i have witnessed car audio black magic

[imaspaceguy90 10+ year member]

Its aprolly a high rated max amp or way underated or as u said... Black amgic.

 

[nissanrider06 10+ year member]

he said all running off the amp, but maybe he wasnt sure?

 

[Phred168]

It's quite easy. Just a passive xover network. It might throw up some odd loads to the amp, but you can do it if you have the patience.

 

[jaygeorge1979 10+ year member]

ok fellas, i said ALL the speakers are driven off of the amp...i know this because there are two signal wire inputs running into the amp...one of them is the front preouts from the HU and the other is the sub preouts from the HU....there are NO signal outs connected to the HU...when i disconnect the signal cable from the amp, the speakers stop playing, ALL of them....when i adjust the gains, ALL the speakers change....if there were speakers hooked up to the HU, or a diff amp, then cutting off the signal to the 4 channel amp would NOT cause these to shut off also...thus, all 8 speakers are hooked up to an 8 channel amp...

i like the idea of a passive crossover...the location for the speakers are as follows: 3.5" in dash, 6x9" in holes in the walls in the rear, tweeters RIGHT next to the 6x9...when i listen to the 6x9 with my ear right up on it, i cant hear very much highs...they aare there, but VERY quiet...however, the tweeter right above it is loud as can be....maybe there is a passive crossover hidden behind the 6x9 that sends highs to the tweet, and mids/lows to the 6x9...that would allow the amp to see a 2 ohm load per channel, since each channel would "see" two 4 ohm drivers...

....right? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[jaygeorge1979 10+ year member]

ok car has been ripped apart, and here is my findings:

there are two wires running from each of the two availible channels on the amp...for one channel: one set of speaker wires run to the speakers in the dash, and one set runs to the 6x9...spliced into the wire before the 6x9 is the tweeter, which has as 12db/octave passive crossover wired into the speaker wire....

what does this do for impedence? assuming all 4 ohm drivers (including the tweeter)....what load would one channel of the amplifier see?

thanks for those who stuck with me thru this difficult time //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[thylantyr 10+ year member]

You can connect abnormal loads to amplifiers and have them work fine as long

as you don't exceed the amplifier's safe operating area. It's easier to do this

with 'dumb amplifiers', ones with no protection circuits to shutdown the amp.

Tweeters, 3.5", 6x9, it's an easy load inspite if you had it wired for low impedance.

I run 0.8 ohms nominal on my home amp in bridge mode, it's only rated for 4 ohms in bridged

mode.. it works because the load isn't placing a big burden on the amp.

 

[jaygeorge1979 10+ year member]

i never realized this...i figured a low impedence is a low impedence, regardless of what drivers are wired to it...you are saying that an amp whose channels are only rated @ 2 ohms can handle a one ohm load since the speakers are small? (edit: the 3.5 is actualy a 4x6....blame my buddy for that lil piece of misinformation //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif )...what exactly do you mean by the amplifiers "safe operating area"? is this impedence you are referring to? what is an example of a load that WOULD place a big burden on an amp and therefore be a bad idea?

thanks for stopping by thy

 

[thylantyr 10+ year member]

There are many variables that allow cheating.

Impedance can vary with frequency.

Music is low in duty cycle.

Speakers may operate in a passband.

Passive crossovers are a load, active is not.

Amplifiers are over-rated/under-rated in specs.

Drivers are over-rated/under-rated in specs.

The person turning the volume knob can affect system performance.

Few examples.

* woofer + box may have a different impedance than nomimal, maybe it's higher

in the frequency range it operates?

* Music is an easy load on an amplifier vs. rms testing. The type of music can

affect how much heat an amplifier generates because the duty cycle is different.

ie, play a Slayer album then play a Jazz one, the Slayer session will cause your amp

to run hotter. Play a keyboard note for 1 minute and the amp is working continously, crying for help,

getting creating more heat. Or, hit the snare drum once every 1/2 second for a minute, the amp is

yawning, not getting warm.

* If you do an active setup, 1 amp for tweeters, 1 amp for mids, etc., each one

of those amplifiers will run cooler because each amp is operating in a limited frequency range, could be less strain on the amp. The tweeter amp has the easy

job, the woofer amp will have the difficult job.

* If your passive crossover is simple, the load on the amplifier is light. If you have

a complex passive, the load can be greater. If you have active, there is no

crossover load at all. ie, If your speakers have only a capacitor for crossover, that is an easy load.

* I don't trust published driver and amplifier specs. To me they are just ballpark

figures. Even amplifiers with RMS ratings are suspicious. How long do they operate

the amplifier to get it's RMS rating? Do they follow a certain standard and is that

standard good ? For instance, I tested a 3400w amp at 2kw rms for 10 seconds

before it shutdown, but I can drive it all day at 1.5kw rms. So, how do you rate this amp? In this case, it's a proamp which uses a different set of rules for testing

and using that method, 3400w is valid as it's a method that mimicks 'music'. If you placed a rms spec, do you call it 2kw rms because it can do it or do you do a more

conservative approach and say it can do 1.5kw ?

* You paralleled four 15w rms rated tweeters for 1 ohm load, the amplifier is rated

for a 100w/ch, 4 ohm. If you play a sine wave to test power handling and the tweeters draw 15w x 4 = 60w rms. Drive the amp more, the tweeters will smoke.

The amplifier is rated for 100w and only sees a 60w draw even if it's a 1 ohm

load. It's within it's safe operating area, it works unless a protection circuit raises

the red flag. If the amp has protection circuits, those circuits may react and not

let you cheat. A dumb amplifier would just keep playing until it blew up regardless

of load, even a short circuit. Sometimes is nice to have a dumb amp if you want to

something esoteric.

The last variable. Lets say you have some dumb amps and very low impedance loads. You can turn up the music at a low level and the system should play well.

If you turn that volume knob higher you can exceed the safe operating area of the amp.