Is it ok to do this?

[stay_high 10+ year member]

Ok so i have a set of components running off of the front 2 channels of a PPi 900.4 for front stage. They are 4 ohm. I have a single 8 ohm speaker I want to put in the rear. Can i run the single 8 ohm speaker off one of the rear channels of the amp? Like is it ok to mix ohm loads to an amp like that? TO clear things up, it would a 4 ohm set of comps on the front two channels and a single 8 ohm speaker on one of the rear channels. Safe?

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[trumpet 5,000+ posts]

Not every car amplifier is fine with an 8 ohm speaker, but it will likely work the way you suggested.

 

[bubbagumper6 5,000+ posts]

Ok so i have a set of components running off of the front 2 channels of a PPi 900.4 for front stage. They are 4 ohm. I have a single 8 ohm speaker I want to put in the rear. Can i run the single 8 ohm speaker off one of the rear channels of the amp? Like is it ok to mix ohm loads to an amp like that? TO clear things up, it would a 4 ohm set of comps on the front two channels and a single 8 ohm speaker on one of the rear channels. Safe?

Yes it should be fine.

Not every car amplifier is fine with an 8 ohm speaker, but it will likely work the way you suggested.

Just curious what amplifier's you're talking about?

 

[trumpet 5,000+ posts]

Just curious what amplifier's you're talking about?

It seemed like I'd read something about this a while ago, so I thought I'd err on the side of caution. I have not personally had an issue with 8 ohm speakers on car amplifiers, but then again I don't use 8 ohm speakers, period.

 

[bumpasauras 10+ year member]

run the comps off the front half of the amp as you are doing and bridge the back 2 channles to the 8 ohm sub

 

[bubbagumper6 5,000+ posts]

It seemed like I'd read something about this a while ago, so I thought I'd err on the side of caution. I have not personally had an issue with 8 ohm speakers on car amplifiers, but then again I don't use 8 ohm speakers, period.

The impedance of a speaker is not constant though, a '4 ohm' speaker only presents an actual 4 ohm load at a single frequency. It's impedance is greater than 4 ohms at all other frequencies, so amplifiers are actually seeing a very wide range. I can think of no reason electrically why an amplifier would have a problem with an 8 ohm speaker unless it was designed to run at a higher impedance.

 

[BoomTaco64]

run the comps off the front half of the amp as you are doing and bridge the back 2 channles to the 8 ohm sub

yes...yes do this...it will be great....better than just running one of the rear channels, bridge to make one channel for the sub.

 

[maylar 10+ year member]

Ok so i have a set of components running off of the front 2 channels of a PPi 900.4 for front stage. They are 4 ohm. I have a single 8 ohm speaker I want to put in the rear. Can i run the single 8 ohm speaker off one of the rear channels of the amp? Like is it ok to mix ohm loads to an amp like that? TO clear things up, it would a 4 ohm set of comps on the front two channels and a single 8 ohm speaker on one of the rear channels. Safe?

What is the 8 ohm speaker, and how much power can it take? If it's a sub, I'd agree with the guys above that bridging it to the rear channels would be the way to go.

The PPI 900.4 can make about 250 watts bridged to 8 ohms.

 

[bumpasauras 10+ year member]

yes...yes do this...it will be great....better than just running one of the rear channels, bridge to make one channel for the sub.

Are you silly why the hell would an 8 ohm load to an amp that has a min imp of 2 ohm cause any problems??? I own 3 ppi 900.4's I know them well what is the problem with my suggestion. The sub will see more powa the amp will be seeing 2 4ohm loads per side for a total of 8 wtf?? Am i missing something here?

 

[bumpasauras 10+ year member]

What is the 8 ohm speaker, and how much power can it take? If it's a sub, I'd agree with the guys above that bridging it to the rear channels would be the way to go.
The PPI 900.4 can make about 250 watts bridged to 8 ohms.

All of mine bench over 250 per channle at 14.00 flat great amp

 

[BoomTaco64]

Are you silly why the hell would an 8 ohm load to an amp that has a min imp of 2 ohm cause any problems??? I own 3 ppi 900.4's I know them well what is the problem with my suggestion. The sub will see more powa the amp will be seeing 2 4ohm loads per side for a total of 8 wtf?? Am i missing something here?

i am recommending doing what you are saying. run the components on the front two channels and bridge the rear two. your upset i am agreeing with you?

