Car Audio wiring question.

Jovec

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I have a car that came with a proprietary audio system. The head unit sent a single L/R line level signal to the custom amp, which then split the signal to various speakers: front mids, front tweeters, rear mids, front center, and a single sub. The amp appears dead and replacements run in the $2,500+ range. I am just trying to get the system (mostly) working again on the cheap with a spare head unit I had. I am just using the head unit's built in amp to power the front mids/tweeters via a set of passive crossovers, but I am curious if I can get the sub working the same way. I am thinking to use another set of crossovers, three-way this time, to split the rear signal from the head unit into 3 sets of outputs - 1) woofer, 2) mid, and 3) highs. The mid outputs will be wired into the rear mid speakers and the tweeter outputs will be unused. My question is about the woofer outputs. The sub is a single voice channel. I've read enough to know that I should not simply wire the L/R + and L/R- to the sub, but what about just using a single +/- from the left channel (for example) off the crossover while leaving nothing connected to same right channel. Any technical issues with this setup? Is there a way to wire in the L/R+ and L/R- together by adding in 4-ohm resistors or otherwise make it into a mono circuit? If not I can always leave the sub un-used and it still sounds okay.
 
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brekk

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Why not just get a 4.1 channel amplifier? Run headunit to that and it powers 4 speakers and 1 subwoofer.
 

DirkDonkeyroot

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You're going to need an amp to drive that sub most likely, I would find a 2 channel amp with low level inputs, scrap the rear mid fill and power the sub off the amp.

Edit:
"Kicker DXA125.2 DX-Series 2 x 125W Car Amplifier" from www.parts-express.com!

Set the gain properly and it should be ok, if not it's a good excuse to get a better sub. Let me know if you have questions, I installed car audio for about 10 years.
 
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Xarpolis

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When dealing with factory systems, it's a difficult thing to say for sure. I know many "premium audio" systems have independent smaller amps across every speaker. Definitely on the sub. In some cases they work fine, assuming you just connect the lead cable up, telling the amp to turn itself on. Other cases, you need to just replace the factory speakers all together with something aftermarket.

Which type of vehicle and sound system do you have? I'm sure other message boards would have people a little more advanced than the shit I just said. I know Phoenix Gold used to have a board, but there was another that I've used in the past. Let me see if I can dig it up.


Here's a great knowledge forum. Ask your question there, and I'm sure people know the answer or could walk you through it.
CarAudio.com

Any chance you live out in the Cleveland area? If so, I know a guy that is magical with car audio.
 

Jovec

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Why not just get a 4.1 channel amplifier? Run headunit to that and it powers 4 speakers and 1 subwoofer.
Because I am not looking to throw any real money (or time) at the car audio. If I buy an amp than I will want to update the spare kenwood head unit to something more modern, like a double-din with built-in bluetooth, etc. Then I will want to run RCA cables from the head unit to the amp for a cleaner and better shielded source signal. Then upgrade the power delivery to the amp and run better speaker wiring. Toss in a capacitor. Then may as well add a back-up camera, etc... My younger self would have already done all of this.

I leveraged the existing wiring from the trunk-mounted amp that runs to the speakers. The head unit only had a pair of line level outpouts (so four wires) to send the signal to the amp, so I clipped the center channel speaker wires for a 3rd pair and clipped another set from the head unit to the amp (aux power and remote turn on I think) for the fourth pair. The result was not having to run any cables front to back or to any speaker and everything is just being powered by the head unit's built-in amp.

The car is an older Lexus GS430 with the Mark Levinson audio package. The amp problem is a known issue, and Lexus is extra shitty by coating the entire amp circuit board in a clear resin or epoxy to make repairs difficult. I've seen used amps for $800+ and new over $2500. I do not believe that there are separate amps for every speaker. Everything I could see and read indicates there is a single amp.

I'm just curious if the unbalanced load will cause any damage or audio issues, since my plan is to have the left rear output sent to a 3-way crossover but only connect the midrange to a speaker, while the right rear will have the midrange and woofer connected off of a second crossover. From what I can read the amp (in this case the head unit) will run a bit hotter on the side that does not have the sub connected since it will have less load.
 

brekk

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I was not advocating for some high end setup, 4.1 amps have become rather common allowing a single device to power the full speaker system plus a sub. Something along the lines of this.

For your three way crossover setup, I would just send eveything but the subwoofer portion to the mids, no reason to filter out the tweeter signal, mids can run the high frequencies fine. However, the built in signal on a headunit, which is usually 22W RMS per channel (Advertised as 50W Peak per channel) will not be able to push a sub woofer.
 

