weird distortion

[Nadis]

So i have built studio 350 stereo amplifier with 5200/1943 transistors and my version of visaton pentaton speakers. Speakers are made of 1 bg20 in a midlle and 4 cheap wofers each.
My problem is that playing songs as bass test on full power that those 4 woofers can take i think they are diping on impedans so low that my amplifier starts distorting like crasy. But nothing on it gets hot. Tried same songs on 200w rms woofer and it works fine to as much as i can give him.
anyone can tell me if its some kind of protection kiking in or amplifier doesnt like to be driven that low or i should make some kind compensation filter .
tried wiring speaker to 4 8 ohm 16 ohm and distortion doesnt go away.
for notice when i hold one woofer with my hand so it couldt move rest of the woofer works fine aNd distortion goes away.
so my maby i can change a resistor or any other component om my sc 350 amplifiers so they could handle those dips in impedance?

 

[rayma]

when i hold one woofer with my hand so it couldt move rest of the woofer works
fine aNd distortion goes away.

Is the voice coil rubbing?

 

[sgrossklass]

Sounds like the "cheap woofers" are hitting their mechanical limits. Could be a construction problem of the speaker enclosure(s) or just a low Xmax or something.

 

[Nadis]

Speakers mechanicaly are fine. Tried them on lm3886t eatch. Enclosures ar not ported each giving more liters than drivers need. Distortion starts as a poping sound near x max on the woofers untill then amps work fine. P.s. Distortion is like playing amplifier with resistors inserted in fuses place.