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Skin Effect - Page 2

post #16 of 26
topher,

I was thinking about ppl's idea (the link I provided was found by a friend at work and is unrelated to ppl) - but my question is what actually ppl's idea IS - to run two lengths of coax to speakers and use CENTER conductor in each run ONLY, leaving outer not connected to anything? I don't think that using single coax would be a good idea at all - coax is extremely non-symmetrical construction, not to mention one "conductor" surrounds the other, plus there is no shield in that case. So the idea is to use each coax as a single thick wire, with outer conductor as shield. Right?
post #17 of 26
Thread Starter 
Hey,

That kinda make sense. That will prevent RF pick up thru negative feedback.

Tophor, I think all waveguide has modes. It have got to. But then you are right that the freq range will with more broader. This makes Coax cable performance very very dependent on the dimension of the cables. Pick right ones and you get good cable. But pick wrong and you get very very poor sounding cable, right? I think you will get definite low corner freq drop.

Tomo
post #18 of 26
aos,
when I do it, I will use one coax to each driver.
That uses the single coax exactly as it should be.


If you twisted two coax a little and used the
center wires for speaker connections, you would
have twice the lumped capacitance, and a LOT more
lumped inductance. But I doubt it would be a
problem unless you amp is _very_ sensitive to
loads. But I don't see an advantage myself. If
you try it I would connect the "shields" to the
amp ground but to no part of the speaker.

Tomo,
A coax is not a waveguide. It doesn't have modes.
When you "design" one, the only reason you pay
attention to dimensions is to get the
characteristic impedance you want (50ohm, 75 ohm)
but the characteristic impedance is not a function
of frequency.

Morphsci,
I hope you try ppl's 13ga coax. I would guess
your single coax experience was driven by the fact
that you were driving your speaker with the tiny
center conductor of the single coax versus using
the outer braid for both conductors in the dual
coax case.

With the 13ga coax, you should have the best of
all worlds, but who knows? At least you have
trained your ears to the point you can tell the
difference. I would really like to find out your
review of the big stuff.
post #19 of 26
I don't see why the capacitance would be large. In fact it should be much smaller since conductors are rather far away (each in its own coax). I don't plan on twisting coaxes at all. Apart from being next to impossible even with thinner versions (let alone with large gauge), I don't think there's much need for it since there's already a shield.

As for inductance, most speaker cables are two long pieces of wire anyway. However, I have not seen solid large gauge wire being used, it's mostly many thin ones making up the gauge.

Every cable I've seen for speakers is symmetrical. Coax is decidedly not, if you use both conductors.

At any rate, we should try this, both ways. Hopefully I'll find where to buy them.
post #20 of 26
aos,
You are thinking of the capacitance of center
conductor to center conductor. If the "sleeves"
are grounded that is _vastly_ reduced, but not
reduced much if the sleeves are not grounded.

The _amp_ sees twice as much capacitance _to_
_ground_, if you use two lengths and ground the
"sleeves".

While the coax lengths don't need to be twisted,
it is probably the easiest way to keep them
together, even if only a couple of turns.

You want to do that for the same reason speaker
cables are twin wires of some sort. Inductance.

The inductance of most speakers is larger than
this effect, but if they are not the normal cones
or have zobels to look resistive, the one loop
inductor formed by the separated coax lengths can
get large enough due to the loop area to be the
largest inductance the system has.

I understand why a symmetrical cable "feels"
better. But think about it. The AC current
in coax always does the same thing. There is
exactly as much current in the center conductor
as is going the opposite direction in the outer
conductor. In a ham setup sending kilowatts to
the antenna or an EKG sending picowatts at 4Hz.
post #21 of 26
>The _amp_ sees twice as much capacitance _to_
>_ground_, if you use two lengths and ground the
>"sleeves".

That's true...

But, couldn't one put a resistor between shield and amp ground, therefore reducing the effect of this to-ground capacitance?

Also, I don't think that even non-grounded shield version would have large capacitance. I can't remember formula for capacitance of two wires (yeah, I know, it's taught during first year) but provided they're sufficiently apart, capacitance should really not be large. Whichever way you lay the wires, thanks to the think isolation they'll always be quite a ways apart.

