Audiophiles - Engine Noise in Speakers

Hampton

Hampton

Air Defense Dept
TECHNICAL Contributor
Nov 26, 2006
7,628
Panama City, Fl
Boat Info
2008 44 Sedan Bridge
Engines
Cummins QSC-500's
Straight Drives
I recently installed two JL Audio 7.7" tower speakers and enclosures. When running, the engines come through the speakers at high frequencies, moderate volume. When the genny is on, it comes through loud and clear.

So naturally, I put my ear to my other speakers, and to a lesser extent - same thing. The JL's just have such pure highs that the engine noise is loud and clear.

The line out from the head unit runs forward and downward to the 3 amps under the salon couch. So does the hot wire and ground. They are close through the one opening I have. Do I have to separate them out? Can I filter the noise? Should I try resistor plugs in the genny or is that 70's stuff? Can I insulate the wires?
 
I'd start with a potential grounding problem as well. Do you have the power and ground cable connected directly to the battery? How is it split to the 3 amps? Ideally you would have a direct connection to the battery for both power and ground and then distribution blocks to route power to the accessories. Is this a new problem or something you've had for awhile? Any changes to the system?

If you have the RCA cables routed with the power/ground cables then they can pick up noise as well. One way to see what is going on is to disconnect the RCA cables from the source and see if any engine noise is present. If it is then disconnect the RCA cables at the amps and see if the noise is still present. Hopefully the noise will go away with one or both methods and you have a couple of options. You can route the cables in a different manner to isolate them as much as possible or you can try a different RCA cable - even if it is a temp run directly from the source to the amps. Another troubleshooting method is to take a headphone/RCA cable and connect a MP3 player directly to the amps and see if you have a problem that way.
 
Another question might be,do you think it's ignition spark noise or alternator noise or fuel pump noise?
 
Excellent article - I will look for the potential problems listed.

I had intended to begin to trouble shoot, but you have added some great insight as to how to go about it.

Thanks.
 
Spookeay said:
Another question might be,do you think it's ignition spark noise or alternator noise or fuel pump noise?
Click to expand...

Not fuel pump - varies very tightly with RPM, so I'm thinking either spark or alt.
 
I would start out with getting a few ferrite chokes and wrap the individual power lines to your radio and amplifier around them.

pRS1C-2265709w345.jpg
 
LTD.330 said:
I would start out with getting a few ferrite chokes and wrap the individual power lines to your radio and amplifier around them.

pRS1C-2265709w345.jpg
Click to expand...

I'm going to have to look into this further.

Lots of analysis today. There are two sources of the noise. The first is most baffling. With either the genny or shore power providing AC power, when the "Oulets" switch is turned on, a med-frequency noise begins. It can only be heard with the volume way up and low music volume (music pauses, CD changes...) It does not matter what source the music is from. Is does not matter what is plugged in. It does not matter if I trip the GFCI's (one at a time, haven't tried both yet). There is nothing running off of outlets when I do this - no frig, AC converter, TV, DVD, nothing. This noise is there when Outlets is turned on. It gets louder with the volume control on the stereo. It doesn't matter if I disconnect the high power amps, 2/3 speaker controls (have to leave at least one on to hear it), aux input... If the stereo is on and turned up, and one set of speakers is on, this noise goes on and off with the AC outlets switch.

Engine noise: This one is NOT stereo volume dependent. If you turn the stereo down, it goes up and down with RPM of the engines (and genny). If you turn the stereo up, it gets drowned out. It doesn't matter which source the stereo is playing, which amps are on, which speakers are selected - nothing. If there is an engine running, the volume of this high pitched noise goes up and down with RPM only.

Solutions for now. I have checked every connection. I have wiggled every wire. I have moved wires around. The "outlets" one is easy. Turn off the outlets, or don't play quiet stuff with the volume way up with the outlets on. The engine one is fairly easy - turn the stereo up a little when an engine is running. My systems are soooo pure, I hear any imperfection.

What do you all think?
 
John, it sounds like you need some type of filter system (like what was used in car stereos at a time). I know you have a lot of high end audio on your boat, so you might want to try a car audio shop nearby and ask them what they suggest by way of filters. They're not that expensive at all. Also like one of the other members suggested, SEPARATE the power/hot to the amps away from the RCA wires as best you can. Good Luck to ya Buddy.:thumbsup:
 
Was the battery charger on or off while you were conducting your tests? If it was on, the charging circuit could introduce RFI/EMI (Radio Frequency Interference / Electro Magnetic Interference) noise directly into the 12V electrical system or just by proximity to your radio.

