Tube Discussion Microphonics?

I have read in quite a few places where someone complained of this tube or that being microphonic. I understand what is meant in a discussion of matching output parameters but I have heard people say that a pair, or quad, of tubes were matched but still microphonic.

What does it mean for a tube to microphonic? How does this translate into audible identification? I mean how do you tell by listening whether a tube is microphonic or is just not a good sounding tube or not good sounding with a particular component?
I'm with the Clueless one here. Yikes, talk about an unpredictable tone control/ reverb pedal! Microphonics be bad, very bad!
I appreciate the responses and I will give my case in point. I recently bought a quad of 60's Telefunken 6922's for my linestage. They tested (16.0, 16.0), (15.5, 16.0), (16.0, 15.5), (15.0, 15.0). I had original Sovteks that sounded dry and did not have very good extension. I tried some Tesla that were so-so as far as extension but the midrange was like back in the next room.

I installed the Teles and the soundstage is great, midrange super, and highs brilliant and detailed (but not edgy). However, the low end, especially mid to low bass is really bloated. I had basically the same Teles in a linestage previously and the bass was very tight and controlled. So, I am wondering if this is a tube component mismatch or if it is a problem with one or more tube(s).

If any of the tubes were microphonic, would I have audible problems throughout the range or could it be frequency-specific?
If the tube is only slightly microphonic when you tap on it, then what is the problem? I agree 100% that a tube that is microphonic in normal use is a piece of junk.

Folks including Kevin Deal at Upscale Audio, who sells some of the best NOS tubes, has said similar things.

If all distortion is bad, then why do they add white noise on purpose in CD playback?
tapping and sound pressure have extra large differences in values so ain't no need to compare or giving such examples.

microphony of tubes is realy brand and quality depended. it's caused by loose electrodes as a result of tube's aging or becomming unfunctional in vast majority of cases.

folks at upscale audio despite being respected and honest dealers try to create illusion as many of audiophiles do that microphony is good. it does however help the tube business. well, it was never good and it was a big issue upto mid- 40-s.

not precicely sure but probably different vacuum technology and electrode mounting was introduced ever since and surely tubes produced in 50's are not microphonic. i was never shopping for NOS tubes and don't know if any of the tubes are sold manufactured before mid- 40's but i guess they're too few... therefore if the tube is microphonic you can bet 1000 against 1 that it's already bad.

i'll repeat myself about tapping being not a good example and it can blow the speakers. but you can realy tap on component chassis or mounting board next to the tube to check the microphony.
Tube microphonics, generally, degrade soundstage imaging and detail. As to an "identifying" sound, tubes do not have a sonic character - the sound is a product of its environment (circuitry). Bias, gain, plate voltages, feedback loops, etc., will identify the sound a tube gives you in a particular unit while external elements such as vibration degrade the presentation.

As to the "tube sound" (warmth, LF bloat, etc), it's attibuted mostly to distortion that's inherent in its construction and function as a gain device, especially at the clipping point. I also think that the microphonic characteristics of tubes contribute to the effect, so I'll take Sugarbries' side on this one.