Squeeky Voice-coil,Linkwitz Transform causing it? - diyAudio
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Old 27th January 2007, 05:22 PM   #1
mikee55 is offline mikee55  United Kingdom
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Unhappy Squeeky Voice-coil,Linkwitz Transform causing it?

Hello Y'all,

As you may or may not know, I've built a Linkwitz Transform sub recently, and have a new problem today. This time its not my electronics, but my driver. My cheapo SPLX 12" car subwoofer occasionaly makes a squeek in time with the bass, that seems to eminate from the centre of the cone. Could be something to do with the voice-coil stressing perhaps?

Can anyone tell me whats going on?

Cheers Mikee55
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Old 27th January 2007, 06:32 PM   #2
sek is offline sek  Germany
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Hi Mike,

could likely be the voice coil former touching the back plate of the magnet assembly.

This is nothing to worry about as such, you just have reached your mechanical excursion limit for that driver. The likelihood of destruction is small if it doesn't happen too often, but don't challenge your voice coil former too much, though - the back plate is stronger.

Could also be something else, e.g. clipping of an amplifier stage. This would have to be determined before a solution can be found, I'm afraid.

One question: by writing "occasionally", do you mean something like: at exceptional excursions due to high SPL and/or low bass content?

Cheers,
Sebastian.
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Old 27th January 2007, 07:55 PM   #3
mikee55 is offline mikee55  United Kingdom
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Default Hmm..

Hello Sebastian,

I think an op-amp could be clipping. Because I'm using a car amplifier running off an old AT powersupply, and the fact that the protector light goes out at the same time, suggests clipping. The AT supply is only putting out 8amps max. Also I'm not sure how powerfull this car amp is. I also think that if the coil former is hitting the back plate, it would be a knocking sound, more than a squeek.

What do you think?

Cheers Mike
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Old 27th January 2007, 09:12 PM   #4
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Whatever the exact cause, mechanical noise from the driver means you're pushing it too hard. I suspect the LT circuit has too much gain, pushing your driver to its limits and overloading the amp and power supply at the same time. LTs put huge demands on the system, and if it can't cope, it will go bang eventually.
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Old 27th January 2007, 09:32 PM   #5
mikee55 is offline mikee55  United Kingdom
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Default Hello pinkmouse

If I reduce the gain, will I loose the ability for the system to go as low as I designed for,(20hz)? I was playing some drum and bass at the time. Maybe I need to filter off the cone flap.

Cheers Mike
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Old 27th January 2007, 11:06 PM   #6
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Yes. For LT to work at low frequencies, you need a good driver, and a powerful amp with a good PSU. With respect, it sounds like you have neither.
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Old 27th January 2007, 11:30 PM   #7
mikee55 is offline mikee55  United Kingdom
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Default Hi pinkmouse

I wanted to find how an uncomfortable drive felt before I bought something flashy.

I had bought the driver 'cause I got it cheap, I was given the box and amp, and the powersupply wasn't bin-worthy. The whole project is for education and fun and to see how the ride could go if I were to spend some cash on it. Its a compact way to get some serious bass. I can talk on the phone while it shakes my kitchen, mad, its doing its job and I ain't turned the volume up yet.

Cheers Mike
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Old 27th January 2007, 11:39 PM   #8
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Hey, don't get me wrong, I'm all for fun!

Okay, you can run it like that, and it will have a short, but happy life. Or, if you really want to use this as a learning tool, then you could post your simulation graphs and models, and we might be able to help you make it better!
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Old 28th January 2007, 12:03 AM   #9
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Hi mikee55,

Your AT supply is 8A 12V that makes 96W. How much power does your amp draw, or supposed to give?
A voltmeter or much better a scope will tell if your 12V is up to the task.
pinkmouse is right, LT is going to put severe stress on amp and driver. How much gain diff from LT do you have at most within your wanted sub bandwidth?
Have you done any driver excursion analysis with your LT applied?
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Old 28th January 2007, 12:11 PM   #10
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Default "Mornin"

Hello, pinkmouse I don't wish for you to take me the wrong way either, I just felt I'd be laughed at for throwing together a load of cheap parts in a design like this. I can't afford 1000 watts of muscle to drive a Tempest or Peerless XXLS, I'm just getting along the best I can. I've had too many people laugh at me in my life it makes it difficult to ask for help without feeling small or I shouldn't be asking. I've had a lousy childhood, and that effected my education. Everything I have learnt has been through asking people like on here. My confidence is low, so I feel inferior.
Sorry for waffling...

I was originaly using a Technics amp, that was dead on one channel it was a Technics SU-V2 and I'm now using this car amp. A post on an ICE forum has just thrown up that its a cheapy amp of which lots were made.Its 4 Channel Mosfet job so I assumed it would have been advertised as 4 x 100 watts. Its chassis isn't as long as the 600W version.I'm using just one channel. The only graph I can show is of the Transform spreadsheet. I have the T/S parameters written down too.

Cheers Mike
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