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How Far Can I Turn it Up?

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Rotorbar View Drop Down
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    Posted: 07 December 2009 at 10:18pm
We used to just turn up the PA until it was loud enough, and we occasionally blew drivers.  I'm trying to bring a little science into the picture.  I get asked about this, and I find I really don't know, and therefore have no good answer.  Is it good enough to model your PA and then use an SPL meter to see how close you are to destroying your system as compared to that model?  Is there a better way? Maybe I'm just no good at listening, but I find the ears to be pretty subjective, room to room.  I also know that loudest isn't always what you want.

By "model" I mean you took driver sensitivity, input watts (dB above 1w/1m), thermal and mechanical driver limits, etc. into account.

Once I heard a racer asking another racer how to tell if an engine was over-revved.  The second racer stood there a moment, and finally said "Connecting rods sticking out through the side of the engine block are a pretty sure sign."

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Rotorbar
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cilla.scope View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cilla.scope Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2009 at 10:19pm
11
My girlfriend thinks I'm a stalker.
Well, she's not exactly my girlfriend yet ...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DjMidKnight Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2009 at 10:36pm
by ear is how i roll man, of course i strive to build my system so that my amps cant kill my speakers. point and case nothing will destroy a speaker faster than amplified distortion. basically if your keeping your amp out of clipping and your not sending way to much signal to said amp(djs running the gain to high/redline mixer), you should be good to go.
reality is meerly a compilation of what our limited sences precieve as being fact therefore there is no true universal reality and as such i propose that space and time can be bent twisted and altered
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saul Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2009 at 10:46pm
Originally posted by cilla.scope cilla.scope wrote:

11

mine goes to 12. 
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thepersonunknown View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote thepersonunknown Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2009 at 11:17pm
not a very good answer but it might help:
the manuals for your amps should quote you the relation between input and output voltages. using this you can work out the rms output of your amps at a cirtain input level with a give style of music/duty cycle. its all very ballparkish, but if you set light compression a bit higher than the point where your speakers hit their program rateing and a brick wall limiter at a point a little lower than where the speakers would be peaking, it should help a little with protecting your speakers. the ´soft knee´ function on a compressor sort of does this. the worst thing about this is that it is slightly audible even when the system is no where near its peak, but i gues thats better than fried drivers. anyway its a bit of a rubbish answer but i did warn at the top of the post. im not even sure if its a safe/correct way of limmiting but it did work for me no a systrem that was out every week end for over a year. i never blew a driver, although the main threat to the drivers in that cas acros all the bands apart from the highs was clipping/squarewave from amps. im sure theirs someone out there who could better explain how to accuratly set limiters. i for one would be most interested to learn. 
 
Edit: the light compression can have the threshold raised when used for short term and lowered when in prolonged use.
+ bare in mind that once the compression point is passed the duty cycle/rms output of the amp will increase at a faster rate as the input gain is incresed (definetly not one for dry hires) 


Edited by thepersonunknown - 07 December 2009 at 11:47pm
looking for Crown MA amps.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rich_gale Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2009 at 11:29pm
i try to use an amp that will deliver 1.5-2 times the power of the speaker i will be running.  assuming they are good quality, under rated like PD you can run the amps until you start to see a clip light flicker now and then and then i know i dont really want to put much more into the speaker.

with eminence, celestion,fane id probably follow the same system, but use an amp that is the same power as the speaker.

if you are being careful and notching up gradually you end up smelling the vc glue/former/copper heating up (i love the smell).  at this point you need to back down a bit.  its always a lovely feeling when a room stinks of vc's and you get back worrying if you need a recone but then you check and the drivers are all fine and the worrying was all for nothing.
REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RUS Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2009 at 11:37pm
wrong section Confused


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Post Options Post Options   Thanks (0) Thanks(0)   Quote pfly Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2009 at 12:03am
I've been doing just fine with limiters set up according to the max output of the amp in question.

For example if I have a driver that could take 800W RMS, but in the box it is in, its Xmax is reached around 500 watts, and I use amp that is capable of 1100W RMS for that speaker, I check when I hit amps limits, then I may set the limiter 3dB down from that point. This way that amp should give maximum of 550 watts for that speaker and all should be well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonminns Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2009 at 12:07am
if you can't do it by ear you may as well give up
4 ohms is for wimps
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rich_gale Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2009 at 12:24am
Originally posted by pfly pfly wrote:

I've been doing just fine with limiters set up according to the max output of the amp in question.

For example if I have a driver that could take 800W RMS, but in the box it is in, its Xmax is reached around 500 watts, and I use amp that is capable of 1100W RMS for that speaker, I check when I hit amps limits, then I may set the limiter 3dB down from that point. This way that amp should give maximum of 550 watts for that speaker and all should be well.

why not run a speaker to just under its xlim?  xmax is purely the point where its optimum excursion limit is at the point of becoming below optimum isnt it?  a speaker still goes louder after going past its xmax, or thats always been my belief.  
REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote thepersonunknown Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2009 at 12:29am
@ jonminns.
personaly i find it hard to determine what rms power is going into a speaker by ear. untill u start to hit peak values i think its almost imposible to hear. that is no problem if your only going to be running your rig a couple of hours at a time but when its going for 24 or even more hours non stop on a regular basis its quite important that the rms rateings are not passed too much. this will realy take some of the lifespan out of your drivers.
 
sound quality starts to drop after driver xmas as the motor starts to lose control over the cone
 
im sure their must be some science to doing this. wheres all the electronics techs at?  


Edited by thepersonunknown - 08 December 2009 at 12:31am
looking for Crown MA amps.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rotorbar Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2009 at 12:34am
Mr. RUS,
At first read, I thought "he's right, I should have posted this in the newbie section."  Now I'm not so sure.  Virtually every answer I've read is non-scientific.  I don't mean to belittle them.  They obviously seem to work for their advocates.  Mr. Gale seems to enjoy using the sniff test.  OK, that's fine, but my nose is poor, and I'd be better off putting a smoke detector above each PA stack.  I think that most all will agree with his mentioning using at least 2X amplifier capacity.  Mr. DJMK mentions not letting your system feed the speakers with distorted material.  Good idea, too.  Mr. Unknown mentions using compression/limiting to save drivers.  Good idea, too.  The trouble is, these ideas are based on good judgment, which comes from experience, which comes from bad judgment.  I was hoping to quantify all that good judgment into something that might save others from paying for all that expensive experience.  I think Mr. Pfly has a good point on a practical way to make sure you don't over-xmax a driver.

I guess where I was going was something like: give me the types of drivers you have, and information on their horns/enclosures, crossover points, etc. and I'll tell you how much power you can feed them, and what SPL you will get from them.  There may be limits based on characteristic frequency content of various music types, but the engineering behind the drivers can't be voodoo.

Assuming you're going for reasonably flat response, One example might be:  Highs: if you want 130 dB, and your horn driver sensitivity is 110dB at 1w/1m, then you need 20 dB (100 watts) into that driver.  Mids:  If you want 130dB and your mids drivers (qty 2) are 101 dB 1w/1m, then you need 26dB (400 watts) into each of the mids.  101 + 26 gets you to 127dB, and doubling the drivers gets you to 130 dB.  Will they each take 400W?  No.  They might go thermal limit, or they might go mechanical limit, but either way, you need more mids to get where you want to go...

I realize there are wild cards, like unanticipated distortion, prolonged feedback, and so on, but I hate telling someone new to the business "Oh, just smoke a few diaphrams, and you'll figure out what the tops will take."  I've been there, and have the box of old voice coils to prove it.

Regards,
Rotorbar
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