Tech crew blowing speakers too frequently...

[tenor_singer]

Originally Posted by DMXtools

A neat trick is to put a lightbulb in series with your tweeters. An 1156 (used as a back-up light on a lot of cars and available at most auto-parts stores) works well.
Tungsten (the metal the filament is made of) has a very low resistance when it's cold, and won't interfere with the signal at normal levels. However, its resistance rises exponentially as it heats up. Power levels large enough to damage the tweeter are also large enough to light the bulb, raising its resistance. Then the bulb (under a dollar) takes the brunt of the power surge and protects the speaker. Note that this is just for the tweeter, not the whole speaker system. If you mount the bulb where it can be seen from the booth, the sound tech can watch and pull back the gain if the light comes on. In four years of running these tweeter lights in four cabinets I've burned out one bulb and NO tweeters.

I am not an engineer by trade (I actually teach mathematics and physics at a high school). How would you go about doing this? Would this be something that I would be better off asking an experienced person to do? I am sure my one friend would help me, but I really don't like bothering him that much (he lives a good hour away from my school).

Thanks everybody for the information. Please keep it coming:D.

Tenor

[TimoteusR]

My non-scientific test say no DC will appear at the amp outputs when clipping. This was tested with a signal source, my mixer and a fluke 112 true RMS meter. I apllied the signal and tested for DC then I clipped the signal intenionaly by overdriving the preamp and checked for DC again. Clipping was verified with a piezo, and a rise in AC voltage. No DC was registered at any time

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Timoteus Ruotsalainen

[tenor_singer]

I will be editing this post as I find more information about my equipment from our TD.

SPEAKERS:

I have EV Sx300 speakers.

I am not a sound engineer, so I have found EV's engineering specs on the net. Here is the web page:

http://www.electrovoice.com/electrovoice/EVfiles.nsf/lookup/Sx300_EDS/$File/534694.pdf


AMPLIFIER: Samson S1000

Rugged stereo and mono-bridgeable power amplifier

Produces 500 watts per channel into 4 ohms (stereo mode) and 1000 watts into 8 ohms (bridged mono mode)

Linear frequency response for exceptional audio performance

Dual temperature-sensitive, speed-controlled fans

Stable bipolar design

Front panel input level controls with 42 detents

3-segment output LED metering

Dual protection LEDs and relay-controlled outputs linked to protection LEDs

Banana jack outputs with Speakon(tm) connectors

XLR inputs and locking TRS inputs

Parallel outputs to "daisy-chain" a number of amps together

MIXER:

I have a Behringer Eurodesk MX2442A

Channel inputs 24
Mono channels 16
Stereo channels 4
Subgroups 4
INVISIBLE MIC PREAMPs 16
EQ (mono channels)
High, low, 2 x semi-parametric mids, low-cut
3-band
EQ (stereo channels) 4-band
Aux sends 6
Stereo aux returns 2
Channel inserts 16
Talkback mic internal
Phantom power +48 V

OUTBOARDS:

I am not sure what this is. I do not have any inserts or sub-inserts other than a feedback destroyer.

MICROPHONES:

I use audio technica boundary microphones (3... l-stage, c-stage and r-stage). I keep the center up only unless the action moves to l or r stage.

I also use audio technica wireless uhf microphones (10 - 16 depending on the show). I am not sure of the specs, but they are not programable (again... a very poor school district).

CABLING:

Um.... my sound engineering friend got it for me and said plug it there and there. That is all I can say. It is a heavy gauge wire, though with speaker easy ends (at least that is what a sales person told me they were)...

POWER:

I run my sound system off of a 20-A breaker that feeds 7 different outlets around our gymnasium.



Thanks again for the help.

Tenor

[TimoteusR]

Is your amplifier a Samson S1000?
http://www.samsontech.com/products/p...D=77&brandID=2


If it is i suggest you run it with the following configuration:

The amp will only about 340W per speaker (according to the 2xRMS rule 480W would be minimum). Underpowering speakers makes it easier to clip the amp when trying to get more volume. Just run one speakon cable to each speaker and connect on speaker per amp channel. If you run a stereo signal to the amp you can use this setup with pannings.


When using the setup make sure that your gain structure is good. Also make sure that the CLIP light on the amp (it's the third light from left to right on the amp face) isn't flashing (and flashing on every kick drum hit is very bad). This light tells you the amp is clipping. In other words your trying to make the amp provide more than it can.

I wonder if Samson uses one power supply for both channels. If so you could use a trick that I learned from Dave Rat of RatSound. It can be found on LAB. I think it's called "Fighting for power". Basicly you reverse polarity on one of the input signals and reverse it again on the output. This way the L channel will pull "+" power while the R pulls "-" power. It supposedly gives greater headroom. At least the description sounds good.

Whatever you do, be sure to document everything carefuly. You could even make a drawing with every component and how they are conneted together. This helps troubleshooting.

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Timoteus Ruotsalainen

[TimoteusR]

I'll give you some basic sound info on your setup.

