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Old 17th November 2014, 07:27 PM   #1
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Default Consumer grade JBL's + 300 w/ch amp = Disaster?

Speakers - JBL S312 SII:

http://www.jbl.com/resources/Brands/...312II%20ts.pdf

Amp - Behringer nu3000dsp:

Behringer iNuke NU3000 Measurements

Not my gear. This will be used at maximum output for hours at a time in a basement party room. Will be setup this weekend. Thoughts?

Last edited by turbodawg; 17th November 2014 at 07:36 PM.
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Old 17th November 2014, 10:01 PM   #2
sreten is online now sreten  United Kingdom
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Hi,

It can be used at healthy output for hours at a time.

Drunken attempts at running it as loud as
possible for hours will always end in tears.

Setting it to max volume is simply turning it up
and backing it off at the first signs of audible
compression from the speakers, needless to say
this should be done sober, and then things should
be arranged such that it can be turned up no further.

If its not loud enough bite the bullet and use PA speakers.

rgds, sreten.
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Old 17th November 2014, 10:12 PM   #3
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Follow the 'setting max volume' procedure described by sreten. And make really sure that it is impossible to turn the volume higher than that.

A lot of speakers are killed by DC from a clipping amp. With the above amp, you should be far from clipping.

Another way of killing speakers is by mechanical or thermal overload. Audible compression and/or distortion effects indicate overload conditions.

Regards,
Rundmaus
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Old 17th November 2014, 10:15 PM   #4
JMFahey is offline JMFahey  Argentina
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Agre and add: you might fuse the speaker leads.

A 5A standard (fast blow) speaker allows 200W RMS into an 8 ohm speaker and *should* be safe.

By the way, music program at that level is quite distorted.

Worst case, having one of them popping and muting a speaker during the party is a strong indication of unsafe levels.

You just replace the fuse and go on, at a slightly reduced volume.

Better than the speaker "muting" on its own ... irreversibly.
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Old 17th November 2014, 10:18 PM   #5
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Thanks guys!

I have limiters available in the DSP of the amp, and know how to use them. Any opinions on where they should be set?
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Old 18th November 2014, 03:11 PM   #6
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Quote:
Originally Posted by Rundmaus View Post
A lot of speakers are killed by DC from a clipping amp.
A clipping amp does not produce DC.

Clipping amps produce high levels of odd harmonics which were not present in the original signal thus frying tweeters.

If the amp were to produce DC it could not possibly kill tweeters since there will always (at least with passive speakers) be a capacitor in line with the tweeter whose impedance at DC is infinite.
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Old 18th November 2014, 03:45 PM   #7
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well ..id say limit them to 100W rms allow some room for a bit of overdrive .....
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Old 18th November 2014, 07:38 PM   #8
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Quote:
Originally Posted by Charles Darwin View Post
A clipping amp does not produce DC.
Sorry for my unprecise language. Of course you are right, but I am not wrong nevertheless: Assuming a DC coupled output stage, as long as the clipping condition persists within a signal peak, the output signal is the corresponding rail voltage = DC. If we are seriously deep in clipping condition, the output will quickly change to the opposite rail when the signal zero crosses.

So the output of a really heavy clipping amp will resemble a square wave, with all these nasty harmonics killing tweeters. (And the square wave consists of many many small regions where the output is DC )

Regards,
Rundmaus
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Old 19th November 2014, 10:14 AM   #9
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No DC, just lots of odd order harmonics which are sines.

Like this:http://upload.wikimedia.org/wikipedi...SquareWave.gif
(the red one is an idealised square which require unlimited bandwidth so it will never occur in reality)
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Old 19th November 2014, 04:29 PM   #10
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Agree that it will be hard to produce real clipping with this amp, with the limiter set it should avoid that. It might have some sort of soft clipping feature? Regardless I have seen them ride the limiter on it with their previous speakers.

Highpass will be set to avoid bottoming out the woofer below tuning. However, without having any xmax specs for the woofer or other parameters, it's impossible to tell if it will bottom the woofer above port tuning...? But highly unlikely. I'd say it's more likely to thermally damage them, or overpower the tweeters or mids somehow....?
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