Film-Tech Forum ARCHIVE: Speaker Wire

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Posted by Adam Fraser (Member # 1074) on 04-19-2002, 10:49 PM:

This is just a question out of curiosity...
How much loss of sound is there with hundreds of feet of speaker wire between the amplifier/processor and the speakers? And what effect does the quality of speaker wire have on sound loss? Most theatres I have seen seem to use a fairly mid grade of speaker wire and I was wondering how much difference (sound quality and loss) there may be between running the top of the line wire compared to average run-of-the-mill wire.
Thanks for your comments.

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Adam Fraser
www.pinestheatre.com

Posted by David Stambaugh (Member # 1102) on 04-19-2002, 11:16 PM:

I was kind of surprised when I saw a sample of the type of speaker wire typically used in theaters. It looked like 14-gauge stranded copper zip cord to me, like lamp cord (I think that's 14-gauge). Now I'm not a big believer in high-end audio cable voodoo myself, but for those long runs, and considering the huge power being pumped out, zip cord seems kind of questionable. That kind of speaker cable would be considered the absolute minimum for decent home audio, where the distances are much shorter. I don't have any data, but have done a lot of reading about exotic cables and such as it applies to home audio. Some high-end audiophile believers would have a coronary if they found out their favorite THX-certified 1000-seat SRD/DTS/SDDS movie theater is running the stage speakers on Radio Shack Zip Cord.

A THX-certified Mann theater in Laguna Hills or Laguna Niguel (Calif) or someplace close to that advertised that it used Monster Cable speaker wiring. They had a big one-sheet in the lobby promoting it. This was in the late 80s.

Posted by Dave Macaulay (Member # 813) on 04-19-2002, 11:25 PM:

The loss depends on the length and wire gauge. There is a purely resistive loss of power in the wire that does not directly affect the sound quality but long runs and small wire can waste a good percentage of the amp power as heat. Essentially, larger wire will compensate for a longer run.
The sound is affected by resistance indirectly because speaker cable resistance reduces the effective damping factor of the amplifier. A high damping factor helps control the speaker cone movement and improves the "fidelity" of the sound.

Quality of wire? I may get flamed for this - but "high quality" wire is ridiculous. If you think paying extra for "Monster Cable" or other "superwire" is a good idea, go ahead. You get a nice looking wire and it's really flexible. So what. Compared to the same gauge "normal" stranded wire there is absolutely no electrical difference that will affect the sound quality.

Posted by David Stambaugh (Member # 1102) on 04-19-2002, 11:46 PM:

The only thing I would add is that by using something like Monster Cable, you would probably be assured of having better than the minimum gauge to do the job efficiently. But you would be spending way more $$ than necessary to get there.

(You mean you don't believe that oxygen-free 99.99%-pure copper wire with the the crystals aligned in the direction of current flow and a genuine Teflon jacket would improve a theater's sound??)

Posted by Paul G. Thompson (Member # 655) on 04-20-2002, 02:36 AM:

Dave Macaulay is correct.

Some amplifier operator's manuals have a chart which explains the damping factor characteristics. It is nothing more than an arbitrary number, but the higher the better. The chart usually gives an idea as what might be expected by the size and length of the wire used. The higher the number, the better.

Posted by John Anastasio (Member # 607) on 04-20-2002, 06:41 AM:

If you're concerned about resistance, just run another length of the same 14AWG wire and you'll have the same resistance as 7AWG wire....but you'll just be wasting wire and increasing something else that will have more of an effect on the high frequencies....the capacitance of the wire. The capacitive reactance (dynamic resistance to certain frequencies) increases with surface area. The longer, or the wider, the wire, the more the capacitance. The more the capacitance, the more the filtering effect on high frequencies. Eventually, after a few miles of wire, they all disappear....ask any telephone engineer. It's why you can't get DSL out in the boonies...the wire can't handle the higher frequencies. I'd say not to worry about that 14 gauge zip cord. It should handle a constant draw of up to 15 amperes of current at very low resistance over the distances you're working with....more than enough to blow out any speaker you've got without affecting frequency response.

