AL3 Problem

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Martin1970
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Re: AL3 Problem

Post by Martin1970 » Fri Oct 28, 2016 10:19 am

Hope this doesn't cause any hard feelings. Here we go ...
UncleMeat wrote:OK, here's something we have not taken into account. The 300uF is to allow high frequency signal to pass to ground instead of going through the woofer. If you are passively bi-amping and running the amp full range, a large percentage of the signal is going to be sent across the capacitor, with little resistance, to ground.
I had a similar fundamental misunderstanding of crossovers years ago:
Martin1970 wrote:A large percentage of the power you throw at your speakers gets sent to ground through passive crossovers.
Mark set that straight for me:
Radioeng2 wrote: In a crossover, the high or low pass part doesn't dump what's not passed to the driver, to ground. The impedance goes high and therefore just doesn't draw any power at those freq's.

If it helps...think of it at DC for a minute. A resistor across a supply. When the resistor value is way high, little current flows and little heat is evident in the resistor. On the other hand, when the value goes low the resistor can get HOT. That's because you're now drawing a lot of current.

So now think of the portion of the crossover going to, lets say, the woofer. It's a low pass. So the component values used just don't really come into play while passing a low freq and the full drive goes to the woofer. Now on the other hand, when the frequency is high, the values used are such to just not allow any current to flow anywhere. Not to the driver and not shunted to ground either. So you'd see the voltage present on the wire side if you looked with a scope, but no power is being absorbed at the load, the speaker end.

Hope I said that all correctly and it's even understandable...

Mark
Source:
http://thecarversite.com/yetanotherforu ... #post68470
http://thecarversite.com/yetanotherforu ... #post68480

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Re: AL3 Problem

Post by UncleMeat » Fri Oct 28, 2016 3:45 pm

Yeah, I figured I'd get in trouble posting about technical electronics stuff. Sorry if I wrote the incorrect analysis of the way a crossover blocks signal from going to the woofer. Thanks for correcting me Martin.

That 300uF capacitor should be allowing low frequency to bridge across it (meaning it shunts HF). I'm not sure why it's in parallel with the woofer, could someone explain this crossover circuit? If the 300uF is bad (shorting) it would allow current to flow to ground, correct?

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Re: AL3 Problem

Post by UncleMeat » Sun Oct 30, 2016 4:23 pm

So again; I've got it backwards! ](*,) Larger capacitors are going to present a high impedance to low frequency. But, let's go back to what I posted earlier about HF signal bridging across the 300uF capacitor (that it's going to pass HF)
(Wikipedia on Capacitors) Impedance decreases with increasing capacitance and increasing frequency. This implies that a higher-frequency signal or a larger capacitor results in a lower voltage amplitude per current amplitude—an AC "short circuit" or AC coupling. Conversely, for very low frequencies, the reactance will be high, so that a capacitor is nearly an open circuit in AC analysis—those frequencies have been "filtered out".
I realize that the HF signal going through the 300uF cap is not going directly to ground, it also travels through the 3.5mH inductor. So calculating the reactance of the 3.5mH inductor gives a value 3.3 Ohms at 150 Hz, going higher as frequency increases.

It's possible the 3.5mH inductor has failed allowing the HF signal to pass and present a low impedance to the amp. When you hook up the speaker with no crossover all frequencies are forced to go through the voice coil which has an increasing impedance with increasing frequency. It's either the capacitor passing too much low frequency or the inductor not blocking enough HF; or both.

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sea
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Re: AL3 Problem

Post by sea » Sun Oct 30, 2016 5:06 pm

UncleMeat wrote:So again; I've got it backwards! ](*,) Larger capacitors are going to present a high impedance to low frequency. But, let's go back to what I posted earlier about HF signal bridging across the 300uF capacitor (that it's going to pass HF)
(Wikipedia on Capacitors) Impedance decreases with increasing capacitance and increasing frequency. This implies that a higher-frequency signal or a larger capacitor results in a lower voltage amplitude per current amplitude—an AC "short circuit" or AC coupling. Conversely, for very low frequencies, the reactance will be high, so that a capacitor is nearly an open circuit in AC analysis—those frequencies have been "filtered out".
I realize that the HF signal going through the 300uF cap is not going directly to ground, it also travels through the 3.5mH inductor. So calculating the reactance of the 3.5mH inductor gives a value 3.3 Ohms at 150 Hz, going higher as frequency increases.

