back speakers with sub

[woodscomp]

Picked up a new Avic 6000nex, my question is the instructions say not to hookup the back speakers wires if using a sub. Why? Currently I am running a 2012 pioneer DVD unit with the back speakers wired in and a sub.

 

I listen to many things, not everything uses the sub, such as podcasts etc.. Therefore I like to have all four speakers hooked up.

 

Is there a reason why Pioneer says not to hookup the back speakers if your using a 4 ohm sub and one of the back speakers if using a 2 ohm sub? Will it hurt anything to have them hooked up?

[Shackleton]

Do not hook them both to the head unit speaker wires. sorry for the misprint

[woodscomp]

Did I miss something here?

[Bigchief]

I've got an 8000NEX running a sub with the rear speakers hooked up.  I think the issue is if you hook the sub directly to the head unit via speaker wires rather than running it through an amp via rcas.  I could be wrong but thats what makes sense to me.

[tickerguy]

Correct.

 

There are two sub outputs on the back of the unit; they're RCA jacks, not the ones on the wires, under the reverse camera and aux in video inputs.

 

That's where the sub goes if you're using an aftermarket sub that has line-level inputs (and that's what you want to use.)

[Bigchief]

I just installed all my stuff the past couple days and had the sub hooked up to the rear output rcas at first and everything worked.  Then I found the dedicated sub output rca jacks and swapped over.

[woodscomp]

Thanks, that makes sense. I went through three sets of Kenwood excelon speakers with my current head unit. Till I finally changed over to some polks. Don't really know what the issue was with them. But after that the third set I had enough. Those were rated for 3 ohms which is just odd to begin with. Didn't want to make any mistakes with this setup and jeopardize anything that cost more than those speakers did.

[tickerguy]

If you're blowing speakers (ESPECIALLY tweeters) you're probably clipping.

 

You have to understand how it happens -- most of the energy in music is actually in the lower frequencies.  When you overdrive the amplifier the output gets squared off; this produces a LOT of harmonics of the original frequency and the energy goes into those harmonics.

 

The tweeter, in particular, can only handle a few watts of power because it's small and that's all the power it needs to handle to reproduce the high frequencies.  When you clip the amp you send the whole 20 watts down to it and it burns up.

 

Now here's the math on this.  You have a 12V supply in the amp.  E = IR (Ohm's law) so if E = 12 and "R" is 4 (ohms) then I = 3 (amps.)

 

3 x 12 = 36, which is the MAXIMUM wattage a 12V powered amp into 4 ohms can produce.  Ever.  In truth it's probably closer to 25 watts because you don't want distortion and the closer to the V+ rail you get the more you'll get.

 

If you want more than that ~25 watts of output you need an amp that has a DC-DC converter in it so you can get more voltage.  Those are expensive, especially if you'd like them to be electrically quiet (that is, the DC is "clean" so you don't hear the converter in the sound!)  Thus they're not in the head units -- you have to buy a nice expensive external amp to get one.

 

The reason the Polks didn't blow up is that they're quite efficient.  In fact, they're one of the more efficient speaker brands out there.  The Excelons are good speakers, but they're not very efficient; by comparison they're typically rated around 85-88db @ 1 watt, where the Polks are typically rated at ~92-93.  That doesn't sound like a lot but it is; 10db of difference is twice as loud subjectively, so you're talking about a speaker set that is 50% louder for the same applied amplifier power in the Polks as the Excelons.

 

My guess is that you were driving the amp into clipping with the Excelons and destroying them while you're not with the Polks.

 

In general too much power doesn't destroy speakers -- too little does, believe it or not.

[Shackleton]

Are you talking about amp hook up or speaker level hook up. The manual is stating that you should not hook up back speakers and a sub to the back speaker out put at the same time. I don't know why anyone would hook a sub up to the head unit speaker out put anyway.

[woodscomp]

No, front speakers were blowing straight off the HU, no external amp installed. Plus it wasn't the tweeters, it was the low end that would go out. Called Crutchfield after the second set blew asking for help. They said it was a head unit issue, if I wanted to do a warranty return I would have to call pioneer. Supposedly they had quite a few complaints about the pioneer HU's and how they distribute power.

 

I opted to try the polks, been good for over a year now.

[tickerguy]

There's no problem with the Pioneer head units and how they "distribute" power.  There is a BIG problem with driving any speaker into clipping; it will be destroyed at WELL below it's "rated" power handling capability. That Crutchfield ran that line of garbage on you is both surprising and does a great deal of damage to their credibility with anyone who knows what is actually going on in the audio environment when these failures occur.

 

An oscilloscope can detect clipping instantly if connected across the speaker.  My money is on that being the problem; indeed, I'll bet virtually any amount of money on it.  The reason the Polks don't blow is that the're more efficient and require well under half the power of the Excelon's to produce the same listening level.

 

Better power amps in the professional world have a "clipping" indicator on the front panel.  Car head units don't but probably should.  It's not terribly difficult to provide; light an indicator at 90% of the V+ rail for the power amp and stretch the pulse width to a few hundred milliseconds minimum so you can see it if the LED comes on.  Under a buck of components and you've got it.

[woodscomp]

Okay tickerguy. Interestingly enough the "new" updated installation manual from pioneer explicitly states not to use speakers rated below 4 ohms, in a caption all of it's own.

 

Having gone through three sets of speakers myself. I highly doubt the HU was clipping anything, especially at my listening levels. They lasted anywhere from a couple of months to a few days, depending on what I was listening to. And it always happened to the same speaker. Ran new speaker wire, with the same results.

[tickerguy]

 

 

Okay tickerguy. Interestingly enough the "new" updated installation manual from pioneer explicitly states not to use speakers rated below 4 ohms, in a caption all of it's own.

That's because the amp isn't stable below 4 ohms -- the risk is to the amp, not the speakers.  Pretty common for head unit amps; if you want an amp that can drive a 2 ohm load then you need an external amplifier.

[drenyce311]

I used my multimeter to tune my amps for clipping. And some 40-1000htz tones