Originally Posted by chrapladm
Because I dont want to ruin some else's thread I will ask here.
DIY SG what is the generic way of adjusting BL for all drivers?
The generic method involves adjusting the value of Bl. The formula for determining the new value of Bl to use in your sim is included in the paper linked in post 1. If you are using Hornresp you can let the program do the work for you, just use the Loudspeaker Wizard and check the "Large Coil" checkbox. Hornresp uses the same formula that's in the paper.
The generic formula is a scaled tweak based on normalized Le (Le/Re), the higher the normalized Le the lower the tweaked Bl value will be. Drivers like the Dayton HO don't need much Bl adjustment because the normalized Le is very low, drivers like some of the Fi products have absurdly high normalized Le so they need a sizable Bl adjustment to get a more accurate sim.
I only ask because I was wondering how can we tell the difference of inductance between one design verse another?
If FI and Sundown use different VC's they must be different in their inductance. SO I wasnt sure if the HR large coil adjustment was just a general one. My simulated response shapes for my drivers I wanted to use have gone to crap now that I used the new adjustment. SO I am curious to know more about what exactly causes this inductance to see if its possible to have a new VC made for an existing motor for much less inductance.
Read the paper and you will see how the tweak was formulated. I took 30 measurements of 22 drivers, simulated the enclosures the drivers (with measured t/s) were measured in, in dimensionally correct enclosures and adjusted the Bl to curve fit the sim to the measurement. Then I plotted normalized inductance vs the Bl multiplier required to make the sim match the measurement and derived the formula from the plotted data.
So yes it's a generic formula. As you can see from the scatter chart in the paper some drivers match the trend line much better than others, so the generic formula will be more accurate for some drivers than others.
There's also a way to get a more accurate tweak - do your own curve fit. Measure your driver in a small sealed box. Sim the driver (with measured t/s) in that small sealed box. Adjust Bl until the sim matches the measurement. Then use that value of Bl for all successive sims.
When adjusting Bl the sim will come out a couple db below the measured value but the frequency response curve and all other graphs the simulator provides should be pretty accurate. Nothing was done to account for the couple db less sensitivity in a Bl adjusted graph, but you can just easily add a couple db to your tweaked sims.
The adjustment is not perfectly accurate, but as the 30 examples in the paper show, it's a lot more accurate than not doing the adjustment. The 30 examples in the paper are shown using the generic tweak - the formula in the paper as used by Hornresp. The curve fit method is even more accurate, that's how the generic version was formulated, I simulated each of the 30 measured enclosures, plotted the normalized Le vs Bl multiplier and derived the adjustment formula from that trend line.