>There is
>exactly as much current in the center conductor
>as is going the opposite direction

I just don't like the fact that one conductor surrounds the other. The effects of the field generated by current flowing in one direction in center, to the outer shield, will be different than the effects of the current through the shield, to the center conductor. The current going out will be the same as the one going in but the equivalent circuit (cross-inductances and capacitances etc.) will be different. This will make a difference as to what signal is delivered to the speaker terminals.

Even if not, think of it this way - there is a big difference in the surface area of those two conductors, thus the skin effect would be different to both... Is this beneficial, or detrimental? Well, I don't know...
post #22 of 26
Hi: Glad you liked my Coax Sugestion. I did this to Keep RF out of my Amps feedback Loop since this is where most of that kind of stuff enters an Amp at. I used it in the Standard configuation Center Conductor to Hot. Shield to Ground at Both Ends. The Part NO of the Cable Is Alpha wire #9008-X The RG Type is RG8U the Specs are Center Conductor=13 Ga. stranded (7/21). Cap. Per Foot=29.5 Pf. Jacket Dia= 0.405". Center Insulator Dia=0.285"

This Cable seemes to make most amps show an improvement in speed and seem to take some of the sharpness out of some solid State Amps. My cable for Comparrison is the Kimber 8TC run in all practical Combonations. I havent tried alot of the Other High End Audio Speaker cables and i heared that some one is making an Audio Grade Coax Speaker cable. Can't think of The name at the moment. However the RG8U stuff is low Cost sounds Great on Most SolidState amps and Keeps the Radio & TV signals out of my amp. There maight be better cable to use as i sed Only use a limited number of Cables Butyou all can try it and report back to us. It works good for me and i think most of you will also like this cable. The Key point with this and any other Speaker cable is Proper Instlation of the Termanations Details like scraping the oxide off the Outside of the Copper wire Evean on new cable. The use of Crimp on Spade Lugs (I am NOT Fond of Banna Plugs) Then silver soldering to isolate the Cleen conection from futher oxidation. Hope this Help's
post #23 of 26
Pbbb You all suck with your "Coax" and other puny wires... I, a TRUE audiophile demand nothing less than high quality 100% silver WAVEGUIDES for connecting my equipment together. True they're a tad inconvenient... mine are vacuum sealed to get maximum propogation velocity, and to have proper frequency response down to 15 Hz are somewhat large (6,209.41 miles wide), but the sound is all that matters. Bother me no more with your so called "interconnects", for they are mere styrofoam cups with a string tied between them in comparasion.
post #24 of 26
LOL: I know us headwizers may not be true Audiophiles but since we like Headphones the Cup with a string attached is what we Like. But We use the New versions with Electroacoustic Transdducers and replace the String with a Electrical Wire. This is doubeled up since stereo is Nice to have. But glad the wave Guides work for ya. Us Mear mortals have to do with the Materials Available to Mortals since we havent obtained God statis as of Yet.
post #25 of 26
I remember seeing a speaker cable using high quality Satellite coax and making a set myself to try. There are two separate cables to each speaker and the center solid wire is soldered to the shield as the instructions stated.
This speaker cable sounded horrible compared to simple lampcord twisted. It seemed to suck the highs right out of the signal.
I'll try to find the link for it. I want to try Cat 5 cable next but actually am interested in solid single flat wire but it costs so much.
I have a bunch of AR RCA plugs which attach to this type of coax cable without soldering and plan to make some video cables with it. After this experience I do not like coax used for speaker cables though.
Dan
post #26 of 26
Dan: I think the method you discribed is talked about in a above post where as the speaker cable is made by connecting two coaxes using the center conductor. This may indeed reduce the High's due to Capacitence. I However am not into Cables alot. I most often just use Kimber in what ever form is required for the Applification. Kimber sounds good to me so any wire i use is compaired to Kimber. I have tried the Ribbin Cable from straightwire and it sounded Thin and Bright. My Coax sugestion is just that a sugestion It is low cost like 0.12 per Ft. and hay if it sounds worse than what your using it is a simple matter to just go back.
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