Post by: jack smith on September 30, 2009, 01:40:18 PM
I listened to you guys when you said that even though I set the gain structure and don't exceed 0db on the mixer, I might need to run the vu meters into the yellow lights in order to get the right voltage for the amplifer to give out the power its supposed to.
Post by: Whit Hutchinson on September 30, 2009, 01:57:29 PM
If you have another outlet on the same circuit, you can insert the leads as the system is playing near full volume and see if you are having large voltage dips. I don't think you guys suffer from that as much as we do here in the US.
You silly UK people with your stiff voltage supplies
Edit:
And I just realized that you are trying to check the voltage from the speaker terminals. You will need to set it to something in the 100v to see the speaker output terminal voltage. Be sure to select the AC voltage selection as well when testing speaker output.
Post by: Mike Christy on September 30, 2009, 02:42:33 PM
If your measuring the output of the amplifier and not the AC wall socket the 200V AC setting will be fine. Use the AC setting, not DC as when you measured the battery.
To get an accurate reading it is best to test with a steady state test signal, such as a sine wave, not program or pink noise material. One usually does not do this with the speakers connected either - so this will cause you a problem if your trying to see if your mains are stiff enough - Im kind of confused at what your testing is to accomplish.
Your meter will measure the AC RMS value of the signal. Multiply this value by 1.414 to calculate the peak value. To see the full output voltage swing at the amp output terminals apply a test signal at the amp's sensitivity voltage as measured at the input, RMS.
edit: And if your meter only supports line frequencies, you will only be able to test at 50Hz/60Hz.
Mike
Post by: jack smith on September 30, 2009, 07:43:30 PM
| Whit Hutchinson wrote on Wed, 30 September 2009 12:57 |
And I just realized that you are trying to check the voltage from the speaker terminals. You will need to set it to something in the 100v to see the speaker output terminal voltage. Be sure to select the AC voltage selection as well when testing speaker output. |
My multimeter doesn't have a 100v setting. Here's a picture of it :
http://www.diy.com/diy/jsp/bq/nav.jsp?action=detail&fh_s econdid=9288723&fh_view_size=10&fh_location=%2f%2fca talog01%2fen_GB&fh_search=multimeter&fh_eds=%C3%9F&a mp;fh_refview=search&ts=1254353708844&isSearch=true
As you can see, on the AC side, its only got 200v and 600v, while on the DC side its got 2v, 20, 200v and 600v.
I want to find out the voltage going to my speakers because I want to make sure that the correct line voltage is going to the amplifier to produce the output its rated as giving out. I've seen on the Crown K2 data sheet that it says it has a voltage gain of 23.88db at 1.4 volts sensitivity and 25db gain at 3.0 volts sensitivity. I'm not sure what that means, but I know if I dont put enough line voltage into the amplifier, I wont get as much volume as I could safely get without clipping the amplifier.
Post by: Art Welter on September 30, 2009, 08:25:04 PM
| jack smith wrote on Wed, 30 September 2009 17:43 | ||
My multimeter doesn't have a 100v setting. Here's a picture of it : http://www.diy.com/diy/jsp/bq/nav.jsp?action=detail&fh_s econdid=9288723&fh_view_size=10&fh_location=%2f%2fca talog01%2fen_GB&fh_search=multimeter&fh_eds=%C3%9F&a mp;a mp;a mp;fh_refview=search&ts=1254353708844&isSearch=true As you can see, on the AC side, its only got 200v and 600v, while on the DC side its got 2v, 20, 200v and 600v. I want to find out the voltage going to my speakers because I want to make sure that the correct line voltage is going to the amplifier to produce the output its rated as giving out. I've seen on the Crown K2 data sheet that it says it has a voltage gain of 23.88db at 1.4 volts sensitivity and 25db gain at 3.0 volts sensitivity. I'm not sure what that means, but I know if I dont put enough line voltage into the amplifier, I wont get as much volume as I could safely get without clipping the amplifier. |
Jack,
As has been pointed out, voltage readings on music will not tell you much, you need to use sine wave tones, which can burn speakers up rather quickly.
Running the amp without a load won't load the mains down.
As well as checking the mains voltage with the meter to check for voltage drop, a regular house lamp plugged in on the same circuit with the amp will dim if there is instantaneous voltage drop.