Lambourne

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#7
If I'm reading it right you are asking if it's okay to split the speaker signal unevenly (tweeters and mid on one side, tweeter mid and amp on the other)? Should be fine. What kills stuff is not having enough resistance/impedance, an amplifier input has very high impedance and will not cause any trouble. I've used this same kind of setup (minus the crossover) on my cars to add a subwoofer. Basically just wire in the amp parallel to one of the rear speakers (using speaker level input on the amp, use a line out converter if it doesn't have one but they almost all do nowadays)
 

Xarpolis

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What actually kills a speaker is clipping. Any time the sound a speaker tops or bottoms out making a |_| instead of a U with the signal, that flat spot does nothing but generates heat. As long as there is movement, there's no heat. Heat will eventually melt the voice coil (well, damage it), thus blowing a speaker. You can put an unlimited amount of power into ANY speaker and it'll work fine as long as you don't clip the signal.
 

Jovec

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If I'm reading it right you are asking if it's okay to split the speaker signal unevenly (tweeters and mid on one side, tweeter mid and amp on the other)? Should be fine.
Basically. I understand that there could be audio issues (differing volume levels between the left and right channels since one will have two speakers and the other one. And the sub crossover frequency isn't as low as I would like, so there will be the occasional stereo effect that gets missed since the sub will only be getting one-half of a stereo source. In theory there will be some load differences - crossovers keep the load close to 4 ohms but without the sub on one side in theory there can be very little load if only low frequencies are played. I could fix this somewhat by using the three way crossover only on one speaker ouput, and the two way on the other. That way the loads will be more balanced across the frequency spectrum.

I might try bridging the sub outputs from the crossover since the power levels in question aren't that high. As was mentioned, just 22w RMS. The general consensus I've read is that this isn't the best idea, but partly that is due to the lowered impedance from bridging (which I really won't have). All of the summing circuits I came across seem to be meant for the line level source, not the speaker outputs. I can always scrap the sub and just wire in the reae mids and be done.

brekk brekk - I'm probably being careless with my terms since the online reference refers to the 4 speakers as mids when perhaps woofer would be more correct. Anyway, in my initial testing (of what wires were what) I had the speakers wired directly to the head unit and the highs were lacking. Adding the crossver helped with that, but also probably put the bug into my head to get the sub working. My (limited) previous experience with aftermarket midrange speakers always had them with that built-in tweeter inside the woofer, which I do not think mine have.

This is the kind of project that usually starts cheap, and ends up costing more in than the end that just doing it right in the first place.
 

Jovec

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brekk brekk - I'm probably being careless with my terms since the online reference refers to the 4 speakers as mids when perhaps woofer would be more correct. Anyway, in my initial testing (of what wires were what) I had the speakers wired directly to the head unit and the highs were lacking. Adding the crossver helped with that, but also probably put the bug into my head to get the sub working. My (limited) previous experience with aftermarket midrange speakers always had them with that built-in tweeter inside the woofer, which I do not think mine have.

This is the kind of project that usually starts cheap, and ends up costing more in than the end that just doing it right in the first place.
Looks like I was wrong. I was trying to find the specs on the speakers and came across this parts page. No specs given, but from the drawings they appear to be full mid range speakers in all four doors. It still sounds better moving the highs to the tweeters in the A pillars instead of only having it down by my feet.
 

Lambourne

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Basically. I understand that there could be audio issues (differing volume levels between the left and right channels since one will have two speakers and the other one. And the sub crossover frequency isn't as low as I would like, so there will be the occasional stereo effect that gets missed since the sub will only be getting one-half of a stereo source. In theory there will be some load differences - crossovers keep the load close to 4 ohms but without the sub on one side in theory there can be very little load if only low frequencies are played. I could fix this somewhat by using the three way crossover only on one speaker ouput, and the two way on the other. That way the loads will be more balanced across the frequency spectrum.

I might try bridging the sub outputs from the crossover since the power levels in question aren't that high. As was mentioned, just 22w RMS. The general consensus I've read is that this isn't the best idea, but partly that is due to the lowered impedance from bridging (which I really won't have). All of the summing circuits I came across seem to be meant for the line level source, not the speaker outputs. I can always scrap the sub and just wire in the reae mids and be done.
It won't really affect volume levels because the added impedance from the amplifier input is very low, because you will be adding it in parellel. So you the load you are adding is very small compared to the speakers. You don't need the rear crossovers really, because they're still run off the head unit. Just wire the amp in parellel with one of the rear speakers and you'll be fine. Bass is present on both channels in music. Use the low pass filter on the amp to keep the sub from playing higher frequencies.

What actually kills a speaker is clipping. Any time the sound a speaker tops or bottoms out making a |_| instead of a U with the signal, that flat spot does nothing but generates heat. As long as there is movement, there's no heat. Heat will eventually melt the voice coil (well, damage it), thus blowing a speaker. You can put an unlimited amount of power into ANY speaker and it'll work fine as long as you don't clip the signal.
A common misconception on car audio forums. Heat is what kills speakers and output stages alike. The high power levels associated with an amplifier driven to its maximum (ie clipping) is why it can blow a speaker (or the amp, depending on the setup). It's absolutely possible to blow things with unclipped music or a sine wave signal if the speaker is overheated or hits excursion limits.
 

