| Cloth Ears |
Gents,
I've got a 1200W amp that's going to be feeding an 11ohm load. Is there a formula that will tell me what the minimum wire size I should be using to ensure no over-heating/melting etc? |
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| MJL21193 |
| Think of the wire on a hairdryer. That consumes 1200 watts and has an internal resistance of about 11 ohms... |
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| Cloth Ears |
D'uh! Why didnae I thinka that? I'll probably go a little thicker, as my wire is encased in something a little softer (and probably with a lower melting point).
Just checking as I didn't want to end up with a little red line between the amp and the speakers.
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| Cal Weldon |
I think the length of the run determines your wire guage. Up to 20 feet should be OK with 14ga.
Remember big drivers use big electrons to drive them so use big wire. ;) |
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| Cloth Ears |
OK. I've done some figuring, and I've already got enough good cable sitting around. But, is there any way to work out heat dissipation from cables?
From my figures (and these would only be if I went insane and turned the thig up all the way), and a deal of help from the guys at the12volt.com, I've worked out that I'd have:- 1200 Watts
- into 11 ohms
- running 10.5 amps
- at 115 volts
Now, using Nelson Pass' 1980 cable article, that shows 18ga zip as having a resistance of .014 ohms/foot, I've worked out (using the figures above) that it would need to dissipate 1.5 Watts/foot.
Does anyone have an idea of what sort of temperature change this causes for the run of cable (or do we then get into surface areas of cable and such)?
And Cal, don't those big electrons go by another name once they reach a certain size (big cojones)? |
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| Cal Weldon |
I use 16 ga inside the box, 14 ga for runs up to 20 feet and 10 ga for when I take the speakers next door.
The hair dryer probably uses 16 - 18 ga and would warm slightly so why not up it to 14 or 12 and be done with it? How long is the run?
I think the really big ones are called jumbo electrons.
And don't forget to elevate your amp above the speakers so they flow easier. ;) |
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| FastEddy |
Cal: " ... I use 16 ga inside the box, 14 ga for runs up to 20 feet and 10 ga for when I take the speakers next door. The hair dryer probably uses 16 - 18 ga and would warm slightly so why not up it to 14 or 12 and be done with it? ..."
What he said ... stranded, of course. (FYI: 1200 watts into 11 ohms is enough voltage to exceed commercial building codes in the USA for running outside of EMT pipe ... down under, burn baby burn that ol' dance hall down.)
The "golden ear" types will suggest teflon insulation ... so I look for THHN (the stuff with the shiney skin). |
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| Cloth Ears |
| quote: | Originally posted by Cal Weldon
And don't forget to elevate your amp above the speakers so they flow easier. ;) |
No problem. I'm looking at mounting it vertically, so that the jumbo electrons flow out the back of the amplifier at the bottom and straight into the subwoofer box. It's going to be mounted rather like a child in a back-pack - but hopefully no squealing or funny smells;)
Excellent. From this, if I'm running 10amps though 20awg, the wire will heat up to 80 degrees Celcius. So, by using 10awg, I would be barely above ambient temperature.
Now, gents (and ladies), I'm not planning on running that sort of current, although after I've finished EQ, I might end up with 5amps (not sure yet). So hopefully, I won't be burning anything down.
Fasteddy, this is a commercially available, plug in the wall (ie. not 3-phase) amplifier - the Behringer EP2500. And it's also available in the US of A, so hopefully it self-protects before any fires start. It does have plastic covers for the speaker binding posts, to prevent shocks, and they recommend no exposed wiring. I expect that if I follow recommendations then I will probably be safe:)
Did you mean TSWTSS? |
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| FastEddy |
" ... From this, if I'm running 10amps though 20awg, the wire will heat up to 80 degrees Celcius. So, by using 10awg, I would be barely above ambient temperature. ..."
This will make a nice hand warmer, too. You want to take those charts with a grain of salt. They were designed as absolute minimums for inexpensive construction, not optimosed for audio. There is a serious school of audiophile thought that believes that bigger speaker wires are better ... and even I can tell the difference, if the difference is great enough or the speaker run is long enough. A compromise would be to follow Cal's advise = #12 AWG stranded.
And it is really not the heat so much as the downstream resistance of a long run to the speakers. Fortunately your case is a very short run, so #14 will probably be plenty. Especially if none of them jumbos have to run up hill ... :smash:
Also, at least here in the states, the costs between ten feet of #12 and ten feet of #14 or even #18 is about a wash ... |
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| MJL21193 |
| Have you taken into consideration the "skin effect"? How those sneaky jumbo electo like to slide along the shiney surface of the wire!:rolleyes: :rolleyes: |
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| roddyama |
The current carrying capacity is one parameter to consider for "best" possible performance from a given wire. Other things that might be considered is total resistance/impedance presented to the amp or the insulation voltage rating (with a 1200W amp).