Posted by Bruce Hansen (Member # 281) on 04-20-2002, 09:09 AM:

It would be my guess that the THX theater mentioned above, got the Monster Cable for free by putting that one sheet in their lobby. In my opinion, the only thing you are improving by using Monster Cable, is Monster Cable's bottom line.

Posted by Phil Hill (Member # 371) on 04-20-2002, 10:01 AM:

The comments from Paul and Dave Macaulay are on target.

Also, circuit resistance does become half of the original resistance if you parallel a conductor with another of the same AWG. The new equivilant AWG is 3 wire sizes smaller, NOT cut in half. 14AWG + 14AWG = 11 AWG.
In high-power special venue and large format theaters where it's common that the audio power exceeds 30kW to use 14 AWG, 12 AWG, and 10 AWG for each of the HF, MF, and LF drivers of a speaker system. What is sometimes overlooked is the voltage rating of the insulation. High-power amplifiers can put out more than 120 volts of signal and require class I speaker wiring usually something like THHN in conduits.

>>> Phil

Posted by Gordon McLeod (Member # 33) on 04-20-2002, 10:23 AM:

I use twisted pairs of 12 AWG minimum and 10 for longer runs
West Penn makes a nice jacketed twisted pair if you like purple colour
Twisting is important to eliminate RF pick up
Monster cable and the like is for the birds
And bareing the wrath of S.G. I still use the drill to twist THNN stranded wire

Posted by Adam Fraser (Member # 1074) on 04-20-2002, 11:04 AM:

Thanks for all the reponses guys.. Very helpful

------------------
Adam Fraser
www.pinestheatre.com

Posted by John Walsh (Member # 168) on 04-20-2002, 11:14 AM:

We like regualar 10ga also, twisted with a drill. Although, people complain about getting all the strands into the terminations at the speaker and amps.

Monster cable does look good, and does have nice terminations on the ends. Sometimes for hi-end jobs, you might need that. But, there is no difference in sound quality, unless basic physics has changed since I was at school.

Posted by Paul G. Thompson (Member # 655) on 04-20-2002, 04:17 PM:

If you twist your wire in an electric drill, be careful what direction you twist it. If you go the opposite direction of the lay of the strands, damage to the wire will result. Also, keep in mind not to "Over-twist" the wire.

One idea of twisting the wire is to cancel each other's magnetic induction. This will make the wire look resistive to the amplifier, and not inductive.

Posted by Jerry Chase (Member # 660) on 04-20-2002, 05:40 PM:

..and remember that more isn't better. The amount of twist needed is quite small - something like 1 twist every 18" is plenty, IIRC. I used to get the grunt work helping my dad install PA systems and stuff.

Posted by Steve Guttag (Member # 268) on 04-21-2002, 12:42 AM:

John,

Check your math before giving someone bad advice. 14awg is often inadequate wire in theatre applications.

Lets say your subwoofer line needs or will demand 2000 watts of power and you use say 4 8-Ohm subwoofers to handle the power and present a 2Ohm load to the amplifier...you will need nearly 32 amps of carrying capacity from your wire. 14awg won't cut it and you wont be blowing your speakers, necessarily. Heck, only 750 watts into an 4-ohm LF cabinet of a typical stage speaker (that can hanle 1200 watts) will bring you nearly up to 14amps. The JBL 4648-4, when driven to full power will draw over 17 amps without damaging the drivers. Instantaneous power consumption can double that!

Both of the above examples are valid for typical theatres today.

This isn't a case where we want the wire to current limit our signal either thus larger wire should be used. While damping factor is almost never a concern for speaker wire, power limiting is.

As for THX, they do have their hand in choosing the speaker wire gauge. I believe it was HPS-4000 though that got on the Monster cable bandwagon.

However, there are plenty of cases where 14awg is just fine. It really depends on the length of run and the power needed.

