Members Unalaska Posted March 30, 2015 Members Share Posted March 30, 2015 I had one of those moments last night where I'm glad I properly power my system. Ironically it was a benefit for a fellow sound guy who passed a way a few weeks ago (he worked a lot of shows for me in the last 8 years). the short story is I used a splitter snake with the box by the drum kit. I sent L/R down return 1/2 and patched into ch15/16 on the mon split. Took 15-16 and patched to the amp rack. I have no clue why but the instant I plugged in the left side it sent full on noise to the amp rack and board. Scared the hell outta me and the others there. Using amps rated a bit below RMS means (most likely) nothing got damaged. 3db more power and it would have been a bad night. Amps went into DDT immediately, I don't know what the qsc CX amp on HF did. the culprit was using the AC closest to FOH for board power. After this I ran 75' of ac and powered it off the same circuit as monitor world. So that's the second lesson. Oh well. Link to comment Share on other sites More sharing options...
Members Crownman Posted March 30, 2015 Members Share Posted March 30, 2015 I had a guy ask me to help him sort out his system and suggest some things. Then he completely ignored everything I said. At his next gig, after he had it all hooked up, I sat and watched him turn on the board, no problem, turn on the 2 RMX5050's run bridged and turn them all the way up, AND THEN...... he turns on the Driverack and BOOM....... All subs blown. HAHAHAHAHAHA dumbass. He had two 4 ohm double 18 cabs loaded with Black Widows (the 2400W peak version) and had a 5050 bridged on each one. He immediately looked over at me. I took the last gulp of my drink and walked out without saying a word. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted March 30, 2015 Members Share Posted March 30, 2015 Did the limiters kick in? Link to comment Share on other sites More sharing options...
Members Gregidon Posted March 31, 2015 Members Share Posted March 31, 2015 It's funny. Someone over at "another forum" just posted a similar topic about the value of properly sizing your amps, stating damaged high frequency drivers. You can read it for yourself, but the consensus is that no limited is fast enough to protect against the first cycle (I'm not sure this is true and there isn't really a reason why it has to be true, Aged?). It's great that people seem to be coming around to reality! Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 31, 2015 Members Share Posted March 31, 2015 Limiters in general need to be slow enough not to modulate or pump on the low frequency material, where the DC control voltage from the detector to the VCA remains DC enough. If the time constant of the CV filter is too low, the resulting ripple modulates the VCA and the gain cell goes up and down with the ripple. As you increase the time constant, the ripple goes away at the expense of the high frequency response time, because it takes several to tens of cycles at high frequency to build up the CV. It's a total compromise, though in powered speakers, these parameters can be optimized within DSP in ways that we can't do external (to any practical matter) "Massive Signal Events" are where being somewhat conservative can mean the difference between total failure and being able to go on intact. In house systems that get used day after day, maybe 200-250 event days a year, each event day is an opportunity for an accident. After 10 years (2000-2500 event days), a properly sized and protected house system is likely to remain fully functional which represents a significant value to the owner given the cost of such a system. My house system ran for over 10 years without a single failure, even when being exposed to "wildcard" inputs, "wildcard" engineers, etc. It makes going to work less stressful when you know the system is robust and reliable and all you have to do is worry about things that are out of your control. Link to comment Share on other sites More sharing options...
Members Unalaska Posted March 31, 2015 Author Members Share Posted March 31, 2015 I also read Ivan's post, mostly dealt with matching HF amp to HF drivers. I'd really like to know what expensive mistake led to this new position on power. Link to comment Share on other sites More sharing options...
