Woofer Tester 2 - LE14A Fs

[Zilch]

Heh, heh....

Screen shot jpeg's are pretty big, 104K. Gotta work on a protocol here.

Surprised it even runs on this worthless old piece-o'-crap Compaq Win98SE system.

It's certainly no wonder them old LE14A's sound bad before refoaming. :p

[4313B]

:rotfl:

I honestly can't believe everyone didn't take advantage of the free recones JBL did for so many years to replace Lans-a-Loy.
Good thing for JBL (and all of us) the WWW didn't exist yet or they'd have gone under fulfilling all the warranty claims.

[spkrman57]

We did not know. I would not have sold off my 4 LE-14A's except that no-one seemed to have the proper surrounds.

Oh well, they are gone for some time now and it don't matter.


Ron

[4313B]

I think it was around 1985 when JBL finally did away with the free recones for all transducers with Lans-a-Loy surrounds.
It was quite the good will gesture while it lasted - roughly ten years. :yes:

[Zilch]

It wanted 27.6 nickels. Maybe use handkerchief next time.

Fs doesn't present the sweep data in results. Gotta do an arbitrary scan to get that, apparently.

[p.s.: They're BEASTS, substantially as advertised.... :p ]

[Zilch]

After 10 hours pink noise, 80 dBa @ 1M, LE14H-3 dropped Fs only 1.15 Hz. Vas increased somewhat. Butyl surround LE14H-3 has only minor parameter shifts after break-in:

[Earl K]

Hi Zilch

Re: le14h-3 and your published MMS figures for them ;

- Are you confident in those figures being accurate ? ( in that those fourteens' mms figures are in the plus 200 grams range ?) ( I'm a bit sceptical that this particular motor can support that sort of cone weight ).

- As a sort of control figure , could you obtain some mms figures for your newly refoamed le14a woofers ?
( This will offer a reasonable test of "The Woofer Tester II" )

Thanks <. EarlK :cheers:

PS ; What project are these 14s' meant for ?

[4313B]

The mass has to be fixed to the cone.
Use double stick tape.
http://www.rockler.com/ecom7/product_details.cfm?offerings_id=689&filter=50492

Make sure vents aren't blocked on the backs of any drivers.

[Zilch]

I'm measuring an array of 5 different "flavors" of LE14's here, actually, and the Mms results are varying widely. I've started a spreadsheet to compare results. I consulted with the WT2 designer yesterday, and here's what I found out:

"The act of testing a box automatically re-calculates Vas. Testing a box is the same as doing a delta-compliance Vas test. Does this make sense? I consider delta-compliance better than delta-mass since it tests your driver in the act of doing what is is designed for: playing low freqs in an appropriately designed box. The Vas returned in delta-compliance should be reasonably close to the Vas returned in the delta-mass test. I consider the Vas returned by delta-compliance to be the most accurate Vas number."

Mms is computed. WT2 provides two (actually three) different methods of determing Vas. The delta-mass method using nickels is less accurate than the delta-compliance method using a known vented box. I'm using Citation 7.4 as the standard box, and will compare the results. I quickly learned you gotta use a noodle on the drivers to get a decent seal. None came with the LE14H-3's, of course.

Using the nickels is a convenient method of accomplishing delta-mass. But if you hafta stick them on there, it becomes a PITA, as that should be done on the rear of the cone, most likely. I'm switchin' to delta-compliance here, except for "ball-park" determinations. Using clay with a scale is too diffucult, and I don't like the idea of stickin' stuff to old Aquaplas, either.

For testing outside the box, I'm just setting the drivers face up on the concrete floor. There's some discussion in the instructions regarding the influence of test bench resonances, and, at least in this respect, the solid floor is a good approach.

Considering the rear pole vent problem, the cone movements are very small, and the irregularities in the concrete provide multiple "leak" paths. I did sequential runs on one unit with the driver propped up about 1/4" and did not find a significant difference, but this requires more investigation. I'm also considering making a vented aluminimum or stainless steel ring as a base for testing vented drivers.

