Motor strength, a good measure of performance?

[Guest]

<font color='#000000'>In various statistics I have found what magazines call BI or motor strength which they say is measured in Tesla meters. How important is this to the performance of a speaker. I would guess it would be very indicative of sound quality, as would be moving mass (cone weight) power handling, and excursion capabilities.

Another quesiton, can anyone explain to me the relationship between how loud a speaker it and how much power is being put to it. For instance if you have a 12 inch sub powered by a 300 watt rms amp moving 7 milimeters, will it be the same volume or spl as the same sub moving the same distance with twice that amount of power. How is BI or motor strenght related to spl or volume, I would think it would come into play in the accuracy of the speaker, but probably it would be less indicative of overall spl, (you just have to get the air moving, it doesn't matter how bad it sounds). Assuming the sub can handle this amount of power easily.

Any reply would be greatly appreciated</font>

 

[annunaki]

<font color='#000000'>Bl will tell you how powerful that speaker's motor is but the single spec alone leaves many other unknowns. For instance, the motor has a lot of force but how linear is the motor? Linear motor designs have been proven to offer much lower distotion than other designs.  (check out http://www.adireaudio.com &nbsp;( http://www.adireaudio.com/tech_papers/xbl2_motors.htm ), this will help give you an idea of what I am getting at) One needs not to be concentrating so much on one specification but rather how well all specs work together as a unit.

Referring to your analogy above a 12 woofer (woofer A) with 300 watts moving 7mm will be just as loud as the 12 woofer (woofer B) moving 7mm with 600 watts. This is only if they both have the same amount of surface area. What would that tell us? It tells us woofer A is more efficent than woofer B. It also would suggest woofer B may have a higher powerhandling. That may not always be the case though. Based upon your analogy above if we have the same woofer using different amounts of power the one with 600 watts will in almost all cases move farther. Unless the woofer is at its peak rms power and excursion limits. Then we would basically be adding extra heat to the voicecoil with little to no benefit. In otherwords we would be experiencing power compression. If this woofer was at its peak rms power and excursion limits at 300 watts all we did by adding another 300 watts was shorten its life. However, if the driver was not at its limits then theoretically we would experience a 3 db increase in output. Unfortunately, this is the real world, and physics says that due to speakers being only about 1%-2% efficent at turning available power into motion, we are more likely to see a 1.5-2 db increase in output. If you have more questions or would like more explanation, send me an email or pm. Hope this helps a little.</font>