8. How can I test the repair?

8. How can I test the repair?
Feeling whether or not the speaker rasps is often insufficient (!):
  • When the unit is mounted in the casing, the weight of the cone pushes downwards slightly. If the tolerance is low,  the unit will still cause interference
  • In that case, simply push the cone down and it may cause interference in case of an outwards movement. See below: this speaker should pass this ‘test’.
It is also insufficient to check whether you hear a ‘rasping’ sound by means of test signals (see above).
What is the right way to do it, then?
Testsignals allow you to properly test the speakers. You can do so by means of separate units, connected to your amplifier or with the repaired speaker in the casing, once built in. With our unique repair method, you already know whether or not the speaker is properly centred. Only a local faulty glue-joint, for instance, could cause a problem. Be careful with test signals (!!). Do not turn up your volume if you do not hear anything! The test signals and this text are, of course, the property of Audiofriends. The following signals are ones that you can use (at your own risk):
Woofer (bass loudspeaker):
20-500 Hertz
20-2000 Hertz
Middle tone unit:
500-8000 Hertz
Test method:
  1. You burn the test signals to a CD. We assume it concerns a woofer in this case.
  2. For the woofer, you first use the 20 - 2000 Hertz (sweep). TE: do not turn up the volume of the amplifier too much, certainly not if you do not hear anything. If you do not hear anything, you first have to listen to the entire sweep, and only turn up the volume a bit afterwards. NOTE: do not turn up the volume of the sweep, if it decreases at a certain frequency. You may not hear the signals, but the speaker does feel them.
  3. Listen whether the sweep produces an even sound. If there is a parasitic tone at a certain frequency, it could be caused by a small problem. You hear a parasitic tone if something starts to co-vibrate at another frequency than the one you hear through the speakers. Note: I daresay that even many new speakers have parasitic sounds. If the volume is turned up, some cables or filters may start to vibrate, or the fast movement of air may cause some sounds in the bass reflex. Small parasitic tones, which cannot be heard in various types of music (even after being aware of them), are less important.
  4. Go ahead and try the 20-500 Hertz signal. Problems most often occur at this frequency. We also performed revisions for others and we always tested each refoamed speaker as part of our standard procedure. We always used the 20-20.000 Hertz signal for woofers, since small woofers in particular may significantly deviate towards the high spectrum. Obviously, the 20-20.000 Hertz signal also allows you to test the entire speaker sound range. See also 3 above.
Do you have further questions? Audiofriends has 14 years of experience, so please feel free to ask us anything you want to know.