Xarpolis

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That's pretty much exactly what I said, but worded differently. I talked about both clipping music and excursion (topping and bottoming out). And yes, I'm well educated on the audio front. The other issue with unlimited power comes from the physical makeup of a speaker not being able to handle said power, where you literally tear it to pieces. It's much rarer, but possible.

In one of the old SPL contests of yester year, someone fabricated a giant 30" subwoofer and hooked it onto an engine. The engine would turn at 3600 RPM (60 per second), making a 60 Hz sound. It physically tore the speaker apart. Pretty interesting in theory, though.

Here's a good bit of audio information condensed into a quick video for those not in the know.
 

Xarpolis

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Combination of problems with that. First up, a sub really isn't meant to see frequency above 80 hz. The overall size of the speaker just can't realistically move that fast. 500-80 range is for the mid-bass. Where as tweeters go everywhere from 20k down to 500.

So yeah, that was moving WAY too fast, which is why the paper cone tore off. Then it ran into an issue where it no longer traveled within the magnetic confines of the voice coil. As soon as the center popped out, it was a straight short and fire happened. I've never tried it, but I wonder what would happen with a standard 5 1/2" mid-bass woofer doing the same treatment.
 

mkopec

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Man I remember those days. Having 1000W ripping SLAYER through my 91 saturn. I even took out my first bank loan ($5000) to help fund the system, lol.
 

brekk

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The frequency is fine, AC is at 60hz which is totally in the normal range for a Sub. Problem is the voltage.

Depending on the Ohm's on that sub it saw anywhere from [email protected] all the way up to [email protected] god forbid it was a dual coil running at 1 ohm, or .5 ohm.
 

Xarpolis

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good call. 60 cycles per second regardless of the voltage. My bad.
 

Jovec

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Yeah, so... The sub is blown anyway. The cone has separated from the rubber. I suppose I could try a repair (glue/kits) but the back seat has to be removed to remove the subwoofer, so I am just going to replace it. It's also a 14-ohm sub, so the head unit was going to have trouble anyway. I will be looking at replacement amps too, so I am not sure yet which way I will go, but I am thinking of going with:

  • Reuse current spare head unit (can be upgraded later if needed)
  • Buy replacement free air 10" sub with DVC
  • Buy a 4 channel amp with ability to use high-level/speaker inputs
  • 3 way crossover for the front amp output for highs (front A pillar tweeters), mids (front door), lows (rear sub)
  • Rear amp output to the read door speaks with a high pass filter (separate or from amp)
  • Reuse existing door speakers (can be upgraded later if needed)
This would mean that the only parts of the factory system not being used are the center dash speaker and front door speakers not getting highs. As mentioned previously, the later sounds better with highs at the pillar tweeters instead of the door speakers (if I had to choose one and I can't come up with a cheap/easy solution to use both). As to the center dash speaker, I could look to a two-way cross for the rears and bridge the highs to the center dash speaker. I am guessing that would sound better for the driver and we rarely have anyone in the back anyway. The DVC sub would keep the ohm load balanced between the left and right amp channels and that would be the only wiring I would run (speaker wire from trunk amp to rear-deck mounted sub).

I can also just ignore the read door speakers and bridge the rear amp channel to the sub. Or possibly power them from the head-unit directly.

I big issue for me is cabling (and/or my laziness to run cable). I need 9 lines running from the head unit to the back (8 for the 4 channels, 1 for remote turn on), which I should already have in place by reusing the factory cabling. But what I don't have are RCA cables. In theory I should be able to solder RCA jacks on to the copper wire already in place to take advantage of the low-level outs from the head unit, correct? If not, then I would just need an amp that accepted speaker outputs as inputs.

By keeping the power in check I should be fine with the existing power runs that are already in place. The old sub had two 12V inputs but the wiring is like 16 gauge. I think I should be able to tie them together for a little added safety prior to feeding them into the new amp but it is something I need to check.

I will also look at 4.1 channel amps too, but I will probably need to run new power lines for a 4.1. The in-place 12v lines running to the amp have 30amp fuses and 4.1 amps need more power. And the subwoofer is just an open-air rear deck mount, so the sub power needs to be kept in check anyway if it is not in an enclosure (IIRC). I can always replace the 4 door speakers if I need to in the future. And the head unit too.
 
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mkopec

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Dont forget about the ground wire from amps/power block/fuse block. That is the most important thing not to forget because if you do you will get drive-train whine. You want that wire connected to bare sheetmetal somewhere. Even more preferably the underbody rails.
 

brekk

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I would definitely move to a non-OEM sub if the stock is 14ohm, gonna be really hard to run that resistance on normal aftermarket audio equipment.