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Old 22nd July 2012, 02:11 PM   #1
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Default PA speaker resistor blew... quick question.

The resistors on my speaker cabinets blew out, I ordered new ones. would it mess anything up to change out this resistor with a 5w 8ohm one instead of the 5w 4 ohm one?

Im using a soundtech 500w 8ohm PA head and 2 15"+tweeter cabinets...
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Old 22nd July 2012, 03:28 PM   #2
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Yes, going from 4 Ohms to 8 Ohms will mess things up!
(Cross-over frequency wise or maybe volume of one of the drivers)

But, going from 5 Watts to 10 Watts would be good.
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Old 22nd July 2012, 03:35 PM   #3
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More importantly, you have to ask why the resistor blew in the first place. I suspect you've been overdriving the amp, causing clipping. Replacing with a higher wattage may just cause the drivers to blow next time.
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Old 22nd July 2012, 07:19 PM   #4
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if that is in series with the drivers, you might consider putting a lightbulb of appropriate size in series with the entire HF xover or right before the tweeters... the resistance raises when excess current flows and lights the bulb... it doubles as a fuse... an automotive tail light bulb is commonly used for this.
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Old 23rd July 2012, 04:16 PM   #5
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Quote:
Originally Posted by bear View Post
if that is in series with the drivers, you might consider putting a lightbulb of appropriate size in series with the entire HF xover or right before the tweeters... the resistance raises when excess current flows and lights the bulb... it doubles as a fuse... an automotive tail light bulb is commonly used for this.
Or a cheaper alternative would be a halogen bulb
Click the image to open in full size.

They can be had for next to nothing and have similar performance
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Old 23rd July 2012, 05:44 PM   #6
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They have brittle filaments, I would not use in a situation where I needed to rely upon the speaker. Auto bulbs have rugged filaments designed to work under constant vibration... Plus you can solder to them.

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Old 23rd July 2012, 10:55 PM   #7
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My bad. I've haven't tried it myself. but seen it used several times, newer thought about the vibration part
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Old 24th July 2012, 03:24 AM   #8
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hey, no bad. good thought! I think they make halogen automotive bulbs!!
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Old 24th July 2012, 04:00 AM   #9
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That would be a great idea to use a light-bulb for protection (I have heard of the concept).......To take the idea to a higher level, one could incorporate an automotive bayonet base into the front baffle, giving easy access & function as a visual aid.

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Old 24th July 2012, 04:16 AM   #10
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The bulbs work a treat. They do not really light up though - unless i suppose you were trying really really hard to blow things up. Though at that point I suspect that a dimly glowing bulb would be something less of an indication than the noise and smoke emanating from the speaker!

Used the bulb trick in some cabinets for my brother. You want to characterise the particular bulbs you use. I found two 12volt 12watt bulbs to be just right. You could probably drop these in place Of a 4 ohm resistor as their resistance was from memory an ohm or two.
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