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PA Loudspeaker XO refurbishment
PA Loudspeaker XO refurbishment
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Old 11th October 2018, 05:13 PM   #1
CarlJames is offline CarlJames
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Default PA Loudspeaker XO refurbishment

Dear all,

As I privately use some PA speakers from Community CSX/CSV 52´s and lot´s of EV old Sentry´s IV, I have some questions regarding XO refurbishment when burnt, worn and well overloaded. broken or in many cases out of spec.

I want to get rid of all lamps (Sylvania SK2,3..) Bipolars (electrolytics) etc. and only use PPTC (Littlefuse) and Panasonic ECW (metalized polypropylene) all being the cheapest together with std. wirewound and open air inductors, then high performance 18db/oct can be made to suit the tweeters and also the midrange units at a very low cost.

Eminence APT50 and Alpha 6 series with various horns have been used a lot since they can be had at bulk for very low cost per unit. The art being able to push the drivers to absolute maximum before overheat and burnout.

First problem, the dimensioning of the PPTC is precarious because of the transition state between the hold and trip current, making it difficult to get the most out of e.i APT50 before drop out to resistor. Would direct contact between PPTC and APT50 body help temp compensation?

The Eminence Alpha 6 sounds harsh near maximum output, can this also be adjusted to retract load before this happens?

Your input is most appreciated. Yours sincerely, C.J
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Old 11th October 2018, 10:09 PM   #2
chrisb is offline chrisb
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It might be better to post such inquiries to the multi-way or PA sub-forums?
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Old 12th October 2018, 02:24 AM   #3
anatech is offline anatech  Canada
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PA Loudspeaker XO refurbishment
Hi Carl,
I strongly recommend that you stay with the electrolytic capacitors. Firstly, the film capacitors will sound a lot different and the design was compensated for the electrolytic capacitors you see in the crossover. Secondly, film capacitors are not designed to pass current. They will suffer from foil burn off over time. This reduces their capacitance. Basically, the wrong part for the job.

I can see why you might want to get rid of the lamps, but they are effective. Speakers are not generally designed to be used at their maximum ratings. In the systems I design, I run them from 75% to 85% of their max rating, normally 75%. The problem is that the speaker voice coils are good and hot, and you are losing efficiency by running them at those levels. You are much further ahead using more speakers at lower power. It will sound much cleaner as well by doing that.

What's the application if I may ask?

-Chris
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Old 12th October 2018, 02:46 AM   #4
CarlJames is offline CarlJames
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In my case, protection is the game. The units are used in venues where they suffer from heavy overload.

i thought the new metalized poly´s would handle more current, as I have noticed that the bipolars often are degraded (distorsion), but I am sure you´re right, I will test better bipolars.

However, I do need help to get rid of the lamps, they are difficult to find, handle and are unreliable. I have tested PPTC, way better, but finding it difficult to get it just right in the transition area. between I(hold) to I(trip).
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Old 12th October 2018, 04:00 AM   #5
anatech is offline anatech  Canada
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PA Loudspeaker XO refurbishment
Hi Carl,
You could go to foil type film capacitors. They are more expensive, but they will handle current long term.

-Chris
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Old 12th October 2018, 04:44 AM   #6
CarlJames is offline CarlJames
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Yes, but they are more expensive.

With all respect, today in 2018 Metalized polypropylene are up to it: http://www.rubycon.co.jp/en/catalog/...film/e_PCK.pdf also the new Panasonic ECWFD series can take a lot more current. There are limits of course, but for tweeters and midrange they work, where as inductive voltage spikes seem to degrade bipolars.

Back to the lamps, they should have gone already in the early 80ies when Raychem Corp. introduced the PPTC. I need to find out the derivative of the driver, in order to match the trip of the PPTC. Bypass resistor being set to a secure level. The slope of the 18db/oct in enough to set the optimal frequency shift the driver can handle at maximum output.
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