First of all. The mixer has a 3 band EQ for mic channels (1-16). It has hig,mid and low bands. The high band is at 12khz and the low band at 80hz. The middle on has two knobs. The top one controls the amoun of boost or cut (from -15db to +15db). The bottom one controls the frequency between 100hz and 8khz. So if you want to cut 4khz turn the frequency knob to the middle and the cut/boost knob to 9'o clock to cut the frequencies. Stereo channels (17-24) have 4 band EQ. They have the same high and low frequencies at 12khz and 80hz. they also have a high-mid band at 3khz and a low-mid band at 500hz. These work just like the high and low eq's on the mic channels. Turn left to cut or to right to boost at the frequency printed on the mixer. Just remerber cutting is always better than boosting. If you need to boost highs you could try lowering the lows and boosting overall volume. In addition to the eq's your mixer has a low-cut filter at 75hz. What it basicly does is cut all frequencies under 75hz by a certain amount. This filter should be enabled on at least vocal mics. If you are using only the sx300 (no subs or other speakers) I would enable it on everything except for drums/bass and maybe piano.

Your mixer is advertised to have 6 auxes but in reality only 4 can be used at the same time. auxes can be either pre- or post fader. That means the send is either taken before (pre) or after (post) the channel fader. Prefade send are used for monitors. This way adjusting the faders will not affect the monitors (if run from FOH). Postfade sends are used for effects. On your mixer 1-2 are switchable either pre/postfade and auxes 3-4 (and 5-6)
are permanently postfade.


Remember amps DON'T HAVE VOLUME CONTROLS. They are called sensitivity controls. They control how much input is needed to drive the amp to maximum output.

I'll post a guide for setting proper gain structure later.

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Timoteus Ruotsalainen

[tenor_singer]

Timoteus,

Thank you for all of your information. I really wish that my theater background was in technical theater. I truly feel as though I am guessing every time I set up my sound system and light system and many of the explainations here today are right at that threshold of my understanding.

To be honest, when I get equipment I take a couple thousand dollars (which is the result of two to three years worth of fundraising by my students) and tell my TD friend not to spend more than that and to use his head with purchases. He was the one who bought me the system I described earlier.

I think next year I will have people from area colleges come in and give inservices to my tech kids. They're great boys and girls, but their knowledge has been hampered by my lack of knowledge.... which pretty much amounts to plug that there and there and don't ask why because I don't know... lol. As a teacher this truly upsets me because I am failing at my job of showing them the true approach to technical theater. However I can block the hell out of a show.

Again thanks!


Tenor.

[TimoteusR]

Tell your TD friend that he did a great job ;) If budget is 2K$ then the system you have is pretty good, actually really good considering you have 3 boundry mics + wireless. If I were to upgrade something it would probably be the power amplifier. Used rocks in power amps. you can get more out of those speakers (you can almost double the power going to them) if you want. And when buying remember. Buy what fits your budget and gets the job done period. If you don't need something at that time (like more power) don't buy it.

I'm writing a guide right now. It's about 2 pages long already. If you like it you can use it as a guide if you mention my name somewhere in the material ;) It's even custom made for you. lol

Make sure the college kids don't abuse your system. Many people in this industry feel that Behringer sucks. It does if used in wrong places (pro audio) but in your case it's perfectly good.

If you don't understand something please ask. there are no such things as stupid questions. As a teacher you must have same kind of situations with your students as you're having right now ;) maybe you can learn something.

And i'm pretty confident the only way to learn this stuff is to do it. Take you students and put the system on, lower the main faders a little so the volume won't be overwhelming if you mess up. Then take the manual and start trying different things. Have one of your students talk to a microphone (they can take turns doing whatever they like. Maybe imitating a sports game or singing or telling jokes. play with the eq's. one of the students might have a minidisc player which you can use to record the practices ;) they might enjoy it.

And remember if things go wild and you don't know what to do, just shut down the power amp from the front switch.

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Timoteus Ruotsalainen

[TimoteusR]

Ok I have waaaayy too much time ;)

Here's a small guide for setting up your system. If ControlBooth wants to use this somewhere (maybe a general guide *hint, hint*) you are free to do so as long as i get credit. This goes to all other previous post in this thread.

If your setup doesn't change you shouldn't have to do this more than once. Make sure the amps are turned off and the feedback distroier is unplugged. Remember how it was plugged in case you want to change back to that setup. If you just want to test the gain structure you can skip the microphone part.


Let's start with your microphone's. I can't comment on the boundary mics other than test different setups. Try moving them around a little. Or try adding a plexiglass sheet under them and hanging them. If it's possible try and locate the wireless receivers near the stage. If you can position them on either SR or SL (stage right or stage left). Them use line level cabling to go back to your mixer. You can still plug them into the same channels. Just use the "Line in" jack located near the "mic input" (it's the middle jack). Then activate the Low-cut filter on every channel (as your not using any sources with low frequency content this will also clear up some of the stage wash). You could also play with completely turning down the low eq's (at 80hz) if your only using vocals. Remember if it sounds goo it IS good.

