BL Motor

[son-yah-tive]

What does BL motor mean? Does it have to do with the Subs Amp or Voice Coil? What is 'BL'? 'Bass Linear'?

 

[GranteedEV]

BL is not a motor. BL means literally, B * L

where (forgive me if my physics is off, it's been a while)

B = magnetic flux density (tesla... I think it has something do with gauss's law but that might be electricity)
L = length of voice coil (I think) (m)

so BL is measured in Tesla-meters. BL alone means nothing as it's a somewhat arbritrary rating which changes and its effect is dependant on the nature of the driver as a whole.. But keeping BL consistent is important if you want a linear driver. It's just a measurement which we can apply to understand the behaviour of a speaker.

Now, an XBL^2 motor is a patented technology which maintains BL nicely as excursion rises, leading to similar control (higher BL) at high excursion as would be experienced at low excursion (highest BL).

 

[son-yah-tive]

BL is not a motor. BL means literally, B * L

where (forgive me if my physics is off, it's been a while)

B = magnetic field (tesla)
L = length of voice coil (I think) (m)

so BL is measured in Tesla-meters. BL alone means nothing as it's a somewhat arbritrary rating which changes and its effect is dependant on the nature of the driver as a whole.. But keeping BL consistent is important if you want a linear driver. It's just a measurement which we can apply to understand the behaviour of a speaker.

Now, an XBL^2 motor is a patented technology which maintains BL nicely as excursion rises, leading to similar control (higher BL) at high excursion as would be experienced at low excursion (lower BL).

Thanks for narrowing that down. I didn't think it was an actual motor. It's just a phrase manufactuers use. I had a feeling it had something to do with the Voice Coil, or the movement of the Cone. So, it has to do with the FORCE the CONE moves then. Thank you

 

[Kyle_K]

Force is the vector product B*L*I where I is current. The tricky thing with BL is that increasing the resistance of the coil will not lower the BL but it will loser the effective force under the same power load rendering the driver less efficient because you'll get less current with the same power, here is a quicky example:

1 ohm, 1 volt will give us 1 amp and 1 watt.

if we increased our coil to 2 ohms but the BL did not change then:

2 ohms, 1 volt gives us 0.5 watts, so we need to increase our voltage to 1.41...(or root 2) volts to maintain 1 watt to compare to our previous example. But now our current is I=V/R = 1.41/2 = 0.707... amps

going back to our force, B*L*1 is going to be 3dB louder than B*L*0.707. Our force is less using the same power.

The equation BL^2/R will give you a relative force factor of any given motor for the small signal parameters. This force factor is only good at the rest position. Many speakers lose BL AND sensitivity rapidly as displacement occurs and at different rates, hence fast and lose xmax spec!

 

[son-yah-tive]

Thank you Kyle for extending the explanation. The more I learn, the more I have to learn. And I thought I knew a lot.