Used my new wt3 on a monster subwoofer!

[Brian Steele]

OK I suspended the sub between chairs and the consitencey was WAY better.

175 gram test
* Piston Diameter = 400.1 mm
* f(s)= 38.36 Hz
* R(e)= 9.67 Ohms

Re still seems suspect. Did you run the WT3 through the calibration and test lead resistance routines?

If Re is off, Qes and Qts will also be off. Confirm the Re measurement with a MM if possible.

[rogoll]

Most woofers have a vent on the back, so they need to be supported in some way that allows free flow for the vent. Setting them directly on a table top would block the air flow.

[Taterworks]

- Break the driver in by running it to its Xmax for an extended period. This is best accomplished by applying a sine wave tone at the driver's Fs, and increasing the amplitude until distortion from overexcursion becomes audible. If you hear 'clacking' or 'popping' from the cone, decrease the amplitude.

-Don't use delta-mass Vas testing on drivers with a large Mmd (heavy moving structure). As a rule of thumb, you probably shouldn't be using delta-mass testing on anything more than an 8" driver, and you shouldn't use delta-mass testing on long-excursion drivers. For delta-mass testing to be valid, the Fs of the driver must be shifted downward by 25% or more as a rule of thumb, and accomplishing this with drivers that already have heavy moving structures can require an extremely large mass to do this - so heavy that the voice coil will be offset in the magnetic gap. Professional sound drivers (large cones, short voice coils, floppy suspensions are typical) suffer more from VC offset issues than a driver with a stiffer suspension and smaller cone area.

-When performing delta-mass testing, the mass must be rigidly attached or bonded to the cone, not simply placed on it, because with the diaphragm facing up, on an inward stroke, the acceleration of the mass element will be that of a body in free fall (9.81 m/s downward), while the acceleration of the cone may be much more. Modeling clay is a favorite material for delta-mass testing, and another good material is the silica-based Mortite speaker sealing caulk sold by Parts Express. The residue left behind by sticking clay or Mortite putty to a speaker cone can be wiped away with a slightly damp sponge, but even this may not be possible on some untreated paper, kevlar/paper, wood pulp or carbon/paper composite cones that absorb moisture. Delta-mass testing on titanium cones should be avoided because any significant localized pressure on the cone surface can leave an indentation. The mass must be attached or bonded near the center of the cone. As a test, when the driver is tilted vertically, if the mass simply falls off the cone, the bonding isn't sufficient to get good data.

-Delta-compliance Vas testing (putting the driver in a tiny sealed box, which changes the overall compliance) results in data that is typically more reliable than delta-mass Vas testing.

At the tent sale, I saw a technician measuring drivers with a WT3 by placing a large rubber O-ring on them for delta-compliance testing. This would not be a valid method for measuring Vas, and the data from that testing is probably inaccurate, because the mass is not bonded or rigidly mounted to the cone. Also, I remember a fiasco where a member of another major speaker-building forum accused a small-run driver builder of publishing inaccurate parameters for a long-excursion 15" driver because they had measured the drivers themselves and their own measurements were greatly off from the published specs. Guess what? They were using delta-mass Vas testing, and they were not using nearly enough mass, and simply placing it on the cone instead of bonding it.

[Taterworks]

(In this day and age, it shouldn't be possible to double-post! Dammit...)

[PapaEcho]

Re still seems suspect. Did you run the WT3 through the calibration and test lead resistance routines?

If Re is off, Qes and Qts will also be off. Confirm the Re measurement with a MM if possible.

calibrated test leads as well as resistor and used .999 as the muli meter displayed for resistor not the stock number.

I then used my mastech true rms meter on the woofer and it read 9.7 with test leads being calibrated for this meter as well.

All checks GOOD.

[PapaEcho]

-Delta-compliance Vas testing (putting the driver in a tiny sealed box, which changes the overall compliance) results in data that is typically more reliable than delta-mass Vas testing.

I will need to build some small enclosures for furthur testing.

[johnnyrichards]

Sounds like a giant 12 ohm mid-woofer.

[johnnyrichards]

Also, there are very few, if any, universally accepted methods to obtain accurate T/S results. This topic comes up from time to time... Delta Mass vs. Delta Compliance. Horizontal vs. Vertical. Small signal vs large signal. Extended break-in vs nominal break-in.

Who has the measurements to prove one method is more accurate?

[Jeff B.]

Also, there are very few, if any, universally accepted methods to obtain accurate T/S results. This topic comes up from time to time... Delta Mass vs. Delta Compliance. Horizontal vs. Vertical. Small signal vs large signal. Extended break-in vs nominal break-in.

Who has the measurements to prove one method is more accurate?