BTW Carol and Belden also make fine jacketed red/black speaker cables down to 12awg. If you don't mind wht/blk then one can often go larger, West penn just introduced a 10awg. International Wire and Cable will make larger gauges in red/black...I've seen them use 10awg.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Paul G. Thompson (Member # 655) on 04-21-2002, 02:31 AM:

Steve, is some of that wire nickel or silver plated like some of the wiring I have seen in ORC equipment? I am not sure what it was plated with, but I do remember seeing lots of that type of wire used in military applications (especially aircraft) that had heavy current draw using small AWG wire.....Enlighten me.

Posted by Steve Guttag (Member # 268) on 04-21-2002, 09:20 AM:

None of the speaker wire I have used is nickel plated though I don't doubt that there are plated speaker wires (probably more like tin-plated).

Heck you could use platinum wire or the ultimate....mercury filled glass tubes...however the twisting part with those could be a bit tricky if not dangerous!

For me, wire isn't where I put the money...THHN stranded is often just fine. The official speaker wires from the various cable manufacturers tend to have a higher strand count.

In response to Mr. Walsh's comments on fitting the ends of larger cables into the speaker or amps...

What is it with the speaker/amp industry? It is like a conspiracy to ensure anything larger than 12awg just won't fit! The push terminals used by JBL and others just won't take larger than 12awg and they barely take that and can often pull out. On the amplifier end...the 5-way binding post is also a 12awg device though some bannana plugs made specifically for speaker use can go down to 8awg. In recent years we had the wonderful connector introduced by Neutrik called the SPEAKON (as in speaker connector)...it is a quick disconnect, can't shock yourself connector that locks in. It's rated wire gauge is approximately 13awg (though 12awg can fit)...Even many amplifier barrier strips flip you the bird at the magical 12awg limit. Ever tried using 10awg on them (eg QSC)? I often divide up the strands so an equal amount goes on either side of the screw when dealing with 10awg. Either that or use crimp terminals (more often than not). Nowadays, speakers and amps should be taking 8awg wire with no problem and should even consider 6awg as a safety margin. We have amplifiers that can put out 30+ amps of juice per side it only makes sense that wire that can handle that power should be able to fit.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Rick Long Jr (Member # 541) on 04-21-2002, 02:48 PM:

I do believe there may be something to "Oxygen Free" cable. Ever try to tin or solder really old zip-cord? (or old Dolby fanning strips for that matter).

Posted by Paul G. Thompson (Member # 655) on 04-21-2002, 02:50 PM:

Rick, you noticed that, too.

Posted by Ian Price (Member # 14) on 04-21-2002, 03:08 PM:

I have used 14,12, and 10-gauge wire with excellent results in all gauges. UA tended to use 12 for the main stage speakers and 10 for the subs. When I did my little theatres I used Belden shielded 14-gauge because I had a spool of it left over from by Audio Video days.

Last year my tech ran across a company that makes a wire bundle for movie theatres. They ran 8 twisted pair for the run behind the screen and then single twisted pair for the surrounds. You could spec the gauge you wanted for each run and each pair were a different color for easy channel identification.

Bobby Pinkston thinks it was done by an electrician in Dallas named Ed Davis.

They used standard electrical wire because it is vastly cheaper than Belden wire. Electrical inspectors don’t like Belden wire because it doesn’t have the UL listings in the jacket but you have to look it up in a book. Regular electrical wire has the UL information written right on the wire itself.

I'll ask my tech what company that was when he is available.

Posted by John F. Allen (Member # 218) on 04-21-2002, 03:21 PM:

“I believe it was HPS-4000 though that got on the Monster cable bandwagon.”

Not so.

I have spent and wasted many hours testing speaker wire. There is no question that the wrong wire can have a negative impact on sound quality. Excessive resistance, capacitance or reactance can all reduce the quality of the amplifier/speaker connection -- which should be the best possible. However, one does not need expensive and fancy wire with big claims to get the job done quite well.

The HPS-4000® specification for speaker wire is simply that the round trip resistance should not exceed 1/4 ohm. This means that were I to use #10 AWG THHN wire, the largest theatre where I would use that size wire would be around 50 feet long. This assumes a 50 foot long theatre would require perhaps a 125 foot long screen-speaker wire run.

