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Old 10th July 2012, 08:01 AM   #1
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Default PA speakers help ...

I own 4 of these as seen in the pictures bellow .Usually working in small venue or open are for a crowd of 800 people max ( depending on the application with subs or not )

I run them at about 500W per speaker Inside exist a passive crossover between woofs and tweeters

the original speaker can be found either as sound king F2215 or audiomaster F2215

Original 1.75 drivers inside failed quite often and actually not form coil issues but from mechanical pov I replaced them PSD20028S from eminence

After that had no driver issues but the middle of the speaker was kinda weird emphasis somewhere in 2K required serious equalization to produce a listenable result . I had in mind that this was an xover issue but run it like that with absolutely no probs from failure aspects

last night decided to listen to them active used a xover from behringer 2 way and out of the blue the speaker become very rich and balanced no equalization needed both controls at 0db an cross them at 3.2 KHZ

------------------------------------------------------------------------

Question 1
I dlike some advice if the xover frequency is ok ( sounds ok to me and also have the impression that i could go even higher without producing a problem in the high mid or in the mid generally

Question 2
If i decide to run them active do you recommend any aditional safety measures in the HF driver such is a lamp (s) or a capacitor or is it enough to connect directly the HF driver to the amplifier ?


any other ideas are welcome

here is some pictures of the speaker , the woofers and the drivers

thanks for your time

kind regards
sakis

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Old 11th July 2012, 02:33 PM   #2
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The first rule is:
1. The higher the crossover frequency, the more power the horn can take--in other words, the higher you cross it, the less likely it is to burn out.
If the speaker reaches 4 or 5 Khz, then the horn should be above that.
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Old 11th July 2012, 02:41 PM   #3
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its nearly impossible to have a linear performance that high ( 4-5khz ) .... but after all yes .... i go with your approach
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Old 11th July 2012, 02:50 PM   #4
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Manufacturers always cross the horns or tweeters too low.................assuring that they will sell hoards of replacement diaphragms.
The passive crossover point for a horn is often 800Hz! This destroys the horn very fast.

And now rule two:
2. Always use an amp that NEVER clips. Amazingly, it's distortion that blows speakers and horns, not usually the clean power output.
You have a pair of speakers that are rated 200 watts, you have a 200 watt amp...
Of course the speakers WILL burn.
The amp runs out of power and clips, the clipping (is DC) melts the voice coils.
If you were using a 500 watt amp, the amp did not clip, the 200 watt speakers did not burn.
Starting to get it now? As long as the amp won't clip, the speakers will be OK.
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Old 11th July 2012, 10:16 PM   #5
tomi is offline tomi  Wales
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Take the above advice with a pinch of salt - whilst there is truth in it, it doesn't mean that it's ok to drive a 10W speaker with a 1000W amp as long as you don't clip the amp - the amp will happilly deliver it's rated power, cleanly, and toast the driver.
Chances are your HF amp will have plenty more power than the compresion driver will handle. The ideal situation would be to have an independent limiter for HF and LF between xover and amp - this is the aproach taken almost exclusively in professional multi-way systems. I'd expect the Behringer unit you used will have an output limiter facility.
Remember to take into accout the disspersion angle of the 15"s at the crossover point too - thay could be very direcitonal at 4-5k, depending upon how much the cone flexes and how much the dustcap radiates.

I guess you'd have to do some pretty careful measurements on the existing passive xover networks to excertain how they're behaving under load - that could get complicated and tedious!
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Old 12th July 2012, 06:22 AM   #6
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Really, I would say that this advice is worth a bag of diaphragms, more than a grain of salt.
I think that if this advice were followed, most of the diaphragms and speakers I have replaced (for other people) would have been avoided. That's a few...
A. I mean, you have to see how many underpowered PA systems there are...that are driven into clipping all the while. (no clipping allowed)
B. And the number of systems that have a disproportionate number of high frequency drivers. (6 speakers=1 tweeter)
C. And the crossover points...(horn crossed too low) Sure the horn is really loud, but it burns up really fast.
D. And the fourth rule:
Ten times the power required for the lows, as compared to mids and highs. If I define "lows," I'm thinking 70Hz and below.
This is why your system should be 3 way, with sub woofers. The 12 inch speakers can't really handle lows and mids at the same time. And there is not enough power in a 500 watt amp to power it.
Of course every speaker has a saturation point, and you cannot deliberately drive it that far without overheating it...
But on the other hand, it is not uncommon to leave 10 times the headroom above where a system is normally driven, just to make sure it never clips.
I think it's that headroom that saves it.
I would prefer to put limiters after the electronic crossover outputs. So, a separate limiter for highs, and a separate one for lows, in stereo I suppose.
This would sound considerably more natural than a single full range limiter.

But to answer the original question, I would use the type of protection that shunts excess tweeter current to a light bulb.
This type is used by Electrovoice. It seems to sound the best, if you really want to run protection. (purists don't use protection)
In my philosophy, crossing the horn at a higher frequency, running a limiter on the high frequency output of the crossover gives me the protection I want. I don't really feel like I need more than that.
However- there are enough engineers that run the board into the red...and I can see that this would be a potential problem, and no matter what you do, if somebody (some idiot) is overloading the mixer into distortion, then it's going to create problems.

Last edited by soundguruman; 12th July 2012 at 06:38 AM.
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Old 12th July 2012, 06:47 AM   #7
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Quote:
Originally Posted by sakis View Post
its nearly impossible to have a linear performance that high ( 4-5khz ) .... but after all yes .... i go with your approach
Don't be obsessed with linearity, the cabinet itself produces a frequency peak (hot spot) just because of the cabinet design.
You have to remove that peak with the equalizer, or the system will ring.
So the fantastic efficiency is lost when the EQ makes it (adjusts it) linear...and the ideal is somewhere between linear and efficiency.
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Old 12th July 2012, 07:52 PM   #8
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i agree in 99% of the things you say sound guru .. Thanks for verifying what i had in mind

i ll go with that and see how its going to be ..
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Old 12th July 2012, 08:17 PM   #9
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Although it seems crazy at first, a 1/3 octave EQ is what you really want. That's 31 bands. And it really turns out to be true, you need to correct for the room and the speakers, in the end it makes all the last big difference.
Although you may be avoiding the spending of money, someday, the electronic X over, the compressor limiters (for each frequency output), the 31 band EQ is what you eventually, really want.
Added on to any system, that's what will get the most from it.
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