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Dear Pano, what do you think of this Celestion 15" as OB woofer?
It sounds fine to me, and played up to several kHz in the sweep test.
the Dipole15's BL/mms ratio seems rather low
Hey John, Your write up is 100% accurate. If the driver moved any "faster" it would be playing a different wavelength. However, what I have found is that when someone listens to a pair of speakers and says, wow, that bass is really fast, or that bass sounds really slow, it has nothing to do with the acceleration of the driver. What makes the bass sound fast or slow is all about how fast or slow it can return to rest. A driver that immediately stops sounds much cleaner and tighter. A heavy moving mass and a loose suspension tends to take a lot longer to dissipate stored energy, taking much longer to return to rest, and giving bass a sluggish or smeared sound with no clear start/stop points.
What makes the bass sound fast or slow is all about how fast or slow it can return to rest. A driver that immediately stops sounds much cleaner and tighter. A heavy moving mass and a loose suspension tends to take a lot longer to dissipate stored energy, taking much longer to return to rest, and giving bass a sluggish or smeared sound with no clear start/stop points.
And don't forget you are listening to the system (amp --> speaker cable --> speaker --> room) so isolating the contribution from the bass driver is going to be EXTREMELY difficult.
There is some merit to this, however not for the reasons you believe. Restoring force should not come from suspension. The coil needs to be positioned at all times by the motor itself. Any force put on in by the suspension only decreases the accuracy of the placement of the coil. The suspension can never increase how fast the coil gets to where it should, it can only decrease the accuracy. So in a perfect world the suspension will have no effect on the driver at all.
Force = mass x acceleration. Acceleration = B*l*i where B is the flux in the gap, L is length of wire in the gap and i is the current being applied. Mass is a constant. So the only way to change acceleration is to change current. The lower the inductance of the driver, the lower the resistance as you go higher in frequency so the higher the current and higher the acceleration. As current is removed there is no acceleration so the coil should stop immediately. In many cases though that isn't the case. Lets see why.One of the most overlooked things in drivers is flux modulation. If you have a permanent magnetic field that does not move at all, the coil will at all times be accelerated and stopped as it should. Current is applied and it will instantly move. Current is removed and the flux field will instantly stop the coil. However, it is a rare case that the permanent field doesn't move. If you have ever taken a magnet and waved it by a TV or computer monitor, you could see the effects of how the field is moving. It is somewhat wavy and slow. You take a VC and energize it and it becomes a strong electromagnet. Now you move this electromagnet back and forth through the permanent magnetic field many times a second. Every time it moves through the gap it is pushing and moving the permanent magnetic field. If the VC moves from rest to its full outward position, the permanent flux field is greatly distorted and no longer looks like it did when the coil was at rest. People spend so much time trying use static FEA to get perfect symmetry in the flux field, but as soon as the coil moves it all changes anyway. Now as the current is removed, the coil cannot be returned to the proper rest position until the flux field first returns. THIS is one of the biggest issues with drivers.99% of all drivers do nothing to address this issue. The closer the flux field is to saturation, the harder it is to move so that helps. The only way to totally fix the issue is to keep flux from moving. The copper sleeve we put on the pole does this. As the coil moves, huge eddy currents are created in the copper sleeve and will short out. This keeps the flux field from moving and assures the the coil is positioned as it should be in both stopping and starting.
Force = mass x acceleration. Acceleration = B*l*i The lower the inductance of the driver, the lower the resistance as you go higher in frequency so the higher the current and higher the acceleration.
If you are not contributing to the discussion and only advertising something for sale then shouldn't you do that in your own circle of industry ads?