Earl: Y'all KNOW where this is goin', surely.... :p

[I'll get something up in the "project" thread in a couple of days, probably. For now, I'm stumblin' over LE14's all over the place here....]

[4313B]

Yeah, G.T. has stated he prefers test boxes while the "other guys" prefer to slather clay all over the cones (thus ruining them). :p

You can read about the cone volume here and make yourself a little spreadsheet you can plug the variables into for easier computation.

http://sound.westhost.com/tsp.htm

[spkrman57]

I usually had around 3 test cabinets available to test drivers.

It is much faster than the mass-weighted test also.

Ron

[Zilch]

Results became stable with standard box testing for Vas, and realization that there was a low-pass filter hidden in the Citation 7.4 box that had to be bypassed. Looks like unknown black-face reconed "H-U" was done with a H-1 cone, as suspected:

[Zilch]

And the H-3's:

[Yeah, I know, too much data. But after redoing them all three times....] :p

Tips:

Q, Fs testing done sitting on (spanning) two 1/4" stainless plates so pole vents are open to the concrete floor.

Vas testing done with test box horizontal so driver faces up, same as Q, Fs.

In theory, Fsb should be the same for all of these similar drivers. Indeed, Fmins came out the same. I don't know what's going on with the calculation of Fsb there, but will inquire....

[4313B]

I don't know what's going on with the calculation of Fsb there, but will inquire....Yeah, see what they have to say.

Looks like your LE14A is nice and strong. Zap it with a kilowatt burst or drop it on the floor and see if you reduce the Bl. :p

[WTPRO]

Hi Zilch

Look at the three points, Flo, Fhi and Fmid corresponding to the zero phase points in your data. Fsb is then calculated as shown below. Note how the driver with very low Fsb has both lower than normal Flo and Fhi.

Fsb = Flo*Fhi/Fmid;

The 'bouncing nickel' problem is created when you have a strong motor and light cone producing a high velocity, and therefor high acceleration. If the downward acceleration exceeds gravity (9.8m/s^2), the weight free falls as the cone is pulled from underneath faster than the weight can fall.

Suggestions
1) Lower the Idrive
2) Glue multiple nickels into stacks
3) A pivoting motion in the weights can also cause trouble (lots of nickels laying against each other?)
4) Add something sticky to the weight. This will sometimes keep the weight from lifting or rocking.
5) Be sure to have free air flow for the vent

Some purists will also tell you the driver needs to be as far from a surface as possible and will go to great extremes to hang a speaker in mid air using strings. Free weights wont work, so you will need to use clay/caulking.

What is interesting is that if comparison Q/Fs measurements are made for 'free air' and 'table top' a difference pops up. In free air, not only is the cone/coil a reaction mass, but so is the magnet. The ratio of the two now need to be worked in!

So what happens if your driver is put on a table top? Now you need to consider that the table top is a reaction mass and spring! A big heavy speaker cabinet tends to work well. If you have two, put your test subject between them.

Or, use a vented or closed test box... but then you have to a) have a test box and b) make an assumption about the volume of the test box. Box flexure/loss can skew the data, but at least the box should be consistent.

Cheers,

[4313B]

Thanks WTPRO! :)

[Zilch]

Indeed, many thanks, WTPRO!

[So many sweeps; so little time.... :p ]

[WTPRO]

I am a bit new to this message board style and almost missed the 'page 2'. I found you guys with a google and thought I might toss in a few pointers (and something to add to the Help file).

Also, If you keep an eye on C&S Audio's web site www.woofertester.com, a 1.02 'beta' will probably be posted in a few weeks.

[Zilch]

Comprising 4 ea. 25-Ohm, 10W wirewounds in parallel with 6 mH, 0.83 Ohm laminate-core inductor, all in series with the LE14H-1 woofer. Hidden behind the insulation, it caused me three days of agonizing doubt regarding woofer and box measurements. Note polarity reversal to make AES Standard H-1 conform to JBL (-) polarity. :D

[Or something....]

