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Old 6th November 2006, 05:03 PM   #21
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Ive been running Car subs as part of two seperate large PA systems for 2 years now without any problems.. But then again my subs have 2 4 ohm voice coils and are wired 8 ohm each and theres two per cabinet wired parrallell to give each cabinet overall impedance of 4 ohm.. both systems are identical in the sub department and both systems use a nice old H&H Amp bridged per set of subs and there are two sets in each system makeing 4 seperate amplifiers driving 4 setys of car subs.. but these arent exactly cheap subs...
OWen
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Old 6th November 2006, 07:54 PM   #22
sss is offline sss  Israel
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Quote:
Originally posted by AndrewT
Hi all,
are posts 16 & 17 a wind up?
The authors cannot seriously expect us to believe that nonsense.
i'm not joking , but i'm not expecting u to believe that "nonsense" either


Quote:
Originally posted by ilimzn


Wrong, the diodes are not there for that purpose. Under normal operating conditions they never conduct, regardless of impedance. The amplifier output stage is responsible for returning inductive current to the power supplies under normal conditions, which is why reactive loads increase power dissipation in the output stage.
The diodes are there to prevent the inductive load producing 'flyback' pulses that can be signifficantly higher than the power rail voltage (even several hundred V is not uncommon) when the output stage is cut off mid cycle due to protection activation. Many amps actually don't have these diodes when they should - resulting in output stage destruction by their own output stage protection circuits being activated in the presence of an inductive load!
u said it yourself "The amplifier output stage is responsible for returning inductive current to the power supplies under normal conditions, which is why reactive loads increase power dissipation in the output stage."
when the reactive energy stored is too high .... bye bye output stage
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Old 6th November 2006, 09:37 PM   #23
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Hi sss
Sure,when too high energy is stored a power stage will be destroy,but the purpose of the diodes connected from the output to the supply rails is not for discharge this energy but for protected the output transistor to the high voltage spike like correctly said from ilimzn.
A similar thing happens with the relay.
A good amplifier for subwoofer(car or home) would never have to neglect these protections.
Best regards

Vittorio
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Old 6th November 2006, 10:03 PM   #24
Duo is offline Duo  Canada
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This is quite amusing.

There is -no- important difference between car and house subwoofers, or speakers in general for that matter.

Electrically they act the same.

The only differentiation is their -intended- use, and the fact that it's easier to deal with low impedance speakers in the automotive world because of the low voltages available.

Some car speakers may be designed to handle weather a bit more, but that's no big deal.

Another thing I'd like to get off my chest: voice coil inductance rarely causes problems with too much reactive current in output stages. I've had more problems with it related to oscillation in any case. The bigger reactive component I have experienced with subwoofers is because of the speaker's physical environment. You must remember that air itself is very much like electricity and that a tuned speaker cabinet is mathematically no different from a tuned electrical circuit. The real difference is the acoustic enclosure just has a lot more quirks that aren't readily apparent.

Too many people get a strong misconception about car audio subwoofers in comparison with those intended for use in the house.
I will say as others have said, the first posts about voice coils getting out of gap and sending huge EMF pulses has nothing to do with car speakers in specific and is complete nonsense. Speakers are reactive, and do cause reactive currents in the amplifier/speaker interface, but this applies no matter what sort of speaker you use.
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Old 6th November 2006, 10:14 PM   #25
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Efficiency of the speaker is so low so I do not believe ic can produce the current needed to damage amplifier.

Here you go, car drivers in isobaric construction, 12" Alpine, 2 Ohm, driven by 500W amp.

Click the image to open in full size.
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Old 6th November 2006, 10:22 PM   #26
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Hi Duo
electrically a dynamic speaker it works similar to another.
In car audio some differences in comparison to home sub are made in the construction and parameters,moreover for the SPL components.
Many car subwoofers have some extreme parameters....
But EMF pulses is a strange thing
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Old 6th November 2006, 10:27 PM   #27
lndm is offline lndm  Australia
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For one thing, I have found that some typical car woofers appear to rely more heavily on mechanical damping than electrical. They have stiffer suspensions that domestic units (and/or a wider magnetic gap for vibration/environmental reasons...in the past at least), and so Vas is not large (which is also convenient for cars)

FWIW I have seen two different domestic 8 ohm rated amps die as a result of using car woofers, but I think this was only to be expected.
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Old 6th November 2006, 10:32 PM   #28
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.....and various car amplifiers are in my lab in repair....
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Old 6th November 2006, 10:40 PM   #29
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Quote:
Originally posted by parsecaudio
.....and various car amplifiers are in my lab in repair....
...because it is really hard to drive low impedances. Also, temperature conditions are hard...

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Old 6th November 2006, 11:38 PM   #30
bawang is offline bawang  Malaysia
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Gentlemen (and ladies too), unfortunately the Car Audio world is fill with myths, half-truths, and sheer twisted lies..... Ask 10 installers and you'll get 10 different stories..... Personally have heard an installer arguing about the size of cable to be used for a tweeter. He said that for a tweeter, the cable size MUST not be smaller than xx AWG, else the inductance will destroy the tweeter. Judge for yourselves.

FWIW, car audio speakers IS the same as home audio speakers...... Just that the impedance of car loudspeakers are normally rated at 4 ohms to extract the most power from the rail voltages of an amp, provided the output stage of the amp can handle the load.

Referring to Post #12, I have seen (and still in possession of) a good 18" subwoofer with its dual winding voice coil physically expelled (literally) by the amp, as the voice coils were connected to the outputs of the amp in stereo mode. This will cause the windings to mechanically sum the movement of the voice coil. At one point or another, at extremely high excursions, the glue will fail due to the stresses involved with the mechanical summation.

Other than this, have used car speakers at home and vice versa without any problems..... Just a little common sense and judgement, without resorting to myths.....

My 2 cents.....
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