Post by: Don Ernst on September 30, 2009, 08:35:33 PM
Post by: Ivan Beaver on September 30, 2009, 10:35:20 PM
| jack smith wrote on Wed, 30 September 2009 19:43 |
[I want to find out the voltage going to my speakers because I want to make sure that the correct line voltage is going to the amplifier to produce the output its rated as giving out. . |
First of all you are talking about two different (or more) things.
The gain of the amp is fixed in the the two positions-the AC voltage does not change that.
If you find that your AC mains are not high enough-what do you plan on doing about it? There is nothing you can do-except use larger AC cables and possibly tie in power (not recommended for you).
And if the voltage is low coming to the building-well then that is the way it is-deal with it.
There is no way you will be able to measure any type of output voltage with that meter (it is not fast enough)-unless it is sine waves and right around 60Hz. And if you try to put sine wave to your loudspeakers at full power-you can kiss them goodbye.
Post by: Whit Hutchinson on September 30, 2009, 11:23:54 PM
Completely overkill and at the venue's expense of course.
Post by: jack smith on October 01, 2009, 03:53:10 AM
Post by: Ivan Beaver on October 01, 2009, 07:41:03 AM
There is nothing you can do-or nay setting you can make that will allow you to get more level out of your system-that is determined purely by the cabinets used and the amplifier power.
But you can make the quiet moment quieter-by lowering the noise floor. I get the impression there are not many quiet moments during your events.
Why bother measuing the input voltage-it is what it is and you can't do anything about it.
And if it is a little bit low-I really doubt you will be able to tell if you are not getting full power to the loudspeakers. It would only be a couple of dB at most.
Don't waste your time on things you cannot do anything about.
You can't "make sure" you are getting the proper voltage.
What are you going to do-call up the power company and say "Hey I'm Jack and I am at so and so address and the voltage is a tad low-can you crank up the voltage at the plant so I can make my sound system as loud as it can possibly go"
What you need to do is to bring more rig than you need. That way you don't have to woory about the voltage so much (It sounds like you are going to use it as an excuse "well it wouldn't get as loud as I want because the voltage is low"
NOT!, AND you don't have to worry so much about tearing up your gear-whcih I get the feeling is going to be a common occurance. It will be if you always run your rig at full potential.
Post by: jack smith on October 01, 2009, 08:37:43 AM
Thats all I want to know. Simple hey?
Am I right in saying that any level past 0db is clipping the system, and go into the red lights is very serious clipping that could fry the speakers? At least am I right on this point?
Post by: TJ (Tom) Cornish on October 01, 2009, 09:15:25 AM
1: The input voltage and current available to your amp from the wall socket. As others have pointed out, there's pretty much nothing you can do about this. It also doesn't likely matter much - firstly because you can't fix it, and secondly because it won't affect the output very much.
2: Gain structure. The idea here is to set your equipment so that you have access to all of the power your amp can deliver (if you need it), but also aren't using too much gain (amplification - either at your power amp or at some preamp stage inside your mixer or crossover) so that you get hiss.
3: Setting limiters to prevent clipping and reduce the chance of speaker damage.
I don't see at least in this thread what equipment you are using. Please tell us which amps, what speakers, and if you have any kind of crossover or other processor in the middle. This will help.
Read up on gain structure both by searching on the forum, and by reading stuff here:
http://www.rane.com/library.html
Also check out how limiters work.
One piece of good advice that you have received is to "have enough rig for the gig". There are 2 ways to look at this - either lower your expectations to what the gear you currently own can handle, or get a bigger system.
Sound pressure and electrical power are not linear in this context. After you get up a ways into the output of your speakers, it takes a lot more electrical power to make a small sound pressure difference. This large electrical power difference also determines whether your speakers are humming along comfortably, or being pushed to the limit. This is why Ivan and others are saying to not sweat the last little bit - even leaving 10% or 20% of your amp unused (if that's happening - I expect it's not), that only equals 1 or 2 dB of less output.
After you get the concepts sorted out you'll know where to go. And don't feel bad about buying the meter - you'll use it plenty going forward. I never bring gear without one.
Post by: Ivan Beaver on October 01, 2009, 09:15:58 AM
That is NOT an easy thing to determine-as has been already beaten to death.
In any dynamic environment-saftey factors are much harder (read impossible as there are to many variables) to determine so that on occasion you come right up to the limit-but other times you are will below it.
