SwedeSpeed - Volvo Performance Forum banner
1 - 4 of 4 Posts

·
Registered
Joined
·
1,534 Posts
Discussion Starter · #1 ·
Looking at various images of stereo installs on this site I notice heavier gauge twisted pair wiring is
in use between the amp and speakers. My 2011 S60 uses twisted pair (as seen at the amp end).
In some cases the twist rates even vary by speaker (tweeter, etc.) (although that appears to be
after the crossover -- first photo).

Why would they do that? My understanding is twisted pair prevents unwanted external
electromagnetic interference (EMI) from getting in. All I can come up with is to prevent
the wire from becoming an unintended antenna for a spurious high frequency signal.
Over engineering? Just curious.

Example URLs:

http://i1101.photobucket.com/albums/g436/kilteddoc/IMG_1246.jpg

http://i161.photobucket.com/albums/t215/rushin_album/9aspeaker.jpg

http://216.119.100.190/_sharedpics/doorspeaker.jpg

http://216.119.100.190/_sharedpics/factoryamp.jpg

http://img65.imageshack.us/img65/835/dscn1551mediumjt1.jpg
 

·
Registered
Joined
·
1,283 Posts
Twisted sprk wires will reject (i.e. not respond) to RF. Parallel wires make a great RF antenna. Lots of RF in todays cars due to all the electronics.
 

·
Registered
Joined
·
2,704 Posts
Twisted pair wires are quite common in aftermarket stereo setups due to their ability to reject RF interference. Its good to see OEMs adopting them.
 

·
Registered
Joined
·
2,167 Posts
My 2011 S60 uses twisted pair, in some cases the twist rates even vary by speaker.

Why would they do that?

My understanding is twisted pair prevents unwanted external electromagnetic interference (EMI) from getting in. All I can come up with is to prevent the wire from becoming an unintended antenna for a spurious high frequency signal.

Over engineering? Just curious.
Great question!

You are correct in stating that twisted pair reduces the effect of external EMI. Unshielded twisted pair (UTP) like the wire used in our cars, is primarily used to minimize the effect of crosstalk, or electromagnetic coupling, between wires run in close proximity over long distances. The goal is to ensure both wires in the pair are an equal distance from the source of interference for about the same amount of time, so that interference is coupled equally into both wires. Different twist rates are commonly used to ensure that two UTP circuits can't align, which would defeat the purpose.

That said, receiving EMI (RF or otherwise) is irrelevant for heavy gauge speaker wire, which passes a high power (many watts) to a low impedance (a few ohms, say 8). No transmitter obtainable without a FCC license would have any chance of inducing more than a few microwatts in this sort of circuit, twisted or not.

So why would they twist the speaker wires? Because it works both ways: While twisted pair reduces the EMI induced into a circuit, it also reduces the EMI induced in other nearby circuits.

Modern car stereos use "Class D" amplifiers for their high efficiency and low cost. By design, these sort of amplifiers send a high frequency pulse-width-modulated square wave to the speaker. The speaker acts as a low pass filter, being an inductance (electrical lowpass) and a rather large inertia (mechanical lowpass), so we don't hear the RF signal. But there are many feet of wire between the amplifier and speaker carrying high power RF pulses, and the fast square wave is very rich in higher order harmonics.

Untwisted, this high power, HF rich signal could easily couple to nearby conductors in the harness. Since the CAN communication bus has clock frequencies in the same range as the Class D switching frequencies (125-250kbps), this could be a serious problem when a CAN run follows speaker wires. Over untwisted cable, the noise could also couple to V+ or ground, messing with computers and such even without a common wire run.

So no over engineering here :beer:

Jacob
 
1 - 4 of 4 Posts
Top