OzMikeH said:
No, I've found yellow (with blue and red stripes) cords from Bunnings to be really effective. And you can use the red/blue stripes to work out that your cords are running in the right direction.
The secret is to remember which end of the cord you cut which plug off (as the electrons flow from the wall into the other end, don't they?). And the electrons (jumbo ones from big amps) flow from the negative to the positive nodes of the amp. BUT, omigod, when I connect it up in bridged mode I have to use both positive speaker binding posts! What am I to do...
?Hi,
even our novices know that electrons go in all directions (was it Brown? or was he on about gases?) and not just when AC flows.
It's the general drift that is seen as current flow and it's the drift in alternating directions that we interpret as AC.
Just to compound it the drift in a particular direction is negative flow.
And then we go and reverse it into our conventional current flow.
Stupid us (we expect novices to learn this!!).
even our novices know that electrons go in all directions (was it Brown? or was he on about gases?) and not just when AC flows.
It's the general drift that is seen as current flow and it's the drift in alternating directions that we interpret as AC.
Just to compound it the drift in a particular direction is negative flow.
And then we go and reverse it into our conventional current flow.
Stupid us (we expect novices to learn this!!).
I must apologise also. Even though this is not a DIY amplifier we are talking about, the voltages and amperages (?is that a word?) that it can generate could be uncomfortable, if not down-right dangerous.I do not wish to contribute to the Darwin awards, even if inadvertantly.
Don't worry, Mike, I know just enought to keep knitting needles out of the sockets in the wall - and that jumbo electrons go any damn way they want to!
Oh dont forget the impossibility and importance of oxygen free cables!!!!!! We dont want those jumbo electrons to breath!!!!!! Its way better for them to hold there breath from the amp to the driver. Otherwise they might slow down or decide to live and build homes and then breed inside the cable!!!!!!
?
Cloth Ears said:
Greets!
Power wire runs are all about voltage drop (Vd) over distance, so for such a short run/11 ohms/~1453 W (based on 34 dB gain) with fractional Vd you only need ~2979 CM, or 15 ga. if copper, so anything bigger is essentially wasted, though of course it doesn't hurt performance in a sub app. Anyway, the terminations are typically the weak link in high power transient situations, with cold weld (properly crimped) connections to ring tongue connectors for stud or screw mounting being preferred over typical consumer speaker connectors.
Plenty close enough.
GM
Here is an interesting calculator that shows the effect of wire gauge/length on damping factor.
http://www.bcae1.com/dampfact.htm
http://www.bcae1.com/dampfact.htm
Cloth Ears said:
Greets!
You're welcome!
No trade secrets, I use to list the math, but folks primarily just wanted an answer, so quit posting it. Here's one response I saved from years ago, so the values aren't pertinent to your app:
When wire is used as a filter element, then this subject can get
complicated, otherwise you select wire based on voltage drop over distance.
Solid core has the lowest losses/ft and can't oxidize between the strands
like lampcord, so my preference is solid core, preferably silver plated.
WRT tiny wire in the cab, the wire to the LF/one side of the XO should be
the same size as what you ran from the amp, and its length should be
included in the gauge calc. The rest of the wiring can be sized based on the
distance from XO since its the actual run for the mids/HF.
FWIW, I use 10ga ROMEX less the sheath, etc., and twisted together at ~eight
wraps/ft. After the XO is 24ga magnet wire twisted together. Terminations
are the weak link in any wire run, so if you're up to it, converting the
typical pitiful terminals on the back of the amps and the speakers to screw
lugs so ring tongue connectors can be used is a cheap/effective tweak. I
also recommend using an anti-corrosive conductive paste, such as T&B or
Burndy's available at an electrical supply house to ensure the best
practical current carrying junction, and stay that way.
To calculate the required gauge:
Assuming you don't want the wire to act as a resistor to either flatten a
rising response or better match the impedance of a tube amp, then the size
is determined by how much voltage drop you consider acceptable.
Using the driver's Pe, Re (or total Pe, Re if multiple drivers are used),
then with the formula:
I = sqrt P(Pe) / R(Re)
you can calculate ~ max current draw capability. If this number is >the
amp's rating, then you may clip it on loud passages.
To determine wire size required:
Circular Mils (CM) = (2*L*I*10.8)/Vd
Where:
L = length of wire in ft
I = max current of circuit
Vd = voltage drop
Some rounded off CM values:
32ga = 64
30ga = 100
28ga = 159
26ga = 320
24ga = 404
22ga = 640
20ga = 1024
18ga = 1624
16ga = 2580
14ga = 4109
12ga = 6529
10ga = 10384
8ga = 16512
Example:
Pe or short term peak rating = 400W
Re = 3.4 ohms
wire run (one way) = 20 ft
VD = 1V (this is considered the max acceptable, I usually use 0.3-0.5V)
Sqrt 400/3.4 = 10.846A
(2 x 20 x 10.846 x 10.8)/1 = 4685.472CM, or 12ga.
As you can see, small wire/long distances can eat up amp headroom. Conversely, if the amp is near/on the speaker, acceptable wire size becomes tiny (or Vd vanishingly low if a large gauge is used).
At what point downsizing the wire becomes audible is of course dependent on the individual and his system/room.
HTH,
GM
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