mix speakers?

I have an Alpine PDX-5 running the factory 2 ohm speakers in my wife's Mercedes. I have replaced the factory subwoofer though with an aftermarket Pioneer, but cannot for the life of me remember which one.

We have developed a bad static problem on one of the channels (OF door...not the subwoofer) and I need to do some isolation work to see where the problem is. I get it after you hit a bump in the road. Getting inside the door panel is a real pain and I don't want to do that if I don't have to...and I don't think I will. What I want to do is just set a cheap 4 ohm speaker in the car and run separate wires to it for testing purposes so I can see if the problem is in the wiring from the head unit to the amp, amp to the speaker, or the head unit itself. Can I safely run this 4 ohm speaker for a few days while I figure out what's going on? Keep in mind, this thing NEVER sees anywhere near high volume. Thanks for helping out.

As long as it is not connected in parallel with the installed door speaker, sure you can do that.  However, the most likely source for the type of issue you describe is a bad speaker or speaker wire.  If you did not rewire the door speakers, then the issue is likely at the amp.  On the other hand, the PDX is likely providing too much power for the OEM door speakers and you may have just fried one of them in such a way that it only shows up during physical bouncing.  Rare, but possible.  One other thing, the four main channels of the PDX-5 are not rated for use into 2-ohms.  You are likely over-driving the amp and you will eventually fry it.  It really needs 4-ohm speakers on channels 1 through 4.

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The reason I got the PDX-5 was because it WAS rated for 2 ohm speakers. I had a heck of a time finding one that was. This is from their website:

"Same Power Output - 2Ω or 4Ω Configuration

PDX amplifiers have the unique capability to deliver the same power output regardless of 2Ω and 4Ω loads."

So now you have me wondering...and I don't know what to think. But since we never, ever power that thing anywhere near it's capability, we shouldn't be overloading it. We've never had it overheat, etc.

I do believe you are correct on the wiring. That is what I want to isolate. What I did was wire from the amp, to the factory connector for all the speakers by finding another female connector and soldering the leads from the amp. This connector is located in the right rear trunk well. This way, you utilize all the factory speaker wiring. The factory Mercedes sound system isn't cheap, so I felt comfortable using as much as possible...plus it makes a very clean installation.

By using a test speaker, I should be able to find out if it's the speaker itself, or the wiring from the head unit to the amp, or amp to the speaker. Those Alpine connectors leave a lot to be desired as well IMO.

I certainly appreciate your input.

The fifth channel of the PDX is rated into 2-ohms, but the front four are not.  Now it may handle that load especially if it's not being pushed too hard, but these ICE-based class D amps are notorious for not liking being overloaded.  That's not likely to be causing your problem, of course.  If it was distortion from overload it would occur no matter what was happening with the vehicle.  Most likely you have a bad speaker wire connection or a blown speaker.

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could also be a loose rca connection. i had a problem like that on an older MTX amp where i would randomly get noise when i hit bumps and thats what it turned out to be.

funny, i could swear that the PDX amps were rated for 4 or 2 ohm loads. id have to look at the box but im almost positive that my PDX-f4 is but maybe the pdx 5 isnt...?

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well, DYohn is right, copied straight from alpine website:

Features and Specification

SPECIFICATIONS

CEA-2006 Power Ratings
CEA-2006 Power Rating: (4 I? @14.4V Ƈ% THD+N, S/N: 77dBA, ref:1W into 4 I? and 2I? for mono ch.) 75W x 4 + 300W x 1
RMS Power Ratings
Per channel into 4 Ohms: (@ 14.4V Ƈ%THD+N, 20Hz - 20kHz @ 4I? for 4ch.) 75W x 4
Per channel into 2 Ohms: (@ 14.4V Ƈ%THD+N, 20Hz - 200Hz @ 2I? for Mono ch.) 300W x 1


its for the marine version of the PDX-5 but they are the same amp. the specs are a little hard to understand though. it must only be the five channel though because my PDX-F4 is rated for a 2 ohm load per channel. not sure where you bought the amp from but a lot of websites have a tendency to mislabel product specs

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All of the PDX amplifiers are stable into a 2 ohm per channel load. They do not give the 2 ohm rating because they specifically state that the amps produce the same power into a 4 ohm or 2 ohm per channel load.

i am an idiot wrote:

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All of the PDX amplifiers are stable into a 2 ohm per channel load. They do not give the 2 ohm rating because they specifically state that the amps produce the same power into a 4 ohm or 2 ohm per channel load.

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they need to still be more clear about that in the specs. every other pdx amp gives you both specs

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This is all really good information.

As soon as I finish up the project I have going on, I will start running separate wires and speaker for that channel and see if I can resolve the issue. At least I know I won't damage anything using a 4 ohm test speaker I can set on a seat somewhere.

I can't thank you enough for your help.

The PDX-5 will run 2-ohms on the sub channel only. Please see the spec sheet, excerpted here:


Nowhere does it mention 2-ohm operation on channels 1-4.

That's besides the point... Check your RCA's first. Drive around with an iPod connected to the inputs, and see if it goes away. If so - deck or signal wires. If not, speakers or OEM wiring.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

The New Alpine Amps has those Specs(2-4 Ohm)... The PDX-5, i believe, is an old part #... https://www.alpine-usa.com/product/view/pdx-v9/Specs

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M.E.C.P & First-Class
Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

PDX-V9 and PDX-5 are two different models, yes.

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The original PDX-5 and all of the PDX multichannel amplifiers are 2 ohm stable. Granted they claim no more power into 2 than 4, they are all capable of driving 2 ohm loads.

I have been trying like crazy to find my original manual and paperwork. I SWEAR it states my amp is usable with 2 or 4 ohm speakers on all channels. That is the reason I bought it...I didn't want to have to go in and replace all the speakers in the car. I believe Alpine has changed the wording since I bought mine two or three years ago.

I can't say enough what a great help you have all been. Thanks again!

Did you find your problem?

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I am so embarrassed...I've only started to look at it. I have two other projects I need to get completed so I have room to work on that one. But I know exactly where I'm going to look from the suggestions here. I too suspect it's the rca's. I will post up the answer once I find it. Problem is, it's not constant. It comes and goes. Seems to happen when you hit a bump. But I'll find it.

Finally an update. First...I found the original data sheet and instructions to my PDX-5. It indeed is fully rated for 2 ohm speakers across the board. Nowhere does it differentiate between subwoofer and other speakers. Which is why I bought it in the first place as the 'Benz uses 2 ohm speakers and I wanted to keep them.

Next, what I did was swap the rca's from the head unit into the amp to see if the problem followed to the other speaker. It did. So I knew the problem was before the amp. I pulled the head unit out of the car and totally removed the wires from the connector that are used for powering speakers without an amp. I had them all cut to different lengths and taped off, but you never know. Then I rearranged the wiring behind the head unit. My rca's were already taped. I bolted it back together. It's been several days now and not a peep of noise. Not sure exactly what the problem was, but as long as it's gone, I am one happy camper. Thanks for all the help.

Excellent, glad you got it figured out.  And a lesson for everyone in the importance of a proper installation job! 

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