About

QLoud is a tool to measure a loudspeaker frequency response and distortions. This is just an attempt of porting it to QT5. The original app page is here:

http://gaydenko.com/qloud/

Writing this app was inspired by excellent applications written by Fons Adriaensen:

http://users.skynet.be/solaris/linuxaudio/

Theoretical background belongs to Angelo Farina:

http://pcfarina.eng.unipr.it/

In particular, this method was used:

http://pcfarina.eng.unipr.it/Public/Papers/134-AES00.PDF

Target use

• loudspeakers DIY-ing (xover tuning).

Measurement chain

• the app, generating excitation signal,
• sound card line out,
• power amplifier,
• loudspeaker under testing,
• measurement microphone (with mic preamp),
• sound card line in,
• the app, capturing loudspeaker response.

Result

After audio system response capturing is done, IR (Impulse Response) is calculated. Currently these IR-aware analysis outcomes are available:

• plotting of SPL (Sound Pressure Level) as function of frequency (dB/Hz scale),
• plotting of IR-power as function of time (dB/s),
• plotting of Step Response as function of time (amp/s),
• plotting of harmonics as function of frequency (dB/Hz scale):
  • 2nd – green
  • 3rd – red
  • 4th – light green
  • 5th – light red

IR-power plot is useful to see a room reflections behaviour. Step Response plot is useful for speakers time alignment in multiway loudspeakers. All plots support zooming with history and panning.

A few hints

• move mouse above “?” sign at plot window and wait,
• to change a measurement description double-click it,
• to delete a measurement, use context menu on measurements table,
• to see what the app do, just connect app’s JACK ports directly and try,
• to see what your sound card do, use loopback for line in/out,
• take into account your measurement mic slope at high frequencies when observing harmonics plot.