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-   -   Long cables: speaker or line-level? (http://www.diyaudio.com/forums/solid-state/4630-long-cables-speaker-line-level.html)

schizeckinosy 17th July 2002 03:40 PM

Long cables: speaker or line-level?
 
Hi all,

I'm working on a set of 2-way active speakers. I was planning on building a separate amplifier/crossover chassis, and running 2 pars of speaker cables to each speaker, rather than power each speaker and run 1 signal cable. I always thought that long speaker cable runs were preferable to long signal runs because they were more resistant to noise and attenuation (being at a higher voltage). Plus I'll only need one power supply, and I don't have to plug my speakers in.

Now I am seeing opinions that are contrary to my thinking.

Considering that the eventual place for these speakers will be as surrounds in an HT setup, and that the cable runs will be around 40 feet, which would be the way to go? I have the parts to make a power supply for each speaker, which would be ridiculously over-spec'd for only one channel, but I'd like to save those for my next pair if I could.

Thanks, Dan

Hoffmeyer 17th July 2002 03:59 PM

Hi Dan.
In general you can ad the cable-impedance to the amplifiers output-impedance, and thereby get the system output impedance, wich you're using to calculate the damping-factor.
A 40 feet cable typically has a lot higher impedance than a typical amplifier output-impedance, and therefor ruins the dampingfactor.

In your case, though, driving a pair of rear surround-sound speakers, it is IMHO way overkill to make two separate amps. I'd recomend the long speakercables.

Bill Fitzpatrick 17th July 2002 04:13 PM

This question has the potential to start another flame war and before you know it there will be many replies, none of which will go very far in answering your question.

I'd make the 40' run with #12 speaker wire.

schizeckinosy 17th July 2002 05:20 PM

Thanks for the replys.

FYI, these are going to be basically active "Dayton III's". My 16yo DIY main speakers have shredded their woofer surrounds, and rather than repair them, I'm going to make this new pair. They will be my main speakers until I can build the eventual main speakers, which will be active hybrid electrostatics.

Cheers, Dan

dc 17th July 2002 05:34 PM

Dan,

I'm in the same boat - thanks for posting your question.

I'm building a pair of H-frame open baffle woofers (2x Peerless 830500 for each of the rear channels) matched with a Manger transducer on top, and crossed at either 100Hz or 150Hz. I'd like to put the XO and both amps in the back of the room, running line level interconnects from the preamp about 25-30'. I want to do this primarily to keep the XO box and two amps out of my already over-flowing equipment rack, but would this be a bad idea? I've seen several others here (Hpotter, for one) placing amps as close to the speakers as possible. Does this somehow change with longer IC's?

BTW, without trying to start an exotic cable flame-a-thon (like the ongoing power cable debate on another thread) I'm thinking of riding the fence a bit by using moderately-priced, but still somewhat respectable cables until I have time to experiment further by building J. Risch's Belden 89259/89248 IC's and using T14 speaker cable. Any comments on problems with either of these cables in the proposed setup above?

thanks.

brad

MRehorst 17th July 2002 05:45 PM

Quote:

Originally posted by dc
Dan,

snip!
but still somewhat respectable cables until I have time to experiment further by building J. Risch's Belden 89259/89248 IC's and using T14 speaker cable. Any comments on problems with either of these cables in the proposed setup above?

brad

Only one comment. IC is an abbreviation for integrated circuit.
:D

If you must run long interconnect cables, use balanced lines. But you probably don't have balanced I/O on your preamp/power amp... Long interconnect cables are subject to noise pick-up which then gets amplified along with the audio being applied to the speakers.

Go with long speaker cables. Since there is no gain between the speaker and the amplifier, it is the best place for a long cable run.
If you're really worried about the cables affecting the sound, make some speaker cables out of twisted pair ribbon cable. besides the low inductance, they lay flat under carpet.

MR

dc 17th July 2002 05:56 PM

Thanks for the reply. I've definitely seen IC used for Integrated Circuit, but I've also seen it used for interconnect... or was that I-C? I'll try the twisted pair of ribbon cable you suggested, even though I don't have any carpet.

sam9 17th July 2002 06:25 PM

sam9
 
It seems to me the most direct solution to noise in long runs of interconnects is balanced cables and XLR connectors. However, there is, it seems, only one right way to do this but mant wrong ways. Suggest taking a look at an article on this subject at www.rane.com. I think the topic is gounding.

gromanswe 17th July 2002 07:53 PM

Use Balanced Sending & Receiving ICs
 
If you do not have balanced output/input devices,
you can use these high quality ICs
dedicated for this purpose.
SSM2142, converts unbalanced to balanced, drives the line, XLR
SSM2141, converts balanced to unbalanced, receives the line, XLR
Have very low Total Harmonic Distortion, THD
You can find datasheets, schematics on Web

nania 17th July 2002 11:44 PM

I'm glad I came across this topic. I had a friend who wanted to change the connector on her Kenwood turntable from RCA (plus separate ground fork) to XLR. I wasn't able to help her but I told her that if I ever found out how to do it I would let her know. She just used an XLR to RCA adapter but she would have liked to put the connector on the raw wires. Assuming this was possible, how would you pin it out?

RCA pin->
RCA gnd->
wire gnd->

Any help would be appreciated


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