I need some parameters for running speaker wire in a small (250 seat) theatre. I’m looking to locate the power amps back near the board at the rear of the main floor, from where they’ve been situated offstage. One amp is 300 watts per channel and is running a pair of JBL two-way PA speakers. A couple of others are smaller and are running stage monitors. If I do this I’ll need to run a total of 6 speaker wires, the longest being close to 100 feet. Is this within range? I need to get the amps and EQs back near the operator rather than leaving them up on stage where s/he cannot get to them easily if there’s a problem during a show. Most of the setup of this type that I’ve done has been in control rooms where the amps and speakers are a few yards apart at most. Input appreciated.
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Romex. 14ga <50'> 12ga
SamT
Now if I could just remember that I am a businessman with a hammer and not a craftsman with a business....."anonymous". . .segundo
Romex for speaker wire? Get a grip.
"I cut this piece four times and it's still too short."
I 've pulled #10 THHN for speakers in multiplexes.
.
.
.Wer ist jetzt der Idiot
?
What?
Musical electrons are special?
They be too hoighty toighty for that lo-classs tradesmans wire?
If you have some facts or knowledge that says otherwise, let us know, but don't go pulling that don't be stupid on me.
With an electronics and signal processing background I understand that there could be some issues with using solid strand single pair untwisted over using multi strand single pair untwisted, but I can't see any.
So what do you know that I don't?SamT
Now if I could just remember that I am a businessman with a hammer and not a craftsman with a business....."anonymous". . .segundo <!----><!---->
Hey SamT, You are going to expose the truth to audiophiles, but they won't listen! They only listen to the "experts" that use Monster Wire. You know audio electrons have to sound better through expensive copper wire than ordinary copper exposed to oxygen! gggFrank DuVal You can never make something foolproof because fools are so ingenious.
I've hooked up a lot of speakers, never with solid copper wire. Stranded copper electrical wire would probably work fine, but I think the strands are thicker than with audio wire.
The only difference between stranded and solid is flexibility. The "skin effect" only comes into play at gigahertz frequencies, and when the "skin effect" is in effect a stranded wire "looks" like solid to the electrons -- the inner strands don't carry current.
People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck
>> The "skin effect" only comes into play at gigahertz frequenciesNot exactly true... skin effect is measurable at all frequencies but is significant at higher frequencies. From William Hart Hayt, Engineering Electromagnetics Seventh Edition,(2006) --frequency -- d
60 Hz -- 8.57 mm
10 kHz -- 0.66 mm
100 kHz -- 0.21 mm
1 MHz -- 66 µm
10 MHz -- 21 µm
skin effect is the same thing as skin depth right? Wow I never though about it but if you are running a subwoofer you really do need beefy cables I guess. What happens when the skin depth is more than the wire diameter?Daniel Neuman
Oakland CA
Crazy Home Owner
> What happens when the skin depth is more than the wire diameter?The entire wire is conducting, rather than just the "skin". And when the skin effect takes over, it doesn't even mean that the current-carrying capacity of the wire is reduced. Through the oddities of electron dynamics the skin has the same conducting capacity as the entire wire would, absent skin effect. And this is true even if, for the high-frequency case, you replace the middle of the wire with a non-conductor.The skin effect is essentially irrelevant, for the issues of concern here.
People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck
Who said anything about stupid? I said "get a grip". No offense intended.Stranded speaker wire, as you well know, is suited to sending audio over a fair distance but single conductor isn't great when you want to preserve the frequency response, etc at speaker level. In a Low Z send, the cable doesn't have to be particularly heavy but it still needs good shielding and preferably, twisted pair. As you also know, the impedance and output voltage have everything to do with how far and how well the signal will travel.
Have you listened to line audio (High Z) running through Cat5e? It works but the HF content is not great.Besides, musical electrons are happiest going through linear crystal oxygen-free copper wire. lol Ever hear of "Sound Pipes"? Last price I saw was like $150/meter. Someone's gettin' rich off of that one.
"I cut this piece four times and it's still too short."
Ha ha..you said shielding.
Man did I FU big time once..I made an ele. upright bass. Prototype was onstage in a bar...numbnuts me forgot to shield the control cavity with nickle paint.
There we were jamming away..first set...next thing ya know my monitor started getting REALLY wierd sounds blasting back at me.
Turns out everytime they rung up a sale on the cash register, I was picking up the RF from it, I can't imagine how bad the sound was in the bar.
Luckily, I had my fretless five string for a back up..yikes.
Spheramid Enterprises Architectural Woodworks
I have irriatable Vowel syndrome.