No matter how hard you try- you CANNOT put a simple number/solution to a VERY complex problem. That is simple.
And again-if people are suggesting you get enough voltage to the amp-I would ask THEM how do they go about gettting the AC line voltage up if it is low?
Let's assume you are not using a generator that you can adjust the voltage and are simply using the power companies line voltage.
You have what you have-and that is it. Nothing you can do-so don't worry about it.
BTW it is not bashing you, but you seem to be having a hard time understanding what "how loud-peak output" etc means.
I guarantee that I could take the exact same system as you and get louder peaks out of it and still have it playing at the end of the night-assuming you are putting large amps on the system in order to "get the most out of the loudspeakers"-such as 6dB over the "minimum" rating. In the case of the JBL728-if you put the max 6400w/cabinet as is on their spec sheet.
As long as you hit it with very short pulses (and the AVERAGE level is WELL below that)you may be fine-(depending on the freq and overexcursion), but try running your system where you have 0 on your console as the clip point-and allow people to run up to the 0 point. BYE BYE subs.
HOW? by playing material that has a much higher dynamic range (higher crest factor)less compressed. That's it. When you play the type of material you say you do, yes it will be "louder" than what I am talking about-but if you measure the peak loudness-I will be louder-but your average would be higher. I am talking about a night of music-not just one song.
So what is "loudness" the peak-or the average. It is exactly those types of questions that come into play when figuring out what your loudspeakers can take without being torn up.
Put the voltmeter away-it will tell you nothing of any real value.
Post by: jack smith on October 01, 2009, 09:46:41 AM
The equipment I was using years ago were JBL MP418 subs (I was using my friend's). But now my system is going to consist of 2 SRX728 subs, a Rane TTM56 dj mixer, Electrovoice AC One crossover, 2 JBL SRX722 mid/highs (t to you guys for recommending them), Crown K2 amps bridged into 4 ohng the 2 SRX728 subs and a Lab Gruppen LAB4000 amp running the 2 SRX722 mid/highs. I watch the levels very carefully and never let any dj go over the 0db light on the dj mixer all night (I keep checking every 5 minutes to make sure dj's aren't overdriving the system). I'm thinking about getting an XTA DP224 early next year after learning about limiters so to protect my system more by properly setting the DP224 up.
Post by: TJ (Tom) Cornish on October 01, 2009, 10:11:09 AM
Ivan is trying to explain that clipping isn't the major factor that will determine whether you cook your speakers or not - average power is. I'm going to take a leap (please correct me if I'm wrong) and guess that your music type is electronic or hip hop, which means that your source material has very little dynamic range - i.e. it's loud all the time, and not just on kick hits like rock and roll. This means that your speakers will be stressed more than if you had lighter content music, even at the same volume.
How this happens is the driver never has time to cool down between peaks - continuous tones keep putting the heat on. Your driver can handle this, but at a lower level than if you had short spikes with cool down time inbetween.
In the case of your 728s, that means the number that is important to you is 1600 watts. Your K2 can put 2500 watts bridged at 4 ohms, which means it is possible to burn up the speakers if you are putting continuous tones into them with this amp.
Practically speaking, you're on the right track with picking a level on your DJ mixer as your target for everyone to hit. Should it be the 0dB light? Maybe - maybe not. It depends on your gain structure. If you want to know what the clip point of your amps are, you can do the following:
- Unplug your speakers.
- Get a test tone somewhere in the range that speaker will produce. For subs - use 60 - 80Hz.
- Turn up the test tone until the amp clip light is lit.
- Note the position this happens on your mixer meter.
- If you don't like where the amp clip point happens on your mixer, you may be able to move it by changing the gain on your crossover. If you want clip to be 0dB on your mixer, the crossover would be a good place to fine tune the gain so that happens.
This procecure can produce helpful information, but it won't necessarily tell the whole story as you are testing only one band of your system - the subs. A song with tons of bass may clip the sub amp more quickly than a more balanced song.
As Ivan has said - this is a complicated problem, and there isn't a simple formula. If you want simple, the best way to guarantee that you won't damage your speakers is to buy about 6 more 728s and run them all at an easy level.
Post by: jack smith on October 01, 2009, 11:05:14 AM
Actually I just thought, the other type of music i'll be playing is a lot of dance music like trance and techno that has only got single sinewave bass on top of the kick drums and no continuous bass. Its like a bang, bang, bang, bang. Thats how the techno and trance is i'll also be playing, wheras the the oldskool i'll be playing has bass that is like baaaaaaaaaaang, then at a differnt note, baaaaaaaaang continuous kind of bass.
