# High-pitched noise from tweeters... Another case



## Ryebread (Apr 25, 2009)

http://www.diymobileaudio.com/forum/diy-mobile-audio/49030-high-pitch-noise-tweeters-need-help.html - Already read this post a bit, my problem seems a bit different.

I have a JL 300/2 and a JL 500/1. They are hooked up using a Kicker 1/0 Gauge wire set. Ground is under the backseat bracket, made sure to grind the paint of to shiny bare metal. Been running a set of subs with 0 issues, recently installed a set of Focal K2Ps with a JL 300/2.

Power is ran to the right side of car, everything else (RCAs, speaker wire, remote wire) is ran on the left side of the car. No devices are plugged into the cigarette outlets or anything. H/U is an Eclipse 8433.

Symptom - Tweeter makes a high pitched whine. No pulsations, just a constant whine.

Troubleshooting process so far:

Turned on car, turned the radio up a bit. 5 seconds later, turned the radio to 0. High pitched whine comes out of both left/right tweeters. 20 seconds later, the whine fades away to silence. I turn the radio back up and down again, and this cycle will repeat itself over and over.

I tried revving the engine, it does not effect the whine. I then turned off the car so the stereo runs strictly off the battery - same symptom as described above.

Doesn't sound like a ground loop, my guess is the 300/2 is bad - anyone who is more experienced have any input as to what the problem could be? Please, be as specific as you want.

Thanks,

Ryan


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## VP Electricity (Apr 11, 2009)

Not consistent with a ground loop. 

Sounds like the passives are picking up noise, OR a bad amp. 

Test with some speaker wire and get the passives out of the car and try again. Or if you have another tweeter and xover around, hook that up to the 300/2 and see if it makes the same noise...



If it seems to be the amp, test with an iPod and a headphone to RCA adapter.


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## Ryebread (Apr 25, 2009)

Update -

Took advice, moved the passives somewhere else to see what would happen. Same problem.

Hooked up one of the tweeters directly to the amp to rule out passive - after about 2 seconds of testing at low volumes, I realized "this is not such a great idea" as the JL 300/2's HPF only goes up to 500hz. Not very good for tweeters.

Hooked it back up to the passive, did test at low volumes - noticed that it never made the whining noise. I then remembered that my 500/1's "signal sensing" mode was on (turns on when the RCA's are on, rather than remote wire) as I didn't have a relay laying around. At low volumes, the subs never turned on, and I never received the whine. However, when I crank it, the amp turns on, and instantly I hear the whine. It lasts 20 seconds because it takes about that long for the JL 500/1 to finally turn off during signal sensing mode.

My amps are mounted very close together - about an inch or two between them. Is there an x amount of inches that these amps need to be away from each other? FYI, both amps are running off the same power/ground source, using 2 Kicker distribution blocks. Amps are receiving 2 seperate RCA's - I am not using the RCA output feature.

Thanks


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## VP Electricity (Apr 11, 2009)

So if you switch to RTO mode and jump from 12V_+ to the RTO terminal, the tweets whine the whole time?

I would test it that way. Sounds like superheterodyne noise from the two power supplies interfering with each other. Would not consider that normal for JL. Slash amps should work together no matter how close they are. 

Try hardwiring your RTO as a temporary test and see if it changes things.


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## Oliver (Jun 25, 2007)

I like the idea of running a second remote turn on wire [ perhaps a relay wired from HU which turns on both amps simultaneously [ each with a seperate remote wire coming from the relay ]

Turn one amp 180 degrees so the internal electronics are in a different relationship to each other


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## Ryebread (Apr 25, 2009)

Quick update -

I remembered that I did have the passenger side door woofer wired next to the power wire coming from battery - thought for sure that was the problem. I unhooked that woofer from the passive, and tucked it away somewhere, so that woofer/wire is now eliminated from the system.

I also sat both of my passives on top of some plastic, even though there were some rubber underneath them, to make sure it wasn't grounding itself to the chassis.