Beyond that, I also specify the use of (typically) 10-3 solid round Romex wire for the screen speakers. This provides three #10 conductors plus a fourth for bond. These four conductors are twisted in the round jacket. By shorting the two opposing wires at each end, inductance is canceled, and we also get the resistance of a #7 AWG wire -- good enough for theatres up to around 175 feet in length.

It took me a while to become convinced of the efficacy of this approach. I was first shown graphs of the high frequency losses encountered with long runs of stranded wire. The losses looked alarming. However, a treble adjustment would correct for this and we really wouldn't be aware of the HF loss unless we actually measured it. So I measured it.

My client in Hawaii insisted that we should try the Romex approach on a new theatre (the Kahala #1). We had previously used twisted #6 THHN at the Waikiki #3 along with the same speaker systems that were going into the Kahala. When we measured the frequency response at the beginning and the end of each type of wire, we found that there was a high frequency loss at the end of the THHN, where 20 kHz was down -5 dB, while the Romex was essentially flat.

Since the Romex is less expensive and comes twisted, there was no reason not to use it from then on. Over time, I began to also hear a slight difference between the sound systems using the solid Romex wire and those using twisted THHN. The Romex houses sounded slightly smoother, though no one could ever walk into a theatre and know which wire was used.

There have been one or two occasions where local electrical inspectors were uncomfortable with the use of Romex for low voltage applications. Though not strictly illegal, they believed that the was too great a possibility that someone would actually put line voltage on the speaker wires. In such cases, we revert to #8 or #6 THHN.

For surround systems, we use #14-2 twisted and stranded copper wire. It can be the least expensive #14-2 copper wire available. Indeed, zip cord would be fine. However, one can often find #14-2 speaker wire that is relatively inexpensive and marked for polarity as well.

John F. Allen

Posted by Bruce Hansen (Member # 281) on 04-21-2002, 03:50 PM:

I have found that when unsoldering an old connection, it helps to add a little new solder. I don't know what changes about solder "over the years", but "old" solder can be hard to get to melt.

For "hard to solder" things, Kester makes a special solder with an "active" flux, and it really does make a difference. The flux is called 331. It is a little more expensive than "normal" solder, but not much. (No, this is not acid core solder, DO NOT use acid core on electronics).

Posted by Gordon McLeod (Member # 33) on 04-21-2002, 05:26 PM:

John one problem I encounted with romex is with fire inspectors
It isn't usually FT4 rated for free air and they don't like it in conduit either in some areas
Though I did see a interesting stranded Romex direct burial cable used recently that was ft4 rated

Posted by Rick Long Jr (Member # 541) on 04-21-2002, 10:02 PM:

Using Romex for speaker goes against what I was taught.
I always assumed that solid wire would have a tendency to roll of the highs due to the fact that higher frequencies have a tendency to travel along the "skin" of a conductor, which is basically why stranded wire is preferred (more strands=more surface area).

Posted by Aaron Sisemore (Member # 145) on 04-22-2002, 12:43 AM:

AFAIK 'Skin effect' is practically nonexistent at audio frequencies. In the RF spectrum, however, it wreaks all sorts of havoc.

-Aaron

Posted by Phil Hill (Member # 371) on 04-22-2002, 04:00 AM:

Skin Effect!!!!!!!....????? We ain't talkin' RF here! Cut us some slack! Do NOT be BRAINWASHED by the Oxygen-free, Monster, or WETF (What Ever The F*ck)high-end cables they (the so-called and usually self-appointed 'experts')are pushing.

Oh, and tinning has nothing to do with oxygen-free cables but rather surface oxidation. As someone pointed out, add some "fresh" solder and it will bond just fine. The new EPA-friendly solder formulas are "lead-free" and suck. I keep several spools of the good ol' lead-type around just for such cases to repair older equipment. (GOD! I love the smell of rosin-core (5-core), 60/40 solder in the morning....)

I love the "directional-aligned" conductor type of audio cables. I mean, as we *ALL* know, audio is DC. And, the current flows ONLY in one direction, so that those cables will definately be worth mega-bucks. (OH GOD! Save me! I'm not worthy of you.)