If you have headphones you can connect them to the mixer to monitor the signal there (these are optional). Connect headphones to ?headphones 1? jack in the master section (where connectors are, it should be labeled). Make sure ?mon/ctrl? is on and all others (turn the phones volume off) are off in the phones section. Make sure that in the mon & ctrl room section all buttons are off and the pot is at 12?o clock.


Now turn all other microphones off except for one. I'll use SL boundary mic. Turn all controls on that channel to 12'o clock position except the aux sends. Turn the Aux sends completely off (fully CCW, counterclockwise). Make sure that "Mute", "1-2" and "3-4" buttons are in their off position (up, not pressed). Make sure "Main mix" is on. Now ask another person to go to SL and talk to the mic. You could also borrow a boom box and use that if you can't find a person willing to talk while you tweak. Press the "Pfl/solo" button on your mixer. Then make sure the "Channel mode" button in the master section (Solo section on the left) is in the up position (pfl) and the level button is pointing at 12'o clock. Turn both the channel fader for your mic and the and the master faders down. Now with your person talking on stage (or boom box) start turning the "Gain" button on your channel strip clockwise. The left meter in the channel section should show signal. Keep turning the "Gain" until the peaks are hitting the lower red area or your channel peak led starts to flicker. This is the most level you can get from the mic pre without clipping. If you have headphones, you can turn the volume up (in the phones section) careful and hear what the mic picks up. If the person were to go closer to the mic and start screaming you would see your peak leds light. If the peak leds start lighting you need to back off on the ?Gain? to compensate for the higher level the mic is sending. Press the channel ?Pfl/solo? button to turn it off. Now turn the master fader to 0db. Put the channel fader somewhere around 0db now your mixer should be outputting the best signal possible. You should be seeing movement in both of the main meters.

Next you can connect your mixer to the power amp. Make sure the amp is off. Run two XLR (round plug with three prongs) cords to your amps (one left and one right) inputs. They are the upper jacks have the text ?balanced 0dbm? next to them. If the current cables are guitar cable ( 1/4? plug, look at the plug if it has 2 sections it is a TS cable, Tip Ring, and if it has 3 sections it is a TRS, Tip Ring Sleeve cable) you can use them. If you have TS cables you might want to upgrade them at some time to TRS or XLR cable (XLR cable = mic cable). Make sure the switch on the back is set to the middle position (stereo). The bridge position will make amp sum both Left and right power amps into one amp. If you bridge the amp you have to use both of the ?+? sides to feed your speakers (don?t ask why, If you wan?t to read LAB has a pretty good explanation). The parallel setting will feed both amp sections from one signal. This way you only have to run one cable to the amp if you want mono. Set the front panel controls all the way CCW (counterclockwise, the amp will be least sensitive in this setting, It will need more input signal to achive the full power at output). Turn the mixer?s main faders off. Turn the power amp on. Slowly turn up the master faders to 0db. Now you should hear the person on stage speaking into the microphone from your heaphones and from the speakers. Now turn the amp's sensitivity control slowly clockwise until you reach the desired volume. Make sure the CLIP light on the amp never lights if i does light that means it's time to back off on the main faders at your mixer

Now you should have one mic working as I should be. Just repeat the mic procedure for all your mics. Here it is once again in a shorter version:

1. Choose a channel
2. Turn all controls to 12?o clock (auxes off)
3. PFL the channel
4. Adjust gain until the yellow leds are lighting on peaks (maybe one of the red leds sometime)
5. release PFL
6. raise channel fader.

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Timoteus Ruotsalainen

Finland

[TimoteusR]

Here are some links to basic stuff on audio:

http://www.churchsoundcheck.com/mag820.html
http://members.cox.net/pasystem1/noframe.htm
http://www.prosoundweb.com/studyhall/ab_index.php
http://www.prosoundweb.com/studyhall/sr_index.php
http://www.soundcraft.com/palz.asp
http://www.prosoundweb.com/studyhall/ci_index.php



http://www.prosoundweb.com/live/arti...mptricks.shtml

you can try the above amp trick if you want. Dave Rat's test amp showed about a 14% rise in power with this. I have confirmed with Samson that their amp uses one power supply for both channels so this should work fine. If you want to try it, you need a "speakon polarity reverse" cable and a "XLR or TRS polarity reverse" cable. If you show the article to your TD friend he'll know what you mean.

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Timoteus Ruotsalainen

[Nephilim]

Originally Posted by TimoteusR

Basicly you reverse polarity on one of the input signals and reverse it again on the output. This way the L channel will pull "+" power while the R pulls "-" power. It supposedly gives greater headroom. At least the description sounds good.

Modern amps are supposed to do that by default, at least switchmode amps do. The reason you get "zero point crossing" distortion with those (except class I from Crown) is because the switching between the + and - power reservoirs can cause tiny glitches in the signal. I don't recall is AB class amps split like that also.