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Message: <blockquote data-quote="JohnEJanowitz" data-source="post: 3742353" data-attributes="member: 584636">Keep in mind that looking at BL alone is meaningless.  We need to look at BL with respect to the DCR of the coil.  The most generalized method for comparing motor strength is Bl^2/Re.   The higher the number, the stronger the motor.This would actually be creating a higher Q resonance.  The higher the Q, the more narrow the bandwidth, but more peaky.  The lower the Q, the more broad it becomes.  You can create more of a peak, but the magnitude of the peak doesn't change all that much.   The system is really dominated by the enclosure, mass, Sd and motor strength and the compliance of the driver itself has a minimal effect.Higher Bl doesn't necessarily mean higher effects of inductance and back EMF.  If you have a higher Bl because you put more turns on the coil and increase the L, then your inductance would rise. However, I can take the same woofer, machine the pole down to two different OD's to change the amount of flux in the gap and have two different BL's, but the inductance stays the same in both cases.  In this case, effects of back EMF would be greater with the lower Bl driver as there is more air gap.  It is much easier for the flux field to modulate in the air gap than in the steel.   A similar situation could be seen without changing the gap, but more flux put into the system with larger magnets.  This would create more flux in the gap, higher Bl and again inductance woudln't change.  If you can actually saturate the top plate and pole, or come close to doing so, the effects of back EMF are nearly eliminated.Also the cone is much more controlled in a sealed box only below the tuning frequency of the comparable vented enclosure.  At and around tuning, the cone is much more controlled as is evident by the excursion minimum at the tuning frequency.  There is much more pressure inside a vented enclosure than there is in a sealed enclosure.  You are exciting the resonance of the port that can pressurize the air in the enclosure much more than the woofer alone.Higher Bl woofers don't always have more weight.  We have 2 different size motors we use with a 2" coil.  One is higher Bl than the other due to more flux in the gap.  The coil is the same in both cases though and Mms is identical between the two.  The lower Bl driver has a higher Q and is more suited to a sealed enclosure.  The higher Bl driver is more suited to a vented box.It's really not so difficult as most of the things you want the same in both cases.  Either way you want these properties:(1)      Linear magnetic flux levels across the entire VC movement range.(2)     The flux should be fixed permanently and not move, this is however not the case in 99% of speakers.(3)     High heat absorption properties as close to the VC as possible.  The VC if allowed to heat significantly will lower the speaker output Spl very quickly.(4)     Linear inductance as the VC moves through its entire range if the driver has to contribute ANY output above the impedance minima above the Fs of the driver.     The only way to accomplish this is to keep the CORE of the VC the same at all excursions.  The VC is after all an inductor, however this is the only inductor in the whole audio system that varies it's value with low bass excursion.  The low bass creates massive excursions that at the same time changes the parameters of the driver at higher frequencies with every deep in and out stroke.I'm still working on getting the old Lambda white paper edited to get it on my forum.   It discusses the ultimate design for low distortion and talks about all 4 of these aspects.   You can find it here from the old site on the web archive for now:<a href="http://web.archive.org/web/20020220130103/www.lambdacoustics.com/library/whitepapers/lambda001.htm" target="_blank">http://web.archive.org/web/20020220130103/www.lambdacoustics.com/library/whitepapers/lambda001.htm</a>In general though, most people think of SQ woofers as sealed box and SPL as vented.   An SQ woofer can play in a vented box just as well, but the key is tuning low so the effects of group delay aren't audible.  In a properly done vented box, a woofer needs much less input power and much less excursion to produce equal output to a similar woofer in a sealed enclosure.  Less power means less heat and less excursion means the driver operates in a more linear range for any given output.  Both of these translate to the vented enclosure being lower distortion.John</blockquote>

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