PDA

View Full Version : Bl factor versus impedance



Lee in Montreal
03-16-2012, 07:00 AM
While browsing thru different woofers, I realized that the Bl factors are different for 4, 8 or 16 Ohms variations of the same driver.
Per exemple, 2240H has 25 N/A while the 2240G has 17 N/A. How does it affect sound, and most importantly what exactly is a Bl factor? Bl should be the force of the motor/voice coil. Does it mean the 4 Ohms 2240 has less force than the 8 ohm variant?

Odd
03-16-2012, 07:18 AM
Thiele-Small Parameters definitions... (http://www.audioheritage.org/vbulletin/showthread.php?13171-Thiele-Small-Parameters-definitions)

Lee in Montreal
03-16-2012, 07:37 AM
"BL
The magnetic strength of the motor structure. "Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer that moves the cone with authority!"

Damn. So the 4 ohms 2240 (17Newton/A) has less strength than the 8 ohms version (25 Newton/A). Then why would JBL produce an 'handicapped" version of a good driver? ;)

Or is it only that a 4 ohm driver requires more current, which is logical.

pos
03-16-2012, 07:41 AM
No the result is exactly the same.
For example you can calculate the mass break point of a given driver with its MMS, BL and Re, and the result will be the same for a 2226H and a 2226J for example (or a 2446H and 2446J)

ivica
03-16-2012, 09:24 AM
"BL
The magnetic strength of the motor structure. "Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer that moves the cone with authority!"

Damn. So the 4 ohms 2240 (17Newton/A) has less strength than the 8 ohms version (25 Newton/A). Then why would JBL produce an 'handicapped" version of a good driver? ;)

Or is it only that a 4 ohm driver requires more current, which is logical.

from:
http://diy-audio.narod.ru/litr/Keele_1977-05_AES_Preprint_-_LF_Horn_Design_Using_TS_Paras.pdf

it can be seen that (BL)2/Re is very important characteristic of the driver, and its influence.

Ruediger
03-16-2012, 12:58 PM
... where this is explained in detail. Excellent book! Ruediger