THIELE/SMALL PARAMETERS :
SD:
Effective piston area of the cone. It will vary slightly from one 10 inch (or any other size) to another but does not vary enough to make a difference in the performance of the driver. L
Xmax:
By definition it is the peak linear travel of a driver. If you measure the distance that the voice coil can travel in the gap (in one direction) while the number of turns in the gap doesn't change, you have the Xmax. If you go past this point, the actual windings in the voice coil start to leave the gap. The diagram below shows the voice coil at its maximum travel at point of
max linear travel and just past its point of max linear travel.
BL:
BL is determined by the flux density (B) in the magnetic gap and the length (L) of voice coil wire in the gap. A higher BL will generally mean a speaker will have a higher relative sensitivity (efficiency). This doesn't necessarily mean that all speakers with a higher BL will produce a higher SPL. Often speakers with very high BLs have a smaller Xmax. The diagram below shows two different motors (that's what they're called). Motor 'a' is what you might find in a speaker with a relatively low power rating and a relatively short Xmax but its efficiency will be relatively high. Motor 'b' will have a higher Xmax, higher power handling due to the larger voice coil windings and a lower efficiency. The difference in the xmax is due to the difference in overall length of the voice coil. Xmax=voice coil length minus the gap height. The difference in efficiency is due to a different number of windings in the gap. Remember that the voice coil is an electromagnet. The current passing through the coil generates a magnetic field which is distributed along its length. On the shorter voice coil, more of the generated field is in the magnetic gap producing a slightly stronger motor but with a shorter stroke
'RE':
This is the DC resistance of the voice coil. It will be lower than the rated impedance of the speaker. A 4 ohm speaker may have a DC voice coil resistance of 3.3-3.8 ohms.
RESONANCE:
'fs':
Free air (not in an enclosure) resonance of the driver. All speakers have a resonant frequency. At this frequency, the impedance increases significantly.
'fc':
This is the resonant frequency in a sealed enclosure. The resonant frequency will tend to be higher but the impedance will not go as high.
'no':
This is the reference efficiency. It is usually expressed as xdB when driven by one watt and measured at a distance of one meter. Ex: 89dB/1w/1m. See note below for more information related to reference efficiency.
