Hello Clever people,
Over the many years of repairing loudspeakers, I have noticed that occasionally I come across a driver with a failed surround and the cone does not sag down and cause voice coil rub (it does for most for most drivers) I assume that it does not sag because the coil and cone assembly are balanced, i.e. the same mass either side of the spider, is there any acoustic advantages to having a balanced cone/coil assembly, or is it just luck or the way it was designed,
Thanks, Arthur.
Over the many years of repairing loudspeakers, I have noticed that occasionally I come across a driver with a failed surround and the cone does not sag down and cause voice coil rub (it does for most for most drivers) I assume that it does not sag because the coil and cone assembly are balanced, i.e. the same mass either side of the spider, is there any acoustic advantages to having a balanced cone/coil assembly, or is it just luck or the way it was designed,
Thanks, Arthur.
Its very possible that the cone and coil balance around the plane of the spider (I assume you mean when the driver is vertical). If so it is just coincidental. The coils are designed for an impedance,a length and to match the gap in the motor, so the coil mass, which is primarily the copper, is driven by those factors rather than weight or balance.
As to whether some low frequency wobble is reduced when the balance happens, I've never heard of any such claims. Front surround and spider are typically far enough apart that the motion is pretty well constrained.
Regards,
David
As to whether some low frequency wobble is reduced when the balance happens, I've never heard of any such claims. Front surround and spider are typically far enough apart that the motion is pretty well constrained.
Regards,
David
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Actually, many years back there was a patent by some Japanese engineers which discussed the relationship between the coil mass and the cone mass and its effect on vibrations in this system. It was an very interesting read. Although they were more interested in this for a tweeter than a woofer.
I have seen some interesting effects when coil mass got well above the norm, along the lines of some form of decoupling that caused a shelving down of the upper range (it looked a lot like the simulations of dual cone, biflex type units).
One thing worth studying is any lateral motion and how to reduce it. There is always a lot of B wasted in giving enough clearance between coil and gap to prevent rubs in mass produced units. The biggest factor I've seen has been coils that pull sideways at the end of travel. Also coils that are centered but axially angled.
A good solution for those issues would be worthwhile.
David
I think spider stiffness plays a large role in whether or not there will be any sagging; either axially or radially. As we know, spider stiffness varies quite a bit from one driver to another of a different make, brand, specs. etc...
IMO, in general, acoustic suspension woofers tend more to have less-stiff spiders and they are the ones most frought with sagging issues. One common remedy for axial sagging is to rotate the woofer 180 deg.
IMO, in general, acoustic suspension woofers tend more to have less-stiff spiders and they are the ones most frought with sagging issues. One common remedy for axial sagging is to rotate the woofer 180 deg.
I am referring to normal playing position, the drivers that I have noticed to have this effect have been early EV and JBL woofers which have had "soft" spiders and when doing a low(20-300Hz) frequency sweep while held in the normal horizontal playing position without any surround did not rub against the pole piece, I assumed this was because the mass/balance of the cone was equal to the mass/balance of the voice coil, the majority of the other drivers that I have repaired tend to have a sagging cone (ie the bottom edge of the cone gets closer to the bottom edge of the frame and subsequently puts the voice coil out of alignment and makes the voice coil rub ) so I was just wondering if there was some sort of advantage to having this balanced relationship or is it just what happens sometimes?
I would recommend against doing freq. sweeps on drivers with no surround. Particularly in the normal horizontal playing position. If doing a refoam job, take note of where most of the dust has accumulated on which side of the cone and recommend to your customer they install the refoamed woofer 180 deg from that position (towards bottom of cabinet in most cases) - even if it isn't rubbing yet.
It is somewhat intuitive that they should be reasonably close to balanced, as not to rely on the surround to keep it from tilting. I always thought it would be slick if some way were found to put a second spider on the back of the VC for a balance of the spider non-linearity. Don't know how, but always wondered. Maybe it is just a happy coincidence.
I once heard a speaker engineer comment that in the most efficient drivers, the voice coil and the cone have pretty much equal mass. Maybe speaker cones tend to balance around the spider for that reason.
Having spiders on either side of the pole plate would make fitting the cone interesting. Not impossible, but interesting.
Having spiders on either side of the pole plate would make fitting the cone interesting. Not impossible, but interesting.
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