200 Hz square wave into an ESL - Page 1
Forum section: electronics / general

author: Physikfan
author_rank: Regular Contributor
timestamp: January 24, 2019, 05:33:03 pm
content: Using a condenser microphone and the FFT HP3561A analyzer, a 200 Hz square wave signal was fed into an ESL (Martin Logan Sequel II electrostatic loudspeaker):This is the electrostatic speaker:FT signal of the 200 Hz square wave of the function generator:FT signal of the condenser measuring microphone:

author: nsrmagazin
author_rank: Regular Contributor
timestamp: January 24, 2019, 06:27:06 pm
content: Whats your question? I would not call this a square wave. Speakers use AC signal not DC.

author: Physikfan
author_rank: Regular Contributor
timestamp: January 24, 2019, 08:04:38 pm
content: The question was:Is it possible to generate an acoustic square wave as good as possible for testing the response of microphones.To get an quantitative answer I have used this FFT analyzer.

author: VintageNut
author_rank: Frequent Contributor
timestamp: January 24, 2019, 08:27:26 pm
content: I would say no to square.Common test signals for speakersswept sineimpulsemaximum length sequence (MLS)This thread should be posted at diyaudio.com

author: Physikfan
author_rank: Regular Contributor
timestamp: January 24, 2019, 08:51:58 pm
content: The question was:Could I use an ESL to generate an acoustic square wave signal to study the response of different microphones?To check quantitatively the quality of this acoustic square wave I have used this FFT Analyzer.As you can easily see, the acoustic square wave is of no good quality."Common test signals for speakersswept sine"It is true, this an often used standard procedure.What do you mean with testing with "impulse", which shape, comparable to a square wave?

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: January 24, 2019, 09:10:25 pm
content: a DIRAC impulse should do it. no kidding. you may want to have a look at the ARTA audio analyzing software done by Mr. Ivo Mateljan.http://www.artalabs.hr/that software also has a super comprehensive manual, which i highly recommend for reading.when testing audio in, say, echoic chambers like a living room with a testing tone over a prolonged time (be it square or pink noise, for that matter), standing waves and reflections in the room will wreak havoc on the recorded frequency response, although your source (ESL) as well as your microphone may have an ideally flat frequency response. you will actually more likely capture the room characteristics than anythin else.on the other hand, when using a single impulse, you are able to capture that pulse with the microphone before reflected wavefronts are able to disturb the pulse. an FFT of that pulse response should give you then what you were asking for: A_esl(f) x A_mic(f). in order to get to the actual frequency response of the mic under test, you need of course divide the result by the (previously recorded, with a voodoo mic) speaker response.

author: nsrmagazin
author_rank: Regular Contributor
timestamp: January 25, 2019, 08:52:45 am
content: This looks like a very big field. It would be the easiest to put the signal that you will use the speaker for(in terms of frequency and shape).You can look at this:http://www.linkwitzlab.com/Ping_tests/Test_signal.htm

author: kony
author_rank: Regular Contributor
timestamp: January 25, 2019, 11:10:26 am
content: Use sparkgap for generating Dirac pulse. I am not kidding.

author: GregDunn
author_rank: Frequent Contributor
timestamp: January 28, 2019, 02:14:54 am
content: Without a special calibrated testing microphone (and maybe not even then) it'll be hard to tell if the speaker is actually generating a square wave in the first place, or just a harmonically related series of sine waves with skewed or degraded phase relationships. Amplitude is one thing, but the phase of the output of a speaker - even an ESL - is often badly affected by the crossover network, and in the case of an ESL, also the transformer used to step up the voltage to a level sufficient to driver the panels. If you really have to use a speaker to do this, a direct-drive ESL might be a workable solution because the phase relationships are much better.But I concur with the others - a spark gap or similar is what is used to test microphones when looking for a clean and optimum signal source. It's so much more linear than a speaker it's not even close. An impulse, properly generated, is nothing like a square wave - it's a very short, narrow pulse with a near constant distribution of amplitudes and phase. Just what you're looking for, really.

author: Physikfan
author_rank: Regular Contributor
timestamp: February 03, 2019, 09:30:06 pm
content: The Martin Logan ESL with a 200 Hz square wave:Signal of the square wave into the amplifier input at the top, 20 mV/cm, 40 mVpp.At the center of the screen the microphone signal 5 mV/cm, 27 mVpp, is shown.At the bottom of the screen the current signal 1 A/cm, 5 App is shown, (output current of the amplifier into the input of the Martin Logan ESL).FT of the current signal 5 app, center frequency 1 kHz:FT of the current signal 5 app, center frequency 5 kHz:I am looking forward to your comments.

author: Physikfan
author_rank: Regular Contributor
timestamp: February 04, 2019, 11:26:44 am
content: The Martin Logan ESL with 200 Hz sine, the same experimental setup as the 200 Hz square wave:Signal of the sine wave in the amplifier input at the top, 20 mV/cm, 40 mVppCenter: microphone signal 5 mV/cm, 17 mVppAt the bottom: current signal 200 mA/cm, 900 mApp (output current of the amplifier into the input of the Martin Logan ESL).As you can see, in contrast to the square wave, there is full agreement of the waveforms of all three signals (amplifier input, amplifier output or loudspeaker input and microphone signal)FT of the current signal 900 mApp, center frequency 1 kHz:Spectrum-pure sine of 200 Hz of the current signal 900 mApp.

author: Physikfan
author_rank: Regular Contributor
timestamp: February 04, 2019, 04:34:26 pm
content: The Martin Logan ESL with 1 kHz sine wave, the same experimental setup as with the 200 Hz square wave:Low level signal of the sine wave in the amplifier input at the top, 5 mV/cm, 6 mVppMid microphone signal 5 mV/cm, 1 mVppDown current signal 50 mA/cm, 60 mApp (output current of the amplifier into the input of the Martin Logan ESL).As you can see, in contrast to the square wave, there is full agreement of the waveforms of all three signals (amplifier input, amplifier output or loudspeaker input and microphone signal)FT linear of the microphone signal 1 mVpp, center frequency 1 kHz:High level signal of the sine wave in the amplifier input at the top, 20 mV / cm, 40 mVppMid microphone signal 5 mV/cm, 5 mVppDown current signal 200 mA/cm, 400 mApp (output current of the amplifier into the input of the Martin Logan ESL).FT of the current signal 400 mApp, center frequency 1 kHz:FT linear of the microphone signal 5 mVpp, center frequency 1 kHz: