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Weird blown tweeter question

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Anonymous
April 15, 2004 6:45:22 AM

Archived from groups: rec.audio.tech (More info?)

Oh yeah, he's STILL got questions.

During the process of killing and fixing my power amp, I managed to
blow a tweeter in one of my speakers (Advent Prodigy towers). This has
since been replaced (Thanks to Ken Drescher), but the way in which it
blew is odd. There is a _small_ amount of distorted sound that comes out
of it when I hook it up, and when I pull it out to measure, I find that
it has 1.7 ohms resistance! The replacement had 7.2 ohms, which seems
far more in-line with what I was expecting (and works fine, incidentally).

How can a speaker die, such that it drops resistance and still produces
some sound? Is this repairable?

Thanks,
Colin
Anonymous
April 15, 2004 6:45:23 AM

Archived from groups: rec.audio.tech (More info?)

The voice coil was overdriven. The heat caused the insulating lacquer on
the coil winding to break down. Either a number of turns are now shorted
together, or the coil former malformed and some of the turns are shorted via
contact with the magnet gap. It is not repairable.


"Colin B." <cbigam@somewhereelse.nucleus.com> wrote in message
news:407df5f8@news.nucleus.com...
> Oh yeah, he's STILL got questions.
>
> During the process of killing and fixing my power amp, I managed to
> blow a tweeter in one of my speakers (Advent Prodigy towers). This has
> since been replaced (Thanks to Ken Drescher), but the way in which it
> blew is odd. There is a _small_ amount of distorted sound that comes out
> of it when I hook it up, and when I pull it out to measure, I find that
> it has 1.7 ohms resistance! The replacement had 7.2 ohms, which seems
> far more in-line with what I was expecting (and works fine, incidentally).
>
> How can a speaker die, such that it drops resistance and still produces
> some sound? Is this repairable?
>
> Thanks,
> Colin
Anonymous
April 15, 2004 6:35:26 PM

Archived from groups: rec.audio.tech (More info?)

>
>Oh yeah, he's STILL got questions.
>
>During the process of killing and fixing my power amp, I managed to
>blow a tweeter in one of my speakers (Advent Prodigy towers). This has
>since been replaced (Thanks to Ken Drescher), but the way in which it
>blew is odd. There is a _small_ amount of distorted sound that comes out
>of it when I hook it up, and when I pull it out to measure, I find that
>it has 1.7 ohms resistance! The replacement had 7.2 ohms, which seems
>far more in-line with what I was expecting (and works fine, incidentally).
>
>How can a speaker die, such that it drops resistance and still produces
>some sound? Is this repairable?
>
>Thanks,
>Colin
>
>
>
>

The speaker probably overheated and shorted out a bunch of the windings thus
reducing the resistance.

It is not repairable unless you can replace the cone or diaphragm.
Richard H. Kuschel
"I canna change the law of physics."-----Scotty
Related resources
Anonymous
April 15, 2004 8:33:23 PM

Archived from groups: rec.audio.tech (More info?)

Richard Kuschel <rickpv8945@aol.com> wrote:

>>During the process of killing and fixing my power amp, I managed to
>>blow a tweeter in one of my speakers (Advent Prodigy towers). This has
>>since been replaced (Thanks to Ken Drescher), but the way in which it
>>blew is odd. There is a _small_ amount of distorted sound that comes out
>>of it when I hook it up, and when I pull it out to measure, I find that
>>it has 1.7 ohms resistance! The replacement had 7.2 ohms, which seems
>>far more in-line with what I was expecting (and works fine, incidentally).


> The speaker probably overheated and shorted out a bunch of the windings thus
> reducing the resistance.

Y'know, I shouldn't even bother posting on days I haven't had any sleep.

About 4.238 seconds after posting this question, I realised that the way
to bypass a resistor is to...(wait for it) short across it!

Anyways, thanks to everyone for beating me over the head with the obvious.

Colin
February 13, 2013 12:02:46 AM

Hello -

I am doing some tests on some cheap tweeters known as the Pyle 400W tweeter.
The tweeter has a capacitance of 0.12uF, however it is extremely different from a capacitor. Capacitors do not dissipate energy and therefore do not get hot. However the tweeter piezo element is dissipative and will get hot if driven CW. Furthermore the tweeter has a breakdown voltage, and the breakdown voltage drops dramatically of the tweeter element gets hot.
The piezo element inside the tweeter is a very thin film plated on a ceramic base. This tiny film has very little heat capacity and therefore is very easy to heat up, especially if the breakdown voltage is exceeded.

I drove a Pyle 400W tweeter at 25KHz. The maximum power I could deliver before the element began to heat and then draw high current was less than 1 Watt. T was using a +/-20V supply and I measured 43mA of DC current flowing in the power supply while driving an array of three of the speakers, each having a 10-ohm resistor in series. 43mA x 40V = 1.6W for all three tweeters or 0.5Watts per tweeter. If I go higher than +/- 20V, the tweeters break down and draw large currents, which cause destructive heating.

One way to solve the problem is to use a series capacitor and resistor to drive the tweeter. Next place a back-to-back Zener diode across the tweeter. The Zeners will break down first and protect the piezo tweeters from breakdown damage and over heating.

With this network in place, the tweeters should never fail.

-Charles












Quote:
Archived from groups: rec.audio.tech (More info?)

Oh yeah, he's STILL got questions.

During the process of killing and fixing my power amp, I managed to
blow a tweeter in one of my speakers (Advent Prodigy towers). This has
since been replaced (Thanks to Ken Drescher), but the way in which it
blew is odd. There is a _small_ amount of distorted sound that comes out
of it when I hook it up, and when I pull it out to measure, I find that
it has 1.7 ohms resistance! The replacement had 7.2 ohms, which seems
far more in-line with what I was expecting (and works fine, incidentally).

How can a speaker die, such that it drops resistance and still produces
some sound? Is this repairable?

Thanks,
Colin

!