I've not seen nickel-plated or nickel-composite wire other than nichromium that's used for heating elements. Silver-plated wire is used with teflon insulated wire. Free-air current ratings for single conductor and cables in electronic equipment and aircraft is usually higher than NEC because of the insulation is allowed to operate at higher temperatures.

It is VERY important to twist conductors correctly so as not to damage the conductors as Paul mentioned.

Also, I doubt that mercury would be a very good conductor, especially as compared to Gold, Silver, Copper, Aluminum, etc.

And John, I read with interest your post about the 10/3 w/ground Romex cable. I'm surprised at the results especially with certain amplifiers (like the POS Crown amps)that do not like certain types of loads. Romex 3-conductor with ground is NOT formed in a twisted-conductor fashion, but rather wound in a spiral with all conductors parallel to each other.

>>> Phil

Posted by Paul G. Thompson (Member # 655) on 04-22-2002, 04:13 AM:

I don't think solid strand THHN is even acceptable for speaker wire. This is what I was told by other engineers.

Posted by Kelsey Black (Member # 126) on 04-22-2002, 05:06 AM:

Gordon made mention of FT4 ratings.

definition please?

Posted by Gordon McLeod (Member # 33) on 04-22-2002, 06:53 AM:

FT4 refers to the flame spread rateing of the jacket and also i believe the noxious byproducts of its combustion
On old connections I often brush on some solder rosen flux from the tin first
One of the main reasons that the conductors are to be twisted is to reject RF picup. I remember one theatre that used romex and there old cinemcanica soliod state amp output transistors acted like a 25wat crystal radio ( replaced it with twisted cable and problem was gone)

Posted by Bruce Hansen (Member # 281) on 04-22-2002, 10:18 AM:

Surface effect does not even begin to be a factor untill you get above 30 MHz. It is not a factor at or anywhere near audio freqs.
Bipolar transistors clip harsher than tubes, but MOSFETs clip like tubes, eather way, clipping is BAD, I don't care if it's tubes or transistors. If you are clipping you either need to turn down the volume, or get a bigger amp. And getting a bigger amp is much easer in the transistor world that the tube world. By the way that "warm" sound is a combination of a small amount of 60 Hz hum leaking from the filment into the active elements of the tube (not enough for you to hear it as hum, but it does make any audio around 60 Hz sound louder); and high freq. roll off in the output tranformors. In the last days of tubes, I heard a well designed tube amp (and rather expensive). They had gone to the trouble of rectifing and filtering the filment voltage so it was DC, and had "computer designed" output transformers, it sounded just like a transistor amp!

Posted by Paul G. Thompson (Member # 655) on 04-22-2002, 03:22 PM:

Bruce, I respectfully disagree about your 30mhz low limit.

As an example, 1.4mhz will laugh and almost completely ignore a 12 gauge grounding wire. We have to use copper strap 4 inches wide to
provide the RF grounding needed to keep our transmitter RF out of the audio chain.

Posted by Bruce Hansen (Member # 281) on 04-22-2002, 04:14 PM:

I don't believe that is due to skin effect, that may be more inductance. RF grounding is a very different story, snd 1.4MHz is WELL above 20KHz. What are you transmitting at 1.4MHz?

Posted by Paul G. Thompson (Member # 655) on 04-22-2002, 08:02 PM:

Hi, Bruce.
Yes. That is our transmitter frequency. 1430khz on the AM commercial band. The other transmitter is 660AM. The 4-inch wide copper grounding has the surface for the skin effect to take place and carry the unwanted RF to ground, where a 12 gauge wire will carry practically nothing. There simply is not enough surface area to conduct it because of the skin effect, therefore making a 12 gauge wire look like a high-impedance circuit to RF. This likewise holds true for AM stations operating at 550 khz, but they don't need the 4 inch stuff. Three inches seem to work nicely.

I have not looked at a wave form on an oscilloscope for a sustained note on a distorted guitar like some of the hard punk acid rock musicians use, but if I did and measure the rise time and convert that to a frequency, it will fall in the RF range.

Sometime I will do that - just out of curiosity. Just how much attenuation a 12 gauge wire will actually give to a given RF frequency would have to be calculated.