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Weird ring/thump noise when I hit my speaker cable

Help please! I noticed a weird problem which I can't explain for. I hope somebody can tell me what's wrong. When I use my finger to flick at my left speaker cable, my left speaker will produce a short ring/thump sound in time with my flicks.

When I switch off my amp (Unison Research Unico), the problem will immediately disappear, and won't re-emerge immediately after I switch on the amp again. I haven't noticed a pattern of when the problem emerges - sometimes it's there and sometimes it's not.

The sound is also produced when I use my knuckles to knock my hi-fi rack (although not quite as loud as when I hit the speaker cable directly).

I have only noticed this problem when I recently bought the Unico and not before with my old Roksan Kandy. I was wondering whether it's due to one of the tubes having some loose parts that react to the jolts. But then the problem should be there all the time and not only some of the time.
lohkkw51e5
marakanetz's avatar
marakanetz
5,473 posts
 
one of the tubes might be bad. flip tubes to find out.
thsalmon
348 posts
 
Why do you flick your speaker cables?
lohkkw51e5 OP
13 posts
 
Good question Thsalmon. Flicking speaker cables isn't exactly a habit of mine. Actually, I first noticed the sound when I was fiddling around with power cords on my CD player and the cord bumping against the the equipment rack produced the sound. I then went around rapping my knuckles everywhere - the shelves, the pillars, the amp, the CD player, all of which produced the sound. But I found that the sound was loudest when I flicked the left speaker cable with my finger.
sean
6,231 posts
 
If it is happening with you "tapping" on various components physically / electrically tied to your system, you can bet it is happenind at all times when you listen to music. As Gthrush mentioned, this is called microphony and will vary with the intensity of vibrations applied to the components. In such cases, the end effect is smeared sound which gets worse as volume is increased. Due to the increased volume, you've now got more vibrations filling the air, which further modulates the microphonic devices harder.

As Marakanetz suggested, start by checking your tubes. I would first start off by making sure that they are all properly seated before doing anything though. Then again, if you can "flick" your speaker cables and the system picks that up, touching anything in the system may set the problem off. As such, you could be in for some work tracking this problem down. If you can substitute another amp in the system and see if it goes away, you'll know it is something in the amp and can go from there. Sean
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karls
332 posts
 
Even perfectly normal tubes display some degree of microphony, which varies widely depending on the particular tube design. Tap on the glass envelope of any tube with your equipment powered up and you will hear it. Some hardly at all, some a whole lot. Given that music is nothing but vibration, this is one of those things that it's best not to think about too much if you own tube gear. Best to just enjoy the extra ambience it provides...:) But yes, check that everything is seated and working properly, and swap tubes if you need to.
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