What is this strange adapter?

[fx120]

I'll admit that it's stupid, that I, the electrical engineering student, would let myths of my early theatre days get the better of me and electricity is still electricity, be it for a power cord or an audio signal. It's probably never been an issue (at least for me and the people I regularly work with) been because the likelihood of messing around with the TS connectors while pumping a loud signal into the speakers is rather low.

Still, getting shocked being possible, how did 1/4" TS connectors ever make it to market for amplified signals? Especially given how most of them even have metal jackets to them. (to which now that I think back, I do remember a couple occasions getting shocked by these connectors)

Back before the days of the NL4, there weren't a whole lot of other options.

Some of the larger shell Cannon connectors were around in both three and four position, but the cost was high and they were physically large and clunky connectors. XLR's were used as I described in my previous post but were probably dropped in favor of the 1/4" TS to avoid confusion with mic level connections also coming off the stage.

You've also got to keep in mind that in the early days amplifiers were at a practical limit of 60W, voltages were lower and cable gauges were smaller. 1/4" connectors were a convenient and available connector that was fairly inexpensive.

So it became standard, and has just stuck around as power has increased and loads have gotten more demanding.

 

[rwhealey]

I had the pleasure of using god-awful two prong Hubbel mini-twistlocks as speaker connectors where I worked last. They would never quite work right and were completely incompatible with everybody else's equipment.

I ripped them out and replaced everything with Speakons.

Really, I think the devil made that connector just to torture sound techs...

 

[MNicolai]

Alright, devil's advocate. I'm in a bind and really need a speaker cable but I've run out of them and all of audio shops are closed. I have these old extension cords laying around with the connectors crapping out and some spare 1/4" TS connectors floating around. Is there any reason not to just slice the ends off and solder 1/4" TS connectors?

 

[fx120]

Alright, devil's advocate. I these old extension cords laying around with the connectors crapping out. Is there any reason not to just slice the ends off and solder on NL4's, bananas, or 1/4" connectors?

Most of our 12 and 14 AWG NL4 speaker cable is just 4 conductor 300V SJEOOW Seoprene of the kind you'd normally use for A/C mains.

Of course all of our AC mains cable is 600V SOOW or SEOOW.

 

[derekleffew]

Back before the days of the NL4, there weren't a whole lot of other options.

Some of the larger shell Cannon connectors were around in both three and four position, but the cost was high and they were physically large and clunky connectors. ...

Before Speakon, most professional shops used P4, P6, or P8 connectors, and some still do.

RapcoHorizon | Cables>Speaker>Multi Channel

 

[fx120]

Before Speakon, most professional shops used P4, P6, or P8 connectors, and some still do.

RapcoHorizon | Cables>Speaker>Multi Channel

Oh, believe me I know. I've got a stack of 4 conductor cable sitting upstairs.

If my memory serves me they were known as the P-series back in the day, and started out as a 3 position connector suitable for use with microphones. I haven't seen them on any gear dating back past the early-80s however, but I have seen Altec horns from 1968 with 1/4" connectors on them.

 

[zuixro]

One of my friends thought he found an Edison to BNC adapter. It turned out to be something else later though.

 

[epimetheus]

Texas A&M, College Station uses 4-pin XLR for all their speaker runs. Some of the bigger boxes (subs, larger mids & tops) have speakon, but 90% is 4-pin XLR, or at least it was when I attended several years ago.

 

[Footer]

Still, getting shocked being possible, how did 1/4" TS connectors ever make it to market for amplified signals?

You have to remember, this was the same time this thing was being dragged around the country...

I did not matter if it was the best connector for the job. They had a ton of them laying around because every guitar and amp had that connector. 1/4" is a horrible connector to use for an amplified signal, hence the reason everyone has been trying to replace it with better solutions.

 

[SHARYNF]

A lot of us back in the late 60's-70's wound up using two prong twist locks. The xlr'sat that time called Cannon connectors (after ITT cannon) would not accommodate the awg wire for a speaker. Amps were more than 60 watts, most folks were using Crown DC300's and a few of us Phase Linear 700s so the power level was reasonable. 1/4 were just too unreliable in the pro world (remember if you had a failure you had to climb up that "wall of sound"

Sharyn

 

[rwhealey]

Alright, devil's advocate. I'm in a bind and really need a speaker cable but I've run out of them and all of audio shops are closed. I have these old extension cords laying around with the connectors crapping out and some spare 1/4" TS connectors floating around. Is there any reason not to just slice the ends off and solder 1/4" TS connectors?