[Mr. Widget]

For testing outside the box, I'm just setting the drivers face up on the concrete floor. There's some discussion in the instructions regarding the influence of test bench resonances, and, at least in this respect, the solid floor is a good approach.

FWIW:

When measuring the impedance of a woofer with Clio I've noticed quite a difference between sitting the woofer on a surface... any surface, and hanging it in free space. I have had it on a foam covered surface and a carpeted cement floor... they both change the results compared to true free air tests.

How long does the woofer tester take to run a sweep? I have found that if I use a lower resolution I can hold the woofer under test for the few seconds required and the results aren't too much different than from a higher resolution measurement.

Widget

[Zilch]

How long does the woofer tester take to run a sweep?WidgetAbout 2 minutes with 80-point resolution starting at 10 Hz.

15 - 20 seconds using low resolution.

I'm elevating them off the floor on heavy stainless plates now, so the vent is not covered....

[Mr. Widget]

I'm elevating them off the floor on heavy stainless plates now, so the vent is not covered....
I think I'd also use a damping pad or blu tac or something...

Hmmm... 80 points sounds kinda low to me, I'd stay with that resolution. As long as there is no surface to reflect the sound waves back toward the cone you should be OK... obviously also not blocking any vents.

If you want, for kicks, you might bring a tested woofer over and we could run a Clio sweep to do a comparison.

Widget

[4313B]

If you want, for kicks, you might bring a tested woofer over and we could run a Clio sweep to do a comparison.That would be great. Do the WT2 test at the same time in the same environment. It's highly portable and can be up and running in a minute or two.

[WTPRO]

There are several WT2 settings that will allow the tests to run faster.

1) As the pivot point is searched, the search eventually falls out when the 'search ratio min' value is reached. The default 0.1% is pretty darn small. The idea was to make an impression.

2) If you close all child windows and look under options, the WAV buffer size settings and some filtering options can be set. This can effect speed and stability. YMMV (your milage may vary).

Cautions:
Some older PC's, typically with very slow graphics, can barf if the frame size is set where the frame rate exceeds the graphics card update rate. Increase the WAV buffer size to solve.

I cant recall if the values are checked all that well (making a note to myself), so keep to powers of two 8192, 16384, 32768... And if something does go wrong, simply delete the WT2.CFG file and restart to get the defaults.

3) Set SweepLo/SweepHi to bracket the required sweep range for T/S calculations. Keep in mind that in the future Lem, Rem (enhanced T/S modeling) will be supported, so you may want to get used to 20K as the high end. The points of interest for that calculation are the zero phase point above Fs and SweepHi.

4) Step ratio: The default is 1.300 and produces pretty clean looking results. Experimentation here may produce faster times.

Hope this helps
Best regards
Keith

PS: Another new feature that will be going into version 1.02 is a point and click frequency setting with the left mouse button. After the meter settles down, that data point can be added to the current data set with the right moust button. Real nice for cleaning up choppy graphs!

Also, since I see someone measuring crossovers... has anyone noticed that the Z of the supplied test leads can vary as much as j*0.250 ohms (inductive) at 20Khz? This is caused by the area enclosed by the wire loop, which is what goes into the equation for calculating inductance. If you go check various cables and things, you may be surprised. Example plots of this effect using the supplied test leads are given in the help file (the only two plots in fact). These plots are created by compensating the WT2 with a 'zero length' test cable. Basically you plug the CalR and a shorted banana jack directly into the box when asked.

If high frequency accuracy is required, the best solution is to make a test cable out of 3-10 feet of zip cord (any kind of crap cable should work). This keeps the wire spacing constant allowing the WT2 compensation algorithm to do its thing in a consistent way. As long as you compensate the cable, these effects will be nulled. If you compensate properly and do an arbitrary sweep on the calibration resistor you should get a flat line for both Z and phase from 1-20K. You should be looking for +/-10 millohms and +/-0.1 degrees flatness or better.

