• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Audio Measurements

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hotvalve

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Joined 2007
#1
Greetings, and Happy New Year. 🙂

I hope you won't mind me asking, what do you guys use for measuring/plotting frequnecy response and measuring distortion?

I have an old Fluke 8060 DMM which had a dB function for measuring frequnecy response, but this has now given up the ghost, must be 20 years old.

I was wondering if you chaps use software and a PC?

Thinking about software got me thinking about PC distortion analysis.
What do you chaps use?

Your response will be greatly valued.
 
#2
I use ARTA (the STEPS part of the program) both at work and at home for my own use. It is remarkable value for money! At work I'm only measuring amps and speakers for PA applications, so the built-in sound card on the test pc is adequate. At home I use the excellent M-Audio transit external USB audio interface.
 
#3
Software and PC does a more-than-adequate job for most frequency response measurements involving tubes. An HP3581A or any good quality AC voltmeter and a function generator make a suitable backup. Function generators generally have mediocre distortion performance, but very, very flat frequency response.

For high frequency measurement where the sound card can't be used, a function generator and an oscilloscope will do, though for standard analog scopes, the results need to be recorded and plotted by hand.

For distortion analysis, it's hard to beat a good sound card. With an M-Audio 192 and AudioTester, I routinely measure THD to 0.001%.
 
#4
SY: Unfortunately the HP 3581 is getting difficult to source -- everyone found out how good they are.

GenRad also made a quite good wave analyzer -- and their stuff is first rate.

there is a first generation HP Wave Analyzer on EBay at the moment. probably a collectors item.
 
#5
My question is how to interface computer sound card to the device under measurement.

What is the "widget" that I need to interface between output transformer and sound card?
How about the "widget" between the output of a HV driver stage and sound card?
 
#7
Ouroboros said:
I use ARTA (the STEPS part of the program)
Click to expand...

And I mostly use the main ARTA program also for amplifier measurements (tone generator, distortion/spectrum analysis, and FR curves)

Bob Lee said:
My question is how to interface computer sound card to the device under measurement.
Click to expand...

The output from the soundcard fits (usually) directly to to the amp inputs. Use a preamp if levels are not suitable.

The output from the amp need to be adjusted by a voltage divider. Attached is an illustration from the ARTA/STEPS manual. Suitable ressitors might be 10K/1K. The zeners are optional for protection of the PC.
For my own use I have built this together with a 8/4 ohm load, with jacks for voltmeter, scope, and PC.

This circuit is suitable for measurement of amplifier output, but not for internal measurements (do not connect to the anode of a driver stage!).

A scope is still required to look at 10KHz square waves etc. PC soundards are usually limiting bandwidth to 20KHz.

Svein
 

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#8
Measurement software

Hi everybody,

I'm looking for a software to measure the delay from a listening point and each drivers from a 4 ways speakers.

Based on those measurements, the delay for each driver could be adjusted on the digital filter. This would allow to correctly set the phase, i.e the driver would be correctly alligned between each other.

I would like to know if anybody uses one and would recommend it. For example does ARTA does it.

Software which do it generates pink noise and measure the time / distance between a reference and the speaker driver

Thanks
Regards
 
#10
Phase measurement and compensation

EC8010 said:
The Behringer DCX2496 digital active crossover has this measurement and compensation built in. You just plug a microphone into channel C and tell it to calibrate!
Click to expand...

Looks a nice device. Thanks, unfortunately i already use a digital filter from (accuphase df35) where the automated delay calculation does not exist. That's the reason i'm looking for a software. Regards
 
#11
EC8010 said:
The Behringer DCX2496 digital active crossover has this measurement and compensation built in. You just plug a microphone into channel C and tell it to calibrate!
Click to expand...
This is for the sound guy in a band, do a quick set-up in a club. There are some good soft-ware programs for setting up home speaker systems.
 
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