I am working on a sound reinforcement system in a dance studio that has been pre-wired with heavy-duty, probably between 8 and 16 gauge SHIELDED speaker wire, the longest run being less than 100 feet. Someone else who looked at the old system said that the wire should be replaced because the shielding will ruin the impedance of the speakers and blow the amp. Is this possible? I don't see how a shield, that is not making actual contact with anything in line with the speaker (it is not acting as the ground or the negative or anything) could cause such a problem. Any thoughts?
It could affect the capacitance per length of the cable, but that could easily be measured and checked against what the amplifier can take. It could be a good idea to have the shielding there, since it may supress HF noise (from cell phones etc) that otherwise might introduce noise in the system.
Possibly.
Possibly.
The HF noise from speaker elements and wire causes problems in power amp. Depending on the specturum and level of the noise, it can cause unstability in the feedback loop and anyway it eats the amplification to be used to compensate amp's basic non linear function.
In the amps there is typically used small inductor at the output to make sure that amp never sees capacitive load on high fequencies. This same inductor of course filters most of the HF noise from speaker&wire to amp but not all.
In some speakers like Tannoy there is actually dedicated connector so that metal frames of the speaker elements can be grounded to AMP ground. The voice coil is very good HF receiver/antenna.
The inductor at the end of power amp is often neccessary but it has also side effect. It can be heard (most probably) and any way measured. In some high end amps the inductor is not used but this requires different HF compensation in amp so that amp does not oscillate because of capacitive load.
So if target it to go to extremely high, I would use shielded speaker wires and conect also speaker element frames to that same shield.
Couple of years ago I had very difficult oscillation problem in one of my amp proto. It oscillates continously at about 2MHz. Then I found that it oscillates a bit also when power is off!! The reason was DSL carrier in the in the phone line in my house. The level of the signal in amp was not very high but clear anyway. Before I realised the reason I also used several months with oscillating aftive filter problem before I gave up.
In the amps there is typically used small inductor at the output to make sure that amp never sees capacitive load on high fequencies. This same inductor of course filters most of the HF noise from speaker&wire to amp but not all.
In some speakers like Tannoy there is actually dedicated connector so that metal frames of the speaker elements can be grounded to AMP ground. The voice coil is very good HF receiver/antenna.
The inductor at the end of power amp is often neccessary but it has also side effect. It can be heard (most probably) and any way measured. In some high end amps the inductor is not used but this requires different HF compensation in amp so that amp does not oscillate because of capacitive load.
So if target it to go to extremely high, I would use shielded speaker wires and conect also speaker element frames to that same shield.
Couple of years ago I had very difficult oscillation problem in one of my amp proto. It oscillates continously at about 2MHz. Then I found that it oscillates a bit also when power is off!! The reason was DSL carrier in the in the phone line in my house. The level of the signal in amp was not very high but clear anyway. Before I realised the reason I also used several months with oscillating aftive filter problem before I gave up.
Of course this all depends on whether the noise you want to keep out is actually kept out by whatever is used for shielding. That is a whole science in itself, and just assuming that a simple shield keeps out all that's out there is pretty naive.
How many shielded speaker cables are there on the market?
Jan Didden
How many shielded speaker cables are there on the market?
Jan Didden
It is true that finding twin-axial speaker cable is difficult but basic coaxial can be found easily, like this one
http://www.thomann.de/gb/sommer_cable_magellan_240.htm
http://www.thomann.de/gb/sommer_cable_magellan_240.htm
I think the original post is primarily dealing with a commercial application and not a high end tweak. No commercial application will put out $4 or more a foot for a high tech speaker cable when their budget can hardly afford .50 a foot cable.
The idea behind shielding in commercial applications is to try to limit the noise because there is no getting rid of it 100%.
Not to say I haven't used high dollar cable in a studio application where only the best was used.
Getting back to the original post I do believe the person was talking about a 8- 12ga pair with a shield which would be a run of the mill wire for that installation.
I was not entirely pointing at multi $ cables in my link, just wanted to show an example
As for the original question;
I think the person who warned The Paulinator were worried about additional capacitance caused by the screen that would possibly bring the amp into oscillation and blow.
However, Pro amps are usually quite rugged when it comes to capacitive loading.
As for the original question;
I think the person who warned The Paulinator were worried about additional capacitance caused by the screen that would possibly bring the amp into oscillation and blow.
However, Pro amps are usually quite rugged when it comes to capacitive loading.
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