DIY Driver Test Stand - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 15 Old 07-31-2015, 09:47 PM - Thread Starter
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DIY Driver Test Stand

In my quest for the ideal driver break-in rig/process, I decided to not reinvent the wheel and just to take a proven design and make it my own. Sitting drivers on top of my workbench and vibrating them all over the place just wasn't working for me.

So, up front: This is not my design. I copied what I made based on what I saw on Data-bass.com. Thank you, Mr. Ricci for pioneering this design. I'm sure you burned through a lot of 2x4's before coming up with what worked well.

I'll try to be brief. My stand is made from 4"x4"s and 2"x4"s. I used 5/16" lag bolts all around. 6" lags join the 4x4s and 3.5" lags join the 2x4's. No glue. The driver clamp uses 12" x 1/2" all thread, lock washers, flat washers and bolts.

PICS OR YOUR CONTRAPTION DIDN'T HAPPEN! But of course!

Four UM18's wondering "What's going on? Why are we here?" Mwuahahahaha! You'll find out....




Let's fast-forward to some action shots. The design just works. Thank you, Mr. Ricci.






Some pics of the stand. For reference, the long 2x4"s are 68 inches long. The 4x4"s are 25 inches (I think). BTW, all this wood is left over from other projects and I used it as-is. I cut nothing tonight. I keep ALL my scraps from disassembled or failed projects. The fact that the long 2x4s are almost 6 feet long really helps with this stand being almost tip-over-proof. The UM18 is 45 pounds and the stand isn't even close to tipping. I will state that at higher voltages the whole stand gets moving so I had to weight it down b/c it was vibrating too much for my tastes but it was NOT "tippy."






In this picture, you might thing the uprights that hold the driver look weak and unbraced. There are four, 6-inch lag bolts holding each upright to that bottom horizontal piece. It is extremely strong!



THE MONEY SHOT!!!

So, what's a UM18, running free-air at 15Hz and 60 volts sound and look like? Gotcha covered.


Using a Voltage Matrix I downloaded a long time ago, 60 volts @ 4 ohm load = 900 watts. I ran it like this for about 20 minutes; no bad noises from this driver! I then raised it to about 64 volts for a minute, which at 4 ohms is more than 1Kw. Hooray! I lowered the level to 37 volts, which at 4 ohms is 350 watts or about 1/3rd of RMS MAX. I will let it run overnight. I will repeat this test for the remaining 3 drivers and hopefully will have no problems with the remaining 3 drivers.

Initially, I broke-in these four drivers using a 23Hz tone @ 4 volts per driver for about 14 hours. I think THIS break-in can be considered "The Real Deal."


I had fun building this thing. Hope you enjoy this thread.
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Last edited by michaelddd; 07-31-2015 at 10:03 PM.
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post #2 of 15 Old 08-01-2015, 05:38 AM
 
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Using a Voltage Matrix I downloaded a long time ago, 60 volts @ 4 ohm load = 900 watts. I ran it like this for about 20 minutes; no bad noises from this driver! I then raised it to about 64 volts for a minute, which at 4 ohms is more than 1Kw. Hooray! I lowered the level to 37 volts, which at 4 ohms is 350 watts or about 1/3rd of RMS MAX.
When deciding on a safe input voltage the main concern isn't the rated Pe of the driver. You want to model the driver in a sealed box, making the box size 100 cu ft or more, which more or less duplicates no box at all, then raise the input voltage while checking the result on the excursion chart. That will tell you the safe voltage that doesn't reach xmax at any given frequency. Double check it against the maximum power chart, to be sure you don't approach Pe. To prevent the possibility of long term heat build up during the break in process go with as low a break in frequency as possible, for maximum excursion with minimum power. Finally, bring the voltage up slowly, and if you hear a problem back off, no matter what the calculations say the driver should be able to handle.
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post #3 of 15 Old 08-01-2015, 06:46 AM
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Originally Posted by michaelddd View Post
Some pics of the stand. For reference, the long 2x4"s are 68 inches long. The 4x4"s are 25 inches (I think). BTW, all this wood is left over from other projects and I used it as-is. I cut nothing tonight. I keep ALL my scraps from disassembled or failed projects. The fact that the long 2x4s are almost 6 feet long really helps with this stand being almost tip-over-proof. The UM18 is 45 pounds and the stand isn't even close to tipping. I will state that at higher voltages the whole stand gets moving so I had to weight it down b/c it was vibrating too much for my tastes but it was NOT "tippy."
Certainly not how I would have made the stand. For a stable stand that will resist tipping you want to put the center of gravity in the middle of the stand, not right at the edge. You've come pretty close to making a see-saw of sorts. If you put a driver that imparts more of a moment on the pivot point than your outrigger legs it's going to tip over or be very tipsy.
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post #4 of 15 Old 08-01-2015, 08:10 AM
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Certainly not how I would have made the stand. For a stable stand that will resist tipping you want to put the center of gravity in the middle of the stand, not right at the edge. You've come pretty close to making a see-saw of sorts. If you put a driver that imparts more of a moment on the pivot point than your outrigger legs it's going to tip over or be very tipsy.
it really could be made more stable just by mounting the driver facing the opposite direction(facing the long 2x4's)
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post #5 of 15 Old 08-01-2015, 09:05 AM
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Wouldn't you want to break in the driver at its Fs frequency, as that's the impedance peak of the driver, so you'll be getting a lot of excursion with a minimal amount of current to overheat the voice coil.

