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I've got two of the same subs in slightly different ported enclosures. I noticed that at certain frequencies (like 30hz), one sub is working harder than the other. Even though it's using the same amount of power. It's got more excursion. And oddly enough, does not play as loud.

So I want to do a test of various frequencies to compare the two enclosures. Make sure it's not just my eyes that *think* one has more excursion than the other.

Is a ruler the only way? Or is there something more accurate that I can make from my utilities drawer in the kitchen, or with a single trip to home depot.
Which btw, I have to go back to tomorrow. To buy an entire $25 sheet of MDF just to get one 32x36 cut from.

Remember guys..... measure twice, cut once. Especially if it's the HD guy doing the cutting. :rant:
 

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Elite Shackster
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Sounds like the tuning frequencies are slightly different between the subs. As the subwoofer plays near it's tuning frequency, cone excursion decreases but port output increases. Sounds counter intuitive but that's how it works. There's no way of measuring the actual excursion that I'm aware of but you can simulate it using WinISD which is free subwoofer modeling software.

Are you dissapointed in their performance?
 

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Klippel measures excursion using a laser range finder shining onto a little reflective surface that you tape onto the diaphragm.

I suppose you could rig up something like this on your own, but you'll have to make sure the laser samples as least double the frequencies you're measuring...
 

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Discussion Starter #4
I'm not sure it's safe to let me have lasers. lol

Goon, you're correct. 19hz vs. 17hz for the tuning frequences in either box. I understand what you're saying also. I'd like to check it against WinISD to compare real life vs. simulation!

There must be something I can rig up. I don't necessarily need to know how many mm's the excursion is, but rather how far a cone is moving outward. Just to know whether one cone is extending more or less than the other.

A couple of small rulers might work if I were to have one vertical and the other horizontal. Like a "t".
 

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There must be something I can rig up. I don't necessarily need to know how many mm's the excursion is, but rather how far a cone is moving outward. Just to know whether one cone is extending more or less than the other.
Of course one will move more than the other considering the different port tuning :daydream: Why does it matter though?
 

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There's no way of measuring the actual excursion that I'm aware of but you can simulate it using WinISD which is free subwoofer modeling software.
+1.With WinISD Alpha Pro you can see graphically exactly what's going on, including the difference in outputs.
 

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How about trying a wedge micrometer? Doesn't get much simpler than this!



Dr V
It doesn't give an accurate result as it may measure overshoot. The current definition of xmax is either the difference between the plate and coil thickness or the excursion at which THD is 10%, whichever is the greater. Overshoot would give a result longer than the first method, and probably have a higher THD than the second.
 

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It doesn't give an accurate result as it may measure overshoot. The current definition of xmax is either the difference between the plate and coil thickness or the excursion at which THD is 10%, whichever is the greater. Overshoot would give a result longer than the first method, and probably have a higher THD than the second.
Interesting.. but I thought the OP wanted to measure just cone excursion not xmax?

Dr V
 

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Interesting.. but I thought the OP wanted to measure just cone excursion not xmax?

Dr V
True, sidetracked I was. Addressing the original question it's still easier to see what's going on via modeling, which will also point the way to fixing it.
 

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A laser rangefinder sounds expensive!

How about a cheap laser pointer from the hobby shop and a small bit 'o mirror....

 

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Collo,
That is a great idea, but the problem is how to attach the mirror securely to the cone without damaging or marking it up? The mirror would have to be decently sized for a subwoofer too.



Here's a highly scientific method...:sarcastic:. Video the excursion. Take stills out of the video with a tape measure next to the driver. Paint it up. Not very accurate at all of course due to the camera angle, tape measure angle, distance, etc. Probably within plus or minus 10mm though. Seriously though, being careful with a very slow sine wave sweep and getting eye level with the profile of the driver and having a ruler handy is not a bad way without getting too technical. If there is an obvious difference between the drivers you should be able to tell.






XXXmaxstill-mark.JPG
 

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The mirror would have to be decently sized for a subwoofer too
Egads! you're right!
With the mirror at 45 degrees, its size has to be sqr(2) times the p-p excursion.
for a sub with an Xmax of 30mm, the length of the mirror would be around 80mm.

Swapping the positions of the scale and the laser alows a tiny mirror to be used.
This would get the weight down to the point where some blu-tac might be sufficient to hold it.
 

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Hmm, interesting thread this is now. I have laser measuring device that’s used for checking if wall or floor etc is straight. As for the mirror I guess it has to be extremely lightweight and are there pictures that show how to mount this successively I saw the diagram and it was little rough to tell.

Merry Christmas
 

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The drawing now becomes.....


The mirror only has to be as wide as the laser beam. If you have an old faulty CD or DVD drive laying about, you can find such a mirror inside.

For the reflected beam to clear the basket of the driver, the mirror may need to be mounted on a post. A small section of plastic drinking straw would be sufficient.

Mounting could utilise blue-tac, or even better, some hot-melt glue or silicone, both of which should be removable.
 

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The drawing now becomes.....


The mirror only has to be as wide as the laser beam. If you have an old faulty CD or DVD drive laying about, you can find such a mirror inside.

For the reflected beam to clear the basket of the driver, the mirror may need to be mounted on a post. A small section of plastic drinking straw would be sufficient.

Mounting could utilise blue-tac, or even better, some hot-melt glue or silicone, both of which should be removable.
Yes, yes, yes, I see it now I was tired earlier on I was just stocking my cat and it mellowed me and then it clicked while I was reading another thread and glancing over at my sub. Yes I see it now.

I’ll get some sticky type tape or other not to damage the dust cap and get a cheap ruler with millimetres on it. I’ll modify the laser as the beam puts out horizontal straight line I’ll just place some tape over the beam splitter to place a small dot on the reflective surface. I have blutack and silicone in the cupboard.

Cheers for that other diagram.:T

Merry Charismas
 
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