It's possible the 3.5mH inductor has failed allowing the HF signal to pass and present a low impedance to the amp. When you hook up the speaker with no crossover all frequencies are forced to go through the voice coil which has an increasing impedance with increasing frequency. It's either the capacitor passing too much low frequency or the inductor not blocking enough HF; or both.
There are two coils in the woofer section. I checked both and I have continuity across them. Is it possible for the coil to be "bad" without shorting? Never really heard of a coil going bad unless it was fried.

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Re: AL3 Problem

Post by UncleMeat » Sun Oct 30, 2016 7:24 pm

An inductor is just coiled wire; so it will always show continuity even if the windings lose their insulation and adjacent wires bridge and internally 'short'. I think the only way to tell for sure is to see what it's response is on an o-scope. The length of the coil in the coil is what makes the inductor "resist" higher frequencies. The reason I point to the 3.5mH inductor is because it's in series with both the woofer&inductor and the capacitor (the only pathway to ground).

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sea
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Re: AL3 Problem

Post by sea » Sun Oct 30, 2016 10:04 pm

UncleMeat wrote:An inductor is just coiled wire; so it will always show continuity even if the windings lose their insulation and adjacent wires bridge and internally 'short'. I think the only way to tell for sure is to see what it's response is on an o-scope. The length of the coil in the coil is what makes the inductor "resist" higher frequencies. The reason I point to the 3.5mH inductor is because it's in series with both the woofer&inductor and the capacitor (the only pathway to ground).

Thanks. That makes sense.

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sea
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Re: AL3 Problem

Post by sea » Mon Nov 07, 2016 2:00 pm

Now I have replaced the 300uf cap with a brand new one. Same Problem ](*,) ](*,) ](*,) I am at a total loss!!!!!

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Miko1971
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Re: AL3 Problem

Post by Miko1971 » Mon Nov 07, 2016 2:42 pm

Start pulling the woofers out one by one and see what happens.

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sea
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Re: AL3 Problem

Post by sea » Mon Nov 07, 2016 3:15 pm

Miko1971 wrote:Start pulling the woofers out one by one and see what happens.
The AL3 only has one woofer. When it is removed and connected directly to amp all is fine.

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Re: AL3 Problem

Post by Miko1971 » Mon Nov 07, 2016 5:42 pm

Lucky you have the one then.. I know which model your talking about now. I'd look for a suitable replacement.

I'd jam this bad boy in there...
image.jpeg
image.jpeg (30.95 KiB) Viewed 3998 times
http://stereointegrity.com/product/hst11-11-subwoofer/

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Re: AL3 Problem

Post by UncleMeat » Mon Nov 07, 2016 10:24 pm

So the cap is known to be good since it's new so I think you have an inductor that is passing the HF. The impedance of the HF signal that the crossover is designed to attenuate is not getting blocked and therefore the impedance seen by the amp is too low. When you use the woofer without the crossover the natural roll-off of the woofer's VC is attenuating the HF, but also causing more heating of the VC as energy is absorbed.

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sea
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Re: AL3 Problem

Post by sea » Tue Nov 08, 2016 7:09 am

UncleMeat wrote:So the cap is known to be good since it's new so I think you have an inductor that is passing the HF. The impedance of the HF signal that the crossover is designed to attenuate is not getting blocked and therefore the impedance seen by the amp is too low. When you use the woofer without the crossover the natural roll-off of the woofer's VC is attenuating the HF, but also causing more heating of the VC as energy is absorbed.
How would I go about confirming this? Remove the coils from the circuit one at a time? It is hard to imagine that a coil or coils would be bad in both speakers.

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Re: AL3 Problem

Post by UncleMeat » Tue Nov 08, 2016 7:07 pm

Put a replacement inductor in of the similar value; or have a tech test it's response with an o-scope. I think test equipment for measuring inductance are very expensive IIRC.

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