In essence, the unshielded power wires act like antennas picking up the RF noise in the area. Any electrical motor, like the belt driven alternator on the engine, will produce an RF signature.

The ferrite chokes reduce this noise by canceling out the magnetic field generated by the current flowing through the electrical wire. Simply clamping the choke around the wire will do the job, but wrapping a loop through the choke will enhance the performance.
 
For the "Outlets" problem, I turned off every piece of AC powered equipment in the boat that I could find, including the Batt Charger. Without any current flow, when the outlets switch is turned on, the noise comes through the speakers. It's almost as if there was a short between the AC outlets and some portion of the stereo - there was no movement on the AC meters when I turned the outlets on. Once again, this issue is with the volume way up and no music on. The engine noise is a bigger issue.

I'll look into the chokes.
 
Wrap the power lines around the chokes?
 
If you disconnect the shore power cord from the boat do you still have the hum?

Here is pseudo example of wrapping the wire around the choke. This particular example is used in high frequency electronics and shows multiple turns (you'll only need one), but the principle is the same.

f9-3.gif



Previously when I mentioned wrapping the individual wires, I was trying to say to split or pull apart the red and black wires and wrap each wire around a choke. Granted this is way overkill, but if you got problems, why knot?
 
LTD.330 said:
If you disconnect the shore power cord from the boat do you still have the hum?

Here is pseudo example of wrapping the wire around the choke. This particular example is used in high frequency electronics and shows multiple turns (you'll only need one), but the principle is the same.

f9-3.gif



Previously when I mentioned wrapping the individual wires, I was trying to say to split or pull apart the red and black wires and wrap each wire around a choke. Granted this is way overkill, but if you got problems, why knot?
Click to expand...

Thanks, makes sense. The wires shown are the power wires to the head unit? Disconnecting the amps had no effect.

Yes. Shore power had no effect whatsoever, on and off, with and without genny...

I tried every combo of every item. The engines noise is the worst - the other requires extremely high volume levels with no music coming out - very rare.
 
Yes, the wires that feed the head unit typically let the RFI into the system and protecting them goes a long way to reducing the unwanted noise.

The reference to the the power amp was that if you had a separate Power Supply feeding the amp, then that PS was susceptible to the same RFI noise as the the head unit.

To clarify earlier statements, in this application, the most important thing is to get at least one wrap around the ferrite choke verses splitting the individual power leads and choking them out.

ETA: When you said the shore power was off, was the shore power cable physically disconnected from the boat?
 
Last edited:
Disconnected from the shore power box, like the boat was gone from the dock. They were still connected at the boat, but just as dead ends.
 
John - have you tried unplugging the RCA inputs into the amps? Or running a temporary connection from an MP3 to the amps? This can help narrow the noise down to either cable routing (separate the power/signal cables), bad cables (replace RCAs) or noise being introduced at the source.
 
tdappleman said:
John - have you tried unplugging the RCA inputs into the amps? Or running a temporary connection from an MP3 to the amps? This can help narrow the noise down to either cable routing (separate the power/signal cables), bad cables (replace RCAs) or noise being introduced at the source.
Click to expand...

Yes. This didn't change the noise at all. I disconnected the RCA's at each of the amps, all of the amps, and at the back of the stereo (Aux) as well. No change. The one thing I didn't do is disconnect the speaker wires. The article above says long speaker wires can cause a problem, but there's nothing I can do about that except to wrap them in a ferrite dealy close to the amp.
 
Hampton said:
Yes. This didn't change the noise at all. I disconnected the RCA's at each of the amps, all of the amps, and at the back of the stereo (Aux) as well. No change. The one thing I didn't do is disconnect the speaker wires. The article above says long speaker wires can cause a problem, but there's nothing I can do about that except to wrap them in a ferrite dealy close to the amp.
Click to expand...


John:

Run power and ground for the amplifier in question directly to the battery...no other circuits. Unplug the rca cables from the amp also and listen for the noise. 9 times out of 10 the ground is the problem not rca cables or chokes etc.

Please let me know how she does with the power and ground running straight to the battery.

Kendall
 
You must log in or register to reply here.

Forum statistics

Threads
113,283
Messages
1,430,014
Members
61,151
Latest member
KMadden
Back
Top