# driver excursion with various tunings but same volume and power



## Ryan Anderson (Jul 20, 2009)

So once in a while I play around and learn a little from it. I've always noticed a weird trend when modeling up the same driver, same volume, same power...just different tunings. When I only compare 2 or 3 different tunings it appears there are drastic differences where Xmax is reached. But if you do many, a pattern developes and I'm just wondering if anyone else makes anything of it?


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## Ricci (May 23, 2007)

Yep. Obviously the reduction in excursion is your tuning. The excursion tracks the same you are just choosing where the notch is. If you remove the port altogether you'll have basically the same excursion excursion profile with a sealed box until you get below the port tuning. The same sort of thing happens even with a BP4, 6, or even 8th order. 8th just has 3 notches and 6th has 2. 

Start looking at your impedance graph too. You'll have a spike at the excursion maximum above tune in a ported design but the impedance will be relatively low or normal at the port tune. This is why you can fry a driver at tune so easy. The driver is heavily loaded and taking a lot of power for the output developed, but it isn't moving much to cool itself. Now the impedance spike above tune is another interesting thing. It's the opposite. The impedance is high so the system is very efficient there and little wattage produces a lot of output and the highest driver movement in the intended passband. This usually causes a situation where the mechanical limits of the driver can be reached if your amp is capable of swinging enough voltage. That area also doesn't suffer much compression until the driver suspension starts running out because of the fact that the driver is only receiving 1/4 or even 1/8th of the power as at other freq ranges. 

Bass can be broken down to displacement with sealed and even ported cabs too at the bottom of the bass range. At the top you are talking about efficiency that is the main limitation. There's only so much power you can realistically use on a driver. This is why pro audio subs make such a big deal about efficiency. The switchoff is usually in the 25-35hz range somewhere depending on a whole slew of variables.


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## lsiberian (Mar 24, 2009)

I remind folks these are models and not actual behavior. Models are only tell part of the story. There aren't many drivers that deliver as they approach x-max either.

You will see that the lower tunings follow the slope of the previous one before the port comes into play. This is because the port reinforce those frequencies.


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## Ryan Anderson (Jul 20, 2009)

Can this be moved to DIY please? My mistake... this cleanup and reorganising threw me off!

I see that excursion is actually much worse when tuning into the single digits... I've heard it said that when building an LLT if you tune around 10Hz or lower you don't need a HP filter... but it looks to me like you need one more if you tune lower?


the other thing I noticed yesterday, was hoping someone mensioned (I haven't read replies yet) is that there seems to be a common terminating excursion, the closer you get to 1Hz, they all seem to end close... whether you tune to 30Hz 15Hz or 10Hz... they align toward the end and they all follow a curve pattern except where tuning crests and unloading peaks


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## Ryan Anderson (Jul 20, 2009)

Ricci said:


> Yep. Obviously the reduction in excursion is your tuning. The excursion tracks the same you are just choosing where the notch is. If you remove the port altogether you'll have basically the same excursion excursion profile with a sealed box until you get below the port tuning. The same sort of thing happens even with a BP4, 6, or even 8th order. 8th just has 3 notches and 6th has 2.
> 
> Start looking at your impedance graph too. You'll have a spike at the excursion maximum above tune in a ported design but the impedance will be relatively low or normal at the port tune. This is why you can fry a driver at tune so easy. The driver is heavily loaded and taking a lot of power for the output developed, but it isn't moving much to cool itself. Now the impedance spike above tune is another interesting thing. It's the opposite. The impedance is high so the system is very efficient there and little wattage produces a lot of output and the highest driver movement in the intended passband. This usually causes a situation where the mechanical limits of the driver can be reached if your amp is capable of swinging enough voltage. That area also doesn't suffer much compression until the driver suspension starts running out because of the fact that the driver is only receiving 1/4 or even 1/8th of the power as at other freq ranges.
> 
> Bass can be broken down to displacement with sealed and even ported cabs too at the bottom of the bass range. At the top you are talking about efficiency that is the main limitation. There's only so much power you can realistically use on a driver. This is why pro audio subs make such a big deal about efficiency. The switchoff is usually in the 25-35hz range somewhere depending on a whole slew of variables.


Excellent info ricci! The high impedance peak in "The Saddle" is a lot of what I've been delaing with over the years. Since I like to tune so low to get that .5% in music, the other 99.5% I have over excursion issues at the high excursion part. I never fry drivers, I bottom them. I am really surprised to see thopugh that tuning "High", 25Hz or 30Hz, still has the same excursion as tuning lower way down at the bottom? I thought once you went below tuning more than 5Hz you seriousely unload and its similar but not as bad as free air. I can't believe excursion from 1-10Hz can be so close when tuning to 30Hz vs 20Hz or 15Hz.


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## Ryan Anderson (Jul 20, 2009)

I was surprised to see the upper saddle peak is very close for all of them but the bottom is spread out. Why is that?










nothing notable to me about SPL, maybe someone else knows something interesting...


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