From William Hart Hayt, Engineering Electromagnetics Seventh Edition,(2006) --
frequency -- d60 Hz -- 8.57 mm10 kHz -- 0.66 mm100 kHz -- 0.21 mm1 MHz -- 66 µm10 MHz -- 21 µm
Thanks Zooguy
B&S Gauge
Actual Diameter
12
2.05 mm
14
1.63 mm
16
1.29 mm
18
1.02 mm
20
0.81 mm
22
0.64 mm
24
0.51 mm
At 60hz the signal is fully within both 14ga and 12ga, so the electron fileds are present in each strand of your wire, but at that frequency, who cares?
But in the 10k to 20k and up frequencies, the signal field is only in the outer 1/3 or less of whatever wire we're talking about. The center of the mass of conductor(s) is no longer relevant to the signal. Skin effect is starting to take over. Oh yeah, skin effect appears over the entire mass of the conductor, not individual strands.
I don't remember the formula for conductor impedence (Z) but it relates the diameter of the conductors, whether they are paired or coaxed, the frequency of the signal, the distance between the conductors and the material seperating them.
Ever hear of "Sound Pipes"?
No, are they like copper plumbing pipes(|:>) Whatever happened to plasma speakers? Where a flame was the transducing medium.
Back in the '70s when I had more spendable money than sense, I compared the three best speakers in the world and I could tell there was a difference between them. Now I can't hear the difference between a 50 gal barrel and a snare drum.
Two of those systems were American made, AR LST and Tower of Power, and the third was German. The AR's were $1500 each and the Germans, $1100 each. 6 years later the German one was being sold by Radio Shack for $100 a pair. They are the grandfather of the shelf sized aluminum bodied speakers RS sells now.
People would come over and I'ld have the tunes cranked up on my really nice system and they'ld be looking for the speakers. Expecting to find some huge boxey furniture stuff. They would freak when I pointed to two little pocketbook sized things on a shelf.SamT
Now if I could just remember that I am a businessman with a hammer and not a craftsman with a business....."anonymous". . .segundo <!----><!---->
You are so correct. I have over 20 yrs in dinking around with audio, and basically, if ya can't hear it at all..it don't matter.
Noise cancellation was the hide to strip at one time, then Dolby went into the field ...fat wire became monster wire, ....
I can take a 2x4 and affix a PU at both ends and hit it with a hammer...no strings. OK, so it's a dead thud, but it works for the BLUEMAN group.
Seriously, if you like percussion from drain pipes..you MUST see what these guys can do..you will laff away the seriousness of sound.
Spheramid Enterprises Architectural Woodworks
I have irriatable Vowel syndrome.
Romex for speaker wire? Get a grip
Seen some of the prices wanted for 16ga "speaker wire" versus 14ga romex?
The 'real' audiophiles are all convinced that they need product that's priced by the meter (and end connections extra, per each).
Now, if you mean for the 'average' person--well, yeah, decent 18ga lamp cord (or the 16ga stuff from radioshack) works just fine.
In this application, for OP, it does not sound like "overkill" at all to me. There's not always a lot of "smarts" between the band and the "sound man"--some will try to get 5 gallons out of a 3 gallon pipe "just because" (you ask, and the answer always is "It's [disaster] never happened yet" with all the confidence one has of never having lived through a "yet" . . . )Occupational hazard of my occupation not being around (sorry Bubba)
AudioPILES can KMA when they get all "tweaky". Romex is not made for audio. Speaker cable is not made for AC power supply. If you go by conventional audiophile (and some real world) theory, high frequencies travel on the skin of the wire and the more strands you have, the better the HF content will be. Romex, having only one conductor for +/- won't be great. Even running Cat5e for line audio loses a lot of highs. Everything needs to be terminated properly and there are converters (called baluns) for just about any type of signal to travel on another kind of conductor (like component video over Cat5e instead of coax). Also, a lot of speaker cable it twisted pair and this cancels some noise while Romex is parallel conductors.I really don't care about audiopiles, I do low voltage electrical and I care about ease of installation, reliability & durability, sound quality and cost. Size the speaker cable for worst case at that distance. The amps will put out what they can. If some nimrod overdrives the input and clips, the tweets are gonna go away anyway but it won't be from too much power. Live music venues are using fiber from the board(s) to the amps with a converter at the amp end. The best signal transfer, it can run much farther with no loss and they'll never have a ground loop over fiber- there's no electrical connection at all. Just a matter of time till smaller venues can afford it.
"I cut this piece four times and it's still too short."
> Even running Cat5e for line audio loses a lot of highs.Interesting, since Cat5e is good to something like 350Mhz.