Currently, the only time power/ground wires run across signal is at the amplifier end (on the jl 300/2). Don't think that's a problem, as when I run the 300/2 by itself, I experience no noise. My amps are mounted on the backseat (with MDF wood between them), so I put one backseat up and one backseat down - so they were pretty far away from each other. I then was able to use the signal sensing on/off switch to toggle the amp on and off. When it turns on, I instantly hear the whine. When I turn off, about 15-20 seconds later, the whine fades away.

The JL 500/2 isn't hooked up to any woofers right now. Currently, it has RCA, Ground, and Power hooked up to it. Again, speaker wire/RCA/remote wire are all bundled on one side, and power/ground is on the other side. Using high quality Kicker hyperflex wire for power/ground/remote wire, and KnuKonceptz Karma 12/16 gauge wire for speaker wire/RCA.

Would it make a difference if I had 2 remote wires at this point? I'm willing to try it (the signal sensing option was just a temporary thing until I get a relay), but I'm just thinking logically how that would help anything.


Edit - Just thinking of possible causes here. I'm not an expert when it comes to power/ground and how loops occur, etc., so I'm going to throw this out there to see if this WAS the case, would it be a problem. So...

Backseat has sheet metal on the back. Amp is mounted to the sheet metal with wood in between it. However, maybe one of the screws that went through the MDF to sheet metal is touching the amplifier, so the amp is being grounded accidentally.

The main ground wire is hooked up to the bracket that holds the seat to the chassis. That ground wire is going to the amplifier. So, the amp is grounded to the seat twice.

Would this cause an issue? I put electric tape over all the screws that I put into the MDF to be safe, but who knows, maybe one piece fell off somehow, I dunno.

And there IS a ground loop occuring - it is so faint I can barely hear it, but when I have the music on mute (and the JL 500/1 is off, so no whining is occuring), I hear very tiny pops that get faster when I rev the engine. When I turn the engine off, the pops stop. With the engine off and the radio on, music is fine, but once i turn on that jl 500/1, I still get that whine. Is it safe to say that ground loop is independent of the whine?


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## Oliver (Jun 25, 2007)

This is common one amp is causing issues when the other amp is powered.

You don't need any rcas connected to the 500/1, just power . . . the issue is b'tween the 2 amps electronics.

Put a guitar next to an amp or microphone . . . what happens ?

FEEDBACK


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## Ryebread (Apr 25, 2009)

I understand that - but I know I'm not the first guy to have two amplifiers in one car  There has to be a reason, a fixable reason, why there is interference. Again, these amps are a good 1-2 feet apart when I put one of the seats up, and there is no change in the whining noise.

I appreciate all of the help and advice I've been given so far. Hopefully we can figure this out...

Good news is, with just the 300/2 on, my K2P's sound great!

Edit - by the way, I acknowledge that the RCA doesn't need to be plugged into that amp, just the remote wire. I'll get a relay tomorrow and single out the RCA.


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## bobduch (Jul 22, 2005)

You said ground is under the backseat bracket. Is it using a seat bolt?
This is going to sound strange. It is. I had noise problems a few years ago. 
I was using a zinc plated screw for ground because they had higher strength ratings so I figured a could crank on it to get the ground tight. Very tight. I tried all kids of things to get rid of the noise. No luck. A friend comes over and looks at the ground and sees the zinc plated screw. Says to replace the screw. I think he is nuts but I do it. Noise gone. I mean all of it. Gone. Makes no sense. I go on ECA and ask how this could be. I mean all this screw does is squeeze the grounds to the car body. Get a reply from Werewolf (many here know of him) and he explains why it does matter, a lot. It was a rather technical explanation and I will admit I did not understand all of it but in short he said "your not crazy, yes the zinc plated screw was the problem".
My Honda seats are bolted in with zinc plated bolts. That's why I asked if your grounds were using the back seat bolts (if the back seat uses bolts). If so, try a separate ground with a non-zinc plated screw.


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## Ryebread (Apr 25, 2009)

Bob - thanks for your input. I'm going to single out the RCA as the problem tomorrow and that doesn't solve it, I'm looking for another ground location. Thanks so much for your input.


