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.

[4313B]

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.

[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.... ]

[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

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...9&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....

[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).

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....]

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.

[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,