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Brass for voice coil?

1970zHiFiGuy

1970zHiFiGuy

Active Member
I recently picked up a pair of Realistic Optimus 5B speakers which are very nice indeed . At www.radioshackcatalogs.com I was reading about RS speakers and I was a bit surprised by the voice coil material in a few which is a brass? voice coil . I can't recall any other speakers with them . Were there others?
 
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Maybe it is a damping ring, short circuiting the magnetically induced voltage in the brass conductor. I'd think that would severely weaken the magnetic field in the V.C. gap.
 
I've seen 3 materials used to wind voice coils, copper, aluminum, and copper clad aluminum.

Are you sure the brass being mentioned wasn't for the voice coil "former"?
 
Brass? Seriously unlikely as Brass is Mo' $ a lesser conductor and far less ductile
This is 'Realistic' speaker after all.. 'nuff said.
 
Agree with Bare above, the resistance of brass in the alloy with the most copper in it is 3 times that of copper, and still more than twice that of aluminum. Other forms of brass will have even higher resistance.

A brass former OTOH, would dissipate heat better than paper, and it would be a clever way of adding mass in an ideal location for a design that required increased mass of the moving assembly.
 
I don't think brass is suitable for either one, but a VC former doesn't make any sense to me at all. I sure don't like the idea of brass wire either.
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At least brass is completly non-magnetic (not ferromagnetic, and not significantly paramagnetic or diamagnetic) and thus won't distort the VC's magnetic field under no signal (quiescent) conditions.
 
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Brass is conductive and will short circuit when it moved thru the magnetic flux. It then has current which tries to oppose its motion, so it seems to me that it will reduce the magnetic field in the VC. Thats why it makes no sense to put a short-circuited metal in the VC. The coil is not short circuited but it connected to the crossover.
 
Infinity used a "phosphor" bronze voice coil "for a better transient response and heat dispersion".
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No they didn't. They used a Phosphor Bronze voice coil FORMER Refer to old literature, infinity mentioned the phosphor bronze formers often.

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Brass is conductive and will short circuit when it moved thru the magnetic flux.
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You need to understand the difference between an electrical circuit, and a magnetic circuit. You do not.

Your above statement would also apply to Aluminum which is further up the electrical conductivity scale than any alloy of brass, there are several and their electrical conductivity varies with the concentration of Copper in the alloy. Aluminum is still currently used for HUNDREDS of voice coil formers.

Brass and Aluminum are ideal former materials because they are magnetically inert, and conduct heat away from the coil well. The electrical conductivity of a voice coil former is mostly irrelevant. Thermal conductivity, and perhaps mass are the advantage of those materials as formers.
 
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A circuit moving thru a magnetic field will have current induced in the circuit such that the magnetic field induced in such circuit will oppose the original magnetic field causing it. Thus the resutant magnetic field will be reduced.

Two circuits exist in a voice coil with a metal former : the metal former will be a short circuit to the induced current, and the voice coil connected to the crossover circuit in turn connected to the amplifier output. I hope this is more clear.
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Also since the current induced in the former is proportional to its velocity thru the magnetic field, and thus its restraining magnetic force, the effect of the metal former will be to dampen the motion of the voice coil. Another effect is that the current in the voice coil wiring will induce another current in the metal former which will affect to some extent the total forces impressed on the voice coil and on the acoustic driver it is coupled to. Unless I am missing something important (which certainly is possible), this is basic physics.
 
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Many of Tandy/RS speakers used a brass former, with a thin adhesive tape/paper coating to which the copper voice coil was wound. It is not unusual for them and not debatable.

They also used paper, cardboard, aluminium, nomex and kapton over the years when using various manufacturer's drivers.

I dissected many of them for the purposes of determining warranty claims back in the day.
 
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restorer-john said:
Many of Tandy/RS speakers used a brass former, with a thin adhesive tape/paper coating to which the copper voice coil was wound. It is not unusual for them and not debatable.

They also used paper, cardboard, aluminium, nomex and kapton over the years when using various manufacturer's drivers.

I dissected many of them for the purposes of determining warranty claims back in the day.
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How you feel about the Optimus 5B in the Big picture of the RS line up?
 
They were very early speakers that were bettered many times, but for a period system, they would be good at the right price. Very efficient IIRC, but squawky in the mid and a bit dull in the top end. I remember seeing a pair that the owner had oiled the cabinet and polished them so much they looked a million dollars. The had a lovely cabinet and $100 each wasn't cheap in '72. I primarily saw later speakers, 80s onwards and usually within their 5 year warranty period. Most of those old ones had hit the land fills by then.

The magnets may be AlNiCo on the bass driver- they had some early 12" with non ferrite magnets.
 
restorer-john said:
They were very early speakers that were bettered many times, but for a period system, they would be good at the right price. Very efficient IIRC, but squawky in the mid and a bit dull in the top end. I remember seeing a pair that the owner had oiled the cabinet and polished them so much they looked a million dollars. The had a lovely cabinet and $100 each wasn't cheap in '72. I primarily saw later speakers, 80s onwards and usually within their 5 year warranty period. Most of those old ones had hit the land fills by then.

The magnets may be AlNiCo on the bass driver- they had some early 12" with non ferrite magnets.
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I haven't opened them up yet mostly because they are really mint , just needed some oil . Optimus 5B alnico? I doubt it maybe Optimus 5 were. What were some favorite RS models?
 
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