The current (and voltage) through the speaker, and therefore the wire is always AC so it's the RMS current that is of concern. It's true the bass will tend to be more steady state than the higher frequencies but it be far from constant. Trasient (impulse) sounds like the kick drum will require the amp deliver very high instantaneous power. The RMS power is still quite low but for very brief instant, the amp could be putting out near full power. If the amp is truely capable of 1200W into even 16ohm (giving it the benefit of the doubt) the amp's rail voltage will need to be capable of 80V and double that if the amp is rated into an 8ohm load. That's RMS so the peak voltages will be ~1.4 X that or over 200V. The insulation will need to be able to handle this. Of course most insulation will so it's usually not an issue,... at least when its new. Once it ages and gets kicked around and stepped on some, that situation will change. Insulation with marginal voltage ratings could fail.
The 18ga mentioned for NP's article seems to have low resistance at only 0.014 ohm/ft but 20 feet of this is 0.28ohm. This is not a high value but what would be the sense of paying what you do for amps and speakers only to put the bare minimum into the speaker cables. This is not to say you should go buy $300 cables but 10ga "zipcord" (like Monster Cable from Best Buys) would cut the resistance to a third for a few dollars more in cost.
Stranded or solid will make little difference in terms of performance in the bass region. Of course stranded will be a lot easier to work with. Skin effect will lower the effective current carrying cross section of the wire and stranded would help in this regard but skin effect won't come into play until the frequency is above 1kHz and even than will not be significant until you're into the upper 2 octaves of the audible range and higher. |
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| Cloth Ears |
Roddyama, thanks for the info.
FYI on this amp/subwoofer, I am expecting a total of about 6 feet of cable total. 18 inches to the first terminal, 18 inches connecting the 2 drivers (in series), 36 inches back from the second driver to the amp.
This may end up being less, but I'm allowing for being tidy rather than the shortest possible wiring path.
The long run will probably be from the crossover to the amp (balanced XLR run). But I don't know how long it will be, yet.
The amplifiers manual says for bridged mono:
1300W 20-20kHz at 8ohms, 0.1%THD
1500W 1kHz at 8ohms, 0.1%THD
2400W 1kHz at 4ohms, 1%THD
Voltage gain is specified as 34dB and power consumption at 5A for the 240V model. Output circuit is a Class H complementary linear output type (whatever that is).
I have many pieces of cable as left-overs. Depending on my feeling at the time, I might even use more than one for each run, to allow those "sneaky jumbo electrons...to slide along the shiney surface" of more than one wire;)
When I do 2 runs of cable, it subtracts 3 from the AWG rating, doesn't it? So, 2 runs of 16, gives 13, and 4 runs of 16 gives 10. that's right, isn't it? |
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| roddyama |
| quote: | Originally posted by Cloth Ears
Roddyama, thanks for the info.
FYI on this amp/subwoofer, I am expecting a total of about 6 feet of cable total. 18 inches to the first terminal, 18 inches connecting the 2 drivers (in series), 36 inches back from the second driver to the amp.
This may end up being less, but I'm allowing for being tidy rather than the shortest possible wiring path.
The long run will probably be from the crossover to the amp (balanced XLR run). But I don't know how long it will be, yet.
The amplifiers manual says for bridged mono:
1300W 20-20kHz at 8ohms, 0.1%THD
1500W 1kHz at 8ohms, 0.1%THD
2400W 1kHz at 4ohms, 1%THD
Voltage gain is specified as 34dB and power consumption at 5A for the 240V model. Output circuit is a Class H complementary linear output type (whatever that is).
I have many pieces of cable as left-overs. Depending on my feeling at the time, I might even use more than one for each run, to allow those "sneaky jumbo electrons...to slide along the shiney surface" of more than one wire;)
When I do 2 runs of cable, it subtracts 3 from the AWG rating, doesn't it? So, 2 runs of 16, gives 13, and 4 runs of 16 gives 10. that's right, isn't it? |
It sounds fine and should not be a problem. If you already have the extra cable it doesn't cost and it surely won't hurt. Be careful with your connectors. Multiple cables in a single connection can be troublesome if you're not careful to be sure the crimp is good and tight and all the wires have been captured. Don't be afraid to give the cables a firm tug. If you can pull them out, the connection was no good anyway. |
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| Cloth Ears |
| quote: | Originally posted by roddyama
It sounds fine and should not be a problem. If you already have the extra cable it doesn't cost and it surely won't hurt. Be careful with your connectors. Multiple cables in a single connection can be troublesome if you're not careful to be sure the crimp is good and tight and all the wires have been captured. Don't be afraid to give the cables a firm tug. If you can pull them out, the connection was no good anyway. |
If I do that, then I'll be heat-shrinking them together also. But I do expect only about 4 inches of cable will actually be 'exposed'. The rest will be inside the sub-woofer enclosure or under the binding posts plastic shield. |
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| AndrewT |
Hi,
our mains cables running at 220/240Vac must be double insulated.