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## Ryebread (Apr 25, 2009)

I switched the RCA's behind the HU, and then switched the RCA's on the amps. Problem still persists.

I am now, just in case, going to eliminate the RCA going into the 500/1, and see if the problem persists. I then will switch the RCA going into the 300/2 (still leaving the RCA out of the 500/1) and see if it persists. This will rule out any RCA issues.

Then I'll re-ground and see what happens. I'm concerned about the possibility of the 500/1 being grounded twice (one from the ground wire, one from a screw on the amp possibly going too far into the rack and touching the backseat metal), so switching the ground may not fix my issue. I just need time at this point (11 hour work days until the weekend)...

I'm going to try to eliminate the RCA's completely tonight though. Thanks for the help everyone.


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## Ryebread (Apr 25, 2009)

Interesting development - my order of operations:

NOTE: I found that the "auto-sensing" switch (which turns on when it gets a signal through RCA) can also be used as a on/off switch, but it turns off after 10 seconds of not getting a signal. So, I used this to my advantage when testing my amplifiers.

1) Unplugged RCA A from JL 500/1 and from behind HU (it is now eliminated from the system). Plugged RCA B into 300/2 and HU. Music starts playing - turn on 500/1 (using the "auto sensing" switch) - noise occurs.

2) Switched RCA B with RCA A (RCA B is now eliminated from the system) - Music is playing - turned on 500/1 with switch - noise occurs

3) Unplugged RCA from both amps - turned on HU, no music is playing of course. Turned on 500/1 using switch - NO noise.

The noise should come through without a signal from the HU if the amps are turned on and interfering - right? I guess this tells me that they're not interfering and something else is going on.

I can say that the right channel RCA on my JL 300/2 is significantly loose - don't know if that would make a difference.


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## Ryebread (Apr 25, 2009)

Update - tried using a remote wire to turn on amp instead of signal sensing - still get the whine.

Eliminated RCA's completely (behind HU and at the amps), used an iPod with a headphone -> RCA adapter. Same problem - no noise when 500/1 is off, noise when 500/1 is on. Noise stops when RCA's are unplugged from 300/2.

Not much left to do other than remove amp from amp rack (in case it's been accidentally grounded with a screw) and find a new ground location. Anyone else have any other ideas? I'm at a loss here...


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## VP Electricity (Apr 11, 2009)

Sounds like you have pretty much determined that the amplifier is causing the noise. (One of them). 

If you pull the fuse for the bass amp and just use the front amp, there is no noise? Smply having the sub amp ON causes the noise, correct?


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## Ryebread (Apr 25, 2009)

Today, the only connections going into the 300/2 were ground, power, remote, and RCA. The 500 had power, ground. Nothing else. Switching it on, I heard noise. Switching it off, the noise fades away.


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## VP Electricity (Apr 11, 2009)

Bad amp... Bad, naughty, wicked amp... And it must be punished!


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## Ryebread (Apr 25, 2009)

I have an engineer I knew from college looking into the problem, he has a bunch of ideas. We may be looking at this weekend. I'll keep this thread posted with any developments - a bad ground doesn't sound like the problem as of right now.


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## VP Electricity (Apr 11, 2009)

Hasn't sounded like it for some time. 
Working on this with an EE should be long and painful and eventually find that you have a bad amp


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## Ryebread (Apr 25, 2009)

Haha, if I end up having a "bad amp" I'll just deal with the low pitched squeal I only hear when the system is muted 

He's a good guy and he wants to try re-routing the power. We'll see what happens...


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## VP Electricity (Apr 11, 2009)

If rerouting power fixes it, I will PayPal you $5.


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## Ryebread (Apr 25, 2009)

Yeah... I know. I want to entertain his ideas out of respect and humbleness. I'm willing to try anything, as long as there is a chance of fixing the problem and not getting one of those "cleansweep" type deals that filter out the sound.


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## bobduch (Jul 22, 2005)

Can you get ahold of another amp that you know works and try that in place of the "problem" amp?