Well actually, a couple of those shouldn't really be debatable, unless people don't understand the topic. First, even though it won't matter too much with many drivers - all woofers are designed for the suspension to properly center the voice coil in a vertical orientation. When positioned horizontally some could find the coil off-center from the gap. Second, T/S parameters are DEFINED as small signal parameters. It's no arguement that they may turn out differently with a higher signal, but this no longer meets the definition, and the box model we use won't produce the same accuracy in results. So, if we really want to do it correctly the driver, especially if it has a high Mms or a high compliance, should be tested vertically and with a small signal. As for break-in, it needs to be "enough". That's different for different drivers. I find delta mass to work well, so I have no problem with using that simple method.

[johnnyrichards]

What about designing for downfiring or upfiring? There are also people who claim that some drivers have too high an MMS to yield usable results with small signals.

I don't know, I just read more contradictions than affirmations on this topic.

[PapaEcho]

Well I test horizontally with it suspended about 3-4 feet from the ground and my measurements are now repeatable, that for one was my first hurdle (repeativeness). Now I can prodce the same results using 200-300 grams of play-doh. It seems to me that everyone has their own opinion so I have formed my own. I will continue to test in different manners. To see what I come up with. I suggest there be a cumulitive thread started on the wt3 to see what everyone comes up with. Much like the one done for the lab12 and/or the bill fitz subs.

[Jeff B.]

What about designing for downfiring or upfiring? There are also people who claim that some drivers have too high an MMS to yield usable results with small signals.

I don't know, I just read more contradictions than affirmations on this topic.

There is a simple formula for determining the amount of sag you would expect to see from the suspension if mounted horizontally, but this still doesn't change the correct way to measure T/S parameters. For what it's worth, I have only found one driver that I had a hard time measuring accurately using small signal analysis and it was a very unusual driver (I think I could have stood on this driver without moving the suspension). All of the TC Sounds and Lambda woofers with the fairly high Mms cones still measured fine with a small signal. However, they HAD to be positioned vertically or the heavy mass and compliant suspension allowed enough sag to throw off the parameters. With lighter small drivers you will see almost no difference in measurements between the two positions. The internet is full of contradictions and debates, and "experts" abound. I'm not one, but I can at least say that I have read the real expert's papers, and they are pretty consistent (and don't always line up with the "experts" on the internet).

[Jeff B.]

Well I test horizontally with it suspended about 3-4 feet from the ground and my measurements are now repeatable, that for one was my first hurdle (repeativeness). Now I can prodce the same results using 200-300 grams of play-doh. It seems to me that everyone has their own opinion so I have formed my own. I will continue to test in different manners. To see what I come up with. I suggest there be a cumulitive thread started on the wt3 to see what everyone comes up with. Much like the one done for the lab12 and/or the bill fitz subs.

From what I can tell from reading the thread - your measurments are fine.

[johnnyrichards]

I wasn't trying to be contentious or posing as an expert - just honestly curious and lost in the debate.

[PapaEcho]

From what I can tell from reading the thread - your measurments are fine.

These motor structures are not super power houses, everytime I ran the test I heard the sweep so they were ALL audible. Is the Mass measurement semi accurate?

[Brian Steele]

I find delta mass to work well, so I have no problem with using that simple method.

Another argument for the delta-compliance method is it's a better reflection of how the driver is actually going to be used. You hardly see speaker systems which involve mass added to the driver rather than the driver enclosed in some type of box .


The only pro-argument I can see for the delta-mass method is that it's easier (you don't need a test box). Of course, if you've built a test box already, that point is moot.

[Brian Steele]

Sounds like a giant 12 ohm mid-woofer.

Or an OB or IB driver designed to be used in pairs.

Just out of curiousity, what's the cost of this driver?

[Jeff B.]

I wasn't trying to be contentious or posing as an expert - just honestly curious and lost in the debate.

I wasn't referring to you. I was only saying that in many of these debates I notice a lot of "experts" who don't really have all of their facts straight. It is certainly true that there is more than one way to do some of this. However, in the end you may find that some of this ways net nearly identical results anyway.

[PapaEcho]

Or an OB or IB driver designed to be used in pairs.

Just out of curiousity, what's the cost of this driver?

2-18's Free!

I do side work for this company (ie web building, speaker testing, technical opinions, etc)

They retail for 150 shipped each. I found a sub on PE somewhere with similar specs and it was hundreds more.

Not sure what the best use of a sub with these parameters are but there are others out there similar.

[Jeff B.]

Another argument for the delta-compliance method is it's a better reflection of how the driver is actually going to be used. You hardly see speaker systems which involve mass added to the driver rather than the driver enclosed in some type of box .


The only pro-argument I can see for the delta-mass method is that it's easier (you don't need a test box). Of course, if you've built a test box already, that point is moot.

Well I can't argue with that, but getting very accurate weights is very simple too, and the accuracy here matters quite a bit. Whereas a box has a volume and a Ql to deal with, and we need to make sure we are accurate here too. I'm not saying it can't be done, but there is certainly room for error, more so than you are likely to get with a digital scale. Even though adding mass is not exactly the way we use the driver, as you point out, it does still offer an accurate way to determine the compliance mathematically. If we use a test box then we had better make sure we have covered our bases.

Jeff