Post by: TJ (Tom) Cornish on October 01, 2009, 11:21:36 AM
Post by: jack smith on October 01, 2009, 12:02:47 PM
Post by: Ivan Beaver on October 01, 2009, 12:52:31 PM
Let's talk about your body and what it can take.
What is the highest temp your body/skin can take without pain-discomfort or damage?
120
Post by: Ivan Beaver on October 01, 2009, 12:53:40 PM
Post by: jack smith on October 01, 2009, 01:53:10 PM
| Ivan Beaver wrote on Thu, 01 October 2009 11:52 | ||||||
Let's try a different approach at power handling-ie sub damage. Let's talk about your body and what it can take. What is the highest temp your body/skin can take without pain-discomfort or damage? 120 Post by: Art Welter on October 01, 2009, 02:31:08 PM Ivan explained the voice coil heat analogy to running your finger through a candle flame nicely. Your Celestion speakers got 600 watt PEAKS through them for 5 hours continuous. That would only be a small fraction of the average power of a continuous 400 watts RMS of a sine wave, which would be like leaving your finger in the fire rather than passing it through quickly at each kick/snare hit. Any speaker, low, mid or high will burn up when too much average signal is put through them over a long enough time period. In the case of HF diaphragms, the voice coils have very little thermal mass, so it does not take long to burn them with a continuous tone, like feedback- a second could be enough. If you look at your console meters while music is playing and see 10 dB peaks, your speakers are seeing roughly 1/10th of that power on average. If there is only 3 dB peak to average ratio, the speakers are seeing roughly half the peak level. Big difference, with a 600 watt amp which is just driven below clip in the first case, the speaker sees only 60 watts of average power. Second case, 300 watts average power. Ram the 3 dB dynamic range music into a limiter, cutting the peak to average range down further, and the average power could approach 600 watts with no clipping, which could burn a 400 watts rms (AES 2 hours specs) speaker. Art Welter Post by: Jeff Babcock on October 01, 2009, 02:33:50 PM
Jack, I think Ivan has been extremely patient. Try to keep in mind that this subject keeps coming up over and over again on this forum. You say you understand, but I think you are still not seeing the whole picture. Look at the question you asked above about tops vs subs. Why do you think that tops would be immune to the same sort of damage? Your celestion speaker example, how do you know you put 600 watts into those 400W speakers. Just because the amp says it is capable of that wattage does not mean you are sending that wattage to the speakers if you are sending music signal to them. EDIT: Art beat me to it.... Post by: jack smith on October 01, 2009, 02:38:55 PM Post by: Ian Hunt on October 01, 2009, 02:45:19 PM Engage phantom Advance all knobs fully clockwise Adjust all faders fully up Switch the amplifier on Advance amplifier gains to just below 11 Stand clear of the speaker Unplug mic If the distance between the voice coil and the speaker cabinet can be measured on the ruler It's too loud. Post by: Andy Peters on October 01, 2009, 06:42:44 PM
An analog VU meter will read -- get this -- volume units. There is a particular time constant associated with this (google can tell you exactly what), but essentially it is some sort of average. But if you put a 1 kHz tone through the system, when your main output VU meter reads 0 dB, the output voltage at the jacks will be +4 dBu, or about 1.23 Vrms. Now if your mixer has an LED ladder meter, RTFM to determine whether it is a true VU meter, a peak-reading meter, or some random-response thing. Having said that, if you put a 1 kHz tone into the mixer and set it up so that the meter reads 0 dB, then the output voltage at the jacks should still read +4 dBm or 1.23 Vrms. THE EXCEPTION, of course, are the Mackies that have the meter calibrated such that 0 dB on the meter is actually 0 dBu at the output. The point here being that the meters are well-behaved for continuous tones and less so for music signals.
You've never blown a speaker because you are running everything very conservatively. If you set up your console so that its meters read 0 dB on peaks, then its peak output is about 1.23 Vrms (ugh, using rms when talking about peaks) and that voltage is a typical amplifier's input sensitivity (the voltage at which it puts out Full Tilt Boogie). So in other words you don't run the thing into the red. -a Post by: jack smith on October 02, 2009, 06:25:15 AM |