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## mda185 (Dec 14, 2006)

Back in the mid 90's, a fellow named Jason Cuadra posted the following on his website and it sounds like it may apply to your problem. His web site is under construction right now or I would have just given you the link. Here is his write-up in full:

ALTERNATOR WHINE TROUBLESHOOTING
By: Jason Cuadra 
Here's an interesting case study on alternator whine. I don't have much experience in car audio, but my perspective is that of a practicing electronics engineer with an interest in it.

A friend of mine spent some money and an entire day having a car sound tech troubleshoot annoying whine in her car stereo, to no avail. Being a switching power supply designer who deals with electrical noise everyday, I confidently bragged I could solve her noise problem in 2 hours, including breaks for pizza and beer. Well, it took me 3 - so much for my braggadocio.
Symptom: whine volume doesn't change with music volume, but increases with load on alternator. Probably very common, so it would be educational for me.

Setup: amps and active xo in the trunk.

Procedure: I bypassed the xo, and I tried using a 12V motorcycle battery to power the head unit and amp in the trunk, to no effect. This is to check for conducted noise ("ground loop" is technically a misnomer) in the ground wiring of the components. Note, there are 3 ways of noise getting in a system - conducted, capacitive, and inductive.

Most curiously, while fiddling with the shielded cable connecting the head unit and the amp, noise appears only if both left and right channels are connected. If only one channel is connected, neither channel has noise. 
If I plug in one channel (so of course only that channel is playing music), then connect just the ground of the other channel's jack, noise now appears in the channel playing music.

If again I plug in one channel, then connect just the "hot" lead of the other channel's jack (so now both channels play music), the 2nd channel has noise big time and the other not.

Then it dawned on me that the noise was coupling into the cables magnetically, which I first dismissed because magnetic coupling drops at 6dB/oct as you go down in frequency, and alternator charging pulses are in the kHz range, not the 100 kHz range where you'd typically start seeing magnetic noise coming in. Then again, in a car, noise at 4kHz, 50 dB down from full power, would be very audible when the music is playing softly.

An alternators output current is not smooth DC but a rectifed 3 phase current waveform - a DC current with a ripple riding on it. This current flows in a loop, and if this loop forms a large area, it will radiate magnetic (flux) noise.

The concept is of loop area. Any circuit's current flows in a loop. Any current flowing in a loop radiates a magnetic field proportional to the physical area of the loop. A 2nd circuit nearby (the receiver) will pick up that noise, in proportion to its loop area and the derivative of current (time rate of change) of the 1st current, and inversely proportional to distance. The equivalent circuit is a noise voltage in series, in the 2nd loop. The loops are actually one-turn transformer windings.

When I checked the amp's input cct with my ohmmeter, I found out the following: The RCA jacks' ground was isolated from the amp's power ground. The 2 channels' RCA jacks, however, were connected to each other. I suspect this is typical of most amps.

Now the signal current from the on channel of the head unit flows down the "hot" lead of the shielded wire, into the amp's input stage, and back down the shield of the cable (this is the "return current"). Remember current flows in loops. What makes shielded cable work against magnetic noise is that the shield and the center conductor are concentric and so it has effectively no loop area in any particular plane. This is why a twisted wire pair works against magnetic noise too. So, with only one channel connected, there was no noise. Now, the shielded cable is a pair of cables, running side by side, because the cable is actually a stereo cable, which looks like zip cord, except that each side is a shielded cable.

When I connected only one channel, but connected the ground of the other channel the return current split between the 2 shields, and thus created a significant loop area. Voila, noise. When I connected just the "hot" of the other channel, its return current flowed down the other shield so it developed noise, but the fully connected channel did not.

If both channels are fully connected, each channel's return current split between the 2 channels, creating loop area, and so picked up magnetic noise. I thought then, to prevent the return current from flowing in the other shield, the input jacks' grounds should have been separated by the amp designer. But of course the solution was to replace the amp.

I realized then that if I used a single shielded cable, with 2 "hot" conductors, to carry both channels, then the loop area of both channels would be small. Voila, no more noise, even with the active xover reconnected.

