[grsimmon]

I tried googling this, but mostly came up with stuff about large subwoofers in small cars   

I have a class AB solid state amp that seems to work fine,  no problems.  My speakers are 2.5 way reflex design,  about 90 dB sensitive.   My speakers will bump (pulse) 1 time each in sequence,  when I turn the amp off.   Doesn't happen when I power up.   It's not loud but the midbass drivers visibly move.

Why does this happen?  Do I need to be concerned about damage to the speakers?   Is there anything wrong with my amp and/or the passive crossovers in my speakers?

Thanks for any info. you can provide - Greg

[Armaegis]

When they "pulse", are they vibrating or does it look like they're remaining in extended position? how long does this pulse last?

[JohnR]

Some amps do it, related to the power supply rails discharging at different rates.

As to damaging your speakers, how far do they move? If it's only a mm or two I wouldn't worry about it, if it's like 10 then I'd contact the manufacturer about it.

[Folsom]

Mute/standby networks can also have a different voltage value since they may discharge much slower, causing a similar turn off bump.

[Panelhead]

  This also may indicate that once stabilized there is a small dc voltage output from your amp. This causes voice coil offset. Once turned off this goes to zero and causes coil movement.
  Try measing for dc at either the amp outputs or speaker terminals. Many AB amps have 20 -30 mv. Some have servo circuits that drop this to almost zero. If you measure over 100 mv, there is a problem.

[grsimmon]

When they "pulse", are they vibrating or does it look like they're remaining in extended position? how long does this pulse last?

When the speaker drivers move, it's about 5 seconds after I turn the amp off.    They don't vibrate,  nor stay in an extended position.   They actually "suck in"  to the speaker,  but don't bump out.   The excursion is a few mm /  about 1/4 inch and lasts just an instant.   Not super loud, but audible and visible.   I realize I may be being paranoid about this,  but am wondering if there's any long-term negative effects on the drivers or passive crossovers.  I've never seen this in any of my speaker/amp combinations over the years.

[Armaegis]

It sounds very much like the caps discharging and producing some dc offset. If you flip the speaker wires and the cone pops out instead of in, you'll know for certain.

If it lasts just an instant and during normal music your cone moves more than this, then I wouldn't worry about it.

[Early B.]

Turn off the amp first, then turn everything else off.