How's this work? "Fluxtone" adjustable speaker

[Geezer]

I saw this reviewed in the new "Vintage Guitar" mag.

http://fluxtone-speakers.com/Home_Page.html

Any ideas on how it works? (IOW, can it be done easily with a simple circuit, w/out spending $2000?)

In looking thru the website & listening to the demos, it sure seems to work pretty well......

In the VG article, they said that the same basic idea/circuit was used in old theater sound systems(?)

[The Radium King]

dunno, but weber is planning an adjustable speaker also; some info on his page in the 'ted's blog' section. copied here:

Some of the stuff I'm thinking about when I'm not worrying about my damn lungs:
A variable magnet speaker. Many times, the difference between mellow and icepick is not the cone or any other part, it's the energy in the voice coil gap. So, I've been drawing and experimenting with a variable magnet speaker. If it's not too complicated or expensive to make, I'll try my best to make it available. I have people ask me all the time for a less efficient speaker, while some ask for more. Wouldn't it be cool to just dial it in. It's all about the tone you hear anyway, not the numbers.

Along the same lines, I've been messing with what I call Curve Kits for a long time. These are small boxes you put in series with the speaker to roll off the lows, the highs, or scoop the mids. Different modules will do the opposite also. Not sure where this will go, but I've proven the concept and they seem to work well enough to make them worthwhile as a speaker fixer.

[Geezer]

Got some clues from the "Premier Guitar" article linked on the Fluxtone website... http://www.premierguitar.com/Magazine/Issue/2009/Feb/_Why_Can_t_You_Turn_That_Down_An_Interview_with_Steve_Carey_of_FluxTone.aspx

"Yeah, I got an old field coil speaker and built a variable power supply for it."

"The only negative was that field coil speakers were abandoned in the fifties. Who makes them? Nobody."

"Back then nobody ever wanted to reduce the power to the field coil of a speaker. Why would you do that? They were trying to get all the efficiency they could. Not to mention those old speakers operated at lethal voltages! With FluxTone we redesigned the field coil system, and our speakers operate at a completely safe voltage… you can even stick your finger on the field terminals."

"What we did with FluxTone was to vary the speaker’s ability to be loud, by adjusting its magnetic strength. We removed the permanent magnet and replaced it with an electromagnet, and now we vary the power going to that electromagnet."

So he's using a variable field coil......

[Geezer]

>>w/out spending $2000?

Looks like $550 is the list price for one speaker assy w/ the control box to fit into your own speaker cab....not too bad, I guess (if it really does what it promises)

http://fluxtone-speakers.com/Classic_American_50.html

[PRR]

> does not kill your tone while attenuating your volume.

Uh, yeah?

They are simple field-coil speakers, with adjustable field-coil supplies.

Yes, as seen on 1928 sound-movie systems. And many large radios through WWII.

Coil-force is not just amplifier-force, but amplifier TIMES magnet flux. Any sane person will make magnet flux pretty high. He gives you a knob so you can turn it very low.

Interview. He's quite honest about how "dumb" this is. In traditional engineering, if you want less, you don't start big and fail to use 99.9% of the power you made, you start with a smaller amp.

However changing the flux changes the balance between midrange and bass resonance. Maybe not so much on low/no-NFB pentode amps. And maybe he's added a little dope so the bass-resonance does not get totally mad. Maybe bass-boom is good at low volume. Interesting interactions.

Prices are jaw-dropping but really quite right for this much low-production custom fabrication. If youse guys buy several thousand, ramp-up production, price might fall to a $50 premium over a big ceramic magnet, in-line with Alnico prices.

> can it be done easily with a simple circuit, w/out spending $2000?

Take a ceramic-chunk(*) speaker. Remove the ceramic. Fill the space with copper wire winding. Run lots of clean DC through it. Works the same as a permanent magnet, except you pay more electric bill. AND you can make a "smaller weaker" magnet by reducing the DC into the coil.

(*) On typical Alnico speakers, you need to fabricate a soft-iron slug to replace the Alnico. OTOH, on typical ceramic-chunk, you must close-up the space between iron pole-disks with iron. Kinda a hassle either way.


NOT simple. Those ceramic donuts and Alnico slugs are stuck pretty good. You may bend the iron poles before it comes loose. Winding will need some bobbin or guide, and some clue about wire gauge. Then you must put the center pole back in exactly centered and square and so-deep. On table-radio speakers, a couple tired playing-cards could set the gap, but any gitar speaker worth the trouble must be quite carefully aligned. Your first attempt will be much more than $500 worth of materials, effort, head-scratch, and re-work.

[Frankenamp]

What PRR said...
I did a little work & R&d and whatever else for a guy who had a small speaker factory of sorts (he was trying to make a hobby pay...) Quite brilliant actually. It would be simpler and easier to machine a motor (pole pieces, back plate, VC gap plate, using a diameter that can be gotten 'off the shelf' from a coil winder, cone, spider, surround, and terminals... (oh yeah, paint too) than to try to get a ceramic or alnico speaker that has been epoxied or interference (press) fitted together- apart without buggering the whole job. It will probably take a case of chinese import rejects to make one functioning driver (the first time) there's a lot of mistakes and reverse engineering to be done. If I were doing it, I'd start with a proven cone, spider, surround, dustcap combination, and use a weak magnet for the initial flux. The trick would be to use the coil to boost the Bl product (in phase) or try some wierd stuff by reversing the polarity of the coil for some "interesting" effects.  I wouldn't mind having that Hardinge in my garage... I'll be lucky to get a mini lathe hooked up without SWMBO noticing... Fortunatly, she thinks all amps look alike, so I can play presto-chango (as long as tne number stays the same...

[PRR]

> I wouldn't mind having that Hardinge

Can't. Back-Ordered.

You can get the Sherline. It would do some pole-work. Not precision. Not 3 shifts a day. But several speakers.

Ignorant question: when a metal lathe has "3 inch swing", what's the biggest disk it can cut? 3"? or 6"?

[tubesornothing]

swing is the largest **diameter** that can be put in a lathe.  3" swing is super small, probably one of those little desktop lathes.

[Frankenamp]

Lookin' at the sherline, would think that 3" is the largest diameter it can handle. I think it's one of those counter-intuitive specs that implies radius when it means diameter. (But I'm not a real machinist, I just stand back and laugh when the 'trainees' run another bit into the chuck.