The stand isn't a bad idea. I wonder if you could fit two drivers on it, side by side, one facing forward, one facing backward. That'd cancel the motion somewhat. Might need extra hands to do that though.
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post #6 of 15 Old 08-01-2015, 09:36 AM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post
When deciding on a safe input voltage the main concern isn't the rated Pe of the driver. You want to model the driver in a sealed box, making the box size 100 cu ft or more, which more or less duplicates no box at all, then raise the input voltage while checking the result on the excursion chart. That will tell you the safe voltage that doesn't reach xmax at any given frequency. Double check it against the maximum power chart, to be sure you don't approach Pe. To prevent the possibility of long term heat build up during the break in process go with as low a break in frequency as possible, for maximum excursion with minimum power. Finally, bring the voltage up slowly, and if you hear a problem back off, no matter what the calculations say the driver should be able to handle.
Thank you, Bill. This is VERY helpful. I will get cracking with WinISD.


At this point I've verified that two of my four drivers are good. I haven't modeled them "free air" in WinISD, but I did put 60 volts @ 15Hz through them for about 15 mins each. No noises other than a whole lot of air being moved around.
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post #7 of 15 Old 08-01-2015, 09:39 AM - Thread Starter
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it really could be made more stable just by mounting the driver facing the opposite direction(facing the long 2x4's)

Good point! Didn't think of that. I'll do that with Driver #3 ; the 2nd one still needs a few more hours of "stretching."

@Stereodude: Good point...I didn't even think of putting the uprights in the middle. I basically made some notes of what I saw on Data-base and copied it. I can tell you that the uprights that hold the driver are resting on the floor. So the combination of them touching the floor, being securely screwed the horizontal piece and the length of the "sled" it really is not tippy at all. I can lean on the clamp with the driver in there and it does not move.

@rhodesj : I didn't want to chop up any new 2x4's for this project. The clamp pieces were already cut to that length; they aren't long enough to fit two of these beastly drivers. And I would need another set of hands, so it's out on that count too.
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post #8 of 15 Old 08-01-2015, 09:49 AM - Thread Starter
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Ho-lee-blowed-up drivers, Batman!


I modeled a UM18 in a sealed, 150 cubic foot box. At 15Hz the driver reaches XMax with just 42 volts...so it would seem that I've already driven the first two drivers way past XMax with no ill effects, thankfully. I'm glad my ignorance didn't cause a very expensive mistake.

I will be much more careful with the last two drivers. Wow, the more you know!!! You know?

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post #9 of 15 Old 08-01-2015, 09:53 AM
 
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Wouldn't you want to break in the driver at its Fs frequency, as that's the impedance peak of the driver, so you'll be getting a lot of excursion with a minimal amount of current to overheat the voice coil.
I hadn't thought about it, as I'm usually working with pro-sound drivers that have much higher Fs and a higher Pe to xmax ratio as well. With the very long xmax and low Fs of the U18 it does make sense, since it takes so much voltage to get it close to xmax. With a pro-sound driver with a third the xmax and twice the Fs, not so much.
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it would seem that I've already driven the first two drivers way past XMax with no ill effects, thankfully.
You have to go to xlim to cause damage. The purpose for not using enough voltage to exceed xmax is that while power goes up excursion doesn't in a linear fashion, so you're adding more heat for no good reason.
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post #10 of 15 Old 08-01-2015, 09:59 AM - Thread Starter
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Thanks again, Bill. So should I change the break-in frequency to 19.5Hz, which is the UM-18's FS?
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post #11 of 15 Old 08-01-2015, 10:46 AM
 
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Thanks again, Bill. So should I change the break-in frequency to 19.5Hz, which is the UM-18's FS?
It wouldn't be a bad idea, as power dissipation is minimized there, and you have to put a lot of volts in to reach xmax. OTOH you don't have to reach xmax, it just speeds up the break in if you do.
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post #12 of 15 Old 08-01-2015, 10:48 AM
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it really could be made more stable just by mounting the driver facing the opposite direction(facing the long 2x4's)
A very good point.
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post #13 of 15 Old 08-01-2015, 05:15 PM - Thread Starter
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On Driver #3 right now and all looks good. Ran it at 50 volts for a few mins @ 19.5Hz. According to the WinISD "free-air" sim, that put the cone at about 1.5mm under XMax. No funny noises at all. It's now cooking at a happy 35 volts which puts it around 2/3rds of XMax.


Interesting side note: I reversed the driver (cone towards the long side of the sled) and the whole assembly vibrates a lot less. In fact, the stand barely shakes at all. Strange.
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post #14 of 15 Old 08-01-2015, 07:30 PM
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Interesting side note: I reversed the driver (cone towards the long side of the sled) and the whole assembly vibrates a lot less. In fact, the stand barely shakes at all. Strange.
It's not strange. With the driver hanging out away from the base, you have created a moment arm that is attempting to tip your test stand over. With the driver hanging over the legs, the moment arm is exerting force on the legs, which of course is more stable. As someone else pointed out, a 2-3ft long base with the driver mounted in the center would be even sturdier.
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post #15 of 15 Old 02-12-2016, 08:37 PM
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I missed this thread. My stand is setup somewhat different. I'll post some pics when I can. In short the 2×6's are arranged with the driver mounted on one end where the length is away from the driver. I then put 50lb dumbells and sand bags on the top piece to lower the resonance. Even with a lot of mass, stiffness and clamp force there is a resonance that will show up in the system with high mass drivers. The extra added weight drops it down to around 6 Hz where it doesn't interfere with impedance measurements as much.
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