or with use is another factor to look at. I have produced many forming tools for aircraft parts and the best method of forming was a high speed stamping press or hydro-forming. Slow speed forming leaves a lot of internal stress and this can be alleviated with an annealing process bringing the aluminum back to a T-0 state and then rehardening the material afterwards. I would rather use a specialty carbon fiber prepreg for this application, but I don't know where you are and what you are allowed to have. There are some very light weight fabrics in a 3k tow that would probably work well. Perhaps a unidirectional material would be the ultimate as you are applying the bending mode in one direction.

Steven
 
Hey Kindhornman its great to see a bit of interest in this project. I am located in the United States. I have read extensively on ferro-fluid, and have come to the same conclusion. The five factors when choosing ferrofluid being quantity, viscosity, magnetization, compatibility, and volatility. The centering force is dependent upon the magnetization of the ferro-fluid along with the magnetic flux in the air-gap. Placing the ferro-fluid along the outside of the voice-coil only further improves this property. Magnetization has to be balanced with the speakers magnetic flux density and the voice coil excursion. Once the amount of f.f. is determined the viscosity should be selected with respects to the desired amount of dampening. Lastly the quantity is determined by the formula V [µl] = 56500 A [E2+C2-B2-D2]
(where A, B, C, D in inches)
where:
A
= Top plate thickness
B= Radius of pole
C= Inner radius of voice coil
D= Outer radius of voice coil
E= Inner radius of top plate

I plan to outsource the voice-coil if the price is right. The thought of using carbon fiber for the former seems cool and interesting. Do you think i could get it thin enough thought. Maybe something like this Carbon & Fiberglass Sales :: Carbon Fabrics: Tapes, Yards, Rolls :: Carbon/Graphite Veil.
 
Magnasant,
Good your in the right place as to material availability. A few points I would make. On the ferrofluid point I think you may be missing the strongest point here in the centering of the voice-coil. With any fluid there is a tendency, probably not a strong enough word, for a rod or cylinder within another cylinder for the fluid to self center itself due to the fluid pressure distribution equalizing around the diameter. In other words the pressure will always become balanced at all points around the cylinder, think hydraulics here, and that will keep a concentric cylinder centered. This would happen without any magnetic properties, but the magnetic properties keeps the fluid contained to the magnetic field. You do need to make sure that the rear camber behind the fluid is vented to atmosphere or balanced on both sides or it will be pumped out by the motion of the voice-coil. I would definitely think that you would want the voice-coil to be on the bottom and not the top as it would have a tendency to return to the neutral position and not have gravity pulling it down on top. The leaves would be hanging from the top and this would keep things in a fixed position. As far as using carbon fiber for the former that is a questionable application. My thinking is that you would probably use an epoxy thermoset resin and the upper level temperature rating would be marginal at best. I would stay with a Kapton former for this reason as the temperature rating is much higher. Just think about having the Kapton wrapped with a secondary wrap to damp the noise that Kapton does have on its own. Tuffquin is what I think the name of the wrap is.

A source for extremely light weight carbon fabrics is Textile Products, Inc. 2512 Woodland Drive, Anaheim, CA. 92801 1-714-761-0401 They also have other exotic blends of material interwoven into composite fabrics.

Voice-coil source: Precision Econowind Inc. 8940 Nrth Fork Drive, Fort Meyers, Florida, 33903 1- 239-997-3860 www.precisioneconowind.com
 
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I have to look for the article that I have somewhere on the construction of the device. I know I kept that but it has been awhile since I've looked at it. Basically you are building a normal speaker with the leaves replacing the cone with one end of the leaves being fixed, no surround to adsorb movement and the other end attached to the voice-coil former. Something has to give and that is the leaves moving or pulsing like a sphere. A cleaver idea but not really that difficult to understand. Just like in a standard driver the mass of the leaves should set the resonance frequency and lower fs.
 
The next steps that will be coming in the next week are. Making a mold out of carbon fiber using a 110mm pipe that will give me the bending radius of 55mm, And cutting the parts labeled: inner-ring, outer-ring, and outer-support-rods.

Were you able to make the carbon fiber mold? Is the mold to create the support rods or the lamellas? In some of the pictures the lamellas look like carbon fiber or aluminum, and the support rods look metallic.

I just made a silicone mold of a speaker cone and created a cone with fiberglass and epoxy resin. What weight carbon fiber are you using?

Very interesting project! I'm trying to create a unique speaker from scratch myself.
 
Apologies, I just read a post that said you have made carbon fiber lamellas. How have these turned out?

I also see you are sourcing your voice coils from Econowind. What type of voice coil did you go with? I am also trying to locate a vendor instead of ripping up speakers solely for their coils... haha
 
Well I would love to look/learn about your unorthodox speaker design. As you Know I started a new thread with the same name take a look its a no-nonsense thread and I have new images of my project. I have yet to make the carbon fiber lamellas, Because I was busy making the design and machining the metal parts. The diaphragm or lamellas of the speaker have a 55mm bending radius which the 110mm tube gave me as far as the negative mold. I have actually gone ahead and made a mold of the tube from 8 layers of carbon fiber which I will post pictures of later, once the metal machined parts are posted, so that everything can be in sequence. I didn't go with Econowind they were asking too much. What I plan to do is just use hot melt glue to attache the lamellas to the voice-coil when testing. Soon after I Finnish with the metal parts the fun will begin!
 
Just re-read your post and will answer the rest of the questions. The need for econowind was merely for extra voice-coils so that I may test different variables. The use of hot melt glue eliminates that. I purchased a driver for both the voice-coil and motor which fit the bill VERY nicely. I would not use fiberglass due to the weight and stiffness. I am using samurai carbon fiber which is the absolute best available with a weight of 61g/m2. There are a host of factors which influence the type of fabric used Samurai fabric is the lightest stiffest has no spaces in the weave and is flat-towed which mean less crimp. The type of resin also influences the composite greatly. I myself am using MGS resin which again is the absolute best available as far as room cured resins go. Finally the cure system used influences the composite as far as weight and stiffness. I will be using a vac bagging system which will be cured in the oven.
 
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