Measuring driver parameters vs the data sheet values

[ggidzinski]

Originally Posted by DRONE7

Life is a lottery... Specs are Puffery... <snip>

I couldn’t agree more but some of my numbers are so different from the data sheet that my box volume calculations are different by 2X. Because of this I need to make sure that I am measuring correctly before moving on.

Thanks,
George

Originally Posted by wintermute

Clamped securely (in some sort of frame) in free air away from any nearby objects is ideal. Don't sit the driver on it's magnet, especially if it has a vented pole piece.

Tony.

I did have the driver sitting on its magnet so I’ll try different mounting. I did notice that the weighted VAS measurement is very finicky so maybe I still have some errors in technique.

I have noticed a huge difference in listening impressions after a week of break in on a completed set of speakers so maybe breakin is part of the issue. Do you guys break in the raw driver in free air or mount it? Do you use a signal generator or music material?

Thanks,
George

[celef]

I have heard from a manufacturer that drivers should be runned in with music only and at moderate drive levels, using a single tone can have impact on how the glues between parts hardens

[ggidzinski]

I took an Aura Sound NS3-193-8A and tested it:

A) Data sheet
B) In a sealed cabinet
C) Mounted unsealed cabinet
D) Free air suspended by faceplate
E) Free air sitting on the magnet

Most of the measurements were closest when free air sitting on the magnet (E) except Qms:

--------A------B------C-------D------E
Re---7.60---7.79---7.71---7.72---7.72
Fs------80---137----121----125----123
Qts---0.67--1.07---1.02---0.94---0.87
Qes---0.73--1.28---1.22---1.12---1.08
Qms--8.00---6.61--6.15---5.79---4.49


It's on to music break in and another free air measurement.

George

[ggidzinski]

I burned in the driver for 12 hours with music material. It changed the numbers, but not enough to explain the large differences from the data sheet (A). I added those values as a new column (F):


--------A------B------C-------D------E-------F
Re---7.60---7.79---7.71---7.72---7.72---7.78
Fs------80---137----121----125----123---112
Qts---0.67--1.07---1.02---0.94---0.87---0.84
Qes---0.73--1.28---1.22---1.12---1.08---1.03
Qms--8.00---6.61--6.15---5.79---4.49----4.5


What is a cost effective alternative to my DATS2 measuring rig for getting TS parameters from a raw driver that is known to be accurate?

Thanks,

George

[planet10]

T/S are curves, not scalars.

Different measuring kit pulls the number from a different part of the curve, so measures can be significantly different. Also whether the sw estimates the parameters or actually measures them. Short of the pro stuff the factories use (ie $5k-ish), Smith+Larson Woofer Tester 2 is probably the best short of them.

I always start with the factory numbers,i have rarely had to redo a box. Also keep in mind that depending on the manufacturer parameters will vary from plus-minus 5% to plus-minus 20& or more.

I use S+L for driver matching and unknown drivers.

dave

[ggidzinski]

I am beginning to think that measuring TS parameters at my equipment price point is a waste of time and that as you suggested, perhaps I should just go with the spec sheets. The crossover design is different because we measure and listen to the drivers in the box but it sure would suck if the initial box sizing was way off because the data sheet specs are BS.

It almost appears to be easier to have a bunch of crude boxes built at a few different volumes (or make one that is configurable with partitions or something to find the right tuning through experimentation and forget making a commitment to a full up furniture grade cabinet build based on just these wildly variable TS measurements.


George

[wintermute]

On the question of whether there are any cost effective alternatives to your DATS 2 for getting a different reading, then provided you have a sound card already with line out and line in then the answer is yes.

The most cost effective option is to make up a simple cable with one resistor and to use software such as REW or ARTA to measure the impedance and calculate the T/S params.

You need the impedance cable here Cables

Note that for REW and ARTA you ideally should use a 100 ohm resistor not 10 ohms as per the diagram.

Some soundcards struggle to drive a speaker directly. If that is the case then using an amplifier to drive the speaker may be needed, but make sure to keep the levels low. Use a 100Hz sine wave and an AC voltmeter to set your voltage to 1V or less. There is a risk that you can fry your soundcards input if you use and amp and don't have some sort of attenuation.

I myself use a Walin Jig II which I made. http://www.raymondaudio.nl/files/jig.pdf

edit: I posted some rubbish which I have deleted Oh now I see, I'm not going crazy, your latest table has the wrong specs for manufacturer params

Tony.

[celef]

many years ago i used clio lite for measurements, but i found that justmls in lspcad gave me almost identical results so i stopped using it, dos-based as it was. Today i find that justmls gives me almost identical results to stepped sine in limp (arta), mls in i limp differs though.
justmls does not do any calculation so i do the calc by myself, i put the numbers in a excel spreadsheet.
stepped sine in limp works poorly on my computer, it often crashes. limp do t/s calc, but it reads the inductance value in a non standard way, i am not sure what is going on there.
clio seems still to be highly regarded and trustworthy so i would go for clio pocket if i was to buy a new system today, even though i am not sure if the chirp stimuli is the best stimuli for impedance measurment of some drivers

[ente]

...before going on with your discussion about measurement software /systems have a look at this Klippel paper:

https://www.klippel.de/fileadmin/kli...equency_fs.pdf

Regards
Heinrich

[Lojzek]

What's going on with vintage clio system is that its math procedure to calculate L1 and L10 inductance values within TSP evaluation is simply wrong. These figures are useless anyway. I have checked with clio pocket, and there it is set right. I still have got 2 machines to keep the clio board functioning powered by pentium slot1 300Mhz processor. The best investement I made diy wise, clio I mean.