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Old 30th January 2009, 11:49 PM   #2871
tinitus is offline tinitus  Europe
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Quote:
Originally posted by just a guy

Opinions? Which number should I use? An average?

According to the "professors" in the art of measurements you cant trust such "home made" specs...but I really dont know
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Old 31st January 2009, 01:17 AM   #2872
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Quote:
Originally posted by just a guy
I'm hoping to get a reality check on the measured parameters from anyone with experience measuring parameters. I'm pretty sure some of the parameters are good (fs, qts, qes, qms, Le), not so sure about VAS. Re measured using an ohm meter, and corresponds with the lowest spot in the impedance sweep in LIMP.

Click the image to open in full size.

The driver was tested several times over several days, all the while being used in the small sealed box to break in.

The large difference in VAS measurement could be a big problem, not sure which to trust. VAS seems to be a factor used to calculate CMS, RMS, MMD and BL, so it would appear to be incredibly important.

Opinions? Which number should I use? An average?
This stuff used to drive me up the wall. I was using Speaker Workshop to measure drivers and the specs were all over the map. I finally spent $150 on a PE woofer tester II and never looked back. Best $150 I ever spent. I like it so much I even bought a 2nd one when I couldn't figure out where I put the first one! (It's very small, the size of a keychain, and easy to mis-place.)
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Old 31st January 2009, 01:40 AM   #2873
tinitus is offline tinitus  Europe
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Quote:
Originally posted by Patrick Bateman


I finally spent $150 on a PE woofer tester II and never looked back.

Just looked...100USD incl pocket scale

But I honestly dont understand why such a cheap thing would be more reliable than factory specs

Ok, I know drivers vary
But if its that significant there seems to be no point in it anyway
I mean, who wants a right and left speaker with different size
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Old 31st January 2009, 01:54 AM   #2874
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Well, I don't want to buy the woofer tester unless the results are disasterous and I absolutely need to.

I took ALL the results of the individual parameter tests and plugged them into the box design I've been working on for the factory specs. All the closed box parameter tests still look ok in the original design (these closed box parameters suggest the box is a bit too big). All the added mass parameter tests don't look quite so good (these added mass parameters suggest the box is a bit too small). So the original design looks like a good middle of the road compromise which should work reasonably well regardless of which parameters are right. But hopefully the added mass parameters are wrong, they look the worst, and the worst of those would be disaster.

So I just have to take the hornresp data, fold it up, CAD it out to get the angles and make a cut plan, build a prototype, and I should have frequency response measurements within maybe a couple of weeks. Once I get those measurements I should have a reasonable idea of which parameters were right and I can make my set of 4.
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Old 31st January 2009, 02:28 AM   #2875
Mark Kravchenko --- www.kravchenko-audio.com
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Default Try this Link

Just a guy

http://home1.stofanet.dk/cfuttrup/dpc.htm

This program will help you sort things out. It is a bit sparse on the interface but there is a lot that can be learned from it. Input the specs that are certain and it will figure out the rest. There are great tutorials on measurement as well in the readme files.

The Qms is linked to the total mechanical system. That is the cone, spider and surround + cone and dust cap. This measurement is effected also when you do a closed box test. If the box leaks or the seal between the box and the driver leaks you will get wild fluctuations in the measurement. It is very critical to make sure there are absolutely no leaks when you are calculating VAS.

Your specs look good except the VAS The mass added method looks close. It is also critical that you have an accurate idea of how much mass you put on the cone and if the mass is evenly distributed.


If you did the mass method carefully it is quite accurate. I personally tape on nickels to the cone and use them as weights. They are very tightly regulated for weight. You can find their exact weight on the net most years are 3.94 grams for Canadian nickels.

After measuring more drivers the long way then I care to remember I to turned to the little woofer tester. It is some sweet little thing and actually very accurate. Especially when you figure in the cost.

Mark
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Old 31st January 2009, 11:58 AM   #2876
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Thanks, that's a neat little program. Unfortuanately it doesn't help me at all. I don't have any missing parameters, I just need to verify VAS.

My chart has a typo. QMS is wrong for the added mass method, it's supposed to be the same as the closed box method. The chart is supposed to show that all parameters are within a very tight range except VAS.
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Old 9th February 2009, 01:18 AM   #2877
aceinc is offline aceinc  United States
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I'm moving along towards a finished th-spud style sub with Trio 8's. The drivers have arrived, most of the wood is cut, the layout has been drawn on three sides for nailing. I should have it ready for testing next weekend (lord willing & the creek don't rise)

Here's a question I should know the answer to but I'm not sure. When two 8 ohm drivers that have a rated power handling of 200 watts are hooked up in parallel the result is a 4 ohm load of course but what is the resultant power handling? 200 watts? 400 watts?

Also what is the current thoughts on the best way to attach the driver maintenance panel?

Paul
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Old 9th February 2009, 01:59 AM   #2878
FlipC is offline FlipC  United States
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Their power rating will be effected by the enclosure itself.
THs raise the sensitivity but can lower or raise their power handling capabilities depending on the compression put apon them. Do a model of your setup in HR/Akabak to get a good idea of what they can handle.
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Old 9th February 2009, 03:52 AM   #2879
aceinc is offline aceinc  United States
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In Hornresp when using two drivers of the same type, what parameters need to be changed? I assume sd needs to be doubled and Re needs to be halved.

What about;

Mmd - Doubled?
Bl - Doubled?
Cms?
Rms?
Le?

Once I get all the parameters entered, how do I go about determining power handling?

Paul
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Old 9th February 2009, 04:17 AM   #2880
aceinc is offline aceinc  United States
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Never mind, I forgot there was a place to enter the number of drivers.

But I still don't know how to calculate max power handling.

Paul
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