#12588 BLOC 13.2.0: XO-4 max volume produces distortion

Zarro Boogs per Child bugtracker at laptop.org
Thu Jul 18 19:07:30 EDT 2013

#12588: XO-4 max volume produces distortion
           Reporter:  dsd            |       Owner:  dsd                              
               Type:  defect         |      Status:  new                              
           Priority:  blocker        |   Milestone:  13.2.0                           
          Component:  kernel         |     Version:  Development build as of this date
         Resolution:                 |    Keywords:  XO-4 Speaker Audio               
        Next_action:  test in build  |    Verified:  0                                
Deployment_affected:                 |   Blockedby:                                   
           Blocking:                 |  

Comment(by Quozl):

 The speakers are meant to vibrate the air, and as a side-effect they do
 vibrate the upper casing, since the upper casing is full of air.  This is
 an intentional side-effect.

 To find the resonant frequency of the upper casing and speakers, inject
 speaker-test -t pink -c 2
 and observe whether you can hear any particular tone.  An excessive
 resonance will make a tone from this pink noise.  Use Control/C to stop
 the test.

 Speakers, driving amplifiers, and assembly vary slightly across

 We don't want the maximum volume setting to produce distortion in a
 significant number of laptops.  We have a test for this in production.
 You may have a statistical outlier in your hands.

 To check the speaker fastening, find a quiet location, wear hearing
 protection, set the volume to maximum, generate a sine wave output at 500
 speaker-test -t sine -c 2 -f 500
 and during the test use your thumbs to cover and press on individual
 speaker grills, one at a time, and observe:
  * the total sound volume (which should be reduced by a thumb when the
 speaker is being driven),
  * the tonal purity (whether you are hearing a single frequency like a
 flute or a mix of frequencies with buzzing),

 This test switches between speakers.  I'm interested to know if the
 distortion is following a specific speaker, and if the distortion reduces
 radically when pressure is applied to the speaker grills.

 You might also try other frequencies.

Ticket URL: <http://dev.laptop.org/ticket/12588#comment:13>
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