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Old 24th February 2014, 07:27 PM   #11
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I am not worried too much about spl. 80db should be loud enough.

I am hoping to cross over at 60-80 hz if possible. Is that too low for this setup? How far from the listining position do I have to be to cross them that low? I was hoping aprox 10-15'.

If there is a better 7.2 receiver out there in the 6-800$ range I am open to other options. I am just going off of reviews on the aventage.

I am not going to be using single strand cat5 I'll use as many strands as needed.

Two Rythmik subs is all I can swing now. I think they will be enough. If I need more I guess I can add them later. I am planning on running extra wire locations for the subs so placement in the finished room will be easy. At least cat 5 is cheap. Also it dosen't have to be thick for signal wire.
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Old 24th February 2014, 08:18 PM   #12
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Cat 5 is a very small gauge.
It will alter the speaker Q and effect the base response.
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Old 24th February 2014, 08:39 PM   #13
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If the series R is sufficient anyway -depends on loop length.

Not necessarily an issue providing you account for it, & also somewhat dependent on amplifier output impedance since the higher this is, the less impact the wire R has. For the sake of interest, there was a brief fad back around the turn of the century for using single strands of 30ga magnet wire in HE systems (95dB or higher).
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Old 24th February 2014, 10:12 PM   #14
laplace is offline laplace  Australia
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CAT5 has significant capacitance between the conductors, which can be bad for amp stability if you have long cable runs. If you insist on using CAT5, then it would be better to use two CAT5 runs, each acting as a single core.

Simple figure-8 speaker cable is pretty cheap in 100m rolls so just use that. Even the skinny stuff has as much copper as a single CAT5 cable.
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Old 24th February 2014, 11:26 PM   #15
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If there is little difference in sound quality or price I am fine using regular speaker cable. the longest run would be 40-50 feet.
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Old 24th February 2014, 11:36 PM   #16
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Are the mar-ken boxes a good choice considering the room size and crossing over to the subs?
From my experience I find the lower the crossover the better. This is however my first journey into high end systems. I am willing to use a different box if it would make the system better.
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Old 25th February 2014, 12:47 AM   #17
chrisb is offline chrisb  Canada
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If you're still talking 10P (the .3 is metal cone version), in any but a woefully undersized sealed box, I'd imagine with would develop more than adequate LF response to allow for XO as low as 80.

I've built the MarKen for the 10.2. but not yet seen drawings for the .3 or P - so far the only enclosures into which I've put the 10P have been the FHXL and a small BR design ( by Eric Hartmann ?). Embarrassingly enough, after my first audition of the latter, I found that they might have been wired out of phase (see what happens when you're in a rush?), so they need a revisit, hopefully later tonight.

Without reigniting the perennial "wire" debate and all the subset arguments, yes cheap hardware store 18gauge (or less, gadzooks ) can work perfectly fine.

As to CAT5 - once Dave gets his power back on at home he might be able to answer this - didn't Aaron Drabbit publish some tests on this subject well over a decade ago when some of the local DIYers here started using it?

In any case, as I said before, I've been using it for at least that long, but admittedly never in lengths longer than 20ft, and have yet find an amp that had issues with anything from single strand per pole to the elaborate braided snakes of Chris Van Haus. Those are fine if you don't mind blisters and have a proper stripper.

How much capacitance would be considered "acceptable", and for that matter who much would "normal" speaker wire posses?

Anyone remember Polk Audio Cobra Cable? - now that stuff was "affectionately" nicknamed amp killer
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Old 25th February 2014, 04:45 AM   #18
laplace is offline laplace  Australia
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In terms of capacitance, what is acceptable depends on the amplifier. Some are unconditionally stable, some are... not anything like that.

CAT5 is specified as 55pF/m within a single pair, plus (my guess) about half that in inter-pair capacitance. If you split your signal amongst the 4 pairs, you're looking at 220pF/m or 4.4nF for a 20m run. CAT5 is 0.2mm^2 per conductor, or 0.8mm^2 = 18AWG if used as a single cable (a bundle of 4 each way).

Copper resistivity is 1.7e-8 ohm-m, which makes the (two-way, a bundle of 4 cores each way) resistance of CAT5 0.0425 ohms/m. On a 20m run (0.85 ohms), your cable will be eating 10% of your amplifier power with an 8R load, or 18% with a 4R load. Same with 18AWG but without the 4.4nF in parallel. And then go see what that does to your damping factor.

If you must use CAT5, at least don't split individual pairs. Use two colours (green+blue+striped) for negative and the other two colours (brown+yellow+striped) for positive, and that will reduce your capacitance greatly.
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Old 25th February 2014, 04:38 PM   #19
chrisb is offline chrisb  Canada
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As I noted earlier, none of my speaker runs with CAT5 are more than 1/6th of the 20meters (65.6ft) that you postulate, which probably explains why I've not encountered any issue in those cases. I had to actually for a minute about just how long those runs were.

Of course, if one was to get hair-shirt about it, the tightly twisted conductors in each pair could be unraveled and separate by an inch or two into a ribbon with packing tape.



For runs as long as the 60ft, the hardware store 18 AWG is probably fine - the multiple runs of CAT5 that laplace suggests would certainly work, but it's a pain in the *** to untwist and strip 8 conductors per end of each cable - particularly if you don't have an accurately calibrated stripper - the stiff #24 of solid CAT5 is very easy to and break. For my own HT system, I used a roll of Home Depot #18 multi-strand - the way the room is laid out, the run to the furthest rear surround must be close to 50ft.
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Last edited by chrisb; 25th February 2014 at 04:43 PM.
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Old 25th February 2014, 06:08 PM   #20
Octavia is offline Octavia  United States
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Maxximus I think you are right on the money to crossover in the 60Hz to 80Hz region. Recently set up a home theater system for some friends and definitely found 60Hz to work very very well. Ended up watching a ton of live concert videos after dialing them in, very satisfying!
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