This is fine as long as you but 1/4" on both ends. Better if you have Speakons sitting around. You're wasting one conductor, but if you need it now, you need it now.

Just NEVER make an adapter that could connect a speaker cable to AC mains.

 

[FMEng]

Audio guru Rick Chinn has some great pictures of AC plug to audio adapters on his Uneeda Audio website. He has a lot of great stuff there. It's worth spending some time reading.

PZM Modification kit, Phantom Powering, Attenuator Pads, All Things Audio

 

[jared555]

Honestly the likely reason is your teachers don't know what they are talking about in this instance.

Consider say a "1000w" amp driving say a 4 ohm load. Say you have 400w RMS being drawn. By Ohms law, you have 40V and 10A (both RMS). Change this to an 8 ohm load and the voltage goes up to 57 volts. Make it 800w and 8 ohms and you get 80 volts.

Derivation: P=v^2/R so V=SQRT(P*R).

Making sense?

If you have a 400w at 8 ohm amp does it put out 400w or 200w at 16 ohms (is there a point where the output stabilizes?)

Human skin typically has a resistance of 1,000 to 100,000 ohms. I think 1,000 is wet and 100,000 is dry although it may be lower for wet. So unless you have broken/burnt skin or are sticking the plug in your mouth I would think the resistance would be high enough to limit shock potential.

Not that I am saying that there isn't a slight chance of it happening (I wondered this myself at one point) but I have a feeling you are a lot more likely being shocked by a faulty ground connection.

 

[fx120]

This will probably freak some people out:

Yes, they came from the factory with a L14-20 twist lock on the back, and no they're not powered.

 

[avkid]

That was fairly common up until Speakon connectors became common.

 

[Chris15]

If you have a 400w at 8 ohm amp does it put out 400w or 200w at 16 ohms (is there a point where the output stabilizes?)

Neither. It's not a simple relationship. The source impedance is the main factor, but just assume it's not linear. Take for instance a lab.gruppen FP14000. At 2 ohms it's rated to 7000W/ch, at 4R, 4400W, 8R, 2350W, 16R, 1200W.

Human skin typically has a resistance of 1,000 to 100,000 ohms. I think 1,000 is wet and 100,000 is dry although it may be lower for wet. So unless you have broken/burnt skin or are sticking the plug in your mouth I would think the resistance would be high enough to limit shock potential.

Not that I am saying that there isn't a slight chance of it happening (I wondered this myself at one point) but I have a feeling you are a lot more likely being shocked by a faulty ground connection.

You start to feel a tingle with about 1mA of current. If you've got wet skin, this is going to occur at a mere 1V. At 10-20 mA, you experience muscular contraction and can't let go. 10V at worst, 100V at best, normal being somewhere in between. With AC, a current of 60mA can cause ventricular fibrillation. With wet skin, ie. 1k ohm resistance, 60V can cause this...

So yes, it's very much possible...

 

[jared555]

Neither. It's not a simple relationship. The source impedance is the main factor, but just assume it's not linear. Take for instance a lab.gruppen FP14000. At 2 ohms it's rated to 7000W/ch, at 4R, 4400W, 8R, 2350W, 16R, 1200W.



You start to feel a tingle with about 1mA of current. If you've got wet skin, this is going to occur at a mere 1V. At 10-20 mA, you experience muscular contraction and can't let go. 10V at worst, 100V at best, normal being somewhere in between. With AC, a current of 60mA can cause ventricular fibrillation. With wet skin, ie. 1k ohm resistance, 60V can cause this...

So yes, it's very much possible...

I was basing it off of a linear relationship, so yes I definitely think it is possible (I did before but after doing some calculations thought I must have been wrong about it being possible)

 

[dafunkmonster]

It only takes 100mA to kill you. Once your skin burns through, your body has an internal resistance of roughly 500ohms. Muscle paralysis happens at 20mA, breathing stops at about 50-75mA.

Now, 100mA through your hand (thumb to pinky) probably won't kill you. It will hurt like a b***h and result in injury, but it probably won't kill you. However, 100mA through your heart will kill you...or your brain...or anything else vital.

Problem with electricity is...you can't control where the current flows, nor can you predict it.

Also, lethality partially depends on frequency. AC is dangerous, because it induces muscle contractions and sweating, and 60Hz is in the most dangerous range. As little as 25V @ 60Hz can kill you. However, people have survived 40,000V at a million Hertz.

Bottom line is...don't lick cable ends.

And always do green first.