======================================================================================
Comment by mda185: 2 "hot" conductors inside a shield is the configuration commonly used in two places I know of. Pro sound balanced signal cables are constructed like this and low voltage sensor cables in aircraft and aerospace test cells are constructed like this. In a balanced audio cable, the 2 inside conductors are signal + and signal - with neither one being tied to ground. There is no reason that the 2 inner conductors could not be used as left and right. I have several hundred feet of teflon coated MIL spec signal wire that I used to use in test cell applications for the military. If you want to try making a cable like this, PM me and I will help you out.
=======================================================================================

Couple of points. The system design is bad. The car is an electrically noisy environment. Her head unit's output was about 0.2V. Her amp's inputs were neither "fully differential" nor "balanced". The former is evidenced by the non-isolated "grounds" on the input RCA pair of jacks. The above circuitry, which any decent engineer would put in, would cost less than a dollar in mass production. It seems they are only available in the more expensive amps. The penny pinchers and creative marketers are at it again. Incidentally only the devices (whether xover or amp) to which the long cables are connected need "full differential" inputs. 

BTW The offending cable was sold to her by a salesman at a comparatavely hi price, whereas the cable I had at home which I gave her, I'd bought for 30 cents a foot, and the jacks were 50 cents each.

I wonder how many people replaced an amp when changing the cable would work. 

Hope this is educational,
Jason

-- A dude named Lincoln replied:
For $20 you could have made a "sniffer" outta of a cassette recorder and headphones and found the entry point of the noise in the system and then you would have decided to replace (or re-route) the cables within 15 or 20 minutes instead of wasting 3 hours!!! 

To make your own sniffer: Any cassette player with a record function (play/record head) and any headphones. Extend the tape head wires to be a couple of feet long. Start car, press record, put headphones on, adjust volume so you can hear, hold tape head near all connections, equipment, and wire routes...find the loudest places and decide what to do based on your findings. 

That's an excellent tip, using a sniffer. However, I think it should be in "play" mode and not "record". For my own education I'll probably go back to my friend's car and use one and find out where the car is radiating the noise. My guess is it's either in the engine bay or the wiring to the taillights which may happen to be running where the audio cables are running.

--I replied again:
One point I was making was that the cable I described (one shield, two hot wires inside, one for each channel) is superior to two shielded cables (one per channel) when the power amp's (or xover) (in the trunk) RCA jacks' ground terminals are connected to each other, which I suspect is typical of many power amps and processors. The physics of it can't be denied.

Cheers,
Jason


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## mda185 (Dec 14, 2006)

I just re-read your post and Jason's write-up. The key things to determine are these:

Are the shields of your RCA jacks on the 300/2 and the 500/1 all at the same potential? That is engineering speak for "Is the resistance between the shields on the left, right, and subwoofer input RCA jacks zero or something close to zero?"

Is the subwoofer amp being driven by a shielded cable from the head unit or is driven from an output from the 300/2 that low passed? (I don't know if 300/2 has a low pass output.) If the sub amp is being driven by a long cable from the head unit, you may have the same problem described in Jason's article. 

Is the input to the sub amp a stereo input that is only summed to mono at the 500/1 amp? This also could fit the scenario described.

Are the RCA cables from the head unit to the amps twisted shielded pair construction or single center conductor with a shield?


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## Ryebread (Apr 25, 2009)

Thanks for all of that wonderful information!

Like I said in a previous post, the RCA's from my HU going to the amps are completely out of the picture - I am using a single RCA cable (headphone to RCA) coming from my iPod to my 300/2, and the issue still occurs. The 500/1 gave me noise with and without RCA plugged into it. If I can remember correctly, the noise occured as long as at least one of the channels were touching the 300/2 - and I'm pretty sure just the outer-metal (ground) of the RCA needed to be touching, it didn't have to be plugged into the 300/2 for the noise to occur.

My friend has a Rockford mono-block that he just took out of his car, confirmed working with no issues. He's going to let me borrow it and hook up temporarily to see if I still experience the same issue with a different amp.

Edit - here's the cables that I'm using: http://www.knukonceptz.com/productDetail.cfm?prodID=KRY2.6M


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## Jcmamma (Apr 5, 2017)

Was the problem ever figured out?


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