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Old 30th January 2003, 10:34 AM   #1
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Question ticking sound in new woofers - cause, remedy?

I like to test drivers with a 20 Hz signal, carefully increasing drive level up to x_lin displacement.

I am well familiar with the sound of particles in the gap or a deformed or badly centered voice coil.

There is a scraping, gliding or chiming sound. Sometimes, it will start only at a certain drive level, e.g. if the only the neck of the VC former is bent.

Yesterday, I received a Vifa M25 that was still in its original packing. Date code seems to be 86, so its been sitting in a warehouse for a long time. This driver had none of the ususal sounds mentioned above, but instead there is a clearly discernible ticking sound. This sound gets louder as I turn up the volume, but it does not change in character.

I checked for loose terminals etc. but found nothing. Instead, the ticking would stop as long as I was pressing down on a particular point of the spider. It would also grow quieter while I was pulling the surround in a certain direction. So I figure the cause must be a malcentered VC. The M25 is heading straight for the garbage can, but I just can't imagine what kind of a faulty geometry would cause such a distinct ticking that occurs for all drive levels.

The reason I'm asking is that I just received four brand new Vifa XT18WO09, and all of them have a ticking that sounds very much like that of the M25, even if the ticking intensity is different for each unit. The big difference is that that nothing I do (holding on to magnet, terminal, pressing on spider and surround) changes the ticking.

I also received a shipment of four Peerless CSC217R. Out of these, one has the same symptoms.

Is there anything I can do? Shoud I return the drivers?
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Old 30th January 2003, 10:46 AM   #2
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ITS A BOMB!!! lol.. you could always ask the manufacturer what it is? get them to test a few off the shelf and see if they get the same results..
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Old 30th January 2003, 11:00 AM   #3
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Hi, capslock

Could it be your generator?

Hugo
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Old 30th January 2003, 11:27 AM   #4
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No way, it's a test CD and my power amp. Besides, I have tested plenty of drivers that do not make this sort of ticking.
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Old 30th January 2003, 11:43 AM   #5
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It does sound very much like the audio sorce to me.. Try a different CD player.. and amp if possible... If the noise is still there, then I don't really care what it is.. lol.. didn't you say 20Hz?? we can't hear 20Hz... as far as I know none of my music HAS 20Hz.... You can lower the frequency to 10Hz, and turn the volume way up, and the speaker just sits there pulsing in and out.. lol but I am not sure what that proves..
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Old 30th January 2003, 12:06 PM   #6
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Skinny,

please take the time to actually read what I said: It is NOT the source. There are plenty of drivers which do not have this problem.

And 20 Hz makes a whole lot of sense. As you said, correctly, we cannot hear this, so it is an excellent way to exercise the driver and listen carefully, because anything we hear is something that should not be there in an ideal driver.

I can actually get an idea of the amount and distribution of the harmonics a woofer produces just by listening, and it correlates pretty well with my measurements. And it is a good way to find out if anything is wrong with the motor, the suspension and just about everything else that can rattle.

And by the way, if you ever doubt the benefit of good driver venting, just run a vented-magnet driver at 20 Hz and a couple of mm excursion and cover the hole in the magnet. You will then discover that the sound of the air rushing through the gap etc is very similar to what you can hear in an unvented driver.

Regards,

Eric
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Old 30th January 2003, 02:22 PM   #7
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Somebody on a German forum suggested that some glue joint (VC former to cone, surround to basket, spider to basket, etc.) is not covering the whole area it should be covering.

Well, I tested the outer joints of surround and spider and found nothing. How do I test the rest?

Is it really likely that an quality manufacturer like Vifa should have this kind of lousy quality control in their top notch product? Or is it a design problem?
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Old 30th January 2003, 02:57 PM   #8
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Default ticks

capslock

Can you post a little wav or mp3-file of the tick. Maybe then we could explain something more?

/Hugo - likes some tickling now and then...
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