People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck
Yeah, it's good to 350MHZ in the right kind of circuit. A high Z line audio run from one stereo to another is not what it was made for and the highs are definitely lacking. It sends the signal but not as well as if I had a balun on each end. It still works for background, though.
"I cut this piece four times and it's still too short."
It's all a matter of impedance. Low-level audio lines vary from 75 ohms to several K ohms. If you send a 5K ohm impedance signal any distance along twisted pair you'll lose a lot of high frequency. Send a 100 ohm signal on twisted pair, however, and things will fare much better.And keep in mind that most speaker systems run at 2-32 ohms.
People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck
And that is ohms Z, not ohms R.
the Z of any component varies with applied frequency. Audio equipment engineers try really hard to get all components in the signal path to have balanced (equal) Z at as many freqs as possible.
Any change in Z causes power to be reflected back to the source. The bigger the change in Z the bigger the reflect power. An open line is as dangerous to equipment as a shorted line.SamT
Now if I could just remember that I am a businessman with a hammer and not a craftsman with a business....."anonymous". . .segundo <!----><!---->
AudioPILES can KMA
Oh, so you have met some of my clients . . . <g>
And it can be the getting them to stop that can be the problem . . .
Occupational hazard of my occupation not being around (sorry Bubba)
Most live music venues place the amp(s) closer to the speakers. There's more signal loss through speaker wire than a low impedance feed to the amp. The thing that's absolutely critical is having the electrical supply to the amps and all of the other electronics carrying audio signal on the same phase. Pro audio always has grounded power cords and you really don't want to use ground lift adapters. Having an appreciable resistance in the power supply ground path causes what is known as a ground loop, which means that the voltage trying to make up the difference in the ground path will travel on the audio ground because it's usually the path of least resistance. The hum you hear is one symptom and if the amps are on a different circuit, you can hear snapping or other odd noises. Worst case, equipment can burn up.
100' on speaker cable means that a lot of power will be lost, as well as dynamic range, damping of the speakers (farting bass) and frequency response. If you can set up a small rack under the stage with a door, they shouldn't have any problems replacing them or rewiring if needed. High quality cable is needed to get the signal to the amps and no cable runs near power wiring, definitely not parallel to power wiring. Make sure the amp(s) are well ventilated, too, even if they have a fan.
Would you say that 100 feet is fatal? I think we've been running 50 feet from an amp rack one side of the stage to the main on the other side. If I can go another 50 I can get the amps near the console. In case it's not obvious, I run sound there solo and had a major amp failure this weekend. Without someone to assist at the board it is really hard to run backstage and try to do an amp swap. I'm used to a studio environment where the gear is all close.
It can cause an amp failure IF THE CONDITIONS A RIGHT. An oscillation can occur and even though it's not always audible, things puke. It could have taken out your speakers, too. I loaned my Altec 417B speaker and guitar amp to a friend for a charity run one time and he called with the bad news- my speaker quit and it hadn't been running wide open (that would have been good for a visit from the police since the amp puts out 250W and is mostly midrange). Apparently, the amp had a high frequency oscillation and it melted the voice coil. It's nice to have the amp right next to you but the signal and system don't care what's convenient for you. What kind of amp went south?50' isn't usually the end of the world but I would look at the wire gauge and the connectors to see if there are any visible signs of trouble. Shorted wire strands on a plug or jack can cause ugly problems. I watched a pretty light show on the back wall of a club when the speaker output plug shorted on my '58 Bassman. When the short occurred, one of the tube sockets carbon traced and turned the tube into a light bulb. "I cut this piece four times and it's still too short."Edited 12/11/2006 9:10 pm by highfigh
Edited 12/11/2006 9:10 pm by highfigh
You're in the range where you possibly should be looking at a 70-volt system.
70V is fine but it has its own set of limitations, too. Powered speakers are another option. That way, if the signal is fed to them, separate power amps aren't even needed. If it my system to set up, I would place the amps closer to the stage. Low Z loses almost nothing at a distance like this.
"I cut this piece four times and it's still too short."
Just to put a little input into your basic question..you can run speaker cable big enough, that power loss is insignificant. Keeping the damping factor up requires a really low impedence cable run, so you are looking at 8ga to 6 ga stranded cable, but I think there is more than speaker cable issues here.
You don't say what the use of the system will be or whether it is temporary or permanant, but I can guess by your question that there really isn't a proper engineered design plan in place for this system.
Its been almost 40 years since I was in this business, and the basic rules haven't changed but most everything else has. One thing I did learn real well is that an improperly designed and installed sound system will not make you any friends. Dig around, ask around, you should be able to find some currently experienced help.
I have a little experience with this kind of thing. Its always better to legnthen the signal lines and shorten the speaker wires.