A quitck T-S measurement question about useing scope.

[digits]

I would like to follow the routine on T-S Parameter Calculator to do some T-S measurements on a few drivers.

They have this diagram;


My question is, can I use the two channels of my scope in place of the signal counter and ac voltmeter?
The scope can give 5 simultaneous measurements, selectable between the two channels, so I could make probe 1 read voltage and probe 2 frequency, allthough I suspect if the actual probe placement doesn't make a diffirence I could do both measurements with 1 probe, all at the same time.

[digits]

Nothing?

[pinkmouse]

I see no reason why not.

[SaSi]

You can do what you describe, although it would be better to keep the probes firmly attached to the wiring and take measurements from two different channels.

The reason is the driver will need some time to settle when anything is changed. Even a large change in signal frequency will de-stabilize the system requiring several seconds of settling time before you can take an accurate measurement.

Regarding the measurement itself, using the proper driving voltages, expect to read mVolts so to make a reasonably accurate measurement of fs you need at least 3 significant digits worth of voltage measurement precision. Do you have this from your scope?

And frequency should be at least measured to the tenth of the Hz, with higher accuracy welcome if you want to reach the T/S parameters with enough accuracy to design a vented or higher order enclosure. I've found that the measurement process with frequency measured to the Hz and voltage at impedance with 2-3 decimal positions doesn't give enough accuracy to reach the actual values for Vas, Qts, etc.

[digits]

I don't realy have a meter that is any good for AC volts (at least at the signal level), appart from the scope. and even that seems to give only 2 digits after the decimal.

Also I have no idea how accurate it's frequency measurements are, the only other thing I have to measure frequency is on of my cheap multimeters.

I was realy hopeing for a way to do this without that $99 woofer tester.

[speaker dave]

Originally Posted by digits

I would like to follow the routine on T-S Parameter Calculator to do some T-S measurements on a few drivers.

They have this diagram;


My question is, can I use the two channels of my scope in place of the signal counter and ac voltmeter?
The scope can give 5 simultaneous measurements, selectable between the two channels, so I could make probe 1 read voltage and probe 2 frequency, allthough I suspect if the actual probe placement doesn't make a diffirence I could do both measurements with 1 probe, all at the same time.

I wouldn't be worrying about how many digits past the decimal place you can achieve. Most people using different techniques will see a 10 to 20% variation between each others numbers. Do your best and consider it a learning experience. The predicted response from your TS numbers will likely be good enough.

Do be careful in how you ground the test setup when you connect the scope. I've seen inadvertant errors from that.

David S.

[SaSi]

You can get around the frequency measurement chore if you use a "digitally synthesized" sine wave generator in the form of a computer software. You can achieve an excellent accuracy and stability using that.

If your scope can give you 2 decimal digits and you "calibrate" the driving voltage to get another 2 significant digits before the decimal, you'll do fine.

The precision in measurement is only critical in critical applications. If you are designing a sealed enclosure, even 10-20% error in the tuning of the enclosure will have negligible effects in performance and you can generally compensate for smaller volume by adding padding material.

If you are about to model a vented enclosure, then you need higher precision or be prepared to cut and try the vent.

With bandpass enclosures, you don't really need too much accuracy in the T/S parameter measurement phase just lot's of measurements and auditioning in the prototyping phase, so don't really worry too much with these measurements.

[digits]

Hi, OK I will try to digest this, I had an app that could produce tones before... Had no idea that would be more accurate than using the signal generator's output.

The output from the generator or input fropm the scope is not 100% stable though, the last digit tends to creep up and down a little like 2.405kHz, 2.406kHz, 2.405kHz


GFG-8015G



Owon PDS5022s

There are 3 drivers I want to test,
A woofer that goes from mid 30s to 3k
A set of goodmans fullrangers that go from 35Hz to 15k
And a set of mids from a sony 3 way that I'd like to use for something else as the bass drivers in that box is maleing a scrapeing sound.

[Keriwena]

I don't have any trouble with T/S measurements....

It's when I pick up a board and a saw the accuracy goes out the window!

[John Sheerin]

Given that the parameters of the speaker will change as soon as you change the input voltage level, I think all the talk of extreme accuracy is a bit misleading. You should be fine with what you're proposing, although personally I'd just spend the time to set up a computer system to take impedance measurements.