Would your 110V supply to the speakers need to consider the same safety?
What speaker connectors are rated for 110Vac use?
How do the commercial riggers do this? |
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| cujo75 |
To quote Ugly's Electrical References, 14 awg can carry 34 amps at 302 deg.F.. 12 awg can carry 43 amps at the same temp. the ohmic value respectiv. is 5.06 and3.18 ohms per 1000 feet.
Hope this helps
Cujo |
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| OzMikeH |
I see you are an Aussie, go buy an extension cord, cut the plugs off and cut it in half.
Good for 2.4kW at 240V, safe and cheap. Those with golden ears might hear the difference, but not in a sub.
I use supermarket extension cord wire for all sorts of stuff, you can't buy the cable at trade prices for what they charge. |
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| Cloth Ears |
| quote: | Originally posted by OzMikeH
I see you are an Aussie, go buy an extension cord, cut the plugs off and cut it in half.
Good for 2.4kW at 240V, safe and cheap. Those with golden ears might hear the difference, but not in a sub.
I use supermarket extension cord wire for all sorts of stuff, you can't buy the cable at trade prices for what they charge. |
Not a bad idea - I can twist the 3 wires together. And being round is much easier to seal going into the cabinet (I'm doing direct connections).
Do you recommend Coles, Safeway, Woolworths or Big W as having the best sound? |
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| OzMikeH |
just make sure you put the cords in opposite directions, you don't wants the electrons twisting anticlockwise on the way back to the amplifier in the southern hemisphere.
har har har
can even use white and grey cords for polarity. |
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| Foxx510 |
| I seem to recall reading somewhere that wire gauge on subs has a big effect on damping factor. Not sure if there is any substance to it or not.... |
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| AndrewT |
Hi,
all speakers that use a selected Q to tailor the low end response will be affected by extra resistance from the source+ connections.
Low end could just as easily apply to a full ranger or a mid/mass or a bass only or a mid only. |
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| Cloth Ears |
| quote: | Originally posted by OzMikeH
just make sure you put the cords in opposite directions, you don't wants the electrons twisting anticlockwise on the way back to the amplifier in the southern hemisphere.
har har har
can even use white and grey cords for polarity. |
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... :crying:? |
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| OzMikeH |
I must point out to novices here that he is joking, (I hope - because I was with the clockwise thing)
And to set the record straight the electrons go both ways. Any audio signal is alternating current. (yes, technically it can have a dc offset but this is not a good thing for a speaker) |
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| AndrewT |
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!!). |
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| Cloth Ears |
:ashamed: 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! :devilr::whip: |
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| Cameron Glendin |
| 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!!!!!! |
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| Cloth Ears |
| quote: | Originally posted by Cameron Glendin
Otherwise they might slow down or decide to live and build homes and then breed inside the cable!!!!!! |
Will I need breeder resistors to stop them doing that :angel:? |
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| GM |
| quote: | Originally posted by Cloth Ears
FYI on this amp/subwoofer, I am expecting a total of about 6 feet of cable total. 18 inches to the first terminal, 18 inches connecting the 2 drivers (in series), 36 inches back from the second driver to the amp.
When I do 2 runs of cable, it subtracts 3 from the AWG rating, doesn't it? So, 2 runs of 16, gives 13, and 4 runs of 16 gives 10. that's right, isn't it? |
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 |
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| Cloth Ears |
Thanks GM.
How did you come by the figures - or is it a trade secret? |
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| GM |
| quote: | Originally posted by Cloth Ears
Thanks GM.
How did you come by the figures - or is it a trade secret? |
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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| OzMikeH |
| I see very few people use Neutrik Speakon connectors. Why is this? they look like a good design to me. Especially if you parallel the contacts and use them only for 2 poles. |
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| GM |
Greets!
If you mean for consumer or DIY, there's no need for the quick connect feature/high cost.
GM |
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| burnedfingers |
| Altec Lansing had a chart based on length of the run to figure the gauge size of the wire needed. I'll see if I can locate a amplifier manual and post it. |
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| OzMikeH |
Genuine Neutrik Speakon plug = $13, chassis socket = $9 australian.
Not expensive. about $50 for two sets with freight.
I went this way because I didnt want to cut a 2.5 inch hole in my cabinets for a binding post style terminal plate. I only needed a 24mm hole. |
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