Members dboomer Posted March 31, 2015 Members Share Posted March 31, 2015 His recommendation is simply to use an amp rated at the "program power" of the speaker. Same as almost every speaker manufacturer. Nothin new here. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 31, 2015 Members Share Posted March 31, 2015 ... with proper attention paid to things like high pass filtering, and not driving the piss out of the speaker. ie. using common sense, which is somewhat uncommon these days. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted April 1, 2015 Members Share Posted April 1, 2015 Lets talk about a series cap on compression drivers to stop DC and low freq pulse? I have noticed the self powered loudspeakers have no series cap...what are they doing on the amp side to add this protection or not? Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 1, 2015 Members Share Posted April 1, 2015 The amps on the powered speakers generally have the protection built into the amp. The power on/off muting, DC offset protection that shuts down the PWM signal almost immediately, etc. Much better than using a series cap. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted April 2, 2015 Members Share Posted April 2, 2015 Ah ok except the QSC153's I have out in the garage dumped big time DC on the compression drivers and smoked them.A series cap would have saved the diaphragms. I can measure the rail voltage on the high outputs. 35VDC iirc. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted April 2, 2015 Members Share Posted April 2, 2015 But then again an amp can dump the rail voltage on the woofer and poof. I am sure they have worked it out with the poweredloudspeakers. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 2, 2015 Members Share Posted April 2, 2015 The QSC's that you have are much older and are based on an older amp design than the K's and KA's and such. Link to comment Share on other sites More sharing options...
Members Dogoth Posted April 5, 2015 Members Share Posted April 5, 2015 Lets talk about a series cap on compression drivers to stop DC and low freq pulse? I have noticed the self powered loudspeakers have no series cap...what are they doing on the amp side to add this protection or not? Doesn't the series cap increase the slope of the crossover? I've seen cheap speakers where a cap in series is the ONLY crossover (6db per octave I think). I guess if the cap is big enough to filter frequencies well below the already in place crossover (be it active or passive), it's just another safety from DC or lower freqs. I'd think it could add some small phase issues though. Am I off base here? Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted April 5, 2015 Members Share Posted April 5, 2015 Example. I have a set of Altec compression drivers I want to xover at 500hz . I put a series cap that yields a 250hz xover/ 6db slope.This is just a DC blocking cap. It does effect phase shift +90 degrees I believe? A wide open compression diaphragm with noprotection can cost you some money you dont need to spend. This is a driver you plan to use an active filter with.You would use your active xover to get the 500hz at whatever slope you choose.Aged simply stated the new power amps in powered loudspeakers have protection for the compression driver.Of course in a passive design there is a series cap on the compression driver by default.A series cap with an inductor in parallel or what they call shunt will yield a steeper slope from 6db to 12db per octave. Link to comment Share on other sites More sharing options...
Members Audiopile Posted April 5, 2015 Members Share Posted April 5, 2015 A wide open compression diaphragm with no protection can cost you some money you dont need to spend. I recall "back in the day" I commonly used motor start caps in series on compression drivers involved with multi-way systems running active crossovers. I believe I used Mallory brand. As I recall with 16 ohm compression drivers, a 10 uf (microfarad) cap in series started rolling off at a -6dB/octave slope at approx. 1 KHz... 20 uf started rolling off at approx. 500 Hz. I used the motor start caps because (as I recall) they were commonly available at a reasonable price compared to a replacement 2441 diaphragm and had a suitable voltage rating. Link to comment Share on other sites More sharing options...
Members Audiopile Posted April 5, 2015 Members Share Posted April 5, 2015 Concerning using caps for HF driver protection: I just dug out some old notebooks to check-up on myself and my previous post to see if my memory has completely gone to pot or not, and found my notes on capacitor value sizing relative to a driver's resistance and desired crossover frequency... which sparked a question I had decades ago but never discovered or figured out the answer. Question is: Part of the formula includes the constant 6.283, which happens to be as close to 2 times pi as you can get with three decimal places. Coincidence or is there a reason? I always figured sine wave AC is arguably rotational energy converted to electrical energy... or a sine wave is rotation plotted vs. time and maybe that somehow ties into the seeming coincidence. Link to comment Share on other sites More sharing options...
