No Bass - Blown Crossover?

fauzigarib

Member
2007-07-29 9:58 pm
Hi there,

At my wit's end here, and I suspect its mainly because I'm not a very technical guy... at least not to the level of some of the threads I've been studying here.

About a year and a half ago, I was listening to my 10 yr old Krell KSA 300s, paired with my Focal JMLab Electra 936's, when there was a loud high pitched sound, and then a ton of static in the left channel. Of course, in the ensuing panic, I tried a few basic things (changing cables, etc), and found that something had gone seriously wrong in the amp. Tried getting it fixed, but just wasn't able to.

Fast forward to now: After putting the Krell aside for a DIY project (whenever I feel comfortable in my education), I ended up purchasing a Prima Luna Dialog Premium Tube Integrated amp, and hooked it up. Sounded veeeeeery thin. Thought it may need to open up a bit more so ran it in for about 100 hours.. still the same.

After some basic troubleshooting (changing cables, connecting a different amp to the speakers, connecting different speakers to the prima luna) I have found that the issue most likely lies in the speakers. 3 way speakers, with two woofers, one midrange, and one tweeter. All drivers are firing, but the woofers are playing very "recessed". There's very muffled sound coming through them.
And as far as I can tell, all four drivers (2 on each channel) are sounding the same.

I plan on running a basic frequency sweep, but I just wanted to run this question by you fine folk here: Is it possible that the low pass filter in a crossover just dies? i.e., the mid bass and above pass through to the speakers and nothing below that? Is that even possible? And how likely is it that both speakers / crossovers are damaged in the exact same way?

Any help is highly appreciated. Once I get a problem diagnosed, I can find my way to implementing the solution.

Thanks,

Fauzi
 
You might want to check the multiway forum, this is fullrange and we tend not to use crossovers as there is only 1 driver :) A blown cap in the crossover can partially short the speaker and cause problems, Generally inductors do not blow out but if the coil wire insulation is thin, it can potentially go bad and short but that just makes the coil conduct and removes low pass feature sound should still be loud. My guess is a bad capacitor in the crossover circuit.. Use continuity checker to make sure your caps are non conducting. You have some nice equipment there, hope you are able to fix it because that is a lot of $ invested compared to DIY stuff.
 
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fauzigarib

Member
2007-07-29 9:58 pm
Fastbike / xrk971,

Thanks for taking out the time to respond. Much appreciated.

So what you're saying is that it IS possible that a cap on the low pass side on BOTH speakers is bad? Ok will certainly look into that.

Regarding the equipment, I've always bought my equipment used, using only my ears as a guide. Unfortunately I do not have the technical prowess to help me out of a mess when things go bad. But I am a quick learner... Lets see how far I can go in this case. Will certainly be racking the brains of you guys here.

Mods, please move the thread to the multiway forum. Appreciate it.

Fauzi
 

jjrenman

Member
2013-03-01 6:23 pm
It would not be a cap as they are not in series with the woofer. There will be at least one inductor in series but they do not usually melt because the voice coils will go first. It may be that the voice coils are partly melted in which case they will play with a much lower volume than they should. You will have to pull one and measure the resistance to see if it is a near short or not.
 

jjrenman

Member
2013-03-01 6:23 pm
It's rare but with some of the speaker repairs I've done the voice coil had only partially melted. What happens is that the heat will melt the varnish on the voice coil wire allowing the coils to short out so that you have very little "coil" left. Pull a woofer out and measure the resistance. If it is very low, say less than 2 ohms than the voice coils are shot. You should be able to get them re-coned. Use someone good.