Car woofers destroys normal amplifiers?

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Im not really sure about how I should describe the problem but I will give it a shot.

A friend of mine explained to me that most car subwoofers use a shorter voice coil so if a very big power pulse is sent to the woofer the voice coil falls out of the magnet field before the speakers reaches the mechanical excursion limit. (Im not sure I got it roght but I hope you get the point). When the cone is going back into the magnet field again, it sends a MASSIVE pulse back to the amplifier. Cheap car amplifiers supposedly handles but big, powerful and well constructed PA amplifiers break down. Can someone guide to more information about this phenomenon? How should I construct or modify a solid state amplifier to have 150% control of the cone and at the same time handle the return pulse?
 
Hi,
what happens to the voice coil impedance when it partially leaves the magnetic gap?
Does the impedance move towards the resistance of the voice coil.

Car speakers are often 4ohm but many of the bigger ones are 2ohm. The DCR of a 2ohm speaker could be 1r0 to 1r5.

The low impedance would load the amp severely.

I think it is much more likely that it is not the "CAR" speaker that is the problem but the "LOW" impedance load that is the real problem.
 
Wow.....

I thought this was a joke at first..LOL.

Anyway, I'd have to agree with richie00boy 100% on this one. Your first post (or both of them) are complete nonsenese. The entire statement is completely false and makes no sense whatsoever.

In fact, as the overall quality of the vast majority of automotive subwoofers has increased over the last several years or so, a select few have become VERY popular for use in DIY projects in hi-end home theater setups (ie Adire, Ascendant Audio, TC Sounds, Sound Splinter, etc etc). When the correct mobile subwoofer is implemented properly, fantastic results can be achieved, to say the least...especially when taking price/performance ratio into consideration (as with most DIY projects).

As for the "12 inch woofer blast several ouput transistors"...that obviously wasn't the case. The amplifier had to have failed for other reasons than the fact that a woofer designed by a car audio manufacturer was connected to it.

The only thing that COULD be a limiting factor is the 4 ohm load (sometimes 2 ohms, or 1 ohm, or even less). But that pro amplifier you mentioned certainly should have handled just about any load thrown at it.

In a polite manner, I suggest you attempt to inform your friend that he's been misinformed.

[EDIT]:

RAM Audio BUX 3.4:
http://www.ramaudio.com/BUX34.html

Continuous Average Power RMS, 1kHz, 1.0%THD+N
@ 2 ohms 2x 2900W
@ 4 ohms 2x 1750W
@ 8 ohms 2x 970W
Bridge @ 4 ohms 5800W
Bridge @ 8 ohms 3500W

[/EDIT]
 
I'm not familiar with the Ram Audio amplifier so I will withhold comments about the quality of the amplifier.

I will comment on personal experience here however. I have used car woofers on occasion and have caused them to have excessive movement to where the X-max has been severely exceeded. With an amplifier with sufficient number of outputs that was capable of driving a low impedance load no problems were experienced. I have built subwoofer amplifiers and have driven 2 0hm or lower loads with them without any problems.
Even a slight amount of back emf that would be encountered is not going to pose any problem.

No, car woofers do not destroy normal amplifiers. Been there done it as they say.
 
Hi,
now that we are really into commenting on the amplifier.
Here's mine.

My usual method of assessing an amp's output capability is to compare power values into varying loads.
My preference is for a tripling of power delivered when the load changes from twice the intended speaker impedance to half the speaker impedance.

So, if I were choosing the Ram, the 8r power = 970W and the 2r power = 2900W the ratio is 2.99 That, to me, indicates that this is a good 4ohm amplifier. But there is no information to assess it's low impedance ability nor whether it becomes unstable on low impedance loadings.
How hot did the output stage become? No information!
How long was it running for?
How much current was being delivered?
Was it oscillating?
Was the fan turning or blocked?

There is more that we don't know than we do know.
 
burnedfingers said:
These power figures are for 1K sine wave.

After looking at the web page I can tell you that these wouldn't be considered for any large format commercial system at all. They might work for light DJ work.

Just for the record, after looking up the info on that page myself, I absolutely agree. ..Just didn't go back and delete my careless assumption like I should have. :blush:

If a dual 2 ohm woofer were connected paralell to that particular amplifier and either played at fairly high volume for an extended period of time, or just having the amp throw massive amounts of unecessary power at it for some unjustified reason...then yes, I suppose it's likely that something bad could very well happen to the amplifier itself. Otherwise, I just can't see it happening, unless another unknown variable was the culprit (defect within the amplifier).

:dunno: *shrug* Who knows?
 
I always try to use 10x margin so if I build or modify a solid state amp to handle 0.4 ohms I should be able to use a big 4 ohm car audio subwoofer right?

Since I don't very much about these things I depend on the information given to me and I have had no reason to doubt my friends knowledge before.

Thank you all for your help and ideas.
 
Yes an amp designed to handle 0.4 ohms will laugh at 4 ohm speakers all day long. However, it would also be the size of a small engine, need an inductrial power feed, cost a fortune and require 'difficult' construction techniques and parts.

What I'm trying to say is there is no need. If you take into account the reactive nature and design properly for the rated impedance it should be fine.
 
sss said:
all inductive loads return energy back to the amp .
some amps even got protection diodes across the output stage for that purpose.

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!
 
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