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Which Amp for JBL L890 Home theater speakers? I keep blowing tweeters.

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#1 gotacamaro

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Posted 13 October 2013 - 11:57 AM

I have 2 large JBL L890 tower speakers that are 250W RMS each.

Currently I am using a harmon kardon ar3490 amp which is only putting out 120Wx2. So I am underpowering these speakers by half, and I keep having tweeter failure when playing at loud levels. I was told properly powering these speakers may eliminate this problem.

However I am completely clueless when it comes to power amps and crown seems to have so many different models. Are they only for mobile/professional DJs? Or would a crown amp be a good solution for 2 large home theater speakers? If so which model to go with? I dont care bout size, or mobility, just something to sit in the entertainment center.

Is there a better solution then crown for my needs?

I appreciate any help!

#2 dakos

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Posted 13 October 2013 - 12:15 PM

Hello,
sorry to hear you're blowing tweeters. First we need to determine what caused the problem. Drivers are ruined due to over heat or over excursion, my best guess would be that you're clipping the amp at those high levels and overheating them to their melting point. The first thing to do is to open the tweeter and visually inspect the damage and measure the drivers impedance so we can verify which kind of damage happened.

If it's indeed overheat there could be a few things going on, first the clipping issue is my first suspect, my second suspect is that you have some kind of EQ'ing going on (smiley face EQ or maximum treble setting) that boosts the high frequencies.
Avi

#3 gotacamaro

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Posted 13 October 2013 - 03:22 PM

When the tweeters fail, the receiver volume is turned almost all the way up to the max and it is overheating. the receiver ends up turning itself off , and after a few times of that the tweeters completely fail. So would a new amp help me in this situation? Im putting my current receiver to full power to get the job done, where its overheating and underpowering.

#4 Deromax

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Posted 15 October 2013 - 12:53 AM

These speakers with you amplifier will reach about 112 dB each.  This is rock concert level and this even exceed Dolby reference level for theaters by 7 dB, which is a lot.  If you feel this is not sufficient for your usual listening level, you should get pro speakers, as hi-fi speakers won't cut it.

#5 dakos

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Posted 15 October 2013 - 07:10 PM

Well, your amp is going into thermal protection, BUT there is no way to know if it was outputting a clean signal or a heavily clipped signal, do you remember if the sound was distorted when the volume was as high as you describe? A pro grade amp, if operated properly, won't go into thermal limiting.

We need to determine what caused the damage, if it was overheat then we need to determine if there was clipping or not, if there was no clipping and you still fried your tweeter then your amp is already too much for your speakers, if there was clipping (distorted sound), only then a stronger amp would solve your problem. If the damage was due to over excursion (mechanical damage), then the tweeters voice coil should remain in tact and you should see a physical damage to the membrane, then like my friend Deromax suggested, there is nothing to do except change the speakers to pro grade cabs. There are other reasons for driver failure such as bad welds, bad crimp connections and some others but that's not the majority of incidents.

What I can suggest you is to build some kind of tweeter protection circuit as described in this link. It could be as simple as a 1156 light bulb connected in series between your tweeter and passive crossover (a poor mans compressor/limiter/fuse) or one of the more complex circuits on the link I gave you above or in this one. One thing to remember is that tweeter protection circuits are always a compromise.

For more information read this
Avi





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