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Discussion Starter #1 (Edited)
So, I'm kinda tired of buying used/vintage speakers online and having them show up with rubbing VCs. Every time the seller claims they tested fine before sending, and then it turns out they just measured DC resistance and sometimes maybe played some audio through it without paying close enough attention to the output. It seems people think, barring cone tears/rips, that either a speaker works or it doesn't, this is a misconception and I'm here to try to help fix that.

There are 3 basic tests that should be done when buying or selling a speaker:

1) Measure VC DCR. This is basic and I won't go into it here, but the rule is that the value should be less than the expected nominal Impedance rating ( with some, especially older, speakers it may be just barely below the rating like even only 0.1 ohms; this is not weird).

2) Audio test. Again pretty straight forward but I would mention that you should use program material you are intimately familiar with, listen for anything that doesn't sound right such as distortions or other bad noises not in the program material, or lack of top or bottom end ( remember that a speaker not in a cab will naturally not have much bottom end, it is handy to have a second speaker of same size to compare, another idea is to stick yer face right in the cone so that you hear the bass from the front wave before it hits the back wave and cancels - obviously keep the volume low and don't blast yourself - also helps to you use the tone controls or EQ to boost the bass then the treble to highlight issues in these extremes).

3) The manual test. This is what I will focus on here because it is the one people seem to be unaware and scared of but it is essential and has saved me numerous times from buying bad speakers ( the other tests can show no bad signs but this one will). The other advantage is that you need no special tools just your hands and an ear.

Before we get to that, I would just like to say that sometimes you can't perform all these tests - for example you may not have a multimeter with you or there's nowhere to hook up the speaker to an amp. 2 out of 3 tests is enough as long as one of them is the push test ( and as mentioned this is the easy one - no special tools required).

Anyway, I have to make a vid to send a seller about this so gonna 2 bird it and post it here later as well. Life's too short for blown speakers; buyers deserve to know how to protect themselves and sellers should do this because making it right later ( especially in the eBay age) costs too much time and money. I hope this saves both parties unnecessary hassles.
 

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Great post! I might add that another way to test for loose or misaligned voice coils is to tap the magnet from behind with your hand and put your ear close to the center of the cone. You can sometimes hear a loose coil or coil rub using this method.
The other point regarding vintage speakers....and I can't stress this enough...is they will NOT handle the power that they did when new. I've seen many old Jensens, Oxfords etc. with the above described coil problems because the user figured it was capable of handling it's original spec wattage.
 

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Just confirming VC DCR is just DC Ohms? It's not a term I'm familiar with and The Google isn't helping.
 

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Nice job.
It gets a little tough deciding what is the limit of skewing the cone for the test. Different types of speakers have more or less space in the gap and some are very tight tolerance. Some of the tight tolerance ones might rub with a skew that would not make a guitar speaker rub.
But that's nitpicking a bit; overall a very nice tutorial!
 

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Discussion Starter #9
True, but you get a feel for it after a while.
 

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Agreed, but anyone who has developed that 'feel' won't need a tutorial. ;)
I guess it's just a heads-up for novices; you can make any coil rub if you distort the cone enough, so don't over do it. :)
 

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Discussion Starter #11
I dunno about any - EVs and C-V (like the good driver in the vid) have rather flexi cones; one (especially a newb) will back off before they can make it rub because it really starts looking like you're gonna damage the cone . The guys at Santon Audio showed me one how to do this and they really cranked the bugger to prove to me that you're not going to hurt it; not a sound (then they did it to my speaker with half the force/flex and it rubbed like a dog). With stiffer cones this could be an issue because you can excert more pressure, but I was wondering the other day when I was making the vid: if the coil is straight and you apply equal balanced pressure (implied in the vid - 2 hands on opposite sides - but not explicitly stated; my bad), will it actually kick out that much or at all? I dunno.

So yeah, try linear pressure first (the worst cases of rub will be found that way) and then try a bit more progressive flex, and don't overdo it , would be good advice.
 

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I dunno about any - EVs and C-V (like the good driver in the vid) have rather flexi cones; one (especially a newb) will back off before they can make it rub because it really starts looking like you're gonna damage the cone . The guys at Santon Audio showed me one how to do this and they really cranked the bugger to prove to me that you're not going to hurt it; not a sound (then they did it to my speaker with half the force/flex and it rubbed like a dog). With stiffer cones this could be an issue because you can excert more pressure, but I was wondering the other day when I was making the vid: if the coil is straight and you apply equal balanced pressure (implied in the vid - 2 hands on opposite sides - but not explicitly stated; my bad), will it actually kick out that much or at all? I dunno.

So yeah, try linear pressure first (the worst cases of rub will be found that way) and then try a bit more progressive flex, and don't overdo it , would be good advice.
I usually apply equal pressure with with one hand and my fingers spread out around the dust cover and gently push on the cone first before going underneath and applying pressure from behind. As you state, applying pressure in an uneven fashion has the potential for giving erroneous results.
 

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Nice work ! If I can just add that there is sometimes some increased stiffness with a vintage speaker that might be attributed to hardening of materials used in construction of the spider or the surround. I have an antique Rola that even tho the gap had some debris in it, the brittle spider was the cause of most of the crunch in my case, evident at very low power levels. Either way, the speaker was unusable.
 
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