 

[bumpasauras 10+ year member]

ahh my bad

 

[BoomTaco64]

no worries...i was just happy someone was giving good advice as well...//content.invisioncic.com/y282845/emoticons/cool.gif.3bcaf8f141236c00f8044d07150e34f7.gif

 

[shizzzon 10+ year member]

The only reason i could see high impedance causing a problem with an amplifier.. if it did is the following-

Let's assume we are talking about an 8 ohm speaker on an amp that is 1ohm stable.

Wiring to 8ohm will rise WAY over 8ohm during play.

The switching rail voltage can be so high that it could cause unwanted stress on components.

This is something that would never happen immediately but overtime. Eventually, if possible, the amp would just die and not work anymore with no warning signs prior.

If anything, high impedance killed it.

IE-

Amp does 4900w @1ohm.

70v\70a

Assuming stupid perfect world, lol.. doubling impedance halves power but that doesn't normally work..

At least either will truthful power ratings or a more effective amplifier design.

The interesting thing about the real world is.. voltage rail does NOT stay the same..

Less current out, less SAG = Higher Rail!

So, some REALISTIC results(estimated)-

4900w= 70v/70a 1ohm

3042w= 78v/39a 2ohm

1849w= 86v/21.5a 4ohm

1058w= 92v/11.5a 8ohm

576w= 96v/6a 16ohm

The rail has went up from 70 to 96v.. What if the rail at a given dc voltage starts to clip at 100v?

Well, that means rising to 16-32ohms, you would hit clipping before you run out of CLEAN headroom..

this means you would have reached a point where the rail voltage is conflicting with the normal operations of the amplifier.

So, i'm not saying this is a definite will happen, etc, because without actually knowing the rail voltage values of a particular amp, no one can assume what the limit is..

But i can say if running a high ohm load speaker on an amp is bad or can eventually, overtime, harm it, this is one for sure way to do it.

 

[bubbagumper6 5,000+ posts]

The only reason i could see high impedance causing a problem with an amplifier.. if it did is the following-
Let's assume we are talking about an 8 ohm speaker on an amp that is 1ohm stable.

Wiring to 8ohm will rise WAY over 8ohm during play.

The switching rail voltage can be so high that it could cause unwanted stress on components.

This is something that would never happen immediately but overtime. Eventually, if possible, the amp would just die and not work anymore with no warning signs prior.

If anything, high impedance killed it.

IE-

Amp does 4900w @1ohm.

70v\70a

Assuming stupid perfect world, lol.. doubling impedance halves power but that doesn't normally work..

At least either will truthful power ratings or a more effective amplifier design.

The interesting thing about the real world is.. voltage rail does NOT stay the same..

Less current out, less SAG = Higher Rail!

So, some REALISTIC results(estimated)-

4900w= 70v/70a 1ohm

3042w= 78v/39a 2ohm

1849w= 86v/21.5a 4ohm

1058w= 92v/11.5a 8ohm

576w= 96v/6a 16ohm

The rail has went up from 70 to 96v.. What if the rail at a given dc voltage starts to clip at 100v?

Well, that means rising to 16-32ohms, you would hit clipping before you run out of CLEAN headroom..

this means you would have reached a point where the rail voltage is conflicting with the normal operations of the amplifier.

So, i'm not saying this is a definite will happen, etc, because without actually knowing the rail voltage values of a particular amp, no one can assume what the limit is..

But i can say if running a high ohm load speaker on an amp is bad or can eventually, overtime, harm it, this is one for sure way to do it.

I don't believe you have a clear understanding of what 'rail voltage' actually means and you're confusing it with output voltage. The internal rail voltages should not fluctuate (to my knowledge). In a standard PWM output section the amplifier has both a positive and negative rails, say they're 70V just for example. So one is +70VDC and the other is -70VDC. The input signal (AC) is used to drive transistors open and closed on each rail to cause the output voltage to swing from rail to rail, this is what creates your output AC waveform (after a lot of filtering). The control circuit has no control over how large of a signal it tries to produce, so if you try to produce a waveform that peaks higher that 70V (or lower than -70V) the output voltage will stop rising once it hits the rail voltage (because you cannot create voltage from nothing) which causes the peak or valley to flatten as basically pure DC.

If you're increasing the impedance, the output current should decrease. Less current means less stress on the components, not more.

As I said before, impedance is NOT CONSTANT. A '1 ohm load' is very rarely actually a 1 ohm load on the amplifier. See how the speaker is only actually 8 ohms around a very small frequency band?