[Robh3606]

Hello Keith

I don't have a testor yet but plan too. Thanks for the great information you have supplied.

Rob:)

[4313B]

Comprising 4 ea. 25-Ohm, 10W wirewounds in parallel with 6 mH, 0.83 Ohm laminate-core inductor, all in series with the LE14H-1 woofer. Hidden behind the insulation, it caused me three days of agonizing doubt regarding woofer and box measurements. Note polarity reversal to make AES Standard H-1 conform to JBL (-) polarity. :D

[Or something....]:banghead: You certainly don't need all that junk in your passive sub. That's what active filters or AVR's are for.

[4313B]

There are several WT2 settings that will allow the tests to run faster.While I am a speed freak and will check the settings you recommend I also remember the days of using 50 pound HP vacuum tube test gear and graph paper before we got a Urei plotter. It's hilarious to be able to pick up this little doohicky and the CDROM and take them anywhere I feel like taking them. :p

Thanks for the tips Keith!

[Zilch]

From the looks of that crossover sweep, I'd say we're getting good results.

Perhaps someone can compare it to sim predicted performance.... :)

[4313B]

Here's the voltage drive with an 8 ohm dummy load.

[WTPRO]

Hello Giskard

The WT2 banana jack outputs are connected to a current source that is *not* ground referenced, which is why you dont want to connect it to something that is grounded. For example the ground clip from most oscilloscopes will be (eventually) connected to OSHA ground... AC wall ground... and maybe PC ground (laptops might be floating).

The mini-jack output is a voltage output with a 470 ohm series resistor for protection (simple, but it works). This *is* ground referenced to the PC ground. My only suggestion here is to check the PC grounds with respect to whatever else you are doing. PC's are notoriously bad for such things.

If I am guessing your intentions properly, you want to know the speaker attenuation for a given frequency. The WT2 cant measure this directly, but it can derive the electrical characteristics of all the components. From this, you would be able to use the circuit simulation program.

However, for best results you will need to wait for the software I am working on that includes Xem and Rem. You have no doubt noticed that a speakers impedance increases above Fs, but have you considered how simplistic including (or not) Le is? Xem/Rem are frequency dependent 'correction' factors that can go into a T/S model that more or less correctly resolve Z and Phase at all frequencies.

What you may not realize is that your speaker 'load' can also be represented as an RLC tank circuit in series with Revc. All you would need is something to generate those values. Hmm, this would be easy for a speaker in free air, but vented boxes might be a bit more challenging.

You will also probably quickly point out that the WT2 does not directly measure capacitance (there is a lame reason). You need to put an R in parallel with capacitor to keep the current source from swinging to the rail. Also, the math I was dinking around with was not giving me what I considered full precision at all frequencies.

Dont let this stop you! A 1K resistor will easily keep the current source from saturating and will have minimal effect on the capacitors reactance. A quick reverse calculation of capacitive reactance and voila... you have capacitance. IE, Xc=1/(2*pi*F*C), C=1/(2*pi*X*F).

BTW, the problem was that I wanted at least 3 digits of accuracy accross a fairly wide frequency range before I considered the compensation algorithm 'nailed'.

Or... quite possibly the capacitor I was checking was crap.

Cheers,

[4313B]

Ok!

Now that I know what you were doing in post #19 here's your answer to post #28 -

[Zilch]

Neophyte that I am, I found the exercise with that simple circuit illuminating. Below 10 Hz, it's just the DCR of the coil in parallel with the resistors, basically.

Above 1 kHz, where the coil has gone high impedance, only the resistors remain in play.

Fun stuff, this. :D

Why it was deemed appropriate to let the HF pass at all in Citation 7.4 remains a mystery to me. Perhaps it's an artifact of another design objective there. :blink:

[It certainly messed up my woofer tests for a while, tho.... :p ]