Members dboomer Posted April 5, 2015 Members Share Posted April 5, 2015 Adding a cap is another trade off situation. It gives you a small amount of protection in trade for some sonic artifacts. It really only protects you from dc which I've never had a problem with in over 40 years of building sound systems. There is also some protection from plugin in incorrectly, which you'll never have to worry about with self powered speakers or properly setup amp racks. It's easy to build those so there is no chance of plugging in incorrectly. And yes, it will cause some phase shift. Not a simple 90 degree "group delay" so it will mess with an advanced setup using a DSP. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted April 5, 2015 CMS Author Share Posted April 5, 2015 Concerning using caps for HF driver protection: I just dug out some old notebooks to check-up on myself and my previous post to see if my memory has completely gone to pot or not, and found my notes on capacitor value sizing relative to a driver's resistance and desired crossover frequency... which sparked a question I had decades ago but never discovered or figured out the answer. Question is: Part of the formula includes the constant 6.283, which happens to be as close to 2 times pi as you can get with three decimal places. Coincidence or is there a reason? I always figured sine wave AC is arguably rotational energy converted to electrical energy... or a sine wave is rotation plotted vs. time and maybe that somehow ties into the seeming coincidence. 2*pi is also called "Tau" and is the ratio of a circle's circumference to its radius. So yep, it all relates nicely with AC current. Link to comment Share on other sites More sharing options...
Members Audiopile Posted April 6, 2015 Members Share Posted April 6, 2015 2*pi is also called "Tau" and is the ratio of a circle's circumference to its radius. So yep, it all relates nicely with AC current. I figured that, but how? I understand that the charge is built and discharged sinusidolly, maybe roughly 90 degrees phase shifted current to voltage flow wise... not too sure how that happens and in what order? And how does the relationship of a circle's diameter to it's circumference figure into this? Cool stuff to me... but then school was tough for me as I personally had to understand how to derive the formula to understand (and pass with something that passed for a passing grade), and never did well at memorizing formulas and plugging and chugging well enough to "pass" otherwise. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted April 6, 2015 Members Share Posted April 6, 2015 I remember back in like 83 I was on the road full time and a BE for a midwest rock act at that time. I remember we had been on the road for a few days and got to a venue and a few of us were setting up and one of the guys (not me!) plugged the what was to be plugged into the double scoop into the JBL 2440 driver/horn. After everything was setup I wanted a drum check. Gimmie kick please I said...and POP. Shattered that diaphragm and we had to have one shipped to us. Costly mistake but a series cap would have saved the day. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 6, 2015 Members Share Posted April 6, 2015 Zc=2xPixFxC That's where 2Pi come into it. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 6, 2015 Members Share Posted April 6, 2015 I remember back in like 83 I was on the road full time and a BE for a midwest rock act at that time. I remember we had been on the road for a few days and got to a venue and a few of us were setting up and one of the guys (not me!) plugged the what was to be plugged into the double scoop into the JBL 2440 driver/horn. After everything was setup I wanted a drum check. Gimmie kick please I said...and POP. Shattered that diaphragm and we had to have one shipped to us. Costly mistake but a series cap would have saved the day. Maybe, or maybe not. They were mostly used for DC offset protection. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted April 7, 2015 Members Share Posted April 7, 2015 Zc=2xPixFxC That's where 2Pi come into it. I always just use 1000000/2Pi = 159000, real easy to remember on the calculator pad if you think about it . This lets you guesstimate things like: R(ohms) = 159000 / ( F(hz) x C(uf) ) F = 159000 / ( R x C ) C = 159000 / ( F x R ) Real easy to remember that you just divide 159000 by the two knowns to get the unknown . Close enough to estimate 3db points, I suppose one should tweak that a bit for the 90 degree phase shift, I never bothered as I used more precise methods if precision was needed... Link to comment Share on other sites More sharing options...
Members Audiopile Posted April 7, 2015 Members Share Posted April 7, 2015 Zc=2xPixFxC That's where 2Pi come into it. I was curious of the physics as to why 2pi? Link to comment Share on other sites More sharing options...
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