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-   -   Both my base cones staged a gradual death in the same month (http://www.diyaudio.com/forums/multi-way/38394-both-my-base-cones-staged-gradual-death-same-month.html)

VvvvvV 25th July 2004 10:40 AM

Both my base cones staged a gradual death in the same month
 
I have two decent floor standing 100w speakers from an independent business venture manufacturer of some years back, running off a run of the mill 75w Hitachi amplifier.
Last month, the base on one of them started cutting out completely and rumbling on and off at high bass levels, it took about a week to die, and now the bass cone is completely dead. The same happened to the other side a month later.

The sound from both sides was always sweet, no clipping/overdriven sounds. What could possibly happened for them to die so slowly, and what new ones can I get? I would really like to repair them, but I can't imagine what has broken.

Paradise_Ice 25th July 2004 11:01 AM

It does sound strange how your drivers died within the same time frame almost,
I am sorry but i would suspect somebody else if you have been a careful owner, have u been away, They may have been subject to a party?
There a so many drive units these days replacments are not a problem, just the sizes and parametres can be.

Hans L 25th July 2004 12:35 PM

Is the amp putting out DC (offset from centre, even without any sourcesignal fed through the amp)? Have you listened to a new cd/dvd lately with a lot of ultralow bass content (which would mean you see the woofers moving wildly)?

VvvvvV 25th July 2004 01:15 PM

This is my first time with speaker Electronics, and I must say I am completely confused.
I have tried measuring the crossover and various voltages with a standard industrial multimeter and the voltages I find are in millivolts, the only sensible re the only logical readout I can obtain is the ohms value, which is also confusing for me.

I have played my speakers very loud but the amplifier has a roof of 75W which is lower than the speakers and it is impossible to get the amplifier to clip. I have on many occasions played with the bass setting of the amplifier maximised and very loud. All the while though, the bass was crystalline.

It is a very old amplifier, and I am hoping it is as good quality as our 25-year-old hitatchi television. What should I measure & how should I use the multimeter to see what is actually happening?

Shpoop 25th July 2004 01:50 PM

well if theyre pretty old, i guess it could be a decayed foam surround...thats happened to me a good many times

but you would probably have noticed that

Hans L 25th July 2004 02:01 PM

An amp at max setting normally means you are well into clipping. I'm reasonably sure your amp isn't any different from others in that respect. What is the exact spec of the amp? 75watt continuous at 8ohm? Maybe 130Watt or so at 4ohm? And the woofer? Was that 100Watt nominal power or peak power? What is the stated impedance of the woofer (4/8ohm)?

First thing you can do is measure the resistance of the woofer. If it shows something at or near zero ohm, the voicecoil has shortcircuited, probably by melting due to excessive power.

To check for DC, you can connect the amp to a unit (midbass or bass, not too weeny), turn on the amp and without any sourcesignal present attach/detach one of the wires to the speaker to see if the speaker moves from its centre position. If it moves, there is a constant current comping out of the amp (DC) which forces the speaker in an offset centre position. This lowers the excursion capability considerably and DC also heats up the coil.

If those two check out, you might want to consider having a look at the voicecoil of the speaker to see if it was physically damaged due to excesive excursion.

ashok 25th July 2004 02:15 PM

Did you check the woofer leads ?
 
It is possible that the bass drivers were moving more than they were designed for ( especially at very low frequencies) and the lead out wire from the cones are broken.
You will need to remove the drive unit and look at the lead out wires that start on the cone and terminate on the chassis of the speaker. These do break sometimes especially on old drivers.
There are two wires coming out of the rear of the cone and terminating on the chassis.

If that is the case it is easy to get some flexible stranded wire meant for this purpose. Just resolder it in place of the old one. Get help from someone who has experience doing such things. You don't want a small problem from becoming a major disaster.

If you want we could also give you instructions in case you want to do it yourself.
Cheers.

VvvvvV 25th July 2004 05:37 PM

The speakers are TDL Electronics rtl2 transmission line floor standing speakers.
8 ohms 100 W. When I got to these I remember reading they are 100 W per channel
http://digilander.libero.it/piani/ca...dl/tline_2.jpg
http://digilander.libero.it/piani/ca...dl/tline_3.jpg
the amplifier is an 8/16 ohms 10-year-old integrated CD player with an auxiliary coming from a balanced computer production audio card. It is rated at 150 W. and volume knob goes up to 10, but only values up to six have an effect on the volume. This is why I have never heard it clipping.

The speakers are from the late Nineties.
It was one of the best speaker companies in the UK for a while.

The worst treatment the speakers got from the amplifier was so that the frequency spectrum was distorted as if it was coming through graphic equaliser. All the sounds were still smooth. (I did not have sexual relations with that woman, Monica Lewinsky)
it seems I must have overloaded them! booo then again, it could be the the age.

I have just tried the bass cones soldered points with a bare amplified signal and all I could hear was the tweeter, it surprises me that the signal goes through the cross wiring to the tweeter, but this is probably normal.
I wonder what I should do next, possibly a comprehensive upgrade. I will research the best way to refurbish, I have some linkwitzd electrets.

Thanks for all suggestions regarding the cones wires and testing the amplified voltage, I shall certainly make sure it is all as you say.

pinkmouse 25th July 2004 06:31 PM

Nice speakers, I used to love my TDL3s.

You can probably get some near replacement drivers from here:

http://www.wilmslow-audio.co.uk

TheoM 25th July 2004 08:24 PM

dead woofers?
 
Same month? They must have been traumatized. DC is a good theory. I fried a pair one time, slow cooked, with a perfect amplifier that was dutifully amplifying DC is the source signal. Your hitachi probably has some protection for that but maybe not.

Hook up the woofer directly to a sound signal source - even a 1.5 volt battery to see if it jumps when you connect it. If it does not, its dead. Cut it open and small the coil - if it smells like burned insulation it was DC in which case you must replace your amp.

If it does work then the problem might be in a fuse (light bulb) in your crossover, or some other thing in the crossover.


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