Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Tom Young]

I just came across this WT3 impedance measurement system from Dayton Audio.

See: http://www.daytonaudio.com/wt3.html

It appears that it may be a viable means to conduct shop measurements of just-received loudspeakers and also field measurements of installed loudspeakers.

Any comments, including from those of you who may be using this ?

TIA-

[Hal Bissinger/COMSYSTEC]

I think Craig Hauber mentioned that in a previous thread about 70.7v system troubleshooting. A bit overkill for simple impedance measurements but looks to be very useful as you state.

-Hal

[Silas Pradetto]

Hal Bissinger/COMSYSTEC wrote on Tue, 30 December 2008 11:13

I think Craig Hauber mentioned that in a previous thread about 70.7v system troubleshooting. A bit overkill for simple impedance measurements but looks to be very useful as you state. -Hal

I've always wanted to be able to measure impedance in my shop, what's a cheap and easy way to do this? I have a function generator and an oscilloscope, can I do it with those?

[Ivan Beaver]

Silas Pradetto wrote on Tue, 30 December 2008 22:36

Hal Bissinger/COMSYSTEC wrote on Tue, 30 December 2008 11:13 I think Craig Hauber mentioned that in a previous thread about 70.7v system troubleshooting. A bit overkill for simple impedance measurements but looks to be very useful as you state. -Hal I've always wanted to be able to measure impedance in my shop, what's a cheap and easy way to do this? I have a function generator and an oscilloscope, can I do it with those?

If your generator has a flat output level you can.  But it would be easier with a voltmeter that is accurate across the audio band.

Of course the easiest way is to simply use an impedance meter.  For quick stuff I use the Audio Toolbox.  For more accurate-printable stuff I use the TEF.

http://en.wikipedia.org/wiki/Electrical_impedance

[John Roberts {JR}]

Silas Pradetto wrote on Tue, 30 December 2008 21:36

I've always wanted to be able to measure impedance in my shop, what's a cheap and easy way to do this? I have a function generator and an oscilloscope, can I do it with those?

Yes, it's no big deal... Basically you create a simple pad or resistive divider with a known fixed resistance in series with the varying speaker impedance. Then you can calculate from the voltage drop or ratio what the speaker impedance is at any given frequency.

This can be done at low amplitude so you don't exceed the current output of your signal generator.

When I designed the TS-1, I built the fixed resistor (51 ohm) into the sine wave output, and put a look up table in the book that came with the test set,

The math is just like a simple 2 resistor pad. When the speaker impedance is equal to the series resistance the drop will be 6dB or 1/2 input voltage, and so on.

If you don't have a sensitive meter to read low level signals, perhaps drive the speaker from a low impedance resistor driven by a small power amp.

JR

[Silas Pradetto]

John Roberts  {JR} wrote on Wed, 31 December 2008 10:05

Silas Pradetto wrote on Tue, 30 December 2008 21:36 I've always wanted to be able to measure impedance in my shop, what's a cheap and easy way to do this? I have a function generator and an oscilloscope, can I do it with those? Yes, it's no big deal... Basically you create a simple pad or resistive divider with a known fixed resistance in series with the varying speaker impedance. Then you can calculate from the voltage drop or ratio what the speaker impedance is at any given frequency. This can be done at low amplitude so you don't exceed the current output of your signal generator. When I designed the TS-1, I built the fixed resistor (51 ohm) into the sine wave output, and put a look up table in the book that came with the test set, The math is just like a simple 2 resistor pad. When the speaker impedance is equal to the series resistance the drop will be 6dB or 1/2 input voltage, and so on. If you don't have a sensitive meter to read low level signals, perhaps drive the speaker from a low impedance resistor driven by a small power amp. JR

I transferred out of Rensselaer Polytechnic Institute after only a year as an EE major; I don't know why I didn't think of this myself!

Thanks guys!

[Hal Bissinger/COMSYSTEC]

Many years ago I built a "box" for impedance measurement. I guess that was before there were any affordable (to me) meters available. It had 5-ways for the input from a signal generator or amp, the DUT and a volt meter. I remember it had a rotary switch for three ranges and would indicate impedance directly on the AC volts scale. It also had a two position calibrate/test switch. If I remember corectly you would select your range then put the setup switch in the "calibrate" position and adjust your input level until it read something like 1 volt. Then flip it to "test" to read your impedance.

I doubt that I have a schematic anymore and since I have CRS don't ask me how I did it. That information and a little thinking though should allow someone to figure it out. It was the simple two resister voltage divider taken several steps farther for ease of use.

-Hal